Comparative study of resist stabilization techniques for metal etch processing

NASA Astrophysics Data System (ADS)

Becker, Gerry; Ross, Matthew F.; Wong, Selmer S.; Minter, Jason P.; Marlowe, Trey; Livesay, William R.

1999-06-01

This study investigates resist stabilization techniques as they are applied to a metal etch application. The techniques that are compared are conventional deep-UV/thermal stabilization, or UV bake, and electron beam stabilization. The electron beam tool use din this study, an ElectronCure system from AlliedSignal Inc., ELectron Vision Group, utilizes a flood electron source and a non-thermal process. These stabilization techniques are compared with respect to a metal etch process. In this study, two types of resist are considered for stabilization and etch: a g/i-line resist, Shipley SPR-3012, and an advanced i-line, Shipley SPR 955- Cm. For each of these resist the effects of stabilization on resist features are evaluated by post-stabilization SEM analysis. Etch selectivity in all cases is evaluated by using a timed metal etch, and measuring resists remaining relative to total metal thickness etched. Etch selectivity is presented as a function of stabilization condition. Analyses of the effects of the type of stabilization on this method of selectivity measurement are also presented. SEM analysis was also performed on the features after a compete etch process, and is detailed as a function of stabilization condition. Post-etch cleaning is also an important factor impacted by pre-etch resist stabilization. Results of post- etch cleaning are presented for both stabilization methods. SEM inspection is also detailed for the metal features after resist removal processing.

A brief review of models of DC-DC power electronic converters for analysis of their stability

NASA Astrophysics Data System (ADS)

Siewniak, Piotr; Grzesik, Bogusław

2014-10-01

A brief review of models of DC-DC power electronic converters (PECs) is presented in this paper. It contains the most popular, continuous-time and discrete-time models used for PEC simulation, design, stability analysis and other applications. Both large-signal and small-signal models are considered. Special attention is paid to models that are used in practice for the analysis of the global and local stability of PECs.

Probabilistic stability analysis: the way forward for stability analysis of sustainable power systems.

PubMed

Milanović, Jovica V

2017-08-13

Future power systems will be significantly different compared with their present states. They will be characterized by an unprecedented mix of a wide range of electricity generation and transmission technologies, as well as responsive and highly flexible demand and storage devices with significant temporal and spatial uncertainty. The importance of probabilistic approaches towards power system stability analysis, as a subsection of power system studies routinely carried out by power system operators, has been highlighted in previous research. However, it may not be feasible (or even possible) to accurately model all of the uncertainties that exist within a power system. This paper describes for the first time an integral approach to probabilistic stability analysis of power systems, including small and large angular stability and frequency stability. It provides guidance for handling uncertainties in power system stability studies and some illustrative examples of the most recent results of probabilistic stability analysis of uncertain power systems.This article is part of the themed issue 'Energy management: flexibility, risk and optimization'. © 2017 The Author(s).

The NASA Monographs on Shell Stability Design Recommendations: A Review and Suggested Improvements

NASA Technical Reports Server (NTRS)

Nemeth, Michael P.; Starnes, James H., Jr.

1998-01-01

A summary of existing NASA design criteria monographs for the design of buckling-resistant thin-shell structures is presented. Subsequent improvements in the analysis for nonlinear shell response are reviewed, and current issues in shell stability analysis are discussed. Examples of nonlinear shell responses that are not included in the existing shell design monographs are presented, and an approach for including reliability based analysis procedures in the shell design process is discussed. Suggestions for conducting future shell experiments are presented, and proposed improvements to the NASA shell design criteria monographs are discussed.

The NASA Monographs on Shell Stability Design Recommendations: A Review and Suggested Improvements

NASA Technical Reports Server (NTRS)

Nemeth, Michael P.; Starnes, James H., Jr.

1998-01-01

A summary of the existing NASA design criteria monographs for the design of buckling-resistant thin-shell structures is presented. Subsequent improvements in the analysis for nonlinear shell response are reviewed, and current issues in shell stability analysis are discussed. Examples of nonlinear shell responses that are not included in the existing shell design monographs are presented, and an approach for including reliability-based analysis procedures in the shell design process is discussed. Suggestions for conducting future shell experiments are presented, and proposed improvements to the NASA shell design criteria monographs are discussed.

Orbital stability analysis in biomechanics: a systematic review of a nonlinear technique to detect instability of motor tasks.

PubMed

Riva, F; Bisi, M C; Stagni, R

2013-01-01

Falls represent a heavy economic and clinical burden on society. The identification of individual chronic characteristics associated with falling is of fundamental importance for the clinicians; in particular, the stability of daily motor tasks is one of the main factors that the clinicians look for during assessment procedures. Various methods for the assessment of stability in human movement are present in literature, and methods coming from stability analysis of nonlinear dynamic systems applied to biomechanics recently showed promise. One of these techniques is orbital stability analysis via Floquet multipliers. This method allows to measure orbital stability of periodic nonlinear dynamic systems and it seems a promising approach for the definition of a reliable motor stability index, taking into account for the whole task cycle dynamics. Despite the premises, its use in the assessment of fall risk has been deemed controversial. The aim of this systematic review was therefore to provide a critical evaluation of the literature on the topic of applications of orbital stability analysis in biomechanics, with particular focus to methodologic aspects. Four electronic databases have been searched for articles relative to the topic; 23 articles were selected for review. Quality of the studies present in literature has been assessed with a customised quality assessment tool. Overall quality of the literature in the field was found to be high. The most critical aspect was found to be the lack of uniformity in the implementation of the analysis to biomechanical time series, particularly in the choice of state space and number of cycles to include in the analysis. Copyright © 2012 Elsevier B.V. All rights reserved.

State fusion entropy for continuous and site-specific analysis of landslide stability changing regularities

NASA Astrophysics Data System (ADS)

Liu, Yong; Qin, Zhimeng; Hu, Baodan; Feng, Shuai

2018-04-01

Stability analysis is of great significance to landslide hazard prevention, especially the dynamic stability. However, many existing stability analysis methods are difficult to analyse the continuous landslide stability and its changing regularities in a uniform criterion due to the unique landslide geological conditions. Based on the relationship between displacement monitoring data, deformation states and landslide stability, a state fusion entropy method is herein proposed to derive landslide instability through a comprehensive multi-attribute entropy analysis of deformation states, which are defined by a proposed joint clustering method combining K-means and a cloud model. Taking Xintan landslide as the detailed case study, cumulative state fusion entropy presents an obvious increasing trend after the landslide entered accelerative deformation stage and historical maxima match highly with landslide macroscopic deformation behaviours in key time nodes. Reasonable results are also obtained in its application to several other landslides in the Three Gorges Reservoir in China. Combined with field survey, state fusion entropy may serve for assessing landslide stability and judging landslide evolutionary stages.

An Analysis of the Effects of Wing Aspect Ratio and Tail Location on Static Longitudinal Stability Below the Mach Number of Lift Divergence

NASA Technical Reports Server (NTRS)

Axelson, John A.; Crown, J. Conrad

1948-01-01

An analysis is presented of the influence of wing aspect ratio and tail location on the effects of compressibility upon static longitudinal stability. The investigation showed that the use of reduced wing aspect ratios or short tail lengths leads to serious reductions in high-speed stability and the possibility of high-speed instability.

Flight-determined stability analysis of multiple-input-multiple-output control systems

NASA Technical Reports Server (NTRS)

Burken, John J.

1992-01-01

Singular value analysis can give conservative stability margin results. Applying structure to the uncertainty can reduce this conservatism. This paper presents flight-determined stability margins for the X-29A lateral-directional, multiloop control system. These margins are compared with the predicted unscaled singular values and scaled structured singular values. The algorithm was further evaluated with flight data by changing the roll-rate-to-aileron command-feedback gain by +/- 20 percent. Minimum eigenvalues of the return difference matrix which bound the singular values are also presented. Extracting multiloop singular values from flight data and analyzing the feedback gain variations validates this technique as a measure of robustness. This analysis can be used for near-real-time flight monitoring and safety testing.

Flight-determined stability analysis of multiple-input-multiple-output control systems

NASA Technical Reports Server (NTRS)

Burken, John J.

1992-01-01

Singular value analysis can give conservative stability margin results. Applying structure to the uncertainty can reduce this conservatism. This paper presents flight-determined stability margins for the X-29A lateral-directional, multiloop control system. These margins are compared with the predicted unscaled singular values and scaled structured singular values. The algorithm was further evaluated with flight data by changing the roll-rate-to-aileron-command-feedback gain by +/- 20 percent. Also presented are the minimum eigenvalues of the return difference matrix which bound the singular values. Extracting multiloop singular values from flight data and analyzing the feedback gain variations validates this technique as a measure of robustness. This analysis can be used for near-real-time flight monitoring and safety testing.

The Stability of Vocational Interests from Early Adolescence to Middle Adulthood: A Quantitative Review of Longitudinal Studies

ERIC Educational Resources Information Center

Low, K. S. Douglas; Yoon, Mijung; Roberts, Brent W.; Rounds, James

2005-01-01

The present meta-analysis examined the stability of vocational interests from early adolescence (age 12) to middle adulthood (age 40). Stability was represented by rank-order and profile correlations. Interest stability remained unchanged during much of adolescence and increased dramatically during the college years (age 18-21.9), where it…

Development of Modal Analysis for the Study of Global Modes in High Speed Boundary Layer Flows

NASA Astrophysics Data System (ADS)

Brock, Joseph Michael

Boundary layer transition for compressible flows remains a challenging and unsolved problem. In the context of high-speed compressible flow, transitional and turbulent boundary-layers produce significantly higher surface heating caused by an increase in skin-friction. The higher heating associated with transitional and turbulent boundary layers drives thermal protection systems (TPS) and mission trajectory bounds. Proper understanding of the mechanisms that drive transition is crucial to the successful design and operation of the next generation spacecraft. Currently, prediction of boundary-layer transition is based on experimental efforts and computational stability analysis. Computational analysis, anchored by experimental correlations, offers an avenue to assess/predict stability at a reduced cost. Classical methods of Linearized Stability Theory (LST) and Parabolized Stability Equations (PSE) have proven to be very useful for simple geometries/base flows. Under certain conditions the assumptions that are inherent to classical methods become invalid and the use of LST/PSE is inaccurate. In these situations, a global approach must be considered. A TriGlobal stability analysis code, Global Mode Analysis in US3D (GMAUS3D), has been developed and implemented into the unstructured solver US3D. A discussion of the methodology and implementation will be presented. Two flow configurations are presented in an effort to validate/verify the approach. First, stability analysis for a subsonic cylinder wake is performed and results compared to literature. Second, a supersonic blunt cone is considered to directly compare LST/PSE analysis and results generated by GMAUS3D.

A Quasi-Steady Flexible Launch Vehicle Stability Analysis Using Steady CFD with Unsteady Aerodynamic Enhancement

NASA Technical Reports Server (NTRS)

Bartels, Robert E.

2011-01-01

Launch vehicles frequently experience a reduced stability margin through the transonic Mach number range. This reduced stability margin is caused by an undamping of the aerodynamics in one of the lower frequency flexible or rigid body modes. Analysis of the behavior of a flexible vehicle is routinely performed with quasi-steady aerodynamic lineloads derived from steady rigid computational fluid dynamics (CFD). However, a quasi-steady aeroelastic stability analysis can be unconservative at the critical Mach numbers where experiment or unsteady computational aeroelastic (CAE) analysis show a reduced or even negative aerodynamic damping. This paper will present a method of enhancing the quasi-steady aeroelastic stability analysis of a launch vehicle with unsteady aerodynamics. The enhanced formulation uses unsteady CFD to compute the response of selected lower frequency modes. The response is contained in a time history of the vehicle lineloads. A proper orthogonal decomposition of the unsteady aerodynamic lineload response is used to reduce the scale of data volume and system identification is used to derive the aerodynamic stiffness, damping and mass matrices. The results of the enhanced quasi-static aeroelastic stability analysis are compared with the damping and frequency computed from unsteady CAE analysis and from a quasi-steady analysis. The results show that incorporating unsteady aerodynamics in this way brings the enhanced quasi-steady aeroelastic stability analysis into close agreement with the unsteady CAE analysis.

Dynamic Characteristics and Stability Analysis of Space Shuttle Main Engine Oxygen Pump

NASA Technical Reports Server (NTRS)

Gunter, Edgar J.; Branagan, Lyle

1991-01-01

The dynamic characteristics of the Space Shuttle high pressure oxygen pump are presented. Experimental data is presented to show the vibration spectrum and response under actual engine operation and also in spin pit testing for balancing. The oxygen pump appears to be operating near a second critical speed and is sensitive to self excited aerodynamic cross coupling forces in the turbine and pump. An analysis is presented to show the improvement in pump stability by the application of turbulent flow seals, preburner seals, and pump shaft cross sectional modifications.

In-Flight Stability Analysis of the X-48B Aircraft

NASA Technical Reports Server (NTRS)

Regan, Christopher D.

2008-01-01

This report presents the system description, methods, and sample results of the in-flight stability analysis for the X-48B, Blended Wing Body Low-Speed Vehicle. The X-48B vehicle is a dynamically scaled, remotely piloted vehicle developed to investigate the low-speed control characteristics of a full-scale blended wing body. Initial envelope clearance was conducted by analyzing the stability margin estimation resulting from the rigid aircraft response during flight and comparing it to simulation data. Short duration multisine signals were commanded onboard to simultaneously excite the primary rigid body axes. In-flight stability analysis has proven to be a critical component of the initial envelope expansion.

Advanced composite vertical stabilizer for DC-10 transport aircraft

NASA Technical Reports Server (NTRS)

Stephens, C. O.

1978-01-01

The structural design configuration for the Composite Vertical Stabilizer is described and the structural design, analysis, and weight activities are presented. The status of fabrication and test activities for the development test portion of the program is described. Test results are presented for the skin panels, spar web, spar cap to cover, and laminate properties specimens. Engineering drawings of vertification test panels and root fittings, rudder support specimens, titanium fittings, and rear spar specimen analysis models are included.

Crash problem definition and safety benefits methodology for stability control for single-unit medium and heavy trucks and large-platform buses

DOT National Transportation Integrated Search

2009-10-01

This report presents the findings of a comprehensive engineering analysis of electronic stability control (ESC) and roll stability control (RSC) systems for single-unit medium and heavy trucks and large-platform buses. This report details the applica...

Principal Stability and the Rural Divide

ERIC Educational Resources Information Center

Pendola, Andrew; Fuller, Edward J.

2018-01-01

This article examines the unique features of the rural school context and how these features are associated with the stability of principals in these schools. Given the small but growing literature on the characteristics of rural principals, this study presents an exploratory analysis of principal stability across schools located in different…

Aeroelastic stability analyses of two counter rotating propfan designs for a cruise missile model

NASA Technical Reports Server (NTRS)

Mahajan, Aparajit J.; Lucero, John M.; Mehmed, Oral; Stefko, George L.

1992-01-01

Aeroelastic stability analyses were performed to insure structural integrity of two counterrotating propfan blade designs for a NAVY/Air Force/NASA cruise missile model wind tunnel test. This analysis predicted if the propfan designs would be flutter free at the operating conditions of the wind tunnel test. Calculated stability results are presented for the two blade designs with rotational speed and Mach number as the parameters. A aeroelastic analysis code ASTROP2 (Aeroelastic Stability and Response of Propulsion Systems - 2 Dimensional Analysis), developed at LeRC, was used in this project. The aeroelastic analysis is a modal method and uses the combination of a finite element structural model and two dimensional steady and unsteady cascade aerodynamic models. This code was developed to analyze single rotation propfans but was modified and applied to counterrotating propfans for the present work. Modifications were made to transform the geometry and rotation of the aft rotor to the same reference frame as the forward rotor, to input a non-uniform inflow into the rotor being analyzed, and to automatically converge to the least stable aeroelastic mode.

Defending the beauty of the Invariance Principle

NASA Astrophysics Data System (ADS)

Barkana, Itzhak

2014-01-01

Customary stability analysis methods for nonlinear nonautonomous systems seem to require a strict condition of uniform continuity. Although extensions of LaSalle's Invariance Principle to nonautonomous systems that mitigate this condition have been available for a long time, they have remained surprisingly unknown or open to misinterpretations. The large scope of the Principle might have misled the prospective users and its application to Control problems has been received with amazing yet clear uneasiness. Counterexamples have been used in order to claim that the Invariance Principle cannot be applied to nonlinear nonautonomous systems. Because the original formulation of the Invariance Principle still imposes conditions that are not necessarily needed, this paper presents a new Invariance Principle that further mitigates previous conditions and thus further expands the scope of stability analysis. A brief comparative review of various alternatives to stability analysis of nonautonomous nonlinear systems and their implications is also presented in order to illustrate that thorough analysis of same examples may actually confirm the efficiency of the Invariance Principle approach when dealing with stability of nonautonomous nonlinear systems problems that may look difficult or even unsolvable otherwise.

Bundle Adjustment-Based Stability Analysis Method with a Case Study of a Dual Fluoroscopy Imaging System

NASA Astrophysics Data System (ADS)

Al-Durgham, K.; Lichti, D. D.; Detchev, I.; Kuntze, G.; Ronsky, J. L.

2018-05-01

A fundamental task in photogrammetry is the temporal stability analysis of a camera/imaging-system's calibration parameters. This is essential to validate the repeatability of the parameters' estimation, to detect any behavioural changes in the camera/imaging system and to ensure precise photogrammetric products. Many stability analysis methods exist in the photogrammetric literature; each one has different methodological bases, and advantages and disadvantages. This paper presents a simple and rigorous stability analysis method that can be straightforwardly implemented for a single camera or an imaging system with multiple cameras. The basic collinearity model is used to capture differences between two calibration datasets, and to establish the stability analysis methodology. Geometric simulation is used as a tool to derive image and object space scenarios. Experiments were performed on real calibration datasets from a dual fluoroscopy (DF; X-ray-based) imaging system. The calibration data consisted of hundreds of images and thousands of image observations from six temporal points over a two-day period for a precise evaluation of the DF system stability. The stability of the DF system - for a single camera analysis - was found to be within a range of 0.01 to 0.66 mm in terms of 3D coordinates root-mean-square-error (RMSE), and 0.07 to 0.19 mm for dual cameras analysis. It is to the authors' best knowledge that this work is the first to address the topic of DF stability analysis.

Stability analysis of a reinforced carbon carbon shell

NASA Technical Reports Server (NTRS)

Agan, W. E.; Jordan, B. M.

1977-01-01

This paper presents the development of a stability analysis for the nose cap of the NASA Space Shuttle Orbiter. Stability is evaluated by the differential stiffness analysis of the NASTRAN finite-element computer code, addressing those nonstandard characteristics in the nose cap such as nonuniform curvature, asymmetrical and nonuniform loads, support fixity, and various combinations of membrane and bending stresses. A full-sized nose cap, thinner than production, was statically tested and stability analyzed. The failing load level correlated to within 30%. The region and mode of buckling that occurred during test was accurately predicted by analysis. The criterion for predicting instability is based on the behavior of the nonlinear deflections. The deflections are nonlinear elastic in that the stresses are well within the elastic range of the material, but the geometry-load relationship produces nonlinear deflections. The load-deflection relationship is well defined by differential stiffness analysis up to the zero-slope portion of the curve, the point of neutral stability or where the shell 'snaps through' just prior to general instability.

Stability analysis of free piston Stirling engines

NASA Astrophysics Data System (ADS)

Bégot, Sylvie; Layes, Guillaume; Lanzetta, François; Nika, Philippe

2013-03-01

This paper presents a stability analysis of a free piston Stirling engine. The model and the detailed calculation of pressures losses are exposed. Stability of the machine is studied by the observation of the eigenvalues of the model matrix. Model validation based on the comparison with NASA experimental results is described. The influence of operational and construction parameters on performance and stability issues is exposed. The results show that most parameters that are beneficial for machine power seem to induce irregular mechanical characteristics with load, suggesting that self-sustained oscillations could be difficult to maintain and control.

On-Line Robust Modal Stability Prediction using Wavelet Processing

NASA Technical Reports Server (NTRS)

Brenner, Martin J.; Lind, Rick

1998-01-01

Wavelet analysis for filtering and system identification has been used to improve the estimation of aeroservoelastic stability margins. The conservatism of the robust stability margins is reduced with parametric and nonparametric time- frequency analysis of flight data in the model validation process. Nonparametric wavelet processing of data is used to reduce the effects of external disturbances and unmodeled dynamics. Parametric estimates of modal stability are also extracted using the wavelet transform. Computation of robust stability margins for stability boundary prediction depends on uncertainty descriptions derived from the data for model validation. The F-18 High Alpha Research Vehicle aeroservoelastic flight test data demonstrates improved robust stability prediction by extension of the stability boundary beyond the flight regime. Guidelines and computation times are presented to show the efficiency and practical aspects of these procedures for on-line implementation. Feasibility of the method is shown for processing flight data from time- varying nonstationary test points.

Efficient sensitivity analysis and optimization of a helicopter rotor

NASA Technical Reports Server (NTRS)

Lim, Joon W.; Chopra, Inderjit

1989-01-01

Aeroelastic optimization of a system essentially consists of the determination of the optimum values of design variables which minimize the objective function and satisfy certain aeroelastic and geometric constraints. The process of aeroelastic optimization analysis is illustrated. To carry out aeroelastic optimization effectively, one needs a reliable analysis procedure to determine steady response and stability of a rotor system in forward flight. The rotor dynamic analysis used in the present study developed inhouse at the University of Maryland is based on finite elements in space and time. The analysis consists of two major phases: vehicle trim and rotor steady response (coupled trim analysis), and aeroelastic stability of the blade. For a reduction of helicopter vibration, the optimization process requires the sensitivity derivatives of the objective function and aeroelastic stability constraints. For this, the derivatives of steady response, hub loads and blade stability roots are calculated using a direct analytical approach. An automated optimization procedure is developed by coupling the rotor dynamic analysis, design sensitivity analysis and constrained optimization code CONMIN.

Analysis of wind-tunnel stability and control tests in terms of flying qualities of full-scale airplanes

NASA Technical Reports Server (NTRS)

Kayten, Gerald G

1945-01-01

The analysis of results of wind-tunnel stability and control tests of powered airplane models in terms of the flying qualities of full-scale airplanes is advocated. In order to indicated the topics upon which comments are considered desirable in the report of a wind-tunnel stability and control investigation and to demonstrate the nature of the suggested analysis, the present NACA flying-qualities requirements are discussed in relation to wind-tunnel tests. General procedures for the estimation of flying qualities from wind-tunnel tests are outlined.

Stability analysis of piecewise non-linear systems and its application to chaotic synchronisation with intermittent control

NASA Astrophysics Data System (ADS)

Wang, Qingzhi; Tan, Guanzheng; He, Yong; Wu, Min

2017-10-01

This paper considers a stability analysis issue of piecewise non-linear systems and applies it to intermittent synchronisation of chaotic systems. First, based on piecewise Lyapunov function methods, more general and less conservative stability criteria of piecewise non-linear systems in periodic and aperiodic cases are presented, respectively. Next, intermittent synchronisation conditions of chaotic systems are derived which extend existing results. Finally, Chua's circuit is taken as an example to verify the validity of our methods.

Power System Transient Stability Based on Data Mining Theory

NASA Astrophysics Data System (ADS)

Cui, Zhen; Shi, Jia; Wu, Runsheng; Lu, Dan; Cui, Mingde

2018-01-01

In order to study the stability of power system, a power system transient stability based on data mining theory is designed. By introducing association rules analysis in data mining theory, an association classification method for transient stability assessment is presented. A mathematical model of transient stability assessment based on data mining technology is established. Meanwhile, combining rule reasoning with classification prediction, the method of association classification is proposed to perform transient stability assessment. The transient stability index is used to identify the samples that cannot be correctly classified in association classification. Then, according to the critical stability of each sample, the time domain simulation method is used to determine the state, so as to ensure the accuracy of the final results. The results show that this stability assessment system can improve the speed of operation under the premise that the analysis result is completely correct, and the improved algorithm can find out the inherent relation between the change of power system operation mode and the change of transient stability degree.

Transverse beam stability measurement and analysis for the SNS accumulator ring

DOE PAGES

Xie, Zaipeng; Deibele, Craig; Schulte, Michael J.; ...

2015-07-01

In a Field-programmable gate array (FPGA) based transverse feedback damper system we implemented in the Spallation Neutron Source (SNS) accumulator ring with the intention to stabilize the electron-proton (e-p) instability in a frequency range from 1 MHz to 300 MHz. The transverse damper could also be used as a diagnostic tool by measuring the beam transfer function (BTF). An analysis of the BTF measurement provides the stability diagram for the production beam at SNS. Our paper describes the feedback damper system and its set-up as the BTF diagnostic tool. Experimental BTF results are presented and beam stability analysis is performedmore » based on the BTF measurements for the SNS accumulator ring.« less

Aeroelastic effects in multirotor vehicles. Part 2: Methods of solution and results illustrating coupled rotor/body aeromechanical stability

NASA Technical Reports Server (NTRS)

Venkatesan, C.; Friedmann, P. P.

1987-01-01

This report is a sequel to the earlier report titled, Aeroelastic Effects in Multi-Rotor Vehicles with Application to Hybrid Heavy Lift System, Part 1: Formulation of Equations of Motion (NASA CR-3822). The trim and stability equations are presented for a twin rotor system with a buoyant envelope and an underslung load attached to a flexible supporting structure. These equations are specialized for the case of hovering flight. A stability analysis, for such a vehicle with 31 degrees of freedom, yields a total of 62 eigenvalues. A careful parametric study is performed to identify the various blade and vehicle modes, as well as the coupling between various modes. Finally, it is shown that the coupled rotor/vehicle stability analysis provides information on both the aeroelastic stability as well as complete vehicle dynamic stability. Also presented are the results of an analytical study aimed at predicting the aeromechanical stability of a single rotor helicopter in ground resonance. The theoretical results are found to be in good agreement with the experimental results, thereby validating the analytical model for the dynamics of the coupled rotor/support system.

Stability Properties and Cross Coupling Performance of the Control Allocation Scheme CAPIO

NASA Technical Reports Server (NTRS)

Yildiz, Yildiray; Kolmanovsky, Ilya V.

2010-01-01

This paper presents a stability analysis and an application of a recently developed Control Allocator for recovery from Pilot Induced Oscillations (CAPIO). When actuators are rate-saturated due to either aggressive pilot commands, high gain ight control systems or some anomaly in the system, the effective delay in the control loop may increase. This effective delay increase manifests itself as a phase shift between the commanded and actual system signals and can instigate Pilot induced Oscillations (PIO). CAPIO reduces the e ective time delay by minimizing the phase shift between the commanded and the actual attitude accelerations. We present a stability analysis of CAPIO for a scalar system. In addition, we present simulation results for aircraft with cross-coupling which demonstrates the potential of CAPIO serving as an effective PIO handler in adverse conditions.

Solar Dynamic Power System Stability Analysis and Control

NASA Technical Reports Server (NTRS)

Momoh, James A.; Wang, Yanchun

1996-01-01

The objective of this research is to conduct dynamic analysis, control design, and control performance test of solar power system. Solar power system consists of generation system and distribution network system. A bench mark system is used in this research, which includes a generator with excitation system and governor, an ac/dc converter, six DDCU's and forty-eight loads. A detailed model is used for modeling generator. Excitation system is represented by a third order model. DDCU is represented by a seventh order system. The load is modeled by the combination of constant power and constant impedance. Eigen-analysis and eigen-sensitivity analysis are used for system dynamic analysis. The effects of excitation system, governor, ac/dc converter control, and the type of load on system stability are discussed. In order to improve system transient stability, nonlinear ac/dc converter control is introduced. The direct linearization method is used for control design. The dynamic analysis results show that these controls affect system stability in different ways. The parameter coordination of controllers are recommended based on the dynamic analysis. It is concluded from the present studies that system stability is improved by the coordination of control parameters and the nonlinear ac/dc converter control stabilize system oscillation caused by the load change and system fault efficiently.

Stability and Bifurcation Analysis of a Three-Species Food Chain Model with Delay

NASA Astrophysics Data System (ADS)

Pal, Nikhil; Samanta, Sudip; Biswas, Santanu; Alquran, Marwan; Al-Khaled, Kamel; Chattopadhyay, Joydev

In the present paper, we study the effect of gestation delay on a tri-trophic food chain model with Holling type-II functional response. The essential mathematical features of the proposed model are analyzed with the help of equilibrium analysis, stability analysis, and bifurcation theory. Considering time-delay as the bifurcation parameter, the Hopf-bifurcation analysis is carried out around the coexisting equilibrium. The direction of Hopf-bifurcation and the stability of the bifurcating periodic solutions are determined by applying the normal form theory and center manifold theorem. We observe that if the magnitude of the delay is increased, the system loses stability and shows limit cycle oscillations through Hopf-bifurcation. The system also shows the chaotic dynamics via period-doubling bifurcation for further enhancement of time-delay. Our analytical findings are illustrated through numerical simulations.

Pressure potential and stability analysis in an acoustical noncontact transportation

NASA Astrophysics Data System (ADS)

Li, J.; Liu, C. J.; Zhang, W. J.

2017-01-01

Near field acoustic traveling wave is one of the most popular principles in noncontact manipulations and transportations. The stability behavior is a key factor in the industrial applications of acoustical noncontact transportation. We present here an in-depth analysis of the transportation stability of a planar object levitated in near field acoustic traveling waves. To more accurately describe the pressure distributions on the radiation surface, a 3D nonlinear traveling wave model is presented. A closed form solution is derived based on the pressure potential to quantitatively calculate the restoring forces and moments under small disturbances. The physical explanations of the effects of fluid inertia and the effects of non-uniform pressure distributions are provided in detail. It is found that a vibration rail with tapered cross section provides more stable transportation than a rail with rectangular cross section. The present study sheds light on the issue of quantitative evaluation of stability in acoustic traveling waves and proposes three main factors that influence the stability: (a) vibration shape, (b) pressure distribution and (c) restoring force/moment. It helps to provide a better understanding of the physics behind the near field acoustic transportation and provide useful design and optimization tools for industrial applications.

Risk analysis of gravity dam instability using credibility theory Monte Carlo simulation model.

PubMed

Xin, Cao; Chongshi, Gu

2016-01-01

Risk analysis of gravity dam stability involves complicated uncertainty in many design parameters and measured data. Stability failure risk ratio described jointly by probability and possibility has deficiency in characterization of influence of fuzzy factors and representation of the likelihood of risk occurrence in practical engineering. In this article, credibility theory is applied into stability failure risk analysis of gravity dam. Stability of gravity dam is viewed as a hybrid event considering both fuzziness and randomness of failure criterion, design parameters and measured data. Credibility distribution function is conducted as a novel way to represent uncertainty of influence factors of gravity dam stability. And combining with Monte Carlo simulation, corresponding calculation method and procedure are proposed. Based on a dam section, a detailed application of the modeling approach on risk calculation of both dam foundation and double sliding surfaces is provided. The results show that, the present method is feasible to be applied on analysis of stability failure risk for gravity dams. The risk assessment obtained can reflect influence of both sorts of uncertainty, and is suitable as an index value.

Aeromechanical stability analysis of COPTER

NASA Technical Reports Server (NTRS)

Yin, Sheng K.; Yen, Jing G.

1988-01-01

A plan was formed for developing a comprehensive, second-generation system with analytical capabilities for predicting performance, loads and vibration, handling qualities, aeromechanical stability, and acoustics. This second-generation system named COPTER (COmprehensive Program for Theoretical Evaluation of Rotorcraft) is designed for operational efficiency, user friendliness, coding readability, maintainability, transportability, modularity, and expandability for future growth. The system is divided into an executive, a data deck validator, and a technology complex. At present a simple executive, the data deck validator, and the aeromechanical stability module of the technology complex were implemented. The system is described briefly, the implementation of the technology module is discussed, and correlation data presented. The correlation includes hingeless-rotor isolated stability, hingeless-rotor ground-resonance stability, and air-resonance stability of an advanced bearingless-rotor in forward flight.

Incompressible boundary-layer stability analysis of LFC experimental data for sub-critical Mach numbers. M.S. Thesis

NASA Technical Reports Server (NTRS)

Berry, S. A.

1986-01-01

An incompressible boundary-layer stability analysis of Laminar Flow Control (LFC) experimental data was completed and the results are presented. This analysis was undertaken for three reasons: to study laminar boundary-layer stability on a modern swept LFC airfoil; to calculate incompressible design limits of linear stability theory as applied to a modern airfoil at high subsonic speeds; and to verify the use of linear stability theory as a design tool. The experimental data were taken from the slotted LFC experiment recently completed in the NASA Langley 8-Foot Transonic Pressure Tunnel. Linear stability theory was applied and the results were compared with transition data to arrive at correlated n-factors. Results of the analysis showed that for the configuration and cases studied, Tollmien-Schlichting (TS) amplification was the dominating disturbance influencing transition. For these cases, incompressible linear stability theory correlated with an n-factor for TS waves of approximately 10 at transition. The n-factor method correlated rather consistently to this value despite a number of non-ideal conditions which indicates the method is useful as a design tool for advanced laminar flow airfoils.

A simplified approach for slope stability analysis of uncontrolled waste dumps.

PubMed

Turer, Dilek; Turer, Ahmet

2011-02-01

Slope stability analysis of municipal solid waste has always been problematic because of the heterogeneous nature of the waste materials. The requirement for large testing equipment in order to obtain representative samples has identified the need for simplified approaches to obtain the unit weight and shear strength parameters of the waste. In the present study, two of the most recently published approaches for determining the unit weight and shear strength parameters of the waste have been incorporated into a slope stability analysis using the Bishop method to prepare slope stability charts. The slope stability charts were prepared for uncontrolled waste dumps having no liner and leachate collection systems with pore pressure ratios of 0, 0.1, 0.2, 0.3, 0.4 and 0.5, considering the most critical slip surface passing through the toe of the slope. As the proposed slope stability charts were prepared by considering the change in unit weight as a function of height, they reflect field conditions better than accepting a constant unit weight approach in the stability analysis. They also streamline the selection of slope or height as a function of the desired factor of safety.

Nonlinear stability analysis of Darcy’s flow with viscous heating

PubMed Central

Alves, Leonardo S. de B.; Barletta, Antonio

2016-01-01

The nonlinear stability of a rectangular porous channel saturated by a fluid is here investigated. The aspect ratio of the channel is assumed to be variable. The channel walls are considered impermeable and adiabatic except for the horizontal top which is assumed to be isothermal. The viscous dissipation is acting inside the channel as internal heat generator. A basic throughflow is imposed, and the nonlinear convective stability is investigated by means of the generalized integral transform technique. The neutral stability curve is compared with the one obtained by the linear stability analysis already present in the literature. The growth rate analysis of different unstable modes is performed. The Nusselt number is investigated for several supercritical configurations in order to better understand how the system behaves when conditions far away from neutral stability are considered. The patterns of the neutrally stable convective cells are also reported. Nonlinear simulations support the results obtained by means of the linear stability analysis, confirming that viscous dissipation alone is indeed capable of inducing mixed convection. Low Gebhart or high Péclet numbers lead to a transient overheating of the originally motionless fluid before it settles in its convective steady state. PMID:27279772

Stability and bifurcation analysis of a generalized scalar delay differential equation.

PubMed

Bhalekar, Sachin

2016-08-01

This paper deals with the stability and bifurcation analysis of a general form of equation D(α)x(t)=g(x(t),x(t-τ)) involving the derivative of order α ∈ (0, 1] and a constant delay τ ≥ 0. The stability of equilibrium points is presented in terms of the stability regions and critical surfaces. We provide a necessary condition to exist chaos in the system also. A wide range of delay differential equations involving a constant delay can be analyzed using the results proposed in this paper. The illustrative examples are provided to explain the theory.

An analysis of the effects of aeroelasticity on static longitudinal stability and control of a swept-back-wing airplane

NASA Technical Reports Server (NTRS)

Skoog, Richard B

1951-01-01

A theoretical analysis of the effects of aeroelasticity on the stick-fixed static longitudinal stability and elevator angle required for balance of an airplane is presented together with calculated effects for a swept-wing bomber of relatively high flexibility. Although large changes in stability due to certain parameters are indicated for the example airplane, the over-all stability change after considering all parameters was quite small, compared to the individual effects, due to the counterbalancing of wing and tail contributions. The effect of flexibility on longitudinal control for the example airplane was found to be of little real importance.

Steady-state and transient analysis of a squeeze film damper bearing for rotor stability

NASA Technical Reports Server (NTRS)

Barrett, L. E.; Gunter, E. J.

1975-01-01

A study of the steady-state and transient response of the squeeze film damper bearing is presented. Both the steady-state and transient equations for the hydrodynamic bearing forces are derived. The bearing equivalent stiffness and damping coefficients are determined by steady-state equations. These coefficients are used to find the bearing configuration which will provide the optimum support characteristics based on a stability analysis of the rotor-bearing system. The transient analysis of rotor-bearing systems is performed by coupling the bearing and journal equations and integrating forward in time. The effects of unbalance, cavitation, and retainer springs are included in the analysis. Methods of determining the stability of a rotor-bearing system under the influence of aerodynamic forces and internal shaft friction are discussed with emphasis on solving the system characteristic frequency equation and on producing stability maps. It is shown that for optimum stability and low force transmissability the squeeze bearing should operate at an eccentricity ratio epsilon 0.4.

Linear and nonlinear stability characteristics of whistlers

NASA Technical Reports Server (NTRS)

Brinca, A. L.

1972-01-01

Linear and nonlinear propagating characteristics of right-hand polarized, slow electromagnetic, magnetoplasma waves (whistlers) are discussed in terms of stability and dispersion. An analysis of the stability of whistlers propagating at an angle to the static magnetic field is presented. A new mechanism is derived for the onset of stimulated emissions, and modulational instability for nonlinear whistlers are discussed.

Stability analysis of dynamic collaboration model with control signals on two lanes

NASA Astrophysics Data System (ADS)

Li, Zhipeng; Zhang, Run; Xu, Shangzhi; Qian, Yeqing; Xu, Juan

2014-12-01

In this paper, the influence of control signals on the stability of two-lane traffic flow is mainly studied by applying control theory with lane changing behaviors. We present the two-lane dynamic collaboration model with lateral friction and the expressions of feedback control signals. What is more, utilizing the delayed feedback control theory to the two-lane dynamic collaboration model with control signals, we investigate the stability of traffic flow theoretically and the stability conditions for both lanes are derived with finding that the forward and lateral feedback signals can improve the stability of traffic flow while the backward feedback signals cannot achieve it. Besides, direct simulations are conducted to verify the results of theoretical analysis, which shows that the feedback signals have a significant effect on the running state of two vehicle groups, and the results are same with the theoretical analysis.

Power System Transient Stability Improvement by the Interline Power Flow Controller (IPFC)

NASA Astrophysics Data System (ADS)

Zhang, Jun; Yokoyama, Akihiko

This paper presents a study on the power system transient stability improvement by means of interline power flow controller (IPFC). The power injection model of IPFC in transient analysis is proposed and can be easily incorporated into existing power systems. Based on the energy function analysis, the operation of IPFC should guarantee that the time derivative of the global energy of the system is not greater than zero in order to damp the electromechanical oscillations. Accordingly, control laws of IPFC are proposed for its application to the single-machine infinite-bus (SMIB) system and the multimachine systems, respectively. Numerical simulations on the corresponding model power systems are presented to demonstrate their effectiveness in improving power system transient stability.

Stability, performance and sensitivity analysis of I.I.D. jump linear systems

NASA Astrophysics Data System (ADS)

Chávez Fuentes, Jorge R.; González, Oscar R.; Gray, W. Steven

2018-06-01

This paper presents a symmetric Kronecker product analysis of independent and identically distributed jump linear systems to develop new, lower dimensional equations for the stability and performance analysis of this type of systems than what is currently available. In addition, new closed form expressions characterising multi-parameter relative sensitivity functions for performance metrics are introduced. The analysis technique is illustrated with a distributed fault-tolerant flight control example where the communication links are allowed to fail randomly.

Development of a sensitivity analysis technique for multiloop flight control systems

NASA Technical Reports Server (NTRS)

Vaillard, A. H.; Paduano, J.; Downing, D. R.

1985-01-01

This report presents the development and application of a sensitivity analysis technique for multiloop flight control systems. This analysis yields very useful information on the sensitivity of the relative-stability criteria of the control system, with variations or uncertainties in the system and controller elements. The sensitivity analysis technique developed is based on the computation of the singular values and singular-value gradients of a feedback-control system. The method is applicable to single-input/single-output as well as multiloop continuous-control systems. Application to sampled-data systems is also explored. The sensitivity analysis technique was applied to a continuous yaw/roll damper stability augmentation system of a typical business jet, and the results show that the analysis is very useful in determining the system elements which have the largest effect on the relative stability of the closed-loop system. As a secondary product of the research reported here, the relative stability criteria based on the concept of singular values were explored.

Endotoxin Studies And Biosolids Stabilization Research

EPA Science Inventory

This presentation has three parts; a review of bench-scale endotoxin research, a review of observations from a field scale endotoxin release study, and discussion of biosolids stabilization and characterization by PLFA/FAME microbial community analysis. Endotoxins are part of th...

The prospects for magnetohydrodynamic stability in advanced tokamak regimes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Manickam, J.; Chance, M.S.; Jardin, S.C.

1994-05-01

Stability analysis of advanced regime tokamaks is presented. Here advanced regimes are defined to include configurations where the ratio of the bootstrap current, [ital I][sub BS], to the total plasma current, [ital I][sub [ital p

Hydrodynamic Stability Analysis on Sheared Stratified Flow in a Convective Flow Environment

NASA Astrophysics Data System (ADS)

Xiao, Yuan; Lin, Wenxian; Armfiled, Steven; Kirkpatrick, Michael; He, Yinghe; Fluid Dynamics Research Group, James Cook University Team; Fluid Dynamics Research Group, University of Sydney Team

2014-11-01

A hydrodynamic stability analysis on the convective sheared boundary layer (SCBL) flow, where a sheared stratified flow and a thermally convective flow coexist, is carried out in this study. The linear unstable stratifications representing the convective flow are included in the TaylorGoldstein equations as an unstable factor Jb. A new unstable region corresponding to the convective instability, which is not present in pure sheared stratified flows, is found with the analysis. It is also found that the boundaries of the convective instability regions expand with increasing Jb and interact with the sheared stratified instability region. More results will be presented at the conference

Stability of sequences generated by nonlinear differential systems. [for analysis of glider jet aircraft motion

NASA Technical Reports Server (NTRS)

Brown, R. L.

1979-01-01

A local stability analysis is presented for both the analytic and numerical solutions of the initial value problem for a system of ordinary differential equations. It is shown that, using a proper choice of Liapunov function, a connected region of stable initial values of both the analytic solution and the one-leg k-step numerical solution can be approximated. Attention is given to the example of the two-dimensional problem involving the stability of the longitudinal equations of motion of a gliding jet aircraft.

Applying the methodology of Design of Experiments to stability studies: a Partial Least Squares approach for evaluation of drug stability.

PubMed

Jordan, Nika; Zakrajšek, Jure; Bohanec, Simona; Roškar, Robert; Grabnar, Iztok

2018-05-01

The aim of the present research is to show that the methodology of Design of Experiments can be applied to stability data evaluation, as they can be seen as multi-factor and multi-level experimental designs. Linear regression analysis is usually an approach for analyzing stability data, but multivariate statistical methods could also be used to assess drug stability during the development phase. Data from a stability study for a pharmaceutical product with hydrochlorothiazide (HCTZ) as an unstable drug substance was used as a case example in this paper. The design space of the stability study was modeled using Umetrics MODDE 10.1 software. We showed that a Partial Least Squares model could be used for a multi-dimensional presentation of all data generated in a stability study and for determination of the relationship among factors that influence drug stability. It might also be used for stability predictions and potentially for the optimization of the extent of stability testing needed to determine shelf life and storage conditions, which would be time and cost-effective for the pharmaceutical industry.

Stability analysis using SDSA tool

NASA Astrophysics Data System (ADS)

Goetzendorf-Grabowski, Tomasz; Mieszalski, Dawid; Marcinkiewicz, Ewa

2011-11-01

The SDSA (Simulation and Dynamic Stability Analysis) application is presented as a tool for analysing the dynamic characteristics of the aircraft just in the conceptual design stage. SDSA is part of the CEASIOM (Computerized Environment for Aircraft Synthesis and Integrated Optimization Methods) software environment which was developed within the SimSAC (Simulating Aircraft Stability And Control Characteristics for Use in Conceptual Design) project, funded by the European Commission 6th Framework Program. SDSA can also be used as stand alone software, and integrated with other design and optimisation systems using software wrappers. This paper focuses on the main functionalities of SDSA and presents both computational and free flight experimental results to compare and validate the presented software. Two aircraft are considered, the EADS Ranger 2000 and the Warsaw University designed PW-6 glider. For the two cases considered here the SDSA software is shown to be an excellent tool for predicting dynamic characteristics of an aircraft.

Stability Metrics for Simulation and Flight-Software Assessment and Monitoring of Adaptive Control Assist Compensators

NASA Technical Reports Server (NTRS)

Hodel, A. S.; Whorton, Mark; Zhu, J. Jim

2008-01-01

Due to a need for improved reliability and performance in aerospace systems, there is increased interest in the use of adaptive control or other nonlinear, time-varying control designs in aerospace vehicles. While such techniques are built on Lyapunov stability theory, they lack an accompanying set of metrics for the assessment of stability margins such as the classical gain and phase margins used in linear time-invariant systems. Such metrics must both be physically meaningful and permit the user to draw conclusions in a straightforward fashion. We present in this paper a roadmap to the development of metrics appropriate to nonlinear, time-varying systems. We also present two case studies in which frozen-time gain and phase margins incorrectly predict stability or instability. We then present a multi-resolution analysis approach that permits on-line real-time stability assessment of nonlinear systems.

Stability and Interaction of Coherent Structure in Supersonic Reactive Wakes

NASA Technical Reports Server (NTRS)

Menon, Suresh

1983-01-01

A theoretical formulation and analysis is presented for a study of the stability and interaction of coherent structure in reacting free shear layers. The physical problem under investigation is a premixed hydrogen-oxygen reacting shear layer in the wake of a thin flat plate. The coherent structure is modeled as a periodic disturbance and its stability is determined by the application of linearized hydrodynamic stability theory which results in a generalized eigenvalue problem for reactive flows. Detailed stability analysis of the reactive wake for neutral, symmetrical and antisymmetrical disturbance is presented. Reactive stability criteria is shown to be quite different from classical non-reactive stability. The interaction between the mean flow, coherent structure and fine-scale turbulence is theoretically formulated using the von-Kaman integral technique. Both time-averaging and conditional phase averaging are necessary to separate the three types of motion. The resulting integro-differential equations can then be solved subject to initial conditions with appropriate shape functions. In the laminar flow transition region of interest, the spatial interaction between the mean motion and coherent structure is calculated for both non-reactive and reactive conditions and compared with experimental data wherever available. The fine-scale turbulent motion determined by the application of integral analysis to the fluctuation equations. Since at present this turbulence model is still untested, turbulence is modeled in the interaction problem by a simple algebraic eddy viscosity model. The applicability of the integral turbulence model formulated here is studied parametrically by integrating these equations for the simple case of self-similar mean motion with assumed shape functions. The effect of the motion of the coherent structure is studied and very good agreement is obtained with previous experimental and theoretical works for non-reactive flow. For the reactive case, lack of experimental data made direct comparison difficult. It was determined that the growth rate of the disturbance amplitude is lower for reactive case. The results indicate that the reactive flow stability is in qualitative agreement with experimental observation.

Floquet stability analysis of the longitudinal dynamics of two hovering model insects

PubMed Central

Wu, Jiang Hao; Sun, Mao

2012-01-01

Because of the periodically varying aerodynamic and inertial forces of the flapping wings, a hovering or constant-speed flying insect is a cyclically forcing system, and, generally, the flight is not in a fixed-point equilibrium, but in a cyclic-motion equilibrium. Current stability theory of insect flight is based on the averaged model and treats the flight as a fixed-point equilibrium. In the present study, we treated the flight as a cyclic-motion equilibrium and used the Floquet theory to analyse the longitudinal stability of insect flight. Two hovering model insects were considered—a dronefly and a hawkmoth. The former had relatively high wingbeat frequency and small wing-mass to body-mass ratio, and hence very small amplitude of body oscillation; while the latter had relatively low wingbeat frequency and large wing-mass to body-mass ratio, and hence relatively large amplitude of body oscillation. For comparison, analysis using the averaged-model theory (fixed-point stability analysis) was also made. Results of both the cyclic-motion stability analysis and the fixed-point stability analysis were tested by numerical simulation using complete equations of motion coupled with the Navier–Stokes equations. The Floquet theory (cyclic-motion stability analysis) agreed well with the simulation for both the model dronefly and the model hawkmoth; but the averaged-model theory gave good results only for the dronefly. Thus, for an insect with relatively large body oscillation at wingbeat frequency, cyclic-motion stability analysis is required, and for their control analysis, the existing well-developed control theories for systems of fixed-point equilibrium are no longer applicable and new methods that take the cyclic variation of the flight dynamics into account are needed. PMID:22491980

Study report on guidelines and test procedures for investigating stability of nonlinear cardiovascular control system models

NASA Technical Reports Server (NTRS)

Fitzjerrell, D. G.

1974-01-01

A general study of the stability of nonlinear as compared to linear control systems is presented. The analysis is general and, therefore, applies to other types of nonlinear biological control systems as well as the cardiovascular control system models. Both inherent and numerical stability are discussed for corresponding analytical and graphic methods and numerical methods.

Stability and performance tradeoffs in bi-lateral telemanipulation

NASA Technical Reports Server (NTRS)

Hannaford, Blake

1989-01-01

Kinesthetic force feedback provides measurable increase in remote manipulation system performance. Intensive computation time requirements or operation under conditions of time delay can cause serious stability problems in control-system design. Here, a simplified linear analysis of this stability problem is presented for the forward-flow generalized architecture, applying the hybrid two-port representation to express the loop gain of the traditional master-slave architecture, which can be subjected to similar analysis. The hybrid two-port representation is also used to express the effects on the fidelity of manipulation or feel of one design approach used to stabilize the forward-flow architecture. The results suggest that, when local force feedback at the slave side is used to reduce manipulator stability problems, a price is paid in terms of telemanipulation fidelity.

On the stability analysis of approximate factorization methods for 3D Euler and Navier-Stokes equations

NASA Technical Reports Server (NTRS)

Demuren, A. O.; Ibraheem, S. O.

1993-01-01

The convergence characteristics of various approximate factorizations for the 3D Euler and Navier-Stokes equations are examined using the von-Neumann stability analysis method. Three upwind-difference based factorizations and several central-difference based factorizations are considered for the Euler equations. In the upwind factorizations both the flux-vector splitting methods of Steger and Warming and van Leer are considered. Analysis of the Navier-Stokes equations is performed only on the Beam and Warming central-difference scheme. The range of CFL numbers over which each factorization is stable is presented for one-, two-, and three-dimensional flow. Also presented for each factorization is the CFL number at which the maximum eigenvalue is minimized, for all Fourier components, as well as for the high frequency range only. The latter is useful for predicting the effectiveness of multigrid procedures with these schemes as smoothers. Further, local mode analysis is performed to test the suitability of using a uniform flow field in the stability analysis. Some inconsistencies in the results from previous analyses are resolved.

Stability of Dynamical Systems with Discontinuous Motions:

NASA Astrophysics Data System (ADS)

Michel, Anthony N.; Hou, Ling

In this paper we present a stability theory for discontinuous dynamical systems (DDS): continuous-time systems whose motions are not necessarily continuous with respect to time. We show that this theory is not only applicable in the analysis of DDS, but also in the analysis of continuous dynamical systems (continuous-time systems whose motions are continuous with respect to time), discrete-time dynamical systems (systems whose motions are defined at discrete points in time) and hybrid dynamical systems (HDS) (systems whose descriptions involve simultaneously continuous-time and discrete-time). We show that the stability results for DDS are in general less conservative than the corresponding well-known classical Lyapunov results for continuous dynamical systems and discrete-time dynamical systems. Although the DDS stability results are applicable to general dynamical systems defined on metric spaces (divorced from any kind of description by differential equations, or any other kinds of equations), we confine ourselves to finite-dimensional dynamical systems defined by ordinary differential equations and difference equations, to make this paper as widely accessible as possible. We present only sample results, namely, results for uniform asymptotic stability in the large.

Towards Stability Analysis of Jump Linear Systems with State-Dependent and Stochastic Switching

NASA Technical Reports Server (NTRS)

Tejada, Arturo; Gonzalez, Oscar R.; Gray, W. Steven

2004-01-01

This paper analyzes the stability of hierarchical jump linear systems where the supervisor is driven by a Markovian stochastic process and by the values of the supervised jump linear system s states. The stability framework for this class of systems is developed over infinite and finite time horizons. The framework is then used to derive sufficient stability conditions for a specific class of hybrid jump linear systems with performance supervision. New sufficient stochastic stability conditions for discrete-time jump linear systems are also presented.

Photothermal Stability of an E-Beam Pre-Crosslinked EVA Encapsulant and Its Performance Degradation on a-Si Submodules: Preprint

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pern, F. J.; Watson, G. L.; Glick, S. H.

2001-10-01

Presented at the 2001 NCPV Program Review Meeting: Study of photothermal stability of special EVA encapsulant by accelerated exposure testing and analysis of causes of performance degradation on a-Si modules.

Linear stability analysis of a levitated nanomagnet in a static magnetic field: Quantum spin stabilized magnetic levitation

NASA Astrophysics Data System (ADS)

Rusconi, C. C.; Pöchhacker, V.; Cirac, J. I.; Romero-Isart, O.

2017-10-01

We theoretically study the levitation of a single magnetic domain nanosphere in an external static magnetic field. We show that, apart from the stability provided by the mechanical rotation of the nanomagnet (as in the classical Levitron), the quantum spin origin of its magnetization provides two additional mechanisms to stably levitate the system. Despite the Earnshaw theorem, such stable phases are present even in the absence of mechanical rotation. For large magnetic fields, the Larmor precession of the quantum magnetic moment stabilizes the system in full analogy with magnetic trapping of a neutral atom. For low magnetic fields, the magnetic anisotropy stabilizes the system via the Einstein-de Haas effect. These results are obtained with a linear stability analysis of a single magnetic domain rigid nanosphere with uniaxial anisotropy in a Ioffe-Pritchard magnetic field.

Effects of friction dampers on aerodynamically unstable rotor stages

NASA Technical Reports Server (NTRS)

Griffin, J. H.; Sinha, A.

1983-01-01

Attention is given to the physical concepts and mathematical techniques useful in the analysis of the stabilizing effect of friction on aerodynamically unstable rotor stages. Results are presented for three-, four-, and five-bladed disks. In the present multidegree-of-freedom model of an aerodynamically unstable rotor stage, a harmonic steady state solution due to the friction dampers may be either a stability limit, a stable cycle limit, or neither. A criterion is established in the form of an energy function which determines whether the solution is a stability limit. In the event that the initial displacement and velocity exeed those associated with the steady state solution corresponding to a stability limit, the reponse becomes unbounded.

Spherical gyroscopic moment stabilizer for attitude control of microsatellites

NASA Astrophysics Data System (ADS)

Keshtkar, Sajjad; Moreno, Jaime A.; Kojima, Hirohisa; Uchiyama, Kenji; Nohmi, Masahiro; Takaya, Keisuke

2018-02-01

This paper presents a new and improved concept of recently proposed two-degrees of freedom spherical stabilizer for triaxial orientation of microsatellites. The analytical analysis of the advantages of the proposed mechanism over the existing inertial attitude control devices are introduced. The extended equations of motion of the stabilizing satellite including the spherical gyroscope, for control law design and numerical simulations, are studied in detail. A new control algorithm based on continuous high-order sliding mode algorithms, for managing the torque produced by the stabilizer and therefore the attitude control of the satellite in the presence of perturbations/uncertainties, is presented. Some numerical simulations are carried out to prove the performance of the proposed mechanism and control laws.

An Investigation of the Aerodynamic Characteristics of an 0.08-Scale Model of the Chance Vought XF7U-1 Airplane in the Langley High-Speed 7- by 10-Foot Tunnel. Part II - Basic Lateral Stability Characteristics TED No. NACA DE308. Part 2; Basic Lateral Stability Charactistics, TED No. NACA DE308

NASA Technical Reports Server (NTRS)

Kemp, William B., Jr.; Goodson, Kenneth W.; Kuhn, Richard E.

1947-01-01

Tests have been conducted in the Langley high-speed 7- by 10-foot tunnel over a Mach number range from 0.40 to 0.91 to determine the stability and control characteristics of an 0.08-scale model of the Chance Vought XF7U-1 airplane. The basic lateral stability characteristics of the complete model with undeflected control surfaces are presented in the present report with a very limited analysis of the results.

Attitude stability of a spinning spacecraft during appendage deployment/retraction

NASA Technical Reports Server (NTRS)

Fitz-Coy, Norman; Fullerton, Wayne

1994-01-01

The work presented is motivated by the need for a national satellite rescue policy, not the ad hoc policy now in place. In studying different approaches for a national policy, the issue of capture and stabilization of a tumbling spacecraft must be addressed. For a rescue mission involving a tumbling spacecraft, it may be advantageous to have a rescue vehicle which is compact and 'rigid' during the rendezvous/capture phase. After capture, passive stabilization techniques could be utilized as an efficient means of detumbling the resulting system (i.e., both the rescue vehicle and captures spacecraft). Since the rescue vehicle is initially compact and 'rigid,' significant passive stabilization through energy dissipation can only be achieved through the deployment of flexible appendages. Once stabilization is accomplished, retraction of the appendages before maneuvering the system to its final destination may also prove advantageous. It is therefore of paramount interest that we study the effect of appendage deployment/retraction on the attitude stability of a spacecraft. Particular interest should be paid to appendage retraction, since if this process is destabilizing, passive stabilization as proposed may not be useful. Over the past three decades, it has been an 'on-again-off-again affair' with the problem of spacecraft appendage deployment. In most instances, these studies have been numerical simulations of specific spacecraft configurations for which there were specific concerns. The primary focus of these studies was the behavior of the appendage during deployment; the effects of appendage retraction was considered only in one of these studies. What is missing in the literature is a thorough study of the effects of appendage deployment/retraction on the attitude stability of a spacecraft. This paper presents a rigorous analysis of the stability of a spinning spacecraft during the deployment or the retraction of an appendage. The analysis is simplified such that meaningful insights into the problem can be inferred; it is not overly simplified such that critical dynamical behavior is neglected. The system is analyzed assuming that the spacecraft hub is rigid. The appendage deployment mechanism is modeled as a point mass on a massless rod whose length undergoes prescribed changes. Simplified flexibility effects of the appendage are included. The system is examined for stability by linearizing the equations in terms of small deviations from steady, noninterfering coning motion. Routh's procedure for analyzing small deviations from steady motion in dynamical systems is utilized in the analysis. The system of equations are nondimensionalized to facilitate parametric studies. The results are presented in terms of a reduced number of nondimensional parameters so that some general conclusions may be drawn. Verification of the linear analysis is presented through numerical simulations of the complete nonlinear, nonautonomous, coupled equations.

Effect of Ionic Soil Stabilizers on Soil-Water Characteristic of Special Clay

NASA Astrophysics Data System (ADS)

Cui, D.; Xiang, W.

2011-12-01

The engineering properties of special clay are conventionally improved through the use of chemical additive such as ionic soil stabilizer (ISS). Such special clays are often referred to as stabilized or treated clays. The soil-water characteristic curves (SWCC) of special clays from Henan province and Hubei province were measured both in natural and stabilized conditions using the pressure plate apparatus in the suction range of 0-500 kPa. The SWCC results are used to interpret the special clays behavior due to stabilizer treatment. In addition, relationships were developed between the basic clay and stabilized properties such as specific surface area and pore size distribution. The analysis showed that specific surface area decreases, cumulative pore volume and average pore size diameter decrease, dehydration rate slows and the thickness of water film thins after treatment with Ionic Soil Stabilizer. The research data and interpretation analysis presented here can be extended to understand the water film change behaviors influencing the mechanical and physical properties of stabilized special clay soils. KEY WORDS: ionic soil stabilizer, special clay, pore size diameter, specific surface area, soil water characteristic curve, water film

Sensitivity analysis of automatic flight control systems using singular value concepts

NASA Technical Reports Server (NTRS)

Herrera-Vaillard, A.; Paduano, J.; Downing, D.

1985-01-01

A sensitivity analysis is presented that can be used to judge the impact of vehicle dynamic model variations on the relative stability of multivariable continuous closed-loop control systems. The sensitivity analysis uses and extends the singular-value concept by developing expressions for the gradients of the singular value with respect to variations in the vehicle dynamic model and the controller design. Combined with a priori estimates of the accuracy of the model, the gradients are used to identify the elements in the vehicle dynamic model and controller that could severely impact the system's relative stability. The technique is demonstrated for a yaw/roll damper stability augmentation designed for a business jet.

Influence of fracture network physical properties on stability criteria of density-driven flow in a dual-porosity system

NASA Astrophysics Data System (ADS)

Hassanzadeh, H.; Jafari Raad, S. M.

2017-12-01

Linear stability analysis is conducted to study the onset of buoyancy-driven convection involved in solubility trapping of CO2 into deep fractured aquifers. In this study, the effect of fracture network physical properties on the stability criteria in a brine-rich fractured porous layer is investigated using dual porosity concept for both single and variable matrix block size distributions. Linear stability analysis results show that both fracture interporosity flow and fracture storativity factors play an important role in the stability behavior of the system. It is shown that a diffusive boundary layer under the gravity field in a fractured rock with lower fracture storativity and/or higher fracture interporosity flow coefficient is more stable. We present scaling relations that relate the onset of convective instability in fractured aquifers. These findings improve our understanding of buoyancy driven flow in fractured aquifers and are particularly important in estimation of potential storage capacity, risk assessment, and storage sites characterization and screening.Keywords: CO2 sequestration; fractured rock; buoyancy-driven convection; stability analysis

Probing the pH sensitivity of R-phycoerythrin: investigations of active conformational and functional variation.

PubMed

Liu, Lu-Ning; Su, Hai-Nan; Yan, Shi-Gan; Shao, Si-Mi; Xie, Bin-Bin; Chen, Xiu-Lan; Zhang, Xi-Ying; Zhou, Bai-Cheng; Zhang, Yu-Zhong

2009-07-01

Crystal structures of phycobiliproteins have provided valuable information regarding the conformations and amino acid organizations of peptides and chromophores, and enable us to investigate their structural and functional relationships with respect to environmental variations. In this work, we explored the pH-induced conformational and functional dynamics of R-phycoerythrin (R-PE) by means of absorption, fluorescence and circular dichroism spectra, together with analysis of its crystal structure. R-PE presents stronger functional stability in the pH range of 3.5-10 compared to the structural stability. Beyond this range, pronounced functional and structural changes occur. Crystal structure analysis shows that the tertiary structure of R-PE is fixed by several key anchoring points of the protein. With this specific association, the fundamental structure of R-PE is stabilized to present physiological spectroscopic properties, while local variations in protein peptides are also allowed in response to environmental disturbances. The functional stability and relative structural sensitivity of R-PE allow environmental adaptation.

Extremum seeking with bounded update rates

DOE PAGES

Scheinker, Alexander; Krstić, Miroslav

2013-11-16

In this work, we present a form of extremum seeking (ES) in which the unknown function being minimized enters the system’s dynamics as the argument of a cosine or sine term, thereby guaranteeing known bounds on update rates and control efforts. We present general n-dimensional optimization and stabilization results as well as 2D vehicle control, with bounded velocity and control efforts. For application to autonomous vehicles, tracking a source in a GPS denied environment with unknown orientation, this ES approach allows for smooth heading angle actuation, with constant velocity, and in application to a unicycle-type vehicle results in control abilitymore » as if the vehicle is fully actuated. Our stability analysis is made possible by the classic results of Kurzweil, Jarnik, Sussmann, and Liu, regarding systems with highly oscillatory terms. In our stability analysis, we combine the averaging results with a semi-global practical stability result under small parametric perturbations developed by Moreau and Aeyels.« less

Research study on stabilization and control: Modern sampled data control theory

NASA Technical Reports Server (NTRS)

Kuo, B. C.; Singh, G.; Yackel, R. A.

1973-01-01

A numerical analysis of spacecraft stability parameters was conducted. The analysis is based on a digital approximation by point by point state comparison. The technique used is that of approximating a continuous data system by a sampled data model by comparison of the states of the two systems. Application of the method to the digital redesign of the simplified one axis dynamics of the Skylab is presented.

Stability analysis and application of a mathematical cholera model.

PubMed

Liao, Shu; Wang, Jin

2011-07-01

In this paper, we conduct a dynamical analysis of the deterministic cholera model proposed in [9]. We study the stability of both the disease-free and endemic equilibria so as to explore the complex epidemic and endemic dynamics of the disease. We demonstrate a real-world application of this model by investigating the recent cholera outbreak in Zimbabwe. Meanwhile, we present numerical simulation results to verify the analytical predictions.

Dynamic Stability Analysis of Linear Time-varying Systems via an Extended Modal Identification Approach

NASA Astrophysics Data System (ADS)

Ma, Zhisai; Liu, Li; Zhou, Sida; Naets, Frank; Heylen, Ward; Desmet, Wim

2017-03-01

The problem of linear time-varying(LTV) system modal analysis is considered based on time-dependent state space representations, as classical modal analysis of linear time-invariant systems and current LTV system modal analysis under the "frozen-time" assumption are not able to determine the dynamic stability of LTV systems. Time-dependent state space representations of LTV systems are first introduced, and the corresponding modal analysis theories are subsequently presented via a stability-preserving state transformation. The time-varying modes of LTV systems are extended in terms of uniqueness, and are further interpreted to determine the system's stability. An extended modal identification is proposed to estimate the time-varying modes, consisting of the estimation of the state transition matrix via a subspace-based method and the extraction of the time-varying modes by the QR decomposition. The proposed approach is numerically validated by three numerical cases, and is experimentally validated by a coupled moving-mass simply supported beam experimental case. The proposed approach is capable of accurately estimating the time-varying modes, and provides a new way to determine the dynamic stability of LTV systems by using the estimated time-varying modes.

An extended continuum model accounting for the driver's timid and aggressive attributions

NASA Astrophysics Data System (ADS)

Cheng, Rongjun; Ge, Hongxia; Wang, Jufeng

2017-04-01

Considering the driver's timid and aggressive behaviors simultaneously, a new continuum model is put forwarded in this paper. By applying the linear stability theory, we presented the analysis of new model's linear stability. Through nonlinear analysis, the KdV-Burgers equation is derived to describe density wave near the neutral stability line. Numerical results verify that aggressive driving is better than timid act because the aggressive driver will adjust his speed timely according to the leading car's speed. The key improvement of this new model is that the timid driving deteriorates traffic stability while the aggressive driving will enhance traffic stability. The relationship of energy consumption between the aggressive and timid driving is also studied. Numerical results show that aggressive driver behavior can not only suppress the traffic congestion but also reduce the energy consumption.

Interpreting Popov criteria in Lure´ systems with complex scaling stability analysis

NASA Astrophysics Data System (ADS)

Zhou, J.

2018-06-01

The paper presents a novel frequency-domain interpretation of Popov criteria for absolute stability in Lure´ systems by means of what we call complex scaling stability analysis. The complex scaling technique is developed for exponential/asymptotic stability in LTI feedback systems, which dispenses open-loop poles distribution, contour/locus orientation and prior frequency sweeping. Exploiting the technique for alternatively revealing positive realness of transfer functions, re-interpreting Popov criteria is explicated. More specifically, the suggested frequency-domain stability conditions are conformable both in scalar and multivariable cases, and can be implemented either graphically with locus plotting or numerically without; in particular, the latter is suitable as a design tool with auxiliary parameter freedom. The interpretation also reveals further frequency-domain facts about Lure´ systems. Numerical examples are included to illustrate the main results.

Rotorcraft aeroelastic stability

NASA Technical Reports Server (NTRS)

Ormiston, Robert A.; Warmbrodt, William G.; Hodges, Dewey H.; Peters, David A.

1988-01-01

Theoretical and experimental developments in the aeroelastic and aeromechanical stability of helicopters and tilt-rotor aircraft are addressed. Included are the underlying nonlinear structural mechanics of slender rotating beams, necessary for accurate modeling of elastic cantilever rotor blades, and the development of dynamic inflow, an unsteady aerodynamic theory for low-frequency aeroelastic stability applications. Analytical treatment of isolated rotor stability in hover and forward flight, coupled rotor-fuselage stability in hover and forward flight, and analysis of tilt-rotor dynamic stability are considered. Results of parametric investigations of system behavior are presented, and correlation between theoretical results and experimental data from small and large scale wind tunnel and flight testing are discussed.

An analysis of lateral stability in power-off flight with charts for use in design

NASA Technical Reports Server (NTRS)

Zimmerman, Charles H

1937-01-01

The aerodynamic and mass factors governing lateral stability are discussed and formulas are given for their estimation. Relatively simple relationships between the governing factors and the resulting stability characteristics are presented. A series of charts is included with which approximate stability characteristics may be rapidly estimated. The effects of the various governing factors upon the stability characteristics are discussed in detail. It is pointed out that much additional research is necessary both to correlate stability characteristics with riding, flying, and handling qualities and to provide suitable data for accurate estimates of those characteristics of an airplane while it is in the design stage.

The stability of coupled renewal-differential equations with econometric applications

NASA Technical Reports Server (NTRS)

Rhoten, R. P.; Aggarwal, J. K.

1969-01-01

Concepts and results are presented in the fields of mathematical modeling, economics, and stability analysis. A coupled renewal-differential equation structure is presented as a modeling form for systems possessing hereditary characteristics, and this structure is applied to a model of the Austrian theory of business cycles. For realistic conditions, the system is shown to have an infinite number of poles, and conditions are presented which are both necessary and sufficient for all poles to lie strictly in the left half plane.

Discrete time modeling and stability analysis of TCP Vegas

NASA Astrophysics Data System (ADS)

You, Byungyong; Koo, Kyungmo; Lee, Jin S.

2007-12-01

This paper presents an analysis method for TCP Vegas network model with single link and single source. Some papers showed global stability of several network models, but those models are not a dual problem where dynamics both exist in sources and links such as TCP Vegas. Other papers studied TCP Vegas as a dual problem, but it did not fully derive an asymptotic stability region. Therefore we analyze TCP Vegas with Jury's criterion which is necessary and sufficient condition. So we use state space model in discrete time and by using Jury's criterion, we could find an asymptotic stability region of TCP Vegas network model. This result is verified by ns-2 simulation. And by comparing with other results, we could know our method performed well.

The influence of ship's stability on safety of navigation

NASA Astrophysics Data System (ADS)

Hanzu-Pazara, R.; Duse; Varsami, C.; Andrei, C.; Dumitrache, R.

2016-08-01

Ship's stability is one of the most important and complex concept about safety of ship and safety of navigation and it is governed by maritime law as well as maritime codes. The paper presents the importance of ship's intact stability as part of the general concept of ship's seaworthiness. There is always a correlation between ship’ stability and safety of ship and safety of navigation. Loss of ship's stability is presented as a threat to safety of navigation. We are going to present the causes that lead to ship stability failure and their impact on safety of navigation. A study of various ship stability casualties in heavy weather conditions are going to be presented, the causes are going to be analyzed and the possible ways of stability failures are assessed. Vessel's intact stability is a fundamental component of seaworthiness so it is in the interest of all owners/operators to learn about this topic and ensure that their vessel possesses a satisfactory level of stability in order to ensure its safety as well as that of the people on board the ship. Understanding ship's stability, trim, stress, and the basics of ship's construction is a key to keeping a ship seaworthy. The findings of this study can be beneficial to the maritime safety administrations to adopt decision-making on maritime safety management, but it is also important to carry out statistics and analysis of marine casualties to help to adopt proper safety management measures. Moreover, the study can be a useful guidance for masters and officers on board vessel in order to understand the factors that contribute to ship stability failure during the voyage not only in port during loading operations and to take preventive measures to avoid to put the ship in such a dangerous situations.

Comments on the "Byzantine Self-Stabilizing Pulse Synchronization" Protocol: Counter-examples

NASA Technical Reports Server (NTRS)

Malekpour, Mahyar R.; Siminiceanu, Radu

2006-01-01

Embedded distributed systems have become an integral part of many safety-critical applications. There have been many attempts to solve the self-stabilization problem of clocks across a distributed system. An analysis of one such protocol called the Byzantine Self-Stabilizing Pulse Synchronization (BSS-Pulse-Synch) protocol from a paper entitled "Linear Time Byzantine Self-Stabilizing Clock Synchronization" by Daliot, et al., is presented in this report. This report also includes a discussion of the complexity and pitfalls of designing self-stabilizing protocols and provides counter-examples for the claims of the above protocol.

Aeroelastic loads and stability investigation of a full-scale hingeless rotor

NASA Technical Reports Server (NTRS)

Peterson, Randall L.; Johnson, Wayne

1991-01-01

An analytical investigation was conducted to study the influence of various parameters on predicting the aeroelastic loads and stability of a full-scale hingeless rotor in hover and forward flight. The CAMRAD/JA (Comprehensive Analytical Model of Rotorcraft Aerodynamics and Dynamics, Johnson Aeronautics) analysis code is used to obtain the analytical predictions. Data are presented for rotor blade bending and torsional moments as well as inplane damping data obtained for rotor operation in hover at a constant rotor rotational speed of 425 rpm and thrust coefficients between 0.0 and 0.12. Experimental data are presented from a test in the wind tunnel. Validation of the rotor system structural model with experimental rotor blade loads data shows excellent correlation with analytical results. Using this analysis, the influence of different aerodynamic inflow models, the number of generalized blade and body degrees of freedom, and the control-system stiffness at predicted stability levels are shown. Forward flight predictions of the BO-105 rotor system for 1-G thrust conditions at advance ratios of 0.0 to 0.35 are presented. The influence of different aerodynamic inflow models, dynamic inflow models and shaft angle variations on predicted stability levels are shown as a function of advance ratio.

Influence of the type of aqueous sodium silicate on the stabilization and rheology of kaolin clay suspensions

NASA Astrophysics Data System (ADS)

Izak, Piotr; Ogłaza, Longin; Mozgawa, Włodzimierz; Mastalska-Popławska, Joanna; Stempkowska, Agata

2018-05-01

To avoid agglomeration and sedimentation of grains, ceramic slurries should be modified by stabilizers in order to increase the electrostatic interactions between the dispersed particles. In this study we present the spectral analysis of aqueous sodium silicates obtained by different synthesis methods and their influence on the rheological properties of kaolin based slurries. Infrared and Raman spectra can be used to describe the structure of silicate structural units present in aqueous sodium silicates. It was confirmed that the best stabilization results possess aqueous sodium silicates of the silicate moduli of about 2 and the optimal concentration of the used fluidizer is 0.3 wt% to the kaolin clay dry mass. One of the most important conclusions is that the synthesis method of the fluidizer has no significant effect on its stabilization properties but used medium does create adequate stabilization mechanism depending on the silicate structures present in the sodium silicate solution.

Experimental and numerical analysis of the influence of tyres' properties on the straight running stability of a sport-touring motorcycle

NASA Astrophysics Data System (ADS)

Cossalter, Vittore; Doria, Alberto; Formentini, Matteo; Peretto, Martino

2012-03-01

The behaviour of a motorcycle on the road is largely governed by tyre properties. This paper presents experimental and numerical analyses dealing with the influence of tyre properties on the stability of weave and wobble in straight running. The final goal is to find optimal sets of tyre properties that improve the stability of a motorcycle. The investigation is based on road tests carried out on a sport-touring motorcycle equipped with sensors. Three sets of tyres are tested at different speeds in the presence of weave and wobble. The analysis of telemetry data highlights significant differences in the trends of frequency and damping of weave and wobble against speed. The experimental analysis is integrated by a parametric numerical analysis. Tyre properties are varied according to the design of experiments method, in order to highlight the single effects on stability of lateral and cornering coefficient of front and rear tyres.

Flight test report of the NASA icing research airplane: Performance, stability, and control after flight through natural icing conditions

NASA Technical Reports Server (NTRS)

Jordan, J. L.; Platz, S. J.; Schinstock, W. C.

1986-01-01

Flight test results are presented documenting the effect of airframe icing on performance and stability and control of a NASA DHC-6 icing research aircraft. Kohlman System Research, Inc., provided the data acquisition system and data analysis under contract to NASA. Performance modeling methods and MMLE techniques were used to determine the effects of natural ice on the aircraft. Results showed that ice had a significant effect on the drag coefficient of the aircraft and a modest effect on the MMLE derived longitudinal stability coefficients (code version MMLE). Data is also presented on asymmetric power sign slip maneuvers showing rudder floating characteristics with and without ice on the vertical stabilizer.

Numerical analysis of stiffened shells of revolution. Volume 1: Theory manual for STARS-2S, 2B, 2V digital computer programs

NASA Technical Reports Server (NTRS)

Svalbonas, V.

1973-01-01

The theoretical analysis background for the STARS-2 (shell theory automated for rotational structures) program is presented. The theory involved in the axisymmetric nonlinear and unsymmetric linear static analyses, and the stability and vibrations (including critical rotation speed) analyses involving axisymmetric prestress are discussed. The theory for nonlinear static, stability, and vibrations analyses, involving shells with unsymmetric loadings are included.

Proceedings of the 6. international conference on stability and handling of liquid fuels. Volume 2

DOE Office of Scientific and Technical Information (OSTI.GOV)

Giles, H.N.

Volume 2 of these proceedings contain 42 papers arranged under the following topical sections: Fuel blending and compatibility; Middle distillates; Microbiology; Alternative fuels; General topics (analytical methods, tank remediation, fuel additives, storage stability); and Poster presentations (analysis methods, oxidation kinetics, health problems).

LMI-based stability and performance conditions for continuous-time nonlinear systems in Takagi-Sugeno's form.

PubMed

Lam, H K; Leung, Frank H F

2007-10-01

This correspondence presents the stability analysis and performance design of the continuous-time fuzzy-model-based control systems. The idea of the nonparallel-distributed-compensation (non-PDC) control laws is extended to the continuous-time fuzzy-model-based control systems. A nonlinear controller with non-PDC control laws is proposed to stabilize the continuous-time nonlinear systems in Takagi-Sugeno's form. To produce the stability-analysis result, a parameter-dependent Lyapunov function (PDLF) is employed. However, two difficulties are usually encountered: 1) the time-derivative terms produced by the PDLF will complicate the stability analysis and 2) the stability conditions are not in the form of linear-matrix inequalities (LMIs) that aid the design of feedback gains. To tackle the first difficulty, the time-derivative terms are represented by some weighted-sum terms in some existing approaches, which will increase the number of stability conditions significantly. In view of the second difficulty, some positive-definitive terms are added in order to cast the stability conditions into LMIs. In this correspondence, the favorable properties of the membership functions and nonlinear control laws, which allow the introduction of some free matrices, are employed to alleviate the two difficulties while retaining the favorable properties of PDLF-based approach. LMI-based stability conditions are derived to ensure the system stability. Furthermore, based on a common scalar performance index, LMI-based performance conditions are derived to guarantee the system performance. Simulation examples are given to illustrate the effectiveness of the proposed approach.

Stability analysis of implicit time discretizations for the Compton-scattering Fokker-Planck equation

NASA Astrophysics Data System (ADS)

Densmore, Jeffery D.; Warsa, James S.; Lowrie, Robert B.; Morel, Jim E.

2009-09-01

The Fokker-Planck equation is a widely used approximation for modeling the Compton scattering of photons in high energy density applications. In this paper, we perform a stability analysis of three implicit time discretizations for the Compton-Scattering Fokker-Planck equation. Specifically, we examine (i) a Semi-Implicit (SI) scheme that employs backward-Euler differencing but evaluates temperature-dependent coefficients at their beginning-of-time-step values, (ii) a Fully Implicit (FI) discretization that instead evaluates temperature-dependent coefficients at their end-of-time-step values, and (iii) a Linearized Implicit (LI) scheme, which is developed by linearizing the temperature dependence of the FI discretization within each time step. Our stability analysis shows that the FI and LI schemes are unconditionally stable and cannot generate oscillatory solutions regardless of time-step size, whereas the SI discretization can suffer from instabilities and nonphysical oscillations for sufficiently large time steps. With the results of this analysis, we present time-step limits for the SI scheme that prevent undesirable behavior. We test the validity of our stability analysis and time-step limits with a set of numerical examples.

Stability and Bifurcation Analysis of a Three-Species Food Chain Model with Fear

NASA Astrophysics Data System (ADS)

Panday, Pijush; Pal, Nikhil; Samanta, Sudip; Chattopadhyay, Joydev

In the present paper, we investigate the impact of fear in a tri-trophic food chain model. We propose a three-species food chain model, where the growth rate of middle predator is reduced due to the cost of fear of top predator, and the growth rate of prey is suppressed due to the cost of fear of middle predator. Mathematical properties such as equilibrium analysis, stability analysis, bifurcation analysis and persistence have been investigated. We also describe the global stability analysis of the equilibrium points. Our numerical simulations reveal that cost of fear in basal prey may exhibit bistability by producing unstable limit cycles, however, fear in middle predator can replace unstable limit cycles by a stable limit cycle or a stable interior equilibrium. We observe that fear can stabilize the system from chaos to stable focus through the period-halving phenomenon. We conclude that chaotic dynamics can be controlled by the fear factors. We apply basic tools of nonlinear dynamics such as Poincaré section and maximum Lyapunov exponent to identify the chaotic behavior of the system.

Theory of buckling and post-buckling behavior of elastic structures

NASA Technical Reports Server (NTRS)

Budiansky, B.

1974-01-01

The present paper provides a unified, general presentation of the basic theory of the buckling and post-buckling behavior of elastic structures in a form suitable for application to a wide variety of special problems. The notation of functional analysis is used for this purpose. Before the general analysis, simple conceptual models are used to elucidate the basic concepts of bifurcation buckling, snap buckling, imperfection sensitivity, load-shortening relations, and stability. The energy approach, the virtual-work approach, and mode interaction are discussed. The derivations and results are applicable to continua and finite-dimensional systems. The virtual-work and energy approaches are given separate treatments, but their equivalence is made explicit. The basic concepts of stability occupy a secondary position in the present approach.

Aging effects on vertical graphene nanosheets and their thermal stability

NASA Astrophysics Data System (ADS)

Ghosh, S.; Polaki, S. R.; Ajikumar, P. K.; Krishna, N. G.; Kamruddin, M.

2018-03-01

The present study investigates environmental aging effects and thermal stability of vertical graphene nanosheets (VGN). Self-organized VGN is synthesized by plasma enhanced chemical vapor deposition and exposed to ambient conditions over 6-month period to examine its aging behavior. A systematic inspection is carried out on morphology, chemical structure, wettability and electrical property by scanning electron microscopy, Raman spectroscopy, X-ray photoelectron spectroscopy, water contact angle and four-probe resistivity measurements at regular intervals, respectively. Detailed microscopic and spectroscopic analysis substantiated the retention of graphitic quality and surface chemistry of VGN over the test period. An unchanged sheet resistance and hydrophobicity reveals its electrical and wetting stability over the time, respectively. Thermogravimetric analysis ensures an excellent thermal stability of VGN up to 575 °C in ambient atmosphere. These findings of long-term morphological, structural, wetting, electrical and thermal stability of VGN validate their potential utilization for the next-generation device applications.

Optimal model of PDIG based microgrid and design of complementary stabilizer using ICA.

PubMed

Amini, R Mohammad; Safari, A; Ravadanegh, S Najafi

2016-09-01

The generalized Heffron-Phillips model (GHPM) for a microgrid containing a photovoltaic (PV)-diesel machine (DM)-induction motor (IM)-governor (GV) (PDIG) has been developed at the low voltage level. A GHPM is calculated by linearization method about a loading condition. An effective Maximum Power Point Tracking (MPPT) approach for PV network has been done using sliding mode control (SMC) to maximize output power. Additionally, to improve stability of microgrid for more penetration of renewable energy resources with nonlinear load, a complementary stabilizer has been presented. Imperialist competitive algorithm (ICA) is utilized to design of gains for the complementary stabilizer with the multiobjective function. The stability analysis of the PDIG system has been completed with eigenvalues analysis and nonlinear simulations. Robustness and validity of the proposed controllers on damping of electromechanical modes examine through time domain simulation under input mechanical torque disturbances. Copyright © 2016 ISA. Published by Elsevier Ltd. All rights reserved.

Formation stability analysis of unmanned multi-vehicles under interconnection topologies

NASA Astrophysics Data System (ADS)

Yang, Aolei; Naeem, Wasif; Fei, Minrui

2015-04-01

In this paper, the overall formation stability of an unmanned multi-vehicle is mathematically presented under interconnection topologies. A novel definition of formation error is first given and followed by the proposed formation stability hypothesis. Based on this hypothesis, a unique extension-decomposition-aggregation scheme is then employed to support the stability analysis for the overall multi-vehicle formation under a mesh topology. It is proved that the overall formation control system consisting of N number of nonlinear vehicles is not only asymptotically stable, but also exponentially stable in the sense of Lyapunov within a neighbourhood of the desired formation. This technique is shown to be applicable for a mesh topology but is equally applicable for other topologies. A simulation study of the formation manoeuvre of multiple Aerosonde UAVs (unmanned aerial vehicles), in 3-D space, is finally carried out verifying the achieved formation stability result.

Analyses of a heterogeneous lattice hydrodynamic model with low and high-sensitivity vehicles

NASA Astrophysics Data System (ADS)

Kaur, Ramanpreet; Sharma, Sapna

2018-06-01

Basic lattice model is extended to study the heterogeneous traffic by considering the optimal current difference effect on a unidirectional single lane highway. Heterogeneous traffic consisting of low- and high-sensitivity vehicles is modeled and their impact on stability of mixed traffic flow has been examined through linear stability analysis. The stability of flow is investigated in five distinct regions of the neutral stability diagram corresponding to the amount of higher sensitivity vehicles present on road. In order to investigate the propagating behavior of density waves non linear analysis is performed and near the critical point, the kink antikink soliton is obtained by driving mKdV equation. The effect of fraction parameter corresponding to high sensitivity vehicles is investigated and the results indicates that the stability rise up due to the fraction parameter. The theoretical findings are verified via direct numerical simulation.

Shaking video stabilization with content completion

NASA Astrophysics Data System (ADS)

Peng, Yi; Ye, Qixiang; Liu, Yanmei; Jiao, Jianbin

2009-01-01

A new stabilization algorithm to counterbalance the shaking motion in a video based on classical Kandade-Lucas- Tomasi (KLT) method is presented in this paper. Feature points are evaluated with law of large numbers and clustering algorithm to reduce the side effect of moving foreground. Analysis on the change of motion direction is also carried out to detect the existence of shaking. For video clips with detected shaking, an affine transformation is performed to warp the current frame to the reference one. In addition, the missing content of a frame during the stabilization is completed with optical flow analysis and mosaicking operation. Experiments on video clips demonstrate the effectiveness of the proposed algorithm.

Utilizing Flight Data to Update Aeroelastic Stability Estimates

NASA Technical Reports Server (NTRS)

Lind, Rick; Brenner, Marty

1997-01-01

Stability analysis of high performance aircraft must account for errors in the system model. A method for computing flutter margins that incorporates flight data has been developed using robust stability theory. This paper considers applying this method to update flutter margins during a post-flight or on-line analysis. Areas of modeling uncertainty that arise when using flight data with this method are investigated. The amount of conservatism in the resulting flutter margins depends on the flight data sets used to update the model. Post-flight updates of flutter margins for an F/A-18 are presented along with a simulation of on-line updates during a flight test.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Degenhardt, R.; PFH, Private University of Applied Sciences Goettingen, Composite Engineering Campus Stade; Araujo, F. C. de

European aircraft industry demands for reduced development and operating costs. Structural weight reduction by exploitation of structural reserves in composite aerospace structures contributes to this aim, however, it requires accurate and experimentally validated stability analysis of real structures under realistic loading conditions. This paper presents different advances from the area of computational stability analysis of composite aerospace structures which contribute to that field. For stringer stiffened panels main results of the finished EU project COCOMAT are given. It investigated the exploitation of reserves in primary fibre composite fuselage structures through an accurate and reliable simulation of postbuckling and collapse. Formore » unstiffened cylindrical composite shells a proposal for a new design method is presented.« less

[Features of emotional stability in volunteers of gerontology programs].

PubMed

Dolgova, V I

2014-01-01

The paper presents an analysis of the characteristics of emotional stability in volunteers of gerontology programs (among the students of the Faculty of Psychology), depending on the structure of their life meaning and values, personal factors and professional important qualities. It is shown that the emotional stability of volunteers determines the main directions to explore the potential of the psyche of volunteers; modeling appropriate professiogram; organization of volunteer work in a particular program.

Stability-Derivative Determination from Flight Data

NASA Technical Reports Server (NTRS)

Holowicz, Chester H.; Holleman, Euclid C.

1958-01-01

A comprehensive discussion of the various factors affecting the determination of stability and control derivatives from flight data is presented based on the experience of the NASA High-Speed Flight Station. Factors relating to test techniques, determination of mass characteristics, instrumentation, and methods of analysis are discussed. For most longitudinal-stability-derivative analyses simple equations utilizing period and damping have been found to be as satisfactory as more comprehensive methods. The graphical time-vector method has been the basis of lateral-derivative analysis, although simple approximate methods can be useful If applied with caution. Control effectiveness has been generally obtained by relating the peak acceleration to the rapid control input, and consideration must be given to aerodynamic contributions if reasonable accuracy is to be realized.. Because of the many factors involved In the determination of stability derivatives, It is believed that the primary stability and control derivatives are probably accurate to within 10 to 25 percent, depending upon the specific derivative. Static-stability derivatives at low angle of attack show the greatest accuracy.

New generation aircraft design problems relative to turbulence stability, aeroelastic loads and gust alleviation

NASA Technical Reports Server (NTRS)

Heimbaugh, Richard M.

1987-01-01

Past history, present status, and future of discrete gusts are schematically presented. It is shown that there are two approaches to the gust analysis: discrete and spectral density. The role of these two approaches to gust analysis are discussed. The idea of using power spectral density (PSD) in the analysis of gusts is especially detailed.

Aeroelastic Stability of Idling Wind Turbines

NASA Astrophysics Data System (ADS)

Wang, Kai; Riziotis, Vasilis A.; Voutsinas, Spyros G.

2016-09-01

Wind turbine rotors in idling operation mode can experience high angles of attack, within the post stall region that are capable of triggering stall-induced vibrations. In the present paper rotor stability in slow idling operation is assessed on the basis of non-linear time domain and linear eigenvalue analysis. Analysis is performed for a 10 MW conceptual wind turbine designed by DTU. First the flow conditions that are likely to favour stall induced instabilities are identified through non-linear time domain aeroelastic analysis. Next, for the above specified conditions, eigenvalue stability simulations are performed aiming at identifying the low damped modes of the turbine. Finally the results of the eigenvalue analysis are evaluated through computations of the work of the aerodynamic forces by imposing harmonic vibrations following the shape and frequency of the various modes. Eigenvalue analysis indicates that the asymmetric and symmetric out-of-plane modes have the lowest damping. The results of the eigenvalue analysis agree well with those of the time domain analysis.

Automatic generation of the non-holonomic equations of motion for vehicle stability analysis

NASA Astrophysics Data System (ADS)

Minaker, B. P.; Rieveley, R. J.

2010-09-01

The mathematical analysis of vehicle stability has been utilised as an important tool in the design, development, and evaluation of vehicle architectures and stability controls. This paper presents a novel method for automatic generation of the linearised equations of motion for mechanical systems that is well suited to vehicle stability analysis. Unlike conventional methods for generating linearised equations of motion in standard linear second order form, the proposed method allows for the analysis of systems with non-holonomic constraints. In the proposed method, the algebraic constraint equations are eliminated after linearisation and reduction to first order. The described method has been successfully applied to an assortment of classic dynamic problems of varying complexity including the classic rolling coin, the planar truck-trailer, and the bicycle, as well as in more recent problems such as a rotor-stator and a benchmark road vehicle with suspension. This method has also been applied in the design and analysis of a novel three-wheeled narrow tilting vehicle with zero roll-stiffness. An application for determining passively stable configurations using the proposed method together with a genetic search algorithm is detailed. The proposed method and software implementation has been shown to be robust and provides invaluable conceptual insight into the stability of vehicles and mechanical systems.

Computer Programs for Calculating and Plotting the Stability Characteristics of a Balloon Tethered in a Wind

NASA Technical Reports Server (NTRS)

Bennett, R. M.; Bland, S. R.; Redd, L. T.

1973-01-01

Computer programs for calculating the stability characteristics of a balloon tethered in a steady wind are presented. Equilibrium conditions, characteristic roots, and modal ratios are calculated for a range of discrete values of velocity for a fixed tether-line length. Separate programs are used: (1) to calculate longitudinal stability characteristics, (2) to calculate lateral stability characteristics, (3) to plot the characteristic roots versus velocity, (4) to plot the characteristic roots in root-locus form, (5) to plot the longitudinal modes of motion, and (6) to plot the lateral modes for motion. The basic equations, program listings, and the input and output data for sample cases are presented, with a brief discussion of the overall operation and limitations. The programs are based on a linearized, stability-derivative type of analysis, including balloon aerodynamics, apparent mass, buoyancy effects, and static forces which result from the tether line.

Effects of the pH and Concentration on the Stability of Standard Solutions of Proteinogenic Amino Acid Mixtures.

PubMed

Kato, Megumi; Yamazaki, Taichi; Kato, Hisashi; Yamanaka, Noriko; Takatsu, Akiko; Ihara, Toshihide

2017-01-01

To prepare metrologically traceable amino acid mixed standard solutions, it is necessary to determine the stability of each amino acid present in the mixed solutions. In the present study, we prepared amino acid mixed solutions using certified reference standards of 17 proteinogenic amino acids, and examined the stability of each of these amino acids in 0.1 N HCl. We found that the concentration of glutamic acid decreased significantly during storage. LC/MS analysis indicated that the instability of glutamic acid was due to the partial degradation of glutamic acid to pyroglutamic acid in 0.1 N HCl. Using accelerated degradation tests, we investigated several solvent compositions to improve the stability of glutamic acid in amino acid mixed solution, and determined that the change of the pH by diluting the mixed solution improved the stability of glutamic acid.

Analysis of protein stability and ligand interactions by thermal shift assay.

PubMed

Huynh, Kathy; Partch, Carrie L

2015-02-02

Purification of recombinant proteins for biochemical assays and structural studies is time-consuming and presents inherent difficulties that depend on the optimization of protein stability. The use of dyes to monitor thermal denaturation of proteins with sensitive fluorescence detection enables rapid and inexpensive determination of protein stability using real-time PCR instruments. By screening a wide range of solution conditions and additives in a 96-well format, the thermal shift assay easily identifies conditions that significantly enhance the stability of recombinant proteins. The same approach can be used as an initial low-cost screen to discover new protein-ligand interactions by capitalizing on increases in protein stability that typically occur upon ligand binding. This unit presents a methodological workflow for small-scale, high-throughput thermal denaturation of recombinant proteins in the presence of SYPRO Orange dye. Copyright © 2015 John Wiley & Sons, Inc.

Multi-flexible-body analysis for application to wind turbine control design

NASA Astrophysics Data System (ADS)

Lee, Donghoon

The objective of the present research is to build a theoretical and computational framework for the aeroelastic analysis of flexible rotating systems, more specifically with special application to a wind turbine control design. The methodology is based on the integration of Kane's approach for the analysis of the multi-rigid-body subsystem and a mixed finite element method for the analysis of the flexible-body subsystem. The combined analysis is then strongly coupled with an aerodynamic model based on Blade Element Momentum theory for inflow model. The unified framework from the analysis of subsystems is represented as, in a symbolic manner, a set of nonlinear ordinary differential equations with time-variant, periodic coefficients, which describe the aeroelastic behavior of whole system. The framework can be directly applied to control design due to its symbolic characteristics. The solution procedures for the equations are presented for the study of nonlinear simulation, periodic steady-state solution, and Floquet stability of the linearized system about the steady-state solution. Finally the linear periodic system equation can be obtained with both system and control matrices as explicit functions of time, which can be directly applicable to control design. The structural model is validated by comparison of its results with those from software, some of which is commercial. The stability of the linearized system about periodic steady-state solution is different from that obtained about a constant steady-state solution, which have been conventional in the field of wind turbine dynamics. Parametric studies are performed on a wind turbine model with various pitch angles, precone angles, and rotor speeds. Combined with composite material, their effects on wind turbine aeroelastic stability are investigated. Finally it is suggested that the aeroelastic stability analysis and control design for the whole system is crucial for the design of wind turbines, and the present research breaks new ground in the ability to treat the issue.

Enhancing synchronization stability in a multi-area power grid

PubMed Central

Wang, Bing; Suzuki, Hideyuki; Aihara, Kazuyuki

2016-01-01

Maintaining a synchronous state of generators is of central importance to the normal operation of power grids, in which many networks are generally interconnected. In order to understand the condition under which the stability can be optimized, it is important to relate network stability with feedback control strategies as well as network structure. Here, we present a stability analysis on a multi-area power grid by relating it with several control strategies and topological design of network structure. We clarify the minimal feedback gain in the self-feedback control, and build the optimal communication network for the local and global control strategies. Finally, we consider relationship between the interconnection pattern and the synchronization stability; by optimizing the network interlinks, the obtained network shows better synchronization stability than the original network does, in particular, at a high power demand. Our analysis shows that interlinks between spatially distant nodes will improve the synchronization stability. The results seem unfeasible to be implemented in real systems but provide a potential guide for the design of stable power systems. PMID:27225708

Stability of the Baseline Holder in Readout Circuits For Radiation Detectors

PubMed Central

Chen, Y.; Cui, Y.; O’Connor, P.; Seo, Y.; Camarda, G. S.; Hossain, A.; Roy, U.; Yang, G.; James, R. B.

2016-01-01

Baseline holder (BLH) circuits are used widely to stabilize the analog output of application-specific integrated circuits (ASICs) for high-count-rate applications. The careful design of BLH circuits is vital to the overall stability of the analog-signal-processing chain in ASICs. Recently, we observed self-triggered fluctuations in an ASIC in which the shaping circuits have a BLH circuit in the feedback loop. In fact, further investigations showed that methods of enhancing small-signal stabilities cause an even worse situation. To resolve this problem, we used large-signal analyses to study the circuit’s stability. We found that a relatively small gain for the error amplifier and a small current in the non-linear stage of the BLH are required to enhance stability in large-signal analysis, which will compromise the properties of the BLH. These findings were verified by SPICE simulations. In this paper, we present our detailed analysis of the BLH circuits, and propose an improved version of them that have only minimal self-triggered fluctuations. We summarize the design considerations both for the stability and the properties of the BLH circuits. PMID:27182081

Flame analysis using image processing techniques

NASA Astrophysics Data System (ADS)

Her Jie, Albert Chang; Zamli, Ahmad Faizal Ahmad; Zulazlan Shah Zulkifli, Ahmad; Yee, Joanne Lim Mun; Lim, Mooktzeng

2018-04-01

This paper presents image processing techniques with the use of fuzzy logic and neural network approach to perform flame analysis. Flame diagnostic is important in the industry to extract relevant information from flame images. Experiment test is carried out in a model industrial burner with different flow rates. Flame features such as luminous and spectral parameters are extracted using image processing and Fast Fourier Transform (FFT). Flame images are acquired using FLIR infrared camera. Non-linearities such as thermal acoustic oscillations and background noise affect the stability of flame. Flame velocity is one of the important characteristics that determines stability of flame. In this paper, an image processing method is proposed to determine flame velocity. Power spectral density (PSD) graph is a good tool for vibration analysis where flame stability can be approximated. However, a more intelligent diagnostic system is needed to automatically determine flame stability. In this paper, flame features of different flow rates are compared and analyzed. The selected flame features are used as inputs to the proposed fuzzy inference system to determine flame stability. Neural network is used to test the performance of the fuzzy inference system.

Chapter 13: Tools for analysis

Treesearch

William Elliot; Kevin Hyde; Lee MacDonald; James McKean

2007-01-01

This chapter presents a synthesis of current computer modeling tools that are, or could be, adopted for use in evaluating the cumulative watershed effects of fuel management. The chapter focuses on runoff, soil erosion and slope stability predictive tools. Readers should refer to chapters on soil erosion and stability for more detailed information on the physical...

Flight-test data on the static fore-and-aft stability of various German airplanes

NASA Technical Reports Server (NTRS)

Hubner, Walter

1933-01-01

The static longitudinal stability of an airplane with locked elevator is usually determined by analysis and model tests. The present report proposes to supply the results of such measurements. The method consisted of recording the dynamic pressure versus elevator displacement at different center-of-gravity positions in unaccelerated flight.

A Coupled Aeroelastic Model for Launch Vehicle Stability Analysis

NASA Technical Reports Server (NTRS)

Orr, Jeb S.

2010-01-01

A technique for incorporating distributed aerodynamic normal forces and aeroelastic coupling effects into a stability analysis model of a launch vehicle is presented. The formulation augments the linear state-space launch vehicle plant dynamics that are compactly derived as a system of coupled linear differential equations representing small angular and translational perturbations of the rigid body, nozzle, and sloshing propellant coupled with normal vibration of a set of orthogonal modes. The interaction of generalized forces due to aeroelastic coupling and thrust can be expressed as a set of augmenting non-diagonal stiffness and damping matrices in modal coordinates with no penalty on system order. While the eigenvalues of the structural response in the presence of thrust and aeroelastic forcing can be predicted at a given flight condition independent of the remaining degrees of freedom, the coupled model provides confidence in closed-loop stability in the presence of rigid-body, slosh, and actuator dynamics. Simulation results are presented that characterize the coupled dynamic response of the Ares I launch vehicle and the impact of aeroelasticity on control system stability margins.

Stability testing and analysis of a PMAD dc test bed for the Space Station Freedom

NASA Technical Reports Server (NTRS)

Button, Robert M.; Brush, Andrew S.

1992-01-01

The Power Management and Distribution (PMAD) dc Test Bed at the NASA Lewis Research Center is introduced. Its usefulness to the Space Station Freedom Electrical Power (EPS) development and design are discussed in context of verifying system stability. Stability criteria developed by Middlebrook and Cuk are discussed as they apply to constant power dc to dc converters exhibiting negative input impedance at low frequencies. The utility-type Secondary Subsystem is presented and each component is described. The instrumentation used to measure input and output impedance under load is defined. Test results obtained from input and output impedance measurements of test bed components are presented. It is shown that the PMAD dc Test Bed Secondary Subsystem meets the Middlebrook stability criterion for certain loading conditions.

Stability Testing and Analysis of a PMAD DC Test Bed for the Space Station Freedom

NASA Technical Reports Server (NTRS)

Button, Robert M.; Brush, Andrew S.

1992-01-01

The Power Management and Distribution (PMAD) DC Test Bed at the NASA Lewis Research Center is introduced. Its usefulness to the Space Station Freedom Electrical Power (EPS) development and design are discussed in context of verifying system stability. Stability criteria developed by Middlebrook and Cuk are discussed as they apply to constant power DC to DC converters exhibiting negative input impedance at low frequencies. The utility-type Secondary Subsystem is presented and each component is described. The instrumentation used to measure input and output impedance under load is defined. Test results obtained from input and output impedance measurements of test bed components are presented. It is shown that the PMAD DC Test Bed Secondary Subsystem meets the Middlebrook stability criterion for certain loading conditions.

Theoretical considerations of some nonlinear aspects of hypersonic panel flutter

NASA Technical Reports Server (NTRS)

Mcintosh, S. C., Jr.

1974-01-01

A research project to analyze the effects of hypersonic nonlinear aerodynamic loading on panel flutter is reported. The test equipment and procedures for conducting the tests are explained. The effects of aerodynamic linearities on stability were evaluated by determining constant-initial-energy amplitude-sensitive stability boundaries and comparing them with the corresponding linear stability boundaries. An attempt to develop an alternative method of analysis for systems where amplitude-sensitive instability is possible is presented.

A pseudospectra-based approach to non-normal stability of embedded boundary methods

NASA Astrophysics Data System (ADS)

Rapaka, Narsimha; Samtaney, Ravi

2017-11-01

We present non-normal linear stability of embedded boundary (EB) methods employing pseudospectra and resolvent norms. Stability of the discrete linear wave equation is characterized in terms of the normalized distance of the EB to the nearest ghost node (α) in one and two dimensions. An important objective is that the CFL condition based on the Cartesian grid spacing remains unaffected by the EB. We consider various discretization methods including both central and upwind-biased schemes. Stability is guaranteed when α <=αmax ranges between 0.5 and 0.77 depending on the discretization scheme. Also, the stability characteristics remain the same in both one and two dimensions. Sharper limits on the sufficient conditions for stability are obtained based on the pseudospectral radius (the Kreiss constant) than the restrictive limits based on the usual singular value decomposition analysis. We present a simple and robust reclassification scheme for the ghost cells (``hybrid ghost cells'') to ensure Lax stability of the discrete systems. This has been tested successfully for both low and high order discretization schemes with transient growth of at most O (1). Moreover, we present a stable, fourth order EB reconstruction scheme. Supported by the KAUST Office of Competitive Research Funds under Award No. URF/1/1394-01.

Von Neumann stability analysis of globally divergence-free RKDG schemes for the induction equation using multidimensional Riemann solvers

NASA Astrophysics Data System (ADS)

Balsara, Dinshaw S.; Käppeli, Roger

2017-05-01

In this paper we focus on the numerical solution of the induction equation using Runge-Kutta Discontinuous Galerkin (RKDG)-like schemes that are globally divergence-free. The induction equation plays a role in numerical MHD and other systems like it. It ensures that the magnetic field evolves in a divergence-free fashion; and that same property is shared by the numerical schemes presented here. The algorithms presented here are based on a novel DG-like method as it applies to the magnetic field components in the faces of a mesh. (I.e., this is not a conventional DG algorithm for conservation laws.) The other two novel building blocks of the method include divergence-free reconstruction of the magnetic field and multidimensional Riemann solvers; both of which have been developed in recent years by the first author. Since the method is linear, a von Neumann stability analysis is carried out in two-dimensions to understand its stability properties. The von Neumann stability analysis that we develop in this paper relies on transcribing from a modal to a nodal DG formulation in order to develop discrete evolutionary equations for the nodal values. These are then coupled to a suitable Runge-Kutta timestepping strategy so that one can analyze the stability of the entire scheme which is suitably high order in space and time. We show that our scheme permits CFL numbers that are comparable to those of traditional RKDG schemes. We also analyze the wave propagation characteristics of the method and show that with increasing order of accuracy the wave propagation becomes more isotropic and free of dissipation for a larger range of long wavelength modes. This makes a strong case for investing in higher order methods. We also use the von Neumann stability analysis to show that the divergence-free reconstruction and multidimensional Riemann solvers are essential algorithmic ingredients of a globally divergence-free RKDG-like scheme. Numerical accuracy analyses of the RKDG-like schemes are presented and compared with the accuracy of PNPM schemes. It is found that PNPM retrieve much of the accuracy of the RKDG-like schemes while permitting a larger CFL number.

Development of Curved-Plate Elements for the Exact Buckling Analysis of Composite Plate Assemblies Including Transverse-Shear Effects

NASA Technical Reports Server (NTRS)

McGowan, David M.

1999-01-01

The analytical formulation of curved-plate non-linear equilibrium equations including transverse-shear-deformation effects is presented. A unified set of non-linear strains that contains terms from both physical and tensorial strain measures is used. Linearized, perturbed equilibrium equations (stability equations) that describe the response of the plate just after buckling occurs are derived. These equations are then modified to allow the plate reference surface to be located a distance z(sub c) from the centroidal surface. The implementation of the new theory into the VICONOPT exact buckling and vibration analysis and optimum design computer program is described. The terms of the plate stiffness matrix using both classical plate theory (CPT) and first-order shear-deformation plate theory (SDPT) are presented. The effects of in-plane transverse and in-plane shear loads are included in the in-plane stability equations. Numerical results for several example problems with different loading states are presented. Comparisons of analyses using both physical and tensorial strain measures as well as CPT and SDPT are made. The computational effort required by the new analysis is compared to that of the analysis currently in the VICONOPT program. The effects of including terms related to in-plane transverse and in-plane shear loadings in the in-plane stability equations are also examined. Finally, results of a design-optimization study of two different cylindrical shells subject to uniform axial compression are presented.

Whirling and stability of flywheel systems, part I: Derivation of combined and lumped parameter models

NASA Astrophysics Data System (ADS)

Ramanujam, G.; Bert, C. W.

1983-06-01

The objective of this paper is to provide a theoretical foundation to predict many aspects of dynamic behavior of flywheel systems when spin-tested with a quill shaft support and driven by an air turbine. Theoretical analyses for the following are presented: (1) determination of natural frequencies (or for brevity critical speeds of various orders), (2) Routh-type stability analysis to determine the stability limits (i.e., the speed range within which small perturbations attenuate rather than cause catastrophic failure), and (3) forced whirling analysis to estimate the response of major components of the system to flywheel mass eccentricity and initial tilt. For the first and third kinds of analyses, two different mathematical models of the generic system are investigated. One is a seven-degree-of-freedom lumped parameter analysis, while the other is a combined distributed and lumped parameter analysis.

User's manual for rocket combustor interactive design (ROCCID) and analysis computer program. Volume 1: User's manual

NASA Technical Reports Server (NTRS)

Muss, J. A.; Nguyen, T. V.; Johnson, C. W.

1991-01-01

The user's manual for the rocket combustor interactive design (ROCCID) computer program is presented. The program, written in Fortran 77, provides a standardized methodology using state of the art codes and procedures for the analysis of a liquid rocket engine combustor's steady state combustion performance and combustion stability. The ROCCID is currently capable of analyzing mixed element injector patterns containing impinging like doublet or unlike triplet, showerhead, shear coaxial, and swirl coaxial elements as long as only one element type exists in each injector core, baffle, or barrier zone. Real propellant properties of oxygen, hydrogen, methane, propane, and RP-1 are included in ROCCID. The properties of other propellants can easily be added. The analysis model in ROCCID can account for the influence of acoustic cavities, helmholtz resonators, and radial thrust chamber baffles on combustion stability. ROCCID also contains the logic to interactively create a combustor design which meets input performance and stability goals. A preliminary design results from the application of historical correlations to the input design requirements. The steady state performance and combustion stability of this design is evaluated using the analysis models, and ROCCID guides the user as to the design changes required to satisfy the user's performance and stability goals, including the design of stability aids. Output from ROCCID includes a formatted input file for the standardized JANNAF engine performance prediction procedure.

Modeling and Analysis of Large Amplitude Flight Maneuvers

NASA Technical Reports Server (NTRS)

Anderson, Mark R.

2004-01-01

Analytical methods for stability analysis of large amplitude aircraft motion have been slow to develop because many nonlinear system stability assessment methods are restricted to a state-space dimension of less than three. The proffered approach is to create regional cell-to-cell maps for strategically located two-dimensional subspaces within the higher-dimensional model statespace. These regional solutions capture nonlinear behavior better than linearized point solutions. They also avoid the computational difficulties that emerge when attempting to create a cell map for the entire state-space. Example stability results are presented for a general aviation aircraft and a micro-aerial vehicle configuration. The analytical results are consistent with characteristics that were discovered during previous flight-testing.

Analytic theory for the determination of velocity and stability of bubbles in a Hele-Shaw cell. I - Velocity selection. II - Stability

NASA Technical Reports Server (NTRS)

Tanveer, S.

1989-01-01

An asymptotic theory is presented for the determination of velocity and linear stability of a steady symmetric bubble in a Hele-Shaw cell for small surface tension. First the bubble velocity relative to the fluid velocity at infinity is determined for small surface tension by means of a transcendentally small correction to the asymptotic series solution. In addition, a linear stability analysis shows that only the solution branch corresponding to the largest possible bubble velocity for given surface tension is stable, while all the others are unstable.

Stability of a rigid rotor supported on flexible oil journal bearings

NASA Technical Reports Server (NTRS)

Majumdar, B. C.; Brewe, D. E.; Khonsari, M. M.

1988-01-01

This investigation deals with the stability characteristics of oil journal bearings, including the effect of elastic distortions in the bearing liner. Graphical results are presented for (1) steady-state load, (2) stiffness and damping coefficients, and (3) the stability. These results are given for various slenderness ratios, eccentricity ratios, and elasticity parameters. The lubricant is first assumed to be isoviscous. The analysis is then extended to the case of a pressure-dependent viscosity. It has been found that stability decreases with increase of the elasticity parameter of the bearing liner for heavily loaded bearings.

Stability of a rigid rotor supported on flexible oil journal bearings

NASA Technical Reports Server (NTRS)

Majumdar, Bankim C.; Brewe, David E.; Khonsari, Michael M.

1987-01-01

This investigation deals with the stability characteristics of oil journal bearings, including the effect of elastic distortions in the bearing liner. Graphical results are presented for (1) steady-state load, (2) stiffness and damping coefficients, and (3) the stability. These results are given for various slenderness ratios, eccentricity ratios, and elasticity parameters. The lubricant is first assumed to be isoviscous. The analysis is then extended to the case of a pressure-dependent viscosity. It has been found that stability decreases with increase of the elasticity parameter of the bearing liner for heavily loaded bearings.

Nonlinear transient analysis of multi-mass flexible rotors - theory and applications

NASA Technical Reports Server (NTRS)

Kirk, R. G.; Gunter, E. J.

1973-01-01

The equations of motion necessary to compute the transient response of multi-mass flexible rotors are formulated to include unbalance, rotor acceleration, and flexible damped nonlinear bearing stations. A method of calculating the unbalance response of flexible rotors from a modified Myklestad-Prohl technique is discussed in connection with the method of solution for the transient response. Several special cases of simplified rotor-bearing systems are presented and analyzed for steady-state response, stability, and transient behavior. These simplified rotor models produce extensive design information necessary to insure stable performance to elastic mounted rotor-bearing systems under varying levels and forms of excitation. The nonlinear journal bearing force expressions derived from the short bearing approximation are utilized in the study of the stability and transient response of the floating bush squeeze damper support system. Both rigid and flexible rotor models are studied, and results indicate that the stability of flexible rotors supported by journal bearings can be greatly improved by the use of squeeze damper supports. Results from linearized stability studies of flexible rotors indicate that a tuned support system can greatly improve the performance of the units from the standpoint of unbalanced response and impact loading. Extensive stability and design charts may be readily produced for given rotor specifications by the computer codes presented in this analysis.

Elastic stability of biaxially loaded longitudinally stiffened composite structures.

NASA Technical Reports Server (NTRS)

Viswanathan, A. V.; Tamekuni, M.; Tripp, L. L.

1973-01-01

A linear analysis method is presented for the elastic stability of structures of uniform cross section, that may be idealized as an assemblage of laminated plate-strips, flat and curved, and beams. Each plate-strip and beam covers the entire length of the structure and is simply supported on the edges normal to the longitudinal axis. Arbitrary boundary conditions may be specified on any external longitudinal side of plate-strips. The structure or selected plate-strips may be loaded in any desired combination of inplane biaxial loads. The analysis simultaneously considers all modes of instability and is applicable for the buckling of laminated composite structures. Some numerical results are presented to indicate possible applications.

The beauty of simple adaptive control and new developments in nonlinear systems stability analysis

DOE Office of Scientific and Technical Information (OSTI.GOV)

Barkana, Itzhak, E-mail: ibarkana@gmail.com

Although various adaptive control techniques have been around for a long time and in spite of successful proofs of stability and even successful demonstrations of performance, the eventual use of adaptive control methodologies in practical real world systems has met a rather strong resistance from practitioners and has remained limited. Apparently, it is difficult to guarantee or even understand the conditions that can guarantee stable operations of adaptive control systems under realistic operational environments. Besides, it is difficult to measure the robustness of adaptive control system stability and allow it to be compared with the common and widely used measuremore » of phase margin and gain margin that is utilized by present, mainly LTI, controllers. Furthermore, customary stability analysis methods seem to imply that the mere stability of adaptive systems may be adversely affected by any tiny deviation from the pretty idealistic and assumably required stability conditions. This paper first revisits the fundamental qualities of customary direct adaptive control methodologies, in particular the classical Model Reference Adaptive Control, and shows that some of their basic drawbacks have been addressed and eliminated within the so-called Simple Adaptive Control methodology. Moreover, recent developments in the stability analysis methods of nonlinear systems show that prior conditions that were customarily assumed to be needed for stability are only apparent and can be eliminated. As a result, sufficient conditions that guarantee stability are clearly stated and lead to similarly clear proofs of stability. As many real-world applications show, once robust stability of the adaptive systems can be guaranteed, the added value of using Add-On Adaptive Control along with classical Control design techniques is pushing the desired performance beyond any previous limits.« less

Local projection stabilization for linearized Brinkman-Forchheimer-Darcy equation

NASA Astrophysics Data System (ADS)

Skrzypacz, Piotr

2017-09-01

The Local Projection Stabilization (LPS) is presented for the linearized Brinkman-Forchheimer-Darcy equation with high Reynolds numbers. The considered equation can be used to model porous medium flows in chemical reactors of packed bed type. The detailed finite element analysis is presented for the case of nonconstant porosity. The enriched variant of LPS is based on the equal order interpolation for the velocity and pressure. The optimal error bounds for the velocity and pressure errors are justified numerically.

Psychological Stability of a Personality and Capability of Tolerant Interaction as Diverse Manifestations of Tolerance

ERIC Educational Resources Information Center

Belasheva, Irina Valeryevna; Petrova, Nina Fedorovna

2016-01-01

Present article addresses studying tolerance as a factor of personality stability, which manifests on the level of interpersonal relationships and on the level of intra-personal system of stressors resistance. The article includes theoretical analysis of the tolerance construct as an integrative personality formation. It explores the question of…

An approach to attitude determination for a spin-stabilized spacecraft (IMP 1)

NASA Technical Reports Server (NTRS)

Fang, A. C.

1972-01-01

The analysis and the FORTRAN program are presented for the determination of attitude of a spin-stabilized spacecraft. The use of telemetry data that provide information about two reference vectors and their relation to the spin is outlined. A technique for the determination of the spin-axis orientation that employs only simple calculations is described.

Design of Rock Slope Reinforcement: An Himalayan Case Study

NASA Astrophysics Data System (ADS)

Tiwari, Gaurav; Latha, Gali Madhavi

2016-06-01

The stability analysis of the two abutment slopes of a railway bridge proposed at about 359 m above the ground level, crossing a river and connecting two hill faces in the Himalayas, India, is presented. The bridge is located in a zone of high seismic activity. The rock slopes are composed of a heavily jointed rock mass and the spacing, dip and dip direction of joint sets are varying at different locations. Geological mapping was carried out to characterize all discontinuities present along the slopes. Laboratory and field investigations were conducted to assess the geotechnical properties of the intact rock, rock mass and joint infill. Stability analyses of these rock slopes were carried out using numerical programmes. Loads from the foundations resting on the slopes and seismic accelerations estimated from site-specific ground response analysis were considered. The proposed slope profile with several berms between successive foundations was simulated in the numerical model. An equivalent continuum approach with Hoek and Brown failure criterion was initially used in a finite element model to assess the global stability of the slope abutments. In the second stage, finite element analysis of rock slopes with all joint sets with their orientations, spacing and properties explicitly incorporated into the numerical model was taken up using continuum with joints approach. It was observed that the continuum with joints approach was able to capture the local failures in some of the slope sections, which were verified using wedge failure analysis and stereographic projections. Based on the slope deformations and failure patterns observed from the numerical analyses, rock anchors were designed to achieve the target factors of safety against failure while keeping the deformations within the permissible limits. Detailed design of rock anchors and comparison of the stability of slopes with and without reinforcement are presented.

Improved helicopter aeromechanical stability analysis using segmented constrained layer damping and hybrid optimization

NASA Astrophysics Data System (ADS)

Liu, Qiang; Chattopadhyay, Aditi

2000-06-01

Aeromechanical stability plays a critical role in helicopter design and lead-lag damping is crucial to this design. In this paper, the use of segmented constrained damping layer (SCL) treatment and composite tailoring is investigated for improved rotor aeromechanical stability using formal optimization technique. The principal load-carrying member in the rotor blade is represented by a composite box beam, of arbitrary thickness, with surface bonded SCLs. A comprehensive theory is used to model the smart box beam. A ground resonance analysis model and an air resonance analysis model are implemented in the rotor blade built around the composite box beam with SCLs. The Pitt-Peters dynamic inflow model is used in air resonance analysis under hover condition. A hybrid optimization technique is used to investigate the optimum design of the composite box beam with surface bonded SCLs for improved damping characteristics. Parameters such as stacking sequence of the composite laminates and placement of SCLs are used as design variables. Detailed numerical studies are presented for aeromechanical stability analysis. It is shown that optimum blade design yields significant increase in rotor lead-lag regressive modal damping compared to the initial system.

Non Lyapunov stability of a constant spatially developing 2-D gas flow

NASA Astrophysics Data System (ADS)

Balint, Agneta M.; Balint, Stefan; Tanasie, Loredana

2017-01-01

Different types of stabilities (global, local) and instabilities (global absolute, local convective) of the constant spatially developing 2-D gas flow are analyzed in a particular phase space of continuously differentiable functions, endowed with the usual algebraic operations and the topology generated by the uniform convergence on the plane. For this purpose the Euler equations linearized at the constant flow are used. The Lyapunov stability analysis was presented in [1] and this paper is a continuation of [1].

Nonparallel stability of three-dimensional compressible boundary layers. Part 1: Stability analysis

NASA Technical Reports Server (NTRS)

El-Hady, N. M.

1980-01-01

A compressible linear stability theory is presented for nonparallel three-dimensional boundary-layer flows, taking into account the normal velocity component as well as the streamwise and spanwise variations of the basic flow. The method of multiple scales is used to account for the nonparallelism of the basic flow, and equations are derived for the spatial evolution of the disturbance amplitude and wavenumber. The numerical procedure for obtaining the solution of the nonparallel problem is outlined.

DC/DC Converter Stability Testing Study

NASA Technical Reports Server (NTRS)

Wang, Bright L.

2008-01-01

This report presents study results on hybrid DC/DC converter stability testing methods. An input impedance measurement method and a gain/phase margin measurement method were evaluated to be effective to determine front-end oscillation and feedback loop oscillation. In particular, certain channel power levels of converter input noises have been found to have high degree correlation with the gain/phase margins. It becomes a potential new method to evaluate stability levels of all type of DC/DC converters by utilizing the spectral analysis on converter input noises.

Stability and local toxicity evaluation of a liposomal prilocaine formulation.

PubMed

Cereda, Cintia M Saia; Tófoli, Giovana R; de Brito Junior, Rui B; de Jesus, Marcelo B; Fraceto, Leonardo F; Groppo, Francisco C; de Araujo, Daniele R; de Paula, Eneida

2008-01-01

This study reports a physicochemical stability evaluation of a previously reported liposomal prilocaine (PLC(LUV)) formulation (Cereda et al. J. Pharm. Pharmaceut. Sci. 7:235, 2004) before and after steam sterilization as well as its local toxicity evaluation. Prilocaine (PLC) was encapsulated into extruded unilamellar liposomes (LUVs) composed by egg phosphatidylcholine:cholesterol:alfa-tocopherol (4:3:0.07, mole %). Laser light-scattering analysis (p > 0.05) and thiobarbituric acid reaction (p > 0.05) were used to evaluate the liposomes physical (size) and chemical (oxidation) stability, respectively. The prilocaine chemical stability was followed by (1)H-nuclear magnetic resonance. These tests detected no differences on the physicochemical stability of PLC or PLC(LUV), sterilized or not, up to 30 days after preparation (p > 0.05). Finally, the paw edema test and histological analysis of rat oral mucosa were used to assess the possible inflammatory effects of PLC(LUV). PLC(LUV) did not evoke rat paw edema (p > 0.05), and no significant differences were found in histological analysis, when compared to the control groups (p > 0.05). The present work shows that PLC(LUV) is stable for a 30-day period and did not induce significant inflammatory effects both in the paw edema test and in histological analysis, giving supporting evidence for its safety and possible clinical use in dentistry.

Stability and Control Analysis of the F-15B Quiet SpikeTM Aircraft

NASA Technical Reports Server (NTRS)

McWherter, Shaun C.; Moua, Cheng M.; Gera, Joseph; Cox, Timothy H.

2009-01-01

The primary purpose of the Quiet Spike(TradeMark) flight research program was to analyze the aerodynamic, structural, and mechanical proof-of-concept of a large multi-stage telescoping nose spike installed on the National Aeronautics and Space Administration Dryden Flight Research Center (Edwards, California) F-15B airplane. This report describes the preflight stability and control analysis performed to assess the effect of the spike on the stability, controllability, and handling qualities of the airplane; and to develop an envelope expansion approach to maintain safety of flight. The overall flight test objective was to collect flight data to validate the spike structural dynamics and loads model up to Mach 1.8. Other objectives included validating the mechanical feasibility of a morphing fuselage at operational conditions and determining the near-field shock wave characterization. The two main issues relevant to the stability and control objectives were the effects of the spike-influenced aerodynamics on the F-15B airplane flight dynamics, and the air data and angle-of-attack sensors. The analysis covered the sensitivity of the stability margins, and the handling qualities due to aerodynamic variation and the maneuvering limitations of the F-15B Quiet Spike configuration. The results of the analysis and the implications for the flight test program are also presented.

NL(q) Theory: A Neural Control Framework with Global Asymptotic Stability Criteria.

PubMed

Vandewalle, Joos; De Moor, Bart L.R.; Suykens, Johan A.K.

1997-06-01

In this paper a framework for model-based neural control design is presented, consisting of nonlinear state space models and controllers, parametrized by multilayer feedforward neural networks. The models and closed-loop systems are transformed into so-called NL(q) system form. NL(q) systems represent a large class of nonlinear dynamical systems consisting of q layers with alternating linear and static nonlinear operators that satisfy a sector condition. For such NL(q)s sufficient conditions for global asymptotic stability, input/output stability (dissipativity with finite L(2)-gain) and robust stability and performance are presented. The stability criteria are expressed as linear matrix inequalities. In the analysis problem it is shown how stability of a given controller can be checked. In the synthesis problem two methods for neural control design are discussed. In the first method Narendra's dynamic backpropagation for tracking on a set of specific reference inputs is modified with an NL(q) stability constraint in order to ensure, e.g., closed-loop stability. In a second method control design is done without tracking on specific reference inputs, but based on the input/output stability criteria itself, within a standard plant framework as this is done, for example, in H( infinity ) control theory and &mgr; theory. Copyright 1997 Elsevier Science Ltd.

Use of cement-fly ash-based stabilization techniques for the treatment of waste containing aromatic contaminants

NASA Astrophysics Data System (ADS)

Banaszkiewicz, Kamil; Marcinkowski, Tadeusz

2017-11-01

Research on evaluation of evaporation rate of volatile organic compounds from soil beds during processing is presented. For the experiment, soil samples were prepared with the same amounts of benzene and stabilized using a mixture of CEMI 42.5R cement and fly ash from pit-coal combustion. Solidification of soils contaminated with BTEX hydrocarbons using hydraulic binders involves a risk of releasing vapours of these compounds during homogenization of waste with stabilizing mixture introduced and its dilution with water. The primary purposes of the research were: analysis of benzene volume emitted from soil during stabilization/solidification process and characterization of factors that may negatively affect the quality of measurements/the course of stabilization process. Analysis of benzene emission intensity during the process was based on concentration (C6H6) values, recorded with flame-ionization detector above the surface of reacting mixture. At the same time, gaseous contaminants emitted during waste stabilization were passed through pipes filled with activated carbon (SCK, Anasorb CSC). Benzene vapours adsorbed on activated carbon were subjected to analysis using gas chromatograph Varian 450-GC. Evaporation characteristics of benzene during processing contaminated soils revealed the stages creating the highest danger to workers' health, as well as a need for actions connected with modification of technological line.

REVIEW OF THE STABILITY ANALYSIS FOR THE LANL BSL-3 BUILDING FOUNDATION

DOE Office of Scientific and Technical Information (OSTI.GOV)

Heuze, F E; Wagoner, J L

2006-11-30

This work was performed upon request from Dr. Richard Thorpe from NNSA after his review of the LANL report on BSL-3 seismic stability [1]. The authors also reviewed report [1] and concluded, as did Dr. Thorpe, that the stability analysis was inappropriate. There are several reasons for that conclusion: (1) the assumption of a circular failure surface through the combined fill-and-rock foundation does not recognize the geologic structure involved. (2) the assumption of an equivalent static force to an earthquake loading does not represent the multiple cycles of shear loads created by a seismic event that can engender a substantialmore » degradation of shear modulus and shear strength of the soil under the building [2]. (3) there was no credible in-situ strength of the foundation materials (fill and rock mass) available for input into the stability analysis. Following that review, on September 26 the authors made a site visit and held discussions with LANL personnel connected to the BSL-3 building project. No information or evidence was presented to the authors indicating that the static stability of BSL-3 could be an issue. Accordingly, this report focuses on the topic of the BSL-3 site stability under seismic loading.« less

Robust Stability Analysis of the Space Launch System Control Design: A Singular Value Approach

NASA Technical Reports Server (NTRS)

Pei, Jing; Newsome, Jerry R.

2015-01-01

Classical stability analysis consists of breaking the feedback loops one at a time and determining separately how much gain or phase variations would destabilize the stable nominal feedback system. For typical launch vehicle control design, classical control techniques are generally employed. In addition to stability margins, frequency domain Monte Carlo methods are used to evaluate the robustness of the design. However, such techniques were developed for Single-Input-Single-Output (SISO) systems and do not take into consideration the off-diagonal terms in the transfer function matrix of Multi-Input-Multi-Output (MIMO) systems. Robust stability analysis techniques such as H(sub infinity) and mu are applicable to MIMO systems but have not been adopted as standard practices within the launch vehicle controls community. This paper took advantage of a simple singular-value-based MIMO stability margin evaluation method based on work done by Mukhopadhyay and Newsom and applied it to the SLS high-fidelity dynamics model. The method computes a simultaneous multi-loop gain and phase margin that could be related back to classical margins. The results presented in this paper suggest that for the SLS system, traditional SISO stability margins are similar to the MIMO margins. This additional level of verification provides confidence in the robustness of the control design.

Control design for robust stability in linear regulators: Application to aerospace flight control

NASA Technical Reports Server (NTRS)

Yedavalli, R. K.

1986-01-01

Time domain stability robustness analysis and design for linear multivariable uncertain systems with bounded uncertainties is the central theme of the research. After reviewing the recently developed upper bounds on the linear elemental (structured), time varying perturbation of an asymptotically stable linear time invariant regulator, it is shown that it is possible to further improve these bounds by employing state transformations. Then introducing a quantitative measure called the stability robustness index, a state feedback conrol design algorithm is presented for a general linear regulator problem and then specialized to the case of modal systems as well as matched systems. The extension of the algorithm to stochastic systems with Kalman filter as the state estimator is presented. Finally an algorithm for robust dynamic compensator design is presented using Parameter Optimization (PO) procedure. Applications in a aircraft control and flexible structure control are presented along with a comparison with other existing methods.

The Development of a Handbook for Astrobee F Performance and Stability Analysis

NASA Technical Reports Server (NTRS)

Wolf, R. S.

1982-01-01

An astrobee F performance and stability analysis is presented, for use by the NASA Sounding Rocket Division. The performance analysis provides information regarding altitude, mach number, dynamic pressure, and velocity as functions of time since launch. It is found that payload weight has the greatest effect on performance, and performance prediction accuracy was calculated to remain within 1%. In addition, to assure sufficient flight stability, a predicted rigid-body static margin of at least 8% of the total vehicle length is required. Finally, fin cant angle predictions are given in order to achieve a 2.5 cycle per second burnout roll rate, based on obtaining 75% of the steady roll rate. It is noted that this method can be used by flight performance engineers to create a similar handbook for any sounding rocket series.

Coexistence and local μ-stability of multiple equilibrium points for memristive neural networks with nonmonotonic piecewise linear activation functions and unbounded time-varying delays.

PubMed

Nie, Xiaobing; Zheng, Wei Xing; Cao, Jinde

2016-12-01

In this paper, the coexistence and dynamical behaviors of multiple equilibrium points are discussed for a class of memristive neural networks (MNNs) with unbounded time-varying delays and nonmonotonic piecewise linear activation functions. By means of the fixed point theorem, nonsmooth analysis theory and rigorous mathematical analysis, it is proven that under some conditions, such n-neuron MNNs can have 5 n equilibrium points located in ℜ n , and 3 n of them are locally μ-stable. As a direct application, some criteria are also obtained on the multiple exponential stability, multiple power stability, multiple log-stability and multiple log-log-stability. All these results reveal that the addressed neural networks with activation functions introduced in this paper can generate greater storage capacity than the ones with Mexican-hat-type activation function. Numerical simulations are presented to substantiate the theoretical results. Copyright © 2016 Elsevier Ltd. All rights reserved.

Influence of foam on the stability characteristics of immiscible flow in porous media

NASA Astrophysics Data System (ADS)

van der Meer, J. M.; Farajzadeh, R.; Rossen, W. R.; Jansen, J. D.

2018-01-01

Accurate field-scale simulations of foam enhanced oil recovery are challenging, due to the sharp transition between gas and foam. Hence, unpredictable numerical and physical behavior is often observed, casting doubt on the validity of the simulation results. In this paper, a thorough stability analysis of the foam model is presented to validate the simulation results. We study the effect of a strongly non-monotonous total mobility function arising from foam models on the stability characteristics of the flow. To this end, we apply the linear stability analysis to nearly discontinuous relative permeability functions and compare the results with those of highly accurate numerical simulations. In addition, we present a qualitative analysis of the effect of different reservoir and fluid properties on the foam fingering behavior. In particular, we consider the effect of heterogeneity of the reservoir, injection rates, and foam quality. Relative permeability functions play an important role in the onset of fingering behavior of the injected fluid. Hence, we can deduce that stability properties are highly dependent on the non-linearity of the foam transition. The foam-water interface is governed by a very small total mobility ratio, implying a stable front. The transition between gas and foam, however, exhibits a huge total mobility ratio, leading to instabilities in the form of viscous fingering. This implies that there is an unstable pattern behind the front. We deduce that instabilities are able to grow behind the front but are later absorbed by the expanding wave. Moreover, the stability analysis, validated by numerical simulations, provides valuable insights about the important scales and wavelengths of the foam model. In this way, we remove the ambiguity regarding the effect of grid resolution on the convergence of the solutions. This insight forms an essential step toward the design of a suitable computational solver that captures all the appropriate scales, while retaining computational efficiency.

Comparative profiling of sarcoplasmic phosphoproteins in ovine muscle with different color stability.

PubMed

Li, Meng; Li, Zheng; Li, Xin; Xin, Jianzeng; Wang, Ying; Li, Guixia; Wu, Liguo; Shen, Qingwu W; Zhang, Dequan

2018-02-01

The phosphorylation of sarcoplasmic proteins in postmortem muscles was investigated in relationship to color stability in the present study. Although no difference was observed in the global phosphorylation level of sarcoplasmic proteins, difference was determined in the phosphorylation levels of individual protein bands from muscles with different color stability. Correlation analysis and liquid chromatography - tandem mass spectrometry (LC-MS/MS) identification of phosphoproteins showed that most of the color stability-related proteins were glycolytic enzymes. Interestingly, the phosphorylation level of myoglobin was inversely related to meat color stability. As the phosphorylation of myoglobin increased, color stability based on a ∗ value decreased and metMb content increased. In summary, the study revealed that protein phosphorylation might play a role in the regulation of meat color stability probably by regulating glycolysis and the redox stability of myoglobin, which might be affected by the phosphorylation of myoglobin. Copyright © 2017 Elsevier Ltd. All rights reserved.

Design of a high altitude long endurance flying-wing solar-powered unmanned air vehicle

NASA Astrophysics Data System (ADS)

Alsahlani, A. A.; Johnston, L. J.; Atcliffe, P. A.

2017-06-01

The low-Reynolds number environment of high-altitude §ight places severe demands on the aerodynamic design and stability and control of a high altitude, long endurance (HALE) unmanned air vehicle (UAV). The aerodynamic efficiency of a §ying-wing configuration makes it an attractive design option for such an application and is investigated in the present work. The proposed configuration has a high-aspect ratio, swept-wing planform, the wing sweep being necessary to provide an adequate moment arm for outboard longitudinal and lateral control surfaces. A design optimization framework is developed under a MATLAB environment, combining aerodynamic, structural, and stability analysis. Low-order analysis tools are employed to facilitate efficient computations, which is important when there are multiple optimization loops for the various engineering analyses. In particular, a vortex-lattice method is used to compute the wing planform aerodynamics, coupled to a twodimensional (2D) panel method to derive aerofoil sectional characteristics. Integral boundary-layer methods are coupled to the panel method in order to predict §ow separation boundaries during the design iterations. A quasi-analytical method is adapted for application to flyingwing con¦gurations to predict the wing weight and a linear finite-beam element approach is used for structural analysis of the wing-box. Stability is a particular concern in the low-density environment of high-altitude flight for flying-wing aircraft and so provision of adequate directional stability and control power forms part of the optimization process. At present, a modified Genetic Algorithm is used in all of the optimization loops. Each of the low-order engineering analysis tools is validated using higher-order methods to provide con¦dence in the use of these computationally-efficient tools in the present design-optimization framework. This paper includes the results of employing the present optimization tools in the design of a HALE, flying-wing UAV to indicate that this is a viable design configuration option.

Linear morphological stability analysis of the solid-liquid interface in rapidsolidification of a binary system

NASA Astrophysics Data System (ADS)

Galenko, P. K.; Danilov, D. A.

2004-05-01

The interface stability against small perturbations of the planar solid-liquid interface is considered analytically in linear approximation. Following the analytical procedure of Trivedi and Kurz [

The stability of vocational interests from early adolescence to middle adulthood: a quantitative review of longitudinal studies.

PubMed

Low, K S Douglas; Yoon, Mijung; Roberts, Brent W; Rounds, James

2005-09-01

The present meta-analysis examined the stability of vocational interests from early adolescence (age 12) to middle adulthood (age 40). Stability was represented by rank-order and profile correlations. Interest stability remained unchanged during much of adolescence and increased dramatically during the college years (age 18-21.9), where it remained for the next 2 decades. Analyses of potential moderators showed that retest time interval was negatively related to interest stability and that rank-order stability was less stable than profile stability. Although cohort standings did not moderate stability, interests of the 1940s birth cohort were less stable than those of other cohorts. Furthermore, interests reflecting hands-on physical activities and self-expressive/artistic activities were more stable than scientific, social, enterprising, and clerical interests. Vocational interests showed substantial continuity over time, as evidenced by their higher longitudinal stability when compared with rank-order stability of personality traits. The findings are discussed in the context of psychosocial development.

Design and synthesis of a novel multifunctional stabilizer for highly stable uc(dl)-tetrahydropalmatine nanosuspensions and in vitro study

NASA Astrophysics Data System (ADS)

Yan, Beibei; Wang, Yancai; Wang, Lulu; Zhou, Yuqi; Shang, Xueyun; Zhao, Juan; Liu, Yangyang; Du, Juan

2018-05-01

The present study aimed to prepare stable uc(dl)-tetrahydropalmatine (uc(dl)-THP) nanosuspensions of optimized formulation with PEGylated chitosan as a multifunctional stabilizer using the antisolvent precipitation method. A central composite design project of three factors and five-level full factorial (53) was applied to design the experimental program, and response surface methodology analysis was used to optimize the experimental conditions. The effects of critical influencing factors such as PEGylated chitosan concentration, operational temperature, and ultrasonic energy on particle size and zeta potential were investigated. Under the optimization nanosuspension formulation, the particle size was 269 nm and zeta potential was at 37.4 mV. Also, the uc(dl)-THP nanosuspensions maintained good physical stability after 2 months, indicating the potential ability of the multifunctional stabilizer for stable nanosuspension formulation. Hence, the present findings indicated that PEGylated chitosan could be used as the ideal stabilizer to form a physically stable nanosuspension formulation.

Impact of Cannabis Use During Stabilization on Methadone Maintenance Treatment

PubMed Central

Scavone, Jillian L.; Sterling, Robert C.; Weinstein, Stephen P.; Van Bockstaele, Elisabeth J.

2016-01-01

Background and Objectives Illicit drug use, particularly of cannabis, is common among opiate-dependent individuals, and has the potential to impact treatment in a negative manner. Methods To examine this, patterns of cannabis use prior to and during methadone maintenance treatment (MMT) were examined to assess possible cannabis-related effects on MMT, particularly during methadone stabilization. Retrospective chart analysis was used to examine outpatient records of patients undergoing MMT (n=91), focusing specifically on past and present cannabis use and its association with opiate abstinence, methadone dose stabilization, and treatment compliance. Results Objective rates of cannabis use were high during methadone induction, dropping significantly following dose stabilization. History of cannabis use correlated with cannabis use during MMT, but did not negatively impact the methadone induction process. Pilot data also suggested that objective ratings of opiate withdrawal decrease in MMT patients using cannabis during stabilization. Conclusions and Scientific Significance The present findings may point to novel interventions to be employed during treatment for opiate dependence that specifically target cannabinoid-opioid system interactions. PMID:23795873

Role of the Cytoplasmic N-terminal Cap and Per-Arnt-Sim (PAS) Domain in Trafficking and Stabilization of Kv11.1 Channels*

PubMed Central

Ke, Ying; Hunter, Mark J.; Ng, Chai Ann; Perry, Matthew D.; Vandenberg, Jamie I.

2014-01-01

The N-terminal cytoplasmic region of the Kv11.1a potassium channel contains a Per-Arnt-Sim (PAS) domain that is essential for the unique slow deactivation gating kinetics of the channel. The PAS domain has also been implicated in the assembly and stabilization of the assembled tetrameric channel, with many clinical mutants in the PAS domain resulting in reduced stability of the domain and reduced trafficking. Here, we use quantitative Western blotting to show that the PAS domain is not required for normal channel trafficking nor for subunit-subunit interactions, and it is not necessary for stabilizing assembled channels. However, when the PAS domain is present, the N-Cap amphipathic helix must also be present for channels to traffic to the cell membrane. Serine scan mutagenesis of the N-Cap amphipathic helix identified Leu-15, Ile-18, and Ile-19 as residues critical for the stabilization of full-length proteins when the PAS domain is present. Furthermore, mutant cycle analysis experiments support recent crystallography studies, indicating that the hydrophobic face of the N-Cap amphipathic helix interacts with a surface-exposed hydrophobic patch on the core of the PAS domain to stabilize the structure of this critical gating domain. Our data demonstrate that the N-Cap amphipathic helix is critical for channel stability and trafficking. PMID:24695734

Stability of toxic arsenic species and arsenosugars found in the dry alga Hijiki and its water extracts.

PubMed

García-Salgado, Sara; Quijano, M Ángeles

2014-10-01

The achievement of reliable results in speciation analysis requires not only sensitive techniques but also sureness of species stability. Therefore, it is necessary to carry out stability studies because it is important to know with absolute certainty that there is not any species transformation during sample treatment and/or storage. Although several procedures have been recommended for the preservation of species integrity, there is no general agreement, as arsenic species stability depends on the sample matrix, the concentration level and the sample treatment procedure, so it is necessary to assess the arsenic species stability for each case. Thus, the present paper reports the stability tests of arsenic species carried out on the commercially available edible alga Hijiki (Hizikia fusiformis), from Japan, in both the dry sample and its water extracts, which were stored in amber glass and polystyrene containers at -18 and +4°C in the dark. Extractions were carried out with deionized water by microwave-assisted extraction, at a temperature of 90°C and three extraction steps of 5 min each, whereas arsenic speciation analysis was performed by anion exchange high performance liquid chromatography-photo-oxidation-hydride generation-atomic fluorescence spectrometry. The results obtained for the dry alga showed that the arsenic species present in it (arsenate (As(V)), dimethylarsinic acid (DMA) and the arsenosugars glycerol (Gly-sug), phosphate (PO4-sug), sulfonate (SO3-sug) and sulfate (SO4-sug)) were stable for at least 12 months when the sample was stored in polystyrene containers at +20°C in the dark. Regarding water extracts, the best storage conditions consisted of the use of polystyrene containers and a temperature of +4°C, for a maximum storage time of seven days. Therefore, the immediate analysis of Hijiki water extracts would not be necessary, and they could be stored for one week before analysis, ensuring arsenic species stability. This information about species integrity in extracts is especially useful when the sample treatment for arsenic species extraction is time-consuming. Copyright © 2014 Elsevier B.V. All rights reserved.

Robust Trypsin Coating on Electrospun Polymer Nanofibers in Rigorous Conditions and Its Uses for Protein Digestion

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ahn, Hye-Kyung; Kim, Byoung Chan; Jun, Seung-Hyun

2010-12-15

An efficient protein digestion in proteomic analysis requires the stabilization of proteases such as trypsin. In the present work, trypsin was stabilized in the form of enzyme coating on electrospun polymer nanofibers (EC-TR), which crosslinks additional trypsin molecules onto covalently-attached trypsin (CA-TR). EC-TR showed better stability than CA-TR in rigorous conditions, such as at high temperatures of 40 °C and 50 °C, in the presence of organic co-solvents, and at various pH's. For example, the half-lives of CA-TR and EC-TR were 0.24 and 163.20 hours at 40 ºC, respectively. The improved stability of EC-TR can be explained by covalent-linkages onmore » the surface of trypsin molecules, which effectively inhibits the denaturation, autolysis, and leaching of trypsin. The protein digestion was performed at 40 °C by using both CA-TR and EC-TR in digesting a model protein, enolase. EC-TR showed better performance and stability than CA-TR by maintaining good performance of enolase digestion under recycled uses for a period of one week. In the same condition, CA-TR showed poor performance from the beginning, and could not be used for digestion at all after a few usages. The enzyme coating approach is anticipated to be successfully employed not only for protein digestion in proteomic analysis, but also for various other fields where the poor enzyme stability presently hampers the practical applications of enzymes.« less

Bivariate and multivariate analyses of the influence of blood variables of patients submitted to Roux-en-Y gastric bypass on the stability of erythrocyte membrane against the chaotropic action of ethanol.

PubMed

de Arvelos, Leticia Ramos; Rocha, Vanessa Custódio Afonso; Felix, Gabriela Pereira; da Cunha, Cleine Chagas; Bernardino Neto, Morun; da Silva Garrote Filho, Mario; de Fátima Pinheiro, Conceição; Resende, Elmiro Santos; Penha-Silva, Nilson

2013-03-01

The stability of the erythrocyte membrane, which is essential for the maintenance of cell functions, occurs in a critical region of fluidity, which depends largely on its composition and the composition and characteristics of the medium. As the composition of the erythrocyte membrane is influenced by several blood variables, the stability of the erythrocyte membrane must have relations with them. The present study aimed to evaluate, by bivariate and multivariate statistical analyses, the correlations and causal relationships between hematologic and biochemical variables and the stability of the erythrocyte membrane against the chaotropic action of ethanol. The validity of this type of analysis depends on the homogeneity of the population and on the variability of the studied parameters, conditions that can be filled by patients who undergo bariatric surgery by the technique of Roux-en-Y gastric bypass since they will suffer feeding restrictions that have great impact on their blood composition. Pathway analysis revealed that an increase in hemoglobin leads to decreased stability of the cell, probably through a process mediated by an increase in mean corpuscular volume. Furthermore, an increase in the mean corpuscular hemoglobin (MCH) leads to an increase in erythrocyte membrane stability, probably because higher values of MCH are associated with smaller quantities of red blood cells and a larger contact area between the cell membrane and ethanol present in the medium.

Study of stability and control moment gyro wobble damping of flexible, spinning space stations

NASA Technical Reports Server (NTRS)

Berman, H.; Markowitz, J.; Holmer, W.

1972-01-01

An executive summary and an analysis of the results are discussed. A user's guide for the digital computer program that simulates the flexible, spinning space station is presented. Control analysis activities and derivation of dynamic equations of motion and the modal analysis are also cited.

Onset of density-driven instabilities in fractured aquifers

NASA Astrophysics Data System (ADS)

Jafari Raad, Seyed Mostafa; Hassanzadeh, Hassan

2018-04-01

Linear stability analysis is conducted to study the onset of density-driven convection involved in solubility trapping of C O2 in fractured aquifers. The effect of physical properties of a fracture network on the stability of a diffusive boundary layer in a saturated fractured porous media is investigated using the dual porosity concept. Linear stability analysis results show that both fracture interporosity flow and fracture storativity play an important role in the stability behavior of the system. It is shown that a diffusive boundary layer under the gravity field in fractured porous media with lower fracture storativity and/or higher fracture interporosity flow coefficient is more stable. We present scaling relations for the onset of convective instability in fractured aquifers with single and variable matrix block size distribution. These findings improve our understanding of density-driven flow in fractured aquifers and are important in the estimation of potential storage capacity, risk assessment, and storage site characterization and screening.

Bounded Linear Stability Analysis - A Time Delay Margin Estimation Approach for Adaptive Control

NASA Technical Reports Server (NTRS)

Nguyen, Nhan T.; Ishihara, Abraham K.; Krishnakumar, Kalmanje Srinlvas; Bakhtiari-Nejad, Maryam

2009-01-01

This paper presents a method for estimating time delay margin for model-reference adaptive control of systems with almost linear structured uncertainty. The bounded linear stability analysis method seeks to represent the conventional model-reference adaptive law by a locally bounded linear approximation within a small time window using the comparison lemma. The locally bounded linear approximation of the combined adaptive system is cast in a form of an input-time-delay differential equation over a small time window. The time delay margin of this system represents a local stability measure and is computed analytically by a matrix measure method, which provides a simple analytical technique for estimating an upper bound of time delay margin. Based on simulation results for a scalar model-reference adaptive control system, both the bounded linear stability method and the matrix measure method are seen to provide a reasonably accurate and yet not too conservative time delay margin estimation.

Floquet analysis of Kuznetsov-Ma breathers: A path towards spectral stability of rogue waves.

PubMed

Cuevas-Maraver, J; Kevrekidis, P G; Frantzeskakis, D J; Karachalios, N I; Haragus, M; James, G

2017-07-01

In the present work, we aim at taking a step towards the spectral stability analysis of Peregrine solitons, i.e., wave structures that are used to emulate extreme wave events. Given the space-time localized nature of Peregrine solitons, this is a priori a nontrivial task. Our main tool in this effort will be the study of the spectral stability of the periodic generalization of the Peregrine soliton in the evolution variable, namely the Kuznetsov-Ma breather. Given the periodic structure of the latter, we compute the corresponding Floquet multipliers, and examine them in the limit where the period of the orbit tends to infinity. This way, we extrapolate towards the stability of the limiting structure, namely the Peregrine soliton. We find that multiple unstable modes of the background are enhanced, yet no additional unstable eigenmodes arise as the Peregrine limit is approached. We explore the instability evolution also in direct numerical simulations.

Development of Curved-Plate Elements for the Exact Buckling Analysis of Composite Plate Assemblies Including Transverse-Shear Effects

NASA Technical Reports Server (NTRS)

McGowan, David Michael

1997-01-01

The analytical formulation of curved-plate non-linear equilibrium equations including transverse-shear-deformation effects is presented. The formulation uses the principle of virtual work. A unified set of non-linear strains that contains terms from both physical and tensorial strain measures is used. Linearized, perturbed equilibrium equations (stability equations) that describe the response of the plate just after buckling occurs are then derived after the application of several simplifying assumptions. These equations are then modified to allow the reference surface of the plate to be located at a distance z(sub c) from the centroidal surface. The implementation of the new theory into the VICONOPT exact buckling and vibration analysis and optimum design computer program is described as well. The terms of the plate stiffness matrix using both Classical Plate Theory (CPT) and first-order Shear-Deformation Plate Theory (SDPT) are presented. The necessary steps to include the effects of in-plane transverse and in-plane shear loads in the in-plane stability equations are also outlined. Numerical results are presented using the newly implemented capability. Comparisons of results for several example problems with different loading states are made. Comparisons of analyses using both physical and tensorial strain measures as well as CPT and SDPF are also made. Results comparing the computational effort required by the new analysis to that of the analysis currently in the VICONOPT program are presented. The effects of including terms related to in-plane transverse and in-plane shear loadings in the in-plane stability equations are also examined. Finally, results of a design-optimization study of two different cylindrical shells subject to uniform axial compression are presented.

Large-Signal Lyapunov-Based Stability Analysis of DC/AC Inverters and Inverter-Based Microgrids

NASA Astrophysics Data System (ADS)

Kabalan, Mahmoud

Microgrid stability studies have been largely based on small-signal linearization techniques. However, the validity and magnitude of the linearization domain is limited to small perturbations. Thus, there is a need to examine microgrids with large-signal nonlinear techniques to fully understand and examine their stability. Large-signal stability analysis can be accomplished by Lyapunov-based mathematical methods. These Lyapunov methods estimate the domain of asymptotic stability of the studied system. A survey of Lyapunov-based large-signal stability studies showed that few large-signal studies have been completed on either individual systems (dc/ac inverters, dc/dc rectifiers, etc.) or microgrids. The research presented in this thesis addresses the large-signal stability of droop-controlled dc/ac inverters and inverter-based microgrids. Dc/ac power electronic inverters allow microgrids to be technically feasible. Thus, as a prelude to examining the stability of microgrids, the research presented in Chapter 3 analyzes the stability of inverters. First, the 13 th order large-signal nonlinear model of a droop-controlled dc/ac inverter connected to an infinite bus is presented. The singular perturbation method is used to decompose the nonlinear model into 11th, 9th, 7th, 5th, 3rd and 1st order models. Each model ignores certain control or structural components of the full order model. The aim of the study is to understand the accuracy and validity of the reduced order models in replicating the performance of the full order nonlinear model. The performance of each model is studied in three different areas: time domain simulations, Lyapunov's indirect method and domain of attraction estimation. The work aims to present the best model to use in each of the three domains of study. Results show that certain reduced order models are capable of accurately reproducing the performance of the full order model while others can be used to gain insights into those three areas of study. This will enable future studies to save computational effort and produce the most accurate results according to the needs of the study being performed. Moreover, the effect of grid (line) impedance on the accuracy of droop control is explored using the 5th order model. Simulation results show that traditional droop control is valid up to R/X line impedance value of 2. Furthermore, the 3rd order nonlinear model improves the currently available inverter-infinite bus models by accounting for grid impedance, active power-frequency droop and reactive power-voltage droop. Results show the 3rd order model's ability to account for voltage and reactive power changes during a transient event. Finally, the large-signal Lyapunov-based stability analysis is completed for a 3 bus microgrid system (made up of 2 inverters and 1 linear load). The thesis provides a systematic state space large-signal nonlinear mathematical modeling method of inverter-based microgrids. The inverters include the dc-side dynamics associated with dc sources. The mathematical model is then used to estimate the domain of asymptotic stability of the 3 bus microgrid. The three bus microgrid system was used as a case study to highlight the design and optimization capability of a large-signal-based approach. The study explores the effect of system component sizing, load transient and generation variations on the asymptotic stability of the microgrid. Essentially, this advancement gives microgrid designers and engineers the ability to manipulate the domain of asymptotic stability depending on performance requirements. Especially important, this research was able to couple the domain of asymptotic stability of the ac microgrid with that of the dc side voltage source. Time domain simulations were used to demonstrate the mathematical nonlinear analysis results.

A theoretical investigation of the rolling oscillations of an airplane with ailerons free

NASA Technical Reports Server (NTRS)

Cohen, Doris

1944-01-01

An analysis is made of the stability of an airplane with ailerons free, with particular attention to the motions when the ailerons have a tendency to float against the wind. The present analysis supersedes the aileron investigation contained in NACA Technical Report no. 709. The equations of motion are first written to include yawing and sideslipping, and it is demonstrated that the principal effects of freeing the ailerons can be determined without regard to these motions. If the ailerons tend to float against the wind and have a high degree of aerodynamic balance, rolling oscillations, in addition to the normal lateral oscillations, are likely to occur. On the basis of the equations including only the rolling motion and the aileron deflection, formulas derived for the stability and damping of the rolling oscillations in terms of the hinge-moment derivatives are also presented showing the oscillatory regions and stability boundaries for a fictitious airplane of conventional proportion. The effects of friction in the control system are investigated and discussed.

Linear stability analysis of particle-laden hypopycnal plumes

NASA Astrophysics Data System (ADS)

Farenzena, Bruno Avila; Silvestrini, Jorge Hugo

2017-12-01

Gravity-driven riverine outflows are responsible for carrying sediments to the coastal waters. The turbulent mixing in these flows is associated with shear and gravitational instabilities such as Kelvin-Helmholtz, Holmboe, and Rayleigh-Taylor. Results from temporal linear stability analysis of a two-layer stratified flow are presented, investigating the behavior of settling particles and mixing region thickness on the flow stability in the presence of ambient shear. The particles are considered suspended in the transport fluid, and its sedimentation is modeled with a constant valued settling velocity. Three scenarios, regarding the mixing region thickness, were identified: the poorly mixed environment, the strong mixed environment, and intermediate scenario. It was observed that Kelvin-Helmholtz and settling convection modes are the two fastest growing modes depending on the particles settling velocity and the total Richardson number. The second scenario presents a modified Rayleigh-Taylor instability, which is the dominant mode. The third case can have Kelvin-Helmholtz, settling convection, and modified Rayleigh-Taylor modes as the fastest growing mode depending on the combination of parameters.

Sampled control stability of the ESA instrument pointing system

NASA Astrophysics Data System (ADS)

Thieme, G.; Rogers, P.; Sciacovelli, D.

Stability analysis and simulation results are presented for the ESA Instrument Pointing System (IPS) that is to be used in Spacelab's second launch. Of the two IPS plant dynamic models used in the ESA and NASA activities, one is based on six interconnected rigid bodies that represent the IPS and plant dynamic models used in the ESA and NASA activities, one is based on six interconnected rigid bodies that represent the IPS and its payload, while the other follows the NASA practice of defining an IPS-Spacelab 2 plant configuration through a structural finite element model, which is then used to generate modal data for various pointing directions. In both cases, the IPS dynamic plant model is truncated, then discretized at the sampling frequency and interfaces to a PID-based control law. A stability analysis has been carried out in discrete domain for various instrument pointing directions, taking into account suitable parameter variation ranges. A number of time simulations are presented.

Limit Cycle Analysis Applied to the Oscillations of Decelerating Blunt-Body Entry Vehicles

NASA Technical Reports Server (NTRS)

Schoenenberger, Mark; Queen, Eric M.

2008-01-01

Many blunt-body entry vehicles have nonlinear dynamic stability characteristics that produce self-limiting oscillations in flight. Several different test techniques can be used to extract dynamic aerodynamic coefficients to predict this oscillatory behavior for planetary entry mission design and analysis. Most of these test techniques impose boundary conditions that alter the oscillatory behavior from that seen in flight. Three sets of test conditions, representing three commonly used test techniques, are presented to highlight these effects. Analytical solutions to the constant-coefficient planar equations-of-motion for each case are developed to show how the same blunt body behaves differently depending on the imposed test conditions. The energy equation is applied to further illustrate the governing dynamics. Then, the mean value theorem is applied to the energy rate equation to find the effective damping for an example blunt body with nonlinear, self-limiting dynamic characteristics. This approach is used to predict constant-energy oscillatory behavior and the equilibrium oscillation amplitudes for the various test conditions. These predictions are verified with planar simulations. The analysis presented provides an overview of dynamic stability test techniques and illustrates the effects of dynamic stability, static aerodynamics and test conditions on observed dynamic motions. It is proposed that these effects may be leveraged to develop new test techniques and refine test matrices in future tests to better define the nonlinear functional forms of blunt body dynamic stability curves.

Numerical simulation and stability analysis of solutocapillary effect in ultrathin films

NASA Astrophysics Data System (ADS)

Gordeeva, V. Yu.; Lyushnin, A. V.

2017-04-01

Polar fluids, like water or polydimethylsiloxane, are widely used in technical and medical applications. Capillary effects arising from surface tension gradients can be significant in thin liquid films. The present paper is dedicated to investigation of capillary flow due to a surfactant added to a polar liquid under conditions when intermolecular forces and disjoining pressure play an important role. Evolution equations are formulated for a film profile and the surfactant concentration. Stability analysis shows that the Marangoni effect destabilizes the film, and oscillatory modes appear at slow evaporation rates. We find that the film has four stability modes of at slow evaporation: monotonic stable, monotonic unstable, oscillatory stable, and oscillatory unstable, depending on the wave number of disturbances.

[The functional state classification and evaluation of the stability level in mental loads based on the factor structure of heart rate variability parameters].

PubMed

Mashin, V A; Mashina, M N

2004-12-01

In the paper, outcomes of the researches devoted to factor analysis of heart rate variability parameters and definition of the most informative parameters for diagnostics of functional states and an evaluation of level of stability to mental loads, are presented. The factor structure of parameters, which unclude integral level of heart rate variability (1), balance between activity of vagus and brain cortical-limbic systems (2), integrated level of cardiovascular system functioning (3), is substantiated. Factor analysis outcomes have been used for construction of functional state classification, for their differential diagnostics, and for development and check of algorithm for evaluation of the stability level in mental loads.

New Robust Design Guideline forImperfection Sensitive Composite Launcher Structures- The Desicos Project

NASA Astrophysics Data System (ADS)

Degenhardt, Richard

2014-06-01

Space industry demands for reduced development and operating costs. Structural weight reduction by exploitation of structural reserves in composite space and aerospace structures contributes to this aim, however, it requires accurate and experimentally validated stability analysis. Currently, the potential of composite light weight structures, which are prone to buckling, is not fully exploited as appropriate guidelines in the field of space applications do not exist. This paper deals with the state-of-the-art advances and challenges related to coupled stability analysis of composite structures which show very complex stability behaviour. Improved design guidelines for composites structures are still under development. This paper gives a short state-of-the-art and presents a proposal for a future design guideline.

User's manual for rocket combustor interactive design (ROCCID) and analysis computer program. Volume 2: Appendixes A-K

NASA Technical Reports Server (NTRS)

Muss, J. A.; Nguyen, T. V.; Johnson, C. W.

1991-01-01

The appendices A-K to the user's manual for the rocket combustor interactive design (ROCCID) computer program are presented. This includes installation instructions, flow charts, subroutine model documentation, and sample output files. The ROCCID program, written in Fortran 77, provides a standardized methodology using state of the art codes and procedures for the analysis of a liquid rocket engine combustor's steady state combustion performance and combustion stability. The ROCCID is currently capable of analyzing mixed element injector patterns containing impinging like doublet or unlike triplet, showerhead, shear coaxial and swirl coaxial elements as long as only one element type exists in each injector core, baffle, or barrier zone. Real propellant properties of oxygen, hydrogen, methane, propane, and RP-1 are included in ROCCID. The properties of other propellants can be easily added. The analysis models in ROCCID can account for the influences of acoustic cavities, helmholtz resonators, and radial thrust chamber baffles on combustion stability. ROCCID also contains the logic to interactively create a combustor design which meets input performance and stability goals. A preliminary design results from the application of historical correlations to the input design requirements. The steady state performance and combustion stability of this design is evaluated using the analysis models, and ROCCID guides the user as to the design changes required to satisfy the user's performance and stability goals, including the design of stability aids. Output from ROCCID includes a formatted input file for the standardized JANNAF engine performance prediction procedure.

A rumor transmission model with incubation in social networks

NASA Astrophysics Data System (ADS)

Jia, Jianwen; Wu, Wenjiang

2018-02-01

In this paper, we propose a rumor transmission model with incubation period and constant recruitment in social networks. By carrying out an analysis of the model, we study the stability of rumor-free equilibrium and come to the local stable condition of the rumor equilibrium. We use the geometric approach for ordinary differential equations for showing the global stability of the rumor equilibrium. And when ℜ0 = 1, the new model occurs a transcritical bifurcation. Furthermore, numerical simulations are used to support the analysis. At last, some conclusions are presented.

Substructure analysis using NICE/SPAR and applications of force to linear and nonlinear structures. [spacecraft masts

NASA Technical Reports Server (NTRS)

Razzaq, Zia; Prasad, Venkatesh; Darbhamulla, Siva Prasad; Bhati, Ravinder; Lin, Cai

1987-01-01

Parallel computing studies are presented for a variety of structural analysis problems. Included are the substructure planar analysis of rectangular panels with and without a hole, the static analysis of space mast, using NICE/SPAR and FORCE, and substructure analysis of plane rigid-jointed frames using FORCE. The computations are carried out on the Flex/32 MultiComputer using one to eighteen processors. The NICE/SPAR runstream samples are documented for the panel problem. For the substructure analysis of plane frames, a computer program is developed to demonstrate the effectiveness of a substructuring technique when FORCE is enforced. Ongoing research activities for an elasto-plastic stability analysis problem using FORCE, and stability analysis of the focus problem using NICE/SPAR are briefly summarized. Speedup curves for the panel, the mast, and the frame problems provide a basic understanding of the effectiveness of parallel computing procedures utilized or developed, within the domain of the parameters considered. Although the speedup curves obtained exhibit various levels of computational efficiency, they clearly demonstrate the excellent promise which parallel computing holds for the structural analysis problem. Source code is given for the elasto-plastic stability problem and the FORCE program.

Development and Testing of a High Stability Engine Control (HISTEC) System

NASA Technical Reports Server (NTRS)

Orme, John S.; DeLaat, John C.; Southwick, Robert D.; Gallops, George W.; Doane, Paul M.

1998-01-01

Flight tests were recently completed to demonstrate an inlet-distortion-tolerant engine control system. These flight tests were part of NASA's High Stability Engine Control (HISTEC) program. The objective of the HISTEC program was to design, develop, and flight demonstrate an advanced integrated engine control system that uses measurement-based, real-time estimates of inlet airflow distortion to enhance engine stability. With improved stability and tolerance of inlet airflow distortion, future engine designs may benefit from a reduction in design stall-margin requirements and enhanced reliability, with a corresponding increase in performance and decrease in fuel consumption. This paper describes the HISTEC methodology, presents an aircraft test bed description (including HISTEC-specific modifications) and verification and validation ground tests. Additionally, flight test safety considerations, test plan and technique design and approach, and flight operations are addressed. Some illustrative results are presented to demonstrate the type of analysis and results produced from the flight test program.

Soluble fullerene derivatives: The effect of electronic structure on transistor performance and air stability

NASA Astrophysics Data System (ADS)

Ball, James M.; Bouwer, Ricardo K. M.; Kooistra, Floris B.; Frost, Jarvist M.; Qi, Yabing; Domingo, Ester Buchaca; Smith, Jeremy; de Leeuw, Dago M.; Hummelen, Jan C.; Nelson, Jenny; Kahn, Antoine; Stingelin, Natalie; Bradley, Donal D. C.; Anthopoulos, Thomas D.

2011-07-01

The family of soluble fullerene derivatives comprises a widely studied group of electron transporting molecules for use in organic electronic and optoelectronic devices. For electronic applications, electron transporting (n-channel) materials are required for implementation into organic complementary logic circuit architectures. To date, few soluble candidate materials have been studied that fulfill the stringent requirements of high carrier mobility and air stability. Here we present a study of three soluble fullerenes with varying electron affinity to assess the impact of electronic structure on device performance and air stability. Through theoretical and experimental analysis of the electronic structure, characterization of thin-film structure, and characterization of transistor device properties we find that the air stability of the present series of fullerenes not only depends on the absolute electron affinity of the semiconductor but also on the disorder within the thin-film.

The effects of viscosity on the stability of a trailing-line vortex in compressible flow

NASA Technical Reports Server (NTRS)

Stott, Jillian A. K.; Duck, Peter W.

1994-01-01

We consider the effects of viscosity on the inviscid stability of the Batchelor vortex in a compressible flow. The problem is tackled asymptotically, in the limit of large (streamwise and azimuthal) wavenumbers, together with large Mach numbers. Previous studies, with viscous effects neglected, found that the nature of the solution passes through different regimes as the Mach number increases, relative to the wavenumber. This structure persists when viscous effects are included in the analysis. In the present study the mode present in the incompressible case ceases to be unstable at high Mach numbers and a center mode forms, whose stability characteristics are determined primarily by conditions close to the vortex axis. We find generally that viscosity has a stabilizing influence on the flow, while in the case of center modes, viscous effects become important at much larger Reynolds numbers than for the first class of disturbance.

Locating Critical Circular and Unconstrained Failure Surface in Slope Stability Analysis with Tailored Genetic Algorithm

NASA Astrophysics Data System (ADS)

Pasik, Tomasz; van der Meij, Raymond

2017-12-01

This article presents an efficient search method for representative circular and unconstrained slip surfaces with the use of the tailored genetic algorithm. Searches for unconstrained slip planes with rigid equilibrium methods are yet uncommon in engineering practice, and little publications regarding truly free slip planes exist. The proposed method presents an effective procedure being the result of the right combination of initial population type, selection, crossover and mutation method. The procedure needs little computational effort to find the optimum, unconstrained slip plane. The methodology described in this paper is implemented using Mathematica. The implementation, along with further explanations, is fully presented so the results can be reproduced. Sample slope stability calculations are performed for four cases, along with a detailed result interpretation. Two cases are compared with analyses described in earlier publications. The remaining two are practical cases of slope stability analyses of dikes in Netherlands. These four cases show the benefits of analyzing slope stability with a rigid equilibrium method combined with a genetic algorithm. The paper concludes by describing possibilities and limitations of using the genetic algorithm in the context of the slope stability problem.

Laboratory and 3-D distinct element analysis of the failure mechanism of a slope under external surcharge

NASA Astrophysics Data System (ADS)

Li, N.; Cheng, Y. M.

2015-01-01

Landslide is a major disaster resulting in considerable loss of human lives and property damages in hilly terrain in Hong Kong, China and many other countries. The factor of safety and the critical slip surface for slope stabilization are the main considerations for slope stability analysis in the past, while the detailed post-failure conditions of the slopes have not been considered in sufficient detail. There is however increasing interest in the consequences after the initiation of failure that includes the development and propagation of the failure surfaces, the amount of failed mass and runoff and the affected region. To assess the development of slope failure in more detail and to consider the potential danger of slopes after failure has initiated, the slope stability problem under external surcharge is analyzed by the distinct element method (DEM) and a laboratory model test in the present research. A more refined study about the development of failure, microcosmic failure mechanisms and the post-failure mechanisms of slopes will be carried out. The numerical modeling method and the various findings from the present work can provide an alternate method of analysis of slope failure, which can give additional information not available from the classical methods of analysis.

Laboratory and 3-D-distinct element analysis of failure mechanism of slope under external surcharge

NASA Astrophysics Data System (ADS)

Li, N.; Cheng, Y. M.

2014-09-01

Landslide is a major disaster resulting in considerable loss of human lives and property damages in hilly terrain in Hong Kong, China and many other countries. The factor of safety and the critical slip surface for slope stabilization are the main considerations for slope stability analysis in the past, while the detailed post-failure conditions of the slopes have not been considered in sufficient details. There are however increasing interest on the consequences after the initiation of failure which includes the development and propagation of the failure surfaces, the amount of failed mass and runoff and the affected region. To assess the development of slope failure in more details and to consider the potential danger of slopes after failure has initiated, the slope stability problem under external surcharge is analyzed by the distinct element method (DEM) and laboratory model test in the present research. A more refined study about the development of failure, microcosmic failure mechanism and the post-failure mechanism of slope will be carried out. The numerical modeling method and the various findings from the present work can provide an alternate method of analysis of slope failure which can give additional information not available from the classical methods of analysis.

Multivariate approaches for stability control of the olive oil reference materials for sensory analysis - part I: framework and fundamentals.

PubMed

Valverde-Som, Lucia; Ruiz-Samblás, Cristina; Rodríguez-García, Francisco P; Cuadros-Rodríguez, Luis

2018-02-09

Virgin olive oil is the only food product for which sensory analysis is regulated to classify it in different quality categories. To harmonize the results of the sensorial method, the use of standards or reference materials is crucial. The stability of sensory reference materials is required to enable their suitable control, aiming to confirm that their specific target values are maintained on an ongoing basis. Currently, such stability is monitored by means of sensory analysis and the sensory panels are in the paradoxical situation of controlling the standards that are devoted to controlling the panels. In the present study, several approaches based on similarity analysis are exploited. For each approach, the specific methodology to build a proper multivariate control chart to monitor the stability of the sensory properties is explained and discussed. The normalized Euclidean and Mahalanobis distances, the so-called nearness and hardiness indices respectively, have been defined as new similarity indices to range the values from 0 to 1. Also, the squared mean from Hotelling's T 2 -statistic and Q 2 -statistic has been proposed as another similarity index. © 2018 Society of Chemical Industry. © 2018 Society of Chemical Industry.

Certified reference material of volatile organic compounds for environmental analysis: BTEX in methanol.

PubMed

Neves, Laura A; Almeida, Renato R R; Rego, Eliane P; Rodrigues, Janaína Marques; de Carvalho, Lucas Junqueira; de M Goulart, Ana Letícia

2015-04-01

The Brazilian Metrology Institute (National Institute of Metrology, Quality, and Technology, Inmetro) has been developing a certified reference material (CRM) of the volatile organic compounds benzene; toluene; ethylbenzene; and ortho, meta, and para-xylenes (BTEX) in methanol, to ensure quality control for environmental-analysis measurements. The objective of this paper is to present the results of certification studies: uncertainty estimates related to characterization, a homogeneity study, and a stability study on a single lot of CRM composed of BTEX in methanol. The method used analysis of variance (ANOVA), a statistical tool, to evaluate the homogeneity and stability of the BTEX CRM, which complies with ISO Guide 30 series. The homogeneity and stability of the BTEX CRM was confirmed for all analytes and their respective properties. All the procedures used in this study complied with ISO GUIDE 34, ISO GUIDE 35, and the guide to the expression of uncertainty of measurement (GUM).

Analysis of the particle stability in a new designed ultrasonic levitation device.

PubMed

Baer, Sebastian; Andrade, Marco A B; Esen, Cemal; Adamowski, Julio Cezar; Schweiger, Gustav; Ostendorf, Andreas

2011-10-01

The use of acoustic levitation in the fields of analytical chemistry and in the containerless processing of materials requires a good stability of the levitated particle. However, spontaneous oscillations and rotation of the levitated particle have been reported in literature, which can reduce the applicability of the acoustic levitation technique. Aiming to reduce the particle oscillations, this paper presents the analysis of the particle stability in a new acoustic levitator device. The new acoustic levitator consists of a piezoelectric transducer with a concave radiating surface and a concave reflector. The analysis is conducted by determining numerically the axial and lateral forces that act on the levitated object and by measuring the oscillations of a sphere particle by a laser Doppler vibrometer. It is shown that the new levitator design allows to increase the lateral forces and reduce significantly the lateral oscillations of the levitated object.

Qualitative fusion technique based on information poor system and its application to factor analysis for vibration of rolling bearings

NASA Astrophysics Data System (ADS)

Xia, Xintao; Wang, Zhongyu

2008-10-01

For some methods of stability analysis of a system using statistics, it is difficult to resolve the problems of unknown probability distribution and small sample. Therefore, a novel method is proposed in this paper to resolve these problems. This method is independent of probability distribution, and is useful for small sample systems. After rearrangement of the original data series, the order difference and two polynomial membership functions are introduced to estimate the true value, the lower bound and the supper bound of the system using fuzzy-set theory. Then empirical distribution function is investigated to ensure confidence level above 95%, and the degree of similarity is presented to evaluate stability of the system. Cases of computer simulation investigate stable systems with various probability distribution, unstable systems with linear systematic errors and periodic systematic errors and some mixed systems. The method of analysis for systematic stability is approved.

Iterative filtering decomposition based on local spectral evolution kernel

PubMed Central

Wang, Yang; Wei, Guo-Wei; Yang, Siyang

2011-01-01

The synthesizing information, achieving understanding, and deriving insight from increasingly massive, time-varying, noisy and possibly conflicting data sets are some of most challenging tasks in the present information age. Traditional technologies, such as Fourier transform and wavelet multi-resolution analysis, are inadequate to handle all of the above-mentioned tasks. The empirical model decomposition (EMD) has emerged as a new powerful tool for resolving many challenging problems in data processing and analysis. Recently, an iterative filtering decomposition (IFD) has been introduced to address the stability and efficiency problems of the EMD. Another data analysis technique is the local spectral evolution kernel (LSEK), which provides a near prefect low pass filter with desirable time-frequency localizations. The present work utilizes the LSEK to further stabilize the IFD, and offers an efficient, flexible and robust scheme for information extraction, complexity reduction, and signal and image understanding. The performance of the present LSEK based IFD is intensively validated over a wide range of data processing tasks, including mode decomposition, analysis of time-varying data, information extraction from nonlinear dynamic systems, etc. The utility, robustness and usefulness of the proposed LESK based IFD are demonstrated via a large number of applications, such as the analysis of stock market data, the decomposition of ocean wave magnitudes, the understanding of physiologic signals and information recovery from noisy images. The performance of the proposed method is compared with that of existing methods in the literature. Our results indicate that the LSEK based IFD improves both the efficiency and the stability of conventional EMD algorithms. PMID:22350559

Static and dynamic stability of pneumatic vibration isolators and systems of isolators

NASA Astrophysics Data System (ADS)

Ryaboy, Vyacheslav M.

2014-01-01

Pneumatic vibration isolation is the most widespread effective method for creating vibration-free environments that are vital for precise experiments and manufacturing operations in optoelectronics, life sciences, microelectronics, nanotechnology and other areas. The modeling and design principles of a dual-chamber pneumatic vibration isolator, basically established a few decades ago, continue to attract attention of researchers. On the other hand, behavior of systems of such isolators was never explained in the literature in sufficient detail. This paper covers a range of questions essential for understanding the mechanics of pneumatic isolation systems from both design and application perspectives. The theory and a model of a single standalone isolator are presented in concise form necessary for subsequent analysis. Then the dynamics of a system of isolators supporting a payload is considered with main attention directed to two aspects of their behavior: first, the static stability of payloads with high positions of the center of gravity; second, dynamic stability of the feedback system formed by mechanical leveling valves. The direct method of calculating the maximum stable position of the center of gravity is presented and illustrated by three-dimensional stability domains; analytic formulas are given that delineate these domains. A numerical method for feedback stability analysis of self-leveling valve systems is given, and the results are compared with the analytical estimates for a single isolator. The relation between the static and dynamic phenomena is discussed.

EFFECT OF SIMULTANEOUSLY SILICIFIED MICROCRYSTALLINE CELLULOSE AND PREGELATINIZED STARCH ON THE THEOPHYLLINE TABLETS STABILITY.

PubMed

Mazurek-Wadołkowska, Edyta; Winnicka, Katarzyna; Czyzewska, Urszula; Miltyk, Wojciech

2016-07-01

High profitability and simplicity of direct compression, encourages pharmaceutical industry to create universal excipients to improve technology process. Prosolv® SMCC - silicified microcrystalline cellulose and Starch 1500® - pregelatinized starch, are the example of multifunctional excipients. The aim of the present study was to evaluate the stability of theophylline (API) in the mixtures with excipients with various physico-chemical properties (Prosolv® SMCC 90, Prosolv® SMCC HD 90, Prosolv* SMCC 50®, Starch 1500® and magnesium stearate). The study presents results of thermal analysis of the mixtures with theophylline before and after 6 months storage of the tablets at various temperatures and relative humidity conditions (25 ± 2°C/40 ± 5% RH, 40 ± 2°C/75 ± 5% RH). It was shown that high concentration of Starch 1500® (49%) affects the stability of the theophylline tablets with Prosolv® SMCC. Prosolv® SMCC had no effect on API stability as confirmed by the differential scanning calorimetry (DSC). Changes in peak placements were observed just after tabletting process, which might indicate that compression accelerated the incompatibilities between theophylline and Starch 1500. TGA analysis showed loss in tablets mass equal to water content in starch. GC-MS study established no chemical decomposition of theophylline. We demonstrated that high content of Starch 1500® (49%) in the tablet mass, affects stability on tablets containing theophylline and Prosolv® SMCC.

Helicopter aeroelastic stability and response - Current topics and future trends

NASA Technical Reports Server (NTRS)

Friedmann, Peretz P.

1990-01-01

This paper presents several current topics in rotary wing aeroelasticity and concludes by attempting to anticipate future trends and developments. These topics are: (1) the role of geometric nonlinearities; (2) structural modeling, and aeroelastic analysis of composite rotor blades; (3) aeroelastic stability and response in forward flight; (4) modeling of coupled rotor/fuselage aeromechanical problems and their active control; and (5) the coupled rotor-fuselage vibration problem and its alleviation by higher harmonic control. Selected results illustrating the fundamental aspects of these topics are presented. Future developments are briefly discussed.

Nonlinear research of an image motion stabilization system embedded in a space land-survey telescope

NASA Astrophysics Data System (ADS)

Somov, Yevgeny; Butyrin, Sergey; Siguerdidjane, Houria

2017-01-01

We consider an image motion stabilization system embedded into a space telescope for a scanning optoelectronic observation of terrestrial targets. Developed model of this system is presented taking into account physical hysteresis of piezo-ceramic driver and a time delay at a forming of digital control. We have presented elaborated algorithms for discrete filtering and digital control, obtained results on analysis of the image motion velocity oscillations in the telescope focal plane, and also methods for terrestrial and in-flight verification of the system.

Assessment of Walking Stability of Elderly by Means of Nonlinear Time-Series Analysis and Simple Accelerometry

NASA Astrophysics Data System (ADS)

Ohtaki, Yasuaki; Arif, Muhammad; Suzuki, Akihiro; Fujita, Kazuki; Inooka, Hikaru; Nagatomi, Ryoichi; Tsuji, Ichiro

This study presents an assessment of walking stability in elderly people, focusing on local dynamic stability of walking. Its main objectives were to propose a technique to quantify local dynamic stability using nonlinear time-series analyses and a portable instrument, and to investigate their reliability in revealing the efficacy of an exercise training intervention for elderly people for improvement of walking stability. The method measured three-dimensional acceleration of the upper body, and computation of Lyapunov exponents, thereby directly quantifying the local stability of the dynamic system. Straight level walking of young and elderly subjects was investigated in the experimental study. We compared Lyapunov exponents of young and the elderly subjects, and of groups before and after the exercise intervention. Experimental results demonstrated that the exercise intervention improved local dynamic stability of walking. The proposed method was useful in revealing effects and efficacies of the exercise intervention for elderly people.

Robust stability of fractional order polynomials with complicated uncertainty structure

PubMed Central

Şenol, Bilal; Pekař, Libor

2017-01-01

The main aim of this article is to present a graphical approach to robust stability analysis for families of fractional order (quasi-)polynomials with complicated uncertainty structure. More specifically, the work emphasizes the multilinear, polynomial and general structures of uncertainty and, moreover, the retarded quasi-polynomials with parametric uncertainty are studied. Since the families with these complex uncertainty structures suffer from the lack of analytical tools, their robust stability is investigated by numerical calculation and depiction of the value sets and subsequent application of the zero exclusion condition. PMID:28662173

Non Lyapunov stability of the constant spatially developing 1-D gas flow in presence of solutions having strictly positive exponential growth rate

NASA Astrophysics Data System (ADS)

Balint, Stefan; Balint, Agneta M.

2017-01-01

Different types of stabilities (global, local) and instabilities (global absolute, local convective) of the constant spatially developing 1-D gas flow are analyzed in the phase space of continuously differentiable functions, endowed with the usual algebraic operations and the topology generated by the uniform convergence on the real axis. For this purpose the Euler equations linearized at the constant flow are used. The Lyapunov stability analysis was presented in [1] and this paper is a continuation of [1].

Radiation−condensation instability in tokamaks with mixed impurities

DOE Office of Scientific and Technical Information (OSTI.GOV)

Morozov, D. Kh.; Pshenov, A. A., E-mail: Pshenov.andrey@gmail.com

2015-08-15

Radiation−condensation instability (RCI) is one of the possible mechanisms behind the formation of microfaceted asymmetric radiation from the edge (MARFE) of a tokamak. It has been previously shown by the authors that RCI in carbon-seeded plasma can be stabilized using neon injection. Recently, beryllium- and tungsten-seeded plasmas became a subject of great interest. Therefore, in the present paper, RCI stability analysis of the edge plasma seeded with beryllium, tungsten, nitrogen, and carbon is performed. The influence of neutral hydrogen fluxes from the wall on the marginal stability limit is studied as well.

Delay-slope-dependent stability results of recurrent neural networks.

PubMed

Li, Tao; Zheng, Wei Xing; Lin, Chong

2011-12-01

By using the fact that the neuron activation functions are sector bounded and nondecreasing, this brief presents a new method, named the delay-slope-dependent method, for stability analysis of a class of recurrent neural networks with time-varying delays. This method includes more information on the slope of neuron activation functions and fewer matrix variables in the constructed Lyapunov-Krasovskii functional. Then some improved delay-dependent stability criteria with less computational burden and conservatism are obtained. Numerical examples are given to illustrate the effectiveness and the benefits of the proposed method.

Materials Examination of the Vertical Stabilizer from American Airlines Flight 587

NASA Technical Reports Server (NTRS)

Fox, Matthew R.; Schultheisz, Carl R.; Reeder, James R.; Jensen, Brian J.

2005-01-01

The first in-flight failure of a primary structural component made from composite material on a commercial airplane led to the crash of American Airlines Flight 587. As part of the National Transportation Safety Board investigation of the accident, the composite materials of the vertical stabilizer were tested, microstructure was analyzed, and fractured composite lugs that attached the vertical stabilizer to the aircraft tail were examined. In this paper the materials testing and analysis is presented, composite fractures are described, and the resulting clues to the failure events are discussed.

Combined analytical and numerical approaches in Dynamic Stability analyses of engineering systems

NASA Astrophysics Data System (ADS)

Náprstek, Jiří

2015-03-01

Dynamic Stability is a widely studied area that has attracted many researchers from various disciplines. Although Dynamic Stability is usually associated with mechanics, theoretical physics or other natural and technical disciplines, it is also relevant to social, economic, and philosophical areas of our lives. Therefore, it is useful to occasionally highlight the general aspects of this amazing area, to present some relevant examples and to evaluate its position among the various branches of Rational Mechanics. From this perspective, the aim of this study is to present a brief review concerning the Dynamic Stability problem, its basic definitions and principles, important phenomena, research motivations and applications in engineering. The relationships with relevant systems that are prone to stability loss (encountered in other areas such as physics, other natural sciences and engineering) are also noted. The theoretical background, which is applicable to many disciplines, is presented. In this paper, the most frequently used Dynamic Stability analysis methods are presented in relation to individual dynamic systems that are widely discussed in various engineering branches. In particular, the Lyapunov function and exponent procedures, Routh-Hurwitz, Liénard, and other theorems are outlined together with demonstrations. The possibilities for analytical and numerical procedures are mentioned together with possible feedback from experimental research and testing. The strengths and shortcomings of these approaches are evaluated together with examples of their effective complementing of each other. The systems that are widely encountered in engineering are presented in the form of mathematical models. The analyses of their Dynamic Stability and post-critical behaviour are also presented. The stability limits, bifurcation points, quasi-periodic response processes and chaotic regimes are discussed. The limit cycle existence and stability are examined together with their separating roles as attractors and repulsers. Two levels of stability loss (recovery of the system is possible or final collapse is inevitable) as can be observed in softening systems are noted. Time-limited excitation and relevant transition effects (e.g., seismic excitation) are also discussed, together with the evaluation of possible system reliability improvement. The Dynamic Stability investigation of two degrees-of-freedom aero-elastic systems in a linear formulation using several approaches is briefly highlighted. Further systems modelling problems that arise in transport engineering are also outlined. A few hints for applications are given. Some open problems and possible future research strategies are outlined.

Preserving enzymatic activity and enhancing biochemical stability of glutathione transferase by soluble additives under free and tethered conditions.

PubMed

Karamitros, Christos S; Labrou, Nikolaos E

2017-09-01

In the present study, we report the effect of four different soluble additives (sucrose, lactitol, superfloc c577, and dextran sulfate) on the stability of glutathione transferase 1 enzyme from Zea mays (ZmGSTF1-1) under free and tethered conditions at 4 and 25 °C. Among all additives, the best stabilizing effects were observed in the case of superfloc c577 and sucrose at both tested temperatures, yet at distinct concentrations at each condition. Those two stabilizing agents were further combined and potential positive synergistic effects were investigated. In addition, we assessed the long-term storage and operational stability of ZmGSTF1-1 under tethered conditions in the presence of additives, which provided the most conducive effects on its stability under free conditions. Our results strongly suggest that the presence of additives may be beneficial to the stability of the enzyme under both free and tethered conditions. Thermodynamic analysis of the free enzyme in the presence of sucrose, which exhibited the best stabilizing effect at both temperatures, shed light on the possible mechanism of action. Given the considerable importance of the development of GST-based biosensors with prolonged stability, the present work may be of general interest to researchers in the field of applied enzymology. © 2016 International Union of Biochemistry and Molecular Biology, Inc.

Damping torque analysis of VSC-based system utilizing power synchronization control

NASA Astrophysics Data System (ADS)

Fu, Q.; Du, W. J.; Zheng, K. Y.; Wang, H. F.

2017-05-01

Power synchronization control is a new control strategy of VSC-HVDC for connecting a weak power system. Different from the vector control method, this control method utilizes the internal synchronization mechanism in ac systems, in principle, similar to the operation of a synchronous machine. So that the parameters of controllers in power synchronization control will change the electromechanical oscillation modes and make an impact on the transient stability of power system. This paper present a mathematical model for small-signal stability analysis of VSC station used power synchronization control and analyse the impact of the dynamic interactions by calculating the contribution of the damping torque from the power synchronization control, besides, the parameters of controllers which correspond to damping torque and synchronous torque in the power synchronization control is defined respectively. At the end of the paper, an example power system is presented to demonstrate and validate the theoretical analysis and associated conclusions are made.

Mobility performance analysis of an innovation lunar rover with diameter-variable wheel

NASA Astrophysics Data System (ADS)

Sun, Gang; Gao, Feng; Sun, Peng; Xu, Guoyan

2007-11-01

To achieve excellent mobility performance, a four-wheel, all-wheel drive lunar rover with diameter-variable wheel was presented, the wheel can be contracted and extended by the motor equipped in the wheel hub, accompanied with wheel diameter varying from 200mm to 390mm. The wheel sinkage and drawbar pull force were predicated with terramechanics formulae and lunar regolith mechanic parameters employed, furthermore, the slope traversability was investigated through quasi-static modeling mechanic analysis, also the obstacle resistance and the maximum negotiable obstacle height for different wheel radius were derived from the equations of static equilibrium of the rover. Analysis results show that for the innovation lunar rover presented, it will bring much better slope traveling stability and obstacle climbing capability than rovers with normal wheels, these will improve the rover mobility performance and stabilize the rover's frame, smooth the motion of sensors.

Algorithms for Automated Characterization of Three-Axis Stabilized GEOs using Non-Resolved Optical Observations

DTIC Science & Technology

2012-09-01

Daniel Fulcoly AFRL Space Vehicles Directorate Stephen A. Gregory Boeing Corp. Non- resolved optical observations of satellites have been known...to supply researchers with valuable information about satellite status. Until recently most non- resolved analysis techniques have required an expert...rapidly characterizing satellites from non- resolved optical data of 3-axis stabilized geostationary satellites . We will present background information on

76 FR 33798 - Self-Regulatory Organizations; C2 Options Exchange, Incorporated; Order Instituting Proceedings...

Federal Register 2010, 2011, 2012, 2013, 2014

2011-06-09

..., open interest, and trading patterns. The analysis would examine trading in the proposed option product... overall stability of the markets.\\57\\ \\57\\ Data and analysis on p.m. settlement of index derivatives is... parties, including relevant data and analysis, on the issues presented by the proposed rule change. In...

Spanwise effects on instabilities of compressible flow over a long rectangular cavity

NASA Astrophysics Data System (ADS)

Sun, Y.; Taira, K.; Cattafesta, L. N.; Ukeiley, L. S.

2017-12-01

The stability properties of two-dimensional (2D) and three-dimensional (3D) compressible flows over a rectangular cavity with length-to-depth ratio of L/D=6 are analyzed at a free-stream Mach number of M_∞ =0.6 and depth-based Reynolds number of Re_D=502. In this study, we closely examine the influence of three-dimensionality on the wake mode that has been reported to exhibit high-amplitude fluctuations from the formation and ejection of large-scale spanwise vortices. Direct numerical simulation (DNS) and bi-global stability analysis are utilized to study the stability characteristics of the wake mode. Using the bi-global stability analysis with the time-averaged flow as the base state, we capture the global stability properties of the wake mode at a spanwise wavenumber of β =0. To uncover spanwise effects on the 2D wake mode, 3D DNS are performed with cavity width-to-depth ratio of W/D=1 and 2. We find that the 2D wake mode is not present in the 3D cavity flow with W/D=2, in which spanwise structures are observed near the rear region of the cavity. These 3D instabilities are further investigated via bi-global stability analysis for spanwise wavelengths of λ /D=0.5{-}2.0 to reveal the eigenspectra of the 3D eigenmodes. Based on the findings of 2D and 3D global stability analysis, we conclude that the absence of the wake mode in 3D rectangular cavity flows is due to the release of kinetic energy from the spanwise vortices to the streamwise vortical structures that develops from the spanwise instabilities.

Microgravity isolation system design: A modern control analysis framework

NASA Technical Reports Server (NTRS)

Hampton, R. D.; Knospe, C. R.; Allaire, P. E.; Grodsinsky, C. M.

1994-01-01

Many acceleration-sensitive, microgravity science experiments will require active vibration isolation from the manned orbiters on which they will be mounted. The isolation problem, especially in the case of a tethered payload, is a complex three-dimensional one that is best suited to modern-control design methods. These methods, although more powerful than their classical counterparts, can nonetheless go only so far in meeting the design requirements for practical systems. Once a tentative controller design is available, it must still be evaluated to determine whether or not it is fully acceptable, and to compare it with other possible design candidates. Realistically, such evaluation will be an inherent part of a necessary iterative design process. In this paper, an approach is presented for applying complex mu-analysis methods to a closed-loop vibration isolation system (experiment plus controller). An analysis framework is presented for evaluating nominal stability, nominal performance, robust stability, and robust performance of active microgravity isolation systems, with emphasis on the effective use of mu-analysis methods.

Bifurcation analysis of a heterogeneous traffic flow model

NASA Astrophysics Data System (ADS)

Wang, Yu-Qing; Yan, Bo-Wen; Zhou, Chao-Fan; Li, Wei-Kang; Jia, Bin

2018-03-01

In this work, a heterogeneous traffic flow model coupled with the periodic boundary condition is proposed. Based on the previous models, a heterogeneous system composed of more than one kind of vehicles is considered. By bifurcation analysis, bifurcation patterns of the heterogeneous system are discussed in three situations in detail and illustrated by diagrams of bifurcation patterns. Besides, the stability analysis of the heterogeneous system is performed to test its anti-interference ability. The relationship between the number of vehicles and the stability is obtained. Furthermore, the attractor analysis is applied to investigate the nature of the heterogeneous system near its steady-state neighborhood. Phase diagrams of the process of the heterogeneous system from initial state to equilibrium state are intuitively presented.

SiC/Mg multilayer coatings for SCORE coronagraph: long term stability analysis

NASA Astrophysics Data System (ADS)

Pelizzo, Maria Guglielmina; Fineschi, Silvano; Zuppella, Paola; Corso, Alain Jody; Windt, David L.; Nicolosi, Piergiorgio

2011-10-01

SiC/Mg multilayers have been used as coatings of the Sounding-rocket CORonagraphic Experiment (SCORE) telescope mirrors launched during the NASA HERSCHEL program. This materials couple has been largely studied by researchers since it provides higher performances than a standard Mo/Si multilayer; the SCORE mirrors show in fact a peak reflectance of around 40% at HeII 30.4 nm. Nevertheless, long term stability of this coating is an open problem. A study on the aging and stability of this multilayer has been carried on. SiC/Mg multilayer samples characterized by different structural parameters have been deposited. They have been measured just after deposition and four years later to verify degradation based on natural aging. Experimental results and analysis are presented.

Numerical analysis of the Magnus moment on a spin-stabilized projectile

NASA Astrophysics Data System (ADS)

Cremins, Michael; Rodebaugh, Gregory; Verhulst, Claire; Benson, Michael; van Poppel, Bret

2016-11-01

The Magnus moment is a result of an uneven pressure distribution that occurs when an object rotates in a crossflow. Unlike the Magnus force, which is often small for spin-stabilized projectiles, the Magnus moment can have a strong detrimental effect on flight stability. According to one source, most transonic and subsonic flight instabilities are caused by the Magnus moment [Modern Exterior Ballistics, McCoy], and yet simulations often fail to accurately predict the Magnus moment in the subsonic regime. In this study, we present hybrid Reynolds Averaged Navier Stokes (RANS) and Large Eddy Simulation (LES) predictions of the Magnus moment for a spin-stabilized projectile. Velocity, pressure, and Magnus moment predictions are presented for multiple Reynolds numbers and spin rates. We also consider the effect of a sting mount, which is commonly used when conducting flow measurements in a wind tunnel or water channel. Finally, we present the initial designs for a novel Magnetic Resonance Velocimetry (MRV) experiment to measure three-dimensional flow around a spinning projectile. This work was supported by the Department of Defense High Performance Computing Modernization Program (DoD HPCMP).

Composite power system well-being analysis

NASA Astrophysics Data System (ADS)

Aboreshaid, Saleh Abdulrahman Saleh

The evaluation of composite system reliability is extremely complex as it is necessary to include detailed modeling of both generation and transmission facilities and their auxiliary elements. The most significant quantitative indices in composite power system adequacy evaluation are those which relate to load curtailment. Many utilities have difficulty in interpreting the expected load curtailment indices as the existing models are based on adequacy analysis and in many cases do not consider realistic operating conditions in the system under study. This thesis presents a security based approach which alleviates this difficulty and provides the ability to evaluate the well-being of customer load points and the overall composite generation and transmission power system. Acceptable deterministic criteria are included in the probabilistic evaluation of the composite system reliability indices to monitor load point well-being. The degree of load point well-being is quantified in terms of the healthy and marginal state indices in addition to the traditional risk indices. The individual well-being indices of the different system load points are aggregated to produce system indices. This thesis presents new models and techniques to quantify the well-being of composite generation and, direct and alternating current transmission systems. Security constraints are basically the operating limits which must be satisfied for normal system operation. These constraints depend mainly on the purpose behind the study. The constraints which govern the practical operation of a power system are divided, in this thesis, into three sets namely, steady-state, voltage stability and transient stability constraints. The inclusion of an appropriate transient stability constraint will lead to a more accurate appraisal of the overall power system well-being. This thesis illustrates the utilization of a bisection method in the analytical evaluation of the critical clearing time which forms the basis of most existing stability assessments. The effect of employing high-speed-simultaneous or adaptive reclosing schemes is presented in this thesis. An effective and fast technique to incorporate voltage stability considerations in composite generation and transmission system reliability evaluation is also presented. The proposed technique can be easily incorporated in an existing composite power system reliability program using voltage stability constraints that are constructed for individual load points based on a relatively simple risk index. It is believed that the concepts, procedures and indices presented in this thesis will provide useful tools for power system designers, planners and operators and assist them to perform composite system well-being analysis in addition to traditional risk assessment.

A Quality by Design approach to investigate tablet dissolution shift upon accelerated stability by multivariate methods.

PubMed

Huang, Jun; Goolcharran, Chimanlall; Ghosh, Krishnendu

2011-05-01

This paper presents the use of experimental design, optimization and multivariate techniques to investigate root-cause of tablet dissolution shift (slow-down) upon stability and develop control strategies for a drug product during formulation and process development. The effectiveness and usefulness of these methodologies were demonstrated through two application examples. In both applications, dissolution slow-down was observed during a 4-week accelerated stability test under 51°C/75%RH storage condition. In Application I, an experimental design was carried out to evaluate the interactions and effects of the design factors on critical quality attribute (CQA) of dissolution upon stability. The design space was studied by design of experiment (DOE) and multivariate analysis to ensure desired dissolution profile and minimal dissolution shift upon stability. Multivariate techniques, such as multi-way principal component analysis (MPCA) of the entire dissolution profiles upon stability, were performed to reveal batch relationships and to evaluate the impact of design factors on dissolution. In Application II, an experiment was conducted to study the impact of varying tablet breaking force on dissolution upon stability utilizing MPCA. It was demonstrated that the use of multivariate methods, defined as Quality by Design (QbD) principles and tools in ICH-Q8 guidance, provides an effective means to achieve a greater understanding of tablet dissolution upon stability. Copyright © 2010 Elsevier B.V. All rights reserved.

Intra-operative evaluation of cementless hip implant stability: a prototype device based on vibration analysis.

PubMed

Lannocca, Maurizio; Varini, Elena; Cappello, Angelo; Cristofolini, Luca; Bialoblocka, Ewa

2007-10-01

Cementless implants are mechanically stabilized during surgery by a press-fitting procedure. Good initial stability is crucial to avoid stem loosening and bone cracking, therefore, the surgeon must achieve optimal press-fitting. A possible approach to solve this problem and assist the surgeon in achieving the optimal compromise, involves the use of vibration analysis. The present study aimed to design and test a prototype device able to evaluate the primary mechanical stability of a cementless prosthesis, based on vibration analysis. In particular, the goal was to discriminate between stable and quasi-stable implants; thus the stem-bone system was assumed to be linear in both cases. For that reason, it was decided to study the frequency responses of the system, instead of the harmonic distortion. The prototype developed consists of a piezoelectric exciter connected to the stem and an accelerometer attached to the femur. Preliminary tests were performed on four composite femurs implanted with a conventional stem. The results showed that the input signal was repeatable and the output could be recorded accurately. The most sensitive parameter to stability was the shift in resonance frequency of the stem-bone system, which was highly correlated with residual micromotion on all four specimens.

Euclidean distance and Kolmogorov-Smirnov analyses of multi-day auditory event-related potentials: a longitudinal stability study

NASA Astrophysics Data System (ADS)

Durato, M. V.; Albano, A. M.; Rapp, P. E.; Nawang, S. A.

2015-06-01

The validity of ERPs as indices of stable neurophysiological traits is partially dependent on their stability over time. Previous studies on ERP stability, however, have reported diverse stability estimates despite using the same component scoring methods. This present study explores a novel approach in investigating the longitudinal stability of average ERPs—that is, by treating the ERP waveform as a time series and then applying Euclidean Distance and Kolmogorov-Smirnov analyses to evaluate the similarity or dissimilarity between the ERP time series of different sessions or run pairs. Nonlinear dynamical analysis show that in the absence of a change in medical condition, the average ERPs of healthy human adults are highly longitudinally stable—as evaluated by both the Euclidean distance and the Kolmogorov-Smirnov test.

Wind-Tunnel Investigation at Low Speed of the Yawing, Pitching, and Static Stability Characteristics of a 1/10-Scale Model of the Grumman F9F-9 Airplane, TED No. NACA AD 3109

NASA Technical Reports Server (NTRS)

Wolhart, Walter D.; Thomas, David F., Jr.

1955-01-01

An experimental investigation has been made in the Langley stability tunnel to determine the low-speed yawing, pitching, and static stability characteristics of a 1/10-scale model of the Grumman F9F-9 airplane. Tests were made to determine the effects of duct-entrance-fairing plugs on the static lateral and longitudinal stability characteristics of the complete model in the clean condition. The remaining tests were concerned with determining tail contributions as well as the effect of duct-entrance-fairing plugs, slats, flaps, and landing gear on the yawing and pitching stability derivatives. These data are presented without analysis in order to expedite distribution.

Wind-Tunnel Investigation at Low Speed of the Rolling Stability Derivatives of a 1/10-Scale Model of the Grumman F9F-9 Airplane, TED No. NACA AD 3109

NASA Technical Reports Server (NTRS)

Wolhart, Walter D.; Thomas, David F., Jr.

1955-01-01

An experimental investigation has been made in the Langley stability tunnel to determine the low-speed yawing, pitching, and static stability characteristics of a 1/10-scale model of the Grumman F9F-9 airplane. Tests were made to determine the effects of duct-entrance-fairing plugs on the static lateral and longitudinal stability characteristics of the complete model in the clean condition. The remaining tests were concerned with determining tail contributions as well as the effect of duct-entrance-fairing plugs, slats, flaps, and landing gear on the yawing and pitching stability derivatives. These data are presented without analysis in order to expedite distribution.

On the Stability of Periodic Mercury-type Rotations

NASA Astrophysics Data System (ADS)

Churkina, Tatyana E.; Stepanov, Sergey Y.

2017-12-01

We consider the stability of planar periodic Mercury-type rotations of a rigid body around its center of mass in an elliptical orbit in a central Newtonian field of forces. Mercurytype rotations mean that the body makes 3 turns around its center of mass during 2 revolutions of the center of mass in its orbit (resonance 3:2). These rotations can be 1) symmetrical 2π- periodic, 2) symmetrical 4π-periodic and 3) asymmetrical 4π-periodic. The stability of rotations of type 1) was investigated by A.P.Markeev. In our paper we present a nonlinear stability analysis for some rotations of types 2) and 3) in 3rd- and 4th-order resonant cases, in the nonresonant case and at the boundaries of regions of linear stability.

Dynamic stability of unidirectional fiber-reinforced viscoelastic composite plates

NASA Technical Reports Server (NTRS)

Chandiramani, N. K.; Librescu, L.

1989-01-01

This paper deals with a dynamic stability analysis of unidirectional fiber-reinforced composite viscoelastic plates subjected to compressive edge loads. The integrodifferential equations governing the stability problem are obtained by using, in conjunction with a Boltzmann hereditary constitutive law for a three-dimensional viscoelastic medium, a higher-order shear deformation theory of orthotropic plates. Such a theory incorporates transverse shear deformation, transverse normal stress, and rotatory inertia effects. The solution of the stability problem as considered within this paper concerns the determination of the critical in-plane edge loads yielding the asymptotic instability. Numerical applications, based on material properties derived within the framework of Aboudi's micromechanical model, are presented and pertinent conclusions concerning the nature of the loss of stability and the influence of various parameters are outlined.

A study of the problem of designing airplanes with satisfactory inherent damping of the dutch roll oscillation

NASA Technical Reports Server (NTRS)

Campbell, John P; Mckinney, Marion O , Jr

1954-01-01

Considerable interest has recently been shown in means of obtaining satisfactory stability of the dutch roll oscillation for modern high-performance airplanes without resort to complicated artificial stabilizing devices. One approach to this problem is to lay out the airplane in the earliest stages of design so that it will have the greatest practicable inherent stability of the lateral oscillation. The present report presents some preliminary results of a theoretical analysis to determine the design features that appear most promising in providing adequate inherent stability. These preliminary results cover the case of fighter airplanes at subsonic speeds. The investigation indicated that it is possible to design fighter airplanes to have substantially better inherent stability than most current designs. Since the use of low-aspect-ratio swept-back wings is largely responsible for poor dutch roll stability, it is important to design the airplane with the maximum aspect ratio and minimum sweep that will permit attainment of the desired performance. The radius of gyration in roll should be kept as low as possible and the nose-up inclination of the principal longitudinal axis of inertia should be made as great as practicable. (author)

Hydrodynamic-Driven Stability Analysis of Morphological Patterns on Stalactites and Implications for Cave Paleoflow Reconstructions

NASA Astrophysics Data System (ADS)

Camporeale, Carlo; Ridolfi, Luca

2012-06-01

A novel hydrodynamic-driven stability analysis is presented for surface patterns on speleothems, i.e., secondary sedimentary cave deposits, by coupling fluid dynamics to the geochemistry of calcite precipitation or dissolution. Falling film theory provides the solution for the flow-field and depth perturbations, the latter being crucial to triggering patterns known as crenulations. In a wide range of Reynolds numbers, the model provides the dominant wavelengths and pattern celerities, in fair agreement with field data. The analysis of the phase velocity of ridges on speleothems has a potential as a proxy of past film flow rates, thus suggesting a new support for paleoclimate analyses.

Stability of mixed time integration schemes for transient thermal analysis

NASA Technical Reports Server (NTRS)

Liu, W. K.; Lin, J. I.

1982-01-01

A current research topic in coupled-field problems is the development of effective transient algorithms that permit different time integration methods with different time steps to be used simultaneously in various regions of the problems. The implicit-explicit approach seems to be very successful in structural, fluid, and fluid-structure problems. This paper summarizes this research direction. A family of mixed time integration schemes, with the capabilities mentioned above, is also introduced for transient thermal analysis. A stability analysis and the computer implementation of this technique are also presented. In particular, it is shown that the mixed time implicit-explicit methods provide a natural framework for the further development of efficient, clean, modularized computer codes.

Application of long-term simulation programs for analysis of system islanding

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sancha, J.L.; Llorens, M.L.; Moreno, J.M.

1997-02-01

This paper describes the main results and conclusions from the application of two different long-term stability programs to the analysis of a system islanding scenario for a study case developed by Red Electrica de Espana (REE), based on the Spanish system. Two main goals were to evaluate the performance of both the influence of some important control and protection elements (tie-line loss-of-synchronism relays, underfrequency load-shedding, load-frequency control, and power plant dynamics). Conclusions about modeling and computational requirements for system islanding (frequency) scenarios and use of long-term stability programs are presented.

The radial-azimuthal stability of accretion disks - Gas pressure contributions

NASA Technical Reports Server (NTRS)

Mckee, M. R.

1991-01-01

A radial-azimuthal stability analysis of a thin, alpha disk accretion flow is presented. The proportion of radiation pressure, Pr, of the unperturbed flow is allowed to vary according to the parameter beta = Pr/P, where P is the total pressure. As is the case for a purely radial analysis, the disk is stable for beta equal to or less than 0.6. However, the coupling of radial and azimuthal perturbations eliminates the viscous instability for such nonradial modes for all values of beta. The group velocity of the retrograde thermal mode is calculated as a function of beta.

A fast efficient implicit scheme for the gasdynamic equations using a matrix reduction technique

NASA Technical Reports Server (NTRS)

Barth, T. J.; Steger, J. L.

1985-01-01

An efficient implicit finite-difference algorithm for the gasdynamic equations utilizing matrix reduction techniques is presented. A significant reduction in arithmetic operations is achieved without loss of the stability characteristics generality found in the Beam and Warming approximate factorization algorithm. Steady-state solutions to the conservative Euler equations in generalized coordinates are obtained for transonic flows and used to show that the method offers computational advantages over the conventional Beam and Warming scheme. Existing Beam and Warming codes can be retrofit with minimal effort. The theoretical extension of the matrix reduction technique to the full Navier-Stokes equations in Cartesian coordinates is presented in detail. Linear stability, using a Fourier stability analysis, is demonstrated and discussed for the one-dimensional Euler equations.

Engineering Proteins for Thermostability with iRDP Web Server

PubMed Central

Ghanate, Avinash; Ramasamy, Sureshkumar; Suresh, C. G.

2015-01-01

Engineering protein molecules with desired structure and biological functions has been an elusive goal. Development of industrially viable proteins with improved properties such as stability, catalytic activity and altered specificity by modifying the structure of an existing protein has widely been targeted through rational protein engineering. Although a range of factors contributing to thermal stability have been identified and widely researched, the in silico implementation of these as strategies directed towards enhancement of protein stability has not yet been explored extensively. A wide range of structural analysis tools is currently available for in silico protein engineering. However these tools concentrate on only a limited number of factors or individual protein structures, resulting in cumbersome and time-consuming analysis. The iRDP web server presented here provides a unified platform comprising of iCAPS, iStability and iMutants modules. Each module addresses different facets of effective rational engineering of proteins aiming towards enhanced stability. While iCAPS aids in selection of target protein based on factors contributing to structural stability, iStability uniquely offers in silico implementation of known thermostabilization strategies in proteins for identification and stability prediction of potential stabilizing mutation sites. iMutants aims to assess mutants based on changes in local interaction network and degree of residue conservation at the mutation sites. Each module was validated using an extensively diverse dataset. The server is freely accessible at http://irdp.ncl.res.in and has no login requirements. PMID:26436543

Engineering Proteins for Thermostability with iRDP Web Server.

PubMed

Panigrahi, Priyabrata; Sule, Manas; Ghanate, Avinash; Ramasamy, Sureshkumar; Suresh, C G

2015-01-01

Engineering protein molecules with desired structure and biological functions has been an elusive goal. Development of industrially viable proteins with improved properties such as stability, catalytic activity and altered specificity by modifying the structure of an existing protein has widely been targeted through rational protein engineering. Although a range of factors contributing to thermal stability have been identified and widely researched, the in silico implementation of these as strategies directed towards enhancement of protein stability has not yet been explored extensively. A wide range of structural analysis tools is currently available for in silico protein engineering. However these tools concentrate on only a limited number of factors or individual protein structures, resulting in cumbersome and time-consuming analysis. The iRDP web server presented here provides a unified platform comprising of iCAPS, iStability and iMutants modules. Each module addresses different facets of effective rational engineering of proteins aiming towards enhanced stability. While iCAPS aids in selection of target protein based on factors contributing to structural stability, iStability uniquely offers in silico implementation of known thermostabilization strategies in proteins for identification and stability prediction of potential stabilizing mutation sites. iMutants aims to assess mutants based on changes in local interaction network and degree of residue conservation at the mutation sites. Each module was validated using an extensively diverse dataset. The server is freely accessible at http://irdp.ncl.res.in and has no login requirements.

Evolving nucleotide binding surfaces

NASA Technical Reports Server (NTRS)

Kieber-Emmons, T.; Rein, R.

1981-01-01

An analysis is presented of the stability and nature of binding of a nucleotide to several known dehydrogenases. The employed approach includes calculation of hydrophobic stabilization of the binding motif and its intermolecular interaction with the ligand. The evolutionary changes of the binding motif are studied by calculating the Euclidean deviation of the respective dehydrogenases. Attention is given to the possible structural elements involved in the origin of nucleotide recognition by non-coded primordial polypeptides.

Some problems of nonlinear waves in solid propellant rocket motors

NASA Technical Reports Server (NTRS)

Culick, F. E. C.

1979-01-01

An approximate technique for analyzing nonlinear waves in solid propellant rocket motors is presented which inexpensively provides accurate results up to amplitudes of ten percent. The connection with linear stability analysis is shown. The method is extended to third order in the amplitude of wave motion in order to study nonlinear stability, or triggering. Application of the approximate method to the behavior of pulses is described.

Arrhenius time-scaled least squares: a simple, robust approach to accelerated stability data analysis for bioproducts.

PubMed

Rauk, Adam P; Guo, Kevin; Hu, Yanling; Cahya, Suntara; Weiss, William F

2014-08-01

Defining a suitable product presentation with an acceptable stability profile over its intended shelf-life is one of the principal challenges in bioproduct development. Accelerated stability studies are routinely used as a tool to better understand long-term stability. Data analysis often employs an overall mass action kinetics description for the degradation and the Arrhenius relationship to capture the temperature dependence of the observed rate constant. To improve predictive accuracy and precision, the current work proposes a least-squares estimation approach with a single nonlinear covariate and uses a polynomial to describe the change in a product attribute with respect to time. The approach, which will be referred to as Arrhenius time-scaled (ATS) least squares, enables accurate, precise predictions to be achieved for degradation profiles commonly encountered during bioproduct development. A Monte Carlo study is conducted to compare the proposed approach with the common method of least-squares estimation on the logarithmic form of the Arrhenius equation and nonlinear estimation of a first-order model. The ATS least squares method accommodates a range of degradation profiles, provides a simple and intuitive approach for data presentation, and can be implemented with ease. © 2014 Wiley Periodicals, Inc. and the American Pharmacists Association.

Application of Soil Nailing Technique for Protection and Preservation Historical Buildings

NASA Astrophysics Data System (ADS)

Kulczykowski, Marek; Przewłócki, Jarosław; Konarzewska, Bogusława

2017-10-01

Soil nailing is one of the recent in situ techniques used for soil improvement and in stabilizing slopes. The process of soil nailing consists of reinforcing the natural ground with relatively small steel bars or metal rods, grouted in the pre-drilled holes. This method has a wide range of applications for stabilizing deep excavations and steep slopes. Soil nailing has recently become a very common method of slope stabilisation especially where situated beneath or adjacent to historical buildings. Stabilisation by nails drilled into existing masonry structures such as failing retaining walls abutments, provide long term stability without demolition and rebuilding costs. Two cases of soil nailing technology aimed at stabilising slopes beneath old buildings in Poland are presented in this paper. The first concerns application of this technology to repair a retaining wall supporting the base of the dam at the historic hydroelectric power plant in Rutki. The second regards a concept of improving the slope of the Castle Hill in Sandomierz. An analysis of the slope stability for the latter case, using stabilisation technique with the piling system and soil nailing was performed. Some advantages of soil nailing especially for protection of historical buildings, are also underlined. And, the main results of an economic comparison analysis are additionally presented.

Decomposition-aggregation stability analysis. [for large scale dynamic systems with application to spinning Skylab control system

NASA Technical Reports Server (NTRS)

Siljak, D. D.; Weissenberger, S.; Cuk, S. M.

1973-01-01

This report presents the development and description of the decomposition aggregation approach to stability investigations of high dimension mathematical models of dynamic systems. The high dimension vector differential equation describing a large dynamic system is decomposed into a number of lower dimension vector differential equations which represent interconnected subsystems. Then a method is described by which the stability properties of each subsystem are aggregated into a single vector Liapunov function, representing the aggregate system model, consisting of subsystem Liapunov functions as components. A linear vector differential inequality is then formed in terms of the vector Liapunov function. The matrix of the model, which reflects the stability properties of the subsystems and the nature of their interconnections, is analyzed to conclude over-all system stability characteristics. The technique is applied in detail to investigate the stability characteristics of a dynamic model of a hypothetical spinning Skylab.

Important factors in the maximum likelihood analysis of flight test maneuvers

NASA Technical Reports Server (NTRS)

Iliff, K. W.; Maine, R. E.; Montgomery, T. D.

1979-01-01

The information presented is based on the experience in the past 12 years at the NASA Dryden Flight Research Center of estimating stability and control derivatives from over 3500 maneuvers from 32 aircraft. The overall approach to the analysis of dynamic flight test data is outlined. General requirements for data and instrumentation are discussed and several examples of the types of problems that may be encountered are presented.

Numerical proof of stability of roll waves in the small-amplitude limit for inclined thin film flow

NASA Astrophysics Data System (ADS)

Barker, Blake

2014-10-01

We present a rigorous numerical proof based on interval arithmetic computations categorizing the linearized and nonlinear stability of periodic viscous roll waves of the KdV-KS equation modeling weakly unstable flow of a thin fluid film on an incline in the small-amplitude KdV limit. The argument proceeds by verification of a stability condition derived by Bar-Nepomnyashchy and Johnson-Noble-Rodrigues-Zumbrun involving inner products of various elliptic functions arising through the KdV equation. One key point in the analysis is a bootstrap argument balancing the extremely poor sup norm bounds for these functions against the extremely good convergence properties for analytic interpolation in order to obtain a feasible computation time. Another is the way of handling analytic interpolation in several variables by a two-step process carving up the parameter space into manageable pieces for rigorous evaluation. These and other general aspects of the analysis should serve as blueprints for more general analyses of spectral stability.

Resistive MHD Stability Analysis in Near Real-time

NASA Astrophysics Data System (ADS)

Glasser, Alexander; Kolemen, Egemen

2017-10-01

We discuss the feasibility of a near real-time calculation of the tokamak Δ' matrix, which summarizes MHD stability to resistive modes, such as tearing and interchange modes. As the operational phase of ITER approaches, solutions for active feedback tokamak stability control are needed. It has been previously demonstrated that an ideal MHD stability analysis is achievable on a sub- O (1 s) timescale, as is required to control phenomena comparable with the MHD-evolution timescale of ITER. In the present work, we broaden this result to incorporate the effects of resistive MHD modes. Such modes satisfy ideal MHD equations in regions outside narrow resistive layers that form at singular surfaces. We demonstrate that the use of asymptotic expansions at the singular surfaces, as well as the application of state transition matrices, enable a fast, parallelized solution to the singular outer layer boundary value problem, and thereby rapidly compute Δ'. Sponsored by US DOE under DE-SC0015878 and DE-FC02-04ER54698.

Conceptual Design Optimization of an Augmented Stability Aircraft Incorporating Dynamic Response Performance Constraints

NASA Technical Reports Server (NTRS)

Welstead, Jason

2014-01-01

This research focused on incorporating stability and control into a multidisciplinary de- sign optimization on a Boeing 737-class advanced concept called the D8.2b. A new method of evaluating the aircraft handling performance using quantitative evaluation of the sys- tem to disturbances, including perturbations, continuous turbulence, and discrete gusts, is presented. A multidisciplinary design optimization was performed using the D8.2b transport air- craft concept. The con guration was optimized for minimum fuel burn using a design range of 3,000 nautical miles. Optimization cases were run using xed tail volume coecients, static trim constraints, and static trim and dynamic response constraints. A Cessna 182T model was used to test the various dynamic analysis components, ensuring the analysis was behaving as expected. Results of the optimizations show that including stability and con- trol in the design process drastically alters the optimal design, indicating that stability and control should be included in conceptual design to avoid system level penalties later in the design process.

On Bi-Grid Local Mode Analysis of Solution Techniques for 3-D Euler and Navier-Stokes Equations

NASA Technical Reports Server (NTRS)

Ibraheem, S. O.; Demuren, A. O.

1994-01-01

A procedure is presented for utilizing a bi-grid stability analysis as a practical tool for predicting multigrid performance in a range of numerical methods for solving Euler and Navier-Stokes equations. Model problems based on the convection, diffusion and Burger's equation are used to illustrate the superiority of the bi-grid analysis as a predictive tool for multigrid performance in comparison to the smoothing factor derived from conventional von Neumann analysis. For the Euler equations, bi-grid analysis is presented for three upwind difference based factorizations, namely Spatial, Eigenvalue and Combination splits, and two central difference based factorizations, namely LU and ADI methods. In the former, both the Steger-Warming and van Leer flux-vector splitting methods are considered. For the Navier-Stokes equations, only the Beam-Warming (ADI) central difference scheme is considered. In each case, estimates of multigrid convergence rates from the bi-grid analysis are compared to smoothing factors obtained from single-grid stability analysis. Effects of grid aspect ratio and flow skewness are examined. Both predictions are compared with practical multigrid convergence rates for 2-D Euler and Navier-Stokes solutions based on the Beam-Warming central scheme.

Global exponential stability analysis on impulsive BAM neural networks with distributed delays

NASA Astrophysics Data System (ADS)

Li, Yao-Tang; Yang, Chang-Bo

2006-12-01

Using M-matrix and topological degree tool, sufficient conditions are obtained for the existence, uniqueness and global exponential stability of the equilibrium point of bidirectional associative memory (BAM) neural networks with distributed delays and subjected to impulsive state displacements at fixed instants of time by constructing a suitable Lyapunov functional. The results remove the usual assumptions that the boundedness, monotonicity, and differentiability of the activation functions. It is shown that in some cases, the stability criteria can be easily checked. Finally, an illustrative example is given to show the effectiveness of the presented criteria.

Global asymptotic stability analysis of bidirectional associative memory neural networks with time delays.

PubMed

Arik, Sabri

2005-05-01

This paper presents a sufficient condition for the existence, uniqueness and global asymptotic stability of the equilibrium point for bidirectional associative memory (BAM) neural networks with distributed time delays. The results impose constraint conditions on the network parameters of neural system independently of the delay parameter, and they are applicable to all continuous nonmonotonic neuron activation functions. It is shown that in some special cases of the results, the stability criteria can be easily checked. Some examples are also given to compare the results with the previous results derived in the literature.

Dynamic stability analysis of fractional order leaky integrator echo state neural networks

NASA Astrophysics Data System (ADS)

Pahnehkolaei, Seyed Mehdi Abedi; Alfi, Alireza; Tenreiro Machado, J. A.

2017-06-01

The Leaky integrator echo state neural network (Leaky-ESN) is an improved model of the recurrent neural network (RNN) and adopts an interconnected recurrent grid of processing neurons. This paper presents a new proof for the convergence of a Lyapunov candidate function to zero when time tends to infinity by means of the Caputo fractional derivative with order lying in the range (0, 1). The stability of Fractional-Order Leaky-ESN (FO Leaky-ESN) is then analyzed, and the existence, uniqueness and stability of the equilibrium point are provided. A numerical example demonstrates the feasibility of the proposed method.

LMI-based approach to stability analysis for fractional-order neural networks with discrete and distributed delays

NASA Astrophysics Data System (ADS)

Zhang, Hai; Ye, Renyu; Liu, Song; Cao, Jinde; Alsaedi, Ahmad; Li, Xiaodi

2018-02-01

This paper is concerned with the asymptotic stability of the Riemann-Liouville fractional-order neural networks with discrete and distributed delays. By constructing a suitable Lyapunov functional, two sufficient conditions are derived to ensure that the addressed neural network is asymptotically stable. The presented stability criteria are described in terms of the linear matrix inequalities. The advantage of the proposed method is that one may avoid calculating the fractional-order derivative of the Lyapunov functional. Finally, a numerical example is given to show the validity and feasibility of the theoretical results.

Guidelines for Computing Longitudinal Dynamic Stability Characteristics of a Subsonic Transport

NASA Technical Reports Server (NTRS)

Thompson, Joseph R.; Frank, Neal T.; Murphy, Patrick C.

2010-01-01

A systematic study is presented to guide the selection of a numerical solution strategy for URANS computation of a subsonic transport configuration undergoing simulated forced oscillation about its pitch axis. Forced oscillation is central to the prevalent wind tunnel methodology for quantifying aircraft dynamic stability derivatives from force and moment coefficients, which is the ultimate goal for the computational simulations. Extensive computations are performed that lead in key insights of the critical numerical parameters affecting solution convergence. A preliminary linear harmonic analysis is included to demonstrate the potential of extracting dynamic stability derivatives from computational solutions.

Basic principles of stability.

PubMed

Egan, William; Schofield, Timothy

2009-11-01

An understanding of the principles of degradation, as well as the statistical tools for measuring product stability, is essential to management of product quality. Key to this is management of vaccine potency. Vaccine shelf life is best managed through determination of a minimum potency release requirement, which helps assure adequate potency throughout expiry. Use of statistical tools such a least squares regression analysis should be employed to model potency decay. The use of such tools provides incentive to properly design vaccine stability studies, while holding stability measurements to specification presents a disincentive for collecting valuable data. The laws of kinetics such as Arrhenius behavior help practitioners design effective accelerated stability programs, which can be utilized to manage stability after a process change. Design of stability studies should be carefully considered, with an eye to minimizing the variability of the stability parameter. In the case of measuring the degradation rate, testing at the beginning and the end of the study improves the precision of this estimate. Additional design considerations such as bracketing and matrixing improve the efficiency of stability evaluation of vaccines.

Amber fossils demonstrate deep-time stability of Caribbean lizard communities.

PubMed

Sherratt, Emma; del Rosario Castañeda, María; Garwood, Russell J; Mahler, D Luke; Sanger, Thomas J; Herrel, Anthony; de Queiroz, Kevin; Losos, Jonathan B

2015-08-11

Whether the structure of ecological communities can exhibit stability over macroevolutionary timescales has long been debated. The similarity of independently evolved Anolis lizard communities on environmentally similar Greater Antillean islands supports the notion that community evolution is deterministic. However, a dearth of Caribbean Anolis fossils--only three have been described to date--has precluded direct investigation of the stability of anole communities through time. Here we report on an additional 17 fossil anoles in Dominican amber dating to 15-20 My before the present. Using data collected primarily by X-ray microcomputed tomography (X-ray micro-CT), we demonstrate that the main elements of Hispaniolan anole ecomorphological diversity were in place in the Miocene. Phylogenetic analysis yields results consistent with the hypothesis that the ecomorphs that evolved in the Miocene are members of the same ecomorph clades extant today. The primary axes of ecomorphological diversity in the Hispaniolan anole fauna appear to have changed little between the Miocene and the present, providing evidence for the stability of ecological communities over macroevolutionary timescales.

Stabilizing skateboard speed-wobble with reflex delay.

PubMed

Varszegi, Balazs; Takacs, Denes; Stepan, Gabor; Hogan, S John

2016-08-01

A simple mechanical model of the skateboard-skater system is analysed, in which the effect of human control is considered by means of a linear proportional-derivative (PD) controller with delay. The equations of motion of this non-holonomic system are neutral delay-differential equations. A linear stability analysis of the rectilinear motion is carried out analytically. It is shown how to vary the control gains with respect to the speed of the skateboard to stabilize the uniform motion. The critical reflex delay of the skater is determined as the function of the speed. Based on this analysis, we present an explanation for the linear instability of the skateboard-skater system at high speed. Moreover, the advantages of standing ahead of the centre of the board are demonstrated from the viewpoint of reflex delay and control gain sensitivity. © 2016 The Author(s).

Theoretical analyses of Baroclinic flows

NASA Technical Reports Server (NTRS)

Antar, B.

1982-01-01

A stability analysis of a thin horizontal rotating fluid layer which is subjected to arbitrary horizontal and vertical temperature gradients is presented. The basic state is a nonlinear Hadley cell which contains both Ekman and thermal boundary layers; it is given in closed form. The stability analysis is based on the linearized Navier-Stokes equations, and zonally symmetric perturbations in the form of waves propagating in the meridional direction are considered. Numerical methods were used for the stability problem. It was found that the instability sets in when the Richardson number is close to unity and that the critical Richardson number is a non-monotonic function of the Prandtl number. Further, it was found that the critical Richardson number decreases with increasing Ekman number until a critical value of the Ekman number is reached beyond which the fluid is stable.

Application of dynamic programming to evaluate the slope stability of a vertical extension to a balefill.

PubMed

Kremen, Arie; Tsompanakis, Yiannis

2010-04-01

The slope-stability of a proposed vertical extension of a balefill was investigated in the present study, in an attempt to determine a geotechnically conservative design, compliant with New Jersey Department of Environmental Protection regulations, to maximize the utilization of unclaimed disposal capacity. Conventional geotechnical analytical methods are generally limited to well-defined failure modes, which may not occur in landfills or balefills due to the presence of preferential slip surfaces. In addition, these models assume an a priori stress distribution to solve essentially indeterminate problems. In this work, a different approach has been applied, which avoids several of the drawbacks of conventional methods. Specifically, the analysis was performed in a two-stage process: (a) calculation of stress distribution, and (b) application of an optimization technique to identify the most probable failure surface. The stress analysis was performed using a finite element formulation and the location of the failure surface was located by dynamic programming optimization method. A sensitivity analysis was performed to evaluate the effect of the various waste strength parameters of the underlying mathematical model on the results, namely the factor of safety of the landfill. Although this study focuses on the stability investigation of an expanded balefill, the methodology presented can easily be applied to general geotechnical investigations.

Twenty-Five Years of Applications of the Modified Allan Variance in Telecommunications.

PubMed

Bregni, Stefano

2016-04-01

The Modified Allan Variance (MAVAR) was originally defined in 1981 for measuring frequency stability in precision oscillators. Due to its outstanding accuracy in discriminating power-law noise, it attracted significant interest among telecommunications engineers since the early 1990s, when it was approved as a standard measure in international standards, redressed as Time Variance (TVAR), for specifying the time stability of network synchronization signals and of equipment clocks. A dozen years later, the usage of MAVAR was also introduced for Internet traffic analysis to estimate self-similarity and long-range dependence. Further, in this field, it demonstrated superior accuracy and sensitivity, better than most popular tools already in use. This paper surveys the last 25 years of progress in extending the field of application of the MAVAR in telecommunications. First, the rationale and principles of the MAVAR are briefly summarized. Its adaptation as TVAR for specification of timing stability is presented. The usage of MAVAR/TVAR in telecommunications standards is reviewed. Examples of measurements on real telecommunications equipment clocks are presented, providing an overview on their actual performance in terms of MAVAR. Moreover, applications of MAVAR to network traffic analysis are surveyed. The superior accuracy of MAVAR in estimating long-range dependence is emphasized by highlighting some remarkable practical examples of real network traffic analysis.

Use of segmented constrained layer damping treatment for improved helicopter aeromechanical stability

NASA Astrophysics Data System (ADS)

Liu, Qiang; Chattopadhyay, Aditi; Gu, Haozhong; Liu, Qiang; Chattopadhyay, Aditi; Zhou, Xu

2000-08-01

The use of a special type of smart material, known as segmented constrained layer (SCL) damping, is investigated for improved rotor aeromechanical stability. The rotor blade load-carrying member is modeled using a composite box beam with arbitrary wall thickness. The SCLs are bonded to the upper and lower surfaces of the box beam to provide passive damping. A finite-element model based on a hybrid displacement theory is used to accurately capture the transverse shear effects in the composite primary structure and the viscoelastic and the piezoelectric layers within the SCL. Detailed numerical studies are presented to assess the influence of the number of actuators and their locations for improved aeromechanical stability. Ground and air resonance analysis models are implemented in the rotor blade built around the composite box beam with segmented SCLs. A classic ground resonance model and an air resonance model are used in the rotor-body coupled stability analysis. The Pitt dynamic inflow model is used in the air resonance analysis under hover condition. Results indicate that the surface bonded SCLs significantly increase rotor lead-lag regressive modal damping in the coupled rotor-body system.

Posterior dislocation following revision total knee replacement arthroplasty: a case report and literature analysis.

PubMed

Lee, Ho Min; Kim, Jong Pil; Chung, Phil Hyun; Kang, Suk; Kim, Young Sung; Go, Bo Seong

2018-05-24

Knee dislocation following total knee replacement arthroplasty is a rare but serious complication. The incidence of dislocation following primary total knee arthroplasty with posterior stabilized implants ranges from 0.15 to 0.5%, and posterior dislocation after revision total knee arthroplasty is even rarer. Here, we report the case of a 76-year-old male who presented with posterior dislocation after posterior stabilized revision total knee arthroplasty.

Investigation of longitudinal control system for a small hydrofoil boat

NASA Technical Reports Server (NTRS)

Phillips, W. H.; Shaughnessy, J. D.

1976-01-01

An analysis of a hydromechanical system for longitudinal control of a small hydrofoil boat is presented. The system incorporates height and acceleration sensors operating flaps on the foils through a mechanical linkage. Effects of some of the system parameters on the stability and response to waves are shown. The results indicate that the system is capable of providing adequate stability, but the response to stern waves at low frequencies is larger than desired.

Finite-difference solution of the compressible stability eigenvalue problem

NASA Technical Reports Server (NTRS)

Malik, M. R.

1982-01-01

A compressible stability analysis computer code is developed. The code uses a matrix finite difference method for local eigenvalue solution when a good guess for the eigenvalue is available and is significantly more computationally efficient than the commonly used initial value approach. The local eigenvalue search procedure also results in eigenfunctions and, at little extra work, group velocities. A globally convergent eigenvalue procedure is also developed which may be used when no guess for the eigenvalue is available. The global problem is formulated in such a way that no unstable spurious modes appear so that the method is suitable for use in a black box stability code. Sample stability calculations are presented for the boundary layer profiles of a Laminar Flow Control (LFC) swept wing.

Dynamic stability analysis of torsional vibrations of a shaft system connected by a Hooke's joint through a continuous system model

NASA Astrophysics Data System (ADS)

Bulut, Gökhan

2014-08-01

Stability of parametrically excited torsional vibrations of a shaft system composed of two torsionally elastic shafts interconnected through a Hooke's joint is studied. The shafts are considered to be continuous (distributed-parameter) systems and an approximate discrete model for the torsional vibrations of the shaft system is derived via a finite element scheme. The stability of the solutions of the linearized equations of motion, consisting of a set of Mathieu-Hill type equations, is examined by means of a monodromy matrix method and the results are presented in the form of a Strutt-Ince diagram visualizing the effects of the system parameters on the stability of the shaft system.

Structural and Functional Analysis of an mRNP Complex That Mediates the High Stability of Human β-Globin mRNA

PubMed Central

Yu, Jia; Russell, J. Eric

2001-01-01

Human globins are encoded by mRNAs exhibiting high stabilities in transcriptionally silenced erythrocyte progenitors. Unlike α-globin mRNA, whose stability is enhanced by assembly of a specific messenger RNP (mRNP) α complex on its 3′ untranslated region (UTR), neither the structure(s) nor the mechanism(s) that effects the high-level stability of human β-globin mRNA has been identified. The present work describes an mRNP complex assembling on the 3′ UTR of the β-globin mRNA that exhibits many of the properties of the stability-enhancing α complex. The β-globin mRNP complex is shown to contain one or more factors homologous to αCP, a 39-kDa RNA-binding protein that is integral to α-complex assembly. Sequence analysis implicates a specific 14-nucleotide pyrimidine-rich track within its 3′ UTR as the site of β-globin mRNP assembly. The importance of this track to mRNA stability is subsequently verified in vivo using mice expressing human β-globin transgenes that contain informative mutations in this region. In combination, the in vitro and in vivo analyses indicate that the high stabilities of the α- and β-globin mRNAs are maintained through related mRNP complexes that may share a common regulatory pathway. PMID:11486027

Theory of a microfluidic serial dilution bioreactor for growth of planktonic and biofilm populations.

PubMed

Hsu, Sze-Bi; Yang, Ya-Tang

2016-04-01

We present the theory of a microfluidic bioreactor with a two-compartment growth chamber and periodic serial dilution. In the model, coexisting planktonic and biofilm populations exchange by adsorption and detachment. The criteria for coexistence and global extinction are determined by stability analysis of the global extinction state. Stability analysis yields the operating diagram in terms of the dilution and removal ratios, constrained by the plumbing action of the bioreactor. The special case of equal uptake function and logistic growth is analytically solved and explicit growth curves are plotted. The presented theory is applicable to generic microfluidic bioreactors with discrete growth chambers and periodic dilution at discrete time points. Therefore, the theory is expected to assist the design of microfluidic devices for investigating microbial competition and microbial biofilm growth under serial dilution conditions.

Developing a stability assessment method for power electronics-based microgrids

NASA Astrophysics Data System (ADS)

Austin, Peter M.

Modern microgrids with microsources and energy storage are dependent on power electronics for control and regulation. Under certain circumstances power electronics can be destabilizing to the system due to an effect called negative incremental impedance. A careful review of the theory and literature on the subject is presented. This includes stability criteria for both AC and DC systems, as well as a discussion on the limitations posed by the analysis. A method to integrate stability assessment with higher-level microgrid architectural design is proposed. Crucial to this is impedance characterization of individual components, which was accomplished through simulation. DC and AC impedance measurement blocks were created in Matlab simulink to automate the process. A detailed switching-level model of a DC microgrid was implemented in simulink, including wind turbine microsource, battery storage, and three phase inverter. Maximum power point tracking (MPPT) was included to maximize the efficiency of the turbine and was implemented through three rectifier alternatives and control schemes. The stability characteristics of each was compared in the final analysis. Impedance data was collected individually from the components and used to assess stability in the system as a whole. The results included the assessment of stability, margin, and unstable operating points to demonstrate the feasibility of the proposed approach.

MHD stability analysis and global mode identification preparing for high beta operation in KSTAR

NASA Astrophysics Data System (ADS)

Park, Y. S.; Sabbagh, S. A.; Berkery, J. W.; Jiang, Y.; Ahn, J. H.; Han, H. S.; Bak, J. G.; Park, B. H.; Jeon, Y. M.; Kim, J.; Hahn, S. H.; Lee, J. H.; Ko, J. S.; in, Y. K.; Yoon, S. W.; Oh, Y. K.; Wang, Z.; Glasser, A. H.

2017-10-01

H-mode plasma operation in KSTAR has surpassed the computed n = 1 ideal no-wall stability limit in discharges exceeding several seconds in duration. The achieved high normalized beta plasmas are presently limited by resistive tearing instabilities rather than global kink/ballooning or RWMs. The ideal and resistive stability of these plasmas is examined by using different physics models. The observed m/ n = 2/1 tearing stability is computed by using the M3D-C1 code, and by the resistive DCON code. The global MHD stability modified by kinetic effects is examined using the MISK code. Results from the analysis explain the stabilization of the plasma above the ideal MHD no-wall limit. Equilibrium reconstructions used include the measured kinetic profiles and MSE data. In preparation for plasma operation at higher beta utilizing the planned second NBI system, three sets of 3D magnetic field sensors have been installed and will be used for RWM active feedback control. To accurately determine the dominant n-component produced by low frequency unstable RWMs, an algorithm has been developed that includes magnetic sensor compensation of the prompt applied field and the field from the induced current on the passive conductors. Supported by US DOE Contracts DE-FG02-99ER54524 and DE-SC0016614.

Stability of implants placed in fresh sockets versus healed alveolar sites: Early findings.

PubMed

Gehrke, Sergio Alexandre; da Silva Neto, Ulisses Tavares; Rossetti, Paulo Henrique Orlato; Watinaga, Sidney Eiji; Giro, Gabriela; Shibli, Jamil Awad

2016-05-01

The present study measured implant stability quotient (ISQ) values at three different time points after surgical procedures to compare whether the stability values differed between implants placed in fresh extraction sockets versus healed alveolar sites. To measure implant stability, resonance frequency analysis (RFA) was performed in 77 patients (53 women, 24 men) with a total of 120 dental implants. These implants were divided into two groups: Group 1 included 60 implants in healed alveolar sites (22 in the maxilla, 38 in the mandible), and Group 2 included 60 implants in fresh sockets (41 in the maxilla, 19 in the mandible). Implant stability was measured immediately at implant placement (baseline), 90, and 150 days later. Statistical analysis was made using a multivariate regression linear model at implant level (α = 0.05). Overall, the means and standard deviations of the ISQ values were 62.7 ± 7.14 (95% confidence interval [CI], 39-88) at baseline, 70.0 ± 6.22 (95% CI, 46-88) at 90 days, and 73.4 ± 5.84 (95% CI, 58-88) at 150 days. In Group 1, the ISQs ranged between 64.3 ± 6.20 and 75.0 ± 5.69, while in Group 2, presented lower values that ranged between 61.2 ± 8.09 and 71.9 ± 5.99 (P = 0.002). Anatomic location and times periods were the only identified variables with an influence on ISQ values at implant level (P < 0.0001). The stabilities of the implants placed in the fresh sockets and in healed sites exhibited similar evolutions in ISQ values and thus osseointegration; however, the implants in the healed alveolar sites exhibited superior values at all time points. © 2015 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.

Stability analysis of ELMs in long-pulse discharges with ELITE code on EAST tokamak

NASA Astrophysics Data System (ADS)

Wang, Y. F.; Xu, G. S.; Wan, B. N.; Li, G. Q.; Yan, N.; Li, Y. L.; Wang, H. Q.; Peng, Y.-K. Martin; Xia, T. Y.; Ding, S. Y.; Chen, R.; Yang, Q. Q.; Liu, H. Q.; Zang, Q.; Zhang, T.; Lyu, B.; Xu, J. C.; Feng, W.; Wang, L.; Chen, Y. J.; Luo, Z. P.; Hu, G. H.; Zhang, W.; Shao, L. M.; Ye, Y.; Lan, H.; Chen, L.; Li, J.; Zhao, N.; Wang, Q.; Snyder, P. B.; Liang, Y.; Qian, J. P.; Gong, X. Z.; EAST team

2018-05-01

One challenge in long-pulse and high performance tokamak operation is to control the edge localized modes (ELMs) to reduce the transient heat load on plasma facing components. Minute-scale discharges in H-mode have been achieved repeatedly on Experimental Advanced Superconducting Tokamak (EAST) since the 2016 campaign and understanding the characteristics of the ELMs in these discharges can be helpful for effective ELM control in long-pulse discharges. The kinetic profile diagnostics recently developed on EAST make it possible to perform the pedestal stability analysis quantitatively. Pedestal stability calculation of a typical long-pulse discharge with ELITE code is presented. The ideal linear stability results show that the ELM is dominated by toroidal mode number n around 10–15 and the most unstable mode structure is mainly localized in the steep pressure gradient region, which is consistent with experimental results. Compared with a typical type-I ELM discharge with larger total plasma current (I p = 600 kA), pedestal in the long-pulse H-mode discharge (I p = 450 kA) is more stable in peeling-ballooning instability and its critical peak pressure gradient is evaluated to be 65% of the former. Two important features of EAST tokamak in the long-pulse discharge are presented by comparison with other tokamaks, including a wider pedestal correlated with the poloidal pedestal beta and a smaller inverse aspect ratio and their effects on the pedestal stability are discussed. The effects of uncertainties in measurements on the linear stability results are also analyzed, including the edge electron density profile position, the separatrix position and the line-averaged effective ion charge {Z}{{e}{{f}}{{f}}} value.

Aeroelastic stability and response of rotating structures

NASA Technical Reports Server (NTRS)

Keith, Theo G., Jr.

1993-01-01

A summary of the work performed during the progress period is presented. Analysis methods for predicting loads and instabilities of wind turbines were developed. Three new areas of research to aid the Advanced Turboprop Project (ATP) were initiated and developed. These three areas of research are aeroelastic analysis methods for cascades including blade and disk flexibility; stall flutter analysis; and computational aeroelasticity.

Slope Stability Problems and Back Analysis in Heavily Jointed Rock Mass: A Case Study from Manisa, Turkey

NASA Astrophysics Data System (ADS)

Akin, Mutluhan

2013-03-01

This paper presents a case study regarding slope stability problems and the remedial slope stabilization work executed during the construction of two reinforced concrete water storage tanks on a steep hill in Manisa, Turkey. Water storage tanks of different capacities were planned to be constructed, one under the other, on closely jointed and deformed shale and sandstone units. The tank on the upper elevation was constructed first and an approximately 20-m cut slope with two benches was excavated in front of this upper tank before the construction of the lower tank. The cut slope failed after a week and the failure threatened the stability of the upper water tank. In addition to re-sloping, a 15.6-m deep contiguous retaining pile wall without anchoring was built to support both the cut slope and the upper tank. Despite the construction of a retaining pile wall, a maximum of 10 mm of displacement was observed by inclinometer measurements due to the re-failure of the slope on the existing slip surface. Permanent stability was achieved after the placement of a granular fill buttress on the slope. Back analysis based on the non-linear (Hoek-Brown) failure criterion indicated that the geological strength index (GSI) value of the slope-forming material is around 21 and is compatible with the in situ-determined GSI value (24). The calculated normal-shear stress plots are also consistent with the Hoek-Brown failure envelope of the rock mass, indicating that the location of the sliding surface, GSI value estimated by back analysis, and the rock mass parameters are well defined. The long-term stability analysis illustrates a safe slope design after the placement of a permanent toe buttress.

Comprehensive helicopter analysis: A state of the art review

NASA Technical Reports Server (NTRS)

Johnson, W.

1978-01-01

An assessment of the status of helicopter theory and analysis is presented. The technology level embodied in available design tools (computer programs) is examined, considering the problem areas of performance, loads and vibration, handling qualities and simulation, and aeroelastic stability. The effectiveness of the present analyses is discussed. The characteristics of the technology in the analyses are reviewed, including the aerodynamics technology, induced velocity and wake geometry, dynamics technology, and machine limitations.

Application of natural deep eutectic solvents to the extraction of anthocyanins from Catharanthus roseus with high extractability and stability replacing conventional organic solvents.

PubMed

Dai, Yuntao; Rozema, Evelien; Verpoorte, Robert; Choi, Young Hae

2016-02-19

Natural deep eutectic solvents (NADES) have attracted a great deal of attention in recent times as promising green media. They are generally composed of neutral, acidic or basic compounds that form liquids of high viscosity when mixed in certain molar ratio. Despite their potential, viscosity and acid or basic nature of some ingredients may affect the extraction capacity and stabilizing ability of the target compounds. To investigate these effects, extraction with a series of NADES was employed for the analysis of anthocyanins in flower petals of Catharanthus roseus in combination with HPLC-DAD-based metabolic profiling. Along with the extraction yields of anthocyanins their stability in NADES was also studied. Multivariate data analysis indicates that the lactic acid-glucose (LGH), and 1,2-propanediol-choline chloride (PCH) NADES present a similar extraction power for anthocyanins as conventional organic solvents. Furthermore, among the NADES employed, LGH exhibits an at least three times higher stabilizing capacity for cyanidins than acidified ethanol, which facilitates their extraction and analysis process. Comparing NADES to the conventional organic solvents, in addition to their reduced environmental impact, they proved to provide higher stability for anthocyanins, and therefore have a great potential as possible alternatives to those organic solvents in health related areas such as food, pharmaceuticals and cosmetics. Copyright © 2016 Elsevier B.V. All rights reserved.

Power System Analysis

NASA Astrophysics Data System (ADS)

Taniguchi, Haruhito

Electric power generation that relies on various sources as the primary sources of energy is expected to bring down CO2 emissions levels to support the overall strategy to curb global warming. Accordingly, utilities are moving towards integrating more renewable sources for generation, mostly dispersed, and adopting Smart Grid Technologies for system control. In order to construct, operate, and maintain power systems stably and economically in such background, thorough understanding about the characteristics of power systems and their components is essential. This paper presents modeling and simulation techniques available for the analysis of critical aspects such as thermal capacity, stability, voltage stability, and frequency dynamics, vital for the stable operation of power systems.

Parametric Excitation of Marangoni Instability in a Heated Thin Layer Covered by Insoluble Surfactant

NASA Astrophysics Data System (ADS)

Mikishev, Alexander B.; Nepomnyashchy, Alexander A.

2018-05-01

The paper presents the analysis of the impact of vertical periodic vibrations on the long-wavelength Marangoni instability in a liquid layer with poorly conducting boundaries in the presence of insoluble surfactant on the deformable gas-liquid interface. The layer is subject to a uniform transverse temperature gradient. Linear stability analysis is performed in order to find critical values of Marangoni numbers for both monotonic and oscillatory instability modes. Longwave asymptotic expansions are used. At the leading order, the critical values are independent on vibration parameters; at the next order of approximation we obtained the rise of stability thresholds due to vibration.

Numerical simulations and linear stability analysis of a boundary layer developed on wavy surfaces

NASA Astrophysics Data System (ADS)

Siconolfi, Lorenzo; Camarri, Simone; Fransson, Jens H. M.

2015-11-01

The development of passive methods leading to a laminar to turbulent transition delay in a boundary layer (BL) is a topic of great interest both for applications and academic research. In literature it has been shown that a proper and stable spanwise velocity modulation can reduce the growth rate of Tollmien-Schlichting (TS) waves and delay transition. In this study, we investigate numerically the possibility of obtaining a stabilizing effect of the TS waves through the use of a spanwise sinusoidal modulation of a flat plate. This type of control has been already successfully investigated experimentally. An extensive set of direct numerical simulations is carried out to study the evolution of a BL flow developed on wavy surfaces with different geometric characteristics, and the results will be presented here. Moreover, since this configuration is characterized by a slowly-varying flow field in streamwise direction, a local stability analysis is applied to define the neutral stability curves for the BL flow controlled by this type of wall modifications. These results give the possibility of investigating this control strategy and understanding the effect of the free parameters on the stabilization mechanism.

Coupling effect and control strategies of the maglev dual-stage inertially stabilization system based on frequency-domain analysis.

PubMed

Lin, Zhuchong; Liu, Kun; Zhang, Li; Zeng, Delin

2016-09-01

Maglev dual-stage inertially stabilization (MDIS) system is a newly proposed system which combines a conventional two-axis gimbal assembly and a 5-DOF (degree of freedom) magnetic bearing with vernier tilting capacity to perform dual-stage stabilization for the LOS of the suspended optical instrument. Compared with traditional dual-stage system, maglev dual-stage system exhibits different characteristics due to the negative position stiffness of the magnetic forces, which introduces additional coupling in the dual stage control system. In this paper, the coupling effect on the system performance is addressed based on frequency-domain analysis, including disturbance rejection, fine stage saturation and coarse stage structural resonance suppression. The difference between various control strategies is also discussed, including pile-up(PU), stabilize-follow (SF) and stabilize-compensate (SC). A number of principles for the design of a maglev dual stage system are proposed. A general process is also suggested, which leads to a cost-effective design striking a balance between high performance and complexity. At last, a simulation example is presented to illustrate the arguments in the paper. Copyright © 2016 ISA. Published by Elsevier Ltd. All rights reserved.

Kelvin-Helmholtz instability for flow in porous media under the influence of oblique magnetic fields: A viscous potential flow analysis

DOE Office of Scientific and Technical Information (OSTI.GOV)

Moatimid, Galal M.; Obied Allah, M. H.; Hassan, Mohamed A.

2013-10-15

In this paper, the Kelvin-Helmholtz instability of viscous incompressible magnetic fluid fully saturated porous media is achieved through the viscous potential theory. The flow is considered to be through semi-permeable boundaries above and below the fluids through which the fluid may either be blown in or sucked out, in a direction normal to the main streaming direction of the fluid flow. An oblique magnetic field, mass, heat transfer, and surface tension are present across the interface. Through the linear stability analysis, a general dispersion relation is derived and the natural curves are plotted. Therefore, the linear stability condition is discussedmore » in some depth. In view of the multiple time scale technique, the Ginzburg–Landau equation, which describes the behavior of the system in the nonlinear approach, is obtained. The effects of the orientation of the magnetic fields on the stability configuration in linear, as well as nonlinear approaches, are discussed. It is found that the Darcy's coefficient for the porous layers plays a stabilizing role. The injection of the fluids at both boundaries has a stabilizing effect, in contrast with the suction at both boundaries.« less

The Discriminant Value of Phase-Dependent Local Dynamic Stability of Daily Life Walking in Older Adult Community-Dwelling Fallers and Nonfallers

PubMed Central

Ihlen, Espen A. F.; Weiss, Aner; Helbostad, Jorunn L.; Hausdorff, Jeffrey M.

2015-01-01

The present study compares phase-dependent measures of local dynamic stability of daily life walking with 35 conventional gait features in their ability to discriminate between community-dwelling older fallers and nonfallers. The study reanalyzes 3D-acceleration data of 3-day daily life activity from 39 older people who reported less than 2 falls during one year and 31 who reported two or more falls. Phase-dependent local dynamic stability was defined for initial perturbation at 0%, 20%, 40%, 60%, and 80% of the step cycle. A partial least square discriminant analysis (PLS-DA) was used to compare the discriminant abilities of phase-dependent local dynamic stability with the discriminant abilities of 35 conventional gait features. The phase-dependent local dynamic stability λ at 0% and 60% of the step cycle discriminated well between fallers and nonfallers (AUC = 0.83) and was significantly larger (p < 0.01) for the nonfallers. Furthermore, phase-dependent λ discriminated as well between fallers and nonfallers as all other gait features combined. The present result suggests that phase-dependent measures of local dynamic stability of daily life walking might be of importance for further development in early fall risk screening tools. PMID:26491669

Stability and dynamic analysis of a slender column with curved longitudinal stiffeners

NASA Technical Reports Server (NTRS)

Lake, Mark S.

1989-01-01

The results of a stability design study are presented for a slender column with curved longitudinal stiffeners for large space structure applications. Linear stability analyses are performed using a link-plate representation of the stiffeners to determine stiffener local buckling stresses. Results from a set of parametric analyses are used to determine an approximate explicit expression for stiffener local buckling in terms of its geometric parameters. This expression along with other equations governing column stability and mass are assembled into a determinate system describing minimum mass stiffened column design. An iterative solution is determined to solve this system and a computer program incorporating this routine is presented. Example design problems are presented which verify the solution accuracy and illustrate the implementation of the solution routine. Also, observations are made which lead to a greatly simplified first iteration design equation relating the percent increase in column mass to the percent increase in column buckling load. From this, generalizations are drawn as to the mass savings offered by the stiffened column concept. Finally, the percent increase in fundamental column vibration frequency due to the addition of deployable stiffeners is studied.

A new methodology based on functional principal component analysis to study postural stability post-stroke.

PubMed

Sánchez-Sánchez, M Luz; Belda-Lois, Juan-Manuel; Mena-Del Horno, Silvia; Viosca-Herrero, Enrique; Igual-Camacho, Celedonia; Gisbert-Morant, Beatriz

2018-05-05

A major goal in stroke rehabilitation is the establishment of more effective physical therapy techniques to recover postural stability. Functional Principal Component Analysis provides greater insight into recovery trends. However, when missing values exist, obtaining functional data presents some difficulties. The purpose of this study was to reveal an alternative technique for obtaining the Functional Principal Components without requiring the conversion to functional data beforehand and to investigate this methodology to determine the effect of specific physical therapy techniques in balance recovery trends in elderly subjects with hemiplegia post-stroke. A randomized controlled pilot trial was developed. Thirty inpatients post-stroke were included. Control and target groups were treated with the same conventional physical therapy protocol based on functional criteria, but specific techniques were added to the target group depending on the subjects' functional level. Postural stability during standing was quantified by posturography. The assessments were performed once a month from the moment the participants were able to stand up to six months post-stroke. The target group showed a significant improvement in postural control recovery trend six months after stroke that was not present in the control group. Some of the assessed parameters revealed significant differences between treatment groups (P < 0.05). The proposed methodology allows Functional Principal Component Analysis to be performed when data is scarce. Moreover, it allowed the dynamics of recovery of two different treatment groups to be determined, showing that the techniques added in the target group increased postural stability compared to the base protocol. Copyright © 2018 Elsevier Ltd. All rights reserved.

Structure and stability of clusters of β-alanine in the gas phase: importance of the nature of intermolecular interactions.

PubMed

Piekarski, Dariusz Grzegorz; Díaz-Tendero, Sergio

2017-02-15

We present a theoretical study of neutral clusters of β-alanine molecules in the gas phase, (β-ala) n n ≤ 5. Classical molecular dynamics simulations carried out with different internal excitation energies provide information on the clusters formation and their thermal decomposition limits. We also present an assessment study performed with different families of density functionals using the dimer, (β-ala) 2 , as a benchmark system. The M06-2X functional provides the best agreement in geometries and relative energies in comparison with the reference values computed with the MP2 and CCSD(T) methods. The structure, stability, dissociation energies and vertical ionization potentials of the studied clusters have been investigated using this functional in combination with the 6-311++G(d,p) basis set. An exhaustive analysis of intermolecular interactions is also presented. These results provide new insights into the stability, interaction nature and formation mechanisms of clusters of amino acids in the gas phase.

Mapping the Extent and Stability of Montane Wetlands ("Bofedales") in the Andes of Bolivia and Peru using Landsat Imagery, 1980s to Present.

NASA Astrophysics Data System (ADS)

Slayback, D. A.; Hubbard, A. B.; Yager, K.

2017-12-01

Montane wetlands (locally termed "bofedales") in the Andean highlands of Peru and Bolivia provide an important forage resource for camelids (llama and alpaca) in extensive pastoral agriculture systems. For many communities, these systems may provide the only available green forage during the long winter dry season. As a part of a larger project, we are examining the impacts of both current climate change and of socioeconomic drivers on the health and status of these systems. A key part of this analysis requires mapping the current bofedal extent, and observed changes over the recent past, to link to hypothesized drivers. We are therefore mapping bofedal extent using Landsat imagery, from the mid 1980s to present, using a variety of methods (supervised and unsupervised classification, and machine learning). We will present preliminary results from this analysis, showing total regional extent, and observed stability of the bofedales (or lack thereof) over time.

Dynamic stability and bifurcation analysis in fractional thermodynamics

NASA Astrophysics Data System (ADS)

Béda, Péter B.

2018-02-01

In mechanics, viscoelasticity was the first field of applications in studying geomaterials. Further possibilities arise in spatial non-locality. Non-local materials were already studied in the 1960s by several authors as a part of continuum mechanics and are still in focus of interest because of the rising importance of materials with internal micro- and nano-structure. When material instability gained more interest, non-local behavior appeared in a different aspect. The problem was concerned to numerical analysis, because then instability zones exhibited singular properties for local constitutive equations. In dynamic stability analysis, mathematical aspects of non-locality were studied by using the theory of dynamic systems. There the basic set of equations describing the behavior of continua was transformed to an abstract dynamic system consisting of differential operators acting on the perturbation field variables. Such functions should satisfy homogeneous boundary conditions and act as indicators of stability of a selected state of the body under consideration. Dynamic systems approach results in conditions for cases, when the differential operators have critical eigenvalues of zero real parts (dynamic stability or instability conditions). When the critical eigenvalues have non-trivial eigenspace, the way of loss of stability is classified as a typical (or generic) bifurcation. Our experiences show that material non-locality and the generic nature of bifurcation at instability are connected, and the basic functions of the non-trivial eigenspace can be used to determine internal length quantities of non-local mechanics. Fractional calculus is already successfully used in thermo-elasticity. In the paper, non-locality is introduced via fractional strain into the constitutive relations of various conventional types. Then, by defining dynamic systems, stability and bifurcation are studied for states of thermo-mechanical solids. Stability conditions and genericity conditions are presented for constitutive relations under consideration.

Postural stability and ankle sprain history in athletes compared to uninjured controls.

PubMed

Huurnink, Arnold; Fransz, Duncan P; Kingma, Idsart; Verhagen, Evert A L M; van Dieën, Jaap H

2014-02-01

Diminished postural stability is a risk factor for ankle sprain occurrence and ankle sprains result in impaired postural stability. To date, ankle sprain history has not been taken into account as a determinant of postural stability, while it could possibly specify subgroups of interest. Postural stability was compared between 18 field hockey athletes who had recovered from an ankle sprain (mean (SD); 3.6 (1.5) months post-injury), and 16 uninjured controls. Force plate and kinematics parameters were calculated during single-leg standing: mean center of pressure speed, mean absolute horizontal ground reaction force, mean absolute ankle angular velocity, and mean absolute hip angular velocity. Additionally, cluster analysis was applied to the 'injured' participants, and the cluster with diminished postural stability was compared to the other participants with respect to ankle sprain history. MANCOVA showed no significant difference between groups in postural stability (P = 0.68). A self-reported history of an (partial) ankle ligament rupture was typically present in the cluster with diminished postural stability. Subsequently, a 'preceding rupture' was added as a factor in the MANCOVA, which showed a significant association between diminished postural stability and a 'preceding rupture' (P = 0.01), for all four individual parameters (P: 0.001-0.029; Cohen's d: 0.96-2.23). Diminished postural stability is not apparent in all previously injured athletes. However, our analysis suggests that an (mild) ankle sprain with a preceding severe ankle sprain is associated with impaired balance ability. Therefore, sensorimotor training may be emphasized in this particular group and caution is warranted in return to play decisions. Copyright © 2013 Elsevier Ltd. All rights reserved.

Stability and stabilisation of a class of networked dynamic systems

NASA Astrophysics Data System (ADS)

Liu, H. B.; Wang, D. Q.

2018-04-01

We investigate the stability and stabilisation of a linear time invariant networked heterogeneous system with arbitrarily connected subsystems. A new linear matrix inequality based sufficient and necessary condition for the stability is derived, based on which the stabilisation is provided. The obtained conditions efficiently utilise the block-diagonal characteristic of system parameter matrices and the sparseness of subsystem connection matrix. Moreover, a sufficient condition only dependent on each individual subsystem is also presented for the stabilisation of the networked systems with a large scale. Numerical simulations show that these conditions are computationally valid in the analysis and synthesis of a large-scale networked system.

Dynamic stabilization of the Rayleigh-Taylor instability of miscible liquids and the related "frozen waves"

NASA Astrophysics Data System (ADS)

Wolf, Gerd Gerhard H.

2018-02-01

Superimposed miscible liquids, the heavier one on top, when subjected to vibrations vertical to their interface (dynamic stabilization), can only be maintained for a certain period. A mechanism is presented explaining the resulting process of degradation and "anomalous diffusion" through that interface. Superimposed liquids, the lighter one on top, exposed to horizontal vibrations, develop a saw-tooth-like pattern called "frozen waves." These are subject to conditions similar to those of dynamic stabilization and, if miscible, thus can also only be maintained for a certain period. A further analysis of these processes would be desirable, also in view of their relation to analogue phenomena.

Characterization of optical frequency transfer over 154  km of aerial fiber.

PubMed

Gozzard, David R; Schediwy, Sascha W; Wallace, Bruce; Gamatham, Romeo; Grainge, Keith

2017-06-01

We present measurements of the frequency transfer stability and analysis of the noise characteristics of an optical signal propagating over aerial suspended fiber links up to 153.6 km in length. The measured frequency transfer stability over these links is on the order of 10^-11 at an integration time of 1 s dropping to 10^-12 for integration times longer than 100 s. We show that wind-loading of the cable spans is the dominant source of short-timescale noise on the fiber links. We also report an attempt to stabilize the optical frequency transfer over these aerial links.

Stability of Materials in High Temperature Water Vapor: SOFC Applications

NASA Technical Reports Server (NTRS)

Opila, E. J.; Jacobson, N. S.

2010-01-01

Solid oxide fuel cell material systems require long term stability in environments containing high-temperature water vapor. Many materials in fuel cell systems react with high-temperature water vapor to form volatile hydroxides which can degrade cell performance. In this paper, experimental methods to characterize these volatility reactions including the transpiration technique, thermogravimetric analysis, and high pressure mass spectrometry are reviewed. Experimentally determined data for chromia, silica, and alumina volatility are presented. In addition, data from the literature for the stability of other materials important in fuel cell systems are reviewed. Finally, methods for predicting material recession due to volatilization reactions are described.

An Investigation of the Aerodynamic Characteristics of an 0.08-Scale Model of the Chance Vought XF7U-1 Airplane in the Langley High-Speed 7- by 10-Foot Tunnel. Part I - Basic Longitudinal Stability Characteristics, TED No. NACA DE308. Part 1; Basic Longitudinal Stability Characteristics, TED No. NACA DE308

NASA Technical Reports Server (NTRS)

Kemp, William B., Jr.; Kuhn, Richard E.; Goodson, Kenneth W.

1947-01-01

The stability and control characteristics of an 0.08-scale model of the Chance Vought XF7U-1 airplane have been investigated over a Mach number range from 0.40 to 0.91. Results of the basic longitudinal tests of the complete model with undeflected control surfaces are given in the present report with a very limited analysis of the results.

Stability and spatial arrangement of the 2,4-dichlorophenoxyacetic acid and β-cyclodextrin inclusion compound: A theoretical study

NASA Astrophysics Data System (ADS)

Pereira, Robson A.; Anconi, Cleber P. A.; Nascimento, Clebio S.; De Almeida, Wagner B.; Dos Santos, Hélio F.

2015-07-01

The present letter reports results from a comprehensive theoretical analysis of the inclusion process involving 2,4-dichlorophenoxyacetic acid (2,4-D) and β-cyclodextrin (β-CD) for which the experimental data of formation is available. Spatial arrangement and stabilization energies were evaluated in gas phase and aqueous solution through density functional theory (DFT) and through the use of SMD implicit solvation approach. The discussed methodology was applied to predict the stability and identify the most favorable form (deprotonated or neutral) as well as the most probable spatial arrangement of the studied inclusion compound.

Robust controller designs for second-order dynamic system: A virtual passive approach

NASA Technical Reports Server (NTRS)

Juang, Jer-Nan; Phan, Minh

1990-01-01

A robust controller design is presented for second-order dynamic systems. The controller is model-independent and itself is a virtual second-order dynamic system. Conditions on actuator and sensor placements are identified for controller designs that guarantee overall closed-loop stability. The dynamic controller can be viewed as a virtual passive damping system that serves to stabilize the actual dynamic system. The control gains are interpreted as virtual mass, spring, and dashpot elements that play the same roles as actual physical elements in stability analysis. Position, velocity, and acceleration feedback are considered. Simple examples are provided to illustrate the physical meaning of this controller design.

An Investigation of the Elements which Contribute to Statical and Dynamical Stability, and of the Effects of Variation in Those Elements

NASA Technical Reports Server (NTRS)

Klemin, Alexander; Warner, Edward P; Denkinger, George M

1918-01-01

Part 1 gives details of models tested and methods of testing of the Eiffel 36 wing alone and the JN2 aircraft. Characteristics and performance curves for standard JN are included. Part 2 presents a statistical analysis of the following: lift and drag contributed by body and chassis tested without wings; lift and drag contributed by tail, tested without wings; the effect on lift and drift of interference between the wings of a biplane combination; lift and drag contributed by the addition of body, chassis, and tail to a biplane combination; total parasite resistance; effect of varying size of tail, keeping angle of setting constant; effect of varying length of body and size of tail at the same time, keeping constant moment of tail surface about the center of gravity; forces on the tail and the effects of downwash; effect of size and setting of tail on statical longitudinal stability effects of length of body on stability; the effects of the various elements of an airplane on longitudinal stability and the placing of the force vectors. Part 3 presents the fundamental principals of dynamical stability; computations of resistance derivatives; solution of the stability equation; dynamical stability of the Curtiss JN2; tabulation of resistance derivatives; discussion of the resistance derivatives; formation and solution of stability equations; physical conceptions of the resistance derivatives; elements contributing to damping and an investigation of low speed conditions. Part 4 includes a summary of the results of the statistical investigation and a summary of the results for dynamic stability.

A note on the effects of viscosity on the stability of a trailing-line vortex

NASA Technical Reports Server (NTRS)

Duck, Peter W.; Khorrami, Mehdi R.

1992-01-01

The linear stability of the Batchelor (1964) vortex is examined with emphasis on new viscous modes recently found numerically by Khorrami (1991). Unlike the previously reported inviscid modes of instability, these modes are destabilized by viscosity and exhibit small growth rates at large Reynolds numbers. The analysis presented here uses a combination of asymptotic and numerical techniques. The results confirm the existence of the additional modes of instability due to viscosity.

A new sensitivity analysis for structural optimization of composite rotor blades

NASA Technical Reports Server (NTRS)

Venkatesan, C.; Friedmann, P. P.; Yuan, Kuo-An

1993-01-01

This paper presents a detailed mathematical derivation of the sensitivity derivatives for the structural dynamic, aeroelastic stability and response characteristics of a rotor blade in hover and forward flight. The formulation is denoted by the term semianalytical approach, because certain derivatives have to be evaluated by a finite difference scheme. Using the present formulation, sensitivity derivatives for the structural dynamic and aeroelastic stability characteristics, were evaluated for both isotropic and composite rotor blades. Based on the results, useful conclusions are obtained regarding the relative merits of the semi-analytical approach, for calculating sensitivity derivatives, when compared to a pure finite difference approach.

A Wearable Body Controlling Device for Application of Functional Electrical Stimulation

PubMed Central

Jeffery, Nicholas D.

2018-01-01

In this research, we describe a new balancing device used to stabilize the rear quarters of a patient dog with spinal cord injuries. Our approach uses inertial measurement sensing and direct leg actuation to lay a foundation for eventual muscle control by means of direct functional electrical stimulation (FES). During this phase of development, we designed and built a mechanical test-bed to develop the control and stimulation algorithms before we use the device on our animal subjects. We designed the bionic test-bed to mimic the typical walking gait of a dog and use it to develop and test the functionality of the balancing device for stabilization of patient dogs with hindquarter paralysis. We present analysis for various muscle stimulation and balancing strategies, and our device can be used by veterinarians to tailor the stimulation strength and temporal distribution for any individual patient dog. We develop stabilizing muscle stimulation strategies using the robotic test-bed to enhance walking stability. We present experimental results using the bionic test-bed to demonstrate that the balancing device can provide an effective sensing strategy and deliver the required motion control commands for stabilizing an actual dog with a spinal cord injury. PMID:29670039

A Wearable Body Controlling Device for Application of Functional Electrical Stimulation.

PubMed

Taghavi, Nazita; Luecke, Greg R; Jeffery, Nicholas D

2018-04-18

In this research, we describe a new balancing device used to stabilize the rear quarters of a patient dog with spinal cord injuries. Our approach uses inertial measurement sensing and direct leg actuation to lay a foundation for eventual muscle control by means of direct functional electrical stimulation (FES). During this phase of development, we designed and built a mechanical test-bed to develop the control and stimulation algorithms before we use the device on our animal subjects. We designed the bionic test-bed to mimic the typical walking gait of a dog and use it to develop and test the functionality of the balancing device for stabilization of patient dogs with hindquarter paralysis. We present analysis for various muscle stimulation and balancing strategies, and our device can be used by veterinarians to tailor the stimulation strength and temporal distribution for any individual patient dog. We develop stabilizing muscle stimulation strategies using the robotic test-bed to enhance walking stability. We present experimental results using the bionic test-bed to demonstrate that the balancing device can provide an effective sensing strategy and deliver the required motion control commands for stabilizing an actual dog with a spinal cord injury.

Flames in dusty mixtures: Their structure and stability

NASA Technical Reports Server (NTRS)

Buckmaster, J.; Jackson, T.

1993-01-01

The structure and stability of flames in dusty mixtures is investigated. The presence of the dust leads to significant transport of energy by radiation and the fundamental goal of the analysis is to explore to what extent this displaces the classical non-hydrodynamical stability boundaries of the plane degradation. An approximate description of the radiative transport permits analysis for arbitrary values of both the planck length and the Boltzman number. It is shown that the pulsating/traveling-wave instability usually associated with values of Lewis number (L(sub e)) bigger than 1 is stongly enhanced by the presence of radiation and can be present even if L(sub e) is less than 1. On the other hand radiation tends to supress the cellular instability normally associated with values of L(sub e) less than 1. The latter is consisitent with preliminary experimental observations of Abbud-Madrid and Ronney.

Hillslope hydrology and stability

USGS Publications Warehouse

Lu, Ning; Godt, Jonathan

2012-01-01

Landslides are caused by a failure of the mechanical balance within hillslopes. This balance is governed by two coupled physical processes: hydrological or subsurface flow and stress. The stabilizing strength of hillslope materials depends on effective stress, which is diminished by rainfall. This book presents a cutting-edge quantitative approach to understanding hydro-mechanical processes across variably saturated hillslope environments and to the study and prediction of rainfall-induced landslides. Topics covered include historic synthesis of hillslope geomorphology and hydrology, total and effective stress distributions, critical reviews of shear strength of hillslope materials and different bases for stability analysis. Exercises and homework problems are provided for students to engage with the theory in practice. This is an invaluable resource for graduate students and researchers in hydrology, geomorphology, engineering geology, geotechnical engineering and geomechanics and for professionals in the fields of civil and environmental engineering and natural hazard analysis.

Modelling and finite-time stability analysis of psoriasis pathogenesis

NASA Astrophysics Data System (ADS)

Oza, Harshal B.; Pandey, Rakesh; Roper, Daniel; Al-Nuaimi, Yusur; Spurgeon, Sarah K.; Goodfellow, Marc

2017-08-01

A new systems model of psoriasis is presented and analysed from the perspective of control theory. Cytokines are treated as actuators to the plant model that govern the cell population under the reasonable assumption that cytokine dynamics are faster than the cell population dynamics. The analysis of various equilibria is undertaken based on singular perturbation theory. Finite-time stability and stabilisation have been studied in various engineering applications where the principal paradigm uses non-Lipschitz functions of the states. A comprehensive study of the finite-time stability properties of the proposed psoriasis dynamics is carried out. It is demonstrated that the dynamics are finite-time convergent to certain equilibrium points rather than asymptotically or exponentially convergent. This feature of finite-time convergence motivates the development of a modified version of the Michaelis-Menten function, frequently used in biology. This framework is used to model cytokines as fast finite-time actuators.

A dynamic analysis of the motion of a low-wing general aviation aircraft about its calculated equilibrium flat spin mode

NASA Technical Reports Server (NTRS)

Tischler, M. B.; Barlow, J. B.

1980-01-01

The properties of the flat spin mode of a general aviation configuration have been studied through analysis of rotary balance data, numerical simulation, and analytical study of the equilibrium state. The equilibrium state is predicted well from rotary balance data. The variations of yawing moment and pitching moment as functions of sideslip have been shown to be of great importance in obtaining accurate modeling. These dependencies are not presently available with sufficient accuracy from previous tests or theories. The stability of the flat spin mode has been examined extensively using numerical linearization, classical perturbation methods, and reduced order modeling. The stability exhibited by the time histories and the eigenvalue analyses is shown to be strongly dependent on certain static cross derivatives and more so on the dynamic derivatives. Explicit stability criteria are obtained from the reduced order models.

Waves on radial film flows

NASA Astrophysics Data System (ADS)

Cholemari, Murali R.; Arakeri, Jaywant H.

2005-08-01

We study the stability of surface waves on the radial film flow created by a vertical cylindrical water jet striking a horizontal plate. In such flows, surface waves have been found to be unstable and can cause transition to turbulence. This surface-wave-induced transition is different from the well-known Tollmien-Schlichting wave-induced transition. The present study aims at understanding the instability and the transition process. We do a temporal stability analysis by assuming the flow to be locally two-dimensional but including spatial variations to first order in the basic flow. The waves are found to be dispersive, mostly unstable, and faster than the mean flow. Spatial variation is the major destabilizing factor. Experiments are done to test the results of the linear stability analysis and to document the wave breakup and transition. Comparison between theory and experiments is fairly good and indicates the adequacy of the model.

On the effect of Ti on the stability of amorphous indium zinc oxide used in thin film transistor applications

NASA Astrophysics Data System (ADS)

Lee, Sunghwan; Paine, David C.

2011-06-01

In2O3-based amorphous oxide channel materials are of increasing interest for thin film transisitor applications due, in part, to the remarkable stability of this class of materials amorphous structure and electronic properties. We report that this stability is degraded in the presence of Ti, which is widely used as a contact and/or adhesion layer. A cross-sectional transmission electron microscopy analysis, supported by glancing incident angle x-ray and selected area diffraction examination, shows that amorphous indium zinc oxide in contact with Ti undergoes crystallization to the bixbyite phase and reacts to form the rutile phase of TiO2 at a temperature of 200 °C. A basic thermodynamic analysis is presented and forms the basis of a model that describes both the crystallization and the resistivity decrease.

Bright discrete solitons in spatially modulated DNLS systems

DOE PAGES

Kevrekidis, P. G.; Horne, R. L.; Whitaker, N.; ...

2015-08-04

In the present work, we revisit the highly active research area of inhomogeneously nonlinear defocusing media and consider the existence, spectral stability and nonlinear dynamics of bright solitary waves in them. We use the anti-continuum limit of vanishing coupling as the starting point of our analysis, enabling in this way a systematic characterization of the branches of solutions. Our stability findings and bifurcation characteristics reveal the enhanced robustness and wider existence intervals of solutions with a broader support, culminating in the 'extended' solution in which all sites are excited. Our eigenvalue predictions are corroborated by numerical linear stability analysis. Inmore » conclusion, the dynamics also reveal a tendency of the solution profiles to broaden, in line with the above findings. These results pave the way for further explorations of such states in discrete systems, including in higher dimensional settings.« less

A study on the stability of a motorcycle wheel-swingarm suspension with chain transmission

NASA Astrophysics Data System (ADS)

Sorrentino, S.; Leonelli, L.

2017-11-01

The present study describes a possible driving mechanism for a self-excited oscillation observed in motorcycle dynamics, often referred to as chatter. This phenomenon, affecting the performance of road racing motorcycles, has been simulated in straight running braking manoeuvres with multibody motorcycle models. It involves rear suspension bounce and driveline oscillation in the frequency range between 17 and 22 Hz. A simplified model of a motorcycle rear suspension with chain transmission is proposed and its stability in equilibrium configurations is studied via eigenvalue analysis. The sensitivity with respect to all its governing parameters is analysed by means of stability maps and the self-excitation mechanism is explained with the aid of energy balance analysis and phase diagrams. It is found that the key role for the instability onset is played by the gradient of the nonlinear characteristic slip function of the tyre.

Mathematical model and stability analysis of fluttering and autorotation of an articulated plate into a flow

NASA Astrophysics Data System (ADS)

Rostami, Ali Bakhshandeh; Fernandes, Antonio Carlos

2018-03-01

This paper is dedicated to develop a mathematical model that can simulate nonlinear phenomena of a hinged plate which places into the fluid flow (1 DOF). These phenomena are fluttering (oscillation motion), autorotation (continuous rotation) and chaotic motion (combination of fluttering and autorotation). Two mathematical models are developed for 1 DOF problem using two eminent mathematical models which had been proposed for falling plates (3 DOF). The procedures of developing these models are elaborated and then these results are compared to experimental data. The best model in the simulation of the phenomena is chosen for stability and bifurcation analysis. Based on these analyses, this model shows a transcritical bifurcation and as a result, the stability diagram and threshold are presented. Moreover, an analytical expression is given for finding the boundary of bifurcation from the fluttering to the autorotation.

STS-71 Shuttle/Mir mission report

NASA Technical Reports Server (NTRS)

Zimpfer, Douglas J.

1995-01-01

The performance measurements of the space shuttle on-orbit flight control system from the STS-71 mission is presented in this post-flight analysis report. This system is crucial to the stabilization of large space structures and will be needed during the assembly of the International Space Station A mission overview is presented, including the in-orbit flight tests (pre-docking with Mir) and the systems analysis during the docking and undocking operations. Systems errors and lessons learned are discussed, with possible corrective procedures presented for the upcoming Mir flight tests.

Development and Present Situation Analysis of Power Transformer State Maintenance

NASA Astrophysics Data System (ADS)

Lv, Sen; Li, Biao; Li, Huan

2018-02-01

The pivotal status of power transformer in the power system is one of the most important equipment. The safety and reliability of its operation is directly related to the safety and stability of power system. Based on the analysis of the present situation of power transformer state maintenance in home and abroad. The paper points out the deficiency of the current method and provides a theoretical basis for further research, which has a certain guiding significance.

A compilation and analysis of helicopter handling qualities data. Volume 2: Data analysis

NASA Technical Reports Server (NTRS)

Heffley, R. K.

1979-01-01

A compilation and an analysis of helicopter handling qualities data are presented. Multiloop manual control methods are used to analyze the descriptive data, stability derivatives, and transfer functions for a six degrees of freedom, quasi static model. A compensatory loop structure is applied to coupled longitudinal, lateral and directional equations in such a way that key handling qualities features are examined directly.

A Practice-Oriented Bifurcation Analysis for Pulse Energy Converters: A Stability Margin

NASA Astrophysics Data System (ADS)

Kolokolov, Yury; Monovskaya, Anna

The popularity of systems of pulse energy conversion (PEC-systems) for practical applications is due to the heightened efficiency of energy conversion processes with comparatively simple realizations. Nevertheless, a PEC-system represents a nonlinear object with a variable structure, and the bifurcation analysis remains the basic tool to describe PEC dynamics evolution. The paper is devoted to the discussion on whether the scientific viewpoint on the natural nonlinear dynamics evolution can be involved in practical applications. We focus on the problems connected with stability boundaries of an operating regime. The results of both small-signal analysis and computational bifurcation analysis are considered in the parametrical space in comparison with the results of the experimental identification of the zonal heterogeneity of the operating process. This allows to propose an adapted stability margin as a sufficiently safe distance before the point after which the operating process begins to lose the stability. Such stability margin can extend the permissible operating domain in the parametrical space at the expense of using cause-and-effect relations in the context of natural regularities of nonlinear dynamics. Reasoning and discussion are based on the experimental and computational results for a synchronous buck converter with a pulse-width modulation. The presented results can be useful, first of all, for PEC-systems with significant variation of equivalent inductance and/or capacity. We believe that the discussion supports a viewpoint by which the contemporary methods of the computational and experimental bifurcation analyses possess both analytical abilities and experimental techniques for promising solutions which could be practice-oriented for PEC-systems.

Evaluation of primary stability of self-tapping and non-self-tapping dental implants. A 12-week clinical study.

PubMed

Marković, Aleksa; Calvo-Guirado, José Luís; Lazić, Zoran; Gómez-Moreno, Gerardo; Ćalasan, Dejan; Guardia, Javier; Čolic, Snježana; Aguilar-Salvatierra, Antonio; Gačić, Bojan; Delgado-Ruiz, Rafael; Janjić, Bojan; Mišić, Tijana

2013-06-01

The aim of this study was to investigate the relationship between surgical techniques and implant macro-design (self-tapping/non-self-tapping) for the optimization of implant stability in the low-density bone present in the posterior maxilla using resonance frequency analysis (RFA). A total of 102 implants were studied. Fifty-six self-tapping BlueSkyBredent® (Bredent GmbH&Co.Kg®, Senden, Germany) and 56 non-self-tapping Standard Plus Straumann® (Institut Straumann AG®, Waldenburg, Switzerland) were placed in the posterior segment of the maxilla. Implants of both types were placed in sites prepared with either lateral bone-condensing or with bone-drilling techniques. Implant stability measurements were performed using RFA immediately after implant placement and weekly during a 12-week follow-up period. Both types of implants placed after bone condensing achieved significantly higher stability immediately after surgery, as well as during the entire 12-week observation period compared with those placed following bone drilling. After bone condensation, there were no significant differences in primary stability or in implant stability after the first week between both implant types. From 2 to 12 postoperative weeks, significantly higher stability was shown by self-tapping implants. After bone drilling, self-tapping implants achieved significantly higher stability than non-self-tapping implants during the entire follow-up period. The outcomes of the present study indicate that bone drilling is not an effective technique for improving implant stability and, following this technique, the use of self-tapping implants is highly recommended. Implant stability optimization in the soft bone can be achieved by lateral bone-condensing technique, regardless of implant macro-design. © 2011 Wiley Periodicals, Inc.

Critical study of current situation of Vrănicioara tailing pond on Cavnicului Valley, risks and consequences

NASA Astrophysics Data System (ADS)

Bud, I.; Duma, S.; Gusat, D.; Pasca, I.; Bud, A.

2017-05-01

In northern Romania, there are numerous tailing ponds, resulting from mining activities that present significant environmental risks. Some of them, including Vrănicioara tailing pond, were the subject of technical projects for ecological rehabilitation. Vrănicioara pond is located on the right side of Cavnic Valley, downstream Cavnic town, about 4 kilometers far. It has about 500 m length and is located parallel to the road linking Baia Sprie and Cavnic localities. Chemical and physical stability of the tailing pond before rehabilitation interest the research, analysis and conclusions were published in several scientific meetings. In addition, close to the pond at less than 100 m, an open pit has developed, exploiting andesite by mining blast, increasing the risk of physical stability by continuous exposure to vibration. This activity currently continues, advancing towards the tailing pond body. The critical study addresses the current state of Vrănicioara Tailing Pond, analysis of some rehabilitation works done incorrectly, analysis of chemical stability that was not a priority during rehabilitation. Research intention is heading to water analysis confirming the existence of acid drainage that was not stopped or at least reduced. The scientific approach is based on the Technical Standards for Waste Deposits, in force in Romania, providing the rules to ensure physical and chemical stability.

Hip and knee joints are more stabilized than driven during the stance phase of gait: an analysis of the 3D angle between joint moment and joint angular velocity.

PubMed

Dumas, R; Cheze, L

2008-08-01

Joint power is commonly used in orthopaedics, ergonomics or sports analysis but its clinical interpretation remains controversial. Some basic principles on muscle actions and energy transfer have been proposed in 2D. The decomposition of power on 3 axes, although questionable, allows the same analysis in 3D. However, these basic principles have been widely criticized, mainly because bi-articular muscles must be considered. This requires a more complex computation in order to determine how the individual muscle force contributes to drive the joint. Conversely, with simple 3D inverse dynamics, the analysis of both joint moment and angular velocity directions is essential to clarify when the joint moment can contribute or not to drive the joint. The present study evaluates the 3D angle between the joint moment and the joint angular velocity and investigates when the hip, knee and ankle joints are predominantly driven (angle close to 0 degrees and 180 degrees ) or stabilized (angle close to 90 degrees ) during gait. The 3D angle curves show that the three joints are never fully but only partially driven and that the hip and knee joints are mainly stabilized during the stance phase. The notion of stabilization should be further investigated, especially for subjects with motion disorders or prostheses.

Ant Colony Optimization Analysis on Overall Stability of High Arch Dam Basis of Field Monitoring

PubMed Central

Liu, Xiaoli; Chen, Hong-Xin; Kim, Jinxie

2014-01-01

A dam ant colony optimization (D-ACO) analysis of the overall stability of high arch dams on complicated foundations is presented in this paper. A modified ant colony optimization (ACO) model is proposed for obtaining dam concrete and rock mechanical parameters. A typical dam parameter feedback problem is proposed for nonlinear back-analysis numerical model based on field monitoring deformation and ACO. The basic principle of the proposed model is the establishment of the objective function of optimizing real concrete and rock mechanical parameter. The feedback analysis is then implemented with a modified ant colony algorithm. The algorithm performance is satisfactory, and the accuracy is verified. The m groups of feedback parameters, used to run a nonlinear FEM code, and the displacement and stress distribution are discussed. A feedback analysis of the deformation of the Lijiaxia arch dam and based on the modified ant colony optimization method is also conducted. By considering various material parameters obtained using different analysis methods, comparative analyses were conducted on dam displacements, stress distribution characteristics, and overall dam stability. The comparison results show that the proposal model can effectively solve for feedback multiple parameters of dam concrete and rock material and basically satisfy assessment requirements for geotechnical structural engineering discipline. PMID:25025089

Scientific applications of frequency-stabilized laser technology in space

NASA Technical Reports Server (NTRS)

Schumaker, Bonny L.

1990-01-01

A synoptic investigation of the uses of frequency-stabilized lasers for scientific applications in space is presented. It begins by summarizing properties of lasers, characterizing their frequency stability, and describing limitations and techniques to achieve certain levels of frequency stability. Limits to precision set by laser frequency stability for various kinds of measurements are investigated and compared with other sources of error. These other sources include photon-counting statistics, scattered laser light, fluctuations in laser power, and intensity distribution across the beam, propagation effects, mechanical and thermal noise, and radiation pressure. Methods are explored to improve the sensitivity of laser-based interferometric and range-rate measurements. Several specific types of science experiments that rely on highly precise measurements made with lasers are analyzed, and anticipated errors and overall performance are discussed. Qualitative descriptions are given of a number of other possible science applications involving frequency-stabilized lasers and related laser technology in space. These applications will warrant more careful analysis as technology develops.

A multi-scale Q1/P0 approach to langrangian shock hydrodynamics.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shashkov, Mikhail; Love, Edward; Scovazzi, Guglielmo

A new multi-scale, stabilized method for Q1/P0 finite element computations of Lagrangian shock hydrodynamics is presented. Instabilities (of hourglass type) are controlled by a stabilizing operator derived using the variational multi-scale analysis paradigm. The resulting stabilizing term takes the form of a pressure correction. With respect to currently implemented hourglass control approaches, the novelty of the method resides in its residual-based character. The stabilizing residual has a definite physical meaning, since it embeds a discrete form of the Clausius-Duhem inequality. Effectively, the proposed stabilization samples and acts to counter the production of entropy due to numerical instabilities. The proposed techniquemore » is applicable to materials with no shear strength, for which there exists a caloric equation of state. The stabilization operator is incorporated into a mid-point, predictor/multi-corrector time integration algorithm, which conserves mass, momentum and total energy. Encouraging numerical results in the context of compressible gas dynamics confirm the potential of the method.« less

Accelerated Stability Studies on Dried Extracts of Centella asiatica Through Chemical, HPLC, HPTLC, and Biological Activity Analyses.

PubMed

Kaur, Ishtdeep; Suthar, Nancy; Kaur, Jasmeen; Bansal, Yogita; Bansal, Gulshan

2016-10-01

Regulatory guidelines recommend systematic stability studies on a herbal product to establish its shelf life. In the present study, commercial extracts (Types I and II) and freshly prepared extract (Type III) of Centella asiatica were subjected to accelerated stability testing for 6 months. Control and stability samples were evaluated for organoleptics, pH, moisture, total phenolic content (TPC), asiatic acid, kaempherol, and high-performance thin layer chromatography fingerprints, and for antioxidant and acetylcholinesterase inhibitory activities. Markers and TPC and both the activities of each extract decreased in stability samples with respect to control. These losses were maximum in Type I extract and minimum in Type III extract. Higher stability of Type III extract than others might be attributed to the additional phytoconstituents and/or preservatives in it. Pearson correlation analysis of the results suggested that TPC, asiatic acid, and kaempferol can be taken as chemical markers to assess chemical and therapeutic shelf lives of herbal products containing Centella asiatica. © The Author(s) 2016.

Linear stability of compressible Taylor-Couette flow

NASA Technical Reports Server (NTRS)

Kao, Kai-Hsiung; Chow, Chuen-Yen

1992-01-01

A temporal stability analysis of compressible Taylor-Couette flow is presented. The viscous flow studied in this paper is contained between two concentric cylinders of infinite length, which are rotating with different angular velocities and are kept at different surface temperatures. The effects of differential rotation and temperature difference on the stability of Taylor-Couette flow are contrasted for a range of Mach numbers ranging from incompressible to Mach 3.0. The relative motion of the cylinders dramatically affects the characteristics of the Couette flow at the onset of instability. The flow is stabilized or destabilized depending upon the temperature ratio and speeds of the two cylinders. Independent of Mach number and temperature ratio, increasing Reynolds number generally promotes a destabilizing effect, indicating the inviscid nature of the Taylor-Couette flow.

Effects of wing modification on an aircraft's aerodynamic parameters as determined from flight data

NASA Technical Reports Server (NTRS)

Hess, R. A.

1986-01-01

A study of the effects of four wing-leading-edge modifications on a general aviation aircraft's stability and control parameters is presented. Flight data from the basic aircraft configuration and configurations with wing modifications are analyzed to determine each wing geometry's stability and control parameters. The parameter estimates and aerodynamic model forms are obtained using the stepwise regression and maximum likelihood techniques. The resulting parameter estimates and aerodynamic models are verified using vortex-lattice theory and by analysis of each model's ability to predict aircraft behavior. Comparisons of the stability and control derivative estimates from the basic wing and the four leading-edge modifications are accomplished so that the effects of each modification on aircraft stability and control derivatives can be determined.

Analysis and design of negative resistance oscillators using surface transverse wave-based single port resonators.

PubMed

Avramov, Ivan D

2003-03-01

This practically oriented paper presents the fundamentals for analysis, optimization, and design of negative resistance oscillators (NRO) stabilized with surface transverse wave (STW)-based single-port resonators (SPR). Data on a variety of high-Q, low-loss SPR devices in the 900- to 2000-MHz range, suitable for NRO applications, are presented, and a simple method for SPR parameter extraction through Pi-circuit measurements is outlined. Negative resistance analysis, based on S-parameter data of the active device, is performed on a tuned-base, grounded collector transistor NRO, known for its good stability and tuning at microwave frequencies. By adding a SPR in the emitter network, the static transducer capacitance is absorbed by the circuit and is used to generate negative resistance only over the narrow bandwidth of the acoustic device, eliminating the risk of spurious oscillations. The analysis allows exact prediction of the oscillation frequency, tuning range, loaded Q, and excess gain. Simulation and experimental data on a 915-MHz fixed-frequency NRO and a wide tuning range, voltage-controlled STW oscillator, built and tested experimentally, are presented. Practical design aspects including the choice of transistor, negative feedback circuits, load coupling, and operation at the highest phase slope for minimum phase noise are discussed.

An Innovative Structural Mode Selection Methodology: Application for the X-33 Launch Vehicle Finite Element Model

NASA Technical Reports Server (NTRS)

Hidalgo, Homero, Jr.

2000-01-01

An innovative methodology for determining structural target mode selection and mode selection based on a specific criterion is presented. An effective approach to single out modes which interact with specific locations on a structure has been developed for the X-33 Launch Vehicle Finite Element Model (FEM). We presented Root-Sum-Square (RSS) displacement method computes resultant modal displacement for each mode at selected degrees of freedom (DOF) and sorts to locate modes with highest values. This method was used to determine modes, which most influenced specific locations/points on the X-33 flight vehicle such as avionics control components, aero-surface control actuators, propellant valve and engine points for use in flight control stability analysis and for flight POGO stability analysis. Additionally, the modal RSS method allows for primary or global target vehicle modes to also be identified in an accurate and efficient manner.

Dynamic modelling and experimental validation of three wheeled tilting vehicles

NASA Astrophysics Data System (ADS)

Amati, Nicola; Festini, Andrea; Pelizza, Luigi; Tonoli, Andrea

2011-06-01

The present paper describes the study of the stability in the straight running of a three-wheeled tilting vehicle for urban and sub-urban mobility. The analysis was carried out by developing a multibody model in the Matlab/SimulinkSimMechanics environment. An Adams-Motorcycle model and an equivalent analytical model were developed for the cross-validation and for highlighting the similarities with the lateral dynamics of motorcycles. Field tests were carried out to validate the model and identify some critical parameters, such as the damping on the steering system. The stability analysis demonstrates that the lateral dynamic motions are characterised by vibration modes that are similar to that of a motorcycle. Additionally, it shows that the wobble mode is significantly affected by the castor trail, whereas it is only slightly affected by the dynamics of the front suspension. For the present case study, the frame compliance also has no influence on the weave and wobble.

Analysis of airframe/engine interactions - An integrated control perspective

NASA Technical Reports Server (NTRS)

Schmidt, David K.; Schierman, John D.; Garg, Sanjay

1990-01-01

Techniques for the analysis of the dynamic interactions between airframe/engine dynamical systems are presented. Critical coupling terms are developed that determine the significance of these interactions with regard to the closed loop stability and performance of the feedback systems. A conceptual model is first used to indicate the potential sources of the coupling, how the coupling manifests itself, and how the magnitudes of these critical coupling terms are used to quantify the effects of the airframe/engine interactions. A case study is also presented involving an unstable airframe with thrust vectoring for attitude control. It is shown for this system with classical, decentralized control laws that there is little airframe/engine interaction, and the stability and performance with those control laws is not affected. Implications of parameter uncertainty in the coupling dynamics is also discussed, and effects of these parameter variations are also demonstrated to be small for this vehicle configuration.

Slope Stability Estimation of the Kościuszko Mound in Cracow

NASA Astrophysics Data System (ADS)

Wrana, Bogumił; Pietrzak, Natalia

2015-06-01

In the paper, the slope stability problem of the Kościuszko Mound in Cracow, Poland is considered. The slope stability analysis was performed using Plaxis FEM program. The outer surface of the mound has complex geometry. The slope of the cone is not uniform in all directions, on the surface of the cone are pedestrian paths. Due to its complicated geometry it was impossible to do computing by Plaxis input pre-procesor. The initial element mesh was generated using Autodesk Autocad 3D and next it was updated by Plaxis program. The soil parameters were adopted in accordance with the detailed geological soil testing performed in 2012. Calculating model includes geogrids. The upper part was covered by MacMat geogrid, while the lower part of the Mound was reinforced using Terramesh Matt geogrid. The slope analysis was performed by successives reduction of φ /c parameters. The total multiplayer ΣMsf is used to define the value of the soil strength parameters. The article presents the results of slope stability before and after the rainfall during 33 days of precipitation in flood of 2010.

a Numerical Method for Stability Analysis of Pinned Flexible Mechanisms

NASA Astrophysics Data System (ADS)

Beale, D. G.; Lee, S. W.

1996-05-01

A technique is presented to investigate the stability of mechanisms with pin-jointed flexible members. The method relies on a special floating frame from which elastic link co-ordinates are defined. Energies are easily developed for use in a Lagrange equation formulation, leading to a set of non-linear and mixed ordinary differential-algebraic equations of motion with constraints. Stability and bifurcation analysis is handled using a numerical procedure (generalized co-ordinate partitioning) that avoids the tedious and difficult task of analytically reducing the system of equations to a number equalling the system degrees of freedom. The proposed method was then applied to (1) a slider-crank mechanism with a flexible connecting rod and crank of constant rotational speed, and (2) a four-bar linkage with a flexible coupler with a constant speed crank. In both cases, a single pinned-pinned beam bending mode is employed to develop resonance curves and stability boundaries in the crank length-crank speed parameter plane. Flip and fold bifurcations are common occurrences in both mechanisms. The accuracy of the proposed method was also verified by comparison with previous experimental results [1].

Study of Geometric Porosity on Static Stability and Drag Using Computational Fluid Dynamics for Rigid Parachute Shapes

NASA Technical Reports Server (NTRS)

Greathouse, James S.; Schwing, Alan M.

2015-01-01

This paper explores use of computational fluid dynamics to study the e?ect of geometric porosity on static stability and drag for NASA's Multi-Purpose Crew Vehicle main parachute. Both of these aerodynamic characteristics are of interest to in parachute design, and computational methods promise designers the ability to perform detailed parametric studies and other design iterations with a level of control previously unobtainable using ground or flight testing. The approach presented here uses a canopy structural analysis code to define the inflated parachute shapes on which structured computational grids are generated. These grids are used by the computational fluid dynamics code OVERFLOW and are modeled as rigid, impermeable bodies for this analysis. Comparisons to Apollo drop test data is shown as preliminary validation of the technique. Results include several parametric sweeps through design variables in order to better understand the trade between static stability and drag. Finally, designs that maximize static stability with a minimal loss in drag are suggested for further study in subscale ground and flight testing.

Implications for the dynamic health of a glacier from comparison of conventional and reference-surface balances

USGS Publications Warehouse

Harrison, W.D.; Cox, L.H.; Hock, R.; March, R.S.; Pettit, E.C.

2009-01-01

Conventional and reference-surface mass-balance data from Gulkana and Wolverine Glaciers, Alaska, USA, are used to address the questions of how rapidly these glaciers are adjusting (or 'responding') to climate, whether their responses are stable, and whether the glaciers are likely to survive in today's climate. Instability means that a glacier will eventually vanish, or at least become greatly reduced in volume, if the climate stabilizes at its present state. A simple non-linear theory of response is presented for the analysis. The response of Gulkana Glacier is characterized by a timescale of several decades, but its stability and therefore its survival in today's climate are uncertain. Wolverine seems to be responding to climate more slowly, on the timescale of one to several centuries. Its stability is also uncertain, but a slower response time would make it more susceptible to climate changes.

ICI optical data storage tape: An archival mass storage media

NASA Technical Reports Server (NTRS)

Ruddick, Andrew J.

1993-01-01

At the 1991 Conference on Mass Storage Systems and Technologies, ICI Imagedata presented a paper which introduced ICI Optical Data Storage Tape. This paper placed specific emphasis on the media characteristics and initial data was presented which illustrated the archival stability of the media. More exhaustive analysis that was carried out on the chemical stability of the media is covered. Equally important, it also addresses archive management issues associated with, for example, the benefits of reduced rewind requirements to accommodate tape relaxation effects that result from careful tribology control in ICI Optical Tape media. ICI Optical Tape media was designed to meet the most demanding requirements of archival mass storage. It is envisaged that the volumetric data capacity, long term stability and low maintenance characteristics demonstrated will have major benefits in increasing reliability and reducing the costs associated with archival storage of large data volumes.

On spectral techniques in analysis of Boolean networks

NASA Astrophysics Data System (ADS)

Kesseli, Juha; Rämö, Pauli; Yli-Harja, Olli

2005-06-01

In this work we present results that can be used for analysis of Boolean networks. The results utilize Fourier spectra of the functions in the network. An accurate formula is given for Derrida plots of networks of finite size N based on a result on Boolean functions presented in another context. Derrida plots are widely used to examine the stability issues of Boolean networks. For the limit N→∞, we give a computationally simple form that can be used as a good approximation for rather small networks as well. A formula for Derrida plots of random Boolean networks (RBNs) presented earlier in the literature is given an alternative derivation. It is shown that the information contained in the Derrida plot is equal to the average Fourier spectrum of the functions in the network. In the case of random networks the mean Derrida plot can be obtained from the mean spectrum of the functions. The method is applied to real data by using the Boolean functions found in genetic regulatory networks of eukaryotic cells in an earlier study. Conventionally, Derrida plots and stability analysis have been computed with statistical sampling resulting in poorer accuracy.

Dynamic analysis of space robot remote control system

NASA Astrophysics Data System (ADS)

Kulakov, Felix; Alferov, Gennady; Sokolov, Boris; Gorovenko, Polina; Sharlay, Artem

2018-05-01

The article presents analysis on construction of two-stage remote control for space robots. This control ensures efficiency of the robot control system at large delays in transmission of control signals from the ground control center to the local control system of the space robot. The conditions for control stability of and high transparency are found.

The initial instability and finite-amplitude stability of alternate bars in straight channels

USGS Publications Warehouse

Nelson, J.M.

1990-01-01

The initial instability and fully developed stability of alternate bars in straight channels are investigated using linearized and nonlinear analyses. The fundamental instability leading to these features is identified through a linear stability analysis of the equations governing the flow and sediment transport fields. This instability is explained in terms of topographically induced steering of the flow and the associated pattern of erosion and deposition on the bed. While the linear theory is useful for examining the instability mechanism, this approach is shown to yield relatively little information about well-developed alternate bars and, specifically, the linear analysis is shown to yield poor predictions of the fully developed bar wavelength. A fully nonlinear approach is presented that permits computation of the evolution of these bed features from an initial perturbation to their fully developed morphology. This analysis indicates that there is typically substantial elongation of the bar wavelength during the evolution process, a result that is consistent with observations of bar development in flumes and natural channels. The nonlinear approach demonstrates that the eventual stability of these features is a result of the interplay between topographic steering effects, secondary flow production as a result of streamline curvature, and gravitationally induced modifications of sediment fluxes over a sloping bed. ?? 1990.

On the long-term stability of calibration standards in different matrices.

PubMed

Kandić, A; Vukanac, I; Djurašević, M; Novković, D; Šešlak, B; Milošević, Z

2012-09-01

In order to assure Quality Control in accordance with ISO/IEC 17025, it was important, from metrological point of view, to examine the long-term stability of calibration standards previously prepared. Comprehensive reconsideration on efficiency curves with respect to the ageing of calibration standards is presented in this paper. The calibration standards were re-used after a period of 5 years and analysis of the results showed discrepancies in efficiency values. Copyright © 2012 Elsevier Ltd. All rights reserved.

Jeans instability of rotating magnetized dusty plasma

NASA Astrophysics Data System (ADS)

Sharma, S.; Sutar, D. L.; Kumar, V.; Pensia, R. K.

2018-05-01

It has been shown that rotation has to play a predominant important role in the formation of many astrophysical objects and the stability of molecular clouds. In this paper the theoretical investigation of the presence of rotation in the magnetized dusty plasma. The general dispersion relation is obtained normal mode analysis technique, and we found the Alfven mode is modified due to the presence of rotation and magnetic field. The graphical presentation shows that rotation and Alfven wave velocity have a stabilizing in the system.

Design, ancillary testing, analysis and fabrication data for the advanced composite stabilizer for Boeing 737 aircraft, volume 2

NASA Technical Reports Server (NTRS)

Aniversario, R. B.; Harvey, S. T.; Mccarty, J. E.; Parsons, J. T.; Peterson, D. C.; Pritchett, L. D.; Wilson, D. R.; Wogulis, E. R.

1982-01-01

Results of tests conducted to demonstrate that composite structures save weight, possess long term durability, and can be fabricated at costs competitive with conventional metal structures are presented with focus on the use of graphite-epoxy in the design of a stabilizer for the Boeing 737 aircraft. Component definition, materials evaluation, material design properties, and structural elements tests are discussed. Fabrication development, as well as structural repair and inspection are also examined.

Integrated analysis on static/dynamic aeroelasticity of curved panels based on a modified local piston theory

NASA Astrophysics Data System (ADS)

Yang, Zhichun; Zhou, Jian; Gu, Yingsong

2014-10-01

A flow field modified local piston theory, which is applied to the integrated analysis on static/dynamic aeroelastic behaviors of curved panels, is proposed in this paper. The local flow field parameters used in the modification are obtained by CFD technique which has the advantage to simulate the steady flow field accurately. This flow field modified local piston theory for aerodynamic loading is applied to the analysis of static aeroelastic deformation and flutter stabilities of curved panels in hypersonic flow. In addition, comparisons are made between results obtained by using the present method and curvature modified method. It shows that when the curvature of the curved panel is relatively small, the static aeroelastic deformations and flutter stability boundaries obtained by these two methods have little difference, while for curved panels with larger curvatures, the static aeroelastic deformation obtained by the present method is larger and the flutter stability boundary is smaller compared with those obtained by the curvature modified method, and the discrepancy increases with the increasing of curvature of panels. Therefore, the existing curvature modified method is non-conservative compared to the proposed flow field modified method based on the consideration of hypersonic flight vehicle safety, and the proposed flow field modified local piston theory for curved panels enlarges the application range of piston theory.

Statical longitudinal stability of airplanes

NASA Technical Reports Server (NTRS)

Warner, Edward P

1921-01-01

This report, which is a continuation of the "Preliminary report on free flight testing" (report no. NACA-TR-70), presents a detailed theoretical analysis of statical stability with free and locked controls and also the results of many free flight test on several types of airplanes. In developing the theory of stability with locked controls an expression for pitching moment is derived in simple terms by considering the total moment as the sum of the moments due to wings and tail surface. This expression, when differentiated with respect to angle of incidence, enables an analysis to be made of the factors contributing to the pitching moment. The effects of slipstream and down wash are also considered and it is concluded that the C. G. Location has but slight effect or stability, and that stability is much improved by increasing the efficiency of the tail surfaces, which may be done by using an "inverted" tail plane. The results of free flight tests with locked controls are discussed at length and it is shown that the agreement between the experimental results and theory is very satisfactory. The theory of stability with free controls is not amendable to the simple mathematical treatment used in the case of locked controls, but a clear statement of the conditions enables several conclusions to be drawn, one of which is that the fixed tail surfaces should be much larger than the movable surfaces.

Amber fossils demonstrate deep-time stability of Caribbean lizard communities

PubMed Central

Sherratt, Emma; del Rosario Castañeda, María; Garwood, Russell J.; Mahler, D. Luke; Sanger, Thomas J.; Herrel, Anthony; de Queiroz, Kevin; Losos, Jonathan B.

2015-01-01

Whether the structure of ecological communities can exhibit stability over macroevolutionary timescales has long been debated. The similarity of independently evolved Anolis lizard communities on environmentally similar Greater Antillean islands supports the notion that community evolution is deterministic. However, a dearth of Caribbean Anolis fossils—only three have been described to date—has precluded direct investigation of the stability of anole communities through time. Here we report on an additional 17 fossil anoles in Dominican amber dating to 15–20 My before the present. Using data collected primarily by X-ray microcomputed tomography (X-ray micro-CT), we demonstrate that the main elements of Hispaniolan anole ecomorphological diversity were in place in the Miocene. Phylogenetic analysis yields results consistent with the hypothesis that the ecomorphs that evolved in the Miocene are members of the same ecomorph clades extant today. The primary axes of ecomorphological diversity in the Hispaniolan anole fauna appear to have changed little between the Miocene and the present, providing evidence for the stability of ecological communities over macroevolutionary timescales. PMID:26216976

Line-of-sight pointing accuracy/stability analysis and computer simulation for small spacecraft

NASA Astrophysics Data System (ADS)

Algrain, Marcelo C.; Powers, Richard M.

1996-06-01

This paper presents a case study where a comprehensive computer simulation is developed to determine the driving factors contributing to spacecraft pointing accuracy and stability. The simulation is implemented using XMATH/SystemBuild software from Integrated Systems, Inc. The paper is written in a tutorial manner and models for major system components are described. Among them are spacecraft bus, attitude controller, reaction wheel assembly, star-tracker unit, inertial reference unit, and gyro drift estimators (Kalman filter). THe predicted spacecraft performance is analyzed for a variety of input commands and system disturbances. The primary deterministic inputs are desired attitude angles and rate setpoints. The stochastic inputs include random torque disturbances acting on the spacecraft, random gyro bias noise, gyro random walk, and star-tracker noise. These inputs are varied over a wide range to determine their effects on pointing accuracy and stability. The results are presented in the form of trade-off curves designed to facilitate the proper selection of subsystems so that overall spacecraft pointing accuracy and stability requirements are met.

Analysis of the postural stability in individuals with or without signs and symptoms of temporomandibular disorder.

PubMed

Ries, Lilian Gerdi Kittel; Bérzin, Fausto

2008-01-01

The objective of this study was to evaluate the stability and the distribution of weight of individuals with TMD (Temporomandibular Disorder) when placed in an orthostatic position. Forty female volunteers, participating in this study, were distributed into a control and a TMD group. Clinical examinations of the craniomandibular system and of the neck were performed. Postural stability was evaluated using a stabilographic platform. Through this system, the sway index (SI), the maximum medial-lateral distance (MMLD), the maximum anterior-posterior distance (MAPD) and the medial-lateral symmetry (MLS) could be determined. Tests were performed in the mandibular rest position and during isometric and isotonic contraction. The variables were analyzed through repeated measures ANOVA. The level of significance was p < 0.05. The results of this study indicate that individuals with TMD present more pain in the cervical region (p < 0.05). The group with TMD showed a significant reduction in SI (p < 0.05), MMLD (p < 0.05) and MLS (p < 0.01). Individuals with TMD presented greater postural asymmetry, and cervical pain demonstrated a potential link with an increase in postural stability.

Stability analysis on an economic epidemiological model with vaccination Pages : - , and.

PubMed

Avusuglo, Wisdom S; Abdella, Kenzu; Feng, Wenying

2017-08-01

In this paper, an economic epidemiological model with vaccination is studied. The stability of the endemic steady-state is analyzed and some bifurcation properties of the system are investigated. It is established that the system exhibits saddle-point and period-doubling bifurcations when adult susceptible individuals are vaccinated. Furthermore, it is shown that susceptible individuals also have the tendency of opting for more number of contacts even if the vaccine is inefficacious and thus causes the disease endemic to increase in the long run. Results from sensitivity analysis with specific disease parameters are also presented. Finally, it is shown that the qualitative behaviour of the system is affected by contact levels.

Lower Limb Kinematics and Dynamic Postural Stability in Anterior Cruciate Ligament-Reconstructed Female Athletes

PubMed Central

Delahunt, Eamonn; Chawke, Mark; Kelleher, Judy; Murphy, Katie; Prendiville, Anna; Sweeny, Lauren; Patterson, Matt

2013-01-01

Context: Deficits in lower limb kinematics and postural stability are predisposing factors to the development of knee ligamentous injury. The extent to which these deficits are present after anterior cruciate ligament (ACL) reconstruction is still largely unknown. The primary hypothesis of the present study was that female athletes who have undergone ACL reconstruction and who have returned to sport participation would exhibit deficits in dynamic postural stability as well as deficiencies in hip- and knee-joint kinematics when compared with an age-, activity-, and sex-matched uninjured control group. Objective: To investigate dynamic postural stability as quantified by the Star Excursion Balance Test (SEBT) and simultaneous hip- and knee-joint kinematic profiles in female athletes who have undergone ACL reconstruction. Design: Descriptive laboratory study. Setting: University motion-analysis laboratory. Patients or Other Participants: Fourteen female athletes who had previously undergone ACL reconstruction (ACL-R) and 17 age- and sex-matched uninjured controls. Intervention(s): Each participant performed 3 trials of the anterior, posterior-medial, and posterior-lateral directional components of the SEBT. Main Outcome Measure(s): Reach distances for each directional component were quantified and expressed as a percentage of leg length. Simultaneous hip- and knee-joint kinematic profiles were recorded using a motion-analysis system. Results: The ACL-R group had decreased reach distances on the posterior-medial (P < .01) and posterior-lateral (P < .01) directional components of the SEBT. During performance of the directional components of the SEBT, ACL-R participants demonstrated altered hip-joint frontal-, sagittal-, and transverse-plane kinematic profiles (P < .05), as well as altered knee-joint sagittal-plane kinematic profiles (P < .05). Conclusions: Deficits in dynamic postural stability and concomitant altered hip- and knee-joint kinematics are present after ACL reconstruction and return to competitive activity. The extent to which these deficits influence potential future injury is worthy of investigation. PMID:23672381

Soliton solutions, stability analysis and conservation laws for the brusselator reaction diffusion model with time- and constant-dependent coefficients

NASA Astrophysics Data System (ADS)

Inc, Mustafa; Yusuf, Abdullahi; Isa Aliyu, Aliyu; Hashemi, M. S.

2018-05-01

This paper studies the brusselator reaction diffusion model (BRDM) with time- and constant-dependent coefficients. The soliton solutions for BRDM with time-dependent coefficients are obtained via first integral (FIM), ansatz, and sine-Gordon expansion (SGEM) methods. Moreover, it is well known that stability analysis (SA), symmetry analysis and conservation laws (CLs) give several information for modelling a system of differential equations (SDE). This is because they can be used for investigating the internal properties, existence, uniqueness and integrability of different SDE. For this reason, we investigate the SA via linear stability technique, symmetry analysis and CLs for BRDM with constant-dependent coefficients in order to extract more physics and information on the governing equation. The constraint conditions for the existence of the solutions are also examined. The new solutions obtained in this paper can be useful for describing the concentrations of diffusion problems of the BRDM. It is shown that the examined dependent coefficients are some of the factors that are affecting the diffusion rate. So, the present paper provides much motivational information in comparison to the existing results in the literature.

String Stability of a Linear Formation Flight Control System

NASA Technical Reports Server (NTRS)

Allen, Michael J.; Ryan, Jack; Hanson, Curtis E.; Parle, James F.

2002-01-01

String stability analysis of an autonomous formation flight system was performed using linear and nonlinear simulations. String stability is a measure of how position errors propagate from one vehicle to another in a cascaded system. In the formation flight system considered here, each i(sup th) aircraft uses information from itself and the preceding ((i-1)(sup th)) aircraft to track a commanded relative position. A possible solution for meeting performance requirements with such a system is to allow string instability. This paper explores two results of string instability and outlines analysis techniques for string unstable systems. The three analysis techniques presented here are: linear, nonlinear formation performance, and ride quality. The linear technique was developed from a worst-case scenario and could be applied to the design of a string unstable controller. The nonlinear formation performance and ride quality analysis techniques both use nonlinear formation simulation. Three of the four formation-controller gain-sets analyzed in this paper were limited more by ride quality than by performance. Formations of up to seven aircraft in a cascaded formation could be used in the presence of light gusts with this string unstable system.

Data Analysis for the NASA/Boeing Hybrid Laminar Flow Control Crossflow Experiment

NASA Technical Reports Server (NTRS)

Eppink, Jenna L.; Wlezien, Richard

2011-01-01

The Hybrid-Laminar Flow Control (HLFC) Crossflow Experiment, completed in 1995. generated a large database of boundary layer stability and transition data that was only partially analyzed before data analysis was abruptly ended in the late 1990's. Renewed interest in laminar flow technologies prompted additional data analysis, to integrate all data, including some post-test roughness and porosity measurements. The objective is to gain new insights into the effects of suction on boundary layer stability. A number of challenges were encountered during the data analysis, and their solutions are discussed in detail. They include the effect of the probe vibration, the effect of the time-varying surface temperature on traveling crossflow instabilities, and the effect of the stationary crossflow modes on the approximation of wall location. Despite the low turbulence intensity of the wind tunnel (0.01 to 0.02%), traveling crosflow disturbances were present in the data, in some cases at amplitudes up to 1% of the freestream velocity. However, the data suggests that transition was dominated by stationary crossflow. Traveling crossflow results and stationary data in the presence of suction are compared with linear parabolized stability equations results as a way of testing the quality of the results.

Particle circulation and solids transport in large bubbling fluidized beds. Progress report

DOE Office of Scientific and Technical Information (OSTI.GOV)

Homsy, G.M.

1982-04-01

We have undertaken a theoretical study of the possibility of the formation of plumes or channeling when coal particles volatilize upon introduction to a fluidized bed, Fitzgerald (1980). We have completed the analysis of the basic state of uniform flow and are currently completing a stability analysis. We have modified the continuum equations of fluidization, Homsy et al. (1980), to include the source of gas due to volatilization, which we assume to be uniformly distributed spatially. Simplifying these equations and solving leads to the prediction of a basic state analogous to the state of uniform fluidization found when no sourcemore » is present within the medium. We are currently completing a stability analysis of this basic state which will give the critical volatilization rate above which the above simple basic state is unstable. Because of the experimental evidence of Jewett and Lawless (1981), who observed regularly spaced plume-like instabilities upon drying a bed of saturated silica gel, we are considering two-dimensional periodic disturbances. The analysis is similar to that given by Homsy, et al. (1980) and Medlin et al. (1974). We hope to determine the stability limits for this system shortly.« less

Hard-Rock Stability Analysis for Span Design in Entry-Type Excavations with Learning Classifiers

PubMed Central

García-Gonzalo, Esperanza; Fernández-Muñiz, Zulima; García Nieto, Paulino José; Bernardo Sánchez, Antonio; Menéndez Fernández, Marta

2016-01-01

The mining industry relies heavily on empirical analysis for design and prediction. An empirical design method, called the critical span graph, was developed specifically for rock stability analysis in entry-type excavations, based on an extensive case-history database of cut and fill mining in Canada. This empirical span design chart plots the critical span against rock mass rating for the observed case histories and has been accepted by many mining operations for the initial span design of cut and fill stopes. Different types of analysis have been used to classify the observed cases into stable, potentially unstable and unstable groups. The main purpose of this paper is to present a new method for defining rock stability areas of the critical span graph, which applies machine learning classifiers (support vector machine and extreme learning machine). The results show a reasonable correlation with previous guidelines. These machine learning methods are good tools for developing empirical methods, since they make no assumptions about the regression function. With this software, it is easy to add new field observations to a previous database, improving prediction output with the addition of data that consider the local conditions for each mine. PMID:28773653

Hard-Rock Stability Analysis for Span Design in Entry-Type Excavations with Learning Classifiers.

PubMed

García-Gonzalo, Esperanza; Fernández-Muñiz, Zulima; García Nieto, Paulino José; Bernardo Sánchez, Antonio; Menéndez Fernández, Marta

2016-06-29

The mining industry relies heavily on empirical analysis for design and prediction. An empirical design method, called the critical span graph, was developed specifically for rock stability analysis in entry-type excavations, based on an extensive case-history database of cut and fill mining in Canada. This empirical span design chart plots the critical span against rock mass rating for the observed case histories and has been accepted by many mining operations for the initial span design of cut and fill stopes. Different types of analysis have been used to classify the observed cases into stable, potentially unstable and unstable groups. The main purpose of this paper is to present a new method for defining rock stability areas of the critical span graph, which applies machine learning classifiers (support vector machine and extreme learning machine). The results show a reasonable correlation with previous guidelines. These machine learning methods are good tools for developing empirical methods, since they make no assumptions about the regression function. With this software, it is easy to add new field observations to a previous database, improving prediction output with the addition of data that consider the local conditions for each mine.

Bifurcation and Stability Analysis of the Equilibrium States in Thermodynamic Systems in a Small Vicinity of the Equilibrium Values of Parameters

NASA Astrophysics Data System (ADS)

Barsuk, Alexandr A.; Paladi, Florentin

2018-04-01

The dynamic behavior of thermodynamic system, described by one order parameter and one control parameter, in a small neighborhood of ordinary and bifurcation equilibrium values of the system parameters is studied. Using the general methods of investigating the branching (bifurcations) of solutions for nonlinear equations, we performed an exhaustive analysis of the order parameter dependences on the control parameter in a small vicinity of the equilibrium values of parameters, including the stability analysis of the equilibrium states, and the asymptotic behavior of the order parameter dependences on the control parameter (bifurcation diagrams). The peculiarities of the transition to an unstable state of the system are discussed, and the estimates of the transition time to the unstable state in the neighborhood of ordinary and bifurcation equilibrium values of parameters are given. The influence of an external field on the dynamic behavior of thermodynamic system is analyzed, and the peculiarities of the system dynamic behavior are discussed near the ordinary and bifurcation equilibrium values of parameters in the presence of external field. The dynamic process of magnetization of a ferromagnet is discussed by using the general methods of bifurcation and stability analysis presented in the paper.

Spectral analysis of point-vortex dynamics: first application to vortex polygons in a circular domain

NASA Astrophysics Data System (ADS)

Speetjens, M. F. M.; Meleshko, V. V.; van Heijst, G. J. F.

2014-06-01

The present study addresses the classical problem of the dynamics and stability of a cluster of N-point vortices of equal strength arranged in a polygonal configuration (‘N-vortex polygons’). In unbounded domains, such N-vortex polygons are unconditionally stable for N\\leqslant 7. Confinement in a circular domain tightens the stability conditions to N\\leqslant 6 and a maximum polygon size relative to the domain radius. This work expands on existing studies on stability and integrability by a first giving an exploratory spectral analysis of the dynamics of N vortex polygons in circular domains. Key to this is that the spectral signature of the time evolution of vortex positions reflects their qualitative behaviour. Expressing vortex motion by a generic evolution operator (the so-called Koopman operator) provides a rigorous framework for such spectral analyses. This paves the way to further differentiation and classification of point-vortex behaviour beyond stability and integrability. The concept of Koopman-based spectral analysis is demonstrated for N-vortex polygons. This reveals that conditional stability can be seen as a local form of integrability and confirms an important generic link between spectrum and dynamics: discrete spectra imply regular (quasi-periodic) motion; continuous (sub-)spectra imply chaotic motion. Moreover, this exposes rich nonlinear dynamics as intermittency between regular and chaotic motion and quasi-coherent structures formed by chaotic vortices. Dedicated to the memory of Slava Meleshko, a dear friend and inspiring colleague.

A general MHD formulation for plasmas with flow and resistive walls

DOE Office of Scientific and Technical Information (OSTI.GOV)

Guazzotto, L.; Freidberg, J. P.; Betti, R.

2006-11-30

Toroidal rotation, either induced by means of neutral beams (e.g. in NSTX and DIII-D) or appearing spontaneously (e.g. in Alcator C-Mod, JET and Tore Supra) is routinely observed in modem tokamak experiments. Poloidal rotation is also commonly observed, in particular in the edge region of the plasma. Plasma rotation has a major effect on plasma stability. Flow and flow shear stabilize external modes such as the resistive wall mode (as observed e.g. in DIII-D), suppress turbulence when the flow shear is large enough, and also have a significant influence on the stability and nonlinear evolution of the internal kink andmore » ballooning modes. Flow shear can in particular have both a stabilizing (by breaking up unstable structures) and destabilizing (through the Kelvin-Helmoltz mechanism) effect. A self-consistent analysis of the effect of rotation requires the use of numerical tools. In this work, we present a general eigenvalue formulation based on a variational principle stability analysis, including arbitrary (both toroidal and poloidal) plasma rotation and a thin resistive wall of arbitrary shape and resistivity. It is shown that the problem can always be reduced to a classic eigenvalue formulation of the kind i{omega}A double underbar {center_dot} {zeta}-vector = B double underbar {center_dot} {zeta}-vector, where {zeta}-vector is the unknown eigenvector related to the plasma displacement, and {omega} the (complex) evolution frequency of the perturbation. The formulation is well suited for a finite element analysis.« less

Stability and adaptability of soybean cultivars in Minas Gerais.

PubMed

Soares, I O; Bruzi, A T; Zambiazzi, E V; Guilherme, S R; Bianchi, M C; Silva, K B; Fronza, V; Teixeira, C M

2017-08-17

Genotypes x environment (G x E) interaction consists of different behavior of genotypes cultivated in different environments. This interaction occurs due to the performance variation of each genotype in different environments. To reduce the effect of the interaction in soybean crops, some studies have been reported in the literature to study their adaptability and stability. However, these studies are still scarce in Minas Gerais State. Thus, the aim of this study was to verify the adaptability and stability of soybean cultivars and identify the cultivars that contribute least to the G x E interaction in Minas Gerais. Six soybean cultivars were evaluated in 9 different environments. The plots were composed of 4 rows of 5 m with a spacing of 0.5 m between rows, and only the two central rows were harvested. The inoculation with Bradyrhizobium japonicum was performed through sowing furrow. The fertilization followed the recommendations of the Soil Fertility Commission of Minas Gerais. Grain yield was evaluated in kg/ha after conversion to 13% moisture. After individual analysis, the joint analysis was performed by grouping the phenotypic means by the Scott and Knott (1974) test. Wricke's ecovalence methodologies and the Annicchiarico confidence index were applied for the adaptability and stability analysis. The interaction was decomposed into a simple and a complex part. The cultivars BRSMG 820RR and BRSMG 760SRR have wide adaptability and stability. The first one presents a better index of confidence and a small contribution to the interaction.

DC Microgrids–Part I: A Review of Control Strategies and Stabilization Techniques

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dragicevic, Tomislav; Lu, Xiaonan; Vasquez, Juan

2015-01-01

This paper presents a review of control strategies, stability analysis, and stabilization techniques for dc microgrids (MGs). Overall control is systematically classified into local and coordinated control levels according to respective functionalities in each level. As opposed to local control, which relies only on local measurements, some line of communication between units needs to be made available in order to achieve the coordinated control. Depending on the communication method, three basic coordinated control strategies can be distinguished, i.e., decentralized, centralized, and distributed control. Decentralized control can be regarded as an extension of the local control since it is also basedmore » exclusively on local measurements. In contrast, centralized and distributed control strategies rely on digital communication technologies. A number of approaches using these three coordinated control strategies to achieve various control objectives are reviewed in this paper. Moreover, properties of dc MG dynamics and stability are discussed. This paper illustrates that tightly regulated point-of-load converters tend to reduce the stability margins of the system since they introduce negative impedances, which can potentially oscillate with lightly damped power supply input filters. It is also demonstrated that how the stability of the whole system is defined by the relationship of the source and load impedances, referred to as the minor loop gain. Several prominent specifications for the minor loop gain are reviewed. Finally, a number of active stabilization techniques are presented.« less

An assessment of the mechanical stability of wells offshore Nigeria

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lowrey, J.P.; Ottesen, S.

In 1991 lost time due to stuck pipe related drilling problems accounted for approximately 18% of total drilling time in Mobil Producing Nigeria Ultd.`s (MPN) offshore operations. The primary cause of stuck pipe was identified as mechanical wellbore instability. This paper presents an assessment of the mechanical stability of MPN`s wells offshore Nigeria. The objectives of the study were to: (1) determine the magnitude of the in-situ principal stresses and material properties of the troublesome Intra-Biafra and Qua Iboe shale sequences; (2) quantify the drilling fluid densities required to drill mechanically stable wells through these formations; (3) review and recommendmore » well planning and operational parameters which aid in minimizing wellbore stability-related drilling problems. The well-bore stability assessment was carried out with the aid of a 3-dimensional wellbore stability model using field derived data from the study area to corroborate the results. The collection and analysis of drilling data (borehole geometry and density logs, pore pressure, leak-off tests, local geology and other relevant well records) to determine the magnitude of the in-situ principal stresses, together with compressive strength tests on formation cores are discussed. Minimum safe drilling fluid densities to promote wellbore stability as a function of well geometry and depth are presented for the most troublesome shales drilled in the study area. Implementation of the results reduced wellbore stability related problems and associated trouble time to less than 5% in 1992.« less

Stability of the alcohol use disorders identification test in practical service settings

PubMed Central

Sahker, Ethan; Lancianese, Donna A; Arndt, Stephan

2017-01-01

Objective The purpose of the present study is to explore the stability of the Alcohol Use Disorders Identification Test (AUDIT) in a clinical setting by comparing prescreening heavy drinking questions and AUDIT scores over time. Because instrument stability is equal to test–retest reliability at worst, investigating the stability of the AUDIT would help better understand patient behavior change in context and the appropriateness of the AUDIT in a clinical setting. Methods This was a retrospective exploratory analysis of Visit 1 to Visit 2 AUDIT stability (n=1,099; male [75.4%], female [24.6%]) from all patients with first-time and second-time records in the Iowa Screening, Brief Intervention, and Referral to Treatment project, October 2012 to July 7, 2015 (N=17,699; male [40.6%], female [59.4%]). Results The AUDIT demonstrated moderate stability (intraclass correlation=0.56, 95% confidence interval: 0.52–0.60). In a multiple regression predicting the (absolute) difference between the two AUDIT scores, the participants’ age was highly significant, t(1,092)=6.23, p<0.001. Younger participants clearly showed less stability than their older counterparts. Results are limited/biased by the observational nature of the study design and the use of clinical service data. Conclusion The present findings contribute to the literature by demonstrating that the AUDIT changes are moderately dependable from Visit 1 to Visit 2 while taking into account patient drinking behavior variability. It is important to know the stability of the AUDIT for continued use in Screening, Brief Intervention, and Referral to Treatment programming. PMID:28392719

Use of a 90° drill and screwdriver for rib fracture stabilization.

PubMed

Nickerson, Terry P; Kim, Brian D; Zielinski, Martin D; Jenkins, Donald; Schiller, Henry J

2015-03-01

Rib fracture stabilization has become a more accepted practice although stabilization of the most cephalad ribs presents a unique challenge. We present our experience with use of a 90° drill and screwdriver to bridge these difficult rib fractures. This retrospective review included patients who underwent rib fracture stabilization from August 1, 2009, through September 30, 2012. Patients were divided into two groups: those whose procedure used the 90° device and those that did not. Data were compared using standard statistical analysis and reported as percentages and medians [interquartile ranges]. P values <0.05 were considered significant. We identified 89 patients: 29 (33%) had 90° devices used and 60 (67%) did not. There were no differences between groups in age, sex, Trauma-Related Injury Severity Score, the presence of flail chest, occurrence of pneumonia, and intensive care unit or hospital length of stay. The Injury Severity Score was higher in the 90° group (22 vs. 16; P = 0.03). The highest rib stabilized was different between the 2 groups (3 [2-5] vs. 5 [2-9]; P = 0.001), with more third rib stabilizations in the 90° group (38 vs. 20%; P = 0.04) as well as more total number of ribs fixed (5 vs. 4; P = 0.001). There was no difference in operative time between the 2 groups. The surgical reach for rib fracture stabilization has been extended with use of a 90° drill and screwdriver. High fractures under the scapula where access is technically challenging can be stabilized without prolonging operative times.

Stability of the alcohol use disorders identification test in practical service settings.

PubMed

Sahker, Ethan; Lancianese, Donna A; Arndt, Stephan

2017-01-01

The purpose of the present study is to explore the stability of the Alcohol Use Disorders Identification Test (AUDIT) in a clinical setting by comparing prescreening heavy drinking questions and AUDIT scores over time. Because instrument stability is equal to test-retest reliability at worst, investigating the stability of the AUDIT would help better understand patient behavior change in context and the appropriateness of the AUDIT in a clinical setting. This was a retrospective exploratory analysis of Visit 1 to Visit 2 AUDIT stability (n=1,099; male [75.4%], female [24.6%]) from all patients with first-time and second-time records in the Iowa Screening, Brief Intervention, and Referral to Treatment project, October 2012 to July 7, 2015 (N=17,699; male [40.6%], female [59.4%]). The AUDIT demonstrated moderate stability (intraclass correlation=0.56, 95% confidence interval: 0.52-0.60). In a multiple regression predicting the (absolute) difference between the two AUDIT scores, the participants' age was highly significant, t (1,092)=6.23, p <0.001. Younger participants clearly showed less stability than their older counterparts. Results are limited/biased by the observational nature of the study design and the use of clinical service data. The present findings contribute to the literature by demonstrating that the AUDIT changes are moderately dependable from Visit 1 to Visit 2 while taking into account patient drinking behavior variability. It is important to know the stability of the AUDIT for continued use in Screening, Brief Intervention, and Referral to Treatment programming.

Analysis and test evaluation of the dynamic response and stability of three advanced turboprop models

NASA Technical Reports Server (NTRS)

Bansal, P. N.; Arseneaux, P. J.; Smith, A. F.; Turnberg, J. E.; Brooks, B. M.

1985-01-01

Results of dynamic response and stability wind tunnel tests of three 62.2 cm (24.5 in) diameter models of the Prop-Fan, advanced turboprop, are presented. Measurements of dynamic response were made with the rotors mounted on an isolated nacelle, with varying tilt for nonuniform inflow. One model was also tested using a semi-span wing and fuselage configuration for response to realistic aircraft inflow. Stability tests were performed using tunnel turbulence or a nitrogen jet for excitation. Measurements are compared with predictions made using beam analysis methods for the model with straight blades, and finite element analysis methods for the models with swept blades. Correlations between measured and predicted rotating blade natural frequencies for all the models are very good. The IP dynamic response of the straight blade model is reasonably well predicted. The IP response of the swept blades is underpredicted and the wing induced response of the straight blade is overpredicted. Two models did not flutter, as predicted. One swept blade model encountered an instability at a higher RPM than predicted, showing predictions to be conservative.

Simulation and stability analysis of supersonic impinging jet noise with microjet control

NASA Astrophysics Data System (ADS)

Hildebrand, Nathaniel; Nichols, Joseph W.

2014-11-01

A model for an ideally expanded 1.5 Mach turbulent jet impinging on a flat plate using unstructured high-fidelity large eddy simulations (LES) and hydrodynamic stability analysis is presented. Note the LES configuration conforms exactly to experiments performed at the STOVL supersonic jet facility of the Florida Center for Advanced Aero-Propulsion allowing validation against experimental measurements. The LES are repeated for different nozzle-wall separation distances as well as with and without the addition of sixteen microjets positioned uniformly around the nozzle lip. For some nozzle-wall distances, but not all, the microjets result in substantial noise reduction. Observations of substantial noise reduction are associated with a relative absence of large-scale coherent vortices in the jet shear layer. To better understand and predict the effectiveness of microjet noise control, the application of global stability analysis about LES mean fields is used to extract axisymmetric and helical instability modes connected to the complex interplay between the coherent vortices, shocks, and acoustic feedback. We gratefully acknowledge computational resources provided by the Argonne Leadership Computing Facility.

Conceptual Analysis of System Average Water Stability

NASA Astrophysics Data System (ADS)

Zhang, H.

2016-12-01

Averaging over time and area, the precipitation in an ecosystem (SAP - system average precipitation) depends on the average surface temperature and relative humidity (RH) in the system if uniform convection is assumed. RH depends on the evapotranspiration of the system (SAE - system average evapotranspiration). There is a non-linear relationship between SAP and SAE. Studying this relationship can lead mechanistic understanding of the ecosystem health status and trend under different setups. If SAP is higher than SAE, the system will have a water runoff which flows out through rivers. If SAP is lower than SAE, irrigation is needed to maintain the vegetation status. This presentation will give a conceptual analysis of the stability in this relationship under different assumed areas, water or forest coverages, elevations and latitudes. This analysis shows that desert is a stable system. Water circulation in basins is also stabilized at a specific SAP based on the basin profile. It further shows that deforestation will reduce SAP, and can flip the system to an irrigation required status. If no irrigation is provided, the system will automatically reduce to its stable point - desert, which is extremely difficult to turn around.

A novel NOTCH3 mutation identified in patients with oral cancer by whole exome sequencing.

PubMed

Yi, Yanjun; Tian, Zhuowei; Ju, Houyu; Ren, Guoxin; Hu, Jingzhou

2017-06-01

Oral cancer is a serious disease caused by environmental factors and/or susceptible genes. In the present study, in order to identify useful genetic biomarkers for cancer prediction and prevention, and for personalized treatment, we detected somatic mutations in 5 pairs of oral cancer tissues and blood samples using whole exome sequencing (WES). Finally, we confirmed a novel nonsense single-nucleotide polymorphism (SNP; chr19:15288426A>C) in the NOTCH3 gene with sanger sequencing, which resulted in a N1438T mutation in the protein sequence. Using multiple in silico analyses, this variant was found to mildly damaging effects on the NOTCH3 gene, which was supported by the results from analyses using PANTHER, SNAP and SNPs&GO. However, further analysis using Mutation Taster revealed that this SNP had a probability of 0.9997 to be 'disease causing'. In addition, we performed 3D structure simulation analysis and the results suggested that this variant had little effect on the solubility and hydrophobicity of the protein and thus on its function; however, it decreased the stability of the protein by increasing the total energy following minimization (-1,051.39 kcal/mol for the mutant and -1,229.84 kcal/mol for the native) and decreasing one stabilizing residue of the protein. Less stability of the N1438T mutant was also supported by analysis using I-Mutant with a DDG value of -1.67. Overall, the present study identified and confirmed a novel mutation in the NOTCH3 gene, which may decrease the stability of NOTCH3, and may thus prove to be helpful in cancer prognosis.

Design of Launch Vehicle Flight Control Augmentors and Resulting Flight Stability and Control (Center Director's Discretionary Fund Project 93-05, Part III)

NASA Technical Reports Server (NTRS)

Barret, C.

1997-01-01

This publication presents the control requirements, the details of the designed Flight Control Augmentor's (FCA's), the static stability and dynamic stability wind tunnel test programs, the static stability and control analyses, the dynamic stability characteristics of the experimental Launch Vehicle (LV) with the designed FCA's, and a consideration of the elastic vehicle. Dramatic improvements in flight stability have been realized with all the FCA designs; these ranged from 41 percent to 72 percent achieved by the blunt TE design. The control analysis showed that control increased 110 percent with only 3 degrees of FCA deflection. The dynamic stability results showed improvements with all FCA designs tested at all Mach numbers tested. The blunt TE FCA's had the best overall dynamic stability results. Since the lowest elastic vehicle frequency must be well separated from that of the control system, the significant frequencies and modes of vibration have been identified, and the response spectra compared for the experimental LV in both the conventional and the aft cg configuration. Although the dynamic response was 150 percent greater in the aft cg configuration, the lowest bending mode frequency decreased by only 2.8 percent.

A Physics-Based Temperature Stabilization Criterion for Thermal Testing

NASA Technical Reports Server (NTRS)

Rickman, Steven L.; Ungar, Eugene K.

2009-01-01

Spacecraft testing specifications differ greatly in the criteria they specify for stability in thermal balance tests. Some specify a required temperature stabilization rate (the change in temperature per unit time, dT/dt), some specify that the final steady-state temperature be approached to within a specified difference, delta T , and some specify a combination of the two. The particular values for temperature stabilization rate and final temperature difference also vary greatly between specification documents. A one-size-fits-all temperature stabilization rate requirement does not yield consistent results for all test configurations because of differences in thermal mass and heat transfer to the environment. Applying a steady-state temperature difference requirement is problematic because the final test temperature is not accurately known a priori, especially for powered configurations. In the present work, a simplified, lumped-mass analysis has been used to explore the applicability of these criteria. A new, user-friendly, physics-based approach is developed that allows the thermal engineer to determine when an acceptable level of temperature stabilization has been achieved. The stabilization criterion can be predicted pre-test but must be refined during test to allow verification that the defined level of temperature stabilization has been achieved.

Nonlinear Slewing Spacecraft Control Based on Exergy, Power Flow, and Static and Dynamic Stability

NASA Astrophysics Data System (ADS)

Robinett, Rush D.; Wilson, David G.

2009-10-01

This paper presents a new nonlinear control methodology for slewing spacecraft, which provides both necessary and sufficient conditions for stability by identifying the stability boundaries, rigid body modes, and limit cycles. Conservative Hamiltonian system concepts, which are equivalent to static stability of airplanes, are used to find and deal with the static stability boundaries: rigid body modes. The application of exergy and entropy thermodynamic concepts to the work-rate principle provides a natural partitioning through the second law of thermodynamics of power flows into exergy generator, dissipator, and storage for Hamiltonian systems that is employed to find the dynamic stability boundaries: limit cycles. This partitioning process enables the control system designer to directly evaluate and enhance the stability and performance of the system by balancing the power flowing into versus the power dissipated within the system subject to the Hamiltonian surface (power storage). Relationships are developed between exergy, power flow, static and dynamic stability, and Lyapunov analysis. The methodology is demonstrated with two illustrative examples: (1) a nonlinear oscillator with sinusoidal damping and (2) a multi-input-multi-output three-axis slewing spacecraft that employs proportional-integral-derivative tracking control with numerical simulation results.

Analysis of airframe/engine interactions in integrated flight and propulsion control

NASA Technical Reports Server (NTRS)

Schierman, John D.; Schmidt, David K.

1991-01-01

An analysis framework for the assessment of dynamic cross-coupling between airframe and engine systems from the perspective of integrated flight/propulsion control is presented. This analysis involves to determining the significance of the interactions with respect to deterioration in stability robustness and performance, as well as critical frequency ranges where problems may occur due to these interactions. The analysis illustrated here investigates both the airframe's effects on the engine control loops and the engine's effects on the airframe control loops in two case studies. The second case study involves a multi-input/multi-output analysis of the airframe. Sensitivity studies are performed on critical interactions to examine the degradations in the system's stability robustness and performance. Magnitudes of the interactions required to cause instabilities, as well as the frequencies at which the instabilities occur are recorded. Finally, the analysis framework is expanded to include control laws which contain cross-feeds between the airframe and engine systems.

Adaptive Flight Control for Aircraft Safety Enhancements

NASA Technical Reports Server (NTRS)

Nguyen, Nhan T.; Gregory, Irene M.; Joshi, Suresh M.

2008-01-01

This poster presents the current adaptive control research being conducted at NASA ARC and LaRC in support of the Integrated Resilient Aircraft Control (IRAC) project. The technique "Approximate Stability Margin Analysis of Hybrid Direct-Indirect Adaptive Control" has been developed at NASA ARC to address the needs for stability margin metrics for adaptive control that potentially enables future V&V of adaptive systems. The technique "Direct Adaptive Control With Unknown Actuator Failures" is developed at NASA LaRC to deal with unknown actuator failures. The technique "Adaptive Control with Adaptive Pilot Element" is being researched at NASA LaRC to investigate the effects of pilot interactions with adaptive flight control that can have implications of stability and performance.

Stability of Capillary Surfaces in Rectangular Containers: The Right Square Cylinder

NASA Technical Reports Server (NTRS)

Weislogel, M. M.; Hsieh, K. C.

1998-01-01

The linearized governing equations for an ideal fluid are presented for numerical analysis for the stability of free capillary surfaces in rectangular containers against unfavorable disturbances (accelerations,i.e. Rayleigh-Taylor instability). The equations are solved for the case of the right square cylinder. The results are expressed graphically in term of a critical Bond number as a function of system contact angle. A critical wetting phenomena in the corners is shown to significantly alter the region of stability for such containers in contrast to simpler geometries such as the right circular cylinder or the infinite rectangular slot. Such computational results provide additional constraints for the design of fluids systems for space-based applications.

Global stability and periodic solution of the viral dynamics

NASA Astrophysics Data System (ADS)

Song, Xinyu; Neumann, Avidan U.

2007-05-01

It is well known that the mathematical models provide very important information for the research of human immunodeficiency virus-type 1 and hepatitis C virus (HCV). However, the infection rate of almost all mathematical models is linear. The linearity shows the simple interaction between the T cells and the viral particles. In this paper, we consider the classical mathematical model with saturation response of the infection rate. By stability analysis we obtain sufficient conditions on the parameters for the global stability of the infected steady state and the infection-free steady state. We also obtain the conditions for the existence of an orbitally asymptotically stable periodic solution. Numerical simulations are presented to illustrate the results.

Numerical stability of an explicit finite difference scheme for the solution of transient conduction in composite media

NASA Technical Reports Server (NTRS)

Campbell, W.

1981-01-01

A theoretical evaluation of the stability of an explicit finite difference solution of the transient temperature field in a composite medium is presented. The grid points of the field are assumed uniformly spaced, and media interfaces are either vertical or horizontal and pass through grid points. In addition, perfect contact between different media (infinite interfacial conductance) is assumed. A finite difference form of the conduction equation is not valid at media interfaces; therefore, heat balance forms are derived. These equations were subjected to stability analysis, and a computer graphics code was developed that permitted determination of a maximum time step for a given grid spacing.

NASTRAN/FLEXSTAB procedure for static aeroelastic analysis

NASA Technical Reports Server (NTRS)

Schuster, L. S.

1984-01-01

Presented is a procedure for using the FLEXSTAB External Structural Influence Coefficients (ESIC) computer program to produce the structural data necessary for the FLEXSTAB Stability Derivatives and Static Stability (SD&SS) program. The SD&SS program computes trim state, stability derivatives, and pressure and deflection data for a flexible airplane having a plane of symmetry. The procedure used a NASTRAN finite-element structural model as the source of structural data in the form of flexibility matrices. Selection of a set of degrees of freedom, definition of structural nodes and panels, reordering and reformatting of the flexibility matrix, and redistribution of existing point mass data are among the topics discussed. Also discussed are boundary conditions and the NASTRAN substructuring technique.

Recent Advances in Heliogyro Solar Sail Structural Dynamics, Stability, and Control Research

NASA Technical Reports Server (NTRS)

Wilkie, W. Keats; Warren, Jerry E.; Horta, Lucas G.; Lyle, Karen H.; Juang, Jer-Nan; Gibbs, S. Chad; Dowell, Earl H.; Guerrant, Daniel V.; Lawrence, Dale

2015-01-01

Results from recent NASA sponsored research on the structural dynamics, stability, and control characteristics of heliogyro solar sails are summarized. Specific areas under investigation include coupled nonlinear finite element analysis of heliogyro membrane blade with solar radiation pressure effects, system identification of spinning membrane structures, and solarelastic stability analysis of heliogyro solar sails, including stability during blade deployment. Recent results from terrestrial 1-g blade dynamics and control experiments on "rope ladder" membrane blade analogs, and small-scale in vacuo system identification experiments with hanging and spinning high-aspect ratio membranes will also be presented. A low-cost, rideshare payload heliogyro technology demonstration mission concept is used as a mission context for these heliogyro structural dynamics and solarelasticity investigations, and is also described. Blade torsional dynamic response and control are also shown to be significantly improved through the use of edge stiffening structural features or inclusion of modest tip masses to increase centrifugal stiffening of the blade structure. An output-only system identification procedure suitable for on-orbit blade dynamics investigations is also developed and validated using ground tests of spinning sub-scale heliogyro blade models. Overall, analytical and experimental investigations to date indicate no intractable stability or control issues for the heliogyro solar sail concept.

Hypoxia-inducible factor stabilizers and other small-molecule erythropoiesis-stimulating agents in current and preventive doping analysis.

PubMed

Beuck, Simon; Schänzer, Wilhelm; Thevis, Mario

2012-11-01

Increasing the blood's capacity for oxygen transport by erythropoiesis-stimulating agents (ESAs) constitutes a prohibited procedure of performance enhancement according to the World Anti-Doping Agency (WADA). The advent of orally bio-available small-molecule ESAs such as hypoxia-inducible factor (HIF) stabilizers in the development of novel anti-anaemia therapies expands the list of potential ESA doping techniques. Here, the erythropoiesis-stimulating properties and doping relevance of experimental HIF-stabilizers, such as cobaltous chloride, 3,4-dihydroxybenzoic acid or GSK360A, amongst others, are discussed. The stage of clinical trials is reviewed for the anti-anaemia drug candidates FG-2216, FG-4592, GSK1278863, AKB-6548, and BAY85-3934. Currently available methods and strategies for the determination of selected HIF stabilizers in sports drug testing are based on liquid chromatography-electrospray ionization-tandem mass spectrometry (LC-ESI-MS/MS). For the support of further analytical assay development, patents claiming distinct compounds for the use in HIF-mediated therapies are evaluated and exemplary molecular structures of HIF stabilizers presented. Moreover, data concerning the erythropoiesis-enhancing effects of the GATA inhibitors K7174 and K11706 as well as the lipidic small-molecule ESA PBI-1402 are elucidated the context of doping analysis. Copyright © 2012 John Wiley & Sons, Ltd.

Quantitative Analysis of Electrochemical and Electrode Stability with Low Self-Discharge Lithium-Sulfur Batteries

DOE PAGES

Chung, Sheng-Heng; Han, Pauline; Manthiram, Arumugam

2017-06-07

The viability of employing high-capacity sulfur cathodes in building high-energy-density lithium-sulfur batteries is limited by rapid self-discharge, short shelf life, and severe structural degradation during cell resting (static instability). Unfortunately, the static instability has largely been ignored in the literature. We present in this letter a longterm self-discharge study by quantitatively analyzing the control lithium-sulfur batteries with a conventional cathode configuration, which provides meaningful insights into the cathode failure mechanisms during resting. Lastly, utilizing the understanding obtained with the control cells, we design and present low self-discharge (LSD) lithium-sulfur batteries for investigating the long-term self-discharge effect and electrode stability.

Quantitative Analysis of Electrochemical and Electrode Stability with Low Self-Discharge Lithium-Sulfur Batteries

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chung, Sheng-Heng; Han, Pauline; Manthiram, Arumugam

The viability of employing high-capacity sulfur cathodes in building high-energy-density lithium-sulfur batteries is limited by rapid self-discharge, short shelf life, and severe structural degradation during cell resting (static instability). Unfortunately, the static instability has largely been ignored in the literature. We present in this letter a longterm self-discharge study by quantitatively analyzing the control lithium-sulfur batteries with a conventional cathode configuration, which provides meaningful insights into the cathode failure mechanisms during resting. Lastly, utilizing the understanding obtained with the control cells, we design and present low self-discharge (LSD) lithium-sulfur batteries for investigating the long-term self-discharge effect and electrode stability.

Formal Solutions for Polarized Radiative Transfer. III. Stiffness and Instability

NASA Astrophysics Data System (ADS)

Janett, Gioele; Paganini, Alberto

2018-04-01

Efficient numerical approximation of the polarized radiative transfer equation is challenging because this system of ordinary differential equations exhibits stiff behavior, which potentially results in numerical instability. This negatively impacts the accuracy of formal solvers, and small step-sizes are often necessary to retrieve physical solutions. This work presents stability analyses of formal solvers for the radiative transfer equation of polarized light, identifies instability issues, and suggests practical remedies. In particular, the assumptions and the limitations of the stability analysis of Runge–Kutta methods play a crucial role. On this basis, a suitable and pragmatic formal solver is outlined and tested. An insightful comparison to the scalar radiative transfer equation is also presented.

Differential geometry based solvation model I: Eulerian formulation

NASA Astrophysics Data System (ADS)

Chen, Zhan; Baker, Nathan A.; Wei, G. W.

2010-11-01

This paper presents a differential geometry based model for the analysis and computation of the equilibrium property of solvation. Differential geometry theory of surfaces is utilized to define and construct smooth interfaces with good stability and differentiability for use in characterizing the solvent-solute boundaries and in generating continuous dielectric functions across the computational domain. A total free energy functional is constructed to couple polar and nonpolar contributions to the solvation process. Geometric measure theory is employed to rigorously convert a Lagrangian formulation of the surface energy into an Eulerian formulation so as to bring all energy terms into an equal footing. By optimizing the total free energy functional, we derive coupled generalized Poisson-Boltzmann equation (GPBE) and generalized geometric flow equation (GGFE) for the electrostatic potential and the construction of realistic solvent-solute boundaries, respectively. By solving the coupled GPBE and GGFE, we obtain the electrostatic potential, the solvent-solute boundary profile, and the smooth dielectric function, and thereby improve the accuracy and stability of implicit solvation calculations. We also design efficient second-order numerical schemes for the solution of the GPBE and GGFE. Matrix resulted from the discretization of the GPBE is accelerated with appropriate preconditioners. An alternative direct implicit (ADI) scheme is designed to improve the stability of solving the GGFE. Two iterative approaches are designed to solve the coupled system of nonlinear partial differential equations. Extensive numerical experiments are designed to validate the present theoretical model, test computational methods, and optimize numerical algorithms. Example solvation analysis of both small compounds and proteins are carried out to further demonstrate the accuracy, stability, efficiency and robustness of the present new model and numerical approaches. Comparison is given to both experimental and theoretical results in the literature.

Differential geometry based solvation model I: Eulerian formulation

PubMed Central

Chen, Zhan; Baker, Nathan A.; Wei, G. W.

2010-01-01

This paper presents a differential geometry based model for the analysis and computation of the equilibrium property of solvation. Differential geometry theory of surfaces is utilized to define and construct smooth interfaces with good stability and differentiability for use in characterizing the solvent-solute boundaries and in generating continuous dielectric functions across the computational domain. A total free energy functional is constructed to couple polar and nonpolar contributions to the salvation process. Geometric measure theory is employed to rigorously convert a Lagrangian formulation of the surface energy into an Eulerian formulation so as to bring all energy terms into an equal footing. By minimizing the total free energy functional, we derive coupled generalized Poisson-Boltzmann equation (GPBE) and generalized geometric flow equation (GGFE) for the electrostatic potential and the construction of realistic solvent-solute boundaries, respectively. By solving the coupled GPBE and GGFE, we obtain the electrostatic potential, the solvent-solute boundary profile, and the smooth dielectric function, and thereby improve the accuracy and stability of implicit solvation calculations. We also design efficient second order numerical schemes for the solution of the GPBE and GGFE. Matrix resulted from the discretization of the GPBE is accelerated with appropriate preconditioners. An alternative direct implicit (ADI) scheme is designed to improve the stability of solving the GGFE. Two iterative approaches are designed to solve the coupled system of nonlinear partial differential equations. Extensive numerical experiments are designed to validate the present theoretical model, test computational methods, and optimize numerical algorithms. Example solvation analysis of both small compounds and proteins are carried out to further demonstrate the accuracy, stability, efficiency and robustness of the present new model and numerical approaches. Comparison is given to both experimental and theoretical results in the literature. PMID:20938489

On the relationship between finger width, velocity, and fluxes in thermohaline convection

NASA Astrophysics Data System (ADS)

Sreenivas, K. R.; Singh, O. P.; Srinivasan, J.

2009-02-01

Double-diffusive finger convection occurs in many natural processes. The theories for double-diffusive phenomena that exist at present consider systems with linear stratification in temperature and salinity. The double-diffusive systems with step change in salinity and temperature are, however, not amenable to simple stability analysis. Hence factors that control the width of the finger, velocity, and fluxes in systems that have step change in temperature and salinity have not been understood so far. In this paper we provide new physical insight regarding factors that influence finger convection in two-layer double-diffusive system through two-dimensional numerical simulations. Simulations have been carried out for density stability ratios (Rρ) from 1.5 to 10. For each density stability ratio, the thermal Rayleigh number (RaT) has been systematically varied from 7×103 to 7×108. Results from these simulations show how finger width, velocity, and flux ratios in finger convection are interrelated and the influence of governing parameters such as density stability ratio and the thermal Rayleigh number. The width of the incipient fingers at the time of onset of instability has been shown to vary as RaT-1/3. Velocity in the finger varies as RaT1/3/Rρ. Results from simulation agree with the scale analysis presented in the paper. Our results demonstrate that wide fingers have lower velocities and flux ratios compared to those in narrow fingers. This result contradicts present notions about the relation between finger width and flux ratio. A counterflow heat-exchanger analogy is used in understanding the dependence of flux ratio on finger width and velocity.

Quasi-Static Analysis of Round LaRC THUNDER Actuators

NASA Technical Reports Server (NTRS)

Campbell, Joel F.

2007-01-01

An analytic approach is developed to predict the shape and displacement with voltage in the quasi-static limit of round LaRC Thunder Actuators. The problem is treated with classical lamination theory and Von Karman non-linear analysis. In the case of classical lamination theory exact analytic solutions are found. It is shown that classical lamination theory is insufficient to describe the physical situation for large actuators but is sufficient for very small actuators. Numerical results are presented for the non-linear analysis and compared with experimental measurements. Snap-through behavior, bifurcation, and stability are presented and discussed.

Quasi-Static Analysis of LaRC THUNDER Actuators

NASA Technical Reports Server (NTRS)

Campbell, Joel F.

2007-01-01

An analytic approach is developed to predict the shape and displacement with voltage in the quasi-static limit of LaRC Thunder Actuators. The problem is treated with classical lamination theory and Von Karman non-linear analysis. In the case of classical lamination theory exact analytic solutions are found. It is shown that classical lamination theory is insufficient to describe the physical situation for large actuators but is sufficient for very small actuators. Numerical results are presented for the non-linear analysis and compared with experimental measurements. Snap-through behavior, bifurcation, and stability are presented and discussed.

Le Chatelier Principle for Out-of-Equilibrium and Boundary-Driven Systems: Application to Dynamical Phase Transitions.

PubMed

Shpielberg, O; Akkermans, E

2016-06-17

A stability analysis is presented for boundary-driven and out-of-equilibrium systems in the framework of the hydrodynamic macroscopic fluctuation theory. A Hamiltonian description is proposed which allows us to thermodynamically interpret the additivity principle. A necessary and sufficient condition for the validity of the additivity principle is obtained as an extension of the Le Chatelier principle. These stability conditions result from a diagonal quadratic form obtained using the cumulant generating function. This approach allows us to provide a proof for the stability of the weakly asymmetric exclusion process and to reduce the search for stability to the solution of two coupled linear ordinary differential equations instead of nonlinear partial differential equations. Additional potential applications of these results are discussed in the realm of classical and quantum systems.

Le Chatelier Principle for Out-of-Equilibrium and Boundary-Driven Systems: Application to Dynamical Phase Transitions

NASA Astrophysics Data System (ADS)

Shpielberg, O.; Akkermans, E.

2016-06-01

A stability analysis is presented for boundary-driven and out-of-equilibrium systems in the framework of the hydrodynamic macroscopic fluctuation theory. A Hamiltonian description is proposed which allows us to thermodynamically interpret the additivity principle. A necessary and sufficient condition for the validity of the additivity principle is obtained as an extension of the Le Chatelier principle. These stability conditions result from a diagonal quadratic form obtained using the cumulant generating function. This approach allows us to provide a proof for the stability of the weakly asymmetric exclusion process and to reduce the search for stability to the solution of two coupled linear ordinary differential equations instead of nonlinear partial differential equations. Additional potential applications of these results are discussed in the realm of classical and quantum systems.

Stability properties of solitary waves for fractional KdV and BBM equations

NASA Astrophysics Data System (ADS)

Angulo Pava, Jaime

2018-03-01

This paper sheds new light on the stability properties of solitary wave solutions associated with Korteweg-de Vries-type models when the dispersion is very low. Using a compact, analytic approach and asymptotic perturbation theory, we establish sufficient conditions for the existence of exponentially growing solutions to the linearized problem and so a criterium of spectral instability of solitary waves is obtained for both models. Moreover, the nonlinear stability and spectral instability of the ground state solutions for both models is obtained for some specific regimen of parameters. Via a Lyapunov strategy and a variational analysis, we obtain the stability of the blow-up of solitary waves for the critical fractional KdV equation. The arguments presented in this investigation show promise for use in the study of the instability of traveling wave solutions of other nonlinear evolution equations.

The inviscid stability of supersonic flow past heated or cooled axisymmetric bodies

NASA Technical Reports Server (NTRS)

Shaw, Stephen J.; Duck, Peter W.

1992-01-01

The inviscid, linear, nonaxisymmetric, temporal stability of the boundary layer associated with the supersonic flow past axisymmetric bodies (with particular emphasis on long thin, straight circular cylinders), subject to heated or cooled wall conditions is investigated. The eigenvalue problem is computed in some detail for a particular Mach number or 3.8, revealing that the effect of curvature and the choice of wall conditions both have a significant effect on the stability of the flow. Both the asymptotic, large azimuthal wavenumber solution and the asymptotic, far downstream solution are obtained for the stability analysis and compared with numerical results. Additionally, asymptotic analyses valid for large radii of curvature with cooled/heated wall conditions are presented. In general, important differences were found to exist between the wall temperature conditions imposed and the adiabatic wall conditions considered previously.

The inviscid stability of supersonic flow past heated or cooled axisymmetric bodies

NASA Technical Reports Server (NTRS)

Shaw, Stephen J.; Duck, Peter W.

1990-01-01

The inviscid, linear, nonaxisymmetric, temporal stability of the boundary layer associated with the supersonic flow past axisymmetric bodies (with particular emphasis on long thin, straight circular cylinders), subject to heated or cooled wall conditions is investigated. The eigenvalue problem is computed in some detail for a particular Mach number or 3.8, revealing that the effect of curvature and the choice of wall conditions both have a significant effect on the stability of the flow. Both the asymptotic, large azimuthal wavenumber solution and the asymptotic, far downstream solution are obtained for the stability analysis and compared with numerical results. Additionally, asymptotic analyses valid for large radii of curvature with cooled/heated wall conditions, are presented. In general, important differences were found to exist between the wall temperature conditions imposed and the adiabatic wall conditions considered previously.

Combustion Stability Assessments of the Black Brant Solid Rocket Motor

NASA Technical Reports Server (NTRS)

Fischbach, Sean

2014-01-01

The Black Brant variation of the Standard Brant developed in the 1960's has been a workhorse motor of the NASA Sounding Rocket Project Office (SRPO) since the 1970's. In March 2012, the Black Brant Mk1 used on mission 36.277 experienced combustion instability during a flight at White Sands Missile Range, the third event in the last four years, the first occurring in November, 2009, the second in April 2010. After the 2010 event the program has been increasing the motor's throat diameter post-delivery with the goal of lowering the chamber pressure and increasing the margin against combustion instability. During the most recent combustion instability event, the vibrations exceeded the qualification levels for the Flight Termination System. The present study utilizes data generated from T-burner testing of multiple Black Brant propellants at the Naval Air Warfare Center at China Lake, to improve the combustion stability predictions for the Black Brant Mk1 and to generate new predictions for the Mk2. Three unique one dimensional (1-D) stability models were generated, representing distinct Black Brant flights, two of which experienced instabilities. The individual models allowed for comparison of stability characteristics between various nozzle configurations. A long standing "rule of thumb" states that increased stability margin is gained by increasing the throat diameter. In contradiction to this experience based rule, the analysis shows that little or no margin is gained from a larger throat diameter. The present analysis demonstrates competing effects resulting from an increased throat diameter accompanying a large response function. As is expected, more acoustic energy was expelled through the nozzle, but conversely more acoustic energy was generated due to larger gas velocities near the propellant surfaces.

Cooperative control theory and integrated flight and propulsion control

NASA Technical Reports Server (NTRS)

Schmidt, David K.; Schierman, John D.

1994-01-01

This report documents the activities and research results obtained under a grant (NAG3-998) from the NASA Lewis Research Center. The focus of the research was the investigation of dynamic interactions between airframe and engines for advanced ASTOVL aircraft configurations, and the analysis of the implications of these interactions on the stability and performance of the airframe and engine control systems. In addition, the need for integrated flight and propulsion control for such aircraft was addressed. The major contribution of this research was the exposition of the fact that airframe and engine interactions could be present, and their effects could include loss of stability and performance of the control systems. Also, the significance of two directional, as opposed to one-directional, coupling was identified and explained. A multi variable stability and performance analysis methodology was developed, and applied to several candidate aircraft configurations. Also exposed was the fact that with interactions present along with some integrated control approaches, the engine command/limiting logic (which represents an important non-linear component of the engine control system) can impact closed-loop airframe/engine system stability. Finally, a brief investigation of control-law synthesis techniques appropriate for the class of systems was pursued, and it was determined that multi variable techniques, included model-following formulations of LQG and/or H (infinity) methods showed promise. However, for practical reasons, decentralized control architectures are preferred, which is an architecture incompatible with these synthesis methods.

Convergence acceleration of the Proteus computer code with multigrid methods

NASA Technical Reports Server (NTRS)

Demuren, A. O.; Ibraheem, S. O.

1992-01-01

Presented here is the first part of a study to implement convergence acceleration techniques based on the multigrid concept in the Proteus computer code. A review is given of previous studies on the implementation of multigrid methods in computer codes for compressible flow analysis. Also presented is a detailed stability analysis of upwind and central-difference based numerical schemes for solving the Euler and Navier-Stokes equations. Results are given of a convergence study of the Proteus code on computational grids of different sizes. The results presented here form the foundation for the implementation of multigrid methods in the Proteus code.

Riding and handling qualities of light aircraft: A review and analysis

NASA Technical Reports Server (NTRS)

Smetana, F. O.; Summery, D. C.; Johnson, W. D.

1972-01-01

Design procedures and supporting data necessary for configuring light aircraft to obtain desired responses to pilot commands and gusts are presented. The procedures employ specializations of modern military and jet transport practice where these provide an improvement over earlier practice. General criteria for riding and handling qualities are discussed in terms of the airframe dynamics. Methods available in the literature for calculating the coefficients required for a linearized analysis of the airframe dynamics are reviewed in detail. The review also treats the relation of spin and stall to airframe geometry. Root locus analysis is used to indicate the sensitivity of airframe dynamics to variations in individual stability derivatives and to variations in geometric parameters. Computer programs are given for finding the frequencies, damping ratios, and time constants of all rigid body modes and for generating time histories of aircraft motions in response to control inputs. Appendices are included presenting the derivation of the linearized equations of motion; the stability derivatives; the transfer functions; approximate solutions for the frequency, damping ratio, and time constants; an indication of methods to be used when linear analysis is inadequate; sample calculations; and an explanation of the use of root locus diagrams and Bode plots.

An Analysis of the Optimal Control Modification Method Applied to Flutter Suppression

NASA Technical Reports Server (NTRS)

Drew, Michael; Nguyen, Nhan T.; Hashemi, Kelley E.; Ting, Eric; Chaparro, Daniel

2017-01-01

Unlike basic Model Reference Adaptive Control (MRAC)l, Optimal Control Modification (OCM) has been shown to be a promising MRAC modification with robustness and analytical properties not present in other adaptive control methods. This paper presents an analysis of the OCM method, and how the asymptotic property of OCM is useful for analyzing and tuning the controller. We begin with a Lyapunov stability proof of an OCM controller having two adaptive gain terms, then the less conservative and easily analyzed OCM asymptotic property is presented. Two numerical examples are used to show how this property can accurately predict steady state stability and quantitative robustness in the presence of time delay, and relative to linear plant perturbations, and nominal Loop Transfer Recovery (LTR) tuning. The asymptotic property of the OCM controller is then used as an aid in tuning the controller applied to a large scale aeroservoelastic longitudinal aircraft model for flutter suppression. Control with OCM adaptive augmentation is shown to improve performance over that of the nominal non-adaptive controller when significant disparities exist between the controller/observer model and the true plant model.

Theoretical foundations for finite-time transient stability and sensitivity analysis of power systems

NASA Astrophysics Data System (ADS)

Dasgupta, Sambarta

Transient stability and sensitivity analysis of power systems are problems of enormous academic and practical interest. These classical problems have received renewed interest, because of the advancement in sensor technology in the form of phasor measurement units (PMUs). The advancement in sensor technology has provided unique opportunity for the development of real-time stability monitoring and sensitivity analysis tools. Transient stability problem in power system is inherently a problem of stability analysis of the non-equilibrium dynamics, because for a short time period following a fault or disturbance the system trajectory moves away from the equilibrium point. The real-time stability decision has to be made over this short time period. However, the existing stability definitions and hence analysis tools for transient stability are asymptotic in nature. In this thesis, we discover theoretical foundations for the short-term transient stability analysis of power systems, based on the theory of normally hyperbolic invariant manifolds and finite time Lyapunov exponents, adopted from geometric theory of dynamical systems. The theory of normally hyperbolic surfaces allows us to characterize the rate of expansion and contraction of co-dimension one material surfaces in the phase space. The expansion and contraction rates of these material surfaces can be computed in finite time. We prove that the expansion and contraction rates can be used as finite time transient stability certificates. Furthermore, material surfaces with maximum expansion and contraction rate are identified with the stability boundaries. These stability boundaries are used for computation of stability margin. We have used the theoretical framework for the development of model-based and model-free real-time stability monitoring methods. Both the model-based and model-free approaches rely on the availability of high resolution time series data from the PMUs for stability prediction. The problem of sensitivity analysis of power system, subjected to changes or uncertainty in load parameters and network topology, is also studied using the theory of normally hyperbolic manifolds. The sensitivity analysis is used for the identification and rank ordering of the critical interactions and parameters in the power network. The sensitivity analysis is carried out both in finite time and in asymptotic. One of the distinguishing features of the asymptotic sensitivity analysis is that the asymptotic dynamics of the system is assumed to be a periodic orbit. For asymptotic sensitivity analysis we employ combination of tools from ergodic theory and geometric theory of dynamical systems.

Unfolding stabilities of two structurally similar proteins as probed by temperature-induced and force-induced molecular dynamics simulations.

PubMed

Gorai, Biswajit; Prabhavadhni, Arasu; Sivaraman, Thirunavukkarasu

2015-09-01

Unfolding stabilities of two homologous proteins, cardiotoxin III and short-neurotoxin (SNTX) belonging to three-finger toxin (TFT) superfamily, have been probed by means of molecular dynamics (MD) simulations. Combined analysis of data obtained from steered MD and all-atom MD simulations at various temperatures in near physiological conditions on the proteins suggested that overall structural stabilities of the two proteins were different from each other and the MD results are consistent with experimental data of the proteins reported in the literature. Rationalization for the differential structural stabilities of the structurally similar proteins has been chiefly attributed to the differences in the structural contacts between C- and N-termini regions in their three-dimensional structures, and the findings endorse the 'CN network' hypothesis proposed to qualitatively analyse the thermodynamic stabilities of proteins belonging to TFT superfamily of snake venoms. Moreover, the 'CN network' hypothesis has been revisited and the present study suggested that 'CN network' should be accounted in terms of 'structural contacts' and 'structural strengths' in order to precisely describe order of structural stabilities of TFTs.

Transport and stability analyses supporting disruption prediction in high beta KSTAR plasmas

NASA Astrophysics Data System (ADS)

Ahn, J.-H.; Sabbagh, S. A.; Park, Y. S.; Berkery, J. W.; Jiang, Y.; Riquezes, J.; Lee, H. H.; Terzolo, L.; Scott, S. D.; Wang, Z.; Glasser, A. H.

2017-10-01

KSTAR plasmas have reached high stability parameters in dedicated experiments, with normalized beta βN exceeding 4.3 at relatively low plasma internal inductance li (βN/li>6). Transport and stability analyses have begun on these plasmas to best understand a disruption-free path toward the design target of βN = 5 while aiming to maximize the non-inductive fraction of these plasmas. Initial analysis using the TRANSP code indicates that the non-inductive current fraction in these plasmas has exceeded 50 percent. The advent of KSTAR kinetic equilibrium reconstructions now allows more accurate computation of the MHD stability of these plasmas. Attention is placed on code validation of mode stability using the PEST-3 and resistive DCON codes. Initial evaluation of these analyses for disruption prediction is made using the disruption event characterization and forecasting (DECAF) code. The present global mode kinetic stability model in DECAF developed for low aspect ratio plasmas is evaluated to determine modifications required for successful disruption prediction of KSTAR plasmas. Work supported by U.S. DoE under contract DE-SC0016614.

Application of advanced techniques for the assessment of bio-stability of biowaste-derived residues: A minireview.

PubMed

Lü, Fan; Shao, Li-Ming; Zhang, Hua; Fu, Wen-Ding; Feng, Shi-Jin; Zhan, Liang-Tong; Chen, Yun-Min; He, Pin-Jing

2018-01-01

Bio-stability is a key feature for the utilization and final disposal of biowaste-derived residues, such as aerobic compost or vermicompost of food waste, bio-dried waste, anaerobic digestate or landfilled waste. The present paper reviews conventional methods and advanced techniques used for the assessment of bio-stability. The conventional methods are reclassified into two categories. Advanced techniques, including spectroscopic (fluorescent, ultraviolet-visible, infrared, Raman, nuclear magnetic resonance), thermogravimetric and thermochemolysis analysis, are emphasized for their application in bio-stability assessment in recent years. Their principles, pros and cons are critically discussed. These advanced techniques are found to be convenient in sample preparation and to supply diversified information. However, the viability of these techniques as potential indicators for bio-stability assessment ultimately lies in the establishment of the relationship of advanced ones with the conventional methods, especially with the methods based on biotic response. Furthermore, some misuses in data explanation should be noted. Copyright © 2017 Elsevier Ltd. All rights reserved.

Stability switches of arbitrary high-order consensus in multiagent networks with time delays.

PubMed

Yang, Bo

2013-01-01

High-order consensus seeking, in which individual high-order dynamic agents share a consistent view of the objectives and the world in a distributed manner, finds its potential broad applications in the field of cooperative control. This paper presents stability switches analysis of arbitrary high-order consensus in multiagent networks with time delays. By employing a frequency domain method, we explicitly derive analytical equations that clarify a rigorous connection between the stability of general high-order consensus and the system parameters such as the network topology, communication time-delays, and feedback gains. Particularly, our results provide a general and a fairly precise notion of how increasing communication time-delay causes the stability switches of consensus. Furthermore, under communication constraints, the stability and robustness problems of consensus algorithms up to third order are discussed in details to illustrate our central results. Numerical examples and simulation results for fourth-order consensus are provided to demonstrate the effectiveness of our theoretical results.

Launch window analysis of satellites in high eccentricity or large circular orbits

NASA Technical Reports Server (NTRS)

Renard, M. L.; Bhate, S. K.; Sridharan, R.

1973-01-01

Numerical methods and computer programs for studying the stability and evolution of orbits of large eccentricity are presented. Methods for determining launch windows and target dates are developed. Mathematical models are prepared to analyze the characteristics of specific missions.

Intelligent Robotic Systems Study (IRSS), phase 3

NASA Technical Reports Server (NTRS)

1991-01-01

This phase of the Intelligent Robotic Systems Study (IRSS) examines some basic dynamics and control issues for a space manipulator attached to its worksite through a compliant base. One example of this scenario is depicted, which is a simplified, planar representation of the Flight Telerobotic Servicer (FTS) Development Test Flight 2 (DTF-2) experiment. The system consists of 4 major components: (1) dual FTS arms to perform dextrous tasks; (2) the main body to house power and electronics; (3) an Attachment Stabilization and Positioning Subsystem (ASPS) to provide coarse positioning and stabilization of the arms, and (4) the Worksite Attachment Mechanism (WAM) which anchors the system to its worksite, such as a Space Station truss node or Shuttle bay platform. The analysis is limited to the DTF-2 scenario. The goal is to understand the basic interaction dynamics between the arm, the positioner and/or stabilizer, and the worksite. The dynamics and controls simulation model are described. Analysis and simulation results are presented.

Isotope effects in aqueous solvation of simple halides

NASA Astrophysics Data System (ADS)

Videla, Pablo E.; Rossky, Peter J.; Laria, D.

2018-03-01

We present a path-integral-molecular-dynamics study of the thermodynamic stabilities of DOH⋯ X- and HOD⋯ X- (X = F, Cl, Br, I) coordination in aqueous solutions at ambient conditions. In agreement with experimental evidence, our results for the F- case reveal a clear stabilization of the latter motif, whereas, in the rest of the halogen series, the former articulation prevails. The DOH⋯ X- preference becomes more marked the larger the size of the ionic solute. A physical interpretation of these tendencies is provided in terms of an analysis of the global quantum kinetic energies of the light atoms and their geometrical decomposition. The stabilization of the alternative ionic coordination geometries is the result of a delicate balance arising from quantum spatial dispersions along parallel and perpendicular directions with respect to the relevant O-H⋯X- axis, as the strength of the water-halide H-bond varies. This interpretation is corroborated by a complementary analysis performed on the different spectroscopic signals of the corresponding IR spectra.

Verification test results of Apollo stabilization and control systems during undocked operations

NASA Technical Reports Server (NTRS)

Copeland, E. L.; Haken, R. L.

1974-01-01

The results are presented of analysis and simulation testing of both the Skylark 1 reaction control system digital autopilot (RCS DAP) and the thrust vector control (TVC) autopilot for use during the undocked portions of the Apollo/Soyuz Test Project Mission. The RCS DAP testing was performed using the Skylab Functional Simulator (SLFS), a digital computer program capable of simulating the Apollo and Skylab autopilots along with vehicle dynamics including bending and sloshing. The model is used to simulate three-axis automatic maneuvers along with pilot controlled manual maneuvers using the RCS DAP. The TVC autopilot was tested in two parts. A classical stability analysis was performed on the vehicle considering the effects of structural bending and sloshing when under control of the TVC autopilot. The time response of the TVC autopilot was tested using the SLFS. Results indicate that adequate performance stability margins can be expected for the CSM/DM configuration when under the control of the Apollo control systems tested.

Stabilization of Quinapril by Incorporating Hydrogen Bonding Interactions

PubMed Central

Roy, B. N.; Singh, G. P.; Godbole, H. M.; Nehate, S. P.

2009-01-01

In the present study stability of various known solvates of quinapril hydrochloride has been compared with nitromethane solvate. Nitromethane solvate was found to be more stable compared to other known solvates. Single crystal X-ray diffraction analysis of quinapril nitromethane solvate shows intermolecular hydrogen bonding between quinapril molecule and nitromethane. Stabilization of quinapril by forming strong hydrogen bonding network as in case of co-crystals was further studied by forming co-crystal with tris(hydroxymethyl)amino methane. Quinapril free base forms a stable salt with tris(hydroxymethyl)amino methane not reported earlier. Quinapril tris(hydroxymethyl)amino methane salt found to be stable even at 80° for 72 h i.e. hardly any formation of diketopiperazine and diacid impurity. As expected single crystal X-ray diffraction analysis reveals tris(hydroxymethyl)amino methane salt of quinapril shows complex hydrogen bonding network between the two entities along with ionic bond. The properties of this stable salt - stable in solid as well as solution phase, might lead to an alternate highly stable formulation. PMID:20502545

Stability of the iterative solutions of integral equations as one phase freezing criterion.

PubMed

Fantoni, R; Pastore, G

2003-10-01

A recently proposed connection between the threshold for the stability of the iterative solution of integral equations for the pair correlation functions of a classical fluid and the structural instability of the corresponding real fluid is carefully analyzed. Direct calculation of the Lyapunov exponent of the standard iterative solution of hypernetted chain and Percus-Yevick integral equations for the one-dimensional (1D) hard rods fluid shows the same behavior observed in 3D systems. Since no phase transition is allowed in such 1D system, our analysis shows that the proposed one phase criterion, at least in this case, fails. We argue that the observed proximity between the numerical and the structural instability in 3D originates from the enhanced structure present in the fluid but, in view of the arbitrary dependence on the iteration scheme, it seems uneasy to relate the numerical stability analysis to a robust one-phase criterion for predicting a thermodynamic phase transition.

influx_s: increasing numerical stability and precision for metabolic flux analysis in isotope labelling experiments.

PubMed

Sokol, Serguei; Millard, Pierre; Portais, Jean-Charles

2012-03-01

The problem of stationary metabolic flux analysis based on isotope labelling experiments first appeared in the early 1950s and was basically solved in early 2000s. Several algorithms and software packages are available for this problem. However, the generic stochastic algorithms (simulated annealing or evolution algorithms) currently used in these software require a lot of time to achieve acceptable precision. For deterministic algorithms, a common drawback is the lack of convergence stability for ill-conditioned systems or when started from a random point. In this article, we present a new deterministic algorithm with significantly increased numerical stability and accuracy of flux estimation compared with commonly used algorithms. It requires relatively short CPU time (from several seconds to several minutes with a standard PC architecture) to estimate fluxes in the central carbon metabolism network of Escherichia coli. The software package influx_s implementing this algorithm is distributed under an OpenSource licence at http://metasys.insa-toulouse.fr/software/influx/. Supplementary data are available at Bioinformatics online.

Application of parameter estimation to aircraft stability and control: The output-error approach

NASA Technical Reports Server (NTRS)

Maine, Richard E.; Iliff, Kenneth W.

1986-01-01

The practical application of parameter estimation methodology to the problem of estimating aircraft stability and control derivatives from flight test data is examined. The primary purpose of the document is to present a comprehensive and unified picture of the entire parameter estimation process and its integration into a flight test program. The document concentrates on the output-error method to provide a focus for detailed examination and to allow us to give specific examples of situations that have arisen. The document first derives the aircraft equations of motion in a form suitable for application to estimation of stability and control derivatives. It then discusses the issues that arise in adapting the equations to the limitations of analysis programs, using a specific program for an example. The roles and issues relating to mass distribution data, preflight predictions, maneuver design, flight scheduling, instrumentation sensors, data acquisition systems, and data processing are then addressed. Finally, the document discusses evaluation and the use of the analysis results.

Three-dimensional baroclinic instability of a Hadley cell for small Richardson number

NASA Technical Reports Server (NTRS)

Antar, B. N.; Fowlis, W. W.

1985-01-01

A three-dimensional, linear stability analysis of a baroclinic flow for Richardson number, Ri, of order unity is presented. The model considered is a thin horizontal, rotating fluid layer which is subjected to horizontal and vertical temperature gradients. The basic state is a Hadley cell which is a solution of the complete set of governing, nonlinear equations and contains both Ekman and thermal boundary layers adjacent to the rigid boundaries; it is given in a closed form. The stability analysis is also based on the complete set of equations; and perturbation possessing zonal, meridional, and vertical structures were considered. Numerical methods were developed for the stability problem which results in a stiff, eighth-order, ordinary differential eigenvalue problem. The previous work on three-dimensional baroclinic instability for small Ri was extended to a more realistic model involving the Prandtl number, sigma, and the Ekman number, E, and to finite growth rates and a wider range of the zonal wavenumber.

Post-sampling release of free fatty acids - effects of heat stabilization and methods of euthanasia.

PubMed

Jernerén, Fredrik; Söderquist, Marcus; Karlsson, Oskar

2015-01-01

The field of lipid research has made progress and it is now possible to study the lipidome of cells and organelles. A basic requirement of a successful lipid study is adequate pre-analytical sample handling, as some lipids can be unstable and postmortem changes can cause substantial accumulation of free fatty acids (FFAs). The aim of the present study was to investigate the effects of conductive heat stabilization and euthanasia methods on FFA levels in the rat brain and liver using liquid chromatography tandem mass spectrometry. The analysis of brain homogenates clearly demonstrated phospholipase activity and time-dependent post-sampling changes in the lipid pool of snap frozen non-stabilized tissue. There was a significant increase in FFAs already at 2min, which continued over time. Heat stabilization was shown to be an efficient method to reduce phospholipase activity and ex vivo lipolysis. Post-sampling effects due to tissue thawing and sample preparation induced a massive release of FFAs (up to 3700%) from non-stabilized liver and brain tissues compared to heat stabilized tissue. Furthermore, the choice of euthanasia method significantly influenced the levels of FFAs in the brain. The FFAs were decreased by 15-44% in the group of animals euthanized by pentobarbital injection compared with CO2 inhalation or decapitation. Our results highlight the importance of considering euthanasia methods and pre-analytical treatment in lipid analysis, factors which may otherwise interfere with the outcome of the experiments. Copyright © 2014 Elsevier Inc. All rights reserved.

Cooperative folding near the downhill limit determined with amino acid resolution by hydrogen exchange

PubMed Central

Yu, Wookyung; Baxa, Michael C.; Gagnon, Isabelle; Freed, Karl F.; Sosnick, Tobin R.

2016-01-01

The relationship between folding cooperativity and downhill, or barrier-free, folding of proteins under highly stabilizing conditions remains an unresolved topic, especially for proteins such as λ-repressor that fold on the microsecond timescale. Under aqueous conditions where downhill folding is most likely to occur, we measure the stability of multiple H bonds, using hydrogen exchange (HX) in a λYA variant that is suggested to be an incipient downhill folder having an extrapolated folding rate constant of 2 × 105 s−1 and a stability of 7.4 kcal·mol−1 at 298 K. At least one H bond on each of the three largest helices (α1, α3, and α4) breaks during a common unfolding event that reflects global denaturation. The use of HX enables us to both examine folding under highly stabilizing, native-like conditions and probe the pretransition state region for stable species without the need to initiate the folding reaction. The equivalence of the stability determined at zero and high denaturant indicates that any residual denatured state structure minimally affects the stability even under native conditions. Using our ψ analysis method along with mutational ϕ analysis, we find that the three aforementioned helices are all present in the folding transition state. Hence, the free energy surface has a sufficiently high barrier separating the denatured and native states that folding appears cooperative even under extremely stable and fast folding conditions. PMID:27078098

Dynamic Analysis of the Melanoma Model: From Cancer Persistence to Its Eradication

NASA Astrophysics Data System (ADS)

Starkov, Konstantin E.; Jimenez Beristain, Laura

In this paper, we study the global dynamics of the five-dimensional melanoma model developed by Kronik et al. This model describes interactions of tumor cells with cytotoxic T cells and respective cytokines under cellular immunotherapy. We get the ultimate upper and lower bounds for variables of this model, provide formulas for equilibrium points and present local asymptotic stability/hyperbolic instability conditions. Next, we prove the existence of the attracting set. Based on these results we come to global asymptotic melanoma eradication conditions via global stability analysis. Finally, we provide bounds for a locus of the melanoma persistence equilibrium point, study the case of melanoma persistence and describe conditions under which we observe global attractivity to the unique melanoma persistence equilibrium point.

Mathematical analysis of a nutrient-plankton system with delay.

PubMed

Rehim, Mehbuba; Zhang, Zhenzhen; Muhammadhaji, Ahmadjan

2016-01-01

A mathematical model describing the interaction of nutrient-plankton is investigated in this paper. In order to account for the time needed by the phytoplankton to mature after which they can release toxins, a discrete time delay is incorporated into the system. Moreover, it is also taken into account discrete time delays which indicates the partially recycled nutrient decomposed by bacteria after the death of biomass. In the first part of our analysis the sufficient conditions ensuring local and global asymptotic stability of the model are obtained. Next, the existence of the Hopf bifurcation as time delay crosses a threshold value is established and, meanwhile, the phenomenon of stability switches is found under certain conditions. Numerical simulations are presented to illustrate the analytical results.

Front and pulse solutions for the complex Ginzburg-Landau equation with higher-order terms.

PubMed

Tian, Huiping; Li, Zhonghao; Tian, Jinping; Zhou, Guosheng

2002-12-01

We investigate one-dimensional complex Ginzburg-Landau equation with higher-order terms and discuss their influences on the multiplicity of solutions. An exact analytic front solution is presented. By stability analysis for the original partial differential equation, we derive its necessary stability condition for amplitude perturbations. This condition together with the exact front solution determine the region of parameter space where the uniformly translating front solution can exist. In addition, stable pulses, chaotic pulses, and attenuation pulses appear generally if the parameters are out of the range. Finally, applying these analysis into the optical transmission system numerically we find that the stable transmission of optical pulses can be achieved if the parameters are appropriately chosen.

Correlation of analytical and experimental hot structure vibration results

NASA Technical Reports Server (NTRS)

Kehoe, Michael W.; Deaton, Vivian C.

1993-01-01

High surface temperatures and temperature gradients can affect the vibratory characteristics and stability of aircraft structures. Aircraft designers are relying more on finite-element model analysis methods to ensure sufficient vehicle structural dynamic stability throughout the desired flight envelope. Analysis codes that predict these thermal effects must be correlated and verified with experimental data. Experimental modal data for aluminum, titanium, and fiberglass plates heated at uniform, nonuniform, and transient heating conditions are presented. The data show the effect of heat on each plate's modal characteristics, a comparison of predicted and measured plate vibration frequencies, the measured modal damping, and the effect of modeling material property changes and thermal stresses on the accuracy of the analytical results at nonuniform and transient heating conditions.

Thrust vectoring for lateral-directional stability

NASA Technical Reports Server (NTRS)

Peron, Lee R.; Carpenter, Thomas

1992-01-01

The advantages and disadvantages of using thrust vectoring for lateral-directional control and the effects of reducing the tail size of a single-engine aircraft were investigated. The aerodynamic characteristics of the F-16 aircraft were generated by using the Aerodynamic Preliminary Analysis System II panel code. The resulting lateral-directional linear perturbation analysis of a modified F-16 aircraft with various tail sizes and yaw vectoring was performed at several speeds and altitudes to determine the stability and control trends for the aircraft compared to these trends for a baseline aircraft. A study of the paddle-type turning vane thrust vectoring control system as used on the National Aeronautics and Space Administration F/A-18 High Alpha Research Vehicle is also presented.

Physicochemical and mechanical properties of carbamazepine cocrystals with saccharin.

PubMed

Rahman, Ziyaur; Samy, Raghu; Sayeed, Vilayat A; Khan, Mansoor A

2012-01-01

The aim of present research was to investigate the physicochemical, mechanical properties, and stability characteristics of cocrystal of carbamazepine (CBZ) using saccharin (SAC) as a coformer. The cocrystals were prepared by solubility method and characterized by pH-solubility profile, intrinsic dissolution by static disk method, and surface morphology by scanning electron microscopy (SEM), crystallinity by differential scanning calorimetry (DSC) and powder X-ray diffraction (PXRD), and mechanical properties by Heckel analysis. Stability of the cocrystals were assessed by storing them at 60 (°)C for two weeks, 25 (°)C/60%RH, 40 (°)C/75%RH and 40 (°)C/94%RH for one month and compared with the stability of CBZ. The solubility profile of cocrystal was similar to CBZ. The cocrystal and CBZ have shown the same stability profile at all the conditions of studies except at 40 (°)C/94%RH. Unlike the CBZ, cocrystal was stable against dihydrate transformation. The compacts of cocrystal have a greater tensile strength and more compressibility. The Heckel analysis suggested that plastic deformation started at low compression pressure in the cocrystal than CBZ. In summary, the cocrystal form of carbamazepine provides another avenue for product development which is more stable than the parent drug.

Dynamics and Adaptive Control for Stability Recovery of Damaged Aircraft

NASA Technical Reports Server (NTRS)

Nguyen, Nhan; Krishnakumar, Kalmanje; Kaneshige, John; Nespeca, Pascal

2006-01-01

This paper presents a recent study of a damaged generic transport model as part of a NASA research project to investigate adaptive control methods for stability recovery of damaged aircraft operating in off-nominal flight conditions under damage and or failures. Aerodynamic modeling of damage effects is performed using an aerodynamic code to assess changes in the stability and control derivatives of a generic transport aircraft. Certain types of damage such as damage to one of the wings or horizontal stabilizers can cause the aircraft to become asymmetric, thus resulting in a coupling between the longitudinal and lateral motions. Flight dynamics for a general asymmetric aircraft is derived to account for changes in the center of gravity that can compromise the stability of the damaged aircraft. An iterative trim analysis for the translational motion is developed to refine the trim procedure by accounting for the effects of the control surface deflection. A hybrid direct-indirect neural network, adaptive flight control is proposed as an adaptive law for stabilizing the rotational motion of the damaged aircraft. The indirect adaptation is designed to estimate the plant dynamics of the damaged aircraft in conjunction with the direct adaptation that computes the control augmentation. Two approaches are presented 1) an adaptive law derived from the Lyapunov stability theory to ensure that the signals are bounded, and 2) a recursive least-square method for parameter identification. A hardware-in-the-loop simulation is conducted and demonstrates the effectiveness of the direct neural network adaptive flight control in the stability recovery of the damaged aircraft. A preliminary simulation of the hybrid adaptive flight control has been performed and initial data have shown the effectiveness of the proposed hybrid approach. Future work will include further investigations and high-fidelity simulations of the proposed hybrid adaptive Bight control approach.

Nonlinear stability and control of gliding vehicles

NASA Astrophysics Data System (ADS)

Bhatta, Pradeep

In this thesis we use nonlinear systems analysis to study dynamics and design control solutions for vehicles subject to hydrodynamic or aerodynamic forcing. Application of energy-based methods for such vehicles is challenging due to the presence of energy-conserving lift and side forces. We study how the lift force determines the geometric structure of vehicle dynamics. A Hamiltonian formulation of the integrable phugoid-mode equations provides a Lyapunov function candidate, which is used throughout the thesis for deriving equilibrium stability results and designing stabilizing control laws. A strong motivation for our work is the emergence of underwater gliders as an important observation platform for oceanography. Underwater gliders rely on buoyancy regulation and internal mass redistribution for motion control. These vehicles are attractive because they are designed to operate autonomously and continuously for several weeks. The results presented in this thesis contribute toward the development of systematic control design procedures for extending the range of provably stable maneuvers of the underwater glider. As the first major contribution we derive conditions for nonlinear stability of longitudinal steady gliding motions using singular perturbation theory. Stability is proved using a composite Lyapunov function, composed of individual Lyapunov functions that prove stability of rotational and translational subsystem equilibria. We use the composite Lyapunov function to design control laws for stabilizing desired relative equilibria in different actuation configurations for the underwater glider. We propose an approximate trajectory tracking method for an aircraft model. Our method uses exponential stability results of controllable steady gliding motions, derived by interpreting the aircraft dynamics as an interconnected system of rotational and translational subsystems. We prove bounded position error for tracking prescribed, straight-line trajectories, and demonstrate good performance in tracking unsteady trajectories in the longitudinal plane. We present all possible relative equilibrium motions for a rigid body moving in a fluid. Motion along a circular helix is a practical relative equilibrium for an underwater glider. We present a study of how internal mass distribution and buoyancy of the underwater glider influence the size of the steady circular helix, and the effect of a vehicle bottom-heaviness parameter on its stability.

Dynamics of delay-coupled FitzHugh-Nagumo neural rings.

PubMed

Mao, Xiaochen; Sun, Jianqiao; Li, Shaofan

2018-01-01

This paper studies the dynamical behaviors of a pair of FitzHugh-Nagumo neural networks with bidirectional delayed couplings. It presents a detailed analysis of delay-independent and delay-dependent stabilities and the existence of bifurcated oscillations. Illustrative examples are performed to validate the analytical results and to discover interesting phenomena. It is shown that the network exhibits a variety of complicated activities, such as multiple stability switches, the coexistence of periodic and quasi-periodic oscillations, the coexistence of periodic and chaotic orbits, and the coexisting chaotic attractors.

Dynamics of delay-coupled FitzHugh-Nagumo neural rings

NASA Astrophysics Data System (ADS)

Mao, Xiaochen; Sun, Jianqiao; Li, Shaofan

2018-01-01

This paper studies the dynamical behaviors of a pair of FitzHugh-Nagumo neural networks with bidirectional delayed couplings. It presents a detailed analysis of delay-independent and delay-dependent stabilities and the existence of bifurcated oscillations. Illustrative examples are performed to validate the analytical results and to discover interesting phenomena. It is shown that the network exhibits a variety of complicated activities, such as multiple stability switches, the coexistence of periodic and quasi-periodic oscillations, the coexistence of periodic and chaotic orbits, and the coexisting chaotic attractors.

Analysis and testing of aeroelastic model stability augmentation systems. [for supersonic transport aircraft wing and B-52 aircraft control system

NASA Technical Reports Server (NTRS)

Sevart, F. D.; Patel, S. M.

1973-01-01

Testing and evaluation of a stability augmentation system for aircraft flight control were performed. The flutter suppression system and synthesis conducted on a scale model of a supersonic wing for a transport aircraft are discussed. Mechanization and testing of the leading and trailing edge surface actuation systems are described. The ride control system analyses for a 375,000 pound gross weight B-52E aircraft are presented. Analyses of the B-52E aircraft maneuver load control system are included.

Curved-flow, rolling-flow, and oscillatory pure-yawing wind-tunnel test methods for determination of dynamic stability derivatives

NASA Technical Reports Server (NTRS)

Chambers, J. R.; Grafton, S. B.; Lutze, F. H.

1981-01-01

The test capabilities of the Stability Wind Tunnel of the Virginia Polytechnic Institute and State University are described, and calibrations for curved and rolling flow techniques are given. Oscillatory snaking tests to determine pure yawing derivatives are considered. Representative aerodynamic data obtained for a current fighter configuration using the curved and rolling flow techniques are presented. The application of dynamic derivatives obtained in such tests to the analysis of airplane motions in general, and to high angle of attack flight conditions in particular, is discussed.

Characterizing Urban Turbulence Under Haze Pollution: Insights into Temperature-Humidity Dissimilarity

NASA Astrophysics Data System (ADS)

Guo, Xiaofeng; Sun, Yele; Miao, Shiguang

2016-03-01

We present a description of urban boundary-layer turbulence characteristics under conditions of severe haze pollution, an emerging issue of interest to air-pollution-relevant investigations. Comparative analysis between clean and hazy episodes reveals their remarkable difference in atmospheric stability. A stability signature is then identified in temperature-humidity de-correlation and dissimilarity. Such a signature is noteworthy, because the accuracy of a reliable parametrization of the heat-to-moisture transport efficiency is substantiated in unstable and stable conditions rather than in near-neutral conditions.

Geometric approach to nuclear pasta phases

NASA Astrophysics Data System (ADS)

Kubis, Sebastian; Wójcik, Włodzimierz

2016-12-01

By use of the variational methods and differential geometry in the framework of the liquid drop model we formulate appropriate equilibrium equations for pasta phases with imposed periodicity. The extension of the Young-Laplace equation in the case of charged fluid is obtained. The β equilibrium and virial theorem are also generalized. All equations are shown in gauge invariant form. For the first time, the pasta shape stability analysis is carried out. The proper stability condition in the form of the generalized Jacobi equation is derived. The presented formalism is tested on some particular cases.

Market segmentation strategy in internet market

NASA Astrophysics Data System (ADS)

Ren, Yawei; Yang, Deli; Diao, Xinjun

2010-04-01

This paper presents a model to describe the competitive dynamics of web sites on the WWW market and analyze the stability of the model which is composed of one powerful site and two small sites. One of the most important results that emerge from this simple model is that strong competition among websites does not necessarily lead to the demise of the small website on the WWW market. From the stability analysis of the model, we obtain a series of conditions in which small sites can obtain competitive advantages by using the market segmentation strategy.

A linear stability analysis for nonlinear, grey, thermal radiative transfer problems

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wollaber, Allan B., E-mail: wollaber@lanl.go; Larsen, Edward W., E-mail: edlarsen@umich.ed

2011-02-20

We present a new linear stability analysis of three time discretizations and Monte Carlo interpretations of the nonlinear, grey thermal radiative transfer (TRT) equations: the widely used 'Implicit Monte Carlo' (IMC) equations, the Carter Forest (CF) equations, and the Ahrens-Larsen or 'Semi-Analog Monte Carlo' (SMC) equations. Using a spatial Fourier analysis of the 1-D Implicit Monte Carlo (IMC) equations that are linearized about an equilibrium solution, we show that the IMC equations are unconditionally stable (undamped perturbations do not exist) if {alpha}, the IMC time-discretization parameter, satisfies 0.5 < {alpha} {<=} 1. This is consistent with conventional wisdom. However, wemore » also show that for sufficiently large time steps, unphysical damped oscillations can exist that correspond to the lowest-frequency Fourier modes. After numerically confirming this result, we develop a method to assess the stability of any time discretization of the 0-D, nonlinear, grey, thermal radiative transfer problem. Subsequent analyses of the CF and SMC methods then demonstrate that the CF method is unconditionally stable and monotonic, but the SMC method is conditionally stable and permits unphysical oscillatory solutions that can prevent it from reaching equilibrium. This stability theory provides new conditions on the time step to guarantee monotonicity of the IMC solution, although they are likely too conservative to be used in practice. Theoretical predictions are tested and confirmed with numerical experiments.« less

A linear stability analysis for nonlinear, grey, thermal radiative transfer problems

NASA Astrophysics Data System (ADS)

Wollaber, Allan B.; Larsen, Edward W.

2011-02-01

We present a new linear stability analysis of three time discretizations and Monte Carlo interpretations of the nonlinear, grey thermal radiative transfer (TRT) equations: the widely used “Implicit Monte Carlo” (IMC) equations, the Carter Forest (CF) equations, and the Ahrens-Larsen or “Semi-Analog Monte Carlo” (SMC) equations. Using a spatial Fourier analysis of the 1-D Implicit Monte Carlo (IMC) equations that are linearized about an equilibrium solution, we show that the IMC equations are unconditionally stable (undamped perturbations do not exist) if α, the IMC time-discretization parameter, satisfies 0.5 < α ⩽ 1. This is consistent with conventional wisdom. However, we also show that for sufficiently large time steps, unphysical damped oscillations can exist that correspond to the lowest-frequency Fourier modes. After numerically confirming this result, we develop a method to assess the stability of any time discretization of the 0-D, nonlinear, grey, thermal radiative transfer problem. Subsequent analyses of the CF and SMC methods then demonstrate that the CF method is unconditionally stable and monotonic, but the SMC method is conditionally stable and permits unphysical oscillatory solutions that can prevent it from reaching equilibrium. This stability theory provides new conditions on the time step to guarantee monotonicity of the IMC solution, although they are likely too conservative to be used in practice. Theoretical predictions are tested and confirmed with numerical experiments.

The Stability Analysis Method of the Cohesive Granular Slope on the Basis of Graph Theory.

PubMed

Guan, Yanpeng; Liu, Xiaoli; Wang, Enzhi; Wang, Sijing

2017-02-27

This paper attempted to provide a method to calculate progressive failure of the cohesivefrictional granular geomaterial and the spatial distribution of the stability of the cohesive granular slope. The methodology can be divided into two parts: the characterization method of macro-contact and the analysis of the slope stability. Based on the graph theory, the vertexes, the edges and the edge sequences are abstracted out to characterize the voids, the particle contact and the macro-contact, respectively, bridging the gap between the mesoscopic and macro scales of granular materials. This paper adopts this characterization method to extract a graph from a granular slope and characterize the macro sliding surface, then the weighted graph is analyzed to calculate the slope safety factor. Each edge has three weights representing the sliding moment, the anti-sliding moment and the braking index of contact-bond, respectively, . The safety factor of the slope is calculated by presupposing a certain number of sliding routes and reducing Weight repeatedly and counting the mesoscopic failure of the edge. It is a kind of slope analysis method from mesoscopic perspective so it can present more detail of the mesoscopic property of the granular slope. In the respect of macro scale, the spatial distribution of the stability of the granular slope is in agreement with the theoretical solution.

Biomechanical analysis of a newly designed bioabsorbable anterior cervical plate. Invited submission from the joint section meeting on disorders of the spine and peripheral nerves, March 2005.

PubMed

Ames, Christopher P; Acosta, Frank L; Chamberlain, Robert H; Larios, Adolfo Espinoza; Crawford, Neil R

2005-12-01

The authors present a biomechanical analysis of a newly designed bioabsorbable anterior cervical plate (ACP) for the treatment of one-level cervical degenerative disc disease. They studied anterior cervical discectomy and fusion (ACDF) in a human cadaveric model, comparing the stability of the cervical spine after placement of the bioabsorbable fusion plate, a bioabsorbable mesh, and a more traditional metallic ACP. Seven human cadaveric specimens underwent a C6-7 fibular graft-assisted ACDF placement. A one-level resorbable ACP was then placed and secured with bioabsorbable screws. Flexibility testing was performed on both intact and instrumented specimens using a servohydraulic system to create flexion-extension, lateral bending, and axial rotation motions. After data analysis, three parameters were calculated: angular range of motion, lax zone, and stiff zone. The results were compared with those obtained in a previous study of a resorbable fusion mesh and with those acquired using metallic fusion ACPs. For all parameters studied, the resorbable plate consistently conferred greater stability than the resorbable mesh. Moreover, it offered comparable stability with that of metallic fusion ACPs. Bioabsorbable plates provide better stability than resorbable mesh. Although the results of this study do not necessarily indicate that a resorbable plate confers equivalent stability to a metal plate, the resorbable ACP certainly yielded better results than the resorbable mesh. Bioabsorbable fusion ACPs should therefore be considered as alternatives to metal plates when a graft containment device is required.

A Study on Multi-Swing Stability Analysis of Power System using Damping Rate Inversion

NASA Astrophysics Data System (ADS)

Tsuji, Takao; Morii, Yuki; Oyama, Tsutomu; Hashiguchi, Takuhei; Goda, Tadahiro; Nomiyama, Fumitoshi; Kosugi, Narifumi

In recent years, much attention is paid to the nonlinear analysis method in the field of stability analysis of power systems. Especially for the multi-swing stability analysis, the unstable limit cycle has an important meaning as a stability margin. It is required to develop a high speed calculation method of stability boundary regarding multi-swing stability because the real-time calculation of ATC is necessary to realize the flexible wheeling trades. Therefore, the authors have developed a new method which can calculate the unstable limit cycle based on damping rate inversion method. Using the unstable limit cycle, it is possible to predict the multi-swing stability at the time when the fault transmission line is reclosed. The proposed method is tested in Lorenz equation, single-machine infinite-bus system model and IEEJ WEST10 system model.

Global exponential stability of neutral high-order stochastic Hopfield neural networks with Markovian jump parameters and mixed time delays.

PubMed

Huang, Haiying; Du, Qiaosheng; Kang, Xibing

2013-11-01

In this paper, a class of neutral high-order stochastic Hopfield neural networks with Markovian jump parameters and mixed time delays is investigated. The jumping parameters are modeled as a continuous-time finite-state Markov chain. At first, the existence of equilibrium point for the addressed neural networks is studied. By utilizing the Lyapunov stability theory, stochastic analysis theory and linear matrix inequality (LMI) technique, new delay-dependent stability criteria are presented in terms of linear matrix inequalities to guarantee the neural networks to be globally exponentially stable in the mean square. Numerical simulations are carried out to illustrate the main results. © 2013 ISA. Published by ISA. All rights reserved.

Native denaturation differential scanning fluorimetry: Determining the effect of urea using a quantitative real-time thermocycler.

PubMed

Childers, Christine L; Green, Stuart R; Dawson, Neal J; Storey, Kenneth B

2016-09-01

The effect of protein stability on kinetic function is monitored with many techniques that often require large amounts of expensive substrates and specialized equipment not universally available. We present differential scanning fluorimetry (DSF), a simple high-throughput assay performed in real-time thermocyclers, as a technique for analysis of protein unfolding. Furthermore, we demonstrate a correlation between the half-maximal rate of protein unfolding (Knd), and protein unfolding by urea (I50). This demonstrates that DSF methods can determine the structural stability of an enzyme's active site and can compare the relative structural stability of homologous enzymes with a high degree of sequence similarity. Copyright © 2016 Elsevier Inc. All rights reserved.

Results of the Workshop on Two-Phase Flow, Fluid Stability and Dynamics: Issues in Power, Propulsion, and Advanced Life Support Systems

NASA Technical Reports Server (NTRS)

McQuillen, John; Rame, Enrique; Kassemi, Mohammad; Singh, Bhim; Motil, Brian

2003-01-01

The Two-phase Flow, Fluid Stability and Dynamics Workshop was held on May 15, 2003 in Cleveland, Ohio to define a coherent scientific research plan and roadmap that addresses the multiphase fluid problems associated with NASA s technology development program. The workshop participants, from academia, industry and government, prioritized various multiphase issues and generated a research plan and roadmap to resolve them. This report presents a prioritization of the various multiphase flow and fluid stability phenomena related primarily to power, propulsion, fluid and thermal management and advanced life support; and a plan to address these issues in a logical and timely fashion using analysis, ground-based and space-flight experiments.

Modelling and Control of an Annular Momentum Control Device

NASA Technical Reports Server (NTRS)

Downer, James R.; Johnson, Bruce G.

1988-01-01

The results of a modelling and control study for an advanced momentum storage device supported on magnetic bearings are documented. The control challenge posed by this device lies in its dynamics being such a strong function of flywheel rotational speed. At high rotational speed, this can lead to open loop instabilities, resulting in requirements for minimum and maximum control bandwidths and gains for the stabilizing controllers. Using recently developed analysis tools for systems described by complex coefficient differential equations, the closed properties of the controllers were analyzed and stability properties established. Various feedback controllers are investigated and discussed. Both translational and angular dynamics compensators are developed, and measures of system stability and robustness to plant and operational speed variations are presented.

Space shuttle: Aerodynamic stability and control characteristics of the NASA/MSC .006 scale 040-A delta wing orbiter

NASA Technical Reports Server (NTRS)

Click, P. L.; Michana, D. J.; Sarver, D. A.

1971-01-01

Experimental aerodynamic investigations were made on a .006 scale model 040-A delta wing space shuttle orbiter configuration. These tests were conducted to determine six-degree-of-freedom force and moment data for preliminary stability and control analysis. Data were obtained over a Mach number range from 0.6 to 4.96 at angles of attack from -10 deg to 50 deg at zero degrees sideslip and at angles of sideslip from -10 deg to 10 deg at constants angles of attack of 0 deg, 15 deg, 30 deg, and 45 deg. Various aileron, elevator, (elevon) rudder and rudder flare deflection angles were tested to establish the control effectiveness and vehicle stability. Model component buildup data were also obtained to provide a data base for future configuration modifications. Plotted data results are presented in both the body and stability axis system.

Efficient first-principles prediction of solid stability: Towards chemical accuracy

NASA Astrophysics Data System (ADS)

Zhang, Yubo; Kitchaev, Daniil A.; Yang, Julia; Chen, Tina; Dacek, Stephen T.; Sarmiento-Pérez, Rafael A.; Marques, Maguel A. L.; Peng, Haowei; Ceder, Gerbrand; Perdew, John P.; Sun, Jianwei

2018-03-01

The question of material stability is of fundamental importance to any analysis of system properties in condensed matter physics and materials science. The ability to evaluate chemical stability, i.e., whether a stoichiometry will persist in some chemical environment, and structure selection, i.e. what crystal structure a stoichiometry will adopt, is critical to the prediction of materials synthesis, reactivity and properties. Here, we demonstrate that density functional theory, with the recently developed strongly constrained and appropriately normed (SCAN) functional, has advanced to a point where both facets of the stability problem can be reliably and efficiently predicted for main group compounds, while transition metal compounds are improved but remain a challenge. SCAN therefore offers a robust model for a significant portion of the periodic table, presenting an opportunity for the development of novel materials and the study of fine phase transformations even in largely unexplored systems with little to no experimental data.

Stability and synchronization analysis of inertial memristive neural networks with time delays.

PubMed

Rakkiyappan, R; Premalatha, S; Chandrasekar, A; Cao, Jinde

2016-10-01

This paper is concerned with the problem of stability and pinning synchronization of a class of inertial memristive neural networks with time delay. In contrast to general inertial neural networks, inertial memristive neural networks is applied to exhibit the synchronization and stability behaviors due to the physical properties of memristors and the differential inclusion theory. By choosing an appropriate variable transmission, the original system can be transformed into first order differential equations. Then, several sufficient conditions for the stability of inertial memristive neural networks by using matrix measure and Halanay inequality are derived. These obtained criteria are capable of reducing computational burden in the theoretical part. In addition, the evaluation is done on pinning synchronization for an array of linearly coupled inertial memristive neural networks, to derive the condition using matrix measure strategy. Finally, the two numerical simulations are presented to show the effectiveness of acquired theoretical results.

Predicting stability of alpha-helical, orthogonal-bundle proteins on surfaces

NASA Astrophysics Data System (ADS)

Wei, Shuai; Knotts, Thomas A.

2010-09-01

The interaction of proteins with surfaces is a key phenomenon in many applications, but current understanding of the biophysics involved is lacking. At present, rational design of such emerging technologies is difficult as no methods or theories exist that correctly predict how surfaces influence protein behavior. Using molecular simulation and a coarse-grain model, this study illustrates for the first time that stability of proteins on surfaces can be correlated with tertiary structural elements for alpha-helical, orthogonal-bundle proteins. Results show that several factors contribute to stability on surfaces including the nature of the loop region where the tether is placed and the ability of the protein to freely rotate on the surface. A thermodynamic analysis demonstrates that surfaces stabilize proteins entropically and that any destabilization is an enthalpic effect. Moreover, the entropic effects are concentrated on the unfolded state of the protein while the ethalpic effects are focused on the folded state.

Boom Minimization Framework for Supersonic Aircraft Using CFD Analysis

NASA Technical Reports Server (NTRS)

Ordaz, Irian; Rallabhandi, Sriram K.

2010-01-01

A new framework is presented for shape optimization using analytical shape functions and high-fidelity computational fluid dynamics (CFD) via Cart3D. The focus of the paper is the system-level integration of several key enabling analysis tools and automation methods to perform shape optimization and reduce sonic boom footprint. A boom mitigation case study subject to performance, stability and geometrical requirements is presented to demonstrate a subset of the capabilities of the framework. Lastly, a design space exploration is carried out to assess the key parameters and constraints driving the design.

Direct use of linear time-domain aerodynamics in aeroservoelastic analysis: Aerodynamic model

NASA Technical Reports Server (NTRS)

Woods, J. A.; Gilbert, Michael G.

1990-01-01

The work presented here is the first part of a continuing effort to expand existing capabilities in aeroelasticity by developing the methodology which is necessary to utilize unsteady time-domain aerodynamics directly in aeroservoelastic design and analysis. The ultimate objective is to define a fully integrated state-space model of an aeroelastic vehicle's aerodynamics, structure and controls which may be used to efficiently determine the vehicle's aeroservoelastic stability. Here, the current status of developing a state-space model for linear or near-linear time-domain indicial aerodynamic forces is presented.

Application of the comparison principle to analysis of nonlinear systems. [using Lipschitz condition and differential equations

NASA Technical Reports Server (NTRS)

Gunderson, R. W.

1975-01-01

A comparison principle based on a Kamke theorem and Lipschitz conditions is presented along with its possible applications and modifications. It is shown that the comparison lemma can be used in the study of such areas as classical stability theory, higher order trajectory derivatives, Liapunov functions, boundary value problems, approximate dynamic systems, linear and nonlinear systems, and bifurcation analysis.

MOD-1 Wind Turbine Generator Analysis and Design Report, Volume 2

NASA Technical Reports Server (NTRS)

1979-01-01

The MOD-1 detail design is appended. The supporting analyses presented include a parametric system trade study, a verification of the computer codes used for rotor loads analysis, a metal blade study, and a definition of the design loads at each principal wind turbine generator interface for critical loading conditions. Shipping and assembly requirements, composite blade development, and electrical stability are also discussed.

Measurement-Based Investigation of Inter- and Intra-Area Effects of Wind Power Plant Integration

DOE Office of Scientific and Technical Information (OSTI.GOV)

Allen, Alicia J.; Singh, Mohit; Muljadi, Eduard

This paper has a two pronged objective: the first objective is to analyze the general effects of wind power plant (WPP) integration and the resulting displacement of conventional power plant (CPP) inertia on power system stability and the second is to demonstrate the efficacy of PMU data in power system stability analyses, specifically when knowledge of the network is incomplete. Traditionally modal analysis applies small signal stability analysis based on Eigenvalues and the assumption of complete knowledge of the network and all of its components. The analysis presented here differs because it is a measurement-based investigation and employs simulated measurementmore » data. Even if knowledge of the network were incomplete, this methodology would allow for monitoring and analysis of modes. This allows non-utility entities and study of power system stability. To generate inter- and intra-area modes, Kundur's well-known two-area four-generator system is modeled in PSCAD/EMTDC. A doubly-fed induction generator based WPP model, based on the Western Electricity Coordination Council (WECC) standard model, is included to analyze the effects of wind power on system modes. The two-area system and WPP are connected in various configurations with respect to WPP placement, CPP inertia and WPP penetration level. Analysis is performed on the data generated by the simulations. For each simulation run, a different configuration is chosen and a large disturbance is applied. The sampling frequency is set to resemble the sampling frequency at which data is available from phasor measurement units (PMUs). The estimate of power spectral density of these signals is made using the Yule-Walker algorithm. The resulting analysis shows that the presence of a WPP does not, of itself, lead to the introduction of new modes. The analysis also shows however that displacement of inertia may lead to introduction of new modes. The effects of location of inertia displacement (i.e. the effects on modes if WPP integration leads to displacement of inertia in its own region or in another region) and of WPP controls such as droop control and synthetic inertia are also examined. In future work, the methods presented here will be applied to real-world phasor data to examine the effects of integration of variable generation and displacement of CPP inertia on inter- and intra-area modes.« less

Slope Reinforcement with the Utilization of the Coal Waste Anthropogenic Material

NASA Astrophysics Data System (ADS)

Gwóźdź-Lasoń, Monika

2017-10-01

The protection of the environment, including waste management, is one of the pillars of the policy of the Europe. The application which is presented in that paper tries to show a trans-disciplinary way to design geotechnical constructions - slope stability analysis. The generally accepted principles that the author presents are numerous modelling patterns of earth retaining walls as slope stabilization system. The paper constitutes an attempt to summarise and generalise earlier researches which involved FEM numeric procedures and the Z_Soil package. The design of anthropogenic soil used as a material for reinforced earth retaining walls, are not only of commercial but of environmental importance as well and consistent with the concept of sustainable development and the need to redevelop brownfield. This paper tries to show conceptual and empirical modelling approaches to slope stability system used in anthropogenic soil formation such as heaps, resulting from mining, with a special focus on urban areas of South of Poland and perspectives of anthropogenic materials application in geotechnical engineering are discussed.

Non-synchronous rotating damping effects in gyroscopic rotating systems

NASA Astrophysics Data System (ADS)

Brusa, Eugenio; Zolfini, Giacomo

2005-03-01

The effects of non-synchronous rotating damping, i.e., of energy dissipation in elements rotating at a speed different from that of the main rotor, on the dynamic behaviour of the latter have been already studied in a previous paper (J. Rotating Machinery 6 (6) (2000)) for the case of non-gyroscopic rotating systems. A planar model, namely the Jeffcott's rotor, was used. The present study is aimed at investigating, through analytical and numerical models, the behaviour of rotors having a non-negligible gyroscopic effect. The parameters of the system affecting the dynamic stability are identified and the threshold of instability is then computed. A sort of map of stability is provided to allow mechanical engineers predicting possibile range of instability for forward and backward whirling motions. An experimental validation on a simple test rig is presented in order to show the effectiveness of the proposed stability analysis. Non-synchronous rotating damping is implemented by using a non-synchronous electromagnetic damper based on eddy currents.

Influence of stability of polymer surfactant on oil displacement mechanism

NASA Astrophysics Data System (ADS)

Liu, Li; Li, Chengliang; Pi, Yanming; Wu, Di; He, Ying; Geng, Liang

2018-02-01

At present, most of the oilfields of China have entered the late stage of high water-cut development, and three oil recovery technique has become the leading technology for improving oil recovery. With the improvement of three oil recovery techniques, the polymer surfactant flooding technology has been widely promoted in oil fields in recent years. But in the actual field experiment, it has been found that the polymer surfactant has chromatographic separation at the extraction end, which indicates that the property of the polymer surfactant has changed during the displacement process. At present, there was few literature about how the stability of polymer surfactant affects the oil displacement mechanism. This paper used HuaDing-I polymer surfactant to conduct a micro photolithography glass flooding experiment, and then compared the oil displacement law of polymer surfactant before and after static setting. Finally, the influence law of stability of polymer surfactant on the oil displacement mechanism is obtained by comprehensive analysis.

A stability analysis of AVE-4 severe weather soundings

NASA Technical Reports Server (NTRS)

Johnson, D. L.

1982-01-01

The stability and vertical structure of an average severe storm sounding, consisting of both thermodynamic and wind vertical profiles, were investigated to determine if they could be distinguished from an average lag sounding taken 3 to 6 hours prior to severe weather occurrence. The term average is defined here to indicate the arithmetic mean of a parameter, as a function of altitude, determined from a large number of available observations taken either close to severe weather occurrence, or else more than 3 hours before it occurs. The investigative computations were also done to help determine if a severe storm forecast or index could possibly be used or developed. These mean vertical profiles of thermodynamic and wind parameters as a function of severity of the weather, determined from manually digitized radar (MDR) categories are presented. Profile differences and stability index differences are presented along with the development of the Johnson Lag Index (JLI) which is determined entirely upon environmental vertical parameter differences between conditions 3 hours prior to severe weather, and severe weather itself.

Optimal placement of unified power flow controllers to improve dynamic voltage stability using power system variable based voltage stability indices.

PubMed

Albatsh, Fadi M; Ahmad, Shameem; Mekhilef, Saad; Mokhlis, Hazlie; Hassan, M A

2015-01-01

This study examines a new approach to selecting the locations of unified power flow controllers (UPFCs) in power system networks based on a dynamic analysis of voltage stability. Power system voltage stability indices (VSIs) including the line stability index (LQP), the voltage collapse proximity indicator (VCPI), and the line stability index (Lmn) are employed to identify the most suitable locations in the system for UPFCs. In this study, the locations of the UPFCs are identified by dynamically varying the loads across all of the load buses to represent actual power system conditions. Simulations were conducted in a power system computer-aided design (PSCAD) software using the IEEE 14-bus and 39- bus benchmark power system models. The simulation results demonstrate the effectiveness of the proposed method. When the UPFCs are placed in the locations obtained with the new approach, the voltage stability improves. A comparison of the steady-state VSIs resulting from the UPFCs placed in the locations obtained with the new approach and with particle swarm optimization (PSO) and differential evolution (DE), which are static methods, is presented. In all cases, the UPFC locations given by the proposed approach result in better voltage stability than those obtained with the other approaches.

Optimal Placement of Unified Power Flow Controllers to Improve Dynamic Voltage Stability Using Power System Variable Based Voltage Stability Indices

PubMed Central

Albatsh, Fadi M.; Ahmad, Shameem; Mekhilef, Saad; Mokhlis, Hazlie; Hassan, M. A.

2015-01-01

This study examines a new approach to selecting the locations of unified power flow controllers (UPFCs) in power system networks based on a dynamic analysis of voltage stability. Power system voltage stability indices (VSIs) including the line stability index (LQP), the voltage collapse proximity indicator (VCPI), and the line stability index (Lmn) are employed to identify the most suitable locations in the system for UPFCs. In this study, the locations of the UPFCs are identified by dynamically varying the loads across all of the load buses to represent actual power system conditions. Simulations were conducted in a power system computer-aided design (PSCAD) software using the IEEE 14-bus and 39- bus benchmark power system models. The simulation results demonstrate the effectiveness of the proposed method. When the UPFCs are placed in the locations obtained with the new approach, the voltage stability improves. A comparison of the steady-state VSIs resulting from the UPFCs placed in the locations obtained with the new approach and with particle swarm optimization (PSO) and differential evolution (DE), which are static methods, is presented. In all cases, the UPFC locations given by the proposed approach result in better voltage stability than those obtained with the other approaches. PMID:25874560

Kinetic model for the long term stability of contaminated monoatomic nanowires

NASA Astrophysics Data System (ADS)

Vélez, P.; Dassie, S. A.; Leiva, E. P. M.

2010-03-01

The kinetic behavior of pure Au nanowires upon rupture is analyzed in comparison with that of nanowires contaminated with H and C. The latter present larger activation energies for the rupture for all elongations and as a consequence these contaminated wires are predicted to live longer, as observed experimentally. The kinetic analysis is complemented by an analysis in terms of the concept of reaction force. It is found that this is the relevant quantity to analyze when considering the stability of the nanowires in the limit of low elongations rates or relatively high temperatures rather than the longitudinal force acting on the nanowire. The elastic and electronic contributions to the rupture process are obtained for each system. While the latter are similar in all cases, the elastic part is found to play the decisive role to make the difference. The present results suggest that measurement of the force constant of the junction may help to determine the chemical nature of the impurity.

Brazing of Stainless Steels to Yttria Stabilized Zirconia (YSZ) for Solid Oxide Fuel Cells

NASA Technical Reports Server (NTRS)

Shpargel, Tarah P.; Needham, Robert J.; Singh, M.; Kung, Steven C.

2005-01-01

Recently, there has been a great deal of interest in research, development, and commercialization of solid oxide fuel cells. Joining and sealing are critical issues that will need to be addressed before SOFC's can truly perform as expected. Ceramics and metals can be difficult to join together, especially when the joint must withstand up to 900 C operating temperature of the SOFC's. The goal of the present study is to find the most suitable braze material for joining of yttria stabilized zirconia (YSZ) to stainless steels. A number of commercially available braze materials TiCuSil, TiCuNi, Copper-ABA, Gold-ABA, and Gold-ABA-V have been evaluated. The oxidation behavior of the braze materials and steel substrates in air was also examined through thermogravimetric analysis. The microstructure and composition of the brazed regions have been examined by optical and scanning electron microscopy and EDS analysis. Effect of braze composition and processing conditions on the interfacial microstructure and composition of the joint regions will be presented.

Direct Numerical Simulation of a Cavity-Stabilized Ethylene/Air Premixed Flame

NASA Astrophysics Data System (ADS)

Chen, Jacqueline; Konduri, Aditya; Kolla, Hemanth; Rauch, Andreas; Chelliah, Harsha

2016-11-01

Cavity flame holders have been shown to be important for flame stabilization in scramjet combustors. In the present study the stabilization of a lean premixed ethylene/air flame in a rectangular cavity at thermo-chemical conditions relevant to scramjet combustors is simulated using a compressible reacting multi-block direct numerical simulation solver, S3D, incorporating a 22 species ethylene-air reduced chemical model. The fuel is premixed with air to an equivalence ratio of 0.4 and enters the computational domain at Mach numbers between 0.3 and 0.6. An auxiliary inert channel flow simulation is used to provide the turbulent velocity profile at the inlet for the reacting flow simulation. The detailed interaction between intense turbulence, nonequilibrium concentrations of radical species formed in the cavity and mixing with the premixed main stream under density variations due to heat release rate and compressibility effects is quantified. The mechanism for flame stabilization is quantified in terms of relevant non-dimensional parameters, and detailed analysis of the flame and turbulence structure will be presented. We acknowledge the sponsorship of the AFOSR-NSF Joint Effort on Turbulent Combustion Model Assumptions and the DOE Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences, and Biosciences.

On-line analysis capabilities developed to support the AFW wind-tunnel tests

NASA Technical Reports Server (NTRS)

Wieseman, Carol D.; Hoadley, Sherwood T.; Mcgraw, Sandra M.

1992-01-01

A variety of on-line analysis tools were developed to support two active flexible wing (AFW) wind-tunnel tests. These tools were developed to verify control law execution, to satisfy analysis requirements of the control law designers, to provide measures of system stability in a real-time environment, and to provide project managers with a quantitative measure of controller performance. Descriptions and purposes of the developed capabilities are presented along with examples. Procedures for saving and transferring data for near real-time analysis, and descriptions of the corresponding data interface programs are also presented. The on-line analysis tools worked well before, during, and after the wind tunnel test and proved to be a vital and important part of the entire test effort.

Active magnetic bearings applied to industrial compressors

NASA Technical Reports Server (NTRS)

Kirk, R. G.; Hustak, J. F.; Schoeneck, K. A.

1993-01-01

The design and shop test results are given for a high-speed eight-stage centrifugal compressor supported by active magnetic bearings. A brief summary of the basic operation of active magnetic bearings and the required rotor dynamics analysis are presented with specific attention given to design considerations for optimum rotor stability. The concerns for retrofits of magnetic bearings in existing machinery are discussed with supporting analysis of a four-stage centrifugal compressor. The current status of industrial machinery in North America using this new support system is presented and recommendations are given on design and analysis requirements for successful machinery operation of either retrofit or new design turbomachinery.

Supersonic combustion engine testbed, heat lightning

NASA Technical Reports Server (NTRS)

Hoying, D.; Kelble, C.; Langenbahn, A.; Stahl, M.; Tincher, M.; Walsh, M.; Wisler, S.

1990-01-01

The design of a supersonic combustion engine testbed (SCET) aircraft is presented. The hypersonic waverider will utilize both supersonic combustion ramjet (SCRAMjet) and turbofan-ramjet engines. The waverider concept, system integration, electrical power, weight analysis, cockpit, landing skids, and configuration modeling are addressed in the configuration considerations. The subsonic, supersonic and hypersonic aerodynamics are presented along with the aerodynamic stability and landing analysis of the aircraft. The propulsion design considerations include: engine selection, turbofan ramjet inlets, SCRAMjet inlets and the SCRAMjet diffuser. The cooling requirements and system are covered along with the topics of materials and the hydrogen fuel tanks and insulation system. A cost analysis is presented and the appendices include: information about the subsonic wind tunnel test, shock expansion calculations, and an aerodynamic heat flux program.

Severe Weather Forecast Decision Aid

NASA Technical Reports Server (NTRS)

Bauman, William H., III; Wheeler, Mark M.; Short, David A.

2005-01-01

This report presents a 15-year climatological study of severe weather events and related severe weather atmospheric parameters. Data sources included local forecast rules, archived sounding data, Cloud-to-Ground Lightning Surveillance System (CGLSS) data, surface and upper air maps, and two severe weather event databases covering east-central Florida. The local forecast rules were used to set threat assessment thresholds for stability parameters that were derived from the sounding data. The severe weather events databases were used to identify days with reported severe weather and the CGLSS data was used to differentiate between lightning and non-lightning days. These data sets provided the foundation for analyzing the stability parameters and synoptic patterns that were used to develop an objective tool to aid in forecasting severe weather events. The period of record for the analysis was May - September, 1989 - 2003. The results indicate that there are certain synoptic patterns more prevalent on days with severe weather and some of the stability parameters are better predictors of severe weather days based on locally tuned threat values. The results also revealed the stability parameters that did not display any skill related to severe weather days. An interactive web-based Severe Weather Decision Aid was developed to assist the duty forecaster by providing a level of objective guidance based on the analysis of the stability parameters, CGLSS data, and synoptic-scale dynamics. The tool will be tested and evaluated during the 2005 warm season.

Nonlinear stability and control study of highly maneuverable high performance aircraft, phase 2

NASA Technical Reports Server (NTRS)

Mohler, R. R.

1992-01-01

Research leading to the development of new nonlinear methodologies for the adaptive control and stability analysis of high angle of attack aircraft such as the F-18 is discussed. The emphasis has been on nonlinear adaptive control, but associated model development, system identification, stability analysis, and simulation were studied in some detail as well. Studies indicated that nonlinear adaptive control can outperform linear adaptive control for rapid maneuvers with large changes in angle of attack. Included here are studies on nonlinear model algorithmic controller design and an analysis of nonlinear system stability using robust stability analysis for linear systems.

3-D MHD modeling and stability analysis of jet and spheromak plasmas launched into a magnetized plasma

NASA Astrophysics Data System (ADS)

Fisher, Dustin; Zhang, Yue; Wallace, Ben; Gilmore, Mark; Manchester, Ward; Arge, C. Nick

2016-10-01

The Plasma Bubble Expansion Experiment (PBEX) at the University of New Mexico uses a coaxial plasma gun to launch jet and spheromak magnetic plasma configurations into the Helicon-Cathode (HelCat) plasma device. Plasma structures launched from the gun drag frozen-in magnetic flux into the background magnetic field of the chamber providing a rich set of dynamics to study magnetic turbulence, force-free magnetic spheromaks, and shocks. Preliminary modeling is presented using the highly-developed 3-D, MHD, BATS-R-US code developed at the University of Michigan. BATS-R-US employs an adaptive mesh refinement grid that enables the capture and resolution of shock structures and current sheets, and is particularly suited to model the parameter regime under investigation. CCD images and magnetic field data from the experiment suggest the stabilization of an m =1 kink mode trailing a plasma jet launched into a background magnetic field. Results from a linear stability code investigating the effect of shear-flow as a cause of this stabilization from magnetic tension forces on the jet will be presented. Initial analyses of a possible magnetic Rayleigh Taylor instability seen at the interface between launched spheromaks and their entraining background magnetic field will also be presented. Work supported by the Army Research Office Award No. W911NF1510480.

Structural Stability of a Stiffened Aluminum Fuselage Panel Subjected to Combined Mechanical and Internal Pressure Loads

NASA Technical Reports Server (NTRS)

Rouse, Marshall; Young, Richard D.; Gehrki, Ralph R.

2003-01-01

Results from an experimental and analytical study of a curved stiffened aluminum panel subjected to combined mechanical and internal pressure loads are presented. The panel loading conditions were simulated using a D-box test fixture. Analytical buckling load results calculated from a finite element analysis are presented and compared to experimental results. Buckling results presented indicate that the buckling load of the fuselage panel is significantly influenced by internal pressure loading. The experimental results suggest that the stress distribution is uniform in the panel prior to buckling. Nonlinear finite element analysis results correlates well with experimental results up to buckling.

Assessing the extent, stability, purity and properties of silanised detonation nanodiamond

NASA Astrophysics Data System (ADS)

Duffy, Emer; Mitev, Dimitar P.; Thickett, Stuart C.; Townsend, Ashley T.; Paull, Brett; Nesterenko, Pavel N.

2015-12-01

The functionalisation of nanodiamond is a key step in furthering its application in areas such as surface coatings, drug delivery, bio imaging and other biomedical avenues. Accordingly, analytical methods for the detailed characterisation of functionalised nano-material are of great importance. This work presents an alternative approach for the elemental analysis of zero-dimensional nanocarbons, specifically detonation nanodiamond (DND) following purification and functionalisation procedures. There is a particular emphasis on the presence of silicon, both for the purified DND and after its functionalisation with silanes. Five different silylation procedures for purified DND were explored and assessed quantitatively using inductively coupled plasma-mass spectrometry (ICP-MS) for analysis of dilute suspensions. A maximum Si loading of 29,300 μg g-1 on the DND was achieved through a combination of silylating reagents. The presence of 28 other elements in the DND materials was also quantified by ICP-MS. The characterisation of Si-bond formation was supported by FTIR and XPS evaluation of relevant functional groups. The thermal stability of the silylated DND was examined by thermogravimetric analysis. Improved particle size distribution and dispersion stability resulted from the silylation procedure, as confirmed by dynamic light scattering and capillary zone electrophoresis.

High-Alpha Research Vehicle Lateral-Directional Control Law Description, Analyses, and Simulation Results

NASA Technical Reports Server (NTRS)

Davidson, John B.; Murphy, Patrick C.; Lallman, Frederick J.; Hoffler, Keith D.; Bacon, Barton J.

1998-01-01

This report contains a description of a lateral-directional control law designed for the NASA High-Alpha Research Vehicle (HARV). The HARV is a F/A-18 aircraft modified to include a research flight computer, spin chute, and thrust-vectoring in the pitch and yaw axes. Two separate design tools, CRAFT and Pseudo Controls, were integrated to synthesize the lateral-directional control law. This report contains a description of the lateral-directional control law, analyses, and nonlinear simulation (batch and piloted) results. Linear analysis results include closed-loop eigenvalues, stability margins, robustness to changes in various plant parameters, and servo-elastic frequency responses. Step time responses from nonlinear batch simulation are presented and compared to design guidelines. Piloted simulation task scenarios, task guidelines, and pilot subjective ratings for the various maneuvers are discussed. Linear analysis shows that the control law meets the stability margin guidelines and is robust to stability and control parameter changes. Nonlinear batch simulation analysis shows the control law exhibits good performance and meets most of the design guidelines over the entire range of angle-of-attack. This control law (designated NASA-1A) was flight tested during the Summer of 1994 at NASA Dryden Flight Research Center.

Stabilizing effect of resistivity towards ELM-free H-mode discharge in lithium-conditioned NSTX

NASA Astrophysics Data System (ADS)

Banerjee, Debabrata; Zhu, Ping; Maingi, Rajesh

2017-07-01

Linear stability analysis of the national spherical torus experiment (NSTX) Li-conditioned ELM-free H-mode equilibria is carried out in the context of the extended magneto-hydrodynamic (MHD) model in NIMROD. The purpose is to investigate the physical cause behind edge localized mode (ELM) suppression in experiment after the Li-coating of the divertor and the first wall of the NSTX tokamak. Besides ideal MHD modeling, including finite-Larmor radius effect and two-fluid Hall and electron diamagnetic drift contributions, a non-ideal resistivity model is employed, taking into account the increase of Z eff after Li-conditioning in ELM-free H-mode. Unlike an earlier conclusion from an eigenvalue code analysis of these equilibria, NIMROD results find that after reduced recycling from divertor plates, profile modification is necessary but insufficient to explain the mechanism behind complete ELMs suppression in ideal two-fluid MHD. After considering the higher plasma resistivity due to higher Z eff, the complete stabilization could be explained. A thorough analysis of both pre-lithium ELMy and with-lithium ELM-free cases using ideal and non-ideal MHD models is presented, after accurately including a vacuum-like cold halo region in NIMROD to investigate ELMs.

A Systematic Approach Toward Stabilization of CagL, a Protein Antigen from Helicobacter pylori That Is a Candidate Subunit Vaccine

PubMed Central

Choudhari, Shyamal P.; Pendleton, Kirk P.; Ramsey, Joshua D.; Blanchard, Thomas G.; Picking, William D.

2013-01-01

An important consideration in the development of subunit vaccines is loss of activity caused by physical instability of the protein. Such instability often results from suboptimal solution conditions related to pH and temperature. Excipients can help to stabilize vaccines, but it is important to screen and identify excipients that adequately contribute to stabilization of a given formulation. CagL is a protein present in strains of Helicobacter pylori that possess type IV secretion systems. It contributes to bacterial adherence via α5β1 integrin, thereby making it an attractive subunit vaccine candidate. We characterized the stability of CagL in different pH and temperature conditions using a variety of spectroscopic techniques. Stability was assessed in terms of transition temperature (Tm) with the accumulated data then incorporated into an empirical phase diagram (EPD) that provided an overview of CagL physical stability. These analyses indicated maximum CagL stability at pH 4–6 up to 40 °C in the absence of excipient. Using this EPD analysis, aggregation assays were developed to screen a panel of excipients with some found to inhibit CagL aggregation. Candidate stabilizers were selected to confirm their enhanced stabilizing effect. These analyses will help in the formulation of a stable vaccine against H. pylori. PMID:23794457

On the wall-normal velocity of the compressible boundary-layer equations

NASA Technical Reports Server (NTRS)

Pruett, C. David

1991-01-01

Numerical methods for the compressible boundary-layer equations are facilitated by transformation from the physical (x,y) plane to a computational (xi,eta) plane in which the evolution of the flow is 'slow' in the time-like xi direction. The commonly used Levy-Lees transformation results in a computationally well-behaved problem for a wide class of non-similar boundary-layer flows, but it complicates interpretation of the solution in physical space. Specifically, the transformation is inherently nonlinear, and the physical wall-normal velocity is transformed out of the problem and is not readily recovered. In light of recent research which shows mean-flow non-parallelism to significantly influence the stability of high-speed compressible flows, the contribution of the wall-normal velocity in the analysis of stability should not be routinely neglected. Conventional methods extract the wall-normal velocity in physical space from the continuity equation, using finite-difference techniques and interpolation procedures. The present spectrally-accurate method extracts the wall-normal velocity directly from the transformation itself, without interpolation, leaving the continuity equation free as a check on the quality of the solution. The present method for recovering wall-normal velocity, when used in conjunction with a highly-accurate spectral collocation method for solving the compressible boundary-layer equations, results in a discrete solution which is extraordinarily smooth and accurate, and which satisfies the continuity equation nearly to machine precision. These qualities make the method well suited to the computation of the non-parallel mean flows needed by spatial direct numerical simulations (DNS) and parabolized stability equation (PSE) approaches to the analysis of stability.

Perspective On Income Security and Social Services and An Agenda for Analysis.

DTIC Science & Technology

1981-08-13

economic stability of America and the continued viability of the U.S. social system. This report provides a prespective on many of the major issues, identifies present concerns, forecasts future developments, and briefly discusses GAO’s approach to addressing these issues.

Stability of power systems coupled with market dynamics

NASA Astrophysics Data System (ADS)

Meng, Jianping

This Ph.D. thesis presented here spans two relatively independent topics. The first part, Chapter 2 is self-contained, and is dedicated to studies of new algorithms for power system state estimation. The second part, encompassing the remaining chapters, is dedicated to stability analysis of power system coupled with market dynamics. The first part of this thesis presents improved Newton's methods employing efficient vectorized calculations of higher order derivatives in power system state estimation problems. The improved algorithms are proposed based on an exact Newton's method using the second order terms. By efficiently computing an exact gain matrix, combined with a special optimal multiplier method, the new algorithms show more reliable convergence compared with the existing methods of normal equations, orthogonal decomposition, and Hachtel's sparse tableau. Our methods are able to handle ill-conditioned problems, yet show minimal penalty in computational cost for well-conditioned cases. These claims are illustrated through the standard IEEE 118 and 300 bus test examples. The second part of the thesis focuses on stability analysis of market/power systems. The work presented is motivated by an emerging problem. As the frequency of market based dispatch updates increases, there will inevitably be interaction between the dynamics of markets determining the generator dispatch commands, and the physical response of generators and network interconnections, necessitating the development of stability analysis for such coupled systems. We begin with numeric tests using different market models, with detailed machine/exciter/turbine/governor dynamics, in the New England 39 bus test system. A progression of modeling refinements are introduced, including such non-ideal effects as time delays. Electricity market parameter identification algorithms are also studied based on real time data from the PJM electricity market. Finally our power market model is augmented by optimal power flow constraints, allowing study of the so-called congestion problem. These studies show that understanding of potential modes of instability in such coupled systems is of crucial importance both in designing suitable rules for power markets, and in designing physical generator controls that are complementary to market-based dispatch.

Protein Stability in Mixed Solvents: A Balance of Contact Interaction and Excluded Volume

PubMed Central

Schellman, John A.

2003-01-01

Changes in excluded volume and contact interaction with the surface of a protein have been suggested as mechanisms for the changes in stability induced by cosolvents. The aim of the present paper is to present an analysis that combines both effects in a quantitative manner. The result is that both processes are present in both stabilizing and destabilizing interactions and neither can be ignored. Excluded volume was estimated using accessible surface area calculations of the kind introduced by Lee and Richards. The change in excluded volume on unfolding, ΔX, is quite large. For example, ΔX for ribonuclease is 6.7 L in urea and ∼16 L in sucrose. The latter number is greater than the molar volume of the protein. Direct interaction with the protein is represented as the solvent exchange mechanism, which differs from ordinary association theory because of the weakness of the interaction and the high concentrations of cosolvents. The balance between the two effects and their contribution to overall stability are most simply presented as bar diagrams as in Fig. 3. Our finding for five proteins is that excluded volume contributes to the stabilization of the native structure and that contact interaction contributes to destabilization. This is true for five proteins and four cosolvents including both denaturants and osmolytes. Whether a substance stabilizes a protein or destabilizes it depends on the relative size of these two contributions. The constant for the cosolvent contact with the protein is remarkably uniform for four of the proteins, indicating a similarity of groups exposed during unfolding. One protein, staphylococcus nuclease, is anomalous in almost all respects. In general, the strength of the interaction with guanidinium is about twice that of urea, which is about twice that of trimethylamine-N-oxide and sucrose. Arguments are presented for the use of volume fractions in equilibrium equations and the ignoring of activity coefficients of the cosolvent. It is shown in the Appendix that both the excluded volume and the direct interaction can be extracted in a unified way from the McMillan-Mayer formula for the second virial coefficient. PMID:12829469

Asymptotic analysis of stability for prismatic solids under axial loads

NASA Astrophysics Data System (ADS)

Scherzinger, W.; Triantafyllidis, N.

1998-06-01

This work addresses the stability of axially loaded prismatic beams with any simply connected crosssection. The solids obey a general class of rate-independent constitutive laws, and can sustain finite strains in either compression or tension. The proposed method is based on multiple scale asymptotic analysis, and starts with the full Lagrangian formulation for the three-dimensional stability problem, where the boundary conditions are chosen to avoid the formation of boundary layers. The calculations proceed by taking the limit of the beam's slenderness parameter, ɛ (ɛ 2 ≡ area/length 2), going to zero, thus resulting in asymptotic expressions for the critical loads and modes. The analysis presents a consistent and unified treatment for both compressive (buckling) and tensile (necking) instabilities, and is carried out explicitly up to o( ɛ4) in each case. The present method circumvents the standard structural mechanics approach for the stability problem of beams which requires the choice of displacement and stress field approximations in order to construct a nonlinear beam theory. Moreover, this work provides a consistent way to calculate the effect of the beam's slenderness on the critical load and mode to any order of accuracy required. In contrast, engineering theories give accurately the lowest order terms ( O( ɛ2)—Euler load—in compression or O(1)—maximum load—in tension) but give only approximately the next higher order terms, with the exception of simple section geometries where exact stability results are available. The proposed method is used to calculate the critical loads and eigenmodes for bars of several different cross-sections (circular, square, cruciform and L-shaped). Elastic beams are considered in compression and elastoplastic beams are considered in tension. The O( ɛ2) and O( ɛ4) asymptotic results are compared to the exact finite element calculations for the corresponding three-dimensional prismatic solids. The O( ɛ4) results give significant improvement over the O( ɛ2) results, even for extremely stubby beams, and in particular for the case of cross-sections with commensurate dimensions.

Implant Stability of Biological Hydroxyapatites Used in Dentistry

PubMed Central

Ramírez Fernández, Maria Piedad; Gehrke, Sergio A.; Mazón, Patricia; Calvo-Guirado, Jose L.; De Aza, Piedad N.

2017-01-01

The aim of the present study was to monitor implant stability after sinus floor elevation with two biomaterials during the first six months of healing by resonance frequency analysis (RFA), and how physico-chemical properties affect the implant stability quotient (ISQ) at the placement and healing sites. Bilateral maxillary sinus augmentation was performed in 10 patients in a split-mouth design using a bobine HA (BBM) as a control and porcine HA (PBM). Six months after sinus lifting, 60 implants were placed in the posterior maxilla. The ISQ was recorded on the day of surgery from RFA at T1 (baseline), T2 (three months), and T3 (six months). Statistically significant differences were found in the ISQ values during the evaluation period. The ISQ (baseline) was 63.8 ± 2.97 for BBM and 62.6 ± 2.11 for PBM. The ISQ (T2) was ~73.5 ± 4.21 and 67 ± 4.99, respectively. The ISQ (T3) was ~74.65 ± 2.93 and 72.9 ± 2.63, respectively. All of the used HAs provide osseointegration and statistical increases in the ISQ at baseline, T2 and T3 (follow-up), respectively. The BBM, sintered at high temperature with high crystallinity and low porosity, presented higher stability, which demonstrates that variations in the physico-chemical properties of a bone substitute material clearly influence implant stability. PMID:28773005

Effect of the relative shift between the electron density and temperature pedestal position on the pedestal stability in JET-ILW and comparison with JET-C

NASA Astrophysics Data System (ADS)

Stefanikova, E.; Frassinetti, L.; Saarelma, S.; Loarte, A.; Nunes, I.; Garzotti, L.; Lomas, P.; Rimini, F.; Drewelow, P.; Kruezi, U.; Lomanowski, B.; de la Luna, E.; Meneses, L.; Peterka, M.; Viola, B.; Giroud, C.; Maggi, C.; contributors, JET

2018-05-01

The electron temperature and density pedestals tend to vary in their relative radial positions, as observed in DIII-D (Beurskens et al 2011 Phys. Plasmas 18 056120) and ASDEX Upgrade (Dunne et al 2017 Plasma Phys. Control. Fusion 59 14017). This so-called relative shift has an impact on the pedestal magnetohydrodynamic (MHD) stability and hence on the pedestal height (Osborne et al 2015 Nucl. Fusion 55 063018). The present work studies the effect of the relative shift on pedestal stability of JET ITER-like wall (JET-ILW) baseline low triangularity (δ) unseeded plasmas, and similar JET-C discharges. As shown in this paper, the increase of the pedestal relative shift is correlated with the reduction of the normalized pressure gradient, therefore playing a strong role in pedestal stability. Furthermore, JET-ILW tends to have a larger relative shift compared to JET carbon wall (JET-C), suggesting a possible role of the plasma facing materials in affecting the density profile location. Experimental results are then compared with stability analysis performed in terms of the peeling-ballooning model and with pedestal predictive model EUROPED (Saarelma et al 2017 Plasma Phys. Control. Fusion). Stability analysis is consistent with the experimental findings, showing an improvement of the pedestal stability, when the relative shift is reduced. This has been ascribed mainly to the increase of the edge bootstrap current, and to minor effects related to the increase of the pedestal pressure gradient and narrowing of the pedestal pressure width. Pedestal predictive model EUROPED shows a qualitative agreement with experiment, especially for low values of the relative shift.

Assessment of the DORIS network monumentation

NASA Astrophysics Data System (ADS)

Saunier, J.

2016-12-01

Stability of the monumentation is essential for precise positioning applications to minimize velocity uncertainties and noises in the position data. In charge of the DORIS global tracking network deployment since the beginning, IGN, in consultation with CNES, designed three standard monuments compliant with the DORIS system requirements and general geodetic specifications, and suitable for various site configurations: building roofs, concrete pedestals or pillars. This paper describes the monument types in use in the DORIS network according to the current required specifications and provides a comparative assessment of the stability of the monuments over the network based on three methods: a theoretical study of the mechanical behavior of the metallic structures, a misclosure analysis taken during ground surveys and a qualitative approach taking into account different factors. This overview of the network monumentation gives new key numbers following the previous network assessment performed by Fagard (2006). Significant improvements have been made following the continuous efforts to renovate the network monumentation. These results are relevant for the Global Geodetic Observing System (GGOS) goals of measurement stability for the geodetic techniques. Today, two-thirds of the DORIS network monuments are compliant with the standards aiming at stability of 0.1 mm/y. This stability result has been measured for 16 of the 58 stations more than 10 y after its installation while monuments with more than 1 mm antenna tilts are over 10 y old when specifications were less stringent. The grading and scoring grid drawn up for each monument led to the mapping of the stability of the current DORIS network. Finally, we present a number of further actions to monitor the monument stability and provide new elements for the network monumentation assessment, exploring two different approaches: analysis of the time series and direct measurements using devices placed on each monument.

Effect of Propellant Feed System Coupling and Hydraulic Parameters on Analysis of Chugging

NASA Technical Reports Server (NTRS)

Wood, Don J.; Dorsch, Robert G.

1967-01-01

A digital distributed parameter model was used to study the effects of propellant-feed- system coupling and various hydraulic parameters on the analytical prediction of chugging instabilities. Coupling between the combustion chamber and feed system was controlled by varying the compliance of the injector-dome region. The coupling with the feed system above the pump was varied by changing the amount of cavitation compliance at the pump inlet. The stability limits and chugging frequencies proved to be strongly dependent on the degree of feed-system coupling. The maximum stability condition occurred with intermediate coupling. Under conditions of a high degree of feed-system-combustor coupling, the stability limits and chugging frequencies were primarily dependent on the feed-system characteristics; the responses were characterized by beating patterns. For the system analyzed, the pump suction line had little effect on the stability limits or chugging frequencies. Beating, present under the condition of near zero injector -dome compliance, was eliminated when the suction line was decoupled by employing a sufficiently high value of pump-inlet compliance. Under conditions of maximum feed-system coupling, the magnitude and distribution of line losses in the discharge line had a significant effect on the stability limits but had negligible effect on the chugging frequency and beating characteristics. Also, the length of the discharge line greatly affected the stability limits, chugging frequency, and beating characteristics. The length of the suction line, however, had little effect on the stability limits and chugging frequency but did influence the beating pattern. A resistive-shunt device attached to the pump discharge line to suppress chugging was investigated. The analysis showed that the device was effective under conditions of high feed-system coupling.

CSER 01-008 Canning of Thermally Stabilized Plutonium Oxide Powder in PFP Glovebox HC-21A

DOE Office of Scientific and Technical Information (OSTI.GOV)

ERICKSON, D.G.

This document presents the analysis performed to support the canning operation in HC-21A. Most of the actual analysis was performed for the operation in HC-18M and HA-20MB, and is documented in HNF-2707 Rev I a (Erickson 2001a). This document will reference Erickson (2001a) as necessary to support the operation in HC-21A. The plutonium stabilization program at the Plutonium Finishing Plant (PFP) uses heat to convert plutonium-bearing materials into dry powder that is chemically stable for long term storage. The stabilized plutonium is transferred into one of several gloveboxes for the canning process, Gloveboxes HC-18M in Room 228'2, HA-20MB in Roommore » 235B, and HC-21A in Room 230B are to be used for this process. This document presents the analysis performed to support the canning operation in HC-21A. Most of the actual analysis was performed for the operation in HC-I8M and HA-20MB, and is documented in HNF-2707 Rev l a (Erickson 2001a). This document will reference Erickson (2001a) as necessary to support the operation in HC-21A. Evaluation of this operation included normal, base cases, and contingencies. The base cases took the normal operations for each type of feed material and added the likely off-normal events. Each contingency is evaluated assuming the unlikely event happens to the conservative base case. Each contingency was shown to meet the double contingency requirement. That is, at least two unlikely, independent, and concurrent changes in process conditions are required before a criticality is possible.« less

Asymmetrical booster ascent guidance and control system design study. Volume 4: Sampled data stability analysis program (SADSAP) user's guide. [space shuttle development

NASA Technical Reports Server (NTRS)

Wilson, J. L.

1974-01-01

A users guide to the Sampled Data Stability Analysis Program (SADSAP) is provided. This program is a general purpose sampled data Stability Analysis Program capable of providing frequency response on root locus data.

Stability analysis of nonlinear autonomous systems - General theory and application to flutter

NASA Technical Reports Server (NTRS)

Smith, L. L.; Morino, L.

1975-01-01

The analysis makes use of a singular perturbation method, the multiple time scaling. Concepts of stable and unstable limit cycles are introduced. The solution is obtained in the form of an asymptotic expansion. Numerical results are presented for the nonlinear flutter of panels and airfoils in supersonic flow. The approach used is an extension of a method for analyzing nonlinear panel flutter reported by Morino (1969).

Social investment and personality: a meta-analysis of the relationship of personality traits to investment in work, family, religion, and volunteerism.

PubMed

Lodi-Smith, Jennifer; Roberts, Brent W

2007-02-01

Investing in normative, age-graded social roles has broad implications for both the individual and society. The current meta-analysis examines the way in which personality traits relate to four such investments -- work, family, religion, and volunteerism. The present study uses meta-analytic techniques (K = 94) to identify the cross-sectional patterns of relationships between social investment in these four roles and the personality trait domains of agreeableness, conscientiousness, and emotional stability. Results show that the extent of investment in social roles across these domains is positively related to agreeableness, conscientiousness, emotional stability, and low psychoticism. These findings are more robust when individuals are psychologically committed to rather than simply demographically associated with the investment role.

Reconstructed phase spaces of intrinsic mode functions. Application to postural stability analysis.

PubMed

Snoussi, Hichem; Amoud, Hassan; Doussot, Michel; Hewson, David; Duchêne, Jacques

2006-01-01

In this contribution, we propose an efficient nonlinear analysis method characterizing postural steadiness. The analyzed signal is the displacement of the centre of pressure (COP) collected from a force plate used for measuring postural sway. The proposed method consists of analyzing the nonlinear dynamics of the intrinsic mode functions (IMF) of the COP signal. The nonlinear properties are assessed through the reconstructed phase spaces of the different IMFs. This study shows some specific geometries of the attractors of some intrinsic modes. Moreover, the volume spanned by the geometric attractors in the reconstructed phase space represents an efficient indicator of the postural stability of the subject. Experiments results corroborate the effectiveness of the method to blindly discriminate young subjects, elderly subjects and subjects presenting a risk of falling.

A unified perspective on robot control - The energy Lyapunov function approach

NASA Technical Reports Server (NTRS)

Wen, John T.

1990-01-01

A unified framework for the stability analysis of robot tracking control is presented. By using an energy-motivated Lyapunov function candidate, the closed-loop stability is shown for a large family of control laws sharing a common structure of proportional and derivative feedback and a model-based feedforward. The feedforward can be zero, partial or complete linearized dynamics, partial or complete nonlinear dynamics, or linearized or nonlinear dynamics with parameter adaptation. As result, the dichotomous approaches to the robot control problem based on the open-loop linearization and nonlinear Lyapunov analysis are both included in this treatment. Furthermore, quantitative estimates of the trade-offs between different schemes in terms of the tracking performance, steady state error, domain of convergence, realtime computation load and required a prior model information are derived.

Chicago Monostatic Acoustic Vortex Sensing System. Volume IV. Wake Vortex Decay.

DTIC Science & Technology

1982-07-01

analysis here, the peak velocity core radius cannot be directly compared to the present results. If one applies the analysis of Table 10 to the LDV vortex...Tietjens, O.G., Applied Hydro- and Aeromechanics, Dover, New York, 1957, pp. 158-163. 11. Hallock, J.N., "Vortex Advisory System Safety Analysis, Vol. I...Stability and Control Characteristics Model DC-9-30 Jet Transport," LB-32323, Dec. 1966 (revised Oct. 1968), Douglas Aircraft Company , Long Beach, CA. 13

Algorithms for sum-of-squares-based stability analysis and control design of uncertain nonlinear systems

NASA Astrophysics Data System (ADS)

Ataei-Esfahani, Armin

In this dissertation, we present algorithmic procedures for sum-of-squares based stability analysis and control design for uncertain nonlinear systems. In particular, we consider the case of robust aircraft control design for a hypersonic aircraft model subject to parametric uncertainties in its aerodynamic coefficients. In recent years, Sum-of-Squares (SOS) method has attracted increasing interest as a new approach for stability analysis and controller design of nonlinear dynamic systems. Through the application of SOS method, one can describe a stability analysis or control design problem as a convex optimization problem, which can efficiently be solved using Semidefinite Programming (SDP) solvers. For nominal systems, the SOS method can provide a reliable and fast approach for stability analysis and control design for low-order systems defined over the space of relatively low-degree polynomials. However, The SOS method is not well-suited for control problems relating to uncertain systems, specially those with relatively high number of uncertainties or those with non-affine uncertainty structure. In order to avoid issues relating to the increased complexity of the SOS problems for uncertain system, we present an algorithm that can be used to transform an SOS problem with uncertainties into a LMI problem with uncertainties. A new Probabilistic Ellipsoid Algorithm (PEA) is given to solve the robust LMI problem, which can guarantee the feasibility of a given solution candidate with an a-priori fixed probability of violation and with a fixed confidence level. We also introduce two approaches to approximate the robust region of attraction (RROA) for uncertain nonlinear systems with non-affine dependence on uncertainties. The first approach is based on a combination of PEA and SOS method and searches for a common Lyapunov function, while the second approach is based on the generalized Polynomial Chaos (gPC) expansion theorem combined with the SOS method and searches for parameter-dependent Lyapunov functions. The control design problem is investigated through a case study of a hypersonic aircraft model with parametric uncertainties. Through time-scale decomposition and a series of function approximations, the complexity of the aircraft model is reduced to fall within the capability of SDP solvers. The control design problem is then formulated as a convex problem using the dual of the Lyapunov theorem. A nonlinear robust controller is searched using the combined PEA/SOS method. The response of the uncertain aircraft model is evaluated for two sets of pilot commands. As the simulation results show, the aircraft remains stable under up to 50% uncertainty in aerodynamic coefficients and can follow the pilot commands.

Stabilization process of human population: a descriptive approach.

PubMed

Kayani, A K; Krotki, K J

1981-01-01

An attempt is made to inquire into the process of stabilization of a human population. The same age distribution distorted by past variations in fertility is subjected to several fixed schedules of fertility. The schedules are different from each other monotonically over a narrow range. The primary concern is with the process, almost year by year, through which the populations become stable. There is particular interest in the differential impact in the same original age distribution of the narrowly different fixed fertility schedules. The exercise is prepared in 3 stages: general background of the process of stabilization; methodology and data used; and analysis and discussion of the stabilization process. Among the several approaches through which the analysis of stable population is possible, 2 are popular: the integral equation and the projection matrix. In this presentation the interest is in evaluating the effects of fertility on the stabilization process of a population. Therefore, only 1 initial age distribution and only 1 life table but a variety of narrowly different schedules of fertility have been used. Specifically, the U.S. 1963 female population is treated as the initial population. The process of stabilization is viewed in the light of the changes in the slopes between 2 successive age groups of an age distribution. A high fertility schedule with the given initial age distribution and mortality level overcomes the oscillations more quickly than the low fertility schedule. Simulation confirms the intuitively expected positive relationship between the mean of the slope and the level of fertility. The variance of the slope distribution is an indicator of the aging of the distribution.

Thermohydrodynamic analysis of cryogenic liquid turbulent flow fluid film bearings

NASA Technical Reports Server (NTRS)

Andres, Luis San

1993-01-01

A thermohydrodynamic analysis is presented and a computer code developed for prediction of the static and dynamic force response of hydrostatic journal bearings (HJB's), annular seals or damper bearing seals, and fixed arc pad bearings for cryogenic liquid applications. The study includes the most important flow characteristics found in cryogenic fluid film bearings such as flow turbulence, fluid inertia, liquid compressibility and thermal effects. The analysis and computational model devised allow the determination of the flow field in cryogenic fluid film bearings along with the dynamic force coefficients for rotor-bearing stability analysis.

Effect of implant macro-design on primary stability: A prospective clinical study.

PubMed

Lozano-Carrascal, Naroa; Salomó-Coll, Oscar; Gilabert-Cerdà, Marta; Farré-Pagés, Nuria; Gargallo-Albiol, Jordi; Hernández-Alfaro, Federico

2016-03-01

Implant restorations have become a high predictable treatment option. Several caracteristics such as surgical technique and implant design can influence the treatment outcomes. The aim of the present study was to evaluate the influence of implant macro-design on primary stability measured with resonance frequency analysis (RFA) and insertion torque (IT). Material and Mehods: A total of 47 implants divided in two groups: Test group (TI): 22 Tapered MIS® Seven implants; Control group (CI): 25 cylindrical Astra® Osseospeed implants. All implants were inserted following the manufacturers' standard protocols. Implant primary stability was measured at the moment of implant placement by registering insertion torque values (ITv) and ISQ values by means of Osstell™ Mentor (ISQv) (Integration Diagnostic Ltd., Goteborg, Sweden). In the mandible, mean ISQv for tapered implants (TI) was 71.67±5.16 and for cylindrical implants (CI) 57.15±4.83 (p=0.01). Mean insertion torque was 46.67±6.85 Ncm for TI and 35.77±6.72 Ncm for CI (p=0.01). In the maxilla, mean ISQ was 67.2±4.42 for tapered implants and 49.17±15.30 for cylindrical implants (p=0.01). Mean insertion torque for TI was 41.5±6.26 Ncm and for CI 39.17±6.34 Ncm (p>0.05). For tapered implants, no correlation could be found between implant diameter and primary stability. But for cylindrical implants there was a statistically significant correlation between implant diameter and primary stability: ITv (p=0.03); ISQv (p=0.04). Within the limits of the present study, tapered shaped implants achieve higher primary stability measured through ISQ and insertion torque values. Moreover, for cylindrical implants positive correlation has been established between implant diameter and primary stability.

Regional variability of slope stability: Application to the Eel margin, California

USGS Publications Warehouse

Lee, H.; Locat, J.; Dartnell, P.; Israel, K.; Florence, Wong

1999-01-01

Relative values of downslope driving forces and sediment resisting forces determine the locations of submarine slope failures. Both of these vary regionally, and their impact can be addressed when the data are organized in a Geographic Information System (GIS). The study area on the continental margin near the Eel River provides an excellent opportunity to apply GIS spatial analysis techniques for evaluation of slope stability. In this area, swath bathymetric mapping shows seafloor morphology and distribution of slope steepness in fine detail, and sediment analysis of over 70 box cores delineates the variability of sediment density near the seafloor surface. Based on the results of ten geotechnical studies of submarine study areas, we developed an algorithm that relates surface sediment density to the shear strength appropriate to the type of cyclic loading produced by an earthquake. Strength and stress normalization procedures provide results that are conceptually independent of subbottom depth. Results at depth are rigorously applicable if sediment lithology does not vary significantly and consolidation state can be estimated. Otherwise, the method applies only to shallow-seated slope failure. Regional density, slope, and level of anticipated seismic shaking information were combined in a GIS framework to yield a map that illustrates the relative stability of slopes in the face of seismically induced failure. When a measure of predicted relative slope stability is draped on an oblique view of swath bathymetry, a variation in this slope stability is observed on an otherwise smooth slope along the mid-slope region north of a plunging anticline. The section of slope containing diffuse, pockmarked gullies has a lower measure of stability than a separate section containing gullies that have sharper boundaries and somewhat steeper sides. Such an association suggests that our slope-stability analysis relates to the stability of the gully sides. The remainder of the study area shows few obvious indications of slope instability except for a feature that has become known as the 'Humboldt Slide,' but it is too deep-seated to be amenable to the slope-stability-prediction techniques presented herein. In general, few slope failures have been mapped in the Eel margin study area despite the high level of seismicity, the relatively high rates of sediment accumulation, and the extent of gas charging observed by others.

Joint analysis of epistemic and aleatory uncertainty in stability analysis for geo-hazard assessments

NASA Astrophysics Data System (ADS)

Rohmer, Jeremy; Verdel, Thierry

2017-04-01

Uncertainty analysis is an unavoidable task of stability analysis of any geotechnical systems. Such analysis usually relies on the safety factor SF (if SF is below some specified threshold), the failure is possible). The objective of the stability analysis is then to estimate the failure probability P for SF to be below the specified threshold. When dealing with uncertainties, two facets should be considered as outlined by several authors in the domain of geotechnics, namely "aleatoric uncertainty" (also named "randomness" or "intrinsic variability") and "epistemic uncertainty" (i.e. when facing "vague, incomplete or imprecise information" such as limited databases and observations or "imperfect" modelling). The benefits of separating both facets of uncertainty can be seen from a risk management perspective because: - Aleatoric uncertainty, being a property of the system under study, cannot be reduced. However, practical actions can be taken to circumvent the potentially dangerous effects of such variability; - Epistemic uncertainty, being due to the incomplete/imprecise nature of available information, can be reduced by e.g., increasing the number of tests (lab or in site survey), improving the measurement methods or evaluating calculation procedure with model tests, confronting more information sources (expert opinions, data from literature, etc.). Uncertainty treatment in stability analysis usually restricts to the probabilistic framework to represent both facets of uncertainty. Yet, in the domain of geo-hazard assessments (like landslides, mine pillar collapse, rockfalls, etc.), the validity of this approach can be debatable. In the present communication, we propose to review the major criticisms available in the literature against the systematic use of probability in situations of high degree of uncertainty. On this basis, the feasibility of using a more flexible uncertainty representation tool is then investigated, namely Possibility distributions (e.g., Baudrit et al., 2007) for geo-hazard assessments. A graphical tool is then developed to explore: 1. the contribution of both types of uncertainty, aleatoric and epistemic; 2. the regions of the imprecise or random parameters which contribute the most to the imprecision on the failure probability P. The method is applied on two case studies (a mine pillar and a steep slope stability analysis, Rohmer and Verdel, 2014) to investigate the necessity for extra data acquisition on parameters whose imprecision can hardly be modelled by probabilities due to the scarcity of the available information (respectively the extraction ratio and the cliff geometry). References Baudrit, C., Couso, I., & Dubois, D. (2007). Joint propagation of probability and possibility in risk analysis: Towards a formal framework. International Journal of Approximate Reasoning, 45(1), 82-105. Rohmer, J., & Verdel, T. (2014). Joint exploration of regional importance of possibilistic and probabilistic uncertainty in stability analysis. Computers and Geotechnics, 61, 308-315.

Using phase locking for improving frequency stability and tunability of THz-band gyrotrons

NASA Astrophysics Data System (ADS)

Adilova, Asel B.; Gerasimova, Svetlana A.; Melnikova, Maria M.; Tyshkun, Alexandra V.; Rozhnev, Andrey G.; Ryskin, Nikita M.

2018-04-01

Medium-power (10-100 W) THz-band gyrotrons operating in a continuous-wave (CW) mode are of great importance for many applications such as NMR spectroscopy with dynamic nuclear polarization (DNP/NMR), plasma diagnostics, nondestructive inspection, stand-off detection of radioactive materials, biomedical applications, etc. For all these applications, high frequency stability and tunability within 1-2 GHz frequency range is typically required. Apart from different existing techniques for frequency stabilization, phase locking has recently attracted strong interest. In this paper, we present the results of theoretical analysis and numerical simulation for several phase locking techniques: (a) phase locking by injection of the external driving signal; (b) mutual phase locking of two coupled gyrotrons; and (c) selfinjection locking by a wave reflected from the remote load.

Point defect stability in a semicoherent metallic interface

NASA Astrophysics Data System (ADS)

González, C.; Iglesias, R.; Demkowicz, M. J.

2015-02-01

We present a comprehensive density functional theory (DFT) -based study of different aspects of one vacancy and He impurity atom behavior at semicoherent interfaces between the low-solubility transition metals Cu and Nb. Such interfaces have not been previously modeled using DFT. A thorough analysis of the stability and mobility of the two types of defects at the interfaces and neighboring internal layers has been performed and the results have been compared to the equivalent cases in the pure metallic matrices. The different behavior of fcc and bcc metals on both sides of the interface has been specifically assessed. The modeling effort undertaken is the first attempt to study the stability and defect energetics of noncoherent Cu/Nb interfaces from first principles, in order to assess their potential use in radiation-resistant materials.

Verifiable Adaptive Control with Analytical Stability Margins by Optimal Control Modification

NASA Technical Reports Server (NTRS)

Nguyen, Nhan T.

2010-01-01

This paper presents a verifiable model-reference adaptive control method based on an optimal control formulation for linear uncertain systems. A predictor model is formulated to enable a parameter estimation of the system parametric uncertainty. The adaptation is based on both the tracking error and predictor error. Using a singular perturbation argument, it can be shown that the closed-loop system tends to a linear time invariant model asymptotically under an assumption of fast adaptation. A stability margin analysis is given to estimate a lower bound of the time delay margin using a matrix measure method. Using this analytical method, the free design parameter n of the optimal control modification adaptive law can be determined to meet a specification of stability margin for verification purposes.

Preliminary design-lift/cruise fan research and technology airplane flight control system

NASA Technical Reports Server (NTRS)

Gotlieb, P.; Lewis, G. E.; Little, L. J.

1976-01-01

This report presents the preliminary design of a stability augmentation system for a NASA V/STOL research and technology airplane. This stability augmentation system is postulated as the simplest system that meets handling qualities levels for research and technology missions flown by NASA test pilots. The airplane studied in this report is a T-39 fitted with tilting lift/cruise fan nacelles and a nose fan. The propulsion system features a shaft interconnecting the three variable pitch fans and three power plants. The mathematical modeling is based on pre-wind tunnel test estimated data. The selected stability augmentation system uses variable gains scheduled with airspeed. Failure analysis of the system illustrates the benign effect of engine failure. Airplane rate sensor failure must be solved with redundancy.

The preliminary design of a lift-cruise fan airplane flight control system

NASA Technical Reports Server (NTRS)

Gotlieb, P.

1977-01-01

This paper presents the preliminary design of a stability augmentation system for a NASA V/STOL research and technology airplane. This stability augmentation system is postulated as the simplest system that meets handling-quality levels for research and technology missions flown by NASA test pilots. The airplane studied in this report is a modified T-39 fitted with tilting lift/cruise fan nacelles and a nose fan. The propulsion system features a shaft that interconnects three variable-pitch fans and three powerplants. The mathematical modeling is based on pre-wind tunnel test estimated data. The selected stability augmentation system uses variable gains scheduled with airspeed. Failure analysis of the system illustrates the benign effect of engine failure. Airplane rate sensor failure must be solved with redundancy.

Reduced conservatism in stability robustness bounds by state transformation

NASA Technical Reports Server (NTRS)

Yedavalli, R. K.; Liang, Z.

1986-01-01

This note addresses the issue of 'conservatism' in the time domain stability robustness bounds obtained by the Liapunov approach. A state transformation is employed to improve the upper bounds on the linear time-varying perturbation of an asymptotically stable linear time-invariant system for robust stability. This improvement is due to the variance of the conservatism of the Liapunov approach with respect to the basis of the vector space in which the Liapunov function is constructed. Improved bounds are obtained, using a transformation, on elemental and vector norms of perturbations (i.e., structured perturbations) as well as on a matrix norm of perturbations (i.e., unstructured perturbations). For the case of a diagonal transformation, an algorithm is proposed to find the 'optimal' transformation. Several examples are presented to illustrate the proposed analysis.

Robustness properties of discrete time regulators, LOG regulators and hybrid systems

NASA Technical Reports Server (NTRS)

Stein, G.; Athans, M.

1979-01-01

Robustness properites of sample-data LQ regulators are derived which show that these regulators have fundamentally inferior uncertainty tolerances when compared to their continuous-time counterparts. Results are also presented in stability theory, multivariable frequency domain analysis, LQG robustness, and mathematical representations of hybrid systems.

Effect of gravitational and aerodynamic torques on a rigid Skylab-type satellite

NASA Technical Reports Server (NTRS)

Sperling, H. J.

1974-01-01

A theoretical investigation of the influence of the aerodynamic torque on a Skylab-type satellite is presented. Only the case of free flow of uniform velocity and completely diffuse reflection is considered. It is found by linear stability analysis that the satellite has no stable equilibrium.

Control of rabbit myxomatosis in Poland.

PubMed

Górski, J; Mizak, B; Chrobocińska, M

1994-09-01

The authors present an epizootiological analysis of myxomatosis in Poland. The biological, physical and chemical properties of virus strains used for the production and control of 'Myxovac M' vaccine are discussed. The long-term stability, safety and efficacy of the vaccine are demonstrated. Laboratory experiments were confirmed in large-scale field observations.

Orbital stability of solitary waves for Kundu equation

NASA Astrophysics Data System (ADS)

Zhang, Weiguo; Qin, Yinghao; Zhao, Yan; Guo, Boling

In this paper, we consider the Kundu equation which is not a standard Hamiltonian system. The abstract orbital stability theory proposed by Grillakis et al. (1987, 1990) cannot be applied directly to study orbital stability of solitary waves for this equation. Motivated by the idea of Guo and Wu (1995), we construct three invariants of motion and use detailed spectral analysis to obtain orbital stability of solitary waves for Kundu equation. Since Kundu equation is more complex than the derivative Schrödinger equation, we utilize some techniques to overcome some difficulties in this paper. It should be pointed out that the results obtained in this paper are more general than those obtained by Guo and Wu (1995). We present a sufficient condition under which solitary waves are orbitally stable for 2c+sυ<0, while Guo and Wu (1995) only considered the case 2c+sυ>0. We obtain the results on orbital stability of solitary waves for the derivative Schrödinger equation given by Colin and Ohta (2006) as a corollary in this paper. Furthermore, we obtain orbital stability of solitary waves for Chen-Lee-Lin equation and Gerdjikov-Ivanov equation, respectively.

Exact and Approximate Stability of Solutions to Traveling Salesman Problems.

PubMed

Niendorf, Moritz; Girard, Anouck R

2018-02-01

This paper presents the stability analysis of an optimal tour for the symmetric traveling salesman problem (TSP) by obtaining stability regions. The stability region of an optimal tour is the set of all cost changes for which that solution remains optimal and can be understood as the margin of optimality for a solution with respect to perturbations in the problem data. It is known that it is not possible to test in polynomial time whether an optimal tour remains optimal after the cost of an arbitrary set of edges changes. Therefore, this paper develops tractable methods to obtain under and over approximations of stability regions based on neighborhoods and relaxations. The application of the results to the two-neighborhood and the minimum 1 tree (M1T) relaxation are discussed in detail. For Euclidean TSPs, stability regions with respect to vertex location perturbations and the notion of safe radii and location criticalities are introduced. Benefits of this paper include insight into robustness properties of tours, minimum spanning trees, M1Ts, and fast methods to evaluate optimality after perturbations occur. Numerical examples are given to demonstrate the methods and achievable approximation quality.

Genetic analyses using GGE model and a mixed linear model approach, and stability analyses using AMMI bi-plot for late-maturity alpha-amylase activity in bread wheat genotypes.

PubMed

Rasul, Golam; Glover, Karl D; Krishnan, Padmanaban G; Wu, Jixiang; Berzonsky, William A; Fofana, Bourlaye

2017-06-01

Low falling number and discounting grain when it is downgraded in class are the consequences of excessive late-maturity α-amylase activity (LMAA) in bread wheat (Triticum aestivum L.). Grain expressing high LMAA produces poorer quality bread products. To effectively breed for low LMAA, it is necessary to understand what genes control it and how they are expressed, particularly when genotypes are grown in different environments. In this study, an International Collection (IC) of 18 spring wheat genotypes and another set of 15 spring wheat cultivars adapted to South Dakota (SD), USA were assessed to characterize the genetic component of LMAA over 5 and 13 environments, respectively. The data were analysed using a GGE model with a mixed linear model approach and stability analysis was presented using an AMMI bi-plot on R software. All estimated variance components and their proportions to the total phenotypic variance were highly significant for both sets of genotypes, which were validated by the AMMI model analysis. Broad-sense heritability for LMAA was higher in SD adapted cultivars (53%) compared to that in IC (49%). Significant genetic effects and stability analyses showed some genotypes, e.g. 'Lancer', 'Chester' and 'LoSprout' from IC, and 'Alsen', 'Traverse' and 'Forefront' from SD cultivars could be used as parents to develop new cultivars expressing low levels of LMAA. Stability analysis using an AMMI bi-plot revealed that 'Chester', 'Lancer' and 'Advance' were the most stable across environments, while in contrast, 'Kinsman', 'Lerma52' and 'Traverse' exhibited the lowest stability for LMAA across environments.

Metastable tantalum oxide formation during the devitrification of amorphous tantalum thin films

DOE PAGES

Donaldson, Olivia K.; Hattar, Khalid; Trelewicz, Jason R.

2016-07-04

Microstructural evolution during the devitrification of amorphous tantalum thin films synthesized via pulsed laser deposition was investigated using in situ transmission electron microscopy (TEM) combined with ex situ isothermal annealing, bright-field imaging, and electron-diffraction analysis. The phases formed during crystallization and their stability were characterized as a function of the chamber pressure during deposition, devitrification temperature, and annealing time. A range of metastable nanocrystalline tantalum oxides were identified following devitrification including multiple orthorhombic oxide phases, which often were present with, or evolved to, the tetragonal TaO 2 phase. While the appearance of these phases indicated the films were evolving tomore » the stable form of tantalum oxide—monoclinic tantalum pentoxide—it was likely not achieved for the conditions considered due to an insufficient amount of oxygen present in the films following deposition. Nevertheless, the collective in situ and ex situ TEM analysis applied to thin film samples enabled the isolation of a number of metastable tantalum oxides. As a result, new insights were gained into the transformation sequence and stability of these nanocrystalline phases, which presents opportunities for the development of advanced tantalum oxide-based dielectric materials for novel memristor designs.« less

On adaptive modified projective synchronization of a supply chain management system

NASA Astrophysics Data System (ADS)

Tirandaz, Hamed

2017-12-01

In this paper, the synchronization problem of a chaotic supply chain management system is studied. A novel adaptive modified projective synchronization method is introduced to control the behaviour of the leader supply chain system by a follower chaotic system and to adjust the leader system parameters until the measurable errors of the system parameters converge to zero. The stability evaluation and convergence analysis are carried out by the Lyapanov stability theorem. The proposed synchronization and antisynchronization techniques are studied for identical supply chain chaotic systems. Finally, some numerical simulations are presented to verify the effectiveness of the theoretical discussions.

Effect of high-pressure processing on quality and stability of green mango blended mayonnaise.

PubMed

Sethi, Swati; Chauhan, O P; Anurag, Rahul K

2017-07-01

The present work was aimed to study and optimize the high pressure treated green mango blended mayonnaise in terms of oxidative and emulsion stability, as a function of technical parameters; pressure intensity, dwell period and level of green mango pulp. Mayonnaise samples were treated at different combinations of pressure (400-600 MPa), holding time (5-10 min) and level of green mango pulp (10-30%) following Box-Behnken design. Mayonnaise quality was evaluated in terms of oxidative stability and emulsion stability using response surface methodology to optimize the best possible combination among all. Analysis of variance showed that the second-order polynomial model fitted well with the experimental results. Pressure and time were the most important factors determining the oxidative stability (free fatty acids, peroxide value and anisidine value) whereas; the emulsion stability (creaming and thermal creaming) was most significantly affected by the level of green mango pulp. The optimized conditions for preparing green mango blended mayonnaise with high oxidative and emulsion stability were: 435 MPa pressure, 5 min of holding time with the addition of green mango pulp at the rate of 28%. The product prepared at optimum conditions showed good correlations between predicted and actual values.