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1

Stability Analysis for Car Following Model Based on Control Theory

NASA Astrophysics Data System (ADS)

Stability analysis is one of the key issues in car-following theory. The stability analysis with Lyapunov function for the two velocity difference car-following model (for short, TVDM) is conducted and the control method to suppress traffic congestion is introduced. Numerical simulations are given and results are consistent with the theoretical analysis.

Meng, Xiang-Pei; Li, Zhi-Peng; Ge, Hong-Xia

2014-05-01

2

Stability analysis of the ribosome flow model.

Gene translation is a central process in all living organisms. Developing a better understanding of this complex process may have ramifications to almost every biomedical discipline. Recently, Reuveni et al. proposed a new computational model of this process called the ribosome flow model (RFM). In this study, we show that the dynamical behavior of the RFM is relatively simple. There exists a unique equilibrium point e and every trajectory converges to e. Furthermore, convergence is monotone in the sense that the distance to e can never increase. This qualitative behavior is maintained for any feasible set of parameter values, suggesting that the RFM is highly robust. Our analysis is based on a contraction principle and the theory of monotone dynamical systems. These analysis tools may prove useful in studying other properties of the RFM as well as additional intracellular biological processes. PMID:22732691

Margaliot, Michael; Tuller, Tamir

2012-01-01

3

Stability Analysis of a Spinning and Precessing Viscoelastic Rotor Model

NASA Astrophysics Data System (ADS)

The present work deals with stability analysis of a spinning and precessing gyroscopic systems, where the spin axis and precession axis intersect at right angle. The nutation speed is zero, the spin and precession speeds are considered to be uniform and the precession axis is located at one end of the shaft. The properties of the shaft material correspond to a four element type linear viscoelastic model. The shaft disk system is assumed to be axially and torsionally stiff. For analysis, a simple rotor has been considered with the rigid disk placed on a massless viscoelastic shaft at specified locations from one end of the shaft. The governing parametric equations for such a rotor are derived in the simultaneously spinning and precessing frame. A stability analysis is performed considering both two- and four-degree of freedom models. The stability borderlines are computed considering spin and precession speeds as parameters. It is shown that though viscoelastic material may appear attractive for its large material damping, for gyroscopic systems it may lead to unstable vibrations.

Bose, S.; Nandi, A.; Neogy, S.

2013-10-01

4

Adaptive internal model control: Design and stability analysis

This paper shows how adaptation can be combined with an internal model control structure to obtain an adaptive internal model control scheme possessing theoretically provable guarantees of stability. The internal model controller structure is first reviewed in the context of the YJBK parametrization of all stabilizing controllers, and its appropriateness for the control of open-loop stable plants is discussed. Using

Aniruddha Datta; James Ochoa

1996-01-01

5

A Coupled Aeroelastic Model for Launch Vehicle Stability Analysis

NASA Technical Reports Server (NTRS)

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.

Orr, Jeb S.

2010-01-01

6

Models and Stability Analysis of Boiling Water Reactors

We have studied the nuclear-coupled thermal-hydraulic stability of boiling water reactors (BWRs) using a model that includes: space-time modal neutron kinetics based on spatial w-modes; single- and two-phase flow in parallel boiling channels; fuel rod heat conduction dynamics; and a simple model of the recirculation loop. The BR model is represented by a set of time-dependent nonlinear ordinary differential equations, and is studied as a dynamical system using the modern bifurcation theory and nonlinear dynamical systems analysis. We first determine the stability boundary (SB) - or Hopf bifurcation set- in the most relevant parameter plane, the inlet-subcooling-number/external-pressure-drop plane, for a fixed control rod induced external reactivity equal to the 100% rod line value; then we transform the SB to the practical power-flow map used by BWR operating engineers and regulatory agencies. Using this SB, we show that the normal operating point at 100% power is very stable, that stability of points on the 100% rod line decreases as the flow rate is reduced, and that operating points in the low-flow/high-power region are least stable. We also determine the SB that results when the modal kinetics is replaced by simple point reactor kinetics, and we thereby show that the first harmonic mode does not have a significant effect on the SB. However, we later show that it nevertheless has a significant effect on stability because it affects the basin of attraction of stable operating points. Using numerical simulations we show that, in the important low-flow/high-power region, the Hopf bifurcation that occurs as the SB is crossed is subcritical; hence, growing oscillations can result following small finite perturbations of stable steady-states on the 100% rod line at points in the low-flow/high-power region. Numerical simulations are also performed to calculate the decay ratios (DRs) and frequencies of oscillations for various points on the 100% rod line. It is determined that the U.S. NRC requirement of DR is not rigorously satisfied in the low-flow/high-power region; hence, this region should be avoided during normal startup and shutdown operations. The frequency of oscillation is shown to decrease as the flow rate is reduced. Moreover, the simulation frequency of 0.5Hz determined in the low-flow/high-power region is consistent with those observed during actual instability incidents. Additional numerical simulations show that in the low-flow/high-power region, for the same initial conditions, the use of point kinetics leads to damped oscillations, whereas the model that includes the modal neutron kinetics equations results in growing nonlinear oscillations.

John Dorning

2002-04-15

7

This paper deals with the design of a model identification fuzzy adaptive controller with real-time scaling factors adjustment and the stability analysis of nonlinear distributed parameter systems. The solution branch of such systems frequently contains limit points (or turning points) which represent the boundary between stability and instability of the system. Hence, stability analysis is required for the determination of

D. I. Sagias; E. N. Sarafis; C. I. Siettos; G. V. Bafas

2001-01-01

8

Stability analysis of the Interacting Multiple Model algorithm

The interacting multiple model (IMM) algorithm is a well-known state estimation algorithm for hybrid systems. We derive a lower bound and an upper bound for the error covariance of the IMM algorithm for controllable and observable hybrid systems. We then derive sufficient conditions for the exponential stability of the IMM algorithm for a special class of hybrid systems by the

Chze Eng Seah; Inseok Hwang

2008-01-01

9

Stability Analysis of a Model for Foreign Body Fibrotic Reactions

Implanted medical devices often trigger immunological and inflammatory reactions from surrounding tissues. The foreign body-mediated tissue responses may result in varying degrees of fibrotic tissue formation. There is an intensive research interest in the area of wound healing modeling, and quantitative methods are proposed to systematically study the behavior of this complex system of multiple cells, proteins, and enzymes. This paper introduces a kinetics-based model for analyzing reactions of various cells/proteins and biochemical processes as well as their transient behavior during the implant healing in 2-dimensional space. In particular, we provide a detailed modeling study of different roles of macrophages (M?) and their effects on fibrotic reactions. The main mathematical result indicates that the stability of the inflamed steady state depends primarily on the reaction dynamics of the system. However, if the said equilibrium is unstable by its reaction-only system, the spatial diffusion and chemotactic effects can help to stabilize when the model is dominated by classical and regulatory macrophages over the inflammatory macrophages. The mathematical proof and counter examples are given for these conclusions.

Ibraguimov, A.; Owens, L.; Su, J.; Tang, L.

2012-01-01

10

Nuclear power plant modeling and steam generator stability analysis. [TRANSG-P Code

This thesis describes the development of a computer model simulating the transient behavior of a pressurized water reactor (PWR) nuclear steam supply system (NSSS) and a stability analysis of steam generators in an overall NSSS structure. In the analysis of stream generator stability characteristics, an emphasis was placed on the physical interpretation of density wave oscillation (DWO) phenomena in boiling

Kornfilt

1981-01-01

11

Stability analysis of discrete-time BAM neural networks based on standard neural network models

To facilitate stability analysis of discrete-time bidirectional associative memory (BAM) neural networks, they were converted\\u000a into novel neural network models, termed standard neural network models (SNNMs), which interconnect linear dynamic systems\\u000a and bounded static nonlinear operators. By combining a number of different Lyapunov functionals with S-procedure, some useful\\u000a criteria of global asymptotic stability and global exponential stability of the equilibrium

Zhang Sen-lin; Liu Mei-qin

2005-01-01

12

Use of recurrence analysis to measure the dynamical stability of a multi-species community model

NASA Astrophysics Data System (ADS)

Quantifying the effects of species richness and environmental disturbance on the stability of communities is a long-standing challenge in ecology. In this study, multivariate recurrence analysis was used to assess the dynamical stability of modelled ecological communities subject to random, correlated environmental noise. Based on an analysis of biomass time series for each species, we show that two measures computed from the joint recurrence matrix, the Kolmogorov entropy and percent determinism, capture aspects of community stability that are not detected using the coefficient of variation for the whole community. In particular, when population fluctuations are correlated in time, recurrence analysis is a superior method for detecting the stabilizing effect of species richness on a community. We conclude that recurrence analysis is an appropriate tool for the analysis of ecological data, and that it may be particularly useful for detecting the relative importance of exogenous and endogenous drivers on the dynamics of ecological communities.

Proulx, R.; Côté, P.; Parrott, L.

2008-10-01

13

In this paper we demonstrate how the recently developed sum of squares techniques can be used to analyze robust stability and robust performance of quasi-LPV models. We show the effectiveness of the methodology through the analysis of the stability and performance of a nonlinear control law applied to an uncertain quasi-LPV model of the short-period dynamics of an F\\/A-18 aircraft

Antonis Papachristodoulou; Christakis Papageorgiou

2005-01-01

14

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

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

Wu, Jiang Hao; Sun, Mao

2012-09-01

15

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

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.

Wu, Jiang Hao; Sun, Mao

2012-01-01

16

Stability analysis of a stochastic logistic model with infinite delay

NASA Astrophysics Data System (ADS)

This report is concerned with a stochastic logistic equation with infinite delay. We establish the sufficient conditions for global asymptotical stability of the zero solution and the positive equilibrium. Some classical results are improved and extended. Several numerical simulations are introduced to illustrate the main results.

Liu, Meng; Fan, Dejun; Wang, Ke

2013-09-01

17

NASA Astrophysics Data System (ADS)

Linear stability analysis is used to predict the vertical and lateral structure for the diffusivity related to meso-scale eddy buoyancy and potential vorticity fluxes in three-dimensional primitive equation models, following a suggestion by Peter D. Killworth. Using two idealized numerical models as example, it is shown that the linear stability analysis yields a consistent lateral and vertical structure for both lateral diffusivities. Parameterizations based on isopycnal thickness or potential vorticity diffusion are shown to be equivalent for constant diffusivities in quasi-geostrophic approximation. For spatially varying diffusivities they yield similar results in the model experiments, although the corresponding diffusivities show different vertical structure.

Eden, Carsten

2012-11-01

18

A Motorcycle Model for Stability and Control Analysis

The observed dynamic behaviour of motorcycles suggests that interesting and significant motions occur that are not currently understood. The most elaborate modelling exercise completed so far has produced results that need confirmation and extension. The construction of these models necessitates the use of automated methods and one such modelling methodology is described. The automated model building platform that was used

ROBIN S. SHARP; DAVID J. N. LIMEBEER

2001-01-01

19

On the dynamics of ball end milling: modeling of cutting forces and stability analysis

This paper presents a dynamic force model and a stability analysis for ball end milling. The concept of the equivalent orthogonal cutting conditions, applied to modeling of the mechanics of ball end milling, is extended to include the dynamics of cutting forces. The tool is divided into very thin slices and the cutting force applied to each slice is calculated

F. Abrari; M. A. Elbestawi; A. D. Spence

1998-01-01

20

The controlling unstable equilibrium point (CUEP) method developed for the traditional network-reduction power-system (transient-stability) model requires some modification for direct stability analysis of the network-preserving power system model. This is mainly due to the peculiar nonlinear jump behaviors occurring in network-preserving power system model. An extended CUEP method suitable for direct stability analysis of network-preserving models is developed. The extended

Yun Zou; Ming-Hui Yin; Hsiao-Dong Chiang

2003-01-01

21

The stability analysis of the full velocity and acceleration velocity model

The stability analysis is one of the important problems in the traffic flow theory, since the congestion phenomena can be regarded as the instability and the phase transition of a dynamical system. Theoretically, we analyze the stable conditions of the full velocity and acceleration difference model (FVADM), which is proposed by introducing the acceleration difference term based on the previous

Zhao Xiaomei; Gao Ziyou

2007-01-01

22

Stability analysis of the RF linac based on an AR model

NASA Astrophysics Data System (ADS)

We are pursing operational stability of the RF linac with a method of system analysis. The RF phase and the power for the pre-buncher have been measured, together with environmental parameters including temperatures of the main components, the room temperatures and the AC line voltage. The measured data have been analyzed with the autoregressive model, and the feedback structure of the system has been derived from noise contribution ratios and impulse responses analysis. It was found that the AC line voltage and the temperatures of the klystron room significantly affected operational stability of the linac.

Kato, R.; Isaka, S.; Sakaki, H.; Kashiwagi, S.; Isoyama, G.

2004-08-01

23

A stability analysis of fuzzy control system using a generalized fuzzy Petri net model

Stability analysis of a fuzzy control system has been one of the main topics of fuzzy control. A Petri net, representing a discretized fuzzy control system, has been applied to the stability analysis. A theory of asymptotic stability has been derived for the approximated control system. However, this theory guarantees the stability of nominal behavior of a fuzzy control system.

Takeshi Furuhashi; H. Kakami; J. Peters; W. Pedrycz

1998-01-01

24

Analysis of stability and density waves of traffic flow model in an ITS environment

NASA Astrophysics Data System (ADS)

By introducing relative velocities of arbitrary number of cars ahead into the full velocity difference models (FVDM), we present a forward looking relative velocity model (FLRVM) of cooperative driving control system. To our knowledge, the model is an improvement over the similar extension in the forward looking optimal velocity models (FLOVM), because it is more reasonable and realistic in implement of incorporating intelligent transportation system in traffic. Then the stability criterion is investigated by the linear stability analysis with finding that new consideration theoretically lead to the improvement of the stability of traffic flow, and the validity of our theoretical analysis is confirmed by direct simulations. In addition, nonlinear analysis of the model shows that the three waves: triangular shock wave, soliton wave and kink-antikink wave appear respectively in stable, metastable and unstable regions. These correspond to the solutions of the Burgers equation, Korteweg-de Vries (KdV) equation and modified Korteweg-de Vries (mKdV) equation.

Li, Z.-P.; Liu, Y.-C.

2006-10-01

25

A fluid-structure interaction model for stability analysis of shells conveying fluid

NASA Astrophysics Data System (ADS)

In this paper, a fluid-structure interaction model for stability analysis of shells conveying fluid is developed. This model is developed for shells of arbitrary geometry and structure and is based on incompressible potential flow. The boundary element method is applied to model the potential flow. The fluid dynamics model is derived by using an inflow/outflow model along with the impermeability condition at the fluid-shell interface. This model is applied to obtain the flow modes and eigenvalues, which are used for the modal representation of the flow field in the shell. Based on the mode shapes and natural frequencies of the shell obtained from an FEM model, the modal analysis technique is used for structural modeling of the shell. Using the linearized Bernoulli equation for unsteady pressure on the fluid-shell interface in combination with the virtual work principle, the generalized structural forces are obtained in terms of the modal coordinates of the fluid flow and the coupled field equations of the fluid-structure are derived. The obtained model is validated by comparison with results in the literature, and very good agreement is demonstrated. Then, some examples are provided to demonstrate the application of the present model to determining the stability conditions of shells with arbitrary geometries.

Firouz-Abadi, R. D.; Noorian, M. A.; Haddadpour, H.

2010-07-01

26

Sensitivity analysis and calibration of a coupled hydrological/slope stability model (TRIGRS)

NASA Astrophysics Data System (ADS)

Shallow landslides potentially endanger human living in mountain regions worldwide. In order to prevent impacts of such gravitational mass movements it is necessary to fully understand the processes involved. Shallow landslides are usually understood as gravitational mass movements of the translational, slope-parallel type comprising of a mixture of earth and debris with a maximum depth of 1-2 m. Depending on the degree of saturation the initial sliding can turn into a flow-like movement. Numerous approaches for modelling shallow landslide susceptibility with different degrees of complexity exist. Regardless of the modelling approach it is crucial to provide sufficient field data, mainly on regolith characteristics. As for the TRIGRS (Transient Rainfall Infiltration and Grid-Based Regional Slope-Stability) model, numerous hydraulic and geotechnical parameters have to be known area-wide. Hence, as spatial interpolation of these input parameters is generally problematic in terms of accuracy, calibrating the model accordingly is a crucial step before conducting any simulations. This study presents a sensitivity analysis and the calibration of the coupled hydrological/slope stability model TRIGRS for a study area in Vorarlberg (Austria). The results of the sensitivity analysis show that in case of the stability model cohesion is the driving parameter while for the hydrological model it is the initial depth of the water table and the saturated hydraulic conductivity. The calibration of the stability model was carried out using a landslide inventory assuming completely saturated conditions. The use of geotechnical parameters extracted from literature for mapped soil types generally lead to unlikely stable conditions. In order to simulate mapped landslide initial areas correctly values for soil cohesion had to be adapted. However, the calibration of the stability model generally supports the assumption of saturated conditions. In absence of meteorological or hydrological data the hydrological model was calibrated using the landslide inventory aiming at saturated conditions for the respective landslide initial zones. Simulations conducted with the calibrated input parameters generally lead to conservatively unstable conditions. However, it has to be noted that the TRIGRS model does not account for effects of vegetation on slope hydrology and stability (e.g. interception or root cohesion). This work has been conducted within C3S-ISLS, which is funded by the Austrian Climate and Energy Fund, 5th ACRP Program. http://www.uibk.ac.at/geographie/lidar/c3s/c3s.html

Zieher, Thomas; Rutzinger, Martin; Perzl, Frank; Meißl, Gertraud

2014-05-01

27

We present a general approach to generate a linear parametric state-space model, which approximates a nonlinear system with high accuracy. It is optimally suited for LFT-based robust stability analysis and control design. At the beginning a Jacobian-based linearization is applied to generate a set of linearized state-space systems describing the local behavior of the nonlinear plant about the corresponding equilibrium

Harald Pfifer; Simon Hecker

2008-01-01

28

Linear stability analysis of a two-fluid model for air–water bubble columns

Linear stability analysis is performed for the two-dimensional, two-fluid model for gas–liquid flow applied in our previous computational study of bubble columns [Monahan, S.M., Vitankar, V.S., Fox, R.O., 2005. CFD predictions for flow-regime transitions in bubble columns. A.I.Ch.E. Journal 51, 1897–1923]. The growth rate and the velocity of propagation for a small-amplitude disturbance wave are shown to be highly dependent

Sarah M. Monahan; Rodney O. Fox

2007-01-01

29

NASA Technical Reports Server (NTRS)

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.

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

1985-01-01

30

The Distance Constraint Model (DCM) is a computational modeling scheme that uniquely integrates thermodynamic and mechanical descriptions of protein structure. As such, quantitative stability-flexibility relationships (QSFR) that describe the interrelationships of thermodynamics and mechanics can be quickly computed. Using comparative QSFR analyses, we have previously investigated these relationships across a small number of protein orthologs, ranging from two to a dozen [1, 2]. However, our ultimate goal is provide a comprehensive analysis of whole protein families, which requires consideration of many more structures. To that end, we have developed homology modeling and assessment protocols so that we can robustly calculate QSFR properties for proteins without experimentally derived structures. The approach, which is presented here, starts from a large ensemble of potential homology models and uses a clustering algorithm to identify the best models, thus paving the way for a comprehensive QSFR analysis across hundreds of proteins in a protein family. PMID:24061925

Verma, Deeptak; Guo, Jun-Tao; Jacobs, Donald J; Livesay, Dennis R

2014-01-01

31

A lumped model of neural activity in neocortex is studied to identify regions of multi-stability of both steady states and periodic solutions. Presence of both steady states and periodic solutions is considered to correspond with epileptogenesis. The model, which consists of two delay differential equations with two fixed time lags is mainly studied for its dependency on varying connection strength between populations. Equilibria are identified, and using linear stability analysis, all transitions are determined under which both trivial and non-trivial fixed points lose stability. Periodic solutions arising at some of these bifurcations are numerically studied with a two-parameter bifurcation analysis.

2012-01-01

32

NASA Astrophysics Data System (ADS)

For a number of years, the United States Federal Government has been formulating the Next Generation Air Transportation System plans for National Airspace System improvement. These improvements attempt to address air transportation holistically, but often address individual improvements in one arena such as ground or in-flight equipment. In fact, air transportation system designers have had only limited success using traditional Operations Research and parametric modeling approaches in their analyses of innovative operations. They need a systemic methodology for modeling of safety-critical infrastructure that is comprehensive, objective, and sufficiently concrete, yet simple enough to be deployed with reasonable investment. The methodology must also be amenable to quantitative analysis so issues of system safety and stability can be rigorously addressed. The literature suggests that both agent-based models and network analysis techniques may be useful for complex system development and analysis. The purpose of this research is to evaluate these two techniques as applied to analysis of commercial air carrier schedule (route) stability in daily operations, an important component of air transportation. Airline-like routing strategies are used to educe essential elements of applying the method. Two main models are developed, one investigating the network properties of the route structure, the other an Agent-based approach. The two methods are used to predict system properties at a macro-level. These findings are compared to observed route network performance measured by adherence to a schedule to provide validation of the results. Those interested in complex system modeling are provided some indication as to when either or both of the techniques would be applicable. For aviation policy makers, the results point to a toolset capable of providing insight into the system behavior during the formative phases of development and transformation with relatively low investment. Both Agent-Based Modeling and Network Analysis were found to be useful in this context, particularly when applied with an eye towards the system context, and concentrated effort on capturing the salient features of the system of interest.

Conway, Sheila Ruth

33

NASA Astrophysics Data System (ADS)

Magnetic shape memory alloys (MSMAs) are a class of active materials that deform under magnetic and mechanical loading conditions. This work is concerned with the modeling of MSMAs constitutive responses. The hysteretic magneto-mechanical responses of such materials are governed by two major mechanisms which are variant reorientation and field induced phase transformation (FIPT). The most widely used material for variant reorientation is Ni2MnGa which can produce up to 6% magnetic field induced strain (MFIS) under 5 MPa actuation stress. The major drawback of this material is a low blocking stress, which is overcome in the NiMnCoIn material system through FIPT. This magnetic alloy can exhibit 5% MFIS under 125 MPa actuation stress. The focus of this work is to capture the key magneto-thermo-mechanical responses of such mechanisms through phenomenological modeling. In this work a detailed thermodynamic framework for the electromagnetic interaction within a continuum solid is presented. A Gibbs free energy function is postulated after identifying the external and internal state variables. Material symmetry restrictions are imposed on the Gibbs free energy and on the evolution equations of the internal state variables. Discrete symmetry is considered for single crystals whereas continuous symmetry is considered for polycrystalline materials. The constitutive equations are derived in a thermodynamically consistent way. A specific form of Gibbs free energy for FIPT is proposed and the explicit form of the constitutive equations is derived from the generalized formulation. The model is calibrated from experimental data and different predictions of magneto-thermo-mechanical loading conditions are presented. The generalized constitutive equations are then reduced to capture variant reorientation. A coupled magneto-mechanical boundary value problem (BVP) is solved that accounts for variant reorientation to investigate the influence of the demagnetization effect on the magnetic field and the effect of Maxwell stress on the Cauchy stress. The BVP, which mimics a real experiment, provides a methodology to correlate the difference between the externally measured magnetic data and internal magnetic field of the specimen due to the demagnetization effect. The numerical results show that localization zones appear inside the material between a certain ranges of applied magnetic field. Stability analysis is performed for variant reorientation to analyze these numerical observations. Detailed numerical and analytical analysis is presented to investigate these localization zones. Magnetostatic stability analysis reveals that the MSMA material system becomes unstable when localizations appear due to non-linear magnetization response. Coupled magneto-mechanical stability analysis shows that magnetically induced localization creates stress-localizations in the unstable zones. A parametric study is performed to show the constraints on material parameters for stable and unstable material responses.

Haldar, Krishnendu

34

Stability analysis of a viscoelastic model for ion-irradiated silicon

NASA Astrophysics Data System (ADS)

Recently, elastic stress has been among several mechanisms hypothesized to induce the formation of ordered structures in Si irradiated at normal incidence by energetic ions. To test this hypothesis, we model the thin amorphous film atop ion-irradiated Si as a viscoelastic continuum into which the ion beam continually injects biaxial compressive stress. We find that at normal incidence, the model predicts a steady compressive stress of a magnitude comparable to experiment and molecular dynamics simulation. However, linear stability analysis at normal incidence reveals that this mechanism of stress generation is unconditionally stabilizing due to a purely kinematic material flow, depending on none of the material parameters. Thus, despite plausible conjectures in the literature as to its potential role in pattern formation, we conclude that compressive stress induced by normal-incidence ion bombardment is unlikely to be a source of instability at any energy. In fact, with this result, all hypothesized mechanisms suggested to explain structures on pure materials under normal incidence irradiation have now been overturned, supporting recent theories attributing hexagonal ordered dots to the effects of composition. In addition to this result, we find that the elastic moduli appear in neither the steady film stress nor the leading-order smoothening, suggesting that the primary effects of stress can be captured even if elasticity is neglected. This supports the basic framework recently adopted by other authors and should allow future analytical studies of highly nonplanar surface evolution, in which the beam-injected stress is considered to be an important effect.

Norris, Scott A.

2012-04-01

35

Slope Stability Analysis Program

NSDL National Science Digital Library

This site provides information as well as a downloadable demo version of a slope stability and reinforced soil analysis and design software. The software includes an analysis option which analyzes strata profile and groundwater conditions, surcharge loads and earthquake forces, slip surfaces, and reinforced soil options. Data input and editing can also be performed as well as output from the program and graphics.

2008-07-17

36

Stability analysis of a stochastic Gilpin-Ayala model driven by Lévy noise

NASA Astrophysics Data System (ADS)

A stochastic one-dimensional Gilpin-Ayala model driven by Lévy noise is presented in this paper. Firstly, we show that this model has a unique global positive solution under certain conditions. Then sufficient conditions for the almost sure exponential stability and moment exponential stability of the trivial solution are established. Results show that the jump noise can make the trivial solution stable under some conditions. Numerical example is introduced to illustrate the results.

Zhang, Xinhong; Wang, Ke

2014-05-01

37

The improvement of OPC accuracy and stability by the model parameters' analysis and optimization

NASA Astrophysics Data System (ADS)

The OPC model is very critical in the sub 45nm device because the Critical Dimension Uniformity (CDU) is so tight to meet the device performance and the process window latitude for the production level. The OPC model is generally composed of an optical model and a resist model. Each of them has physical terms to be calculated without any wafer data and empirical terms to be fitted with real wafer data to make the optical modeling and the resist modeling. Empirical terms are usually related to the OPC accuracy, but are likely to be overestimated with the wafer data and so those terms can deteriorate OPC stability in case of being overestimated by a small cost function. Several physical terms have been used with ideal value in the optical property and even weren't be considered because those parameters didn't give a critical impact on the OPC accuracy, but these parameters become necessary to be applied to the OPC modeling at the low k1 process. Currently, real optic parameter instead of ideal optical parameter like the laser bandwidth, source map, pupil polarization including the phase and intensity difference start to be measured and those real measured value are used for the OPC modeling. These measured values can improve the model accuracy and stability. In the other hand these parameters can make the OPC model to overcorrect the process proximity errors without careful handling. The laser bandwidth, source map, pupil polarization, and focus centering for the optical modeling are analyzed and the sample data weight scheme and resist model terms are investigated, too. The image blurring by actual laser bandwidth in the exposure system is modeled and the modeling result shows that the extraction of the 2D patterns is necessary to get a reasonable result due to the 2D patterns' measurement noise in the SEM. The source map data from the exposure machine shows lots of horizontal and vertical intensity difference and this phenomenon must come from the measurement noise because this huge intensity difference can't be caused by the scanner system with respect to the X-Y intensity difference specification in the scanner. Therefore this source map should be well organized for the OPC modeling and a manipulated source map improves the horizontal and vertical mask bias and even OPC convergence. The focus parameter which is critical for the process window OPC and ORC should be matched to the tilted Bossung plot which is caused by uncorrectable aberration to predict the CD change in the through focus with a new devised method. Pupil polarization data can be applied into the OPC modeling and this parameter is also used for the unpolarized source and the polarized source and specially this parameter helps Apodization loss to be 0 and is evaluated for the effect into the modeling. With the analysis and optimization about the model parameters the robust model is achieved in the sub 45nm device node.

Chung, No-Young; Choi, Woon-Hyuk; Lee, Sung-Ho; Kim, Sung-Il; Lee, Sun-Yong

2007-10-01

38

Safe distance car-following model including backward-looking and its stability analysis

NASA Astrophysics Data System (ADS)

The focus of this paper is the car-following behavior including backward-looking, simply called the bi-directional looking car-following behavior. This study is motivated by the potential changes of the physical properties of traffic flow caused by the fast developing intelligent transportation system (ITS), especially the new connected vehicle technology. Existing studies on this topic focused on general motors (GM) models and optimal velocity (OV) models. The safe distance car-following model, Gipps' model, which is more widely used in practice have not drawn too much attention in the bi-directional looking context. This paper explores the property of the bi-directional looking extension of Gipps' safe distance model. The stability condition of the proposed model is derived using the linear stability theory and is verified using numerical simulations. The impacts of the driver and vehicle characteristics appeared in the proposed model on the traffic flow stability are also investigated. It is found that taking into account the backward-looking effect in car-following has three types of effect on traffic flow: stabilizing, destabilizing and producing non-physical phenomenon. This conclusion is more sophisticated than the study results based on the OV bi-directional looking car-following models. Moreover, the drivers who have the smaller reaction time or the larger additional delay and think the other vehicles have larger maximum decelerations can stabilize traffic flow.

Yang, Da; Jin, Peter Jing; Pu, Yun; Ran, Bin

2013-03-01

39

Lumped-density population models of pioneer-climax type and stability analysis of Hopf bifurcations.

The effects of population density on the survival and growth of an individual species are modeled by assuming that the species per capita growth rate (i.e., fitness) is a function of a weighted total density. A species is called a pioneer population if it thrives at low density but its fitness decreases monotonically with increasing density. A species is called a climax population if its fitness increases up to a maximum value and then decreases as a function of its total density. Hopf bifurcations for deterministic models of the interaction of pioneer and climax populations are discussed. Stability properties for the Hopf invariant curves in the discrete models are compared to the stability properties of the Hopf periodic orbits in the corresponding continuous models. Examples illustrate that stability may be more common in the discrete models. PMID:8688563

Selgrade, J F; Roberds, J H

1996-07-01

40

Analysis of stability of unsaturated soil slope based on modified cam-clay model

Rainfall is usually the major factor causing the slope failure of unsaturated soils which is due to permeation of rainwater causing the increase of degree of saturation of soils and decrease of shear strength. This paper considers increase of the degree of saturation of soils due to rainfall. Plaxis finite element analysis software is used to analysis the stability of

Ying Cui; Miao Lin-chang

2011-01-01

41

Stability and bifurcation analysis in the cross-coupled laser model with delay

The dynamics of the cross-coupled laser model with delay has been investigated. The investigation confirms that a Hopf bifurcation\\u000a occurs due to the existence of stability switches when the product of the coupling strengths varies. An algorithm for determining\\u000a the stability and direction of the Hopf bifurcation is derived by applying the normal form theory and the center manifold\\u000a theorem.

Junjie Wei; Chunbo Yu

42

Analysis of Composite Load Models on Load Margin of Voltage Stability

While it has been widely accepted that the constant P-Q leads to conservative load margin calculation of voltage stability, lately the studies show that induction motor loads can lead to an even more conservative load margin calculation. This paper analyzes the impacts of the composite load model (the composite of ZIP and induction motor load models) on the load margin

Shao-Hua Li; Hsiao-Dong Chiang; Sheng Liu

2006-01-01

43

Approximate linear stability analysis of a model of adiabatic shear band formation

The formation of adiabatic shear bands in ductile metals under dynamic loading conditions is generally thought to result from a material instability, which is associated with a peak in the curve of engineering plastic flow stress vs. engineering shear strain. This instability arises from the effect of thermal softening, caused by irreversible adiabatic heating, which counteracts the tendency of the material to harden with increasing plastic strain. An approximate linear stability analysis of a one-dimensional rigid-thermoviscoplastic model, based on data taken from dynamic torsion experiments on thin-walled tubes of mild steel, shows that shear band formation in this situation can be interpreted as a bifurcation from a homogeneous simple shearing deformation which occurs at the peak in the homogeneous stess vs. strain curve. The asymptotic method of multiple scales is used to show that the growth rate of small perturbations on the homogeneous deformation is controlled by the ratio of the slope of the homogeneous stress vs. strain curve to the material viscosity, i.e., the rate of change of the plastic flow stress with respect to the strain-rate. In addition, it is shown that this growth rate is essentially independent of wavelength in any small perturbation. Numerical methods are used to show that this growth rate beyond the bifurcation point may not be sufficiently large for the model to account for the experimental data, and some suggestions are made on how to modify the constitutive equation so that it better fits the experimental data.

Burns, T.J.

1985-04-01

44

Approximate linear stability analysis of a model of adiabatic shear-band formation

The formation of adiabatic shear bands in ductile metals under dynamic loading conditions is generally thought to result from a material instability, which is associated with a peak in the curve of engineering plastic flow stress vs engineering shear strain. This instability arises from the effect of thermal softening, caused by irreversible adiabatic heating, which counteracts the tendency of the material to harden with increasing plastic strain. An approximate linear stability analysis of a one-dimensional rigid-thermoviscoplastic model, based on data taken from dynamic torsion experiments on thin-walled tubes of mild steel, shows that shear band formation in this situation can be interpreted as a bifurcation from a homogeneous simple shearing deformation which occurs at the peak in the homogeneous stress vs strain curve. The asymptotic method of multiple scales is used to show that the growth rate of small perturbations on the homogeneous deformation is controlled by the ratio of the slope of the homogeneous stress vs strain curve to the material viscosity, i.e., the rate of change of the plastic flow stress with respect to the strain-rate. In addition, it is shown that this growth rate is essentially independent of wavelength in any small perturbation. Numerical methods are used to show that this growth rate beyond the bifurcation point may not be sufficiently large for the model to account for the experimental data, and some suggestions are made on how to modify the constitutive equation so that it better fits the experimental data.

Burns, T.J.

1983-10-01

45

This paper deals with modeling and stability analysis of a doubly-fed induction generator (DFIG)-based wind-power unit that is interfaced with the grid via a series-compensated transmission line. A detailed mathematical model is developed in this paper that takes into account dynamics of the flux observer, phase-locked loop (PLL), controllers of the power-electronic converter, and wind turbine. Using the model and

Amir Ostadi; Amirnaser Yazdani; Rajiv K. Varma

2009-01-01

46

Design and stability analysis of an indirect variable structure model reference adaptive control

This paper presents the stability and robustness analysis of an indirect adaptive control based variable structure algorithm for uncertain plants with relative degree one. The indirect approach has been proposed as a way to get an easier design of the switching laws, compared to the direct relationship between the plant transfer function parameters and the physical parameters of the system.

J. B. Oliveira; A. D. Araujo

2008-01-01

47

NASA Astrophysics Data System (ADS)

In day-to-day traffic assignment problems travelers’ past experiences have important impact on their cost prediction which influences their route choice and consequently the arising flow patterns in the network. Many travelers execute the same trip in every few days, not daily, which leads to time delays in the system. In this paper, we propose a nonlinear, discrete-time model with driver experience delay. The linear stability of the stochastic user equilibrium is analyzed by studying the eigenvalues of the Jacobian matrix of the system while the nonlinear oscillations arising at the bifurcations are investigated by normal form calculations, numerical continuation and simulation. The methods are demonstrated on a two-route example. By applying rigorous analysis we show that the linearly unstable parameter domain as well as the period of arising oscillations increase with the delay. Moreover, delays and nonlinearities result in an extended domain of bistability where the stochastic user equilibrium coexists with stable and unstable oscillations. This study explains the influence of initial conditions on the dynamics of transportation networks and may provide guidance for network design and management.

Zhao, Xiaomei; Orosz, Gábor

2014-05-01

48

In order to conveniently analyze the stability of various discrete-time recurrent neural networks (RNNs), including bidirectional\\u000a associative memory, Hopfield, cellular neural network, Cohen-Grossberg neural network, and recurrent multiplayer perceptrons,\\u000a etc., the novel neural network model, named standard neural network model (SNNM) is advanced to describe this class of discrete-time\\u000a RNNs. The SNNM is the interconnection of a linear dynamic system

Meiqin Liu

2009-01-01

49

NASA Technical Reports Server (NTRS)

In pursuit of higher performance, the XV-15 Tiltrotor Research Aircraft was modified by the installation of new composite rotor blades. Initial flights with the Advanced Technology Blades (ATB's) revealed excessive rotor control loads that were traced to a dynamic mismatch between the blades and the aircraft control system. The analytical models of both the blades and the mechanical controls were extensively revised for use by the CAMRAD computer program to better predict aeroelastic stability and loads. This report documents the most important revisions and discusses their effects on aeroelastic stability predictions for airplane-mode flight. The ATB's may be flown in several different configurations for research, including changes in blade sweep and tip twist. The effects on stability of 1 deg and 0 deg sweep are illustrated, as are those of twisted and zero-twist tips. This report also discusses the effects of stiffening the rotor control system, which was done by locking out lateral cyclic swashplate motion with shims.

Acree, C. W., Jr.

1993-01-01

50

"Multi-layer" one-dimensional model for stability analysis on partially detached divertor plasmas

NASA Astrophysics Data System (ADS)

We propose a "multi-layer (ML)" 1D model for understanding behaviors of partially detached divertor plasmas. The basic idea is to analyze interaction among the adjacent flux tubes for the attached and detached states in the divertor region. Cross-field transport terms in both SOL and divertor regions are considered in this model. We show some preliminary simulations which indicate necessity of the ML 1D model. According to the simulations, cross-field energy flow in the divertor region can affect stability of a detachment front of partially detached plasmas, i.e. such flow can decrease the front speed towards the X point.

Nakamura, Makoto; Ogawa, Yuichi; Shinji, Naoki; Hiwatari, Ryoji; Okano, Kunihiko

2011-08-01

51

Local and global stability analysis of a two prey one predator model with help

NASA Astrophysics Data System (ADS)

In this paper we propose and study a three dimensional continuous time dynamical system modelling a three team consists of two preys and one predator with the assumption that during predation the members of both teams of preys help each other and the rate of predation of both teams are different. In this work we establish the local asymptotic stability of various equilibrium points to understand the dynamics of the model system. Different conditions for the coexistence of equilibrium solutions are discussed. Persistence, permanence of the system and global stability of the positive interior equilibrium solution are discussed by constructing suitable Lyapunov functional. At the end, numerical simulations are performed to substantiate our analytical findings.

Tripathi, Jai Prakash; Abbas, Syed; Thakur, Manoj

2014-09-01

52

Modelling of rotary converter in electrical railway traction power-systems for stability analysis

The central European 16.7-Hz railway grid is fed-beside by own power sources- by rotary and static converters. In context of recent low-frequency stability problems in the Scandinavia region, primary the interaction of four-quadrant line-side traction-converter control and surrounding rotary converters is a major concern. Therefore, adequate models for time-domain simulation are necessary. In this paper, a set of differential equations-representing

Carsten Heising; Jie Fang; Roman Bartelt; Volker Staudt; Andreas Steimel

2010-01-01

53

Global stability analysis - a key enabler in reduced order models and flow control

NASA Astrophysics Data System (ADS)

In the current study, Reduced Order Models (ROMs) targeting strategies for experimental feedback flow control are discussed. For practical reasons, such models should incorporate a range of flow operating conditions with a small number of degrees of freedom. Standard POD Galerkin models are challenged by overoptimization at one operating condition [1]. The extension of dynamic range with additional global flow stability modes is the first applied technique. Further side constraints for control-oriented ROMs are taken into account by a "least-dimensional" Galerkin approximation based on a novel technique for continuous mode interpolation [2]. This interpolation preserves the model dimension of a single state while covering several states by adjusting (interpolated) modes. The resulting three-dimensional (3D) Galerkin model is presented for the transient flow around NACA-0012 airfoil and shown to be in a good agreement with the corresponding direct numerical simulation (DNS).

Morzy?ski, M.; Stankiewicz, W.; Thiele, F.; Noack, B. R.; Tadmor, G.

2012-01-01

54

Stability analysis of a multibody system model for coupled slosh-vehicle dynamics

NASA Astrophysics Data System (ADS)

The coupled slosh-vehicle dynamics of a rigid body in planar atmospheric flight carrying a sloshing liquid is considered as a multibody system with the sloshing motion modelled as a simple pendulum. The coupled, non-linear equations for the four-degree-of-freedom multibody system are derived using the method of Lagrangian dynamics. Careful non-dimensionalization reveals two crucial parameters that determine the extent of coupling between the rigid body and slosh modes, and also two important frequency parameters. Using a two-parameter continuation method, critical combinations of these four parameters for which the coupled slosh-vehicle dynamics can become unstable are computed. Results are displayed in the form of neutral stability curves (stability boundaries) in parameter space, and an analytical expression incorporating the four parameters that represents the neutral stability curves is obtained. Reduced-order linearized models and key transfer functions are derived in an effort to understand the instability phenomenon. Physically, the sloshing motion is seen to induce a static instability, sometimes called tumbling, in the vehicle pitch dynamics, depending on the slosh mass fraction and the location of the slosh pendulum hinge point above the rigid vehicle center of mass.

Nichkawde, Chetan; Harish, P. M.; Ananthkrishnan, N.

2004-08-01

55

Amyloid-? (A?) oligomers appear to play a pivotal role in Alzheimer’s disease. A 42 residue long alloform, A?42, is closely related to etiology of the disease. In vitro results show evidences of hexamers; however structures of these hexamers have not been resolved experimentally. Here, we use Discrete Molecular Dynamics (DMD) to analyze long duration stabilities of A?42 hexamer models developed previously in our lab. The hydrophobic core of these models is a six-stranded ?-barrel with 3-fold radial symmetry formed by residues 30–40. This core is shielded from water by residues 1–28. The nine models we analyzed differ by the relative positions of the core ?-strands, and whether the other segments surrounding the core contain ? helices or ?-strands. A model of an annular protofibril composed of 36 A? peptides was also simulated. Results of these model simulations were compared with results of aggregation simulations that started from six well separated random coils of A?42 and with simulations of two known ?barrel structures. These results can be categorized into three groups: stable models with properties similar or superior to those of experimentally-determined ?-barrel proteins, aggregation-prone models, and an amorphous aggregate from random coils. Conformations at the end of the simulation for aggregation-prone models have exposed hydrophobic core with dangling ?-strands on the surface. Hydrogen bond patterns within the ?-barrel were a critical factor for stability of the ?-barrel models. Aggregation-prone conformations imply that the association of these hexamers may be possible, which could lead to the formation of larger assemblies.

Yun, Sijung; Yun, Sajung; Guy, H. Robert

2011-01-01

56

Stability analysis of an SIS epidemic model with feedback mechanism on networks

NASA Astrophysics Data System (ADS)

In this paper, an epidemic model with feedback mechanism on networks is investigated. We obtain the basic reproductive number R0, and analyze the stability behaviors of disease-free equilibrium E0 and endemic equilibrium E?. When R0<1, the disease-free equilibrium is globally asymptotically stable, and when R0>1, the endemic equilibrium is asymptotically stable. Although the feedback mechanism cannot change the basic reproductive number R0 as we prove, it should be indicated that it can weaken the spreading of diseases and reduce the endemic level. Finally, the results of the stability and the effectiveness of the feedback mechanism are illustrated by some numerical simulations.

Zhang, Jiancheng; Sun, Jitao

2014-01-01

57

A simplified spatial model for BWR stability

A spatial reduced order model for the study of BWR stability, based on the phenomenological model of March-Leuba et al., is presented. As one dimensional spatial dependence of the neutron flux, fuel temperature and void fraction is introduced, it is possible to describe both global and regional oscillations of the reactor power. Both linear stability analysis and numerical analysis were applied in order to describe the parameters which govern the model stability. The results were found qualitatively similar to past results. Doppler reactivity feedback was found essential for the explanation of the different regions of the flow-power stability map. (authors)

Berman, Y. [Dept. of Physics, Ben-Gurion Univ. of the Negev, Nuclear Research Center-Negev, Beer-Sheva (Israel); Lederer, Y. [Dept. of Physics, Nuclear Research Center-Negev, Beer-Sheva (Israel); Meron, E. [Dept. of Solar Energy and Environmental Physics, Dept. of Physics, Ben-Gurion Univ. of the Negev, Beer-Sheva (Israel)

2012-07-01

58

PrimeSupplier Cross-Program Impact Analysis and Supplier Stability Indicator Simulation Model

NASA Technical Reports Server (NTRS)

PrimeSupplier, a supplier cross-program and element-impact simulation model, with supplier solvency indicator (SSI), has been developed so that the shuttle program can see early indicators of supplier and product line stability, while identifying the various elements and/or programs that have a particular supplier or product designed into the system. The model calculates two categories of benchmarks to determine the SSI, with one category focusing on agency programmatic data and the other focusing on a supplier's financial liquidity. PrimeSupplier was developed to help NASA smoothly transition design, manufacturing, and repair operations from the Shuttle program to the Constellation program, without disruption in the industrial supply base.

Calluzzi, Michael

2009-01-01

59

The stabilization system for observation is Forward Looking Infra-Red system that is attached to the vehicle using the wire rope isolator. Because the wire rope isolator is a nonlinear isolator, the capability of stabilization can't be estimated easily by simulation. So the analytical model of stabilization system applied the wire rope model is needed in process of development. In this

Hwan-Sic Kim; Ju-Seong Park; Sang-Ho Suh

60

Stability analysis of an HIV/AIDS epidemic model with treatment

NASA Astrophysics Data System (ADS)

An HIV/AIDS epidemic model with treatment is investigated. The model allows for some infected individuals to move from the symptomatic phase to the asymptomatic phase by all sorts of treatment methods. We first establish the ODE treatment model with two infective stages. Mathematical analyses establish that the global dynamics of the spread of the HIV infectious disease are completely determined by the basic reproduction number [real]0. If [real]0<=1, the disease-free equilibrium is globally stable, whereas the unique infected equilibrium is globally asymptotically stable if [real]0>1. Then, we introduce a discrete time delay to the model to describe the time from the start of treatment in the symptomatic stage until treatment effects become visible. The effect of the time delay on the stability of the endemically infected equilibrium is investigated. Moreover, the delay model exhibits Hopf bifurcations by using the delay as a bifurcation parameter. Finally, numerical simulations are presented to illustrate the results.

Cai, Liming; Li, Xuezhi; Ghosh, Mini; Guo, Baozhu

2009-07-01

61

Implementation of a Single-Stage-To-Orbit (SSTO) model for stability and control analysis

NASA Technical Reports Server (NTRS)

Three NASA centers: Marshall Space Flight Center (MSFC), Langley Research Center (LaRC), and Johnson Space Center (JSC) are currently involved in studying a family of single-stage- and two-stage-to-orbit (SSTO/TSTO) vehicles to serve as the next generation space transportation system (STS). A rocketed winged-body is the current focus. The configuration (WB001) is a vertically-launched, horizontally-landing system with circular cross-section. Preliminary aerodynamic data was generated by LaRC and is a combination of wind-tunnel data, empirical methods, and Aerodynamic Preliminary Analysis System-(APAS) generated values. JSC's efforts involve descent trajectory design, stability analysis, and flight control system synthesis. Analysis of WB001's static stability indicates instability in 'tuck' (C(sub mu) less than 0: Mach = 0.30, alpha greater than 3.25 deg; Mach = 0.60, alpha greater than 8.04), an unstable dihedral effects (C(sub l(beta)) greater than 0: Mach = 30,alpha less than 12 deg.; Mach = 0.60, alpha less than 10.00 deg.), and, most significantly, an unstable weathercock stability derivative, C(sub n(beta)), at all angles of attack and subsonic Mach numbers. Longitudinal trim solutions for Mach = 0.30 and 0.60 indicate flight path angle possibilities ranging from around 12 (M = 0.30) to slightly over 20 degrees at Mach = 0.60. Trim angles of attack increase from 6.24 at Mach 0.60 and 10,000 feet to 17.7 deg. at Mach 0.30, sea-level. Lateral trim was attempted for a design cross-wind of 25.0 knots. The current vehicle aerodynamic and geometric characteristics will only yield a lateral trim solution at impractical tip-fin deflections (approximately equal to 43 deg.) and bank angles (21 deg.). A study of the lateral control surfaces, tip-fin controllers for WB001, indicate increased surface area would help address these instabilities, particularly the deficiency in C(sub n(beta)), but obviously at the expense of increased vehicle weight. Growth factors of approximately 7 were determined using a design C(sub n(beta)) of 0.100/radian (approximate subsonic values for the orbiter).

Ingalls, Stephen A.

1995-01-01

62

MAP Stability, Design and Analysis

NASA Technical Reports Server (NTRS)

The Microwave Anisotropy Probe (MAP) is a follow-on to the Differential Microwave Radiometer (DMR) instrument on the Cosmic Background Explorer (COBE) spacecraft. The design and analysis of the MAP attitude control system (ACS) have been refined since work previously reported. The full spacecraft and instrument flexible model was developed in NASTRAN, and the resulting flexible modes were plotted and reduced with the Modal Significance Analysis Package (MSAP). The reduced-order model was used to perform the linear stability analysis for each control mode, the results of which are presented in this paper. Although MAP is going to a relatively disturbance-free Lissajous orbit around the Earth-Sun L2 Lagrange point, a detailed disturbance-torque analysis is required because there are only a small number of opportunities for momentum unloading each year. Environmental torques, including solar pressure at L2, and aerodynamic and gravity gradient during phasing-loop orbits, were calculated and simulated. A simple model of fuel slosh was derived to model its effect on the motion of the spacecraft. In addition, a thruster mode linear impulse controller was developed to meet the accuracy requirements of the phasing loop burns. A dynamic attitude error limiter was added to improve the performance of the ACS during large attitude slews. The result of this analysis is a stable ACS subsystem that meets all of the mission's requirements.

Ericsson -Jackson, A.J.; Andrews, S. F.; ODonnell, J. R., Jr.; Markley, F. L.

1998-01-01

63

MAP stability, design, and analysis

NASA Technical Reports Server (NTRS)

The Microwave Anisotropy Probe (MAP) is a follow-on to the Differential Microwave Radiometer (DMR) instrument on the Cosmic Background Explorer (COBE) spacecraft. The design and analysis of the MAP attitude control system (ACS) have been refined since work previously reported. The full spacecraft and instrument flexible model was developed in NASTRAN, and the resulting flexible modes were plotted and reduced with the Modal Significance Analysis Package (MSAP). The reduced-order model was used to perform the linear stability analysis for each control mode, the results of which are presented in this paper. Although MAP is going to a relatively disturbance-free Lissajous orbit around the Earth-Sun L(2) Lagrange point, a detailed disturbance-torque analysis is required because there are only a small number of opportunities for momentum unloading each year. Environmental torques, including solar pressure at L(2), aerodynamic and gravity gradient during phasing-loop orbits, were calculated and simulated. Thruster plume impingement torques that could affect the performance of the thruster modes were estimated and simulated, and a simple model of fuel slosh was derived to model its effect on the motion of the spacecraft. In addition, a thruster mode linear impulse controller was developed to meet the accuracy requirements of the phasing loop burns. A dynamic attitude error limiter was added to improve the performance of the ACS during large attitude slews. The result of this analysis is a stable ACS subsystem that meets all of the mission's requirements.

Ericsson-Jackson, A. J.; Andrews, S. F.; O'Donnell, J. R., Jr.; Markley, F. L.

1998-01-01

64

NASA Technical Reports Server (NTRS)

A feedback control system, called an auxiliary array switch, was designed to connect or disconnect auxiliary solar panel segments from a spacecraft electrical bus to meet fluctuating demand for power. A simulation of the control system was used to carry out a number of design and analysis tasks that could not economically be performed with a breadboard of the hardware. These tasks included: (1) the diagnosis of a stability problem, (2) identification of parameters to which the performance of the control system was particularly sensitive, (3) verification that the response of the control system to anticipated fluctuations in the electrical load of the spacecraft was satisfactory, and (4) specification of limitations on the frequency and amplitude of the load fluctuations.

Wolfgang, R.; Natarajan, T.; Day, J.

1987-01-01

65

Stochastic stability and instability of model ecosystems

NASA Technical Reports Server (NTRS)

In this work, we initiate a stability study of multispecies communities in stochastic environment by using Ito's differential equations as community models. By applying the direct method of Liapunov, we obtain sufficient conditions for stability and instability in the mean of the equilibrium populations. The conditions are expressed in terms of the dominant diagonal property of community matrices, which is a suitable mechanism for resolving the central problem of 'complexity vs stability' in model ecosystems. As a by-product of this analysis we exhibit important structural properties of the stochastic density-dependent models, and establish tolerance of community stability to a broad class of nonlinear time-varying perturbations.

Ladde, G. S.; Siljak, D. D.

1975-01-01

66

Addresses the mathematical modeling and analysis of the quorum sensing system found in unicellular bacteria that exhibit bioluminescence. The luminescence is governed by the expression of genes in the cell, which in turn is controlled by the density of cells in a population. The paper illustrates the application of standard tools in control theory and some tools in hybrid systems

Calin Belta; Jonathan Schug; Thao Dang; Vijay Kumar; George J. Pappas; Harvey Rubin; Paul Dunlap

2001-01-01

67

Stochastic modeling of high-stability ground clocks in GPS analysis

NASA Astrophysics Data System (ADS)

In current global positioning system (GPS) applications, receiver clocks are typically estimated epoch-wise in the data analyses even for clocks with high performance like Hydrogen-masers (H-maser). Applying an appropriate clock model for high-stability receiver clocks should, in view of the strong correlation between the station height and the clock parameters, significantly improve the positioning results. Recent experiments have shown that modeling the deterministic behavior of high-quality receiver clocks can improve the kinematic precise point positioning considerably. In this paper, well-behaving ground clocks are studied in detail applying constraints between subsequent and near-subsequent clock parameters. The influence of different weights for these relative clock constraints on the positioning quality, especially on the height, is investigated. For excellent clocks, an improvement of up to a factor of 3 can be obtained for the repeatability of the kinematic height estimates. This may be essential to detect small but sudden changes in the vertical component (e.g., caused by earthquakes). Troposphere zenith path delays (ZPD) are also heavily correlated with the receiver clock estimates and station heights. All these parameters are usually estimated simultaneously. We show that the use of relative clock constraints allows for a higher time resolution of the ZPD estimates (smaller than 2 h) without compromising the quality of the kinematic height estimates.

Wang, Kan; Rothacher, Markus

2013-05-01

68

Multilocation yield trials on late duration (106-125 days) finger millet genotypes were conducted under early and late transplanting at Bhubaneswar and early direct-sown condition at Berhampur for three years 2004-2006, during kharif season. G×E interaction analysis of grain yield in AMMI (Additive Main and Multiplicative Interaction) model showed differential interaction of the genotypes in the 3 planting conditions. IPCA-1 explained

R. C. Misra; M. C. Patnaik

69

NASA Technical Reports Server (NTRS)

Results of static stability wind tunnel tests of three 62.2 cm (24.5 in) diameter models of the Prop-Fan are presented. Measurements of blade stresses were made with the Prop-Fans mounted on an isolated nacelle in an open 5.5 m (18 ft) wind tunnel test section with no tunnel flow. The tests were conducted in the United Technology Research Center Large Subsonic Wind Tunnel. Stall flutter was determined by regions of high stress, which were compared with predictions of boundaries of zero total viscous damping. The structural analysis used beam methods for the model with straight blades and finite element methods for the models with swept blades. Increasing blade sweep tends to suppress stall flutter. Comparisons with similar test data acquired at NASA/Lewis are good. Correlations between measured and predicted critical speeds for all the models are good. The trend of increased stability with increased blade sweep is well predicted. Calculated flutter boundaries generaly coincide with tested boundaries. Stall flutter is predicted to occur in the third (torsion) mode. The straight blade test shows third mode response, while the swept blades respond in other modes.

Smith, Arthur F.

1985-01-01

70

Decomposition-Aggregation Stability Analysis.

National Technical Information Service (NTIS)

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...

D. D. Siljak S. Weissenberger S. M. Cuk

1973-01-01

71

Voltage stability evaluation using modal analysis

The authors discuss the voltage stability analysis of large power systems by using a modal analysis technique. The method computes, using a steady-state system model, a specified number of the smallest eigenvalues and the associated eigenvectors of a reduced Jacobian matrix. The eigenvalues, each of which is associated with a mode of voltage\\/reactive power variation, provide a relative measure of

B. Gao; G. K. Morison; P. Kundur

1992-01-01

72

Stability analysis of nonequilibrium mean field models by means of self-consistency equations

NASA Astrophysics Data System (ADS)

We consider systems that operator far from thermal equilibrium and can be described by means of nonlinear Fokker-Planck equations using mean field theory. We determine the stability of stationary states by means of Prigogine's Lyapunov functional and self-consistency equations.

Frank, T. D.

2004-06-01

73

Analysis of Stability of Flower Yield of Rugosa Rose Cultivars with AMMI Model

Objective) The aim of this research is to study the stability of flower yield\\/plant of rugosa rose cultivars in different years. Thirteen rugosa rose cultivars were tested, randomized completed block design with 4 replicates and 10-12 individuals for each replicate was employed in this experiment. (Method)The flower yield\\/plant during the continuous two years was measured and analyzed by AMMI (additive

LI Yan-yan; FENG Zhen; ZHAO Lan-yong

74

A Stability Index Analysis of 1-D Patterns of the Gray-Scott Model

In this work, we study the stationary one-pulse solutions of the Gray-Scottmodel, which consists of a coupled pair of singularly perturbed reaction-diffusionequations. In a previous study, we derived formal stability results for these solutionsusing matched asymptotic expansions. The scaling regimes in which thesesolutions are stable, respectively unstable, were identified by reducing the fourthorderlinearized system to a second-order nonlocal eigenvalue problem

Arjen Doelman; Robert A. Gardner; Tasso J. Kaper

1998-01-01

75

Objective. This study was designed to explore relationships of resonance frequency analysis (RFA)—assessed implant stability (ISQ values) with bone morphometric parameters and bone quality in an ex vivo model of dental implants placed in human femoral heads and to evaluate the usefulness of this model for dental implant studies. Material and Methods. This ex vivo study included femoral heads from 17 patients undergoing surgery for femoral neck fracture due to osteoporosis (OP) (n = 7) or for total prosthesis joint replacement due to severe hip osteoarthrosis (OA) (n = 10). Sixty 4.5 × 13?mm Dentsply Astra implants were placed, followed by RFA. CD44 immunohistochemical analysis for osteocytes was also carried out. Results. As expected, the analysis yielded significant effects of femoral head type (OA versus OA) (P < 0.001), but not of the implants (P = 0.455) or of the interaction of the two factors (P = 0.848). Bonferroni post hoc comparisons showed a lower mean ISQ for implants in decalcified (50.33 ± 2.92) heads than in fresh (66.93 ± 1.10) or fixated (70.77 ± 1.32) heads (both P < 0.001). The ISQ score (fresh) was significantly higher for those in OA (73.52 ± 1.92) versus OP (67.13 ± 1.09) heads. However, mixed linear analysis showed no significant association between ISQ scores and morphologic or histomorphometric results (P > 0.5 in all cases), and no significant differences in ISQ values were found as a function of the length or area of the cortical layer (both P > 0.08). Conclusion. Although RFA-determined ISQ values are not correlated with morphometric parameters, they can discriminate bone quality (OP versus OA). This ex vivo model is useful for dental implant studies.

Hernandez-Cortes, Pedro; Galindo-Moreno, Pablo; Catena, Andres; Ortega-Oller, Inmaculada; Salas-Perez, Jose; Gomez-Sanchez, Rafael; Aguilar, Mariano; Aguilar, David

2014-01-01

76

NASA Astrophysics Data System (ADS)

A heuristic nonlinear creep model is used to derive the nonlinear coupled differential equations of motion of a high-speed railway vehicle traveling on a curved track. The vehicle dynamics are modeled using a 21 degree-of-freedom (21-DOF) system which takes account of the lateral displacement and yaw angle of each wheelset, the lateral displacement, vertical displacement, roll angle and yaw angle of the truck frames, and the lateral displacement, vertical displacement, roll angle, pitch angle and yaw angle of the car body. To analyze the respective effects of the major system parameters on the vehicle dynamics, the 21-DOF system is reduced to 20-DOF, 14-DOF and 6-DOF models, respectively, by excluding designated subsets of the system parameters. The validity of the analytical models and the numerical solution procedure is confirmed by comparing the result obtained using the 6-DOF model for the critical velocity of a railway vehicle traveling on a tangent track with the solution presented in the literature. In general, the results obtained in this study show that the critical hunting speed derived using the 6-DOF or 14-DOF model is generally higher than that evaluated using the 20-DOF model. In addition, the critical hunting speed evaluated via the heuristic nonlinear creep model is lower than that derived using a linear creep model.

Cheng, Yung-Chang; Lee, Sen-Yung; Chen, Hsing-Hao

2009-07-01

77

DYNAMIC CHARACTERIZATION AND STABILITY OF A LARGE SIZE MULTIBODY TILTROTOR MODEL BY POD ANALYSIS

A great level of flexibility and accuracy can be gained by em- ploying a multibody approach as the modeling strategy for servo- aeroelastic analyses of rotating wing aircraft. However, the re- sulting models are often large, in terms of degrees of freedom, and fully nonlinear, making the dynamic characterization phase cumbersome and computationally demanding. Moreover, non- minimal set formulations such

Pierangelo Masarati; Giuseppe Quaranta; Massimiliano Lanz; Paolo Mantegazza

78

Energy function analysis for power system stability

Energy Function Analysis for Power System Stability presents the concept of energy function, which has found wide-spread applications for power systems in recent years. The most recent advances in five distinct areas are reviewed: Development of energy functions for structure preserving models, which can incorporate non-linear load models; energy functions which include a detailed model of the generating unit (i.e.

M. A. Pai

1989-01-01

79

Stability and Transient Analysis in the Modelling of Railway Disc Brake Squeal

The paper deals with friction induced vibrations and especially with railway disc brake squeal. The first part of the paper\\u000a is devoted to the strategy used to model the general problem of self-excited vibrations of a rotating disc in frictional contact\\u000a with two pads. Unilateral contact conditions with Coulomb friction and constant friction coefficient are considered. In order\\u000a to predict

X. Lorang; O. Chiello

80

Stability analysis of a new model for floating caliper disk brake

The customers' demand for ride comfort has led the automotive industries to look for the various ways to reduce and control the brake noise. Intensive research on brake squeal (high frequency noise between 1-12 kHz) has been carried out. A large variety of mathematical-mechanical models has been developed, studying various instability phenomena. The squeal is ascribed mainly to three reasons:

T. Jearsiripongkul; G. Chakraborty; P. Hagedorn

2002-01-01

81

Small signal modelling and stability analysis of multiterminal VSC-HVDC

Two control strategies are implemented for multiterminal voltage sourced converter (VSC)-based HVDC (M-VSC-HVDC). A test system consisting of five terminals was developed in PSCAD. InStrategy 1, the Predictive controller is implemented in the inner control loop whereas strategy 2 using proportional–integral–derivative controller (PID). Small signal analytical models for two terminal VSC-HVDC are developed within MATLAB. Simulation is performed using PSCAD

Aleisawee M. Alsseid; D. Jovcic; A. Starkey

2011-01-01

82

Enhanced rotor modeling tailored for rub dynamic stability analysis and simulation

NASA Technical Reports Server (NTRS)

New methods are presented that allow straightforward application of complex nonlinearities to finite element based rotor dynamic analyses. The key features are: (1) the methods can be implemented with existing finite element or dynamic simulation programs, (2) formulation is general for simple application to a wide range of problems, and (3) implementation is simplified because nonlinear aspects are separated from the linear part of the model. The new techniques are illustrated with examples of inertial nonlinearity and torquewhirl which can be important in rubbing turbomachinery. The sample analyses provide new understanding of these nonlinearities which are discussed.

Davis, R. R.

1989-01-01

83

NASA Astrophysics Data System (ADS)

Unified power flow controller (UPFC) has been the most versatile Flexible AC Transmission System (FACTS) device due to its ability to control real and reactive power flow on transmission lines while controlling the voltage of the bus to which it is connected. UPFC being a multi-variable power system controller it is necessary to analyze its effect on power system operation. To study the performance of the UPFC in damping power oscillations using PSCAD-EMTDC software, a de-coupled control system has been designed for the shunt inverter to control the UPFC bus voltage and the DC link capacitor voltage. The series inverter of a UPFC controls the real power flow in the transmission line. One problem associated with using a high gain PI controller (used to achieve fast control of transmission line real power flow) for the series inverter of a UPFC to control the real power flow in a transmission line is the presence of low damping. This problem is solved in this research by using a fuzzy controller. A method to model a fuzzy controller in PSCAD-EMTDC software has also been described. Further, in order to facilitate proper operation between the series and the shunt inverter control system, a new real power coordination controller has been developed and its performance was evaluated. The other problem concerning the operation of a UPFC is with respect to transmission line reactive power flow control. Step changes to transmission line reactive power references have significant impact on the UPFC bus voltage. To reduce the adverse effect of step changes in transmission line reactive power references on the UPFC bus voltage, a new reactive power coordination controller has been designed. Transient response studies have been conducted using PSCAD-EMTDC software to show the improvement in power oscillation damping with UPFC. These simulations include the real and reactive power coordination controllers. Finally, a new control strategy has been proposed for UPFC. In this proposed control strategy, the shunt inverter controls the DC link capacitor voltage and the transmission line reactive power flow. The series inverter controls the transmission line real power flow and the UPFC bus voltage. PSCAD-EMTDC simulations have been conducted to show the viability of the control strategy in damping power oscillations.

Sreenivasachar, Kannan

2001-07-01

84

For normal quiet standing the ankle strategy is used for human posture. The musculoskeletic system can be viewed as an inverted pendulum stabilised by a feedback loop with the lambda control. Mathematical modelling of the musculo-skeletal system under lambda control is presented as a nonlinear system with time-delay in feedback. Necessary conditions of asymptotic stability and a practical analytic expression

P. Micheau; A. Kron; P. Bourassa

2001-01-01

85

Global Stability Analysis for Linear Dynamics

NASA Astrophysics Data System (ADS)

Global stability analysis of fluid flows is presented as a method of extracting physical eigenmodes with associated linear dynamic models. These reduced-order models (ROM) are optimal for the transients near the onset of instability. We describe the computational aspects of the eigenmode extraction in detail. This outline includes (i) the discretization technique of the eigenproblem in the framework of computational fluid dynamics (CFD) and (ii) the solution algorithms for the discretized eigenproblem. As regards physical aspects, the linear ROM are improved by enriching the basis with POD modes and by incorporating weakly nonlinear base flow variations. Results of stability computations are presented for the circular cylinder wake, the flow around a NACA-0012 airfoil and the optimization of passive control. Preliminary 3D eigensolutions show the potential of the global stability method.

Morzy?ski, Marek; Noack, Bernd R.; Tadmor, Gilead

86

Stabilizing hadron resonance gas models

We examine the stability of hadron resonance gas models by extending them to include undiscovered resonances through the Hagedorn formula. We find that the influence of unknown resonances on thermodynamics is large but bounded. We model the decays of resonances and investigate the ratios of particle yields in heavy-ion collisions. We find that observables such as hydrodynamics and hadron yield ratios change little upon extending the model. As a result, heavy-ion collisions at the RHIC and LHC are insensitive to a possible exponential rise in the hadronic density of states, thus increasing the stability of the predictions of hadron resonance gas models in this context. Hadron resonance gases are internally consistent up to a temperature higher than the crossover temperature in QCD, but by examining quark number susceptibilities we find that their region of applicability ends below the QCD crossover.

Chatterjee, S.; Godbole, R. M. [Center for High Energy Physics, Indian Institute of Science, Bangalore 560012 (India); Gupta, Sourendu [Department of Theoretical Physics, Tata Institute of Fundamental Research, Homi Bhabha Road, Mumbai 400005 (India)

2010-04-15

87

Experimental design and modeling of in-use stability testing are presented in this paper. In-use open container degradation is considered in terms of time open container or/and the number of instances that the same container is used. Degradation is estimated based on two models, the fixed and the general model. The fixed model estimates in-use degradation for those fixed time points of closed container where the in-used experimental data is collected. The general model estimates in-use degradation for any time point of closed container using the estimated relationship between closed container time and the degradation rate of open container. Data for in-use open container stability does not have to be collected at a closed container time of interest to estimate in-use degradation at this time point as long as this point is within the range of the experiment. Stability of the product in terms of drift from the initial time to the time of interest is calculated as the sum of closed and in-use open containers drifts. PMID:21802877

Magari, Robert T; Afonina, Elena

2011-12-01

88

NASA Technical Reports Server (NTRS)

Aerodynamic analysis are performed using the Lockheed-Martin Tactical Aircraft Systems (LMTAS) Splitflow computational fluid dynamics code to investigate the computational prediction capabilities for vortex-dominated flow fields of two different tailless aircraft models at large angles of attack and sideslip. These computations are performed with the goal of providing useful stability and control data to designers of high performance aircraft. Appropriate metrics for accuracy, time, and ease of use are determined in consultations with both the LMTAS Advanced Design and Stability and Control groups. Results are obtained and compared to wind-tunnel data for all six components of forces and moments. Moment data is combined to form a "falling leaf" stability analysis. Finally, a handful of viscous simulations were also performed to further investigate nonlinearities and possible viscous effects in the differences between the accumulated inviscid computational and experimental data.

Charlton, Eric F.

1998-01-01

89

Fusion of modified LDL in the arterial wall promotes atherogenesis. Earlier we showed that thermal denaturation mimics LDL remodeling and fusion, and revealed kinetic origin of LDL stability. Here we report the first quantitative analysis of LDL thermal stability. Turbidity data show sigmoidal kinetics of LDL heat denaturation, which is unique among lipoproteins, suggesting that fusion is preceded by other structural changes. High activation energy of denaturation, E(a) = 100 ± 8 kcal/mol, indicates disruption of extensive packing interactions in LDL. Size-exclusion chromatography, nondenaturing gel electrophoresis, and negative-stain electron microscopy suggest that LDL dimerization is an early step in thermally induced fusion. Monoclonal antibody binding suggests possible involvement of apoB N-terminal domain in early stages of LDL fusion. LDL fusion accelerates at pH < 7, which may contribute to LDL retention in acidic atherosclerotic lesions. Fusion also accelerates upon increasing LDL concentration in near-physiologic range, which likely contributes to atherogenesis. Thermal stability of LDL decreases with increasing particle size, indicating that the pro-atherogenic properties of small dense LDL do not result from their enhanced fusion. Our work provides the first kinetic approach to measuring LDL stability and suggests that lipid-lowering therapies that reduce LDL concentration but increase the particle size may have opposite effects on LDL fusion. PMID:22855737

Lu, Mengxiao; Gantz, Donald L; Herscovitz, Haya; Gursky, Olga

2012-10-01

90

Fusion of modified LDL in the arterial wall promotes atherogenesis. Earlier we showed that thermal denaturation mimics LDL remodeling and fusion, and revealed kinetic origin of LDL stability. Here we report the first quantitative analysis of LDL thermal stability. Turbidity data show sigmoidal kinetics of LDL heat denaturation, which is unique among lipoproteins, suggesting that fusion is preceded by other structural changes. High activation energy of denaturation, Ea = 100 ± 8 kcal/mol, indicates disruption of extensive packing interactions in LDL. Size-exclusion chromatography, nondenaturing gel electrophoresis, and negative-stain electron microscopy suggest that LDL dimerization is an early step in thermally induced fusion. Monoclonal antibody binding suggests possible involvement of apoB N-terminal domain in early stages of LDL fusion. LDL fusion accelerates at pH < 7, which may contribute to LDL retention in acidic atherosclerotic lesions. Fusion also accelerates upon increasing LDL concentration in near-physiologic range, which likely contributes to atherogenesis. Thermal stability of LDL decreases with increasing particle size, indicating that the pro-atherogenic properties of small dense LDL do not result from their enhanced fusion. Our work provides the first kinetic approach to measuring LDL stability and suggests that lipid-lowering therapies that reduce LDL concentration but increase the particle size may have opposite effects on LDL fusion.

Lu, Mengxiao; Gantz, Donald L.; Herscovitz, Haya; Gursky, Olga

2012-01-01

91

NASA Technical Reports Server (NTRS)

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.

Sevart, F. D.; Patel, S. M.

1973-01-01

92

NASA Astrophysics Data System (ADS)

Recently global, quasi-two-dimensional instabilities of tachocline latitudinal differential rotation have been studied using a so-called shallow-water model. While purely hydrodynamic shallow-water type disturbances were found to destabilize only the overshoot tachocline, the MHD analysis showed that in the presence of a broad toroidal field, both the radiative and overshoot parts of the tachocline can be unstable. We explore here instability in the shallow-water solar tachocline with concentrated toroidal bands placed at a wide range of latitudes, emulating different phases of the solar cycle. In equilibrium, the poleward magnetic curvature stress of the band is balanced either by an equatorward hydrostatic pressure gradient or by the Coriolis force from a prograde jet inside the band. We find that toroidal bands placed almost at all latitudes make the system unstable to shallow-water disturbances. For bands without prograde jets, the instability persists well above 100 kG peak field, while a jet stabilizes the band at a field of ~40 kG. The jet imparts gyroscopic inertia to the toroidal band inhibiting it from unstably ``tipping'' its axis away from rotation axis. Like previously studied HD and MHD shallow-water instabilities in the tachocline, unstable shallow-water modes found here produce kinetic helicity and hence a tachocline ?-effect these narrow kinetic helicity profiles should generate narrowly confined poloidal fields, which will help formation of the narrow toroidal field. Toroidal bands poleward of 15° latitude suppress midlatitude hydrodynamic ?-effects. However, even strong toroidal bands equatorward of 15° allow this hydrodynamic ?-effect. Such bands should occur during the late declining phase of a solar cycle and, thus, could help the onset of a new cycle by switching on the mid latitude ?-effect.

Dikpati, Mausumi; Gilman, Peter A.; Rempel, Matthias

2003-10-01

93

Assessment of Seismic Slope Stability Using GIS Modeling

In recent years there has been a growing interest in developing GIS based models for mapping and identification of seismically-induced landslide hazards. A review of assumptions in the relationships and the data typically used in GIS seismic slope stability models, shows that there are three components which are commonly used together: pseudo-static slope stability analysis, attenuation of ground shaking models,

Bijan Khazai; Nicholas Sitar

2000-01-01

94

Stability of Hybrid Model Predictive Control

In this paper we investigate the stability of hybrid systems in closed-loop with Model Predictive Controllers (MPC) and we derive a priori sufficient conditions for Lyapunov asymptotic stability and exponential stability. A general theory is presented which proves that Lyapunov stability is achieved for both terminal cost and constraint set and terminal equality constraint hybrid MPC, even though the considered

M. Lazar; W. P. M. H. Heemels; S. Weiland; A. Bemporad

2005-01-01

95

The stability of colorectal cancer mathematical models

NASA Astrophysics Data System (ADS)

Colorectal cancer is one of the most common types of cancer. To better understand about the kinetics of cancer growth, mathematical models are used to provide insight into the progression of this natural process which enables physicians and oncologists to determine optimal radiation and chemotherapy schedules and develop a prognosis, both of which are indispensable for treating cancer. This thesis investigates the stability of colorectal cancer mathematical models. We found that continuous saturating feedback is the best available model of colorectal cancer growth. We also performed stability analysis. The result shows that cancer progress in sequence of genetic mutations or epigenetic which lead to a very large number of cells population until become unbounded. The cell population growth initiate and its saturating feedback is overcome when mutation changes causing the net per-capita growth rate of stem or transit cells exceed critical threshold.

Khairudin, Nur Izzati; Abdullah, Farah Aini

2013-04-01

96

NASA Astrophysics Data System (ADS)

The relaxation property of both Eigen model and Crow-Kimura model with a single peak fitness landscape is studied from phase transition point of view. We first analyze the eigenvalue spectra of the replication mutation matrices. For sufficiently long sequences, the almost crossing point between the largest and second-largest eigenvalues locates the error threshold at which critical slowing down behavior appears. We calculate the critical exponent in the limit of infinite sequence lengths and compare it with the result from numerical curve fittings at sufficiently long sequences. We find that for both models the relaxation time diverges with exponent 1 at the error (mutation) threshold point. Results obtained from both methods agree quite well. From the unlimited correlation length feature, the first order phase transition is further confirmed. Finally with linear stability theory, we show that the two model systems are stable for all ranges of mutation rate. The Eigen model is asymptotically stable in terms of mutant classes, and the Crow-Kimura model is completely stable.

Feng, Xiao-Li; Li, Yu-Xiao; Gu, Jian-Zhong; Zhuo, Yi-Zhong

2009-10-01

97

In this paper, the authors study a laser using a nonlinear Fabry-Perot etalon as a cavity mirror. First, using the semiclassical laser theory and the differential equation for the lossy nonlinear Fabry-Perot etalon, they develop dynamic equations describing this system for single-mode operation. In this model, the frequency-pulling effect, a finite response time of the nonlinear medium, and a finite-cavity round-trip time of the Fabry-Perot etalon are included. Second, based on this model, they analyze the stability of this laser and give some numerical results. The results show that (1) this system can exist in the stable state and in the unstable state; (2) there are not only saddle-node bifurcations but also Hopf bifurcations; (3) the detuning parameter will effect the characteristics of the bistability and the number and distribution of Hopf bifurcation points.

Li, S.; Pons, R. (Autonoma de Barcelona (Spain). Dept. of Fisica); Zhang, Y. (Chongqing Inst. of Posts and Telecommunications, Sichuan (China). Telecommunications Engineering Dept.)

1994-08-01

98

Stabilizing Model Predictive Control of Hybrid Systems

In this note, we investigate the stability of hybrid systems in closed-loop with model predictive controllers (MPC). A priori sufficient conditions for Lyapunov asymptotic stability and exponential stability are derived in the terminal cost and constraint set fashion, while allowing for discontinuous system dynamics and discontinuous MPC value functions. For constrained piecewise affine (PWA) systems as prediction models, we present

M. Lazar; W. P. M. H. Heemels; S. Weiland; A. Bemporad

2006-01-01

99

The stability of the finite-difference approximation of elastic wave propagation in orthotropic homogeneous media in the three-dimensional case is discussed. The model applies second- and fourth-order finite-difference approaches with staggered grid and stress-free boundary conditions in the space domain and second-order finite-difference approach in the time domain. The numerical integration of the wave equation by central differences is conditionally stable and the corresponding stability criterion for the time domain discretisation has been deduced as a function of the material properties and the geometrical discretization. The problem is discussed by applying the method of VonNeumann. Solutions and the calculation of the critical time steps is presented for orthotropic material in both the second- and fourth-order case. The criterion is verified for the special case of isotropy and results in the well-known formula from the literature. In the case of orthotropy the method was verified by long time simulations and by calculating the total energy of the system. PMID:19913266

Veres, István A

2010-03-01

100

Stability Analysis of ISS Medications

NASA Technical Reports Server (NTRS)

It is known that medications degrade over time, and that extreme storage conditions will hasten their degradation. The temperature and humidity conditions of the ISS have been shown to be within the ideal ranges for medication storage, but the effects of other environmental factors, like elevated exposure to radiation, have not yet been evaluated. Current operational procedures ensure that ISS medications are re-stocked before expiration, but this may not be possible on long duration exploration missions. For this reason, medications that have experienced long duration storage on the ISS were returned to JSC for analysis to determine any unusual effects of aging in the low- Earth orbit environment. METHODS Medications were obtained by the JSC Pharmacy from commercial distributors and were re-packaged by JSC pharmacists to conserve up mass and volume. All medication doses were part of the ISS crew medical kit and were transported to the International Space Station (ISS) via NASA's Shuttle Transportation System (Space Shuttle). After 568 days of storage, the medications were removed from the supply chain and returned to Earth on a Dragon (SpaceX) capsule. Upon return to Earth, medications were transferred to temperature and humidity controlled environmental chambers until analysis. Nine medications were chosen on the basis of their availability for study. The medications included several of the most heavily used by US crewmembers: 2 sleep aids, 2 antihistamines/decongestants, 3 pain relievers, an antidiarrheal and an alertness medication. Each medication was available at a single time point; analysis of the same medication at multiple time points was not possible. Because the samples examined in this study were obtained opportunistically from medical supplies, there were no control samples available (i.e. samples aged for a similar period of time on the ground); a significant limitation of this study. Medications were analyzed using the HPLC/MS methods described in the United States Pharmacopeia (USP) to measure the amount of intact active ingredient, identify degradation products and measure their amounts. Some analyses were conducted by an independent analytical laboratory, but certain (Schedule) medications could not be shipped to their facility and were analyzed at JSC. RESULTS Nine medications were analyzed with respect to active pharmaceutical ingredient (API) and degradant amounts. Results were compared to the USP requirements for API and degradants/impurities content for every FDA-approved medication. One medication met USP requirements at 5 months after its expiration date. Four of the nine (44% of those tested) medications tested met USP requirements up to 8 months post-expiration. Another 3 medications (33% of those tested) met USP guidelines 2-3 months before expiration. One medication, a compound classed by the FDA as a dietary supplement and sometimes used as a sleep aid, failed to meet USP requirements at 11 months post-expiration. CONCLUSION Analysis of each medication at a single time point provides limited information on the stability of a medication stored in particular conditions; it is not possible to predict how long a medication may be safe and effective from these data. Notwithstanding, five of the nine medications tested (56%) met USP requirements for API and degradants/impurities at least 5 months past expiration dates. The single compound that failed to meet USP requirements is not regulated as strictly as prescription medications are during manufacture; it is unknown if this medication would have met the requirements prior to flight. Notably, it was the furthest beyond its expiration date. Only more comprehensive analysis of flight-aged samples compared to appropriate ground controls will permit determination of spaceflight effects on medication stability.

Wotring, V. E.

2014-01-01

101

Stability analysis of arbitrary shape landslope by variational calculus and finite difference method

In this paper, a method of numerical analysis is presented, which is suitable for the stability analysis of arbitrary shape landslope, and can be used for the stability analysis of both general artificial landslope and arbitrary natural landslope. The mathematical model of stability analysis is based on the theory of the calculus of variations and using Janbu's simplified model. The

1987-01-01

102

NASA Technical Reports Server (NTRS)

Results of wind tunnel tests at low forward speed for blade dynamic response and stability 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. Low speed stall flutter tests were conducted at Mach numbers from 0.0 to 0.35. Measurements are compared to Eigen-solution flutter boundaries. Calculated 1P stress response agrees favorably with experiment. Predicted stall flutter boundaries correlate well with measured high stress regions. Stall flutter is significantly reduced by increased blade sweep. Susceptibility to stall flutter decreases rapidly with forward speed.

Smith, Arthur F.

1985-01-01

103

Transition prediction using three dimensional stability analysis

NASA Technical Reports Server (NTRS)

Several methods of transition prediction by linear stability analysis are compared. The spectral stability analysis code SALLY is used to analyze flows over laminar flow control wings. It is shown that transition by the envelope method and a new modified wave packet method are comparable in reliability but that the envelope method is more efficient computationally.

Malik, M. R.

1980-01-01

104

A distributed slope stability model for steep forested basins

A distributed, physically based slope stability model (dSLAM), based on an infinite slope model, a kinematic wave groundwater model, and a continuous change vegetation root strength model, is presented. It is integrated with a contour line-based topographic analysis and a geographic information system (GIS) for spatial data extraction and display. The model can be run with either individual rainfall events

Weimin Wu; Roy C. Sidle

1995-01-01

105

Stability Analysis of Exoplanetary Systems

NASA Astrophysics Data System (ADS)

To date 87 extrasolar planetary systems containing 101 giant Jupiter-like planetshave been discovered in Doppler surveys of solar-type stars. In this paperwe perform simulations to investigate three systems: GJ 876 HD 82943 and 55 Cnc. The former systems both have two planets in the 2:1 Mean Motion Resonance(MMR) while the inner two companions of the later seem to be near 3:1 MMR. By integrating hundreds of the planetary orbits of these systems for million years we find that for GJ 876 and HD 82943 the critical argument lambda1-2lambda2+ tilde?1 librates about 0 or 180 degrees indicating 2:1 MMR can play an important role in stabilizing the motion of the planets so that they are protected from close encounters. As for 55 Cnc we further show the resonant argument lambda1-3lambda2+(tilde?1+ tilde?2) undergoes oscillations around 0 degree for 50 Myr which reveals the evidence of 3:1 MMR for this system. Additionally we should emphasize another vital mechanism is the apsidal alignment of the planets for the systems. In the case of GJ 876 and HD 82943 we discover the differences of the apsidal longitudes tilde?1- tilde?2 move about 0 or 180 degrees respectively. Finally we again adopt the relevant analytical models to explain the numerical results.

Ji, J. H.; Liu, L.; Kinoshita, H.; Li, G.; Nakai, J.

2004-01-01

106

Performance and stability analysis of a photovoltaic power system

NASA Technical Reports Server (NTRS)

The performance and stability characteristics of a 10 kVA photovoltaic power system are studied using linear Bode analysis and a nonlinear analog simulation. Power conversion efficiencies, system stability, and system transient performance results are given for system operation at various levels of solar insolation. Additionally, system operation and the modeling of system components for the purpose of computer simulation are described.

Merrill, W. C.; Blaha, R. J.; Pickrell, R. L.

1978-01-01

107

Aerobic digestion batch tests were run on a sludge model that contained only two fractions, the heterotrophic biomass (XH) and its endogenous residue (XP). The objective was to describe the stabilization of the sludge and estimate the endogenous decay parameters. Modeling was performed with Aquasim, based on long-term data of volatile suspended solids and chemical oxygen demand (VSS, COD). Sensitivity analyses were carried out to determine the conditions for unique identifiability of the parameters. Importantly, it was found that the COD/VSS ratio of the endogenous residues (1.06) was significantly lower than for the active biomass fraction (1.48). The decay rate constant of the studied sludge (low bH, 0.025d(-1)) was one-tenth that usually observed (0.2d(-1)), which has two main practical significances. Digestion time required is much more long; also the oxygen uptake rate might be <1.5mgO2/gTSSh (biosolids standards), without there being significant decline in the biomass. PMID:24907570

Martínez-García, C G; Olguín, M T; Fall, C

2014-08-01

108

Stability analysis and stabilization strategies for linear supply chains

NASA Astrophysics Data System (ADS)

Due to delays in the adaptation of production or delivery rates, supply chains can be dynamically unstable with respect to perturbations in the consumption rate, which is known as “bull-whip effect”. Here, we study several conceivable production strategies to stabilize supply chains, which is expressed by different specifications of the management function controlling the production speed in dependence of the stock levels. In particular, we will investigate, whether the reaction to stock levels of other producers or suppliers has a stabilizing effect. We will also demonstrate that the anticipation of future stock levels can stabilize the supply system, given the forecast horizon ? is long enough. To show this, we derive linear stability conditions and carry out simulations for different control strategies. The results indicate that the linear stability analysis is a helpful tool for the judgement of the stabilization effect, although unexpected deviations can occur in the non-linear regime. There are also signs of phase transitions and chaotic behavior, but this remains to be investigated more thoroughly in the future.

Nagatani, Takashi; Helbing, Dirk

2004-04-01

109

Slope stability analysis of Valles Marineris, Mars

NASA Astrophysics Data System (ADS)

Valles Marineris (VM) in the equatorial area of Mars exhibits several gravitational failures which resulted in a series of large landslides up to several hundred cubic kilometers in volume. Questions arise as to forces at play and rock strength in the stability of the walls of VM. In this work we address the stability analysis of the walls of VM by considering the strength of the materials of the chasma walls and the causes of landslides. Using finite element calculations and the limit analysis upper bound method, we explore the range of cohesion and friction angle values associated to realistic failure geometries, and compare predictions with the classical Culmann's wedge model. Our analysis is based both on synthetic, simplified slope profiles and also on the real shape of the walls of VM taken from the MOLA topographic data. Validation of the calibrated cohesion and friction angle values is performed by comparing the computed unstable cross sectional areas with the observed pre- and post-failure profiles and estimated failure surface geometry. This offers a link between rock mass properties, slope geometry and volume of the observed failure. Pseudo-static seismic analyses generated another set of dimensionless charts. Our pseudo-static analyses show that low seismicity events induced by meteoroids impacts compatible with the size of craters could be a cause for some of the observed landslides if poor rock properties for VM is assumed.

Vittorio De Blasio, Fabio; Battista Crosta, Giovanni; Castellanza, Riccardo; Utili, Stefano

2013-04-01

110

NASA Technical Reports Server (NTRS)

Small-signal modeling techniques are used in a system stability analysis of a breadboard version of a complete functional electrical power system. The system consists of a regulated switching dc-to-dc converter, a solar-cell-array simulator, a solar-array EMI filter, battery chargers and linear shunt regulators. Loss mechanisms in the converter power stage, including switching-time effects in the semiconductor elements, are incorporated into the modeling procedure to provide an accurate representation of the system without requiring frequency-domain measurements to determine the damping factor. The small-signal system model is validated by the use of special measurement techniques which are adapted to the poor signal-to-noise ratio encountered in switching-mode systems. The complete electrical power system with the solar-array EMI filter is shown to be stable over the intended range of operation.

Wong, R. C.; Owen, H. A., Jr.; Wilson, T. G.; Rodriguez, G. E.

1980-01-01

111

High beta and second stability region transport and stability analysis

This report describes ideal and resistive studies of high-beta plasmas and of the second stability region. Emphasis is focused on supershot'' plasmas in TFIR where MHD instabilities are frequently observed and which spoil their confinement properties. Substantial results are described from the analysis of these high beta poloidal plasmas. During these studies, initial pressure and safety factor profiles were obtained from the TRANSP code, which is used extensively to analyze experimental data. Resistive MBD stability studies of supershot equilibria show that finite pressure stabilization of tearing modes is very strong in these high {beta}p plasmas. This has prompted a detailed re-examination of linear tearing mode theory in which we participated in collaboration with Columbia University and General Atomics. This finite pressure effect is shown to be highly sensitive to small scale details of the pressure profile. Even when an ad hoc method of removing this stabilizing mechanism is implemented, however, it is shown that there is only superficial agreement between resistive MBD stability computation and the experimental data. While the mode structures observed experimentally can be found computationally, there is no convincing correlation with the experimental observations when the computed results are compared with a large set of supershot data. We also describe both the ideal and resistive stability properties of TFIR equilibria near the transition to the second region. It is shown that the highest {beta} plasmas, although stable to infinite-n ideal ballooning modes, can be unstable to the so called infernal'' modes associated with small shear. The sensitivity of these results to the assumed pressure and current density profiles is discussed. Finally, we describe results from two collaborative studies with PPPL. The first involves exploratory studies of the role of the 1/1 mode in tokamaks and, secondly, a study of sawtooth stabilization using ICRF.

Hughes, M.H.; Phillps, M.W.; Todd, A.M.M.; Krishnaswami, J.; Hartley, R.

1992-09-01

112

Aeroelastic stability analysis of wind turbines using an eigenvalue approach

A design tool for performing aeroelastic stability analysis of wind turbines is presented in this paper. The method behind this tool is described in a general form, as independent of the particular aeroelastic modelling as possible. Here, the structure is modelled by a Finite beam Element Method, and the aerodynamic loads are modelled by the Blade Element Momentum method coupled

M. H. Hansen

2004-01-01

113

The calculated values of stability constants of surface complexes formed by heavy metal ions depend on the assumed model of the electric double layer and its parameters. Using various parameters of the triple-layer model (TLM) (which fit the titration data almost equally well), one obtains stability constants in a range as wide as two orders of magnitude. On the other

Marek Kosmulski

1996-01-01

114

Fuzzy controller design and stability analysis for ship's lift-feedback-fin stabilizer

A Takagi-Sugeno (T-S) fuzzy model of ship's lift-feedback-fin stabilizer control systems is established. Based on character analysis of fuzzy control systems with standard fuzzy partition inputs, a new sufficient condition is proved which guarantees the stability of closed-loop T-S fuzzy control systems via Lyapunov direct method. This approach requires only finding a common positive-definite matrix in each maximal overlapped-rule group.

Zhi-Hong Xiu; Guang Ren

2003-01-01

115

NASA Astrophysics Data System (ADS)

We focus at the interface between multiscale computations, bifurcation theory and social networks. In particular we address how the Equation-Free approach, a recently developed computational framework, can be exploited to systematically extract coarse-grained, emergent dynamical information by bridging detailed, agent-based models of social interactions on networks, with macroscopic, systems-level, continuum numerical analysis tools. For our illustrations we use a simple dynamic agent-based model describing the propagation of information between individuals interacting under mimesis in a social network with private and public information. We describe the rules governing the evolution of the agents emotional state dynamics and discover, through simulation, multiple stable stationary states as a function of the network topology. Using the Equation-Free approach we track the dependence of these stationary solutions on network parameters and quantify their stability in the form of coarse-grained bifurcation diagrams.

Tsoumanis, A. C.; Siettos, C. I.; Bafas, G. V.; Kevrekidis, I. G.

116

Solar Dynamic Power System Stability Analysis and Control

NASA Technical Reports Server (NTRS)

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.

Momoh, James A.; Wang, Yanchun

1996-01-01

117

The controlling unstable equilibrium point (UEP) method is considered to be the most viable for direct stability analysis of practical power systems. The success of the controlling UEP method, however, hinges upon its ability to find the (correct) controlling UEP. Recently, a systematic method, called the boundary of stability region based controlling unstable equilibrium point method (BCU method), to find

Hsiao-Dong Chiang; Chia-Chia Chu

1995-01-01

118

Cutaneous melanoma is disproportionately lethal despite its relatively low incidence and its potential for cure in the early stages. The aim of this study is to foster understanding of the role of microstructure on the occurrence of morphological changes in diseased skin during melanoma evolution. The authors propose a biomechanical analysis of its radial growth phase, investigating the role of intercellular/stromal connections on the initial stages of epidermis invasion. The radial growth phase of a primary melanoma is modelled within the multi-phase theory of mixtures, reproducing the mechanical behaviour of the skin layers and of the epidermal–dermal junction. The theoretical analysis takes into account those cellular processes that have been experimentally observed to disrupt homeostasis in normal epidermis. Numerical simulations demonstrate that the loss of adhesiveness of the melanoma cells both to the basal laminae, caused by deregulation mechanisms of adherent junctions, and to adjacent keratynocytes, consequent to a downregulation of E-cadherin, are the fundamental biomechanical features for promoting tumour initiation. Finally, the authors provide the mathematical proof of a long wavelength instability of the tumour front during the early stages of melanoma invasion. These results open the perspective to correlate the early morphology of a growing melanoma with the biomechanical characteristics of its micro-environment.

Ciarletta, P.; Foret, L.; Ben Amar, M.

2011-01-01

119

Thermodynamic stability of cosmological models

The thermodynamics of homogeneous isotropic universes (k>0, Lambda>0) with conformal scalar radiation is analyzed, in analogy with the thermodynamics of black holes in a cavity, as the mutual equilibrium between two subsystems (quantum thermal bosons and semiclassical conformal metric modes) fluctuating under an energy constraint corresponding to the analytic continuation of one of Einstein's equations. The global stability of the

G. Horwitz; D. Weil

1986-01-01

120

Voltage stability analysis in the new deregulated environment

NASA Astrophysics Data System (ADS)

Nowadays, a significant portion of the power industry is under deregulation. Under this new circumstance, network security analysis is more critical and more difficult. One of the most important issues in network security analysis is voltage stability analysis. Due to the expected higher utilization of equipment induced by competition in a power market that covers bigger power systems, this issue is increasingly acute after deregulation. In this dissertation, some selected topics of voltage stability analysis are covered. In the first part, after a brief review of general concepts of continuation power flow (CPF), investigations on various matrix analysis techniques to improve the speed of CPF calculation for large systems are reported. Based on these improvements, a new CPF algorithm is proposed. This new method is then tested by an inter-area transaction in a large inter-connected power system. In the second part, the Arnoldi algorithm, the best method to find a few minimum singular values for a large sparse matrix, is introduced into the modal analysis for the first time. This new modal analysis is applied to the estimation of the point of voltage collapse and contingency evaluation in voltage security assessment. Simulations show that the new method is very efficient. In the third part, after transient voltage stability component models are investigated systematically, a novel system model for transient voltage stability analysis, which is a logical-algebraic-differential-difference equation (LADDE), is offered. As an example, TCSC (Thyristor controlled series capacitors) is addressed as a transient voltage stabilizing controller. After a TCSC transient voltage stability model is outlined, a new TCSC controller is proposed to enhance both fault related and load increasing related transient voltage stability. Its ability is proven by the simulation.

Zhu, Tong

121

Probabilistic Slope Stability Analysis by Finite Elements

The paper investigates the probability of failure of a cohesive slope using both simple and more advanced probabilistic analysis tools. The influence of local averaging on the probability of failure of a test problem is thoroughly investigated. In the simple approach, classical slope stability analysis techniques are used, and the shear strength is treated as a single random variable. The

D. V. Griths; Gordon A. Fenton

2004-01-01

122

Developments in Cylindrical Shell Stability Analysis

NASA Technical Reports Server (NTRS)

Today high-performance computing systems and new analytical and numerical techniques enable engineers to explore the use of advanced materials for shell design. This paper reviews some of the historical developments of shell buckling analysis and design. The paper concludes by identifying key research directions for reliable and robust methods development in shell stability analysis and design.

Knight, Norman F., Jr.; Starnes, James H., Jr.

1998-01-01

123

Moduli stabilization in stringy ISS models

We present a stringy realization of the ISS metastable SUSY breaking model with moduli stabilization. The mass moduli of the ISS model is stabilized by gauging of a U(1) symmetry and its D-term potential. The SUSY is broken both by F-terms and D-terms. It is possible to obtain de Sitter vacua with a vanishingly small cosmological constant by an appropriate fine-tuning of flux parameters.

Nakayama, Yu; Nakayama, Yu; Yamazaki, Masahito; Yanagida, T.T.

2007-09-28

124

The helix content of a series of peptides containing single substitutions of the 20 natural amino acids in a new designed host sequence, succinyl-YSEEEEKAKKAXAEEAEKKKK-NH2, has been determined using CD spectroscopy. This host is related to one previously studied, in which triple amino acid substitutions were introduced into a background of Glu-Lys blocks completely lacking alanine. The resulting free energies show that only Ala and Glu- prove to be helix stabilizing, while all other side chains are neutral or destabilizing. This agrees with results from studies of alanine-rich peptide modela, but not the previous Glu-Lys block oligomers in which Leu and Met also stabilize helix. The helix propensity scale derived from the previous block oligomers correlated well with the frequencies of occurrence of different side chains in helical sequences of proteins, whereas the values from the present series do not. The role of context in determining scales of helix propensity values is discussed, and the ability of algorithms designed to predict helix structure from sequence is compared.

Yang, J.; Spek, E. J.; Gong, Y.; Zhou, H.; Kallenbach, N. R.

1997-01-01

125

Sand Bank Weakly Nonlinear Stability Analysis

NASA Astrophysics Data System (ADS)

In the continental shelf, tidal currents often give rise to large scale periodic bed forms named sand banks. Sand banks are long ridges (length of the order of several tens of kilometers) with a spacing (crest to crest distance) up to 10 km and a height up to several tens of meters. Their crests are almost aligned with the tidal currents, forming small positive or negative angles. Although reliable models based on linear stability analyses exist to predict the main geometrical characteristics of the sand banks as they start to appear, little is known on the morphodynamic processes that shape and maintain these bed forms in equilibrium conditions. A weakly nonlinear analysis is a powerful tool to investigate the equilibrium configuration attained by unstable bottom perturbations when the parameters of the problem are close to the critical values. However difficulties arise to apply a weakly nonlinear analysis of sand bank dynamics because the linear approaches predict infinite wavelengths of the most unstable mode close to the critical conditions. Here we first revisit the linear approach of Hulscher et al. (1993, Cont. Shelf Res. 13). In particular the time development of small amplitude bottom perturbations forced by tidal currents is studied using a different parameterization of both the bed shear stress and the sediment transport predictor which provides vanishing values of the sediment transport rate when the bottom shear stress is smaller than a critical value and accounts for the deviation of the sediment transport rate from the depth averaged velocity. With these improvements, both clockwise and counterclockwise sand banks are predicted. Moreover the wavelength of the most unstable mode close to the critical conditions turns out to be finite. This result opens the possibility to carry out a weakly nonlinear stability analysis. Then the time development of the most unstable mode is studied for values of the parameters close to the marginal conditions. The analysis provides estimates of the sand bank equilibrium amplitude and predicts equilibrium profiles characterized by crests sharper than the troughs, a feature often observed in field surveys.

Tambroni, N.; Blondeaux, P.

2006-12-01

126

Stability diagram for the forced Kuramoto model.

We analyze the periodically forced Kuramoto model. This system consists of an infinite population of phase oscillators with random intrinsic frequencies, global sinusoidal coupling, and external sinusoidal forcing. It represents an idealization of many phenomena in physics, chemistry, and biology in which mutual synchronization competes with forced synchronization. In other words, the oscillators in the population try to synchronize with one another while also trying to lock onto an external drive. Previous work on the forced Kuramoto model uncovered two main types of attractors, called forced entrainment and mutual entrainment, but the details of the bifurcations between them were unclear. Here we present a complete bifurcation analysis of the model for a special case in which the infinite-dimensional dynamics collapse to a two-dimensional system. Exact results are obtained for the locations of Hopf, saddle-node, and Takens-Bogdanov bifurcations. The resulting stability diagram bears a striking resemblance to that for the weakly nonlinear forced van der Pol oscillator. PMID:19123638

Childs, Lauren M; Strogatz, Steven H

2008-12-01

127

Stability diagram for the forced Kuramoto model

NASA Astrophysics Data System (ADS)

We analyze the periodically forced Kuramoto model. This system consists of an infinite population of phase oscillators with random intrinsic frequencies, global sinusoidal coupling, and external sinusoidal forcing. It represents an idealization of many phenomena in physics, chemistry, and biology in which mutual synchronization competes with forced synchronization. In other words, the oscillators in the population try to synchronize with one another while also trying to lock onto an external drive. Previous work on the forced Kuramoto model uncovered two main types of attractors, called forced entrainment and mutual entrainment, but the details of the bifurcations between them were unclear. Here we present a complete bifurcation analysis of the model for a special case in which the infinite-dimensional dynamics collapse to a two-dimensional system. Exact results are obtained for the locations of Hopf, saddle-node, and Takens-Bogdanov bifurcations. The resulting stability diagram bears a striking resemblance to that for the weakly nonlinear forced van der Pol oscillator.

Childs, Lauren M.; Strogatz, Steven H.

2008-12-01

128

ASTROP2 users manual: A program for aeroelastic stability analysis of propfans

NASA Technical Reports Server (NTRS)

A user's manual is presented for the aeroelastic stability and response of propulsion systems computer program called ASTROP2. The ASTROP2 code preforms aeroelastic stability analysis of rotating propfan blades. This analysis uses a two-dimensional, unsteady cascade aerodynamics model and a three-dimensional, normal-mode structural model. Analytical stability results from this code are compared with published experimental results of a rotating composite advanced turboprop model and of nonrotating metallic wing model.

Narayanan, G. V.; Kaza, K. R. V.

1991-01-01

129

New methods for the reduction of high-order, linear time invariant systems is proposed. The methods are based on the different techniques and generates low order stable models retaining both the initial Markov parameters and time-moments, of the original system. Theses models give a better approximation for both the steady-state as well as the transient part of the time response. The

P. Munaswamy; R. V. S. Satyanarayana

2012-01-01

130

Reliability applied to slope stability analysis

Formally probabilistic methods for the analysis of slope stability have had relatively little impact on practice. Many engineers are not familiar with probabilistic concepts, and it has been difficult to incorporate concepts of reliability into practice. Also, there is confusion over what reliability and probability of failure mean. The most effective applications of probabilistic methods are those involving relative probabilities

John T. Christian; Charles C. Ladd; Gregory B. Baecher

1994-01-01

131

Stability analysis of PD regulation for ball and beam system

Many nonlinear controllers for ball and beam system can achieve in some cases asymptotic stability. Only a few of them apply their nonlinear control theory results in real experiment. On the other hand, many laboratories use PD control for the ball and beam system, but theory analysis is based on a linear approximate model. Little effort has been made to

Wen Yu; Floriberto Ortiz

2005-01-01

132

Use of power electronic equipment has increased and introduced new dynamical phenomena in power systems. For example, new electric rail vehicles (locomotives) equipped with modern power electronic traction chains have caused situations of low-frequency power oscillations and instability in single-phase railway power supply systems. This paper presents the development and implementation of an instantaneous value model and simplified fundamental frequency

Steinar Danielsen; Olav B. Fosso; Marta Molinas; Jon Are Suul; Trond Toftevaag

2010-01-01

133

Stability Analysis of a Uniformly Heated Channel with Supercritical Water

The thermal-hydraulic stability of a uniformly heated channel at supercritical water pressure has been investigated to help understand the system instability phenomena which may occur in Supercritical Water Nuclear Reactors (SCWR). We have extended the modeling approach often used for Boiling Water Nuclear Reactor (BWR) stability analysis to supercritical pressure operation conditions. We have shown that Ledinegg excursive instabilities and pressure-drop oscillations (PDO) will not occur in supercritical water systems. The linear stability characteristics of a typical uniformly heated channel were computed by evaluating the eigenvalues of the model. An analysis of non-linear instability phenomena was also performed in the time domain and the dynamic bifurcations were evaluated. (authors)

Ortega Gomez, T.; Class, A.; Schulenberg, T. [Forschungszentrum Karlsruhe, Hermann-von-Helmholtz-Platz 1 76344 Eggenstein-Leopoldshafen (Germany); Lahey, R.T. Jr. [Center for Multiphase Research, Rensselaer Polytechnic, Troy, NY (United States)

2006-07-01

134

A Simply Stabilized Running Model

The spring-loaded inverted pendulum (SLIP), or monopedal hopper, is an archetypal model for running in numerous animal species. Although locomotion is generally considered a complex taskrequiring sophisticated control strategies to account for coordination and sta- bility, we show that stable gaits can be found in the SLIP with both linear and \\

R. M. Ghigliazza; R. Altendorfer; P. Holmes

2005-01-01

135

NASA Astrophysics Data System (ADS)

The Bjerknes (BJ) stability index is an approximate formula that may be used to analyse the stability of the coupled El Nino/Southern Oscillation (ENSO) mode. The BJ stability index depends on the basic mean state, the atmosphere's sensitivity to sea surface temperature and the ocean's sensitivity to wind forcing. A positive BJ stability index indicates a growth of ENSO stability while a negative BJ stability index signifies the rate of decay with negative contributions coming from damping by mean advection and air-sea heat fluxes while positive contributions from the zonal advective, Ekman pumping and thermocline feedback. Here we employ the BJ stability index to investigate ENSO variability over multi-decadal time scales in the Commonwealth Scientific and Industrial Research Organisation Mark version 3.0L (CSIRO Mk3L) coupled general circulation model and assess the sensitivity of ENSO to changes in tropical climate conditions. Model simulations are forced with atmospheric concentrations fixed at pre-industrial levels and integrated over 1000-years to allow a variety of ENSO events to be simulated. The BJ index points to a simulated ENSO that is damped with the negative contribution from thermal damping by air-sea heat fluxes dominating over the feedback processes. There also exists a significant positive correlation between the ENSO amplitude and ENSO stability such that the BJ index becomes less damped with increasing ENSO variability. We find that significant variations in the ENSO amplitude exist on decadal and centennial time scales. These variations are mainly governed by variations in the strength of the thermocline feedback, which is in turn a function of the coherence between fluctuations of the atmosphere and the ocean in the equatorial Pacific, reflecting the response of winds to temperature gradients and the response of the thermocline to winds. Surprisingly, such decadal and centennial variations are only weakly control by the mean state differences. The implications for interpreting observed ENSO variability will be discussed.

Borlace, S.; Cai, W.; Santoso, A.

2012-12-01

136

NASA Astrophysics Data System (ADS)

We consider an ecological model for biodegradation of toxic substances in aquatic and atmospheric biotic systems. The model, which is described by a nonlinear system of four ordinary differential equations, is known to be experimentally validated. We compute the equilibrium points of the model and study their asymptotic stability. The Maple package BifTools is used to calculate one- and two-parameter bifurcations of the equilibrium points.

Borisov, M.; Dimitrova, N.

2011-11-01

137

Stability Analysis of the Slowed-Rotor Compound Helicopter Configuration

NASA Technical Reports Server (NTRS)

The stability and control of rotors at high advance ratio are considered. Teetering, articulated, gimbaled, and rigid hub types are considered for a compound helicopter (rotor and fixed wing). Stability predictions obtained using an analytical rigid flapping blade analysis, a rigid blade CAMRAD II model, and an elastic blade CAMRAD II model are compared. For the flapping blade analysis, the teetering rotor is the most stable, 5howing no instabilities up to an advance ratio of 3 and a Lock number of 18. With an elastic blade model, the teetering rotor is unstable at an advance ratio of 1.5. Analysis of the trim controls and blade flapping shows that for small positive collective pitch, trim can be maintained without excessive control input or flapping angles.

Johnson, Wayne; Floros, Matthew W.

2004-01-01

138

Stability Analysis of the Slowed-Rotor Compound Helicopter Configuration

NASA Technical Reports Server (NTRS)

The stability and control of rotors at high advance ratio are considered. Teetering, articulated, gimbaled, and rigid hub types are considered for a compound helicopter (rotor and fixed wing). Stability predictions obtained using an analytical rigid flapping blade analysis, a rigid blade CAMRAD II model, and an elastic blade CAMRAD II model are compared. For the flapping blade analysis, the teetering rotor is the most stable, showing no instabilities up to an advance ratio of 3 and a Lock number of 18. A notional elastic blade model of a teetering rotor is unstable at an advance ratio of 1.5, independent of pitch frequency. Analysis of the trim controls and blade flapping shows that for small positive collective pitch, trim can be maintained without excessive control input or flapping angles.

Floros, Matthew W.; Johnson, Wayne

2007-01-01

139

NASA Astrophysics Data System (ADS)

We propose a detailed stability analysis of the Lugiato-Lefever model for Kerr optical frequency combs in whispering-gallery-mode resonators when they are pumped in either the anomalous- or normal-dispersion regime. We analyze the spatial bifurcation structure of the stationary states depending on two parameters that are experimentally tunable; namely, the pump power and the cavity detuning. Our study demonstrates that, in both the anomalous- and normal-dispersion cases, nontrivial equilibria play an important role in this bifurcation map because their associated eigenvalues undergo critical bifurcations that are actually foreshadowing the existence of localized and extended spatial dissipative structures. The corresponding bifurcation maps are evidence of a considerable richness from a dynamical standpoint. The case of anomalous dispersion is indeed the most interesting from the theoretical point of view because of the considerable variety of dynamical behavior that can be observed. For this case we study the emergence of super- and subcritical Turing patterns (or primary combs) in the system via modulational instability. We determine the areas where bright isolated cavity solitons emerge, and we show that soliton molecules can emerge as well. Very complex temporal patterns can actually be observed in the system, where solitons (or soliton complexes) coexist with or without mutual interactions. Our investigations also unveil the mechanism leading to the phenomenon of breathing solitons. Two routes to chaos in the system are identified; namely, a route via the destabilization of a primary comb, and another via the destabilization of solitons. For the case of normal dispersion, we unveil the mechanism leading to the emergence of weakly stable Turing patterns. We demonstrate that this weak stability is justified by the distribution of stable and unstable fixed points in the parameter space (flat states). We show that dark cavity solitons can emerge in the system, and also show how these solitons can coexist in the resonator as long as they do not interact with each other. We find evidence of breather solitons in this normal dispersion regime as well. The Kerr frequency combs corresponding to all these spatial dissipative structures are analyzed in detail, along with their stability properties. A discussion is led about the possibility to gain unifying comprehension of the observed spectra from the dynamical complexity of the system.

Godey, Cyril; Balakireva, Irina V.; Coillet, Aurélien; Chembo, Yanne K.

2014-06-01

140

Modeling wind farms for power system stability studies

Wind energy conversion systems comprise mechanical and electrical equipment and their controls. Modeling these systems for power system stability simulation studies requires careful analysis of the equipment and controls to determine the characteristics that are important in the timeframe and bandwidth of such studies. Just as important, the characteristics must be reviewed to put aside factors that can be important

Y. A. Kazachkov; J. W. Feltes; R. Zavadil

2003-01-01

141

Stability analysis of the particle dynamics in particle swarm optimizer

Previous stability analysis of the particle swarm optimizer was restricted to the assumption that all parameters are nonrandom, in effect a deterministic particle swarm optimizer. We analyze the stability of the particle dynamics without this restrictive assumption using Lyapunov stability analysis and the concept of passive systems. Sufficient conditions for stability are derived, and an illustrative example is given. Simulation

Visakan Kadirkamanathan; Kirusnapillai Selvarajah; Peter J. Fleming

2006-01-01

142

Nonlinear aerostatic stability analysis of suspension bridges

Nonlinear aerostatic stability analysis of long-span suspension bridges is studied by including directly the three combined effects of: (1) nonlinear three-component displacement-dependent wind loads, (2) geometric nonlinearity, and (3) material nonlinearity. The nonlinear three-component displacement-dependent wind loads are included through the static aerodynamic coefficients as a function of angle of attack. The various structural bucklings, such as flexural buckling, torsional

Virote Boonyapinyo; Yingsak Lauhatanon; Panitan Lukkunaprasit

2006-01-01

143

Thermodynamic modeling of natural zeolite stability

Zeolites occur in a variety of geologic environments and are used in numerous agricultural, commercial, and environmental applications. It is desirable to understand their stability both to predict future stability and to evaluate the geochemical conditions resulting in their formation. The use of estimated thermodynamic data for measured zeolite compositions allows thermodynamic modeling of stability relationships among zeolites in different geologic environments (diagenetic, saline and alkaline lakes, acid rock hydrothermal, basic rock, deep sea sediments). This modeling shows that the relative cation abundances in both the aqueous and solid phases, the aqueous silica activity, and temperature are important factors in determining the stable zeolite species. Siliceous zeolites (e.g., clinoptilolite, mordenite, erionite) present in saline and alkaline lakes or diagenetic deposits formed at elevated silica activities. Aluminous zeolites (e.g., natrolite, mesolite/scolecite, thomsonite) formed in basic rocks in association with reduced silica activities. Likewise, phillipsite formation is favored by reduced aqueous silica activities. The presence of erionite, chabazite, and phillipsite are indicative of environments with elevated potassium concentrations. Elevated temperature, calcic water conditions, and reduced silica activity help to enhance the laumontite and wairakite stability fields. Analcime stability increases with increased temperature and aqueous Na concentration, and/or with decreased silica activity.

Chipera, S.J.; Bish, D.L.

1997-06-01

144

Soliton stability in some knot soliton models

We study the issue of stability of static solitonlike solutions in some nonlinear field theories which allow for knotted field configurations. Concretely, we investigate the Aratyn-Ferreira-Zimerman model [Phys. Lett. B 456, 162 (1999); Phys. Rev. Lett. 83, 1723 (1999)], based on a Lagrangian quartic in first derivatives with infinitely many conserved currents, for which infinitely many soliton solutions are known

C. Adam; J. Sánchez-Guillén; A. Wereszczynski

2007-01-01

145

Stability Analysis for HIFiRE Experiments

NASA Technical Reports Server (NTRS)

The HIFiRE-1 flight experiment provided a valuable database pertaining to boundary layer transition over a 7-degree half-angle, circular cone model from supersonic to hypersonic Mach numbers, and a range of Reynolds numbers and angles of attack. This paper reports selected findings from the ongoing computational analysis of the measured in-flight transition behavior. Transition during the ascent phase at nearly zero degree angle of attack is dominated by second mode instabilities except in the vicinity of the cone meridian where a roughness element was placed midway along the length of the cone. The growth of first mode instabilities is found to be weak at all trajectory points analyzed from the ascent phase. For times less than approximately 18.5 seconds into the flight, the peak amplification ratio for second mode disturbances is sufficiently small because of the lower Mach numbers at earlier times, so that the transition behavior inferred from the measurements is attributed to an unknown physical mechanism, potentially related to step discontinuities in surface height near the locations of a change in the surface material. Based on the time histories of temperature and/or heat flux at transducer locations within the aft portion of the cone, the onset of transition correlated with a linear N-factor, based on parabolized stability equations, of approximately 13.5. Due to the large angles of attack during the re-entry phase, crossflow instability may play a significant role in transition. Computations also indicate the presence of pronounced crossflow separation over a significant portion of the trajectory segment that is relevant to transition analysis. The transition behavior during this re-entry segment of HIFiRE-1 flight shares some common features with the predicted transition front along the elliptic cone shaped HIFiRE-5 flight article, which was designed to provide hypersonic transition data for a fully 3D geometric configuration. To compare and contrast the crossflow dominated transition over the HIFiRE-1 and HIFiRE-5 configurations, this paper also analyzes boundary layer instabilities over a subscale model of the HIFiRE-5 flight configuration that was tested in the Mach 6 quiet tunnel facility at Purdue University.

Li, Fei; Choudhari, Meelan M.; Chang, Chau-Lyan; White, Jeffery A.; Kimmel, Roger; Adamczak, David; Borg, Matthew; Stanfield, Scott; Smith, Mark S.

2012-01-01

146

Stability analysis of White Oak Dam

White Oak Dam is located in the White Oak Creek watershed which provides the primary surface drainage for Oak Ridge National Laboratory. A stability analysis was made on the dam by Syed Ahmed in January 1994 which included an evaluation of the liquefaction potential of the embankment and foundation. This report evaluates the stability of the dam and includes comments on the report prepared by Ahmed. Slope stability analyses were performed on the dam and included cases for sudden drawdown, steady seepage, partial pool and earthquake. Results of the stability analyses indicate that the dam is stable and failure of the structure would not occur for the cases considered. The report prepared by Ahmed leads to the same conclusions as stated above. Review of the report finds that it is complete, well documented and conservative in its selection of soil parameters. The evaluation of the liquefaction potential is also complete and this report is in agreement with the findings that the dam and foundation are not susceptible to liquefaction.

NONE

1995-04-11

147

Analysis of the stabilized supralinear network‡

We study a rate-model neural network composed of excitatory and inhibitory neurons in which neuronal input-output functions are power laws with a power greater than 1, as observed in primary visual cortex. This supralinear input-output function leads to supralinear summation of network responses to multiple inputs for weak inputs. We show that for stronger inputs, which would drive the excitatory subnetwork to instability, the network will dynamically stabilize provided feedback inhibition is sufficiently strong. For a wide range of network and stimulus parameters, this dynamic stabilization yields a transition from supralinear to sublinear summation of network responses to multiple inputs. We compare this to the dynamic stabilization in the “balanced network”, which yields only linear behavior. We more exhaustively analyze the 2-dimensional case of 1 excitatory and 1 inhibitory population. We show that in this case dynamic stabilization will occur whenever the determinant of the weight matrix is positive and the inhibitory time constant is sufficiently small, and analyze the conditions for “supersaturation”, or decrease of firing rates with increasing stimulus contrast (which represents increasing input firing rates). In work to be presented elsewhere, we have found that this transition from supralinear to sublinear summation can explain a wide variety of nonlinearities in cerebral cortical processing.

Ahmadian, Yashar; Rubin, Daniel B.; Miller, Kenneth D.

2014-01-01

148

Mathematical Modeling and Simulation of Seated Stability

Various methods have been used to quantify the kinematic variability or stability of the human spine. However, each of these methods evaluates dynamic behavior within the stable region of state space. In contrast, our goal was to determine the extent of the stable region. A 2D mathematical model was developed for a human sitting on an unstable seat apparatus (i.e., the “wobble chair”). Forward dynamic simulations were used to compute trajectories based on the initial state. From these trajectories, a scalar field of trajectory divergence was calculated, specifically a finite time Lyapunov exponent (FTLE) field. Theoretically, ridges of local maxima within this field are expected to partition the state space into regions of qualitatively different behavior. We found that ridges formed at the boundary between regions of stability and failure (i.e., falling). The location of the basin of stability found using the FTLE field matched well with the basin of stability determined by an alternative method. In addition, an equilibrium manifold was found, which describes a set of equilibrium configurations that act as a low dimensional attractor in the controlled system. These simulations are a first step in developing a method to locate state space boundaries for torso stability. Identifying these boundaries may provide a framework for assessing factors that contribute to health risks associated with spinal injury and poor balance recovery (e.g., age, fatigue, load/weight and distribution). Furthermore, an approach is presented that can be adapted to find state space boundaries in other biomechanical applications.

Tanaka, Martin L.; Ross, Shane D.; Nussbaum, Maury A.

2009-01-01

149

Linear stability analysis of dynamical quadratic gravity

NASA Astrophysics Data System (ADS)

We study the linear stability of dynamical, quadratic gravity, focusing on two particular subclasses (the even-parity sector, exemplified by Einstein-Dilaton-Gauss-Bonnet gravity, and the odd-parity sector, exemplified by dynamical Chern-Simons modified gravity) in the high-frequency, geometric optics approximation. This analysis is carried out by studying gravitational and scalar modes propagating on spherically symmetric and axially symmetric, vacuum solutions of the theory and finding the associated dispersion relations. These relations are solved in two separate cases (the scalar regime and the gravitational wave regime, defined by requiring the ratio of the amplitude of the perturbations to be much greater or smaller than unity) and found in both cases to not lead to exponential growth of the propagating modes, suggesting linearly stability. The modes are found to propagate at subluminal and superluminal speeds, depending on the propagating modes' direction relative to the background geometry, just as in dynamical Chern-Simons gravity.

Ayzenberg, Dimitry; Yagi, Kent; Yunes, Nicolás

2014-02-01

150

A Consistent Orbital Stability Analysis for the GJ 581 System

NASA Astrophysics Data System (ADS)

We apply a combination of N-body modeling techniques and automated data fitting with Monte Carlo Markov Chain uncertainty analysis of Keplerian orbital models to RV data to determine long-term stability of the planetary system GJ 581. We find that while there are stability concerns with the four-planet model as published by Forveille et al., when uncertainties in the system are accounted for, particularly stellar jitter, the hypothesis that the four-planet model is gravitationally unstable is not statistically significant. Additionally, the system including proposed planet g by Vogt et al. also shows some stability concerns when eccentricities are allowed to float in the orbital fit, yet when uncertainties are included in the analysis, the system including planet g also cannot be proven to be unstable. We present revised reduced ?2 values for Keplerian astrocentric orbital fits assuming four-planet and five-planet models for GJ 581 under the condition that best fits must be stable, and we find no distinguishable difference by including planet g in the model. Additionally, we present revised orbital element estimates for each, assuming uncertainties due to stellar jitter under the constraint of the system being gravitationally stable.

Joiner, David A.; Sul, Cesar; Dragomir, Diana; Kane, Stephen R.; Kress, Monika E.

2014-06-01

151

Stability of the Einstein static universe in open cosmological models

The stability properties of the Einstein static solution of general relativity are altered when corrective terms arising from modification of the underlying gravitational theory appear in the cosmological equations. In this paper the existence and stability of static solutions are considered in the framework of two recently proposed quantum gravity models. The previously known analysis of the Einstein static solutions in the semiclassical regime of loop quantum cosmology with modifications to the gravitational sector is extended to open cosmological models where a static neutrally stable solution is found. A similar analysis is also performed in the framework of Horava-Lifshitz gravity under detailed balance and projectability conditions. In the case of open cosmological models the two solutions found can be either unstable or neutrally stable according to the admitted values of the parameters.

Canonico, Rosangela; Parisi, Luca [Dipartimento di Fisica 'E. R. Caianiello', Universita di Salerno, Via Ponte Don Melillo, I-84081 Baronissi (Italy); INFN, Sezione di Napoli, GC di Salerno, Via Ponte Don Melillo, I-84081 Baronissi (Italy)

2010-09-15

152

Numerical Analysis of Spine Stabilizers on Lumbar Part of Spine

\\u000a The numerical analysis of spine stabilizers was carried out in the work. The aim of the work was determination of more favourable\\u000a stabilization variant. Moreover, this analysis is the basis to determine an optimal geometry of the stabilizer as well as\\u000a to select mechanical properties of metallic biomaterial. The work presents the results of biomechanical analysis of lumbar\\u000a spine stabilization

Marta Kiel; Jan Marciniak; Marcin Basiaga; Janusz Szewczenko

153

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

National Technical Information Service (NTIS)

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 adapt...

A. K. Ishihara K. Krishnakumar M. Bakhtiari-Nejad N. T. Nguyen

2009-01-01

154

Numerical Analysis of Combustion Oscillation Stabilization by Helmholtz Oscillation Control

NASA Astrophysics Data System (ADS)

Combustion oscillation stabilization by Helmholtz resonator has been investigated for gas turbine combustor, and mechanism of oscillation control has been discussed in terms of analysis model of Helmholtz oscillation, excited between combustor and fuel injector. Amplitude of oscillation pressure is stabilized corresponding to resonator parameters, such as throat diameter and length, and calculated results on combustion oscillation stabilization are compared with experimental results by atmospheric combustion apparatus. In case Helmholtz resonator equipped to combustor is in resonance to combustor chamber, it is shown that amplitude of oscillation pressure can be minimized. However, effectiveness of the resonator may be lessened with decrease of throat diameter or increase of throat length, while throat diameter and length are both tuning parameters of the resonator. Throat resistance, which is determined by both of throat diameter and length, is actually one of the major parameters in Helmholtz oscillation control. Resonator parameters must be optimized in terms of attenuation characteristics as well as resonance frequency.

Shioda, Kazunori; Yamanaka, Susumu; Maeda, Fukuo; Iwabuchi, Kazunori; Tsuchiya, Toshiaki; Okamoto, Masanori

155

Shapes and stability of algebraic nuclear models

NASA Technical Reports Server (NTRS)

A generalization of the procedure to study shapes and stability of algebraic nuclear models introduced by Gilmore is presented. One calculates the expectation value of the Hamiltonian with respect to the coherent states of the algebraic structure of the system. Then equilibrium configurations of the resulting energy surface, which depends in general on state variables and a set of parameters, are classified through the Catastrophe theory. For one- and two-body interactions in the Hamiltonian of the interacting Boson model-1, the critical points are organized through the Cusp catastrophe. As an example, we apply this Separatrix to describe the energy surfaces associated to the Rutenium and Samarium isotopes.

Lopez-Moreno, Enrique; Castanos, Octavio

1995-01-01

156

NASA Astrophysics Data System (ADS)

Solvation structure and conformational stability of the C-peptide fragment of ribonuclease A in pure water have been analyzed using the full reference interaction site model (RISM) theory. The charged groups in the side chains of Lys-1+, Glu-2-, Lys-7+, Arg-10+, and His-12+ (in particular, the four like-charged groups) play substantial roles in stabilizing the conformations. The solvation free energy and the conformational energy are governed by the contribution from the electrostatic interaction with water and the intramolecular Coulombic energy, respectively, and the conformational stability is determined by competition of these two factors. The contributions from the hydrophobic hydration and the van der Waals and torsion terms in the conformational energy are less important, which is in contrast to the result for Met-enkephalin. The Monte Carlo simulated annealing combined with the RISM theory has been applied to the C-peptide using an almost fully extended conformation as the initial one. The conformation first changes in the direction that the charged groups in the side chains are more exposed to water, and in particular, the positively charged groups are closer together. Thus, the solvation free energy decreases greatly in the initial stage. Although this leads to a significant increase in the intramolecular Coulombic repulsion energy, the decrease in the solvation free energy dominates. In the later stage, however, a further decrease in the solvation free energy gives rise to an even larger increase in the intramolecular Coulombic repulsion energy, and the conformational change is greatly decelerated. The conformations thus stabilized in four different runs of the combined program are quite similar. The peptide conformation in water is stabilized far more rapidly than in the gas phase.

Kinoshita, Masahiro; Okamoto, Yuko; Hirata, Fumio

1999-02-01

157

Stability analysis for laminar flow control, part 1

NASA Technical Reports Server (NTRS)

The basic equations for the stability analysis of flow over three dimensional swept wings are developed and numerical methods for their solution are surveyed. The equations for nonlinear stability analysis of three dimensional disturbances in compressible, three dimensional, nonparallel flows are given. Efficient and accurate numerical methods for the solution of the equations of stability theory were surveyed and analyzed.

Benney, D. J.; Orszag, S. A.

1977-01-01

158

Bounded linear stability margin analysis of nonlinear hybrid adaptive control

This paper presents a bounded linear stability analysis for a hybrid adaptive control that blends both direct and indirect adaptive control. Stability and convergence of nonlinear adaptive control are analyzed using an approximate linear equivalent system. A stability margin analysis shows that a large adaptive gain can lead to a reduced phase margin. This method can enable metrics-driven adaptive control

Nhan T. Nguyen; Jovan D. Boskovic

2008-01-01

159

Vector fields during cosmic inflation: Stability analysis and phenomenological signatures

NASA Astrophysics Data System (ADS)

This thesis is based on the study of vector fields during cosmic inflation. Cosmic inflation has proven to be an accurate description of the very early universe, not only because of its success in resolving the classical problems of big bang cosmology, but also for introducing a natural mechanism for the generation of primordial fluctuations which give rise to the structure (galaxies and cluster of galaxies) in the universe. For simplicity, most inflationary scenarios assume that the expansion is driven by a scalar field. However, due to the fact that the underlying particle physics model of inflation is unknown, and due to some features emerged in some studies of the cosmic microwave background data, there have recently been considerable interest in vector field driven models of inflation. In this thesis, I present a complete stability analysis of some of the compelling models where vector fields are assumed to play an important role during inflation. The stability analysis is performed by studying all possible fluctuations around the background solution of these models. It is explicitly proven that for models where the gauge invariance of the vector field is broken, the background solution is unstable. The proof is performed both (1) by studying the quadratic action for the fluctuations, and showing that ghost instabilities are present in the model; and (2) by studying the linearized Einstein equations and showing that the solutions diverge close to horizon crossing. For models that are free of instabilities, relevant power spectra are computed and the resulting phenomenology is discussed.

Himmetoglu, Burak

160

Ancova Approach For Shelf Life Analysis Of Stability Study Of Multiple Factor Designs

For a traditional multiple batch stability design with no other factor, the conventional analysis is analysis of covariance (ANCOVA) modeling using F-tests based on type I sum of squares to determine whether the batches may be pooled for a common estimate of the linear regression line(s). In the last decade, many multiple factor designs were proposed in stability studies. With

Yi Tsong; Wen-Jen Chen; Chi Wan Chen

2003-01-01

161

A simple model for SLC positron stability issues

A simple model is constructed for the SLC positron system to describe the intensity variations induced by beam loading in the linac. It is found that the system can be described by the well known logistic equation. This allows us to use results from the stability analysis to characterize the positron system, to place tolerances on fluctuations. and to slow variations on the scavenger beam intensity.

Krejcik, P.; Ziemann, V.

1992-06-01

162

Bounded Linear Stability Margin Analysis of Nonlinear Hybrid Adaptive Control

NASA Technical Reports Server (NTRS)

This paper presents a bounded linear stability analysis for a hybrid adaptive control that blends both direct and indirect adaptive control. Stability and convergence of nonlinear adaptive control are analyzed using an approximate linear equivalent system. A stability margin analysis shows that a large adaptive gain can lead to a reduced phase margin. This method can enable metrics-driven adaptive control whereby the adaptive gain is adjusted to meet stability margin requirements.

Nguyen, Nhan T.; Boskovic, Jovan D.

2008-01-01

163

Dynamic response and stability analysis of flexible, multibody systems. [spacecraft

NASA Technical Reports Server (NTRS)

A general version of Lagrange's equations, including auxiliary nonholonomic, rheonomic conditions of constraint, is used in the dynamic simulation and stability analysis of interconnected flexible bodies. Modeling of the nonlinear flexible/rigid dynamic coupling effects, the interaction forces/torques, and the elastic deformation effects is discussed. A digital computer program is developed to obtain time-domain solution for the nonlinear response of systems represented as a collection of individual bodies, numerical linearization of system-governing equations, time-domain solution for the perturbation response about a nominal state, and a frequency-domain stability analysis corresponding to the linearization. The digital simulation code is employed to study the dynamic behavior of a typical satellite and a spacecraft with deployable experiment booms.

Bodley, C. S.; Park, A. C.; Devers, A. D.; Frisch, H. P.

1977-01-01

164

BWR stability analysis at Brookhaven National Laboratory

Following the unexpected, but safely terminated, power and flow oscillations in the LaSalle-2 Boiling Water Reactor (BWR) on March 9, 1988, the Nuclear Regulatory Commission (NRC) Offices of Nuclear Reactor Regulation (NRR) and of Analysis and Evaluation of Operational Data (AEOD) requested that the Office of Nuclear Regulatory Research (RES) carry out BWR stability analyses, centered around fourteen specific questions. Ten of the fourteen questions address BWR stability issues in general and are dealt with in this paper. The other four questions address local, out-of-phase oscillations and matters of instrumentation; they fall outside the scope of the work reported here. It was the purpose of the work documented in this report to answer ten of the fourteen NRC-stipulated questions. Nine questions are answered by analyzing the LaSalle-2 instability and related BWR transients with the BNL Engineering Plant Analyzer (EPA) and by performing an uncertainty assessment of the EPA predictions. The tenth question is answered on the basis of first principles. The ten answers are summarized

Wulff, W.; Cheng, H.S.; Mallen, A.N.; Rohatgi, U.S.

1991-12-31

165

BWR stability analysis at Brookhaven National Laboratory

Following the unexpected, but safely terminated, power and flow oscillations in the LaSalle-2 Boiling Water Reactor (BWR) on March 9, 1988, the Nuclear Regulatory Commission (NRC) Offices of Nuclear Reactor Regulation (NRR) and of Analysis and Evaluation of Operational Data (AEOD) requested that the Office of Nuclear Regulatory Research (RES) carry out BWR stability analyses, centered around fourteen specific questions. Ten of the fourteen questions address BWR stability issues in general and are dealt with in this paper. The other four questions address local, out-of-phase oscillations and matters of instrumentation; they fall outside the scope of the work reported here. It was the purpose of the work documented in this report to answer ten of the fourteen NRC-stipulated questions. Nine questions are answered by analyzing the LaSalle-2 instability and related BWR transients with the BNL Engineering Plant Analyzer (EPA) and by performing an uncertainty assessment of the EPA predictions. The tenth question is answered on the basis of first principles. The ten answers are summarized

Wulff, W.; Cheng, H.S.; Mallen, A.N.; Rohatgi, U.S.

1991-01-01

166

Stability of earthquake clustering models: criticality and branching ratios.

We study the stability conditions of a class of branching processes prominent in the analysis and modeling of seismicity. This class includes the epidemic-type aftershock sequence (ETAS) model as a special case, but more generally comprises models in which the magnitude distribution of direct offspring depends on the magnitude of the progenitor, such as the branching aftershock sequence (BASS) model and another recently proposed branching model based on a dynamic scaling hypothesis. These stability conditions are closely related to the concepts of the criticality parameter and the branching ratio. The criticality parameter summarizes the asymptotic behavior of the population after sufficiently many generations, determined by the maximum eigenvalue of the transition equations. The branching ratio is defined by the proportion of triggered events in all the events. Based on the results for the generalized case, we show that the branching ratio of the ETAS model is identical to its criticality parameter because its magnitude density is separable from the full intensity. More generally, however, these two values differ and thus place separate conditions on model stability. As an illustration of the difference and of the importance of the stability conditions, we employ a version of the BASS model, reformulated to ensure the possibility of stationarity. In addition, we analyze the magnitude distributions of successive generations of the BASS model via analytical and numerical methods, and find that the compound density differs substantially from a Gutenberg-Richter distribution, unless the process is essentially subcritical (branching ratio less than 1) or the magnitude dependence between the parent event and the direct offspring is weak. PMID:24483388

Zhuang, Jiancang; Werner, Maximilian J; Harte, David S

2013-12-01

167

Stability of earthquake clustering models: Criticality and branching ratios

NASA Astrophysics Data System (ADS)

We study the stability conditions of a class of branching processes prominent in the analysis and modeling of seismicity. This class includes the epidemic-type aftershock sequence (ETAS) model as a special case, but more generally comprises models in which the magnitude distribution of direct offspring depends on the magnitude of the progenitor, such as the branching aftershock sequence (BASS) model and another recently proposed branching model based on a dynamic scaling hypothesis. These stability conditions are closely related to the concepts of the criticality parameter and the branching ratio. The criticality parameter summarizes the asymptotic behavior of the population after sufficiently many generations, determined by the maximum eigenvalue of the transition equations. The branching ratio is defined by the proportion of triggered events in all the events. Based on the results for the generalized case, we show that the branching ratio of the ETAS model is identical to its criticality parameter because its magnitude density is separable from the full intensity. More generally, however, these two values differ and thus place separate conditions on model stability. As an illustration of the difference and of the importance of the stability conditions, we employ a version of the BASS model, reformulated to ensure the possibility of stationarity. In addition, we analyze the magnitude distributions of successive generations of the BASS model via analytical and numerical methods, and find that the compound density differs substantially from a Gutenberg-Richter distribution, unless the process is essentially subcritical (branching ratio less than 1) or the magnitude dependence between the parent event and the direct offspring is weak.

Zhuang, Jiancang; Werner, Maximilian J.; Harte, David S.

2013-12-01

168

On shape stability for a storage model

We consider stability of shape for a storage model on n nodes. These nodes\\u000asupport {\\\\cal K} neighborhoods S_i\\\\subset \\\\{1,..., n\\\\} and items arrive at the\\u000aS_i as independent Poisson streams with rates \\\\lambda_i, i=1, ..., {\\\\cal K}.\\u000aUpon arrival at S_i an item is stored at node j \\\\in S_i where j is determined\\u000aby some policy. Let X_j(t)

M. V. Menshikov; V. V. Sisko; M. Vachkovskaia

2007-01-01

169

Stability of detonations for an idealized condensed-phase model

NASA Astrophysics Data System (ADS)

The stability of travelling wave Chapmanvon Neumannring type is formulated for a general system that incorporates the idealized gas and condensed-phase (liquid or solid) detonation models. The general model consists of a two-component mixture with a one-step irreversible reaction between reactant and product. The reaction rate has both temperature and pressure sensitivities and has a variable reaction order. The idealized condensed-phase model assumes a pressure-sensitive reaction rate, a constant-=3, and invokes the strong shock limit. A linear stability analysis of the steady, planar, ZND detonation wave for the general model is conducted using a normal-mode approach. An asymptotic analysis of the eigenmode structure at the end of the reaction zone is conducted, and spatial boundedness (closure) conditions formally derived, whose precise form depends on the magnitude of the detonation overdrive and reaction order. A scaling analysis of the transonic flow region for ChapmanJouguet detonations. Neutral stability boundaries are calculated for the idealized condensed-phase model for one- and two-dimensional perturbations. Comparisons of the growth rates and frequencies predicted by the normal-mode analysis for an unstable detonation are made with a numerical solution of the reactive Euler equations. The numerical calculations are conducted using a new, high-order algorithm that employs a shock-fitting strategy, an approach that has significant advantages over standard shock-capturing methods for calculating unstable detonations. For the idealized condensed-phase model, nonlinear numerical solutions are also obtained to study the long-time behaviour of one- and two-dimensional unstable Chapman-Jouguet ZND waves.

Short, M.; Anguelova, I. I.; Aslam, T. D.; Bdzil, J. B.; Henrick, A. K.; Sharpe, G. J.

170

A combination of conformational search, energy minimization, and energetic evaluation using a continuum solvent treatment has been employed to study the stability of various conformations of the DNA fragment d(CGCAGAA)/d(TTCGCG) containing a single adenine bulge. The extra-helical (looped-out) bulge conformation derived from a published x-ray structure and intra-helical (stacked bulge base) model structures partially based on nuclear magnetic resonance (NMR) data were used as start structures for the conformational search. Solvent-dependent contributions to the stability of the conformations were calculated from the solvent exposed molecular surface area and by using the finite difference Poisson-Boltzmann approach. Three classes (I-III) of bulge conformations with calculated low energies can be distinguished. The lowest-energy conformations were found in class I, corresponding to structures with the bulge base stacked between flanking helices, and class II, composed of structures forming a triplet of the bulge base and a flanking base pair. All extra-helical bulge structures, forming class III, were found to be less stable compared with the lowest energy structures of class I and II. The results are consistent with NMR data on an adenine bulge in the same sequence context indicating an intra-helical or triplet bulge conformation in solution. Although the total energies and total electrostatic energies of the low-energy conformations show only relatively modest variations, the energetic contributions to the stability were found to vary significantly among the classes of bulge structures. All intra-helical bulge structures are stabilized by a more favorable Coulomb charge-charge interaction but destabilized by a larger electrostatic reaction field contribution compared with all extra-helical and most triplet bulge structures. Van der Waals packing interactions and nonpolar surface-area-dependent contributions appear to favor triplet class II structures and to a lesser degree also the intra-helical stacked bulge conformations. The large conformational variation found for class III conformers might add a favorable entropic contribution to the stability of the extra-helical bulge form.

Zacharias, M; Sklenar, H

1997-01-01

171

Wellbore stability analysis during the production of a carbonate reservoir

NASA Astrophysics Data System (ADS)

Carbonate reservoirs represent a major part of the world oil and gas reserves. During production, the extraction of hydrocarbons reduces pore pressure and thus causes an increase in the effective stress and mechanical compaction in the reservoir. The compactive deformation and failure may be spatially extensive or localized to the vicinity of the wellbore, but in either case the consequences can be economically severe involving surface subsidence, well failure and various production problems. The analysis of wellbore stability and more generally of deformation and failure in carbonate environments hinges upon a relevant constitutive modeling of carbonate rocks over a wide range of porosities. In this study, we performed a wellbore stability analysis for a lateral wellbore junction in three dimensions. The complex geometry for the wellbore junction was modeled with tetrahedral finite elements considering a rate independent elastic-plastic isotropic material that presented linear behavior during elastic strain and associated flow rule. A finite element model simulating drilling and production phases were done for field conditions from a deep water reservoir in Campos basin, offshore Brazil. In this context, several scenarios were studied considering true 3D orientation for both in situ stresses and geometry of the wellbore junction itself. We discussed the impact of constitutive modeling on the wellbore stability, based on new experimental data on two micritic porous carbonates. Series of conventional triaxial experiments were performed at room temperature in dry and wet conditions on samples of Comiso and Tavel limestones of respective porosity 17 and 16%. The wet samples were deformed in drained conditions with 10 MPa pore pressure. The initial yield stresses were identified as the critical stresses at the onset of shear-enhanced compaction, subsequent yield stresses were considered to depend on hardening given by the plastic volumetric strain. For both limestones, we found that water had a moderate effect on the yield stresses but influenced significantly the hardening behavior of the rocks.

Alves, J.-L.; Coehlo, L.; Baud, P.; Guevara Junior, N.

2009-04-01

172

Stability analysis of superconducting electroweak vortices

NASA Astrophysics Data System (ADS)

We carry out a detailed stability analysis of the superconducting vortex solutions in the Weinberg-Salam theory described in [J. Garaud, M.S. Volkov, Nucl. Phys. B 826 (2010) 174]. These vortices are characterized by constant electric current I and electric charge density I, for I?0 they reduce to Z strings. We consider the generic field fluctuations around the vortex and apply the functional Jacobi criterion to detect the negative modes in the fluctuation operator spectrum. We find such modes and determine their dispersion relation, they turn out to be of two different types, according to their spatial behavior. There are non-periodic in space negative modes, which can contribute to the instability of infinitely long vortices, but they can be eliminated by imposing the periodic boundary conditions along the vortex. There are also periodic negative modes, but their wavelength is always larger than a certain minimal value, so that they cannot be accommodated by the short vortex segments. However, even for the latter there remains one negative mode responsible for the homogeneous expansion instability. This mode may probably be eliminated when the vortex segment is bent into a loop. This suggests that small vortex loops balanced against contraction by the centrifugal force could perhaps be stable.

Garaud, Julien; Volkov, Mikhail S.

2010-11-01

173

Online stability validation using sector analysis

Our previous work has explored the use of compositional stabilization techniques for embedded flight control software[9] based on passivity properties of controller components and systems. Zames[21] presented a compositional behavior-bounding technique for evaluating stability of nonlinear systems based on real intervals representing cones (sectors) that bound possible component behaviors. Many innovations in control theory have developed from his insights. We

Joseph Porter; Graham Hemingway; Nicholas Kottenstette; Gabor Karsai; Janos Sztipanovits

2010-01-01

174

NASA Astrophysics Data System (ADS)

Based on the fluid flow time-delayed model proposed by Misra et al in internet congestion control, one modified time-delayed model is presented, where the influence of the communication delay on the router queue length is investigated in detail. The main advantage of the new model is that its stability domain is larger even without an extra controller. By linear stability analysis and numerical simulation, the effectiveness and feasibility of the novel model in internet congestion control are verified.

Liu, Yu-Liang; Zhu, Jie; Luo, Xiao-Shu

2009-09-01

175

Stability analysis of the discrete-data Large-Space-Telescope system

NASA Technical Reports Server (NTRS)

This paper considers the application of the discrete describing function to the stability analysis of the Large-Space Telescope (LST) system. An analytical model of the CMG gimbal friction is derived, which is then used to arrive at a closed-form analytical expression for the discrete describing function of the nonlinearity. The analysis is used for the study of the fine-pointing stability of the LST vehicle. Simulation results corroborate the conclusions from the analytical analysis.

Kuo, B. C.; Singh, G.; Seltzer, S. M.

1976-01-01

176

Admittance space stability analysis of power electronic systems

Power electronics based power distribution systems (PEDSs) are becoming increasingly common, particularly in marine and aerospace applications. Stability analysis of this class of systems is crucial due to the potential for negative impedance instability. Existing techniques of stability analysis introduce artificial conservativeness, are sensitive to component grouping, and at the same time do not explicitly address uncertainties and variations in

S. D. Sudhoff; S. F. Glover; P. T. Lamm; D. H. Schmucker; D. E. Delisle; S. P. Karatsinides

2000-01-01

177

Thermal and stability analysis of a two-phase natural circulation loop

Natural circulation is an important passive heat-removal mechanism in both existing and next-generation light water reactors. Thermal and stability analyses are performed for a two-phase natural circulation loop. The homogeneous equilibrium model is employed to describe the two-phase flow in the loop. Subsequently, a linear stability analysis is performed in the frequency domain to establish the stability map of a

F. S. Wang; L. W. Hu; C. Pan

1994-01-01

178

Landslide stability analysis on basis of LIDAR data extraction

NASA Astrophysics Data System (ADS)

Currently, existing contradictory between remediation and acquisition from natural resource induces a series of divergences. With regard to open pit mining, legal regulation requires human to fill back the open pit area with water or recreate new landscape by other materials; on the other hand, human can not help excavating the mining area due to the shortage of power resource. However, to engineering geologists, one coincident problem which takes place not only in filling but also in mining operation should be paid more attention to, i.e. the slope stability analysis within these areas. There are a number of construction activities during remediation or mining process which can directly or indirectly cause slope failure. Lives can be endangered since local failure either while or after remediation; for mining process, slope failure in a bench, which carries a main haul road or is adjacent to human activity area, would be significant catastrophe to the whole mining program. The stability of an individual bench or slope is controlled by several factors, which are geological condition, morphology, climate, excavation techniques and transportation approach. The task which takes the longest time is to collect the morphological data. Consequently, it is one of the most dangerous tasks due to the time consuming in mining field. LIDAR scanning for morphological data collecting can help to skip this obstacle since advantages of LIDAR techniques as follows: • Dynamic range available on the market: from 3 m to beyond 1 km, • Ruggedly designed for demanding field applications, • Compact, easily hand-carried and deployed by a single operator. In 2009, scanning campaigns for 2 open pit quarry have been carried out. The aim for these LIDAR detections is to construct a detailed 3D quarry model and analyze the bench stability to support the filling planning. The 3D quarry surface was built up by using PolyWorks 10.1 on basis of LIDAR data. LIDAR data refining takes an important role during surface construction for further more precise analysis purpose. 3D geological model can be built based on the connection between surface model and geological data like borehole data in GOCAD. Regarding the bench stability analysis, LEM (Limit Equilibrium Method) analysis using Janbu and FEM (Finite Element Method) have been adopted during this analyzing task. A program was developed to convert GOCAD 2D section data directly into the FEM software. The meshed model is then used for stability analysis. In one quarry, 3 cross sections have been extracted on basis of LIDAR original data (original 3 cross sections). To evaluate the advantages of LIDAR data for slope analysis, the results of safety factor (SF) were compared to simplified slope models as they are used normally. The comparison showed that variations of the SF reach up to 9%. Additionally, conservative evaluation demonstrated by SF results based on simplified model is not adaptive for decision making of filling.

Hu, Hui; Fernandez-Steeger, Tomas M.; Dong, Mei; Azzam, Rafig

2010-05-01

179

Analysis of temporal stability of autostereoscopic 3D displays

NASA Astrophysics Data System (ADS)

An analysis has been made of the stability of the images generated by electronic autostereoscopic 3D displays, studying the time course of the photometric and colorimetric parameters. The measurements were made on the basis of the procedure recommended in the European guideline EN 61747-6 for the characterization of electronic liquid-crystal displays (LCD). The study uses 3 different models of autostereoscopic 3D displays of different sizes and numbers of pixels, taking the measurements with a spectroradiometer (model PR-670 SpectraScan of PhotoResearch). For each of the displays, the time course is shown for the tristimulus values and the chromaticity coordinates in the XYZ CIE 1931 system and values from the time periods required to reach stable values of these parameters are presented. For the analysis of how the procedure recommended in the guideline EN 61747-6 for 2D displays influenced the results, and for the adaption of the procedure to the characterization of 3D displays, the experimental conditions of the standard procedure were varied, making the stability analysis in the two ocular channels (RE and LE) of the 3D mode and comparing the results with those corresponding to the 2D. The results of our study show that the stabilization time of a autostereoscopic 3D display with parallax barrier technology depends on the tristimulus value analysed (X, Y, Z) as well as on the presentation mode (2D, 3D); furthermore, it was found that whether the 3D mode is used depends on the ocular channel evaluated (RE, LE).

Rubiño, Manuel; Salas, Carlos; Pozo, Antonio M.; Castro, J. J.; Pérez-Ocón, Francisco

2013-11-01

180

Analysis of slope stabilization by soil bioengineering method

NASA Astrophysics Data System (ADS)

The aim of the project is to create a numerical model which will include the impact of vegetation on the slope stability analysis, considering both mechanical and hydrological factors. This will enrich the current knowledge about how roots reinforce the soil layers on the slope and how it influences the increase of shear strength of the soil. This has to be combined together with hydrological effects caused by evapotranspiration: modified soil moisture regime, dissipation of excess pore pressure and established matric suction. Coupled analyses (mechanical and hydrological) are rarely conducted, or only outdated models are used, which leads to overestimation of the additional shear strength of soil. That is why there is a need to support this branch of landslide hazard assessment and develop a new model. This research will help to raise awareness, that soil bioengineering methods of slope stabilization can in some cases be more appropriate and less expensive than traditional methods. As an input to the model, the appropriate slope geometry and soil properties have to be chosen. It is also important to consider different plant types and root properties, as well as different levels of groundwater table. To assess the effect of evapotranspiration it is necessary to know the geographical location of the slope and the weather conditions in the chosen region. The final output of the model, which will help to quantitatively assess the impact of vegetation on the slope stability, is the factor of safety (FOS) for vegetated slope for different types of soil and degrees of saturation. Results may then be compared with different conditions and factors of safety, calculated for the corresponding non-vegetated slope. It will be possible to specify the most favorable and unfavorable conditions. Moreover, the calculations provide also information on changes of cohesion, caused by mechanical and hydrological effects, as well as the change in the friction angle of soil.

Switala, Barbara Maria; Wu, Wei

2013-04-01

181

Stability analysis of a nonlinear rotating blade with torsional vibrations

NASA Astrophysics Data System (ADS)

This paper discusses the stability of a spinning blade having periodically time varying coefficients for both linear model and geometric nonlinear model. To obtain a reduced nonlinear model from nodal space, a standard modal reduction procedure based on matrix operation is developed with essential geometric stiffening nonlinearities retained in the equation of motion. For the linear model, the stability chart with various spinning parameters of the blade is studied via the Bolotin method, and an efficient boundary tracing algorithm is developed to trace the stability boundary of the linear model. For the geometric nonlinear model, the method of multiple time scale is employed to study the steady state solutions, and their stability and bifurcations for the periodically time-varying rotating blade. The backbone curves of steady-state motions are achieved, and the parameter map for stability and bifurcation is developed.

Wang, Fengxia; Zhang, Wei

2012-12-01

182

Absolute exponential stability analysis of delayed neural networks [rapid communication

NASA Astrophysics Data System (ADS)

In this Letter, we investigate the absolute exponential stability of a class of delayed neural networks. A new sufficient condition ensuring existence and uniqueness of equilibrium and its absolute exponential stability is derived. When the neural network model is simplified to one without delays, the present condition is reduced to the well-known additive diagonal stability condition of the interconnection weight matrix, which was previously established and proven to be general enough for ensuring stability of neural networks without delays in the literature. Thus, our condition generalizes the additive diagonal stability condition to the case of neural networks with delays.

Lu, Hongtao

2005-03-01

183

Analysis and prediction of longitudinal stability of airplanes

NASA Technical Reports Server (NTRS)

An analysis has been made of the longitudinal stability characteristics of 15 airplanes as determined in flight. In the correlation of satisfactory and unsatisfactory characteristics with determined values, the derivative that expresses the ratio of static-restoring moments to elevator-control moments was found to represent most nearly the stability characteristics appreciated by the pilots. The analysis was extended to study the effects of various design features on the observed stability characteristics. Design charts and data are included that show the effects on longitudinal stability of relative positions of wing and tail, fuselage size and location, engine nacelles, and horizontal-tail arrangements.

Gilruth, R R; White, M D

1941-01-01

184

We focus at the interface between multiscale computations, bifurcation theory and social networks. In particular we address how the Equation-Free approach, a recently developed computational framework, can be exploited to systematically extract coarse-grained, emergent dynamical information by bridging detailed, agent-based models of social interactions on networks, with macroscopic, systems-level, continuum numerical analysis tools. For our illustrations we use a simple

A. C. Tsoumanis; C. I. Siettos; G. V. Bafas; I. G. Kevrekidis

2010-01-01

185

Perturbative stability of SFT-based cosmological models

NASA Astrophysics Data System (ADS)

We review the appearance of multiple scalar fields in linearized SFT based cosmological models with a single non-local scalar field. Some of these local fields are canonical real scalar fields and some are complex fields with unusual coupling. These systems only admit numerical or approximate analysis. We introduce a modified potential for multiple scalar fields that makes the system exactly solvable in the cosmological context of Friedmann equations and at the same time preserves the asymptotic behavior expected from SFT. The main part of the paper consists of the analysis of inhomogeneous cosmological perturbations in this system. We show numerically that perturbations corresponding to the new type of complex fields always vanish. As an example of application of this model we consider an explicit construction of the phantom divide crossing and prove the perturbative stability of this process at the linear order. The issue of ghosts and ways to resolve it are briefly discussed.

Galli, Federico; Koshelev, Alexey S.

2011-05-01

186

Visual optimality and stability analysis of 3DCT scan positions.

Industrial cone-beam X-Ray computed tomography (CT) systems often face problems due to artifacts caused by a bad placement of the specimen on the rotary plate. This paper presents a visual-analysis tool for CT systems, which provides a simulation-based preview and estimates artifacts and deviations of a specimen's placement using the corresponding 3D geometrical surface model as input. The presented tool identifies potentially good or bad placements of a specimen and regions of a specimen, which cause the major portion of artefacts. The tool can be used for a preliminary analysis of the specimen before CT scanning, in order to determine the optimal way of placing the object. The analysis includes: penetration lengths, placement stability and an investigation in Radon space. Novel visualization techniques are applied to the simulation data. A stability widget is presented for determining the placement parameters' robustness. The performance and the comparison of results provided by the tool compared with real world data is demonstrated using two specimens. PMID:20975189

Amirkhanov, Artem; Heinzl, Christoph; Reiter, Michael; Gröller, Eduard

2010-01-01

187

Stability and Instability in Two Laser Models

In the first part we study linear stability of travelling wave solutions of a system of equations derived from the Maxwell-Bloch system by adiabatically eliminating the polarization. For the reduced system we find exact conditions for stability and instability. We also find that the adiabatic elimination procedure produces a very badly behaved system in the presence of diffraction. The full

Per Kristen Jakobsen

1990-01-01

188

Borehole Stability Analysis of Horizontal Drilling in Shale Gas Reservoirs

NASA Astrophysics Data System (ADS)

Serious wellbore instability occurs frequently during horizontal drilling in shale gas reservoirs. The conventional forecast model of in situ stresses is not suitable for wellbore stability analysis in laminated shale gas formations because of the inhomogeneous mechanical properties of shale. In this study, a new prediction method is developed to calculate the in situ stresses in shale formations. The pore pressure near the borehole is heterogeneous along both the radial and tangential directions due to the inhomogeneity in the mechanical properties and permeability. Therefore, the stress state around the wellbore will vary with time after the formation is drained. Besides, based on the experimental results, a failure criterion is verified and applied to determine the strength of Silurian shale in the Sichuan Basin, including the long-term strength of gas shale. Based on this work, horizontal well borehole stability is analyzed by the new in situ stress prediction model. Finally, the results show that the collapse pressure will be underestimated if the conventional model is used in shale gas reservoirs improperly. The collapse pressure of a horizontal well is maximum at dip angle of 45°. The critical mud weight should be increased constantly to prevent borehole collapse if the borehole is exposed for some time.

Yuan, Jun-Liang; Deng, Jin-Gen; Tan, Qiang; Yu, Bao-Hua; Jin, Xiao-Chun

2013-09-01

189

The objectives of this project were to: provide fundamental relationships between SOFC performance and operating conditions and transient (time dependent) transport properties; extend models to thermo-mechanical stability, thermo-chemical stability, and multilayer structures; incorporate microstructural effects such as grain boundaries and grain-size distribution; experimentally verify models and devise strategies to obtain relevant material constants; and assemble software package for integration into SECA failure analysis models.

Wachsman, E.D.; Duncan, K.L.; Ebrahimi, F.

2005-01-27

190

Analysis of stability of spectral characteristics of multilayer optical coatings

NASA Astrophysics Data System (ADS)

A short survey of methods used to study the effect of variations of parameters of multilayer dielectric systems on their output spectral characteristics is presented. Using the proposed stability function, the stability of a series of synthesized structures, such as dielectric mirrors, beam-splitting coatings, and narrow-band interference filters, is studied. It is shown that the analysis of the stability of spectral characteristics of multilayer interference coatings permits one to justify the practical implementation of the structure.

Kotlikov, E. N.; Ivanov, V. A.; Motsar', E. V.; Novikova, Yu. A.; Tropin, A. N.

2011-09-01

191

Orbital Stability Analysis of GJ 581 and HD 10180

NASA Astrophysics Data System (ADS)

We present self-consistent orbital stability results over 107 years for GJ 581 for models including planets b, c, d, e, and g. We find substantial overlap between constraints on stability for planet e and its radial velocity-derived parameters. We find a smaller overlap between constraints of stability and RV fit for planet g, however not so small as to rule out planet g on stability requirements alone. We perform an F-test on RV fit results with and without planet g subject to the condition of orbital stability and do not find significant evidence for the existence of GJ 581 g given current radial velocity data. We also apply the process to HD 10180 to investigate the stability of 9 planets that have been reported in this system, and present results related to the stability of proposed planet HD 10180 i.

Joiner, David A.; Sul, Cesar; Dragomir, Diana; Kane, Stephen R.; Kress, Monika; Shanks, Kimberly

2014-06-01

192

A critical assessment of the approximate methods for the stability analysis of a pulse-width modulated (PWM) static volt-ampere reactive (VAr) compensator is presented. Different continuous system approximate models for the stability analysis of the system are developed and their validity is investigated. In particular, it is shown that continuous system approximate models, in which only the principal component of the

Hassan Ali Kojori; J. Douglas Lavers; Shashi B. Dewan

1993-01-01

193

CFD Based Computations of Flexible Helicopter Blades for Stability Analysis

NASA Technical Reports Server (NTRS)

As a collaborative effort among government aerospace research laboratories an advanced version of a widely used computational fluid dynamics code, OVERFLOW, was recently released. This latest version includes additions to model flexible rotating multiple blades. In this paper, the OVERFLOW code is applied to improve the accuracy of airload computations from the linear lifting line theory that uses displacements from beam model. Data transfers required at every revolution are managed through a Unix based script that runs jobs on large super-cluster computers. Results are demonstrated for the 4-bladed UH-60A helicopter. Deviations of computed data from flight data are evaluated. Fourier analysis post-processing that is suitable for aeroelastic stability computations are performed.

Guruswamy, Guru P.

2011-01-01

194

Stability analysis of Riccati covariance equations of Kalman filter.

NASA Technical Reports Server (NTRS)

The present paper takes the basic mathematical approach to analyze the stability of Riccati equations. First, a simple stability criterion like that of the linear constant coefficient system is sought for the nonlinear constant Riccati Equation. Then, a complete analysis on the limiting covariance P follows. The analysis is focussed on the main theorem. Finally, the computational aspects of the Riccati equations are analyzed with examples. The application of this analysis is to provide a simple stability criterion for the Kalman filter computation to test and predict filter convergence and thus modify filter parameters accordingly.

Teng, L.; Schmidt, D.

1972-01-01

195

Wind farm model with DFIG for small signal stability study

Appropriate models of wind farm are necessary for the power system stability study with large scale wind farm penetration. In this paper, an aggregated wind farm model with doubly fed induction generator (DFIG) based wind turbine for small signal stability study is proposed to deal with the situation that the wind turbines operate receiving different incoming wind speeds. The different

Hongtao Wang; Yating Zhang; Qinyong Zhou

2011-01-01

196

We focus at the interface between multiscale computations, bifurcation theory\\u000aand social networks. In particular we address how the Equation-Free approach, a\\u000arecently developed computational framework, can be exploited to systematically\\u000aextract coarse-grained, emergent dynamical information by bridging detailed,\\u000aagent-based models of social interactions on networks, with macroscopic,\\u000asystems-level, continuum numerical analysis tools. For our illustrations we use\\u000aa simple

A. C. Tsoumanis; C. I. Siettos; I. G. Kevrekidis; G. V. Bafas

2009-01-01

197

Wellbore stability analysis in carbonate reservoir considering anisotropic behaviour

NASA Astrophysics Data System (ADS)

Carbonate reservoirs represent a major part of the world oil and gas reserves. In particular, recent discoveries in the pre-salt offshore Brazil place big challenges to exploration and production under high temperatures and pressures (HTHP). During production, the extraction of hydrocarbons reduces pore pressure and thus causes an increase in the effective stress and mechanical compaction in the reservoir. The compactive deformation and failure may be spatially extensive or localized to the vicinity of the wellbore, but in either case the consequences can be economically severe involving surface subsidence, well failure and various production problems. The analysis of wellbore stability and more generally of deformation and failure in carbonate environments hinges upon a relevant constitutive modeling of carbonate rocks over a wide range of porosities, in particular, observed microstructure of samples suggests anisotropic behaviour. In this study, we performed a wellbore stability analysis for a lateral wellbore junction in three dimensions. The complex geometry for the wellbore junction was modeled with tetrahedral finite elements considering a rate independent elastic-plastic isotropic material that presented linear behavior during elastic strain and associated flow rule. A finite element model simulating drilling and production phases were done for field conditions from a deep water reservoir in Campos basin, offshore Brazil. In this context, several scenarios were studied considering true 3D orientation for both in situ stresses and geometry of the wellbore junction itself. We discussed the impact of constitutive modeling, considering anisotropic ductile damage and pressure sensitiveness on the wellbore stability. Parameter values for the analysis were based based on experimental data on two micritic porous carbonates. Series of conventional triaxial experiments were performed at room temperature in dry and wet conditions on samples of Comiso and Tavel limestones of respective porosity 17 and 16%. The wet samples were deformed in drained conditions with 10 MPa pore pressure. The initial yield stresses were identified as the critical stresses at the onset of shear-enhanced compaction, subsequent yield stresses were considered to depend on hardening given by the plastic volumetric strain. For both limestones, we found that water had a moderate effect on the yield stresses but influenced significantly the hardening behavior of the rocks.

Alves, José; Guevara, Nestor; Coelho, Lucia; Baud, Patrick

2010-05-01

198

Critical analysis of Goldberger-Wise stabilization of the Randall-Sundrum braneworld scenario

The Goldberger-Wise mechanism of stabilizing modulus in the Randall-Sundrum braneworld, by introducing a bulk scalar field with quartic interaction terms localized at the 3-branes, has been extremely popular as a stabilizing mechanism when the backreaction of the scalar field on the geometry is negligibly small. In this paper we reexamine the mechanism by an exact analysis without resorting to the approximations adopted by Goldberger and Wise. An exact calculation of the stabilization condition indicates the existence of closely spaced minimum and a maximum for the potential and also brings out some new features involved in the context of the stabilization of such braneworld models.

Dey, Anindya; Maity, Debaprasad; SenGupta, Soumitra [Department of Physics, Harish-Chandra Research Institute, Chhatnag Road, Jhusi, Allahabad-211019 (India); Department of Theoretical Physics, Indian Association for the Cultivation of Science, Calcutta-700 032 (India)

2007-05-15

199

Space Shuttle Main Engine real time stability analysis

NASA Astrophysics Data System (ADS)

The Space Shuttle Main Engine (SSME) is a reusable, high performance, liquid rocket engine with variable thrust. The engine control system continuously monitors the engine parameters and issues propellant valve control signals in accordance with the thrust and mixture ratio commands. A real time engine simulation lab was installed at MSFC to verify flight software and to perform engine dynamic analysis. A real time engine model was developed on the AD100 computer system. This model provides sufficient fidelity on the dynamics of major engine components and yet simplified enough to be executed in real time. The hardware-in-the-loop type simulation and analysis becomes necessary as NASA is continuously improving the SSME technology, some with significant changes in the dynamics of the engine. The many issues of interfaces between new components and the engine can be better understood and be resolved prior to the firing of the engine. In this paper, the SSME real time simulation Lab at the MSFC, the SSME real time model, SSME engine and control system stability analysis, both in real time and non-real time is presented.

Kuo, F. Y.

1993-06-01

200

Stability analysis of intershaft squeeze film dampers

Intershaft squeeze film dampers have been investigated for damping of dual rotor aircraft jet engines. Initial investigations indicated that the intershaft dampers would attenuate the amplitude of the engine vibration and decrease the force transmitted through the intershaft bearing, thereby increasing its life. Also it was thought that the intershaft damper would enhance the stability of the rotor-bearing system. Unfortunately,

A. El-Shafei

1991-01-01

201

Stability Analysis of a Symmetrical Induction Machine

A stability study of an induction machine is performed by applying the root-locus criterion to the equations which describe the behavior of the machine during small displacements about a steady-state operating point. This investigation reveals that a symmetrical induction machine may become unstable at low speeds (low frequencies) even though balanced, constant amplitude, sinusoidal voltages are applied to the stator

ROBERT H. NELSON; THOMAS A. LIPO; PAUL C. KRAUSE

1969-01-01

202

Load-Factor Stability Analysis of Embankments on Saturated Soil Deposits

A continuum-based finite-element methodology is established for quantifying the stability of earthen embankments built on saturated soil deposits. Within the methodology the soil is treated as a fluid-solid porous medium, in which the soil skeleton's constitutive behavior is modeled using a smooth elastoplastic cap model that features continuous coupling between deviatoric and volumetric plasticity. In the stability analysis procedure, self-weight

Young-Kyo Seo; Colby C. Swan

2001-01-01

203

Stability of Film Flows Using Simplified Models

NASA Astrophysics Data System (ADS)

Combining a long wave-length expansion of the Navier--Stokes equations to a Galerkin approximation method based on polynoms, we have derived several models of increasing accuracy and complexity.(Ruyer--Quil and Manneville, ``Improved modeling of flows down inclined planes,'' LadHyX preprint (1999).) The simplest model involves just the film thickness h and the flow rate q. It is similar to Shkadov's model(Shkadov, Izv. Ak. Nauk SSSR, Mekh. Zhi. Gaza No 2 (1967) 43--51.) but contains all relevant physical processes (especially viscous dispersion), correctly predicts the critical Reynolds number and faithfully describes the properties of two-dimensional solitary waves in the strongly nonlinear regime as obtained by direct numerical simulations of NS equations.(Salamon et al., Phys. Fluids 6) (1994) 2202--2220. Floquet analysis in the moving frame has been developed to study the secondary instabilities, yielding results in good agreement with theoretical approaches closer to the primitive equations.(Chang et al., J. Fluid Mech 250) (1993) 433--480. Their relevance to experimental findings(Liu et al., Phys. Fluids 7) (1995) 55--67. will be discussed.

Ruyer-Quil, Christian; Manneville, Paul

1999-11-01

204

Stability and phase error analysis of FDTD in dispersive dielectrics

Four FD-TD extensions for the modeling of pulse propagation in Debye or Lorentz dispersive media are analyzed through studying the stability and phase error properties of the coupled difference equations corresponding to Maxwell's equations and to the equations for the dispersion. For good overall accuracy the author shows that all schemes should be run at their Courant stability limit, and

Peter G. Petropoulos

1994-01-01

205

Long-Term Stability of Radio Sources in VLBI Analysis.

National Technical Information Service (NTIS)

Positional stability of radio sources is an important requirement for modeling of only one source position for the complete length of VLBI data of presently more than 20 years. The stability of radio sources can be verified by analyzing time series of rad...

G. Engelhardt V. Thorandt

2010-01-01

206

Ageostrophic linear stability analysis of the Labrador Current

NASA Astrophysics Data System (ADS)

The water mass transformation process in the Labrador Sea during winter plays an important role for the Atlantic meridional overturning circulation and the global climate system. The Labrador Sea Water (LSW) is exported within the deep Labrador Current (LC) after the convection process. LSW takes up large amounts of atmospheric tracer gases as CO2 and oxygen, and is thus one of the major agent for ventilation of the abyssal ocean. It is shown that enhanced eddy kinetic energy (EKE) along the LC shows up in a 1/12° ocean model simulation during the transformation process. Moored in-situ measurements within the LC also show enhanced EKE levels during winter. This instability processes within the LC is important as it might alter the water mass properties of the (LSW) by frontal mixing processes during the water mass transformation and export within the LC. The frontal instability process, which lead to enhanced EKE along the LC during winter is investigated using ageostrophic linear stability analysis. Dense and weakly stratified water masses produced during the wintertime transformation process lead to weaker stratification and a strengthening of the lateral density gradients within the LC. Weak stratification and enhanced vertical shear result in low Richardson numbers and the growth rate of baroclinic waves increases significantly within the shelf break LC during winter. Rapid frontogenesis along the whole LC sets in resulting in enhance EKE. During the rest of the year strong stratification and weak vertical shear leads to larger Richardson numbers and smaller growth rates. Ageostrophic linear stability analysis shows that a geostrophic interior mode has similar wavelengths as the first wavelike disturbances in the model simulations. A shallow mode with lateral scales O (1 km) is also predicted, which can be associated with mixed layer instabilities and submesoscale variability but remains unresolved by the model simulation.

Thomsen, S.; Eden, C.

2012-12-01

207

Thermal analysis: An alternative method of measuring oil stability

Preliminary results using three different thermal analysis techniques to evaluate the relative oxidative stabilities of five\\u000a vegetable oil samples yielded good correlations with the predicted stabilities by the active oxygen method. The thermal analysis\\u000a techniques offer the advantages of good quality control time, being less empirical, and requiring limited equipment and operator\\u000a expertise. In addition, these techniques should be useful

R. L. Hassel

1976-01-01

208

Rotor stability estimation with competing tilting pad bearing models

NASA Astrophysics Data System (ADS)

When predicting the stability of rotors supported by tilting pad journal bearings, it is currently debated whether or not the bearings should be represented with frequency dependent dynamics. Using an experimental apparatus, measurements of pad temperatures, unbalance response and stability are compared with modeling predictions for two tilting pad bearing designs. Predictions based on frequency dependent tilting pad bearing dynamics exhibited significantly better correlation with the stability measurements than those assuming frequency independent dynamics.

Cloud, C. Hunter; Maslen, Eric H.; Barrett, Lloyd E.

2012-05-01

209

Remarks on the Stability Analysis of Reactive Flows.

National Technical Information Service (NTIS)

A simple model of compressible reacting flow is studied. First, a dispersion relation is derived for the linearized problem making a distinction between frozen and equilibrium sound speed. Second, the stability of the Von Neumann-Richtmyer scheme applied ...

B. Scheurer

1987-01-01

210

Theoretical stability analysis of quantum dash distributed Bragg reflector lasers

NASA Astrophysics Data System (ADS)

A detailed theoretical analysis of stability in a quantum dash distributed Bragg reflector (DBR) laser is presented under the small-signal condition. The influence of p-type doping and inhomogeneous line broadening on the hysteresis width of the quantum dash DBR laser is studied using a rate equation model that includes all of the multidiscrete energy levels in the valence and conduction bands. Our calculations show that a large hysteresis width is obtained by detuning the laser by ~10 meV above the ground state energy and doping the dashes by acceptor concentration NA=3.7×1017 cm-3. Also we find that a large self-pulsation frequency is obtained by detuning the laser by -15 meV from the ground state energy and doping the dashes by NA=2.5×1017 cm-3. The laser hysteresis width can be greatly reduced by doping the dashes with NA>1×1018 cm-3.

Qasaimeh, Omar; Qasaimeh, Hadeel

2009-12-01

211

In this paper a technique for analysing aircraft frequency wild power systems with constant power loads is developed and demonstrated. Power electronic based loads often behave as constant power loads, especially when feeding machine or actuator drives under current and speed control. The constant power (CP) loads can affect the stability of the power system. The problem is a particular

K.-N. Areerak; S. V. Bozhko; G. M. Asher; D. W. P. Thomas

2008-01-01

212

In this paper, a model of the wind turbine (WT) with direct-drive permanent magnet generator (DDPMG) and its associated controllers is presented, based on which a small signal stability analysis model is derived. The small signal stability analysis shows that the WT with DDPMG without the controllers is stable, and the controller can improve the small signal stability of the

F. Wu; Xiao-Ping Zhang; P. Ju

2009-01-01

213

Stability analysis and the stabilization of a class of discrete-time dynamic neural networks.

This paper deals with problems of stability and the stabilization of discrete-time neural networks. Neural structures under consideration belong to the class of the so-called locally recurrent globally feedforward networks. The single processing unit possesses dynamic behavior. It is realized by introducing into the neuron structure a linear dynamic system in the form of an infinite impulse response filter. In this way, a dynamic neural network is obtained. It is well known that the crucial problem with neural networks of the dynamic type is stability as well as stabilization in learning problems. The paper formulates stability conditions for the analyzed class of neural networks. Moreover, a stabilization problem is defined and solved as a constrained optimization task. In order to tackle this problem two methods are proposed. The first one is based on a gradient projection (GP) and the second one on a minimum distance projection (MDP). It is worth noting that these methods can be easily introduced into the existing learning algorithm as an additional step, and suitable convergence conditions can be developed for them. The efficiency and usefulness of the proposed approaches are justified by using a number of experiments including numerical complexity analysis, stabilization effectiveness, and the identification of an industrial process. PMID:17526334

Patan, Krzysztof

2007-05-01

214

Structural Stability of Mathematical Models of National Economy

NASA Astrophysics Data System (ADS)

In the paper we test robustness of particular dynamic systems in a compact regions of a plane and a weak structural stability of one dynamic system of high order in a compact region of its phase space. The test was carried out based on the fundamental theory of dynamical systems on a plane and based on the conditions for weak structural stability of high order dynamic systems. A numerical algorithm for testing the weak structural stability of high order dynamic systems has been proposed. Based on this algorithm we assess the weak structural stability of one computable general equilibrium model.

Ashimov, Abdykappar A.; Sultanov, Bahyt T.; Borovskiy, Yuriy V.; Adilov, Zheksenbek M.; Ashimov, Askar A.

2011-12-01

215

Vehicle yaw dynamics modelling and analyzing for yaw stability control

Some vehicle yaw dynamics modelling methods are analyzed and a new control-oriented model is proposed in the paper. These vehicle yaw dynamics models are all obtained through simplifying vehicle original physical dynamics, and they all have strong and weak points. Considering vehicle yaw stability control problem, a new observer-based vehicle yaw dynamics modelling approach for controller design is proposed, which

Hongliang Zhou; Zhiyuan Liu

2011-01-01

216

Aeroelastic stability analysis of wind turbines using an eigenvalue approach

NASA Astrophysics Data System (ADS)

A design tool for performing aeroelastic stability analysis of wind turbines is presented in this paper. The method behind this tool is described in a general form, as independent of the particular aeroelastic modelling as possible. Here, the structure is modelled by a Finite beam Element Method, and the aerodynamic loads are modelled by the Blade Element Momentum method coupled with a Beddoes-Leishman type dynamic stall model in a state-space formulation. The linearization of the equations of motion is performed about a steady-state equilibrium, where the deterministic forcing of the turbine is neglected. To eliminate the periodic coefficients and avoid using the Floquet Theory, the multi-blade transformation is utilized. From the corresponding eigenvalue problem, the eigenvalues and eigenvectors can be computed at any operation condition to give the aeroelastic modal properties: Natural frequencies, damping and mode shapes. An example shows a good agreement between predicted and measured aeroelastic damping of a stall-regulated 600 kW turbine. Copyright

Hansen, M. H.

2004-04-01

217

Self-similar Solutions in the Nonsteady Propellant Burning Rate Theory and their Stability Analysis

The problem of the non-steady burning of the propellant for the decreasing pressure is considered. Self-similar solutions are obtained for two models of the burning: with constant surface temperature and with variable surface temperature. As is shown for the constant surface temperature model there are two solutions of the problem corresponding to the high and low nonsteadinesses. The stability analysis

V. B. LIBROVICH; B. V. NOVOZHILOV

1971-01-01

218

Stability and Bifurcation Analysis of a Spinning Space Tether

NASA Astrophysics Data System (ADS)

A detailed, geometrically exact bifurcation analysis is performed for a model of a power-generating tethered device of interest to the space industries. The structure, a short electrodynamic tether, comprises a thin, long rod that is spun in a horizontal configuration from a satellite in low Earth orbit, with a massive electrically conducting disk at its free end. The system is modelled using a Cosserat formulation leading to a system of Kirchhoff equations for the rod's shape as a function of position and time. Moving to a rotating frame, incorporating the effects of internal damping, intrinsic curvature due to the deployment method and novel force and moment boundary conditions at the contactor, the problem for steady rotating solutions is formulated as a two-point boundary value problem. Using numerical continuation methods, a bifurcation analysis is carried out varying rotation speeds up to many times the critical resonance frequency. Spatial finite differences are used to formulate the stability problem for each steady state and the corresponding eigenvalues are computed. The results show excellent agreement with earlier multibody dynamics simulations of the same problem.

Valverde, J.; Escalona, J. L.; Dominguez, J.; Champneys, A. R.

2006-10-01

219

Stability analysis of correction schemes for spreading resistance measurements

NASA Astrophysics Data System (ADS)

It is illustrated how the stability behaviour of a correction scheme for spreading resistance measurements can be analysed on the basis of its stability curves. This technique is applied on some recent schemes which incorporate a resistivity dependent probe radius. Their behaviour is compared with schemes implementing a fixed radius. From this analysis it follows precisely when the variable radius schemes considered will be stable or unstable. The primary cause for eventual instability is indicated and a new iteration approach is proposed which is able to remove this cause resulting in a drastically improved stability behaviour.

Clarysse, T.; Vandervorst, W.

1990-12-01

220

Stability analysis of ultrasound thick-shell contrast agents

The stability of thick shell encapsulated bubbles is studied analytically. 3-D small perturbations are introduced to the spherical oscillations of a contrast agent bubble in response to a sinusoidal acoustic field with different amplitudes of excitation. The equations of the perturbation amplitudes are derived using asymptotic expansions and linear stability analysis is then applied to the resulting differential equations. The stability of the encapsulated microbubbles to nonspherical small perturbations is examined by solving an eigenvalue problem. The approach then identifies the fastest growing perturbations which could lead to the breakup of the encapsulated microbubble or contrast agent.

Lu, Xiaozhen; Chahine, Georges L.; Hsiao, Chao-Tsung

2012-01-01

221

Determination of Synchronous Machine Stability Study Models. Final Report.

National Technical Information Service (NTIS)

The purpose of EPRI Research Project (RP) 997-4 was to experimentally determine generator model parameters to improve the accuracy of power system dynamic stability simulations. Westinghouse used the standstill frequency response test method on several la...

1981-01-01

222

Stability analysis of the nonlinear dynamics of flexible aircraft

A method for nonlinear analysis of dynamic systems and its application to aircraft is presented. In extension of existing averaging methods this procedure follows the linearizing eigenvalue analysis, but defines the eigenvalues and eigenvectors as functions of the deflection from the examined equilibrium. This approach allows the determination of the systems stability properties beyond the close vicinity of the equilibrium.

N. Siepenkötter; W. Alles

2005-01-01

223

Stability analysis of elite chickpea genotypes tested under diverse environments

Twelve elite chickpea genotypes along with two check varieties were grown at four diverse locations in Punjab province to check their stability. The analysis of variance for seed yield at individual locations showed significant to highly significant differences between genotypes. Pooled analysis of variance over locations displayed highly significant differences between genotypes, locations and genotype x location interaction. Among 14

Babar Manzoor Atta; Tariq Mahmud Shah

224

New Method for 3D and Asymmetrical Slope Stability Analysis

A new three-dimensional (3D) slope stability analysis method is developed based on two-direc- tional moment equilibrium. This method calculates not only the safety factor but also the possible direction of sliding for semispherical and composite failure surfaces. As a result, the possible errors associated with assuming a plane of symmetry in 3D stability analyses are eliminated. Another advantage of the

Ching-Chuan Huang; Cheng-Chen Tsai

2000-01-01

225

Clarifications of the BCU method for transient stability analysis

Energy function methods have been studied for many years, and have been applied to practical power system stability analysis problems of multi-machine power systems. Developments in real-time power system monitoring suggest that dynamic events can be monitored at the power system control centers, and naturally the energy function methods were tried as real-time stability prediction tools. However, a number of

A. Llamas; J. De La Ree Lopez; L. Mili; A. G. Phadke; J. S. Thorp

1995-01-01

226

This paper mainly studies stability and optimal control for networked control systems with the real-time setup of time-driven sensor, event-driven controller and actuator, and with the assumption that network-induced delay is no longer than certain known times of sampling period. The modeling of this class of networked control systems is given. Then, preliminary stochastic stability analysis of it is presented.

Yuequan Yang; De Xu; Min Tan; Xianzhong Dai

2004-01-01

227

Electromagnetic Modeling of the Passive Stabilization Loop at EAST

NASA Astrophysics Data System (ADS)

A passive stabilization loop (PSL) has been designed and manufactured in order to enhance the control of vertical instability and accommodate the new stage for high-performance plasma at EAST. Eddy currents are induced by vertical displacement events (VDEs) and disruption, which can produce a magnetic field to control the vertical instability of the plasma in a short timescale. A finite element model is created and meshed using ANSYS software. Based on the simulation of plasma VDEs and disruption, the distribution and decay curve of the eddy currents on the PSL are obtained. The largest eddy current is 200 kA and the stress is 68 MPa at the outer current bridge, which is the weakest point of the PSL because of the eddy currents and the magnetic fields. The analysis results provide the supporting data for the structural design.

Ji, Xiang; Song, Yuntao; Wu, Songtao; Wang, Zhibin; Shen, Guang; Liu, Xufeng; Cao, Lei; Zhou, Zibo; Peng, Xuebing; Wang, Chenghao

2012-09-01

228

Aeroelastic Stability of Rotor Blades Using Finite Element Analysis

NASA Technical Reports Server (NTRS)

The flutter stability of flap bending, lead-lag bending, and torsion of helicopter rotor blades in hover is investigated using a finite element formulation based on Hamilton's principle. The blade is divided into a number of finite elements. Quasi-steady strip theory is used to evaluate the aerodynamic loads. The nonlinear equations of motion are solved for steady-state blade deflections through an iterative procedure. The equations of motion are linearized assuming blade motion to be a small perturbation about the steady deflected shape. The normal mode method based on the coupled rotating natural modes is used to reduce the number of equations in the flutter analysis. First the formulation is applied to single-load-path blades (articulated and hingeless blades). Numerical results show very good agreement with existing results obtained using the modal approach. The second part of the application concerns multiple-load-path blades, i.e. bearingless blades. Numerical results are presented for several analytical models of the bearingless blade. Results are also obtained using an equivalent beam approach wherein a bearingless blade is modelled as a single beam with equivalent properties. Results show the equivalent beam model.

Chopra, I.; Sivaneri, N.

1982-01-01

229

Analysis and stability of Hyperici oleum.

Hyperici Oleum (St. John's wort oil) used in wound healing contains no hypericin. By using the sunlight maceration method described in the supplement to DAB 6 (EB 6), lipophilic breakdown products of this compound are obtained which lend the oil its red colour. Hyperforin, which is responsible for the oil's therapeutic activity could, for the first time, be identified and quantitatively determined by TLC and HPLC after solid-phase extraction. The stability of hyperforin is limited; sufficient shelf-life could only be achieved by hot maceration of dried flowers with eutanol G and storage in the absence of air. By gradient HPLC further polar hyperforin analogues were detected in those St. John's wort oils in which hyperforin had decomposed. At the same time flavonoids and xanthones could be identified. A procedure for the quantitative determination of flavonoids in St. John's wort was validated. The action of light during preparation of the oil led to a rise in the content of flavonoids. PMID:1438595

Maisenbacher, P; Kovar, K A

1992-08-01

230

Kinematic analysis of rope skipper's stability

NASA Astrophysics Data System (ADS)

There are various kinds of jumping that can be done while performing rope skipping activity. This activity was always associated with injury. But, if the rope skipper can perform the activity in a right way, it is believed that the injury might be reduced. The main purpose of this paper is to observe the stability of rope skipper from a biomechanics perspective, which are the centre of mass, angle at the ankle, knee and hip joints and also the trajectory for the ipsilateral leg between the two types of skip which is one leg and two legs. Six healthy, physically active subject, two males and four females (age: 8.00±1.25 years, weight: 17.90±6.85 kg and height: 1.22±0.08 m) participated in this study. Kinematic data of repeated five cycles of rope skipping activity was captured by using Vicon Nexus system. Based on the data collected, skipping with two legs shows more stable behavior during preparation, flight and landing phases. It is concluded that landing on the balls of the feet, lowering the trajectory positions of the feet from the ground as well as flexion of each joint which would reduce the injury while landing.

Ab Ghani, Nor Atikah; Rambely, Azmin Sham

2014-06-01

231

Modeling sawtooth stabilization by energetic ions from neutral beam injection

Recent advances in modeling the effects of anisotropic energetic ion distributions have enabled the development of a complete coherent physics explanation of sawtooth stabilization in both conventional and spherical tokamaks. As an example, a complete model has been developed to explain the asymmetric stabilization of sawteeth with respect to neutral beam injection direction in the Joint European Torus. This asymmetric sawtooth stabilization [M. Nave et al., Phys. Plasmas 13, 014503 (2006)] arises because of both the destabilizing contribution from the counterpassing ions and the strong modification of the stabilizing contribution of the nonadiabatic trapped ions due to flow shear. The fast particle effects including pressure anisotropy, sheared flows, and the adiabatic response to the internal kink mode have been modeled in general toroidal geometry for the first time.

Chapman, I. T.; Pinches, S. D.; Appel, L. C.; Hastie, R. J.; Hender, T. C.; Saarelma, S.; Sharapov, S. E.; Voitsekhovitch, I.; Graves, J. P. [EURATOM/UKAEA Fusion Association, Culham Science Centre, Abingdon, Oxon OX14 2DE (United Kingdom); CRPP, Association EURATOM-Confederation Suisse, EPFL, 1015 Lausanne (Switzerland)

2007-07-15

232

Modeling sawtooth stabilization by energetic ions from neutral beam injection

NASA Astrophysics Data System (ADS)

Recent advances in modeling the effects of anisotropic energetic ion distributions have enabled the development of a complete coherent physics explanation of sawtooth stabilization in both conventional and spherical tokamaks. As an example, a complete model has been developed to explain the asymmetric stabilization of sawteeth with respect to neutral beam injection direction in the Joint European Torus. This asymmetric sawtooth stabilization [M. Nave et al., Phys. Plasmas 13, 014503 (2006)] arises because of both the destabilizing contribution from the counterpassing ions and the strong modification of the stabilizing contribution of the nonadiabatic trapped ions due to flow shear. The fast particle effects including pressure anisotropy, sheared flows, and the adiabatic response to the internal kink mode have been modeled in general toroidal geometry for the first time.

Chapman, I. T.; Pinches, S. D.; Appel, L. C.; Hastie, R. J.; Hender, T. C.; Saarelma, S.; Sharapov, S. E.; Voitsekhovitch, I.; Graves, J. P.

2007-07-01

233

Stability and performance analysis of networks supporting elastic services

We consider the stability and performance of a model for networks supporting services that adapt their transmission to the available bandwidth. Not unlike real networks, in our model, connection arrivals are stochastic, each has a random amount of data to send, and the number of ongoing connections in the system changes over time. Consequently, the bandwidth allocated to, or throughput

Gustavo de Veciana; Takis Konstantopoulos; Tae-Jin Lee

2001-01-01

234

Remarks on the stability analysis of reactive flows

NASA Technical Reports Server (NTRS)

A simple model of compressible reacting flow is studied. First, a dispersion relation is derived for the linearized problem making a distinction between frozen and equilibrium sound speed. Second, the stability of the Von Neumann-Richtmyer scheme applied to this model is studied. A natural generalization of the C.F.L. condition is found.

Scheurer, B.

1987-01-01

235

Bank Stability Analysis for Predicting Reach Scale Land Loss and Sediment Yield

NASA Astrophysics Data System (ADS)

When extensive lengths of river become stabilized (e.g., by channel incision), riverbank erosion can result in considerable riparian land loss and the delivery of large volumes of sediment downstream. The ability to predict the stability and failure geometry of eroding riverbanks is therefore an important prerequisite in estimating the rate of bank erosion and sediment yield associated with bank erosion. In this paper, a new stability analysis for layered river banks is introduced. The new analysis differs from many previous analyses in that it takes into consideration the effects of positive pore water pressure in the saturated portion, and negative pore water pressure in the unsaturated portion, of the bank as well as the influence of hydrostatic confining pressure due to the water level in the river. In addition, the failure plane is not constrained to pass through the toe of the bank and the bank profile geometry is not restricted to an idealized special case. The predictive ability of the new bank stability analysis is assessed using data from two field sites. Subsequently, a methodology for applying the bank stability analysis at the scale of the river reach (0.1 to 10 km) is discussed. This method involves the use of empirical models of bed level adjustment to estimate the magnitude of incision at specific locations along the reach, with these estimates used to drive the stability analysis. Application of the new method is demonstrated with an example.

Amiri-Tokaldany, Ebrahim; Darby, Stephen E.; Tsswell, Paul

2003-08-01

236

Analysis of Human Body Bipedal Stability for Neuromotor Disabilities

NASA Astrophysics Data System (ADS)

The analysis of different biomechanical aspects of balance and equilibrium is presented in the first part of the paper. We analyzed the posture, balance and stability of human body for a normal person and for a person with loco-motor or neuro-motor disabilities (in the second part). In the third part of the paper we presented the methodology and the experimental setup used to record the human body behavior in postural stability for persons with neuro-motors disabilities. The results and the conclusions are presented in the final part of the paper and also in the future work meant to establish the computer analysis for rehabilitation neuromotor disabilities.

Baritz, Mihaela; Cristea, Luciana; Rogozea, Liliana; Cotoros, Diana; Repanovici, Angela

2009-04-01

237

A short gas-discharge layer sandwiched with a semiconductor layer between planar electrodes shows a variety of spatiotemporal patterns. We focus on the spontaneous temporal oscillations that occur while a dc voltage is applied and while the system stays spatially homogeneous; the results for these oscillations apply equally to a planar discharge in series with any resistor with capacitance. We define the minimal model, identify its independent dimensionless parameters, and then present the results of the full time-dependent numerical solutions of the model as well as of a linear stability analysis of the stationary state. Full numerical solutions and the results of the stability analysis agree very well. The stability analysis is then used for calculating bifurcation diagrams. We find semiquantitative agreement with experiment for the diagram of bifurcations from stationary to oscillating solutions as well as for amplitude and frequency of the developing limit cycle oscillations. PMID:16089875

Sijaci?, Danijela D; Ebert, Ute; Rafatov, Ismail

2005-06-01

238

Improving stability of regional numerical ocean models

An operational limited-area ocean modelling system was developed to supply forecasts of ocean state out to 3 days. This system\\u000a is designed to allow non-specialist users to locate the model domain anywhere within the Australasian region with minimum\\u000a user input. The model is required to produce a stable simulation every time it is invoked. This paper outlines the methodology\\u000a used

Mike Herzfeld

2009-01-01

239

Biomechanical Analysis of Lumbar Spine Stabilization by Means of Transpedicular Stabilizer

The fundamental purpose of research was determination of biomechanical characteristic of lumbar spine–transpedicular stabilizer\\u000a system made of stainless steel (Cr-Ni-Mo) and Ti6Al4V alloy. To define biomechanical characteristic of the system finite element\\u000a method was applied. Geometric models of part spine L3-L4 and stabilizer, was discretised by means of SOLID 95 element. Appropriate\\u000a boundary conditions imitating phenomena in real system with

Jan Marciniak; Janusz Szewczenko; Witold Walke; Marcin Basiaga; Marta Kiel; Ilona Manka

2008-01-01

240

High beta and second stability region transport and stability analysis. Final report

This report describes ideal and resistive studies of high-beta plasmas and of the second stability region. Emphasis is focused on ``supershot`` plasmas in TFIR where MHD instabilities are frequently observed and which spoil their confinement properties. Substantial results are described from the analysis of these high beta poloidal plasmas. During these studies, initial pressure and safety factor profiles were obtained from the TRANSP code, which is used extensively to analyze experimental data. Resistive MBD stability studies of supershot equilibria show that finite pressure stabilization of tearing modes is very strong in these high {beta}p plasmas. This has prompted a detailed re-examination of linear tearing mode theory in which we participated in collaboration with Columbia University and General Atomics. This finite pressure effect is shown to be highly sensitive to small scale details of the pressure profile. Even when an ad hoc method of removing this stabilizing mechanism is implemented, however, it is shown that there is only superficial agreement between resistive MBD stability computation and the experimental data. While the mode structures observed experimentally can be found computationally, there is no convincing correlation with the experimental observations when the computed results are compared with a large set of supershot data. We also describe both the ideal and resistive stability properties of TFIR equilibria near the transition to the second region. It is shown that the highest {beta} plasmas, although stable to infinite-n ideal ballooning modes, can be unstable to the so called ``infernal`` modes associated with small shear. The sensitivity of these results to the assumed pressure and current density profiles is discussed. Finally, we describe results from two collaborative studies with PPPL. The first involves exploratory studies of the role of the 1/1 mode in tokamaks and, secondly, a study of sawtooth stabilization using ICRF.

Hughes, M.H.; Phillps, M.W.; Todd, A.M.M.; Krishnaswami, J.; Hartley, R.

1992-09-01

241

RELATION OF URBAN MODEL PERFORMANCE TO STABILITY

The RAM model performance in estimating SO2 concentrations in St. Louis, MO for 1976 has been discussed in several previous papers by the authors. In these studies the model estimates were compared to the observed concentrations of SO2 at 13 sites in the St. Louis metropolitan ar...

242

Stability of finite difference models containing two boundaries or interfaces

NASA Technical Reports Server (NTRS)

The stability of finite difference models of hyperbolic initial boundary value problems is connected with the propagation and reflection of parasitic waves. Wave propagation ideas are applied to models containing two boundaires or interfaces, where repeated reflection of trapped wave packets is a potential new source of instability. Various known instability phenomena are accounted for in a unified way. Results show: (1) dissipativity does not ensure stability when three or more formulas are concatenated at a boundary or internal interface; (2) algebraic GKS instabilities can be converted by a second boundary to exponential instabilities only when an infinite numerical reflection coefficient is present; and (3) GKS-stability and P-stability can be established in certain problems by showing that all numerical reflection coefficients have modulus less than 1.

Trefethen, L. N.

1984-01-01

243

Computational Aspects of Pseudospectra in Hydrodynamic Stability Analysis

NASA Astrophysics Data System (ADS)

This paper addresses the analysis of spectrum and pseudospectrum of the linearized Navier-Stokes operator from the numerical point of view. The pseudospectrum plays a crucial role in linear hydrodynamic stability theory and is closely related to the non-normality of the underlying differential operator and the matrices resulting from its discretization. This concept offers an explanation for experimentally observed instability in situations when eigenvalue-based linear stability analysis would predict stability. Hence the reliable numerical computation of the pseudospectrum is of practical importance particularly in situations when the stationary "base flow" is not analytically but only computationally given. The proposed algorithm is based on a finite element discretization of the continuous eigenvalue problem and uses an Arnoldi-type method involving a multigrid component. Its performance is investigated theoretically as well as practically at several two-dimensional test examples such as the linearized Burgers equations and various problems governed by the Navier-Stokes equations for incompressible flow.

Gerecht, D.; Rannacher, R.; Wollner, W.

2012-12-01

244

Stability investigations of airfoil flow by global analysis

NASA Technical Reports Server (NTRS)

As the result of global, non-parallel flow stability analysis the single value of the disturbance growth-rate and respective frequency is obtained. This complex value characterizes the stability of the whole flow configuration and is not referred to any particular flow pattern. The global analysis assures that all the flow elements (wake, boundary and shear layer) are taken into account. The physical phenomena connected with the wake instability are properly reproduced by the global analysis. This enhances the investigations of instability of any 2-D flows, including ones in which the boundary layer instability effects are known to be of dominating importance. Assuming fully 2-D disturbance form, the global linear stability problem is formulated. The system of partial differential equations is solved for the eigenvalues and eigenvectors. The equations, written in the pure stream function formulation, are discretized via FDM using a curvilinear coordinate system. The complex eigenvalues and corresponding eigenvectors are evaluated by an iterative method. The investigations performed for various Reynolds numbers emphasize that the wake instability develops into the Karman vortex street. This phenomenon is shown to be connected with the first mode obtained from the non-parallel flow stability analysis. The higher modes are reflecting different physical phenomena as for example Tollmien-Schlichting waves, originating in the boundary layer and having the tendency to emerge as instabilities for the growing Reynolds number. The investigations are carried out for a circular cylinder, oblong ellipsis and airfoil. It is shown that the onset of the wake instability, the waves in the boundary layer, the shear layer instability are different solutions of the same eigenvalue problem, formulated using the non-parallel theory. The analysis offers large potential possibilities as the generalization of methods used till now for the stability analysis.

Morzynski, Marek; Thiele, Frank

1992-01-01

245

Stability analysis of the pulmonary liquid bilayer.

NASA Astrophysics Data System (ADS)

The lung consists of liquid-lined compliant airways that convey air to and from the alveoli where gas exchange takes place. Because the airways are coated with a bilayer consisting of a mucus layer on top of a periciliary fluid layer, a surface tension instability can generate flows within the bilayer and induce the formation of liquid plugs that block the passage of air. This is a problem for example with premature neonates whose lungs do not produce sufficient quantities of surfactant and suffer from respiratory distress syndrome. To study this instability a system of coupled nonlinear evolution equations are derived using lubrication theory for the thicknesses of the two liquid layers which are assumed to be Newtonian. A normal mode analysis is used to investigate the initial growth of the disturbances, and reveals how the grow rate is affected by the ratio of viscosities ?, film thicknesses ? and surface tensions ? of the two layers which can change by disease. Numerical solutions of the evolution equations show that there is a critical bilayer thickness ?c above which closure occurs, and that a more viscous and thicker layer compared to the periciliary layer closes more slowly. However, ?cis weakly dependent on ?, ? and ?. We also examine the potential impact of wall shear stress and normal stress on cell damage. This work is funded by NIH HL85156.

Halpern, David; Grotberg, James

2010-11-01

246

Model Stability and the Subprime Mortgage Crisis

We study the potential model instability problem with respect to mortgage default risk and examine to what extent it helps\\u000a explain the default shock during the recent crisis. We find that econometric default risk models based on historical data\\u000a can be unstable over time. Due to temporal shifts in the parameters, default prediction of the 2006 vintage subprime loans\\u000a based

Xudong An; Yongheng Deng; Eric Rosenblatt; Vincent W. Yao

247

Stability in Gilpin and Ayala's models of competition.

Simple and effective conditions for global stability in a class of models for m competing species are given. A numerical method is used to establish a large finite region of attraction for the feasible equilibrium in Gilpin and Ayala's model of two competing Drosophila populations. PMID:894153

Goh, B S; Agnew, T T

1977-07-19

248

Modelling effects of forest canopies on slope stability

We investigated the potential effects of rainfall intensity smoothing by forest canopies on slope stability by modelling soil responses to measured rainfall and throughfall during high-intensity rain. Field measurements showed that maximum intensities of precipitation were generally reduced under forest canopies at two sites in the Pacific Northwest, USA. Modelling soil water pore- pressure responses of a hypothetical hillslope to

Richard F. Keim; Arne E. Skaugset

2003-01-01

249

M-theory model-building and proton stability.

National Technical Information Service (NTIS)

The authors study the problem of baryon stability in M theory, starting from realistic four-dimensional string models constructed using the free-fermion formulation of the weakly-coupled heterotic string. Suitable variants of these models manifest an enha...

J. Ellis A. E. Faraggi D. V. Nanopoulos

1997-01-01

250

Stability analysis of a reinforced carbon carbon shell

NASA Technical Reports Server (NTRS)

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.

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

1977-01-01

251

GEOTECHNICAL ANALYSIS FOR REVIEW OF DIKE STABILITY (GARDS). TECHNICAL MANUAL

The structure and capabilities of a user-friendly, interactive computer program developed for the stability analysis of dikes (GARDS) are described. The program was developed under the sponsorship of the U.S. Environmental Protection Agency and therefore emphasizes Hazardous Wast...

252

New level sensor system for ship stability analysis and monitor

This paper presents a novel method of measuring liquid level with high accuracy, which can be used to measure the draft values without densimeter. With this method the real time analysis of ship stability will be practicable. In particular, the paper describes the architecture and software of the auto test and monitor system, offering the advantages of the system and

Huayao Zheng; Yunqian Huang; Yinzhong Ye

1999-01-01

253

New level sensor system for ship stability analysis and monitor

A novel method of measuring liquid level with high accuracy is described, in which densimeter is unnecessary; by this way draft values are electrically measured; based on that the real time analysis for ship stability are available. The architecture and software of Auto Test and Monitor System are described. The system advantages and error estimation are also involved

Huayao Zheng; Yunqian Huang; Yinzhong Ye

1997-01-01

254

Aerostatic stability analysis of suspension bridges under parametric uncertainty

This paper presents a new method (series method) for the deterministic aerostatic stability analysis of suspension bridges. The geometric nonlinearity in the deflection theory and the three components of displacement-dependent wind loads are taken into account in the method. The accuracy and efficiency of the method are verified through the comparisons with existing nonlinear and linear methods. Second, an efficient

Jin Cheng; Jian-Jing Jiang; Ru-Cheng Xiao

2003-01-01

255

Stability analysis and control of multiple converter based autonomous microgrid

In this paper, the stability of an autonomous microgrid with multiple distributed generators (DG) is studied through eigenvalue analysis. It is assumed that all the DGs are connected through Voltage Source Converter (VSC) and all connected loads are passive. The VSCs are controlled by state feedback controller to achieve desired voltage and current outputs that are decided by a droop

Ritwik Majumder; Arindam Ghosh; Gerard Ledwich; Firuz Zare

2009-01-01

256

Analysis and stability of aldehydes and terpenes in electropolished canisters

Aldehydes and terpenes are important classes of polar VOC contaminants for which few sampling and analysis methods have been validated. This study reports on the analysis, stability and recovery of seven aldehydes (butanal, pentanal, hexanal, heptanal, octanal, nonanal and benzaldehyde) and four terpenes (?-pinene, ?-pinene, limonene and 3-carene) prepared at trace levels (3–5ppb) and stored in electropolished stainless-steel canisters. Humidified

Stuart A. Batterman; Guo-Zheng Zhang; Melissa Baumann

1998-01-01

257

Complete mode-set stability analysis of magnetically insulated ion diode equilibria

We present the first analysis of the stability of magnetically insulated ion diodes that is fully relativistic and includes electromagnetic perturbations both parallel and perpendicular to the applied magnetic field. Applying this formalism to a simple diode equilibrium model that neglects velocity shear and density gradients, we find a fast growing mode that has all of the important attributes of

S. A. Slutz; R. W. Lemke

1993-01-01

258

Dynamic equivalence to induction generators and wind turbines for power system stability analysis

With increasing installation capacity and energy production, wind power plays more important role in power systems. In transient stability analysis, detailed modeling to each induction generator and wind turbine will introduce lots of calculation effort, which necessitates dynamic equivalence to induction generators and wind turbines in the same wind farm, or wind farms closely located. In this paper, weighted equivalence

Shenghu Li; Zhengkai Liu; Xinjie Hao; Shusen Jia

2010-01-01

259

ENSO stability in coupled climate models and its association with mean state

NASA Astrophysics Data System (ADS)

In this study, using the Bjerknes stability (BJ) index analysis, we estimate the overall linear El Niño-Southern Oscillation (ENSO) stability and the relative contribution of positive feedbacks and damping processes to the stability in historical simulations of Coupled Model Intercomparison Project Phase 5 (CMIP5) models. When compared with CMIP3 models, the ENSO amplitudes and the ENSO stability as estimated by the BJ index in the CMIP5 models are more converged around the observed, estimated from the atmosphere and ocean reanalysis data sets. The reduced diversity among models in the simulated ENSO stability can be partly attributed to the reduced spread of the thermocline feedback and Ekman feedback terms among the models. However, a systematic bias persists from CMIP3 to CMIP5. In other words, the majority of the CMIP5 models analyzed in this study still underestimate the zonal advective feedback, thermocline feedback and thermodynamic damping terms, when compared with those estimated from reanalysis. This discrepancy turns out to be related with a cold tongue bias in coupled models that causes a weaker atmospheric thermodynamical response to sea surface temperature changes and a weaker oceanic response (zonal currents and zonal thermocline slope) to wind changes.

Kim, Seon Tae; Cai, Wenju; Jin, Fei-Fei; Yu, Jin-Yi

2014-06-01

260

Stability diagram for the forced Kuramoto model

We analyze the periodically forced Kuramoto model. This system consists of an infinite population of phase oscillators with random intrinsic frequencies, global sinusoidal coupling, and external sinusoidal forcing. It represents an idealization of many phenomena in physics, chemistry, and biology in which mutual synchronization competes with forced synchronization. In other words, the oscillators in the population try to synchronize with

Lauren M. Childs; Steven H. Strogatz

2008-01-01

261

Stabilizing a Bicycle: A Modeling Project

ERIC Educational Resources Information Center

This article is a project that takes students through the process of forming a mathematical model of bicycle dynamics. Beginning with basic ideas from Newtonian mechanics (forces and torques), students use techniques from calculus and differential equations to develop the equations of rotational motion for a bicycle-rider system as it tips from…

Pennings, Timothy J.; Williams, Blair R.

2010-01-01

262

Constrained model predictive control: Stability and optimality

Model predictive control is a form of control in which the current control action is obtained by solving, at each sampling instant, a finite horizon open-loop optimal control problem, using the current state of the plant as the initial state; the optimization yields an optimal control sequence and the first control in this sequence is applied to the plant. An

David Q. Mayne; James B. Rawlings; Christopher V. Rao; P. O. M. Scokaert

2000-01-01

263

A Robustly Stabilizing Model Predictive Control Algorithm

NASA Technical Reports Server (NTRS)

A model predictive control (MPC) algorithm that differs from prior MPC algorithms has been developed for controlling an uncertain nonlinear system. This algorithm guarantees the resolvability of an associated finite-horizon optimal-control problem in a receding-horizon implementation.

Ackmece, A. Behcet; Carson, John M., III

2007-01-01

264

Laboratory and numerical discontinuum modeling of wellbore stability

Wellbore-stability analyses based on intact wellbore walls can be too conservative because failed/fractured zones around wellbores relieve stress and give support. Wellbore-breakout analyses indicate that most drilled wells experience deformation beyond the rupture stage and that this deformation is acceptable for the drilling process. Validation of the methods available to predict wellbore stability requires a comparison of theoretical models with experimental simulations of wellbore behavior. This paper describes a series of scaled laboratory wellbore-stability experiments carried out under various borehole inclinations and stress conditions. The goal was to investigate the influence of the fractured zone, stress anisotropy, well deviation, and well orientation on wellbore stability. Classic log spiral fracture geometries were obtained around the wellbore, and the effect of the fractured zone on wellbore stability was studied with a distinct-element program called the universal distinct-element code (UDEC). Results show the importance of taking into account the stability of the fractured zone and subsequent wellbore breakout when wellbore stability is considered.

Rawlings, C.G.; Barton, N.R. (Norwegian Geotechnical Inst., Oslo (Norway)); Bandis, S.C. (Aristotle Univ. of Thessaloniki (Greece)); Addis, M.A. (BP Exploration Co. Ltd., Sunburry-on-Thames, London (United Kingdom)); Gutierrez, M.S. (Norwegian Geotechnical Inst., Oslo (Norway). Rock Engineering and Reservoir Mechanics Division)

1993-11-01

265

Extension of the Newcomb equation into the vacuum for the stability analysis of tokamak edge plasmas

NASA Astrophysics Data System (ADS)

The formulation for solving numerically the two-dimensional Newcomb equation has been extended to calculate the vacuum energy integral by using a vector potential method. According to this extension, a stability code MARG2D has been adapted, and coded for parallel computing in order to reduce substantially the CPU time. The MARG2D code enables a fast stability analysis of ideal external MHD modes from low to high toroidal mode numbers on the basis of the single physical model, and then the code works as a powerful tool in an integrated simulation where it is combined with transport codes, and also in the analysis of tokamak edge plasma experiments.

Aiba, Nobuyuki; Tokuda, Shinji; Ishizawa, Tomoko; Okamoto, Masao

2006-08-01

266

NSDL National Science Digital Library

The Marine Modeling and Analysis Branch (MMAB) of the Environmental Modeling Center is responsible for the development of improved numerical weather and marine prediction modeling systems. These models provide analysis and real-time forecast guidance on marine meteorological, oceanographic, and cryospheric parameters over the global oceans and coastal areas of the US. This site provides access to MMAB modeling tools for ocean waves (including an interactive presentation,) sea ice, marine meteorology, sea surface temperature and more. The site also features a mailing list, bibliography of publications, and information about modeling products still in the experimental and development phases.

National Centers For Environmental Prediction, National O.

267

Stability of cluster solutions in a cooperative consumer chain model.

We study a cooperative consumer chain model which consists of one producer and two consumers. It is an extension of the Schnakenberg model suggested in Gierer and Meinhardt [Kybernetik (Berlin), 12:30-39, 1972] and Schnakenberg (J Theor Biol, 81:389-400, 1979) for which there is only one producer and one consumer. In this consumer chain model there is a middle component which plays a hybrid role: it acts both as consumer and as producer. It is assumed that the producer diffuses much faster than the first consumer and the first consumer much faster than the second consumer. The system also serves as a model for a sequence of irreversible autocatalytic reactions in a container which is in contact with a well-stirred reservoir. In the small diffusion limit we construct cluster solutions in an interval which have the following properties: The spatial profile of the third component is a spike. The profile for the middle component is that of two partial spikes connected by a thin transition layer. The first component in leading order is given by a Green's function. In this profile multiple scales are involved: The spikes for the middle component are on the small scale, the spike for the third on the very small scale, the width of the transition layer for the middle component is between the small and the very small scale. The first component acts on the large scale. To the best of our knowledge, this type of spiky pattern has never before been studied rigorously. It is shown that, if the feedrates are small enough, there exist two such patterns which differ by their amplitudes.We also study the stability properties of these cluster solutions. We use a rigorous analysis to investigate the linearized operator around cluster solutions which is based on nonlocal eigenvalue problems and rigorous asymptotic analysis. The following result is established: If the time-relaxation constants are small enough, one cluster solution is stable and the other one is unstable. The instability arises through large eigenvalues of order O1. Further, there are small eigenvalues of order o1 which do not cause any instabilities. Our approach requires some new ideas: (i) The analysis of the large eigenvalues of order O1 leads to a novel system of nonlocal eigenvalue problems with inhomogeneous Robin boundary conditions whose stability properties have been investigated rigorously. (ii) The analysis of the small eigenvalues of order o1 needs a careful study of the interaction of two small length scales and is based on a suitable inner/outer expansion with rigorous error analysis. It is found that the order of these small eigenvalues is given by the smallest diffusion constant ?2(2). PMID:23129393

Wei, Juncheng; Winter, Matthias

2014-01-01

268

Stability Properties of the Starobinsky Cosmological Model

NASA Astrophysics Data System (ADS)

We discuss the instabilities appearing in the cosmological model with a quasi de Sitter phase following from a fourth-order gravity theory. Both the classical equation as well as the quantization in form of a Wheeler - De Witt equation are conformally related to the analogous model with Einstein's theory of gravity with a minimally coupled scalar field. Results are: 1. In the non-tachyonic case, classical fourth-order gravity is not more unstable than Einstein's theory itself. 2. The well-known classically valid conformal relation is also (at least for some typical cases) valid on the level of the corresponding Wheeler - De Witt equations, which turns out to be a non-trivial statement. (to appear in: Proc. Sem. Relativistic Astrophysics Potsdam 1994, Ed .: J. M\\"ucket)

Kasper, U.; Kluske, S.; Rainer, M.; Reuter, S.; Schmidt, H. J.

269

The electrically induced coalescence of water-in-oil emulsions stabilized by interfacially active fractions from crude oils has been studied by means of time domain dielectric spectroscopy at high electric fields. The experiments were designed with a 2{sup 7-3} reduced factorial design. Regression analysis clearly shows that the choice of organic solvent and the amount of asphaltenes, as well as the interplay between these variables, are the most significant parameters for determining the stability of these emulsions. It should be pointed out that the asphaltenes were the only surface active fraction tested. No interplay between, for instance, asphaltenes and resins was investigated. The nonlinearity found in the regression analysis is explained by different aggregation states of asphaltenes in aliphatic and aromatic solvents. The influence of the variables upon the emulsion stability is discussed.

Foerdedal, H.; Midttun, O.; Sjoeblom, J.; Kvalheim, O.M. [Univ. of Bergen (Norway). Dept. of Chemistry] [Univ. of Bergen (Norway). Dept. of Chemistry; Schildberg, Y.; Volle, J.L. [Elf Aquitaine Production, Pau (France)] [Elf Aquitaine Production, Pau (France)

1996-09-01

270

Modelling and transient stability of large wind farms

The paper is dealing with modelling and short-term voltage stability considerations of large wind farms. A physical model of a large offshore wind farm consisting of a large number of windmills is implemented in the dynamic simulation tool PSS\\/E. Each windmill in the wind farm is represented by a physical model of grid-connected windmills. The windmill generators are conventional induction

Vladislav Akhmatov; Hans Knudsen; Arne Hejde Nielsen; Jørgen Kaas Pedersen; Niels Kjølstad Poulsen

2003-01-01

271

NASA Astrophysics Data System (ADS)

If soil organic matter is predominantly microbial biomass, plant inputs that build biomass should also increase SOM. This seems obvious, but the implications fundamentally change how we think about the relationships between plants, microbes and SOM. Plant residues that build microbial biomass are typically characterized by low C/N ratios and high lignin contents. However, plants with high lignin contents and high C/N ratios are believed to increase SOM, an entrenched idea that still strongly motivates agricultural soil management practices. Here we use a combination of meta-analysis with a new microbial-explicit soil biogeochemistry model to explore the relationships between plant litter chemistry, microbial communities, and SOM stabilization in different soil types. We use the MIcrobial-MIneral Carbon Stabilization (MIMICS) model, newly built upon the Community Land Model (CLM) platform, to enhance our understanding of biology in earth system processes. The turnover of litter and SOM in MIMICS are governed by the activity of r- and k-selected microbial groups and temperature sensitive Michaelis-Menten kinetics. Plant and microbial residues are stabilized short-term by chemical recalcitrance or long-term by physical protection. Fast-turnover litter inputs increase SOM by >10% depending on temperature in clay soils, and it's only in sandy soils devoid of physical protection mechanisms that recalcitrant inputs build SOM. These results challenge centuries of lay knowledge as well as conventional ideas of SOM formation, but are they realistic? To test this, we conducted a meta-analysis of the relationships between the chemistry of plant liter inputs and SOM concentrations. We find globally that the highest SOM concentrations are associated with plant inputs containing low C/N ratios. These results are confirmed by individual tracer studies pointing to greater stabilization of low C/N ratio inputs, particularly in clay soils. Our model and meta-analysis results suggest that current ideas about plant-microbe-SOM relationships are unraveling. If so, our reconsideration of the mechanisms stabilizing SOM will also challenge long-held views about how to optimize plant community management to increase SOM.

Grandy, Stuart; Wieder, Will; Kallenbach, Cynthia; Tiemann, Lisa

2014-05-01

272

Application of the Edwards Model to Steric Stabilization of Nanoparticles

NASA Astrophysics Data System (ADS)

The Edwards model for polymers with excluded-volume interaction has been used to study steric stabilization of colloidal dispersions since Dolan and Edwards' work in 1975. Following the standard picture of steric stabilization since 1950s, Dolan and Edwards solved the model by treating the surfaces of colloidal particles as plane surfaces. Consequently, their result was also consistent with the standard picture: Reduction of conformational entropy of the adsorbed homopolymers results in a purely repulsive force that stabilizes the colloidal dispersion. Recently the Edwards model was solved without treating the spherical particle surfaces as plane surfaces. It was found that, contrary to the standard picture, the conformational entropy indeed increases and the force between particles may be either purely attractive or attractive at large particle-particle separation, repulsive at intermediate separation, and again attractive at small separation. Thus, the standard picture of steric stabilization was challenged. This review summarizes this recent progress in the theory of steric stabilization of colloidal dispersions. Reconciliation between the standard picture and the recent result, and possible directions for further research are also discussed.

Roan, Jiunn-Ren

273

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

NASA Technical Reports Server (NTRS)

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.

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

2009-01-01

274

NASA Astrophysics Data System (ADS)

Field observations of major earthquake fault zones show that shear deformation is often confined to principal slipping zones that may be of order 1-100 ?m wide, located within a broader gouge layer of order 10-100 mm wide. This paper examines the possibility that the extreme strain localization observed may be due to the coupling of shear heating, thermal pressurization, and diffusion. In the absence of a stabilizing mechanism shear deformation in a continuum analysis will collapse to an infinitesimally thin zone. Two possible stabilizing mechanisms, studied in this paper, are rate-strengthening friction and dilatancy. For rate-strengthening friction alone, a linear stability analysis shows that uniform shear of a gouge layer is unstable for perturbations exceeding a critical wavelength. Using this critical wavelength we predict a width for the localized zone as a function of the gouge properties. Taking representative parameters for fault gouge at typical centroidal depths of crustal seismogenic zones, we predict localized zones of order 5-40 ?m wide, roughly consistent with field and experimental observations. For dilatancy alone, linearized strain rate perturbations with a sufficiently large wavelength will undergo transient exponential growth before decaying back to uniform shear. The total perturbation strain accumulated during this transient strain rate localization is shown to be largely controlled by a single dimensionless parameter E, which is a measure of the dilatancy of the gouge material due to an increase in strain rate.

Rice, James R.; Rudnicki, John W.; Platt, John D.

2014-05-01

275

The influence of enzyme polysaccharide interaction on enzyme stability and activity was elucidated by covalently binding dextran to a model enzyme, ?-amylase. The conjugation process was optimized with respect to concentration of oxidizing agent, pH of enzyme solution, ratio of dextran to enzyme concentration, temperature and time of conjugate formation, and was found to affect the stability of ?-amylase. ?-Amylase conjugated under optimized conditions showed 5% loss of activity but with enhanced thermal and pH stability. Lower inactivation rate constant of conjugated ?-amylase within the temperature range of 60-80 °C implied its better stability. Activation energy for denaturation of ?-amylase increased by 8.81 kJ/mol on conjugation with dextran. Analysis of secondary structure of ?-amylase after covalent binding with dextran showed helix to turn conversion without loss of functional properties of ?-amylase. Covalent bonding was found to be mandatory for the formation of conjugate. PMID:22944451

Jadhav, Swati B; Singhal, Rekha S

2012-11-01

276

Linearized stability analysis and design of a flyback dc-dc boost regulator.

NASA Technical Reports Server (NTRS)

Analytic expressions for the small-signal power-stage describing functions of a switched dc-dc boost regulator are derived from an approximate continuous circuit model which is developed by a time-averaging technique. Closed-loop stability is attained through the design of frequency compensation of the loop gain. Open- and closed-loop regulator output impedances are derived from the linearized models for the given configuration. The analysis and design are compared with and confirmed by breadboard measurements.

Wester, G. W.

1973-01-01

277

NASA Technical Reports Server (NTRS)

The combustion stability characteristics of engines applicable to the Space Shuttle Orbit Maneuvering System and the adequacy of acoustic cavities as a means of assuring stability in these engines were investigated. The study comprised full-scale stability rating tests, bench-scale acoustic model tests and analysis. Two series of stability rating tests were made. Acoustic model tests were made to determine the resonance characteristics and effects of acoustic cavities. Analytical studies were done to aid design of the cavity configurations to be tested and, also, to aid evaluation of the effectiveness of acoustic cavities from available test results.

Oberg, C. L.

1974-01-01

278

Numerical modeling of laser stabilization by regenerative spectral hole burning

Regenerative transient spectral hole frequency references have provided relative optical stability, measured by the Allan deviation, on the 10?13 scale. These references are comparatively insensitive to vibration and, unlike traditional Fabry–Perot cavities, atomic references, or gated spectral holes, the reference shape and position can depend on the laser input as well as the material properties. Numerical modeling of a frequency

G. J. Pryde; T. Böttger; R. L. Cone

2001-01-01

279

On the stability of steady states in a granuloma model

NASA Astrophysics Data System (ADS)

We consider a free boundary problem for a system of two semilinear parabolic equations. The system represents a simple model of granuloma, a collection of immune cells and bacteria filling a 3-dimensional domain ?(t) which varies in time. We prove the existence of stationary spherical solutions and study their linear asymptotic stability as time increases to infinity.

Friedman, Avner; Lam, King-Yeung

280

A study on dynamics analysis of a small ship and pitch motion stabilization by engine speed control

This paper describes dynamics analysis of a small training ship and a possibility of ship pitching stabilization by adjusting engine speed. First, statistical analysis through multi-variate auto regressive(MAR) model is carried out. After upgrading the navigational system of an actual small training ship, in order to identify the model of the ship, the real data collected by sea trials on

Toshihiko NAKATANI; Keiji SASAYA; Tomoki OKU; Shigeki Tajika; Taizo KANEDA; E. Ura

2010-01-01

281

Mixed neutron-star-plus-wormhole systems: Linear stability analysis

NASA Astrophysics Data System (ADS)

We consider configurations consisting of a neutron star with a wormhole at the core. The wormhole is held open by a ghost scalar field with a quartic coupling. The neutron matter is described by a perfect fluid with a polytropic equation of state. We obtain static regular solutions for these systems. A stability analysis, however, shows that they are unstable with respect to linear perturbations.

Dzhunushaliev, Vladimir; Folomeev, Vladimir; Kleihaus, Burkhard; Kunz, Jutta

2013-05-01

282

Coupled three-dimensional aeroelastic stability analysis of bladed disks

In the present work an algorithm for the coupled aeromechanical computation of three-dimensional compressor cascades vibrating in a traveling-wave mode is presented and applied to the determination of aeroelastic stability of a transonic fan rotor. The initial vibratory modes are computed using a finite-element structural analysis code. The unsteady flow field response to blade vibration is estimated by numerical integration

G. A. Gerolymos

1993-01-01

283

Comprehensive gait analysis in posterior-stabilized knee arthroplasty

Sixteen patients implanted with a posterior-stabilized prosthesis (Insall-Burstein PS II, Zimmer, Warsaw, IN) and 32 age-matched control subjects were evaluated by isokinetic muscle testing and comprehensive gait analysis at a mean 46 months following the index arthroplasty. The contralateral knee was normal in 13 patients and an asymptomatic total knee arthroplasty in 3 patients. No significant differences (P > .05)

Stephen A. Wilson; Peter D. McCann; Robert S. Gotlin; H. K. Ramakrishnan; Mary E. Wootten; John N. Insall

1996-01-01

284

Stability analysis of fixed points via chaos control.

This paper reviews recent advances in the application of chaos control techniques to the stability analysis of two-dimensional dynamical systems. We demonstrate how the system's response to one or multiple feedback controllers can be utilized to calculate the characteristic multipliers associated with an unstable periodic orbit. The experimental results, obtained for a single and two coupled diode resonators, agree well with the presented theory. (c) 1997 American Institute of Physics. PMID:12779684

Locher, M.; Johnson, G. A.; Hunt, E. R.

1997-12-01

285

DYNAMIC MODELLING AND CONFIGURATION STABILIZATION FOR AN X4FLYER

A model for the dynamics of a four rotor vertical take-off and landing (VTOL) vehicle known as an X4-flyer is proposed. The model incorporates the airframe and motor dynamics as well as aerodynamic and gyroscopic effects due to the rotors for quasi-stationary flight conditions. A novel control strategy is proposed for configuration stabilization of quasi-stationary flight conditions. The approach taken

Tarek Hamel; Robert Mahony; Rogelio Lozano; James Ostrowski

2002-01-01

286

A CANDU figure-of-eight flow stability model

A stability model of flow oscillations observed in two-phase flow tests in a CANDU-like experimental rig is developed. The model is derived by linearizing and solving one-dimensional, homogeneous two-phase flow conservation equations. The flow oscillations are explained in terms of the response of the pressure in the two-phase region to a change in the single-phase flow. A simple instability criterion

P. Gulshani; N. J. Spinks

1984-01-01

287

Stability of preclinical models of aggressive renal cell carcinomas

Renal-cell carcinomas (RCC) are often resistant to conventional cytotoxic agents. Xenograft models are used for in vivo preclinical studies and drug development. The validity of these studies is highly dependent on the phenotypic and genotypic stability of the models. Here we assessed the stability of six aggressive human RCC xenografted in nude/NMRI mice. We compared the initial samples (P0), first (P1) and fifth (P5) passages for the following criteria: histopathology, immunohistochemistry for CK7, CD10, vimentin and p53, DNA allelic profiles using 10 microsatellites and CGH-array. Next we evaluated the response to sunitinib in primary RCC and corresponding xenografted RCC. We observed a good overall stability between primary RCC and corresponding xenografted RCC at P1 and P5 regarding histopathology and immunohistochemistry except for cytokeratin 7 (one case) and p53 (one case) expression. Out of 44 groups with fully available microsatellite data (at P0, P1 and P5), 66% (29 groups) showed no difference from P0 to P5 while 34% (15 groups) showed new or lost alleles. Using CGH-array, overall genomic alterations at P5 were not different from those of initial RCC. The xenografted RCC had identical response to sunitinib therapy compared to the initial human RCC from which they derive. These xenograft models of aggressive human RCC are clinically relevant, showing a good histological and molecular stability and are suitable for studies of basic biology and response to therapy.

Varna, Mariana; Bousquet, Guilhem; Ferreira, Irmine; Goulard, Marie; El-Bouchtaoui, Morad; Artus, Pierre Mongiat; Verine, Jerome; de Kerviler, Eric; Hernandez, Lucie; Leboeuf, Christophe; Escudier, Bernard; Legres, Luc; Setterblad, Niclas; Soliman, Hany; Feugeas, Jean-Paul; Janin, Anne; Bertheau, Philippe

2014-01-01

288

Linear stability analysis of a vertically oscillated granular layer.

We present a linear stability analysis of an oscillating granular layer, treating it as an isothermal incompressible fluid with zero surface tension, which undergoes periodic collisions with and separations from an oscillating plate. Because the viscosity of the granular layer is unknown, we use the experimental value of the critical acceleration for the transition from a flat to patterned layer as input for the theory, and use the analysis to calculate the granular viscosity and the wavelength of the most unstable mode. The wavelength compares favorably with the experimental pattern wavelength. Further, we find that the wavelengths are controlled by the viscosity of the granular layer. PMID:11970664

Bizon, C; Shattuck, M D; Swift, J B

1999-12-01

289

Dynamic Response and Stability Analysis of AN Automatic Ball Balancer for a Flexible Rotor

NASA Astrophysics Data System (ADS)

Dynamic stability and time responses are studied for an automatic ball balancer of a rotor with a flexible shaft. The Stodola-Green rotor model, of which the shaft is flexible, is selected for analysis. This rotor model is able to include the influence of rigid-body rotations due to the shaft flexibility on dynamic responses. Applying Lagrange's equation to the rotor with the ball balancer, the non-linear equations of motion are derived. Based on the linearized equations, the stability of the ball balancer around the balanced equilibrium position is analyzed. On the other hand, the time responses computed from the non-linear equations are investigated. This study shows that the automatic ball balancer can achieve the balancing of a rotor with a flexible shaft if the system parameters of the balancer satisfy the stability conditions for the balanced equilibrium position.

Chung, J.; Jang, I.

2003-01-01

290

Validation of IVA Computer Code for Flow Boiling Stability Analysis

IVA is a computer code for modeling of transient multiphase, multi-component, non-equilibrium flows in arbitrary geometry including flow boiling in 3D nuclear reactors. This work presents part of the verification procedure of the code. We analyze the stability of flow boiling in natural circulation loop. Experimental results collected on the AREVA\\/FANP KATHY loop regarding frequencies, mass flows and decay ratio

Ivanov Kolev; Nikolay

2006-01-01

291

Stability analysis is generally used to verify that the solution to phase equilibrium calculations corresponds to a stable state (minimum of the free energy). In this work, tangent plane distance analysis for stability of macroscopic mixtures is also used for analyzing the nucleation process, reconciling thus this analysis with classical nucleation theories. In the context of the revised nucleation theory, the driving force and the nucleation work are expressed as a function of the Lagrange multiplier corresponding to the mole fraction constraint from the minimization problem of stability analysis. Using a van der Waals fluid applied to a ternary mixture, Lagrange multiplier properties are illustrated. In particular, it is shown how the Lagrange multiplier value is equal to one on the binodal and spinodal curves at the same time as the driving force of nucleation vanishes on these curves. Finally, it is shown that, on the spinodal curve, the nucleation work from the revised and generalized nucleation theories are characterized by two different local minima from stability analysis, irrespective of any interfacial tension models. PMID:23061836

Carreón-Calderón, Bernardo

2012-10-14

292

Doubly-fed induction machine models for stability assessment of wind farms

The increasing size of wind farms requires power system stability analysis including dynamic models of the wind power generation. Nowadays, the most widely used generator type for units above 1 MW is the doubly-fed induction machine. Doubly-fed induction machines allow active and reactive power control through a rotor-side converter, while the stator is directly connected to the grid. Detailed models

Markus A. Poller

2003-01-01

293

Stability of a Ricker-type competition model and the competitive exclusion principle

Our main objective is to study a Ricker-type competition model of two species. We give a complete analysis of stability and bifurcation and determine the centre manifolds, as well as stable and unstable manifolds. It is shown that the autonomous Ricker competition model exhibits subcritical bifurcation, bubbles, period-doubling bifurcation, but no Neimark–Sacker bifurcations. We exhibit the region in the parameter

Rafael Luís; Saber Elaydi; Henrique Oliveira

2011-01-01

294

Stabilization of a thermoelastic Mindlin-Timoshenko plate model revisited

NASA Astrophysics Data System (ADS)

This paper is a continuation of our work in Grobbelaar-Van Dalsen (Appl Anal 90:1419-1449, 2011) where we showed the strong stability of models involving the thermoelastic Mindlin-Timoshenko plate equations with second sound. For the case of a plate configuration consisting of a single plate, this was accomplished in radially symmetric domains without applying any mechanical damping mechanism. Further to this result, we establish in this paper the non-exponential stability of the model for a particular configuration under mixed boundary conditions on the shear angle variables and Dirichlet boundary conditions on the displacement and thermal variables when the heat flux is described by Fourier's law of heat conduction. We also determine the rate of polynomial decay of weak solutions of the model in a radially symmetric region under Dirichlet boundary conditions on the displacement and thermal variables and free boundary conditions on the shear angle variables.

Grobbelaar-Van Dalsen, Marié

2013-08-01

295

A charging model for three-axis stabilized spacecraft

NASA Technical Reports Server (NTRS)

A charging model was developed for geosynchronous, three-axis stabilized spacecraft when under the influence of a geomagnetic substorm. The differential charging potentials between the thermally coated or blanketed outer surfaces and metallic structure of a spacecraft were determined when the spacecraft was immersed in a dense plasma cloud of energetic particles. The spacecraft-to-environment interaction was determined by representing the charged particle environment by equivalent current source forcing functions and by representing the spacecraft by its electrically equivalent circuit with respect to the plasma charging phenomenon. The charging model included a sun/earth/spacecraft orbit model that simulated the sum illumination conditions of the spacecraft outer surfaces throughout the orbital flight on a diurnal as well as a seasonal basis. Transient and steady-state numerical results for a three-axis stabilized spacecraft are presented.

Massaro, M. J.; Green, T.; Ling, D.

1977-01-01

296

Stability analysis of position and force control problems for robot arms

NASA Technical Reports Server (NTRS)

A stability analysis for robot manipulators under the influence of external forces is presented. Several control objectives are considered: rejecting the external force as a source of disturbance, complying to the external force as a generalized mass-spring-damper system, and actively controlling the external force when a dynamic model for the environment is available. An explanation of instability is given for the case in which the environment has flexibility and the gains are inappropriately chosen. When the environment is stiff in the force control subspace, robust stability can be achieved via the integral force feedback.

Wen, John T.; Murphy, Steve

1990-01-01

297

Enumeration and stability analysis of simple periodic orbits in Î²-Fermi Pasta Ulam lattice

NASA Astrophysics Data System (ADS)

We study the well-known one-dimensional problem of N particles with a nonlinear interaction. The special case of quadratic and quartic interaction potential among nearest neighbours is the ?-Fermi-Pasta-Ulam model. We enumerate and classify the simple periodic orbits for this system and find the stability zones, employing Floquet theory. Such stability analysis is crucial to understand the transition of FPU lattice from recurrences to globally chaotic behavior, energy transport in lower dimensional system, dynamics of optical lattices and also its impact on shape parameter of bio-polymers such as DNA and RNA.

Sonone, Rupali L.; Jain, Sudhir R.

2014-04-01

298

Parallel processing for efficient 3D slope stability modelling

NASA Astrophysics Data System (ADS)

We test the performance of the GIS-based, three-dimensional slope stability model r.slope.stability. The model was developed as a C- and python-based raster module of the GRASS GIS software. It considers the three-dimensional geometry of the sliding surface, adopting a modification of the model proposed by Hovland (1977), and revised and extended by Xie and co-workers (2006). Given a terrain elevation map and a set of relevant thematic layers, the model evaluates the stability of slopes for a large number of randomly selected potential slip surfaces, ellipsoidal or truncated in shape. Any single raster cell may be intersected by multiple sliding surfaces, each associated with a value of the factor of safety, FS. For each pixel, the minimum value of FS and the depth of the associated slip surface are stored. This information is used to obtain a spatial overview of the potentially unstable slopes in the study area. We test the model in the Collazzone area, Umbria, central Italy, an area known to be susceptible to landslides of different type and size. Availability of a comprehensive and detailed landslide inventory map allowed for a critical evaluation of the model results. The r.slope.stability code automatically splits the study area into a defined number of tiles, with proper overlap in order to provide the same statistical significance for the entire study area. The tiles are then processed in parallel by a given number of processors, exploiting a multi-purpose computing environment at CNR IRPI, Perugia. The map of the FS is obtained collecting the individual results, taking the minimum values on the overlapping cells. This procedure significantly reduces the processing time. We show how the gain in terms of processing time depends on the tile dimensions and on the number of cores.

Marchesini, Ivan; Mergili, Martin; Alvioli, Massimiliano; Metz, Markus; Schneider-Muntau, Barbara; Rossi, Mauro; Guzzetti, Fausto

2014-05-01

299

Time course analysis of RNA stability in human placenta

Background Evaluation of RNA quality is essential for gene expression analysis, as the presence of degraded samples may influence the interpretation of expression levels. Particularly, qRT-PCR data can be affected by RNA integrity and stability. To explore systematically how RNA quality affects qRT-PCR assay performance, a set of human placenta RNA samples was generated by two protocols handlings of fresh tissue over a progressive time course of 4 days. Protocol A consists of a direct transfer of tissue into RNA-stabilizing solution (RNAlater™) solution. Protocol B uses a dissection of placenta villosities before bio banking. We tested and compared RNA yields, total RNA integrity, mRNA integrity and stability in these two protocols according to the duration of storage. Results A long time tissue storage had little effect on the total RNA and mRNA integrity but induced changes in the transcript levels of stress-responsive genes as TNF-alpha or COX2 after 48 h. The loss of the RNA integrity was higher in the placental tissues that underwent a dissection before RNA processing by comparison with those transferred directly into RNA later™ solution. That loss is moderate, with average RIN (RNA Integration Numbers) range values of 4.5–6.05, in comparison with values of 6.44–7.22 in samples directly transferred to RNAlater™ (protocol A). Among the house keeping genes tested, the B2M is the most stable. Conclusion This study shows that placental samples can be stored at + 4°C up to 48 h before RNA extraction without altering RNA quality. Rapid tissue handling without dissection and using RNA-stabilizing solution (RNAlater™) is a prerequisite to obtain suitable RNA integrity and stability.

Fajardy, Isabelle; Moitrot, Emmanuelle; Vambergue, Anne; Vandersippe-Millot, Maryse; Deruelle, Philippe; Rousseaux, Jean

2009-01-01

300

Using tightly-coupled CFD/CSD simulation for rotorcraft stability analysis

NASA Astrophysics Data System (ADS)

Dynamic stall deeply affects the response of helicopter rotor blades, making its modeling accuracy very important. Two commonly used dynamic stall models were implemented in a comprehensive code, validated, and contrasted to provide improved analysis accuracy and versatility. Next, computational fluid dynamics and computational structural dynamics loose coupling methodologies are reviewed, and a general tight coupling approach was implemented and tested. The tightly coupled computational fluid dynamics and computational structural dynamics methodology is then used to assess the stability characteristics of complex rotorcraft problems. An aeroelastic analysis of rotors must include an assessment of potential instabilities and the determination of damping ratios for all modes of interest. If the governing equations of motion of a system can be formulated as linear, ordinary differential equations with constant coefficients, classical stability evaluation methodologies based on the characteristic exponents of the system can rapidly and accurately provide the system's stability characteristics. For systems described by linear, ordinary differential equations with periodic coefficients, Floquet's theory is the preferred approach. While these methods provide excellent results for simplified linear models with a moderate number of degrees of freedom, they become quickly unwieldy as the number of degrees of freedom increases. Therefore, to accurately analyze rotorcraft aeroelastic periodic systems, a fully nonlinear, coupled simulation tool is used to determine the response of the system to perturbations about an equilibrium configuration and determine the presence of instabilities and damping ratios. The stability analysis is undertaken using an algorithm based on a Partial Floquet approach that has been successfully applied with computational structural dynamics tools on rotors and wind turbines. The stability analysis approach is computationally inexpensive and consists of post processing aeroelastic data, which can be used with any aeroelastic rotorcraft code or with experimental data.

Zaki, Afifa Adel

301

Global stability of Gompertz model of three competing populations

NASA Astrophysics Data System (ADS)

The model of three competitive populations with Gompertz growth is studied. The periodic solutions are ruled out by generalized Dulac criteria. On the basis of the analysis, we obtain conditions that ensure the asymptotic behavior of the model is simple.

Yu, Yumei; Wang, Wendi; Lu, Zhengyi

2007-10-01

302

A stability theorem for energy-balance climate models

NASA Technical Reports Server (NTRS)

The paper treats the stability of steady-state solutions of some simple, latitude-dependent, energy-balance climate models. For north-south symmetric solutions of models with an ice-cap-type albedo feedback, and for the sum of horizontal transport and infrared radiation given by a linear operator, it is possible to prove a 'slope stability' theorem, i.e., if the local slope of the steady-state iceline latitude versus solar constant curve is positive (negative) the steady-state solution is stable (unstable). Certain rather weak restrictions on the albedo function and on the heat transport are required for the proof, and their physical basis is discussed.

Cahalan, R. F.; North, G. R.

1979-01-01

303

Stability analysis for a semiconductor laser in an external cavity

A detailed theoretical analysis of stability is presented for a semiconductor laser in an external cavity. The limits of stable operation are determined as a function of the external cavity parameters and the linewidth enhancement factor infinity. Instability is related to jumps of the laser frequency between external cavity modes (frequency bistability) or to feedback-induced intensity pulsations due to the carrier density dependence of the refractive index. The limit of bistability is derived from the steady-state solutions of the rate equations and the intensity pulsation limit is obtained from a small-signal analysis. This analysis also gives the location of zeros in the system determinant and the resulting FM noise spectrum. For practical applications the authors emphasize the determination of the stable tuning range for the phase in the external cavity and the classification of the possible types of instability for various feedback levels.

Tromborg, B.; Olesen, H.; Osmundsen, J.H.

1984-09-01

304

A model for the stability of films stabilized by randomly packed spherical particles.

Particle stabilized thin films occur in a range of industrial applications where their properties affect the efficiency of the process concerned. However, due to their dynamic and unstable nature they are difficult to observe experimentally. As such, a tractable way of gaining insight into the fundamental aspects of this complicated system is to use computer simulations of particles at interfaces. This paper presents modeling results of the effect of nonuniform packing of spherical particles on the stability of thin liquid films. Surface Evolver was used to model cells containing up to 20 particles, randomly packed in a thin liquid film. The capillary pressure required to rupture the film for a specific combination of particle arrangement, packing density, and contact angle was identified. The data from the periodic, randomly packed models has been used to find a relationship between particle packing density, contact angle, and critical capillary pressure which is refined to a simple equation that depends on the film loading and contact angle of the particles it contains. The critical capillary pressure for film rupture obeys the same trends observed for particles in regular 2D and 3D packing arrangements. The absolute values of P*(crit), however, are consistently lower than those for regular packing. This is due to the irregular arrangement of the particles, which allows for larger areas of free film to exist, lowering the critical capillary pressure required to rupture the film. PMID:21812436

Morris, Gareth D M; Neethling, Stephen J; Cilliers, Jan J

2011-09-20

305

REDUCED-ORDER MODELS FOR FEEDBACK STABILIZATION OF LINEAR SYSTEMS WITH A SINGULAR PERTURBATION MODEL

The problem of output feedback stabilization of linear systems based on a reduced-order model is addressed in this paper. New reduced-order models are proposed for the output feedback design of linear systems with a singular perturbation model. An output feedback controller with a zero steady-state gain matrix is proposed for stabilizing this kind of system. It is shown that with

Liyu Cao; Howard M. Schwartz

2005-01-01

306

Linear Stability Analysis of a Channel Flow with Porous Walls

NASA Astrophysics Data System (ADS)

This study is motivated by the extensive use of wall-transpiration in numerical studies related to inhibition and control of wall-turbulence. In general, wall-transpiration has been implemented by providing the wall-normal velocity and imposing a no-slip condition on the wall-tangential velocity. Physically, however, the pores cannot be infinitesimally small and, consequently, it is important to address how the presence of the pores affects the slip velocity at the wall and the stability of the boundary layer. Moreover, our work is motivated by the existence of only few studies on the linear stability of channels with porous walls. Our study considers a parallel-plate channel with porous walls such that a longitudinal pressure gradient induces a laminar flow in both the open channel region and the porous walls. Simplified counterparts to the Orr-Sommerfeld and Squire equations are derived for the porous regions that are valid for small permeablities. The linear stability analysis takes account of the coupling between the three disturbance fields through boundary conditions recently derived by Ochoa-Tapia and Whitaker (Int. J. Heat Mass Transfer, Vol. 38, 1995, pp 2635-2646). The resulting Orr-Sommerfeld spectrum and eigenfunctions reduce to those for Poiseuille flow as the permeability of the walls tends to zero, but are altered for greater values. We discuss symmetrical flows where parameters at both porous walls are identical as well as skewed flows where parameters at the two walls differ.

Tilton, Nils

2005-11-01

307

A general approach for the stability analysis of time-domain finite element method

Considerable attention has been devoted to time-domain numerical methods for simulating electromagnetic transient phenomena. A general approach based on discrete system analysis is developed for investigating the stability behavior of time-domain finite element methods (TDFEM). This approach is applied to a variety of recently developed TDFEM schemes. These include: (1) time-domain finite element modeling of dispersive media; (2) time-domain finite

D. Jiao; Jian-Ming Jin

2001-01-01

308

Stability analysis of the cosmological solutions with induced gravity and scalar field on the brane

NASA Astrophysics Data System (ADS)

We study cosmological dynamics and phase space of a scalar field localized on the Dvali-Gabadadze-Porrati brane. We consider both the minimally and non-minimally coupled scalar quintessence and phantom fields on the brane. In the non-minimal case, the scalar field couples with induced gravity on the brane. We present a detailed analysis of the critical points, their stability and late-time cosmological viability of the solutions in the phase space of the model.

Nozari, Kourosh; Rajabi, F.; Asadi, K.

2012-09-01

309

Stability analysis of position and force control problems for robot arms

NASA Technical Reports Server (NTRS)

Stability issues involving the control of a robot arm under the influence of external forces are discussed. Several different scenarios are considered: position control with the external force as an unmodeled disturbance, compliant control for a bounded external force in some subspace, and compliant control for a force due to the interaction with an environment whose dynamical behavior can be modeled. In each of these cases, a stability analysis using the Lyapunov method is presented. An explanation of instability is put forth for the case in which the environment has flexibility and the gains are inappropriately chosen. When the environment is stiff in the force control subspace, robust stability can be achieved with the integral force feedback.

Wen, John T.; Murphy, Steve

1990-01-01

310

Rotation and plasma stability in the Fitzpatrick-Aydemir model

NASA Astrophysics Data System (ADS)

The rotational stabilization of the resistive wall modes (RWMs) is analyzed within the single-mode cylindrical Fitzpatrick-Aydemir model [R. Fitzpatrick, Phys. Plasmas 9, 3459 (2002)]. Here, the consequences of the Fitzpatrick-Aydemir dispersion relation are derived in terms of the observable growth rate and toroidal rotation frequency of the mode, which allows easy interpretation of the results and comparison with experimental observations. It is shown that this model, developed for the plasma with weak dissipation, predicts the rotational destabilization of RWM in the typical range of the RWM rotation. The model predictions are compared with those obtained in a similar model, but with the Boozer boundary conditions at the plasma surface [A. H. Boozer, Phys. Plasmas 11, 110 (2004)]. Simple experimental tests of the model are proposed.

Pustovitov, V. D.

2007-08-01

311

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

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.

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

2014-01-01

312

Thermal Stability of Nanocrystalline Alloys by Solute Additions and A Thermodynamic Modeling

NASA Astrophysics Data System (ADS)

Nanocrystalline alloys show superior properties due to their exceptional microstructure. Thermal stability of these materials is a critical aspect. It is well known that grain boundaries in nanocrystalline microstructures cause a significant increase in the total free energy of the system. A driving force provided to reduce this excess free energy can cause grain growth. The presence of a solute addition within a nanocrystalline alloy can lead to the thermal stability. Kinetic and thermodynamic stabilization are the two basic mechanisms with which stability of a nanoscale grain size can be achieved at high temperatures. The basis of this thesis is to study the effect of solute addition on thermal stability of nanocrystalline alloys. The objective is to determine the effect of Zr addition on the thermal stability of mechanically alloyed nanocrysatillne Fe-Cr and Fe-Ni alloys. In Fe-Cr-Zr alloy system, nanoscale grain size stabilization was maintained up to 900 °C by adding 2 at% Zr. Kinetic pinning by intermetallic particles in the nanoscale range was identified as a primary mechanism of thermal stabilization. In addition to the grain size strengthening, intermetallic particles also contribute to strengthening mechanisms. The analysis of microhardness, XRD data, and measured grain sizes from TEM micrographs suggested that both thermodynamic and kinetic mechanisms are possible mechanisms. It was found that alpha ? gamma phase transformation in Fe-Cr-Zr system does not influence the grain size stabilization. In the Fe-Ni-Zr alloy system, it was shown that the grain growth in Fe-8Ni-1Zr alloy is much less than that of pure Fe and Fe-8Ni alloy at elevated temperatures. The microstructure of the ternary Fe-8Ni-1Zr alloy remains in the nanoscale range up to 700 °C. Using an in-situ TEM study, it was determined that drastic grain growth occurs when the alpha ? gamma phase transformation occurs. Accordingly, there can be a synergistic relationship between grain growth and alpha ? gamma phase transformation in Fe-Ni-Zr alloys. In addition to the experimental study of thermal stabilization of nanocrystalline Fe-Cr-Zr or Fe-Ni-Zr alloys, the thesis presented here developed a new predictive model, applicable to strongly segregating solutes, for thermodynamic stabilization of binary alloys. This model can serve as a benchmark for selecting solute and evaluating the possible contribution of stabilization. Following a regular solution model, both the chemical and elastic strain energy contributions are combined to obtain the mixing enthalpy. The total Gibbs free energy of mixing is then minimized with respect to simultaneous variations in the grain boundary volume fraction and the solute concentration in the grain boundary and the grain interior. The Lagrange multiplier method was used to obtained numerical solutions. Application are given for the temperature dependence of the grain size and the grain boundary solute excess for selected binary system where experimental results imply that thermodynamic stabilization could be operative. This thesis also extends the binary model to a new model for thermodynamic stabilization of ternary nanocrystalline alloys. It is applicable to strongly segregating size-misfit solutes and uses input data available in the literature. In a same manner as the binary model, this model is based on a regular solution approach such that the chemical and elastic strain energy contributions are incorporated into the mixing enthalpy DeltaHmix, and the mixing entropy DeltaSmix is obtained using the ideal solution approximation. The Gibbs mixing free energy Delta Gmix is then minimized with respect to simultaneous variations in grain growth and solute segregation parameters. The Lagrange multiplier method is similarly used to obtain numerical solutions for the minimum Delta Gmix. The temperature dependence of the nanocrystalline grain size and interfacial solute excess can be obtained for selected ternary systems. As an example, model predictions are compared to experimental results for Fe-Cr-Zr and Fe-Ni-Zr

Saber, Mostafa

313

Fuzzy Current-Mode Control and Stability Analysis

NASA Technical Reports Server (NTRS)

In this paper a current-mode control (CMC) methodology is developed for a buck converter by using a fuzzy logic controller. Conventional CMC methodologies are based on lead-lag compensation with voltage and inductor current feedback. In this paper the converter lead-lag compensation will be substituted with a fuzzy controller. A small-signal model of the fuzzy controller will also be developed in order to examine the stability properties of this buck converter control system. The paper develops an analytical approach, introducing fuzzy control into the area of CMC.

Kopasakis, George

2000-01-01

314

Qualitative analysis of the stability of a continuous vermicomposting system.

A mathematical model was established to describe ecological relationships in a continuous vermicomposting system. The distributions of organic matter, microbes and earthworms on non-dimensional specific growth rates were simulated. The range of specific growth rates were visualized utilizing three-dimensional reconstruction technology. The stability of a vermicomposting system was not influenced by the initial concentrations of microbes and earthworms, only their species. The coordinates of the stable point depended on the dilution rate and initial amount of organic matter. The method described could be help for establishing a stable continuous vermicomposting system. PMID:23127841

Hu, Enzhu; Liu, Hong

2012-12-01

315

Security Modeling and Analysis

NSDL National Science Digital Library

This is a case study that follows the introductory courseware on security in embedded system design. The case study shows a simple domain-specific modeling language that could be used create of embedded systems and their security aspects, and an analysis tool that validates that the system design satsifies the desired properties.

Karsai, Gabor

2009-02-17

316

Stability and stabilization for models of chemostats with multiple limiting substrates.

We study chemostat models in which multiple species compete for two or more limiting nutrients. First, we consider the case where the nutrient flow and species removal rates and input nutrient concentrations are all given as positive constants. In that case, we use Brouwer degree theory to give conditions guaranteeing that the models admit globally asymptotically stable componentwise positive equilibrium points, from all componentwise positive initial states. Then we use the results to develop stabilization theory for a class of controlled chemostats with two or more limiting nutrients. For cases where the dilution rate and input nutrient concentrations can be selected as controls, we prove that many different componentwise positive equilibria can be made globally asymptotically stable. This extends the existing control results for chemostats with one limiting nutrient. We demonstrate our methods in simulations. PMID:22873608

Mazenc, Frédéric; Malisoff, Michael

2012-01-01

317

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

NASA Technical Reports Server (NTRS)

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.

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

2009-01-01

318

In situ vitrification: Application analysis for stabilization transuranic waste

NASA Astrophysics Data System (ADS)

The in situ vitrification process builds upon the electric melter technology previously developed for high-level waste immobilization. In situ vitrification converts buried wastes and contaminated soil to an extremely durable glass and crystalline waste form by melting the materials, in place, using joule heating. Once the waste materials have been solidified, the high integrity waste form should not cause future ground subsidence. Environmental transport of the waste due to water or wind erosion, and plant or animal intrusion, is minimized. Environmental studies are currently being conducted to determine whether additional stabilization is required for certain in-ground transuranic waste sites. An applications analysis was performed to identify several in situ vitrification process limitations which may exist at transuranic waste sites. Based on the process limit analysis, in situ vitrification is well suited for solidification of most in-ground transuranic wastes.

Oma, K. H.; Farnsworth, R. K.; Rusin, J. M.

1982-09-01

319

Stability Analysis of Flow Induced by the Traveling Magnetic Field

NASA Technical Reports Server (NTRS)

Re-circulating flow in molten metal columns can be conveniently induced by the axisymmetric traveling magnetic field. A number of applications can benefit from this technique, such as mixing under microgravity environment, or crysta1 growth from metallic melts. For small magnetic field excitations, the flow is laminar and stationary. As the imposed field increases, a more complex flow will set up in the cylindrical column. Conditions for stable laminar flow are of importance for practical applications. In this work, a linear stability analysis is performed in order to determine the onset of the bifurcation in the system. Here the analysis is restricted to the axisymmetric modes and the low-frequency regime.

Mazuruk, Konstantin

2003-01-01

320

Stability Analysis of Flow Induced by the Traveling Magnetic Field

NASA Technical Reports Server (NTRS)

Re-circulating flow in molten metal columns can be conveniently induced by the axisymmetric traveling magnetic field. A number of applications can benefit from this technique, such as mixing under microgravity environment, or.crysta1 growth from metallic melts. For small magnetic field excitations, the flow is laminar and stationary. As the imposed field increases, a more complex flow will set up in the cylindrical column. Conditions for stable laminar flow are of importance for practical applications. In this work, a linear stability analysis is performed in order to determine the onset of the bifurcation in the system. Here the analysis is restricted to the axisymmetric modes and the low-frequency regime.

Mazuruk, Konstantin

2003-01-01

321

Stability and Robustness Analysis of the AURORA Airship Control System using Dynamic Inversion

This paper presents a stability and robustness analysis of a nonlinear control system for the autonomous airship of the AURORA project. A Dynamic Inversion controller is implemented with desired dynamics given by a linear optimal compensator. The stability analysis of the nonlinear system is done applying Lyapunov’s stability theory. Robustness tests are performed in order to verify the nonlinear controller

Alexandra Moutinho; José R. Azinheira

2005-01-01

322

NASA Astrophysics Data System (ADS)

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 [

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

2004-05-01

323

Coarse-Grained Strategy for Modeling Protein Stability in Concentrated Solutions

We present a coarse-grained approach for modeling the thermodynamic stability of single-domain globular proteins in concentrated aqueous solutions. Our treatment derives effective protein-protein interactions from basic structural and energetic characteristics of the native and denatured states. These characteristics, along with the intrinsic (i.e., infinite dilution) thermodynamics of folding, are calculated from elementary sequence information using a heteropolymer collapse theory. We integrate this information into Reactive Canonical Monte Carlo simulations to investigate the connections between protein sequence hydrophobicity, protein-protein interactions, protein concentration, and the thermodynamic stability of the native state. The model predicts that sequence hydrophobicity can affect how protein concentration impacts native-state stability in solution. In particular, low hydrophobicity proteins are primarily stabilized by increases in protein concentration, whereas high hydrophobicity proteins exhibit richer nonmonotonic behavior. These trends appear qualitatively consistent with the available experimental data. Although factors such as pH, salt concentration, and protein charge are also important for protein stability, our analysis suggests that some of the nontrivial experimental trends may be driven by a competition between destabilizing hydrophobic protein-protein attractions and entropic crowding effects.

Cheung, Jason K.; Truskett, Thomas M.

2005-01-01

324

Transient stability analysis of ac-dc power systems

NASA Astrophysics Data System (ADS)

A non-linear model of a combined high-voltage ac-dc power system was digitally simulated. The model is used for the study and prediction of the effects of transient interactions between a high-voltage-direct-current (HVDC) transmission line and turbine-generator-shaft torsional behavior when the system is subjected to large disturbances. Improvement of a-c line loadability due to the stabilizing influence of a HVDC link was also examined. Turbine-generator torsional interaction studies were based on subsynchronous phenomena requiring an evaluation of the frequency, magnitude and decay of the subsynchronous currents in the ac-dc system following major system disturbances. The complex waveform of subsynchronous current, obtained by digital simulation, was analyzed using the Fast FOURIER Transform technique. Results demonstrate that a HVDC link can affect the incidence of turbine-generator torsionals, can significantly improve the stability of the system in general and can be used to effect increased loadability of the a-c lines.

Teshome, A.

1980-12-01

325

SOSlope 3D: implementing root reinforcement and preferential flow in slope stability modeling

NASA Astrophysics Data System (ADS)

The quantification of root reinforcement represents a key issue in different area of engineering (slope stability, soil protection, silviculture/tree stability, hydraulic). Between all the effects of plants (direct and indirect) on the physical and chemical soil processes, the mechanical effect of roots is considered particularly important for slope stability. The study of root reinforcement is faced with the high complexity of interactions of processes and factors at different spatio-temporal scales. In particular, the hierarchical spatial heterogeneity of vegetation and its effects on soil processes represent a big challenge for quantitative up-scaling methods. The objective of this contribution is to contextualize the complexity of the root-soil interactions in view of slope stability problems, to review the recent scientific contributions in the quantification of root reinforcement, and to discuss the practical meaning of recent research results. In the presentation of an up-scaling framework for the implementation of root reinforcement and preferential flow in slope stability analysis, the following arguments will be discussed: tensile force and pullout force of single roots, apparent elasticity of single roots, strain loading approach for the characterization of root bundle mechanics, meaning of root diameter distribution on root reinforcement, spatial heterogeneity of root distribution, hydro-mechanical and rheological properties of rooted soil under tension and compression, and triggering mechanism of shallow landslides. The above-mentioned factors and processes build up the modules implemented in a numerical model for slope stability calculations, the SOSlope model. The SOSlope model is characterized by the use of a spring-block framework (with 1x1 m cell grid), a strain step loading approach for the redistribution of forces, and the implementation of a spatial distribution of root at the hill slope scale. The results of simulations performed with the SOSlope model serve as background for the discussion on the role of root reinforcement for protection forests management and bioengineering applications.

Schwarz, M.; Cohen, D.

2013-12-01

326

Stability of a Resonant System of Conservation Laws Modeling Polymer Flow with Gravitation

NASA Astrophysics Data System (ADS)

We prove L1 uniqueness and stability for a resonant 2×2 system of conservation laws that arise as a model for two phase polymer flow in porous media. The analysis uses the equivalence of the Eulerian and Lagrangian formulation of this system, and the results are first established for an auxiliary scalar equation. Our methods are based on front tracking approximations for the auxiliary equation, and the Kružkov entropy condition for scalar conservation laws.

Klingenberg, Christian; Risebro, Nils Henrik

327

Modeling and Control of Combustion Dynamics in Lean-Premixed Swirl-Stabilized Combustors

A unified investigation, comprising both numerical simulation and analytical modeling, has been conducted to study the combustion dynamics in lean-premixed (LPM) swirl-stabilized combustors. The numerical analysis treats the conservation equations in three dimensions and takes into account finite-rate chemical reactions and variable thermophysical properties. Turbulence closure is achieved by means of a large-eddy simulation technique. Premixed turbulent combustion is treated

Ying Huang; Vigor Yang

2005-01-01

328

Direct Drive Synchronous Machine Models for Stability Assessment of Wind Farms

The increasing size of wind farms requires power system stability analysis including dynamic wind generator mod- els. For turbines above 1MW, doubly-fed induction machines are the most widely used concept. However, especially in Ger- many, direct-drive wind generators based on converter-driven syn- chronous generator concepts have reached considerable market penetration. This paper presents converter driven synchronous generator models of various

Sebastian Achilles

329

Global stability analysis of competitive neural networks under perturbations

NASA Astrophysics Data System (ADS)

We establish stability results for both competitive neural networks with only neural activity levels and also with different time-scales under parameter perturbations and determine conditions that ensure the existence of exponentially stable equilibria of the perturbed neural system. The perturbed neural system is modeled as nonlinear perturbations to a known nonlinear idealized system and is represented by both a short-term memory subsystem and also by a two time-scale subsystem. Based on the theory of sliding mode control, we can determine for the simple competitive model a reduced-order system and show that if it is asymptotically stable then the full system will also be asymptotically stable. In addition, a region of attraction can be found. For the two time-scales neural systems, we derive a Lyapunov function for the coupled system and a maximal upper bound for the fast time scale associated with the neural activity state.

Meyer-Baese, Anke; Ritter, Helge

2007-05-01

330

Dynamic pressure approach to analysis of reactor fuel plate stability

The dynamic pressure model can conveniently be used to evaluate the critical stress regions as a function of flow velocity. For some of the preliminary advanced neutron source reactor plate designs this could be very significant since the flow velocity could be limited by peak stresses in the plates more than by deflection or stability. The dynamic pressure results predicts the differential pressure across a plate as a function of flow velocity. The pressure differential can then be used to find the deflection and/or stress of the plate using traditional plate analyses. Instability would occur when plates are touching at mid-channel such that rapid oscillations of pressure can occur. The technique is conservative and gives a design limit for the plate. This model is one of several methods being used in the design of the ANS fuel elements. 10 refs., 4 figs.

Swinson, W.F.; Yahr, G.T.

1990-01-01

331

Some remarks to application of bifurcation analysis in BWR stability analysis

Currently, BWR stability analysis is most often performed by application of system codes which provide the time evolution of the neutron flux or thermal power at a defined operational point (OP) after imposing a system parameter perturbation. However, in general, it is impossible to understand the real stability state of the BWR at a specific OP by application of system code analysis alone. Hence, we are searching for methods developed in the nonlinear dynamics field in order to reveal the nature of the BWR stability states when power oscillations are observed. A powerful method is bifurcation analysis. In this paper, we will demonstrate an example of a possible BWR instability phenomenon, which can be understood only in nonlinear terms. (authors)

Lange, C.; Hennig, D.; Hurtado, A. [Dept. of Hydrogen and Nuclear Energy, Inst. of Power Engineering, Technische Universitaet Dresden (Germany)

2012-07-01

332

Reaction diffusion systems are often used to study pattern formation in biological systems. However, most methods for understanding their behavior are challenging and can rarely be applied to complex systems common in biological applications. I present a relatively simple and efficient, nonlinear stability technique that greatly aids such analysis when rates of diffusion are substantially different. This technique reduces a system of reaction diffusion equations to a system of ordinary differential equations tracking the evolution of a large amplitude, spatially localized perturbation of a homogeneous steady state. Stability properties of this system, determined using standard bifurcation techniques and software, describe both linear and nonlinear patterning regimes of the reaction diffusion system. I describe the class of systems this method can be applied to and demonstrate its application. Analysis of Schnakenberg and substrate inhibition models is performed to demonstrate the methods capabilities in simplified settings and show that even these simple models have nonlinear patterning regimes not previously detected. The real power of this technique, however, is its simplicity and applicability to larger complex systems where other nonlinear methods become intractable. This is demonstrated through analysis of a chemotaxis regulatory network comprised of interacting proteins and phospholipids. In each case, predictions of this method are verified against results of numerical simulation, linear stability, asymptotic, and/or full PDE bifurcation analyses. PMID:24158538

Holmes, William R

2014-01-01

333

NASA Technical Reports Server (NTRS)

The atmospheric ionizing radiation (AIR) ER-2 preflight analysis, one of the first attempts to obtain a relatively complete measurement set of the high-altitude radiation level environment, is described in this paper. The primary thrust is to characterize the atmospheric radiation and to define dose levels at high-altitude flight. A secondary thrust is to develop and validate dosimetric techniques and monitoring devices for protecting aircrews. With a few chosen routes, we can measure the experimental results and validate the AIR model predictions. Eventually, as more measurements are made, we gain more understanding about the hazardous radiation environment and acquire more confidence in the prediction models.

Tai, H.; Wilson, J. W.; Maiden, D. L.

2003-01-01

334

Genome-wide analysis of long noncoding RNA stability

Transcriptomic analyses have identified tens of thousands of intergenic, intronic, and cis-antisense long noncoding RNAs (lncRNAs) that are expressed from mammalian genomes. Despite progress in functional characterization, little is known about the post-transcriptional regulation of lncRNAs and their half-lives. Although many are easily detectable by a variety of techniques, it has been assumed that lncRNAs are generally unstable, but this has not been examined genome-wide. Utilizing a custom noncoding RNA array, we determined the half-lives of ?800 lncRNAs and ?12,000 mRNAs in the mouse Neuro-2a cell line. We find only a minority of lncRNAs are unstable. LncRNA half-lives vary over a wide range, comparable to, although on average less than, that of mRNAs, suggestive of complex metabolism and widespread functionality. Combining half-lives with comprehensive lncRNA annotations identified hundreds of unstable (half-life < 2 h) intergenic, cis-antisense, and intronic lncRNAs, as well as lncRNAs showing extreme stability (half-life > 16 h). Analysis of lncRNA features revealed that intergenic and cis-antisense RNAs are more stable than those derived from introns, as are spliced lncRNAs compared to unspliced (single exon) transcripts. Subcellular localization of lncRNAs indicated widespread trafficking to different cellular locations, with nuclear-localized lncRNAs more likely to be unstable. Surprisingly, one of the least stable lncRNAs is the well-characterized paraspeckle RNA Neat1, suggesting Neat1 instability contributes to the dynamic nature of this subnuclear domain. We have created an online interactive resource (http://stability.matticklab.com) that allows easy navigation of lncRNA and mRNA stability profiles and provides a comprehensive annotation of ?7200 mouse lncRNAs.

Clark, Michael B.; Johnston, Rebecca L.; Inostroza-Ponta, Mario; Fox, Archa H.; Fortini, Ellen; Moscato, Pablo; Dinger, Marcel E.; Mattick, John S.

2012-01-01

335

The simplest walking model: stability, complexity, and scaling.

We demonstrate that an irreducibly simple, uncontrolled, two-dimensional, two-link model, vaguely resembling human legs, can walk down a shallow slope, powered only by gravity. This model is the simplest special case of the passive-dynamic models pioneered by McGeer (1990a). It has two rigid massless legs hinged at the hip, a point-mass at the hip, and infinitesimal point-masses at the feet. The feet have plastic (no-slip, no-bounce) collisions with the slope surface, except during forward swinging, when geometric interference (foot scuffing) is ignored. After nondimensionalizing the governing equations, the model has only one free parameter, the ramp slope gamma. This model shows stable walking modes similar to more elaborate models, but allows some use of analytic methods to study its dynamics. The analytic calculations find initial conditions and stability estimates for period-one gait limit cycles. The model exhibits two period-one gait cycles, one of which is stable when 0 < gamma < 0.015 rad. With increasing gamma, stable cycles of higher periods appear, and the walking-like motions apparently become chaotic through a sequence of period doublings. Scaling laws for the model predict that walking speed is proportional to stance angle, stance angle is proportional to gamma 1/3, and that the gravitational power used is proportional to v4 where v is the velocity along the slope. PMID:10412391

Garcia, M; Chatterjee, A; Ruina, A; Coleman, M

1998-04-01

336

Models of cuspy triaxial stellar systems - I. Stability and chaoticity

NASA Astrophysics Data System (ADS)

We used the N-body code of Hernquist & Ostriker to build a dozen cuspy (?? 1) triaxial models of stellar systems through dissipationless collapses of initially spherical distributions of 106 particles. We chose four sets of initial conditions that resulted in models morphologically resembling E2, E3, E4 and E5 galaxies, respectively. Within each set, three different seed numbers were selected for the random number generator used to create the initial conditions, so that the three models of each set are statistically equivalent. We checked the stability of our models using the values of their central densities and of their moments of inertia, which turned out to be very constant indeed. The changes of those values were all less than 3 per cent over one Hubble time and, moreover, we show that the most likely cause of those changes are relaxation effects in the numerical code. We computed the six Lyapunov exponents of nearly 5000 orbits in each model in order to recognize regular, partially and fully chaotic orbits. All the models turned out to be highly chaotic, with less than 25 per cent of their orbits being regular. We conclude that it is quite possible to obtain cuspy triaxial stellar models that contain large fractions of chaotic orbits and are highly stable. The difficulty in building such models with the method of Schwarzschild should be attributed to the method itself and not to physical causes.

Zorzi, A. F.; Muzzio, J. C.

2012-06-01

337

Stability of model flocks in turbulent-like flow

NASA Astrophysics Data System (ADS)

We report numerical simulations of a simple model of flocking particles in the presence of an uncertain background environment. We consider two types of environmental perturbations: random noise applied separately to each particle, and spatiotemporally correlated ‘noise’ provided by a turbulent-like flow field. The effects of these two types of noise are very different; surprisingly, the applied flow field tends to destroy the global order of the flocking model even for vanishingly small flow amplitudes. Local order, however, is preserved in smaller sub-flocks, although their composition changes dynamically. Our results suggest that realistic perturbations must be considered in assessing the stability of models of collective animal behavior, and that random noise is not a sufficient proxy.

Khurana, Nidhi; Ouellette, Nicholas T.

2013-09-01

338

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. PMID:23004000

Camporeale, Carlo; Ridolfi, Luca

2012-06-01

339

A minimal model for stabilization of biomolecules by hydrocarbon cross-linking.

Programmed cell death regulating protein motifs play an essential role in the development of an organism, its immune response, and disease-related cellular mechanisms. Among those motifs the BH3 domain of the BCL-2 family is found to be of crucial importance. Recent experiments showed how the isolated, otherwise unstructured BH3 peptide can be modified by a hydrocarbon linkage to regain function. We parametrized a reduced, dynamic model for the stability effects of such covalent cross-linking and confirmed that the model reproduces the reinforcement of the structural stability of the BH3 motif by cross-linking. We show that an analytically solvable model for thermostability around the native state is not capable of reproducing the stabilization effect. This points to the crucial importance of the peptide dynamics and the fluctuations neglected in the analytic model for the cross-linking system to function properly. This conclusion is supported by a thorough analysis of a simulated Go model. The resulting model is suitable for rational design of generic cross-linking systems in silicio. PMID:16674170

Hamacher, K; Hübsch, A; McCammon, J A

2006-04-28

340

A minimal model for stabilization of biomolecules by hydrocarbon cross-linking

NASA Astrophysics Data System (ADS)

Programmed cell death regulating protein motifs play an essential role in the development of an organism, its immune response, and disease-related cellular mechanisms. Among those motifs the BH3 domain of the BCL-2 family is found to be of crucial importance. Recent experiments showed how the isolated, otherwise unstructured BH3 peptide can be modified by a hydrocarbon linkage to regain function. We parametrized a reduced, dynamic model for the stability effects of such covalent cross-linking and confirmed that the model reproduces the reinforcement of the structural stability of the BH3 motif by cross-linking. We show that an analytically solvable model for thermostability around the native state is not capable of reproducing the stabilization effect. This points to the crucial importance of the peptide dynamics and the fluctuations neglected in the analytic model for the cross-linking system to function properly. This conclusion is supported by a thorough analysis of a simulated Go model. The resulting model is suitable for rational design of generic cross-linking systems in silicio.

Hamacher, K.; Hübsch, A.; McCammon, J. A.

2006-04-01

341

Thermal stability during rotation in space - A scaling and numerical analysis

NASA Technical Reports Server (NTRS)

An analysis of thermal stability in a fluid during rotation is presented. The conditions resulting in thermal stability are examined and numerically verified. It is shown that at least one thermal field exists for any rotating fluid, with or without a gravitational background field, where convection does not occur. The numerical model used is fully nonlinear and 3D. Results are presented on the basis of both steady-state and fully transient models. The thermally stable condition is further investigated in the context of the average net acceleration and the inhomogeneous part of the acceleration field (gradient of acceleration). It is shown that in the thermally stable condition the flow that would result from the average net acceleration is equal and opposite to the flow that would result from the inhomogeneous part of the acceleration field. It is concluded that the thermally stable condition is actually a flow mode transition at Ad = 1.

Arnold, William A.; Regel, Liya L.; Wilcox, William R.

1992-01-01

342

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.

Densmore, Jeffery D [Los Alamos National Laboratory; Warsa, James S [Los Alamos National Laboratory; Lowrie, Robert B [Los Alamos National Laboratory; Morel, Jim E [TEXAS A& M UNIV

2008-01-01

343

Absolute Stability Analysis of a Phase Plane Controlled Spacecraft

NASA Technical Reports Server (NTRS)

Many aerospace attitude control systems utilize phase plane control schemes that include nonlinear elements such as dead zone and ideal relay. To evaluate phase plane control robustness, stability margin prediction methods must be developed. Absolute stability is extended to predict stability margins and to define an abort condition. A constrained optimization approach is also used to design flex filters for roll control. The design goal is to optimize vehicle tracking performance while maintaining adequate stability margins. Absolute stability is shown to provide satisfactory stability constraints for the optimization.

Jang, Jiann-Woei; Plummer, Michael; Bedrossian, Nazareth; Hall, Charles; Jackson, Mark; Spanos, Pol

2010-01-01

344

Power system stability enhancement employing controllers based on a versatile modeling

NASA Astrophysics Data System (ADS)

Rapid advances in power electronics have made it both practicable and economic to design powerful thyristor-controlled devices, such as Flexible AC Transmission Systems (FACTS), for stability enhancements. The discrepancies of existing modeling approaches have limited the feasibility of handling these devices or designing its damping controller. In this thesis, a versatile and generalized approach to model standard power system components is proposed. The more systematic and realistic representation, accompanied by the development of powerful eigenvalue-analysis techniques, facilitates the study of small signal stability (monotonic and oscillatory) of the power systems. In monotonic stability study, the effect of exciter and governor is critically reviewed based on the exploitation of eigenvalues, modal and sensitivity analyses over a wide range of operating conditions. In oscillatory stability study, a common FACTS device, the static var compensator (SVC), is used to improve system damping. This study reveals the inadequacy of many conventional methodologies in SVC design since they have ignored (or cannot handle) some important factors such as SVC mode instability and robustness of the power system. Two approaches, combined sensitivities and Hinfinity algorithms, are introduced to solve these limitations. Finally, an extended Hinfinity algorithm, which is applied to PSS design and successfully solves certain limitations of the existing H infinity based PSS design, is also presented. Although these studies are developed on selected controller devices or typical systems for convenience of discussion, extension to more complex systems can be dealt with in a similar way because of the versatility of the proposed modeling methodology.

Chung, Chi Yung

345

Stability Analysis of Resistive Wall Mode in Rotating High-beta Plasmas in DIII-D

NASA Astrophysics Data System (ADS)

Stability of resistive wall modes (RWM) in rotating high beta DIII-D discharges is analyzed using the MARS-F code. The modes are calculated in axisymmetric toroidal equilibrium using the MHD plasma model with kinetic damping effects. RWM are analyzed for different spacing between the resistive wall and the plasma boundary and for different toroidal rotation profiles. Sensitivity study of the mode's stability on the plasma edge q-profile is made by varying both the edge current profile and the proximity of the plasma boundary to the real X-point geometry. The importance of the edge modeling on accurate RWM stability analysis is revisited. Scans of the mode's growth rate and frequency are made in these settings, and the mode's structure is explored. Quasilinear toroidal torque driven by jxB force due to current and magnetic field perturbations in the RWM is estimated and compared with the experimental estimate of the total toroidal torque on plasma. The dependencies of the RWM growth rate and frequency on the stability and torque parameters are presented.

Svidzinski, V. A.; in, Y.; Kim, J. S.; Chu, M. S.; Liu, Y. Q.

2011-11-01

346

Hilbert-Huang transformation: application to postural stability analysis.

The aim objective of this paper is the analysis of the Centre Of Pressure (COP) time series by the means of the Hilbert Huang Transformation (HHT). The HHT consists of extracting the Intrinsic Mode Functions (IMFs) from an Empirical Mode Decomposition (EMD), and then applying the Hilbert Transformation on the IMFs. The trace of the HHT in the complex plane has a circular form, with each IMF having its own rotation frequency. The area of the circle represents a possible indicator of the postural stability status of the subjects. Experimental results show the effectiveness of the area of this circle in order to identify the post-vibratory effects on standing posture in healthy adult subjects. PMID:18002268

Amoud, Hassan; Snoussi, Hichem; Hewson, David J; Duchêne, Jacques

2007-01-01

347

Coupled three-dimensional aeroelastic stability analysis of bladed disks

In the present work an algorithm for the coupled aeromechanical computation of three-dimensional compressor cascades vibrating in a traveling-wave mode is presented and applied to the determination of aeroelastic stability of a transonic fan rotor. The initial vibratory modes are computed using a finite-element structural analysis code. The unsteady flow field response to blade vibration is estimated by numerical integration of the three-dimensional unsteady Euler equations. Coupling relations are formulated in the frequency domain, using a mode-modification technique, based on modal projection. The vibratory mode is updated at the end of the aerodynamic simulation of each period, and the updated mode is used for the simulation of the next period. A number of results illustrate the method's potential.

Gerolymos, G.A. (Univ. Pierre and Marie Curie, Paris (France))

1993-10-01

348

Stability Analysis of the Planetary System Orbiting Upsilon Andromedae

NASA Technical Reports Server (NTRS)

We present results of long-term numerical orbital integrations designed to test the stability of the three-planet system orbiting Upsilon Andromedae and short-term integrations to test whether mutual perturbations among the planets can be used to determine planetary masses. Our initial conditions are based on the latest fits to the radial velocity data obtained by the planet-search group at Lick Observatory. The new fits result in significantly more stable systems than did the initially announced planetary parameters. An analytic analysis of the star and the two outer planets shows that this subsystem is Hill stable up to five. Our integrations involving all three planets show that the system is stable for at least 100 Myr for up to four. In our simulations, we still see a secular resonance between the outer two planets and in some cases large oscillations in the eccentricity of the inner planet.

Lissauer, Jack J.; Rivera, Eugenio J.; DeVincenzi, Donald (Technical Monitor)

2000-01-01

349

NASA Astrophysics Data System (ADS)

The aim of this work was to understand and reproduce the hydrological dynamics of a slope, which was terraced using dry-stone retaining walls and its response to these processes in terms of stability at the slope scale. The slope studied is located in Valtellina (northern Italy), near the village of Tresenda, and in the last 30 yr has experienced several soil slip/debris flow events. In 1983 alone, such events caused the death of 18 people. Direct observation of the events of 1983 enabled the principal triggering cause of these events to be recognized in the formation of an overpressure at the base of a dry-stone wall, which caused its failure. To perform the analyses it is necessary to include the presence of dry-stone walls, considering the importance they have in influencing hydrological and geotechnical processes at the slope scale. This requires a very high resolution DEM (1 m × 1 m because the walls are from 0.60 m to 1.0 m wide) that has been appositely derived. A hydrogeological raster-based model, which takes into account both the unsaturated and saturated flux components, was applied. This was able to identify preferential infiltration zones and was rather precise in the prediction of maximum groundwater levels, providing valid input for the distributed stability analysis. Results of the hydrogeological model were used for the successive stability analysis. Sections of terrace were identified from the downslope base of a retaining wall to the top of the next downslope retaining wall. Within each section a global method of equilibrium was applied to determine its safety factor. The stability model showed a general tendency to overestimate the amount of unstable areas. An investigation of the causes of this unexpected behavior was, therefore, also performed in order to progressively improve the reliability of the model.

Camera, C.; Apuani, T.; Masetti, M.

2013-02-01

350

Thermal stability and modeling of lithium ion batteries

NASA Astrophysics Data System (ADS)

First-principles mathematical models were developed to examine the effect of the lithium-lithium ion interactions inside the anode particles on the performance of a lithium foil cell. Two different models were developed: the chemical potential model (CPM) that includes the lithium-lithium ion interactions inside the anode particles and the diffusion model (DIM) that does not include the interactions. Significant differences in the thermal and electrochemical performance of the cell were observed between the two approaches. The temperature of the cell predicted by the DFM is higher than the one predicted by the CPM at a given capacity. The discharge time of the cell predicted by the DFM is shorter than the one predicted by the CPM. The results indicate that the cell needs to be modeled using the CPM approach especially at high discharge rates. An evaluation of the numerical techniques, control volume formulation (CVF) and finite difference method (FDM), used for the models was performed. It is shown that the truncation error is the same for both methods when the boundary conditions are of the Dirichlet type, the system of equations are linear and represented in Cartesian coordinates. A new technique to analyze the accuracy of the methods is presented. The only disadvantage of the FDM is that it failed to conserve mass for a small number of nodes when both boundary conditions include a derivative term whereas the CVF did conserve mass for these cases. However, for a large number of nodes the FDM provides mass conservation. It is important to note that the CVF has only (DeltaX) order of accuracy for a Neumann type boundary condition whereas the FDM has (DeltaX) 2 order. The second topic of this dissertation presents a study of the thermal stability of LiPF6 EC:EMC electrolyte for lithium ion batteries. A differential scanning calorimeter (DSC) was used to perform the study of the electrolyte. For first time, the effect of different variables on its thermal stability was evaluated: salt and solvents concentrations, heating rates, water presence, and oxygen presence. The results indicate that all these variables play an important role in the thermal stability of this electrolyte.

Botte, Gerardine Gabriela

2000-10-01

351

Extensions to the time lag models for practical application to rocket engine stability design

NASA Astrophysics Data System (ADS)

The combustion instability problem in liquid-propellant rocket engines (LREs) has remained a tremendous challenge since their discovery in the 1930s. Improvements are usually made in solving the combustion instability problem primarily using computational fluid dynamics (CFD) and also by testing demonstrator engines. Another approach is to use analytical models. Analytical models can be used such that design, redesign, or improvement of an engine system is feasible in a relatively short period of time. Improvements to the analytical models can greatly aid in design efforts. A thorough literature review is first conducted on liquid-propellant rocket engine (LRE) throttling. Throttling is usually studied in terms of vehicle descent or ballistic missile control however there are many other cases where throttling is important. It was found that combustion instabilities are one of a few major issues that occur during deep throttling (other major issues are heat transfer concerns, performance loss, and pump dynamics). In the past and again recently, gas injected into liquid propellants has shown to be a viable solution to throttle engines and to eliminate some forms of combustion instability. This review uncovered a clever solution that was used to eliminate a chug instability in the Common Extensible Cryogenic Engine (CECE), a modified RL10 engine. A separate review was also conducted on classic time lag combustion instability models. Several new stability models are developed by incorporating important features to the classic and contemporary models, which are commonly used in the aerospace rocket industry. The first two models are extensions of the original Crocco and Cheng concentrated combustion model with feed system contributions. A third new model is an extension to the Wenzel and Szuch double-time lag model also with feed system contributions. The first new model incorporates the appropriate injector acoustic boundary condition which is neglected in contemporary models. This new feature shows that the injector boundary can play a significant role for combustion stability, especially for gaseous injection systems or a system with an injector orifice on the order of the size of the chamber. The second new model additionally accounts for resistive effects. Advanced signal analysis techniques are used to extract frequency-dependent damping from a gas generator component data set. The damping values are then used in the new stability model to more accurately represent the chamber response of the component. The results show a more realistic representation of stability margin by incorporating the appropriate damping effects into the chamber response from data. The original Crocco model, a contemporary model, and the two new models are all compared and contrasted to a marginally stable test case showing their applicability. The model that incorporates resistive aspects shows the best comparison to the test data. Parametrics are also examined to show the influence of the new features and their applicability. The new features allow a more accurate representation of stability margin to be obtained. The third new model is an extension to the Wenzel and Szuch double-time lag chug model. The feed system chug model is extended to account for generic propellant flow rates. This model is also extended to incorporate aspects due to oxygen boiling and helium injection in the feed system. The solutions to the classic models, for the single-time lag and the double-time lag models, are often plotted on a practical engine operating map, however the models have presented some difficulties for numerical algorithms for several reasons. Closed-form solutions for use on these practical operating maps are formulated and developed. These models are incorporated in a graphical user interface tool and the new model is compared to an extensive data set. It correctly predicts the stability behavior at various operating conditions incorporating the influence of injected helium and boiling oxygen in the feed system.

Casiano, Matthew J.

352

Quantitative analysis of the ion-dependent folding stability of DNA triplexes

NASA Astrophysics Data System (ADS)

A DNA triplex is formed through binding of a third strand to the major groove of a duplex. Due to the high charge density of a DNA triplex, metal ions are critical for its stability. We recently developed the tightly bound ion (TBI) model for ion-nucleic acids interactions. The model accounts for the potential correlation and fluctuations of the ion distribution. We now apply the TBI model to analyze the ion dependence of the thermodynamic stability for DNA triplexes. We focus on two experimentally studied systems: a 24-base DNA triplex and a pair of interacting 14-base triplexes. Our theoretical calculations for the number of bound ions indicate that the TBI model provides improved predictions for the number of bound ions than the classical Poisson-Boltzmann (PB) equation. The improvement is more significant for a triplex, which has a higher charge density than a duplex. This is possibly due to the higher ion concentration around the triplex and hence a stronger ion correlation effect for a triplex. In addition, our analysis for the free energy landscape for a pair of 14-mer triplexes immersed in an ionic solution shows that divalent ions could induce an attractive force between the triplexes. Furthermore, we investigate how the protonated cytosines in the triplexes affect the stability of the triplex helices.

Chen, Gengsheng; Chen, Shi-Jie

2011-12-01

353

Numerical modeling of a vortex stabilized arcjet thruster

NASA Technical Reports Server (NTRS)

A numerical method to solve the equations governing a vortex stabilized arcjet thruster is being developed. The model will allow the effects of swirling flow and geometry on arcjet thruster performance to be determined. The propellant flow equations, i.e., the axisymmetric, thin layer, Navier-Stokes equations, are solved using a Gauss-Siedel line-relaxation procedure. An implicit FTCS method is used to solve the electromagnetic field equations. A grid generation scheme was developed for an arbitrary arcjet geometry. The model will allow the radial and axial components of velocity and current distributions to be determined from a region upstream of the cathode, through the constrictor, to the exit plane of the nozzle.

Keith, Theo G., Jr.; Pawlas, Gary E.

1989-01-01

354

A multiloop generalization of the circle criterion for stability margin analysis

NASA Technical Reports Server (NTRS)

In order to provide a theoretical tool suited for characterizing the stability margins of multiloop feedback systems, multiloop input-output stability results generalizing the circle stability criterion are considered. Generalized conic sectors with 'centers' and 'radii' determined by linear dynamical operators are employed to specify the stability margins as a frequency dependent convex set of modeling errors (including nonlinearities, gain variations and phase variations) which the system must be able to tolerate in each feedback loop without instability. The resulting stability criterion gives sufficient conditions for closed loop stability in the presence of frequency dependent modeling errors, even when the modeling errors occur simultaneously in all loops. The stability conditions yield an easily interpreted scalar measure of the amount by which a multiloop system exceeds, or falls short of, its stability margin specifications.

Safonov, M. G.; Athans, M.

1979-01-01

355

Suraiya Yasmin. 2007. Evaluation of Promising Wheat Genotypes by the Stability Analysis through Parametric and Non-Parametric Methods. Int. J. Sustain. Crop Prod. 2(3): 9-16 The purpose of the present study was to compare between the application of Non Parametric Stability Analysis (NPSA) and Parametric Stability Analysis (PSA) with appropriate tests in addition to utilization of exact size -? test in

SURAIYA YASMIN

356

Stability Analysis of Superhydrophobic Friction Reduction Polymeric Microchannels

NASA Astrophysics Data System (ADS)

Superhydrophobic surfaces are surfaces where fluid contact angle is larger than 150^o. Superhydrophobic states which allow water droplets to fall off at low sliding angles are termed as Cassie state. It is widely known that drag/friction reduction is closely related to liquid under Cassie state, and studies have been widely performed to achieve such effects. Our research goal is to develop superhydrophobic microfluidic channels with trenches on the side walls and observe the stability of the air pockets formed within these trenches. We have prepared PDMS(poly-dimethylsiloxane) substrates with different trench aspect ratio of 1:1, 1:2, 1:500 and 1:3000. As the aspect ratio of the trench decreases, the pressure in the air pockets tends to resist wetting. However, once penetration of the water into the air pocket occurred, the shallow trenches were wetted in a rapid fashion while the deep trenches were wetted at a slower rate. A compression model of the air pockets as a function of pressure difference and volume change of the air pockets was also developed. In the theoretical model, the air in the pockets is assumed to be an ideal gas. This model was compared and validated against the experimental results.

Kim, Tae Jin; Hidrovo, Carlos

2010-11-01

357

Stability analysis of multiple-robot control systems

NASA Technical Reports Server (NTRS)

In a space telerobotic service scenario, cooperative motion and force control of multiple robot arms are of fundamental importance. Three paradigms to study this problem are proposed. They are distinguished by the set of variables used for control design. They are joint torques, arm tip force vectors, and an accelerated generalized coordinate set. Control issues related to each case are discussed. The latter two choices require complete model information, which presents practical modeling, computational, and robustness problems. Therefore, focus is on the joint torque control case to develop relatively model independent motion and internal force control laws. The rigid body assumption allows the motion and force control problems to be independently addressed. By using an energy motivated Lyapunov function, a simple proportional derivative plus gravity compensation type of motion control law is always shown to be stabilizing. The asymptotic convergence of the tracing error to zero requires the use of a generalized coordinate with the contact constraints taken into account. If a non-generalized coordinate is used, only convergence to a steady state manifold can be concluded. For the force control, both feedforward and feedback schemes are analyzed. The feedback control, if proper care has been taken, exhibits better robustness and transient performance.

Wen, John T.; Kreutz, Kenneth

1989-01-01

358

Stability analysis of jump-linear systems driven by finite-state machines with Markovian inputs

NASA Astrophysics Data System (ADS)

A control system with a fault recovery mechanism in the feedback loop and with faults occurring in a non-deterministic manner can be modeled as a class of hybrid systems, i.e., a dynamical system switched by a finite-state machine or an automaton. When the plant and controller are linear, such a system can be modeled as a jump-linear system driven by a finite-state machine with a random input process. Such fault recovery mechanisms are found in flight control systems and distributed control systems with communication networks. In these critical applications, closed-loop stability of the system in the presence of fault recoveries becomes an important issue. Finite-state machines as mathematical constructs are widely used by computer scientists to model and analyze algorithms. In particular, fault recovery mechanisms that are implemented in hardware with logic based circuits and finite memory can be modeled appropriately with finite-state machines. In this thesis, mathematical tools are developed to determine the mean-square stability of a closed-loop system, modeled as a jump-linear system in series with a finite-state machine driven by a random process. The random input process is in general assumed to be any r-th order Markov process, where r ? 0. While stability tests for a jump-linear system with a Markovian switching rule are well known, the main contribution of the present work arises from the fact that output of a finite-state machine driven by a Markov process is in general not Markovian. Therefore, new stability analysis tools are provided for this class of systems and demonstrated through Monte Carlo simulations.

Patilkulkarni, Sudarshan S.

359

Stability analysis of dispersion-managed solitons controlled by synchronous amplitude modulators

The stability of time-domain transmission control of dispersion-managed (DM) solitons is studied. We show by a linear stability analysis that appropriate positioning of synchronous amplitude modulators in the dispersion map can stabilize the propagation of DM solitons without simultaneous use of bandpass filters when the pulse energy is sufficiently large. It is also shown that the frequency chirp of the

Suttawassuntorn Waiyapot; Masayuki Matsumoto

1999-01-01

360

Quantitative measurement of stability in human gait through computer simulation and Floquet analysis

The purpose of this investigation was to develop and test quantitative measures to assess the dynamic stability of human locomotion in normal and pathologic gait. Through computer simulation the stability of joint trajectories were specified under a variety of conditions. The resulting joint trajectory time series data were used to calculate the overall stability of the walking using Floquet analysis.

A. Scheiner; D. C. Ferencz; Howard J. Chizeck

1995-01-01

361

Modal Voltage Stability Analysis of Multi-infeed HVDC System Considering its Control Systems

NASA Astrophysics Data System (ADS)

This work presents a method for investigating the voltage stability of multi-infeed HVDC systems, which is based on the eigenvalue decomposition technique known as modal analysis. In this method, the eigenvalue of linearized steady-state system power-voltage equations are computed to evaluate the long-term voltage stability. The contributions of this work to modal analysis method are control systems of HVDC system, such as an Automatic Power Regulator (APR) and an Automatic (DC) Current Regulator (ACR) on its rectifier side and a changeover between an Automatic (DC) Voltage Regulator (AVR) and an Automatic extinction advance angle Regulator (A?R) modes on its inverter side, were taken into account, and the formularization for modal analysis considering not only these control systems of HVDC system but also generator and load characteristics was fulfilled and presented in this paper. The application results from an AC/DC model power system with dual HVDC systems verified the efficiency of the proposed method and quantitatively illustrated the influence of control systems of HVDC system on AC/DC system long-term voltage stability.

Wu, Guohong; Minakawa, Tamotsu; Hayashi, Toshiyuki

362

Stabilizing control for a pulsatile cardiovascular mathematical model.

In this paper, we develop a pulsatile model for the cardiovascular system which describes the reaction of this system to a submaximal constant workload imposed on a person at a bicycle ergometer test after a period of rest. Furthermore, the model should allow to use measurements for the pulsatile pressure in fingertips which provide information on the diastolic and the systolic pressure for parameter estimation. Based on the assumption that the baroreceptor loop is the essential control loop in this case, we design a stabilizing feedback control for the pulsatile model which is obtained by solving a linear-quadratic regulator problem for the linearization of a non-pulsatile counterpart of the pulsatile model. We also investigate the behavior of the model with respect to changes in the weight of the term in the cost functional for the linear-quadratic regulator problem which penalizes the deviation of the momentary pressure in the aorta from the pressure at the stationary situation which should be obtained. PMID:24789569

de Los Reyes, Aurelio A; Jung, Eunok; Kappel, Franz

2014-06-01

363

Proton stability and light Z' inspired by string derived models

Proton stability is one of the most perplexing puzzles in particle physics. While the renormalizable standard model forbids proton decay mediating operators due to accidental global symmetries, many of its extensions introduce such dimension four, five and six operators. Furthermore, it is, in general, expected that quantum gravity only respects local gauge, or discreet, symmetries. String theory provides the arena to study particle physics in a consistent framework of perturbative quantum gravity. An appealing proposition, in this context, is that the dangerous operators are suppressed by an Abelian gauge symmetry, which is broken near the TeV scale. A viable U(1) symmetry should also be anomaly free, be family universal, and allow the generation of fermion masses via the Higgs mechanism. We discuss such U(1) symmetries that arise in quasirealistic free fermionic heterotic-string derived models. Ensuring that the U(1) symmetry is anomaly free at the low scale requires that the standard model spectrum is augmented by additional states that are compatible with the charge assignments in the string models. We construct such string-inspired models and discuss some of their phenomenological implications.

Faraggi, Alon E.; Mehta, Viraf M. [Department of Mathematical Sciences, University of Liverpool, Liverpool, L69 7ZL (United Kingdom)

2011-10-15

364

The Savannah River Remediation (SRR) Organization requested that Savannah River National Laboratory (SRNL) develop a Computational Fluid Dynamics (CFD) method to mix and blend the miscible contents of the blend tanks to ensure the contents are properly blended before they are transferred from the blend tank; such as, Tank 50H, to the Salt Waste Processing Facility (SWPF) feed tank. The work described here consists of two modeling areas. They are the mixing modeling analysis during miscible liquid blending operation, and the flow pattern analysis during transfer operation of the blended liquid. The transient CFD governing equations consisting of three momentum equations, one mass balance, two turbulence transport equations for kinetic energy and dissipation rate, and one species transport were solved by an iterative technique until the species concentrations of tank fluid were in equilibrium. The steady-state flow solutions for the entire tank fluid were used for flow pattern analysis, for velocity scaling analysis, and the initial conditions for transient blending calculations. A series of the modeling calculations were performed to estimate the blending times for various jet flow conditions, and to investigate the impact of the cooling coils on the blending time of the tank contents. The modeling results were benchmarked against the pilot scale test results. All of the flow and mixing models were performed with the nozzles installed at the mid-elevation, and parallel to the tank wall. From the CFD modeling calculations, the main results are summarized as follows: (1) The benchmark analyses for the CFD flow velocity and blending models demonstrate their consistency with Engineering Development Laboratory (EDL) and literature test results in terms of local velocity measurements and experimental observations. Thus, an application of the established criterion to SRS full scale tank will provide a better, physically-based estimate of the required mixing time, and elevation of transfer pump for minimum sludge disturbance. (2) An empirical equation for a tank with no cooling coils agrees reasonably with the current modeling results for the dual jet. (3) From the sensitivity study of the cooling coils, it was found that the tank mixing time for the coiled tank was about two times longer than that of the tank fluid with no coils under the 1/10th scale, while the coiled tank required only 50% longer than the one without coils under the full scale Tank 50H. In addition, the time difference is reduced when the pumping U{sub o}d{sub o} value is increased for a given tank. (4) The blending time for T-shape dual jet pump is about 20% longer than that of 15{sup o} upward V-shape pump under the 1/10th pilot-scale tank, while the time difference between the two pumps is about 12% for the full-scale Tank 50H. These results are consistent with the literature information. (5) A transfer pump with a solid-plate suction screen operating at 130 gpm can be located 9.5 inches above settled sludge for 2 in screen height in a 85 ft waste tank without disturbing any sludge. Detailed results are summarized in Table 13. Final pump performance calculations were made by using the established CW pump design, and operating conditions to satisfy the two requirements of minimum sludge disturbance, and adequate blending of tank contents. The final calculation results show that the blending times for the coiled and uncoiled tanks coupled with the CW pump design are 159 and 83 minutes, respectively. All the results are provided in Table 16.

Lee, S.

2011-05-05

365

Stability of the thermohaline circulation in a coupled ocean-atmosphere general circulation model.

National Technical Information Service (NTIS)

The stability of the Atlantic thermohaline circulation against meltwater input is investigated in a coupled ocean-atmosphere general circulation model. We identify four main feedbacks affecting the stability of the thermohaline circulation: the change in ...

A. Schiller U. Mikolajewicz R. Voss

1996-01-01

366

Nonlinear stability analysis of a regular vortex pentagon outside a circle

NASA Astrophysics Data System (ADS)

A nonlinear stability analysis of the stationary rotation of a system of five identical point vortices lying uniformly on a circle of radius R 0 outside a circular domain of radius R is performed. The problem is reduced to the problem of stability of an equilibrium position of a Hamiltonian system with a cyclic variable. The stability of stationary motion is interpreted as Routh stability. Conditions for stability, formal stability and instability are obtained depending on the values of the parameter q = R 2/ R {0/2}.

Kurakin, Leonid G.; Ostrovskaya, Irina V.

2012-09-01

367

Stability Switches in a Host-Pathogen Model as the Length of a Time Delay Increases

NASA Astrophysics Data System (ADS)

The destabilising effects of a time delay in mathematical models are well known. However, delays are not necessarily destabilising. In this paper, we explore an example of a biological system where a time delay can be both stabilising and destabilising. This example is a host-pathogen model, incorporating density-dependent prophylaxis (DDP). DDP describes when individual hosts invest more in immunity when population densities are high, due to the increased risk of infection in crowded conditions. In this system, as the delay length increases, there are a finite number of switches between stable and unstable behaviour. These stability switches are demonstrated and characterised using a combination of numerical methods and analysis.

Reynolds, Jennifer J. H.; Sherratt, Jonathan A.; White, Andrew

2013-12-01

368

Stability of haematological parameters and its relevance on the athlete's biological passport model.

The stability of haematological parameters is crucial to guarantee accurate and reliable data for implementing and interpreting the athlete's biological passport (ABP). In this model, the values of haemoglobin, reticulocytes and out-of-doping period (OFF)-score (Hb-60?Ret) are used to monitor the possible variations of those parameters, and also to compare the thresholds developed by the statistical model for the single athlete on the basis of its personal values and the variance of parameters in the modal group. Nevertheless, a critical review of the current scientific literature dealing with the stability of the haematological parameters included in the ABP programme, and which are used for evaluating the probability of anomalies in the athlete's profile, is currently lacking. In addition, we collected information from published studies, in order to supply a useful, practical and updated review to sports physicians and haematologists. There are some parameters that are highly stable, such as haemoglobin and erythrocytes (red blood cells [RBCs]), whereas others, (e.g. reticulocytes, mean RBC volume and haematocrit) appear less stable. Regardless of the methodology, the stability of haematological parameters is improved by sample refrigeration. The stability of all parameters is highly affected from high storage temperatures, whereas the stability of RBCs and haematocrit is affected by initial freezing followed by refrigeration. Transport and rotation of tubes do not substantially influence any haematological parameter except for reticulocytes. In all the studies we reviewed that used Sysmex instrumentation, which is recommended for ABP measurements, stability was shown for 72 hours at 4 ° C for haemoglobin, RBCs and mean curpuscular haemoglobin concentration (MCHC); up to 48 hours for reticulocytes; and up to 24 hours for haematocrit. In one study, Sysmex instrumentation shows stability extended up to 72 hours at 4 ° C for all the parameters. There are significant differences among methods and instruments: Siemens Advia shows lower stability than Sysmex as regards to reticulocytes. However, the limit of 36 hours from blood collection to analysis as recommended by ABP scientists is reasonable to guarantee analytical quality, when samples are transported at 4 ° C and are accompanied by a certified steadiness of this temperature. There are some parameters that are highly stable, such as haemoglobin and RBCs; whereas others, such as reticulocytes, mean cell volume and haematocrit are more unstable. The stability of haematological parameters might be improved independently from the analytical methodology, by refrigeration of the specimens. PMID:22060177

Lombardi, Giovanni; Lanteri, Patrizia; Colombini, Alessandra; Lippi, Giuseppe; Banfi, Giuseppe

2011-12-01

369

[Octanhydroxamate of iron: synthesis, analysis and investigation of stability].

Hydroxamic acids are found as chelates in plants, as metabolites of bacteria and funges. Some aerobic microorganisms synthesize hydroxamic acids, which transmit iron from environment to the cells of the plants. Fourteen hydroxamic acids were synthesized and their interaction with iron (II and III) was investigated. The purpose of this investigation was synthesis of hydroxamic acids, creation of stable iron chelate with one of these acids, preparation of the methods of analysis, investigation of the stability of chelate and application for prophylaxis and treatment of iron deficiency anemia. We used octanhydroxamic acid for creation of chelate with iron. The synthesis of this acid was the cheapest and compound with iron appeared stable. Iron chelates after acid hydrolysis were analyzed by quantity of iron (9.8-12.3%). We used complexometric titration method with dinatrium salt of ethylendiamintetraacetic acid without indication for quantitative analysis. Iron (II) chelate is less stable, therefore, we used Fe (III) octanhydroxamate for further investigations. Preliminary trials with rabbits confirm rapid assimilation of iron (III) chelate from gastrointestinal tract and activation of erythropoiesis. PMID:14617860

Palma, Palma; Sapragoniene, Marija; Stankevicius, Antanas

2003-01-01

370

GIS-based modelling of deep-seated slope stability in complex geology

NASA Astrophysics Data System (ADS)

We use the model r.slope.stability to explore the chances and challenges of physically-based modelling of deep-seated slope stability in complex geology over broad areas and not on individual slopes. The model is developed as a C and python-based raster module within the GRASS GIS software. It makes use of a modification of the three-dimensional sliding surface model proposed by Hovland (1977) and revised and extended by Xie and co-workers (2006). Given a digital elevation model and a set of thematic layers (lithological classes and related geotechnical parameters), the model evaluates the slope stability for a large number of randomly selected potential slip surfaces, ellipsoidal in shape. The bottoms of soil or bedrock layers can also be considered as potential slip surfaces by truncating the ellipsoids. Any single raster cell may be intersected by multiple sliding surfaces, each associated with a computed safety factor. For each pixel, the lowest value of the safety factor and the depth of the associated slip surface are stored. This information can be used to obtain a spatial overview of the potentially unstable regions in the study area. The r.slope.stability model can be executed both in a soil class-based mode, where the input data are mainly structured according to horizontally defined soil classes, and in a layer-based mode, where the data are structured according to a potentially large number of layers. Here, we test the model for the layer-based mode, allowing for the analysis of relatively complex geologic structures. We test the model in the Collazzone area, Umbria, central Italy, which is susceptible to landslides of different types. According to field observations in this area, morpho-structural settings (i.e., the orientation and dip of the geological layers) play a crucial role for the distribution of the deep-seated landslides. We have prepared a lithological model based on aerial photointerpretation, field survey and surface information on the strike and dip directions of each layer. We have further investigated the geotechnical parameters (cohesion and internal friction angle) associated to the layers using direct shear tests. We execute r.slope.stability for various assumptions of the geotechnical parameters, ellipsoid geometry and seepage direction. In this way, we obtain the spatial probability of slope failures which is validated using a pre-existing landslide inventory map, using an ROC plot. Acknowledging the challenges related to the high natural variability of geotechnical parameters in space, the results satisfactorily reproduce the observed distribution of deep-seated landslides in the study area. The assumed direction of seepage (slope-parallel vs. layer-parallel) strongly influences the model results.

Mergili, Martin; Marchesini, Ivan; Schneider-Muntau, Barbara; Cardinali, Mauro; Fiorucci, Federica; Valigi, Daniela; Santangelo, Michele; Bucci, Francesco; Guzzetti, Fausto

2014-05-01

371

Movement stability under uncertain internal models of dynamics.

Sensory noise and feedback delay are potential sources of instability and variability for the on-line control of movement. It is commonly assumed that predictions based on internal models allow the CNS to anticipate the consequences of motor actions and protect the movements from uncertainty and instability. However, during motor learning and exposure to unknown dynamics, these predictions can be inaccurate. Therefore a distinct strategy is necessary to preserve movement stability. This study tests the hypothesis that in such situations, subjects adapt the speed and accuracy constraints on the movement, yielding a control policy that is less prone to undesirable variability in the outcome. This hypothesis was tested by asking subjects to hold a manipulandum in precision grip and to perform single-joint, discrete arm rotations during short-term exposure to weightlessness (0 g), where the internal models of the limb dynamics must be updated. Measurements of grip force adjustments indicated that the internal predictions were altered during early exposure to the 0 g condition. Indeed, the grip force/load force coupling reflected that the grip force was less finely tuned to the load-force variations at the beginning of the exposure to the novel gravitational condition. During this learning period, movements were slower with asymmetric velocity profiles and target undershooting. This effect was compared with theoretical results obtained in the context of optimal feedback control, where changing the movement objective can be directly tested by adjusting the cost parameters. The effect on the simulated movements quantitatively supported the hypothesis of a change in cost function during early exposure to a novel environment. The modified optimization criterion reduces the trial-to-trial variability in spite of the fact that noise affects the internal prediction. These observations support the idea that the CNS adjusts the movement objective to stabilize the movement when internal models are uncertain. PMID:20554851

Crevecoeur, F; McIntyre, J; Thonnard, J-L; Lefèvre, P

2010-09-01

372

A Complete 2D Stability Analysis of Fast MHD Shocks in an Ideal Gas

: ?An algorithm of numerical testing of the uniform Lopatinski condition for linearized stability problems for 1-shocks is suggested.\\u000a The algorithm is used for finding the domains of uniform stability, neutral stability, and instability of planar fast MHD\\u000a shocks. A complete stability analysis of fast MHD shock waves is first carried out in two space dimensions for the case of\\u000a an

Yuri Trakhinin

2003-01-01

373

NASA Technical Reports Server (NTRS)

A calculation is made of the stability of various relaxation schemes for the numerical solution of partial differential equations. A multigrid acceleration method is introduced, and its effects on stability are explored. A detailed stability analysis of a simple case is carried out and verified by numerical experiment. It is shown that the use of multigrids can speed convergence by several orders of magnitude without adversely affecting stability.

Fay, John F.

1990-01-01

374

Analysis of cavern stability at the West Hackberry SPR site.

This report presents computational analyses that simulate the structural response of caverns at the Strategic Petroleum Reserve (SPR) West Hackberry site. The cavern field comprises 22 caverns. Five caverns (6, 7, 8, 9, 11) were acquired from industry and have unusual shapes and a history dating back to 1946. The other 17 caverns (101-117) were leached according to SPR standards in the mid-1980s and have tall cylindrical shapes. The history of the caverns and their shapes are simulated in a three-dimensional geomechanics model of the site that predicts deformations, strains, and stresses. Future leaching scenarios corresponding to oil drawdowns using fresh water are also simulated by increasing the volume of the caverns. Cavern pressures are varied in the model to capture operational practices in the field. The results of the finite element model are interpreted to provide information on the current and future status of subsidence, well integrity, and cavern stability. The most significant results in this report are relevant to Cavern 6. The cavern is shaped like a bowl with a large ceiling span and is in close proximity to Cavern 9. The analyses predict tensile stresses at the edge of the ceiling during repressuization of Cavern 6 following workover conditions. During a workover the cavern is at low pressure to service a well. The wellhead pressures are atmospheric. When the workover is complete, the cavern is repressurized. The resulting elastic stresses are sufficient to cause tension around the edge of the large ceiling span. With time, these stresses relax to a compressive state because of salt creep. However, the potential for salt fracture and propagation exists, particularly towards Cavern 9. With only 200 ft of salt between the caverns, the operational consequences must be examined if the two caverns become connected. A critical time may be during a workover of Cavern 9 in part because of the operational vulnerabilities, but also because dilatant damage is predicted under the ledge that forms the lower lobe in the cavern. The remaining caverns have no significant issues regarding cavern stability and may be safely enlarged during subsequent oil drawdowns. Predicted well strains and subsidence are significant and consequently future remedial actions may be necessary. These predicted well strains certainly suggest appropriate monitoring through a well-logging program. Subsidence is currently being monitored.

Ehgartner, Brian L.; Sobolik, Steven Ronald

2009-05-01

375

TRACE/PARCS analysis of the OECD/NEA Oskarshamn-2 BWR stability benchmark

On February 25, 1999, the Oskarshamn-2 NPP experienced a stability event which culminated in diverging power oscillations with a decay ratio of about 1.4. The event was successfully modeled by the TRACE/PARCS coupled code system, and further analysis of the event is described in this paper. The results show very good agreement with the plant data, capturing the entire behavior of the transient including the onset of instability, growth of the oscillations (decay ratio) and oscillation frequency. This provides confidence in the prediction of other parameters which are not available from the plant records. The event provides coupled code validation for a challenging BWR stability event, which involves the accurate simulation of neutron kinetics (NK), thermal-hydraulics (TH), and TH/NK. coupling. The success of this work has demonstrated the ability of the 3-D coupled systems code TRACE/PARCS to capture the complex behavior of BWR stability events. The problem was released as an international OECD/NEA benchmark, and it is the first benchmark based on measured plant data for a stability event with a DR greater than one. Interested participants are invited to contact authors for more information. (authors)

Kozlowski, T. [Univ. of Illinois, Urbana-Champaign, IL (United States); Downar, T.; Xu, Y.; Wysocki, A. [Univ. of Michigan, Ann Arbor, MI (United States); Ivanov, K.; Magedanz, J.; Hardgrove, M. [Pennsylvania State Univ., Univ. Park, PA (United States); March-Leuba, J. [Oak Ridge National Laboratory, Oak Ridge, TN (United States); Hudson, N.; Woodyatt, D. [Nuclear Regulatory Commission, Rockville, MD (United States)

2012-07-01

376

NASA Astrophysics Data System (ADS)

Results based on a local linear stability analysis of the Hall thruster discharge are presented. A one-dimensional azimuthal framework is used including three species: neutrals, singly charged ions, and electrons. A simplified linear model is developed with the aim of deriving analytical expressions to characterize the stability of the ionization region. The results from the local analysis presented here indicate the existence of an instability that gives rise to an azimuthal oscillation in the +E × B direction with a long wavelength. According to the model, the instability seems to appear only in regions where the ionization and the electric field make it possible to have positive gradients of plasma density and ion velocity at the same time. A more complex model is also solved numerically to validate the analytical results. Additionally, parametric variations are carried out with respect to the main parameters of the model to identify the trends of the instability. As the temperature increases and the neutral-to-plasma density ratio decreases, the growth rate of the instability decreases down to a limit where azimuthal perturbations are no longer unstable.

Escobar, D.; Ahedo, E.

2014-04-01

377

Lattice refining loop quantum cosmology, anisotropic models, and stability

A general class of loop quantizations for anisotropic models is introduced and discussed, which enhances loop quantum cosmology by relevant features seen in inhomogeneous situations. The main new effect is an underlying lattice which is being refined during dynamical changes of the volume. In general, this leads to a new feature of dynamical difference equations which may not have constant step-size, posing new mathematical problems. It is discussed how such models can be evaluated and what lattice refinements imply for semiclassical behavior. Two detailed examples illustrate that stability conditions can put strong constraints on suitable refinement models, even in the absence of a fundamental Hamiltonian which defines changes of the underlying lattice. Thus, a large class of consistency tests of loop quantum gravity becomes available. In this context, it will also be seen that quantum corrections due to inverse powers of metric components in a constraint are much larger than they appeared recently in more special treatments of isotropic, free scalar models where they were artificially suppressed.

Bojowald, Martin; Cartin, Daniel; Khanna, Gaurav [Institute for Gravitation and the Cosmos, Pennsylvania State University, 104 Davey Lab, University Park, Pennsylvania 16802 (United States); Naval Academy Preparatory School, 197 Elliot Street, Newport, Rhode Island 02841 (United States); Physics Department, University of Massachusetts at Dartmouth, North Dartmouth, Massachusetts 02747 (United States)

2007-09-15

378

NASA Astrophysics Data System (ADS)

In this paper, the dynamic behavior analysis of the electromechanical coupling characteristics of a flywheel energy storage system (FESS) with a permanent magnet (PM) brushless direct-current (DC) motor (BLDCM) is studied. The Hopf bifurcation theory and nonlinear methods are used to investigate the generation process and mechanism of the coupled dynamic behavior for the average current controlled FESS in the charging mode. First, the universal nonlinear dynamic model of the FESS based on the BLDCM is derived. Then, for a 0.01 kWh/1.6 kW FESS platform in the Key Laboratory of the Smart Grid at Tianjin University, the phase trajectory of the FESS from a stable state towards chaos is presented using numerical and stroboscopic methods, and all dynamic behaviors of the system in this process are captured. The characteristics of the low-frequency oscillation and the mechanism of the Hopf bifurcation are investigated based on the Routh stability criterion and nonlinear dynamic theory. It is shown that the Hopf bifurcation is directly due to the loss of control over the inductor current, which is caused by the system control parameters exceeding certain ranges. This coupling nonlinear process of the FESS affects the stability of the motor running and the efficiency of energy transfer. In this paper, we investigate into the effects of control parameter change on the stability and the stability regions of these parameters based on the averaged-model approach. Furthermore, the effect of the quantization error in the digital control system is considered to modify the stability regions of the control parameters. Finally, these theoretical results are verified through platform experiments.

Zhang, Wei-Ya; Li, Yong-Li; Chang, Xiao-Yong; Wang, Nan

2013-09-01

379

Bifurcation analysis of parametrically excited bipolar disorder model

NASA Astrophysics Data System (ADS)

Bipolar II disorder is characterized by alternating hypomanic and major depressive episode. We model the periodic mood variations of a bipolar II patient with a negatively damped harmonic oscillator. The medications administrated to the patient are modeled via a forcing function that is capable of stabilizing the mood variations and of varying their amplitude. We analyze analytically, using perturbation method, the amplitude and stability of limit cycles and check this analysis with numerical simulations.

Nana, Laurent

2009-02-01

380

Unstalled flutter stability predictions and comparisons to test data for a composite prop-fan model

NASA Technical Reports Server (NTRS)

The aeroelastic stability analyses for three graphite/epoxy composite Prop-Fan designs and post-test stability analysis for one of the designs, the SR-3C-X2 are presented. It was shown that Prop-Fan stability can be effectively analyzed using the F203 modal aeroelastic stability analysis developed at Hamilton Standard and that first mode torsion-bending coupling has a direct effect on blade stability. Positive first mode torsion-bending coupling is a destabilizing factor and the minimization of this parameter will increase Prop-Fan stability. It was also shown that Prop-Fan stability analysis using F203 is sensitive to the blade modal data used as input. Calculated blade modal properties varied significantly with the structural analysis used, and these variations are reflected in the F203 calculations.

Turnberg, J. E.

1986-01-01

381

In situ vitrification: application analysis for stabilization of transuranic waste

The in situ vitrification process builds upon the electric melter technology previously developed for high-level waste immobilization. In situ vitrification converts buried wastes and contaminated soil to an extremely durable glass and crystalline waste form by melting the materials, in place, using joule heating. Once the waste materials have been solidified, the high integrity waste form should not cause future ground subsidence. Environmental transport of the waste due to water or wind erosion, and plant or animal intrusion, is minimized. Environmental studies are currently being conducted to determine whether additional stabilization is required for certain in-ground transuranic waste sites. An applications analysis has been performed to identify several in situ vitrification process limitations which may exist at transuranic waste sites. Based on the process limit analysis, in situ vitrification is well suited for solidification of most in-ground transuranic wastes. The process is best suited for liquid disposal sites. A site-specific performance analysis, based on safety, health, environmental, and economic assessments, will be required to determine for which sites in situ vitrification is an acceptable disposal technique. Process economics of in situ vitrification compare favorably with other in-situ solidification processes and are an order of magnitude less than the costs for exhumation and disposal in a repository. Leachability of the vitrified product compares closely with that of Pyrex glass and is significantly better than granite, marble, or bottle glass. Total release to the environment from a vitrified waste site is estimated to be less than 10/sup -5/ parts per year. 32 figures, 30 tables.

Oma, K.H.; Farnsworth, R.K.; Rusin, J.M.

1982-09-01

382

Local analysis of inverse problems: Hölder stability and iterative reconstruction

NASA Astrophysics Data System (ADS)

We consider a class of inverse problems defined by a nonlinear mapping from parameter or model functions to the data, where the inverse mapping is Hölder continuous with respect to appropriate Banach spaces. We analyze a nonlinear Landweber iteration and prove local convergence and convergence rates with respect to an appropriate distance measure. Opposed to the standard analysis of the nonlinear Landweber iteration, we do not assume source and nonlinearity conditions, but this analysis is based solely on the Hölder continuity of the inverse mapping.

de Hoop, Maarten V.; Qiu, Lingyun; Scherzer, Otmar

2012-04-01

383

NASA Technical Reports Server (NTRS)

Implicit, noniterative, finite difference schemes were recently developed by several authors for multidimensional systems of nonlinear hyperbolic partial differential equations. When applied to linear model equations with periodic boundary conditions those schemes are unconditionally stable (A-stable). As applied in practice the algorithms often face a severe time step restriction. A major source of the difficulty is the treatment of the numerical boundary conditions. One conjecture was that unconditional stability requires implicit numerical boundary conditions. An apparent counter example was the space time extrapolation considered by Gustafsson, Kreiss, and Sunstrom. Spatial (implicit) and space time (explicit) extrapolation using normal mode analysis for a finite and infinite number of spatial mesh intervals are examined. The results indicate that for unconditional stability with a finite number of spatial mesh intervals, the numerical boundary conditions must be implicit.

Beam, R. M.; Warming, R. F.; Yee, H. C.

1981-01-01

384

Precessing rotating flows with additional shear: Stability analysis

NASA Astrophysics Data System (ADS)

We consider unbounded precessing rotating flows in which vertical or horizontal shear is induced by the interaction between the solid-body rotation (with angular velocity ?0 ) and the additional “precessing” Coriolis force (with angular velocity -??0 ), normal to it. A “weak” shear flow, with rate 2? of the same order of the Poincaré “small” ratio ? , is needed for balancing the gyroscopic torque, so that the whole flow satisfies Euler’s equations in the precessing frame (the so-called admissibility conditions). The base flow case with vertical shear (its cross-gradient direction is aligned with the main angular velocity) corresponds to Mahalov’s [Phys. Fluids A 5, 891 (1993)] precessing infinite cylinder base flow (ignoring boundary conditions), while the base flow case with horizontal shear (its cross-gradient direction is normal to both main and precessing angular velocities) corresponds to the unbounded precessing rotating shear flow considered by Kerswell [Geophys. Astrophys. Fluid Dyn. 72, 107 (1993)]. We show that both these base flows satisfy the admissibility conditions and can support disturbances in terms of advected Fourier modes. Because the admissibility conditions cannot select one case with respect to the other, a more physical derivation is sought: Both flows are deduced from Poincaré’s [Bull. Astron. 27, 321 (1910)] basic state of a precessing spheroidal container, in the limit of small ? . A Rapid distortion theory (RDT) type of stability analysis is then performed for the previously mentioned disturbances, for both base flows. The stability analysis of the Kerswell base flow, using Floquet’s theory, is recovered, and its counterpart for the Mahalov base flow is presented. Typical growth rates are found to be the same for both flows at very small ? , but significant differences are obtained regarding growth rates and widths of instability bands, if larger ? values, up to 0.2, are considered. Finally, both flow cases are briefly discussed in view of a subsequent nonlinear study using pseudospectral direct numerical simulations, which is a natural continuation of RDT.

Salhi, A.; Cambon, C.

2009-03-01

385

CASE STUDY OF STABILITY AS SESSMENT OF ROCK SLOPE BY LIMIT EQUILIBRIUM ANALYSIS

NASA Astrophysics Data System (ADS)

Simple stability assessment was carried out for the rock slope which collapsed in 2007 and consists of Neogene massive pyroclastic rock. The assessment met hod is the 2-D and 3-D limit equilibrium analysis using tensile strength and tensile stress, which was developed by the authors using the centrifuge model test. As a result, safety factor obtained by 2-D analysis is about 1.0 (1.1). Safety factor by 3-D analysis becomes under 1.0 when the part of intact rock of the block is less than 5.2m and 6.9m by the Crackplane Estimation Method and the Least Crack Angl e Method, respectively. As the both figures are slightly above the figure of the real intact part (5.0m) of the collapsed block, the both methods estimate the block stability precisely and sately. In conclusion, 2-D analysis is suitable for the screening of rock slopes, while 3-D analysis is suitable for more detailed estimation of target slopes.

Kusakabe, Yuki; Miura, Kin-Ya; Ito, Yoshihiko; Omote, Shin-Ya

386

Testing lake energy budget models under varying atmospheric stability conditions

NASA Astrophysics Data System (ADS)

Several variations of a basic energy budget model were tested under varying atmospheric stability conditions using temperature data from Lake Mendota and meteorologic data from nearby Truax Airfield, Madison, Wisconsin. The flux enhancements predicted by Model 1 (Deardorff) for prevailing over-lake lapse conditions were inconsistent with measured changes in lake heat storage. When using the Budyko formulation for sky emissivity, ?, satisfactory energy residuals were obtained by eliminating the lapse enhancement while retaining the suppressive effects of over-lake inversions (Model 2 = modified Deardorff). Here, the best estimate of the 10 m Dalton coefficient was 1.45 × 10 -3 (cgs units; neutral profile). However, when the Koberg model for ? was adopted instead, satisfactory energy residuals were obtained only after eliminating all adjustments for non-neutral conditions, and increasing the 10 m Dalton coefficient to approximately 1.55 × 10 -3 (Model 3). Models 2 and 3 predicted annual evaporation from Lake Mendota of 71 and 86 cm during 1977 (including approximately 6 cm of sublimation during ice cover), bracketing earlier estimates for this locality (76 cm) based on U.S. Weather Bureau Class A pan data, and consistent with intensive studies of Pretty Lake in northern Indiana. My estimates of the 10 m Dalton coefficient (1.45 × 10 -3 to 1.55 × 10 -3) also narrowly bracket values for Lake Hefner and Lake Mead (1.49 × 10 -3), obtained in studies by the U.S. Geological Survey. Moreover, as in the case of the Will Rogers airport near Lake Hefner, meteorologic data collected at Truax Airfield, Wisconsin, proved adequate for estimating sensible and latent heat transfer over the adjacent lake.

Stauffer, Robert E.

1991-11-01

387

The long-term stability of Class II, Division 1 nonextraction therapy, using cervical face-bows with full fixed orthodontic appliances was evaluated for 42 randomly selected patients. Part 1, a study model analysis, was published in the March 1996 issue of the JOURNAL. Each patient was treated by the same practitioner, with the same techniques, and the treatment goals had been attained

T. N. Elms; P. H. Buschang; R. G. Alexander

1996-01-01

388

In this paper a quantitative framework for analysis of the UK commercial property sector is developed, and the possible implications explored for the financial stability of this sector, and for the corporate sector as a whole. There is little previous empirical literature. But where there is, models have either studied particular markets or have developed single-equation approaches. Lack of suitable

John Whitley; Richard Windram

2003-01-01

389

Stability and Bifurcation Analysis of a Spinning Space Tether

A detailed, geometrically exact bifurcation analysis is performed for a model of a power-generating tethered device of interest\\u000a to the space industries. The structure, a short electrodynamic tether, comprises a thin, long rod that is spun in a horizontal\\u000a configuration from a satellite in low Earth orbit, with a massive electrically conducting disk at its free end. The system\\u000a is

J. Valverde; J. L. Escalona; J. Dominguez; A. R. Champneys

2006-01-01

390

NASA Astrophysics Data System (ADS)

In order to evaluate quantitatively the landscape stability of arid areas, a study area was selected in Yuli county of the middle and lower reaches of Tarim river. Remote sensing image data are the main data sources, the image data are processed by the support of RS and GIS technology. The study extracted 11 indices of landscape stability by FRAGSTATS software, and the standard matrix of these indices data are got using Z-Score method, then the comprehensive evaluation model of landscape stability is constructed by principal component analysis method. The study results showed that the range of comprehensive evaluation scores of Yuli's ecological landscape stability is 1.736, which indicated there is a great variation in ecological landscape stability of study area. The stability declines as the following order: forest land - water area- grass land- cultivated land - buildup land -unused land. The landscape stability is always the key scientific issues which should be solved urgently, the study on landscape stability has important theoretical and practical significance.

Wang, Qianfeng; Zhou, Kefa; Sun, Li; Chen, Limou; Ou, Yang; Li, Guangyu; Qin, Yanfang; Wang, Jinlin

2011-01-01

391

NASA Technical Reports Server (NTRS)

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.

Kayten, Gerald G

1945-01-01

392

Modal analysis for Liapunov stability of rotating elastic bodies. Ph.D. Thesis. Final Report

NASA Technical Reports Server (NTRS)

This study consisted of four parallel efforts: (1) modal analyses of elastic continua for Liapunov stability analysis of flexible spacecraft; (2) development of general purpose simulation equations for arbitrary spacecraft; (3) evaluation of alternative mathematical models for elastic components of spacecraft; and (4) examination of the influence of vehicle flexibility on spacecraft attitude control system performance. A complete record is given of achievements under tasks (1) and (3), in the form of technical appendices, and a summary description of progress under tasks two and four.

Colin, A. D.

1973-01-01

393

NASA Astrophysics Data System (ADS)

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.

Ataei-Esfahani, Armin

394

BLSTA: A boundary layer code for stability analysis

NASA Technical Reports Server (NTRS)

A computer program is developed to solve the compressible, laminar boundary-layer equations for two-dimensional flow, axisymmetric flow, and quasi-three-dimensional flows including the flow along the plane of symmetry, flow along the leading-edge attachment line, and swept-wing flows with a conical flow approximation. The finite-difference numerical procedure used to solve the governing equations is second-order accurate. The flow over a wide range of speed, from subsonic to hypersonic speed with perfect gas assumption, can be calculated. Various wall boundary conditions, such as wall suction or blowing and hot or cold walls, can be applied. The results indicate that this boundary-layer code gives velocity and temperature profiles which are accurate, smooth, and continuous through the first and second normal derivatives. The code presented herein can be coupled with a stability analysis code and used to predict the onset of the boundary-layer transition which enables the assessment of the laminar flow control techniques. A user's manual is also included.

Wie, Yong-Sun

1992-01-01

395

Lyapunov Analysis of Neural Network Stability in an Adaptive Flight Control System

The paper presents the role of self-stabilization analysis in the design, verification and validation of the dynamics of an Adaptive Flight Control System (AFCS). Since the traditional self-stabilization approaches lack the flexibility to deal with the continuous adaptation of the neural network within the AFCS, the paper emphasizes an alternate self-stability analysis approach, namely Lyapunov's Second Method. A Lyapunov function

Sampath Yerramalla; Edgar Fuller; Martin Mladenovski; Bojan Cukic

2003-01-01

396

NASA Astrophysics Data System (ADS)

A systematic procedure is presented to derive stability conditions for leap-frog-type finite-difference schemes for the multidimensional constant-coefficient convective-diffusion equation. The treatise includes von Neumann stability analysis for pure initial-value problems and matrix stability analysis for Dirichlet boundary-value problems. Discrepancies on time-step restriction between von Neumann stability analysis and matrix stability analysis are observed.

Kwok, Yue-Kuen; Tam, Kin-Kiu

1993-07-01

397

Physical and numerical model of colloidal silica injection for passive site stabilization

Passive site stabilization is a new technology proposed for nondisruptive mitigation of liquefaction risk at developed sites susceptible to liquefaction. This technology is based on the concept of slow injection of stabilizing materials at the edge of a site and delivery of the stabilizer to the target location, using the natural or augmented groundwater flow. In this research, a box model was used to investigate the ability to uniformly deliver colloidal silica stabilizer to loose sands using low-head injection and extraction wells. Five injection wells and two extraction wells were used to deliver stabilizer in a generally uniform pattern to the loose sand formation. Numerical modeling was used to identify the key parameters affecting stabilizer migration and to determine their effective values for the box experiment. In our modeling approach, the stabilizer is treated as a miscible fluid, the viscosity of which is a function of time and concentration of the stabilizer in the pore water. Inverse modeling techniques are employed to reproduce data from the laboratory experiment for the determination of soil and stabilizer properties. While the details of the stabilizer distribution were difficult to reproduce with the simplified conceptual model employed in this study, the overall system behavior was well captured, providing confidence that numerical simulation is a useful tool for designing centrifuge model tests, pilot tests, and eventually field stabilizer-injection projects.

Gallagher, Patricia M.; Finsterle, Stefan

2004-08-01

398

Reliability-based stability analysis considering GCL shear strength variability

The impact of different levels of uncertainty in geosynthetic clay liner (GCL) shear strength on landfill stability is evaluated in this study. The uncertainty in shear strength of the interface governing landfill stability is defined using statistical parameters obtained from a significant database of GCL internal and GCL-geomembrane interface large-scale direct shear tests. Uncertainty in GCL shear strength arises from

J. S. McCartney; J. G. Zornberg; R. H. Swan Jr; R. B. Gilbert

2004-01-01

399

Stability Analysis of a Reluctance-Synchronous Machine

A stability study of a reluctance-synchronous machine (synchronous-induction machine) is performed by applying the Nyquist stability criterion to the equations which describe the behavior of the machine during small displacements about a steady- state operating point. This investigation reveals that machine instability can occur at low speeds (low frequencies) even though balanced, constant amplitude, sinusoidal voltages are applied to the

THOMAS A. LIPO; PAUL C. KRAUSE

1967-01-01

400

Structural stability and failure analysis using peridynamic theory

The peridynamic theory has been successfully utilized for damage prediction in many problems. However, the elastic stability of structures has not been studied using the peridynamic theory. Therefore, this paper investigates the elastic stability of simple structures to determine buckling characteristics of the peridynamic theory by considering two sets of problems. The first set of problems involves rectangular columns under

B. Kilic; E. Madenci

2009-01-01

401

Experimentation and Modeling of Jet A Thermal Stability in a Heated Tube

NASA Technical Reports Server (NTRS)

High performance aircraft typically use hydrocarbon fuel to regeneratively cool the airframe and engine components. As the coolant temperatures increase, the fuel may react with dissolved oxygen forming deposits that limit the regenerative cooling system performance. This study investigates the deposition of Jet A using a thermal stability experiment and computational fluid dynamics (CFD) modeling. The experimental portion of this study is performed with a high Reynolds number thermal stability (HiRets) tester in which fuel passes though an electrically heated tube and the fuel outlet temperature is held constant. If the thermal stability temperature of the fuel is exceeded, deposits form and adhere to the inside of the tube creating an insulating layer between the tube and the fuel. The HiRets tester measures the tube outer wall temperatures near the fuel outlet to report the effect of deposition occurring inside the tube. Final deposits are also estimated with a carbon burn off analysis. The CFD model was developed and used to simulate the fluid dynamics, heat transfer, chemistry, and transport of the deposit precursors. The model is calibrated to the experiment temperature results and carbon burn-off deposition results. The model results show that the dominant factor in deposition is the heated wall temperature and that most of the deposits are formed in the laminar sublayer. The models predicted a 7.0E-6 kilograms per square meter-sec deposition rate, which compared well to the carbon burn-off analysis deposition rate of 1.0E-6 kilograms per square meter-sec.

Khodabandeh, Julia W.

2005-01-01

402

Linear Stability Analysis of Free Surface Liquid Metal Flow

NASA Astrophysics Data System (ADS)

We study the linear stability of the flow of a liquid metal on a planar surface in the presence of an external magnetic field. The objective is to account for the behavior encountered in a free surface MHD experiment at Princeton, but the model has a range of astrophysical and industrial applications (see companion poster). This class of free surface flow exhibits two mechanisms of linear instability. In the so-called `soft' instability, a downstream propagating surface wave of large wavelength becomes mildly unstable. The second, `hard', instability is of the critical layer type and takes place at shorter wavelengths. Solving the eigenvalue problem posed by the coupled Orr-Sommerfeld and induction equations via a spectral method, we find that in the regime of relevance to the Princeton experiment (Reynolds number, magnetic Reynolds number and Hartmann number up to 10 ^ 5 , 10 ^ - 1 , and 10 ^ 3 , respectively) MHD effects suppress both types of instability. The soft instability is efficiently suppressed via resistive dissipation if the background magnetic field is normal to the basic flow. In contrast, the hard instability is strongly suppressed irrespective of the details of the background magnetic field configuration, even at moderate Hartmann numbers.

Giannakis, D.; Rosner, R.; Fischer, P.; Ji, H.; Burin, M.; McMurtry, K.

2006-10-01

403

Joint regression analysis and AMMI model applied to oat improvement

NASA Astrophysics Data System (ADS)

In our work we present an application of some biometrical methods useful in genotype stability evaluation, namely AMMI model, Joint Regression Analysis (JRA) and multiple comparison tests. A genotype stability analysis of oat (Avena Sativa L.) grain yield was carried out using data of the Portuguese Plant Breeding Board, sample of the 22 different genotypes during the years 2002, 2003 and 2004 in six locations. In Ferreira et al. (2006) the authors state the relevance of the regression models and of the Additive Main Effects and Multiplicative Interactions (AMMI) model, to study and to estimate phenotypic stability effects. As computational techniques we use the Zigzag algorithm to estimate the regression coefficients and the agricolae-package available in R software for AMMI model analysis.

Oliveira, A.; Oliveira, T. A.; Mejza, S.

2012-09-01

404

NASA Astrophysics Data System (ADS)

Molecular modeling was used to investigate factors influencing complex formation between cyclodextrins and guest molecules and predict their stability through a theoretical model based on the search for a correlation between experimental stability constants ( Ks) and some theoretical parameters describing complexation (docking energy, host-guest contact surfaces, intermolecular interaction fields) calculated from complex structures at a minimum conformational energy, obtained through stochastic methods based on molecular dynamic simulations. Naproxen, ibuprofen, ketoprofen and ibuproxam were used as model drug molecules. Multiple Regression Analysis allowed identification of the significant factors for the complex stability. A mathematical model ( r=0.897) related log Ks with complex docking energy and lipophilic molecular fields of cyclodextrin and drug.

Faucci, Maria Teresa; Melani, Fabrizio; Mura, Paola

2002-06-01

405

Genotypic stability and adaptability in tropical maize based on AMMI and GGE biplot analysis.

We evaluated the phenotypic and genotypic stability and adaptability of hybrids using the additive main effect and multiplicative interaction (AMMI) and genotype x genotype-environment interaction (GGE) biplot models. Starting with 10 single-cross hybrids, a complete diallel was done, resulting in 45 double-cross hybrids that were appraised in 15 locations in Southeast, Center-West and Northeast Brazil. In most cases, when the effects were considered as random (only G effects or G and GE simultaneously) in AMMI and GGE analysis, the distances between predicted values and observed values were smaller than for AMMI and GGE biplot phenotypic means; the best linear unbiased predictors of G and GE generally showed more accurate predictions in AMMI and GGE analysis. We found the GGE biplot method to be superior to the AMMI 1 graph, due to more retention of GE and G + GE in the graph analysis. However, based on cross-validation results, the GGE biplot was less accurate than the AMMI 1 graph, inferring that the quantity of GE or G + GE retained in the graph analysis alone is not a good parameter for choice of stabilities and adaptabilities when comparing AMMI and GGE analyses. PMID:19937587

Balestre, M; Von Pinho, R G; Souza, J C; Oliveira, R L

2009-01-01

406

NASA Technical Reports Server (NTRS)

Schlieren methods of flow visualization and hot-wire anemometry for velocity measurements were used to investigate the wakes generated by hovering model propellers and rotors. The research program was directed toward investigating (1) the stability of the tip vortex, (2) the effects produced by various tip shapes on performance and tip vortex characteristics, and (3) the shock formation and noise characteristics associated with various tip shapes. A free-wake analysis was also conducted for comparison with the vortex stability experimental results. Schlieren photographs showing wake asymmetry, interaction, and instability are presented along with a discussion of the effects produced by the number of blades, collective pitch, and tip speed. Two hot-wire anemometer techniques, used to measure the maximum circumferential velocity in the tip vortex, are discussed.

Tangler, J. L.; Wohlfeld, R. M.; Miley, S. J.

1973-01-01

407

Improvement of stability conditions, accuracy and uniqueness of penalty approach in contact modeling

NASA Astrophysics Data System (ADS)

The main objective of this paper is to improve stability conditions, uniqueness and convergence of numerical analysis of metal forming processes with contact constraints enforced by the penalty method. A commonly known drawback of this approach is the choice of penalty factor values. When assumed too low, they result in inaccurate fulfillment of the constraints while when assumed too high, they lead to ill-conditioning of the equations system which affects stability and uniqueness of the solution. The proposed modification of the penalty algorithm consists in adaptive estimation of the penalty factor values for the particular system of finite element equations and for the assumed allowed inaccuracy in fulfillment of the contact constraints. The algorithm is tested on realistic examples of sheet metal forming. The finite element code based on flow approach formulation (for rigid-plastic and rigid-viscoplastic material model) has been used.

Bednarek, Tomasz; Kowalczyk, Piotr

2013-06-01

408

We present an analysis of stability, heating and quench propagation in a 50 Tesla solenoid immersed in a liquid helium bath at 4.2 K, obtained by numerical Finite Element Method (FEM) modeling. The solenoid was assumed to be wound of a cable made of YBCO coated conductor tapes. Full heat transfer curve in the whole temperature range (from 4.2 K

M. Majoros; M. D. Sumption; E. W. Collings

2012-01-01

409

This paper presents an artificial neural network (ANN) based modeling technique for predicting the voltage stability of radial distribution systems. The modeling technique is based on a new voltage stability index for assessment of radial distribution systems Lv . The index is implemented to investigate a 33-bus distribution system. An ANN model which has an input layer with two input

M. M. Hamada; M. A. A. Wahab; N. G. A. Hemdan

2006-01-01

410

Stability and instability of thermocapillary convection in models of float-zone crystal growth

NASA Technical Reports Server (NTRS)

The energy-stability theory has been used to study the stability properties of thermocapillary convection in a half-zone model of the float-zone crystal-growth process. It is concluded that the energy theory provides a sufficient condition for stability to disturbances of arbitrary amplitude. Results of the computation of energy-stability limits are found to be in good agreement with experimentally measured bounds for oscillatory thermocapillary convection.

Neitzel, G. P.; Law, C. C.; Jankowski, D. F.; Mittelmann, H. D.

1991-01-01

411

Slope stability analysis by SRM-based rock failure process analysis (RFPA)

The fundamental principles of the strength reduction method (SRM) are incorporated into the rock failure process analysis (RFPA) code to produce an RFPA–SRM method for analysing the failure process and stability of rock and soil slopes. The RFPA–SRM method not only satisfies the global equilibrium, strain-consistent, and non-linear constitutive relationship of rock and soil materials but also takes into account

L. C. Li; C. A. Tang; C. W. Li; W. C. Zhu

2006-01-01

412

Viscous linear stability analysis of rectangular duct and cavity flows

NASA Astrophysics Data System (ADS)

The viscous linear stability of four classes of incompressible flows inside rectangular containers is studied numerically. In the first class the instability of flow through a rectangular duct, driven by a constant pressure gradient along the axis of the duct (essentially a two-dimensional counterpart to plane Poiseuille flow PPF), is addressed. The other classes of flow examined are generated by tangential motion of one wall, in one case in the axial direction of the duct, in another perpendicular to this direction, corresponding respectively to the two-dimensional counterpart to plane Couette flow (PCF) and the classic lid-driven cavity (LDC) flow, and in the fourth case a combination of both the previous tangential wall motions. The partial-derivative eigenvalue problem which in each case governs the temporal development of global three-dimensional small-amplitude disturbances is solved numerically. The results of Tatsumi & Yoshimura (1990) for pressure-gradient-driven flow in a rectangular duct have been confirmed; the relationship between the eigenvalue spectrum of PPF and that of the rectangular duct has been investigated. Despite extensive numerical experimentation no unstable modes have been found in the wall-bounded Couette flow, this configuration found here to be more stable than its one-dimensional limit. In the square LDC flow results obtained are in line with the predictions of Ding & Kawahara (1998b), Theofilis (2000) and Albensoeder et al. (2001b) as far as one travelling unstable mode is concerned. However, in line with the predictions of the latter two works and contrary to all previously published results it is found that this mode is the third in significance from an instability analysis point of view. In a parameter range unexplored by Ding & Kawahara (1998b) and all prior investigations two additional eigenmodes exist, which are both more unstable than the mode that these authors discovered. The first of the new modes is stationary (and would consequently be impossible to detect using power-series analysis of experimental data), whilst the second is travelling, and has a critical Reynolds number and frequency well inside the experimentally observed bracket. The effect of variable aspect ratio Ain[0.5,4] of the cavity on the most unstable eigenmodes is also considered, and it is found that an increase in aspect ratio results in general destabilization of the flow. Finally, a combination of wall-bounded Couette and LDC flow, generated in a square duct by lid motion at an angle phiin(0,{pi}/{2}) with the homogeneous duct direction, is shown to be linearly unstable above a Reynolds number Rey {=} 800 (based on the lid velocity and the duct length/height) at all phi parameter values examined. The excellent agreement with experiment in LDC flow and the alleviation of the erroneous prediction of stability of wall-bounded Couette flow is thus attributed to the presence of in-plane basic flow velocity components.

Theofilis, V.; Duck, P. W.; Owen, J.

2004-04-01

413

Stability Analysis of Gradient-Based Neural Networks for Optimization Problems

The paper introduces a new approach to analyze the stability of neural network models without using any Lyapunov function. With the new approach, we investigate the stability properties of the general gradient-based neural network model for optimization problems. Our discussion includes both isolated equilibrium points and connected equilibrium sets which could be unbounded. For a general optimization problem, if the

Qiaoming Han; Li-Zhi Liao; Houduo Qi; Liqun Qi

2001-01-01

414

A review is presented of some bioeconomic mathematical models that incorporate constant harvesting. This is followed by a complete qualitative and quantitative analysis of competition and predator-prey Lotka-Volterra bioeconomic models. The trivial and non-trivial equilibrium points of these systems are analyzed and the Routh-Hurwitz criteria are used to determine the necessary and sufficient conditions for stability in relation to the effort parameter eta. Some numerical examples that illustrate the corresponding qualitative stability analysis for the open access and bioeconomic equilibria for the competition and predator-prey systems are given. In the numerical examples analyzed, three different open access and bioeconomic equilibria were found. The non-trivial equilibrium points are unstable and infeasible. A critical level of effort was also derived for the predator-prey numerical example and corresponding management policies were formulated. When only the predator is harvested, it can be shown that the system under analysis undergoes a critical bifurcation at the point E/sub c/.

Castro Ospina, J.M.

1984-01-01

415

APPLICATIONS ANALYSIS REPORT: CHEMFIX TECHNOLOGIES, INC. - SOLIDIFICATION/STABILIZATION PROCESS

In support of the U.S. Environmental Protection Agency's (EPA) Superfund Innovative Technology Evaluation (SITE) Program, this report evaluates the Chemfix Technologies, Inc. (Chemfix), solidification/stabilization technology for on-site treatment of hazardous waste. The Chemfix ...

416

PC Program for Coastal Inlet Stability Analysis Using Escoffier Method.

National Technical Information Service (NTIS)

This Coastal Engineering Technical Note (CETN) provides information for determining coastal inlet stability using a personal computer program which is a tool in the Coastal Inlet Management Package of the Coastal Inlets Research Program. Background on the...

N. C. Kraus W. C. Seabergh

1997-01-01

417

A multiloop generalization of the circle criterion for stability margin analysis

NASA Technical Reports Server (NTRS)

In order to provide a theoretical tool well suited for use in characterizing the stability margins (e.g., gain and phase margins) of multiloop feedback systems, multiloop input-output stability results generalizing the circle stability criterion are considered. Generalized conic sectors with 'centers' and 'radii' determined by linear dynamical operators are employed to enable an engineer to specify the stability margins which he desires as a frequency-dependent convex set of modeling errors (including nonlinearities, gain variations, and phase variations) which the system must be able to tolerate in each feedback loop without instability. The resulting stability criterion gives sufficient conditions for closed-loop stability in the presence of such frequency-dependent modeling errors, even when the modeling errors occur simultaneously in all loops.

Safonov, M. G.; Athans, M.

1981-01-01

418

(Research stability analysis of fluidized-bed equations)

In previous reports we have outlined the equations governing the flow of a mixture of a fluid infused with solid particles, the equations governing the state of uniform fluidization and the equation governing the linearized stability of the state of uniform fluidization. We have also discussed how material function {beta}{sub 01}, the pressure like term, i.e., the spherical part of the stress tensor for the solid constituent, could play a stabilizing role. We have carried out the optimization study for the stability equations and have obtained bounds for this material function {beta}{sub 01}, which will ensure the stability of the state of uniform fluidization for a range of values for the other material parameters. Here, we provide few preliminary results which show the effect of different material parameters on the stability of the state of uniform fluidization. Figures (1) through (10) show the variation of the root of the characteristic equation with the wave number, {sigma}. Negative values for the root implies that the flow is stabe and positive values that the flow is unstable. For the sake of completeness, we provide the section on stability which can also be found in our previous report.

Not Available

1991-01-01

419

A stability analysis is carried out for a mathematical model which describes the electrical firing of a single vasopressin neuron. The model used in a FitzHugh-Nagumo-type system which is driven by impulses. The analysis is based on recent developments in the stability theory of impulsive differential equations. Conditions are derived under which the system of differential equations is stable at two of its equilibrium points. Biologically this bistability represents the cell alternating between periods of electrical activity and silence. The conditions for stability are specified in terms of the amplitude and frequency of the impulses perturbing the system. Both stochastic and deterministic impulses are considered. PMID:9951715

Milne, A E; Chalabi, Z S

1998-12-01

420

Diamond Model of Intrusion Analysis.

National Technical Information Service (NTIS)

This paper presents a novel model of intrusion analysis built by analysts, derived from years of experience, asking the simple question, 'What is the underlying method to our work' The model establishes the basic atomic element of any intrusion activity, ...

A. Pendergast C. Betz S. Caltagirone

2013-01-01