Stability analysis of within-host parasite models with delays
Paris-Sud XI, Université de
Stability analysis of within-host parasite models with delays Abderrahman Iggidr a, Joseph Mbang a. Abstract We provide a global analysis of systems of within-host parasitic infections. The sys- tems studied be thought as systems arising from within-host parasitic systems with distributed continuous delays. We
Stability analysis of carbon nanotubes via continuum models
Q. Wang; V. K. Varadan
2005-01-01
This paper presents the research on the stability analysis of carbon nanotubes (CNTs) via elastic continuum beam and shell models. The estimation of the flexural stiffness of a single-walled nanotube (SWNT) via the elastic beam model is proposed based on the postulate analyzed and provided in the paper. The validation of the stiffness is conducted with the ab initio calculations
Nonlinear stability analysis of a disk brake model
Daniel Hochlenert
2009-01-01
It has become commonly accepted by scientists and engineers that brake squeal is generated by friction-induced self-excited\\u000a vibrations of the brake system. The noise-free configuration of the brake system loses stability through a flutter-type instability\\u000a and the system starts oscillating in a limit cycle. Usually, the stability analysis of disk brake models, both analytical\\u000a as well as finite element based,
Stability analysis of the ?-model during fast elbow movements
Lan Li; Zhu Kuanyi
2007-01-01
In control, stability insures the reproducibility of motions and the robustness to external and internal perturbations. In this short paper, the stability of the ?-model during fast elbow movements are analyzed, and the operation regions of the unmeasurably descending commands are calculated to guarantee the stabilizing ability of the motor control system. In this system, the elbow is modeled as
Hak-Keung Lam; Mohammad Narimani
2010-01-01
This paper presents the stability analysis of fuzzy-model-based (FMB) control systems. Staircase membership functions are introduced to facilitate the stability analysis. Through the staircase membership functions approximating those of the fuzzy model and fuzzy controller, the information of the membership functions can be brought into the stability analysis. Based on the Lyapunov-stability theory, stability conditions in terms of linear-matrix inequalities
An ENSO stability analysis. Part I: results from a hybrid coupled model
Wang, Yuqing
An ENSO stability analysis. Part I: results from a hybrid coupled model Seon Tae Kim · Fei-Fei Jin ENSO stability in coupled models or in observa- tions without a detailed eigen-analysis) stability in a hybrid-coupled model (HCM) with various atmosphere and ocean background states. This HCM
Doubly fed induction generator model for transient stability analysis
Pablo Ledesma; Julio Usaola
2005-01-01
This paper proposes a model of the doubly fed induction generator (DFIG) suitable for transient stability studies. The main assumption adopted in the model is that the current control loops, which are much faster than the electromechanic transients under study, do not have a significant influence on the transient stability of the power system and may be considered instantaneous. The
Quadratic stability analysis of the Takagi-Sugeno fuzzy model
Kiriakos Kiriakidis; Apostolos Grivas; Anthony Tzes
1998-01-01
The nonlinear dynamic Takagi-Sugeno fuzzy model with offset terms is analyzed as a perturbed linear system. A sufficient criterion for the robust stability of this nominal system against nonlinear perturbations guarantees quadratic stability of the fuzzy model. The criterion accepts a convex programming formulation of reduced computational cost compared to the common Lyapunov matrix approach. Parametric robust control techniques suggest
Stability Analysis of -model for Human Motor System
Lan Li; Zhu Kuanyi
2006-01-01
Computer modeling and control of the human motor system may be helpful to the diagnosis and treatment of neuromuscular disorders. In this paper, the brief view of the equilibrium point hypothesis for human motor system modeling is given, and the ?-model derived from this hypothesis is studied. Then, the stability of the ?-model based on equilibrium and Jacobian matrix is
A Structure Preserving Model for Power System Stability Analysis
A. R. Bergen; D. J. Hill
1981-01-01
A new model for the study of power system stability via Lyapunov functions is proposed. The key feature of the model is an assumption of frequency-dependent load power, rather than the usual impedance loads which are subsequently absorbed into a reduced network. The original network topology is explicitly represented. This approach has the important advantage of rigorously accounting for real
Stability analysis of the Euler discretization for SIR epidemic model
Suryanto, Agus [Department of Mathematics, Faculty of Sciences, Brawijaya University, Jl. Veteran Malang 65145 (Indonesia)
2014-06-19
In this paper we consider a discrete SIR epidemic model obtained by the Euler method. For that discrete model, existence of disease free equilibrium and endemic equilibrium is established. Sufficient conditions on the local asymptotical stability of both disease free equilibrium and endemic equilibrium are also derived. It is found that the local asymptotical stability of the existing equilibrium is achieved only for a small time step size h. If h is further increased and passes the critical value, then both equilibriums will lose their stability. Our numerical simulations show that a complex dynamical behavior such as bifurcation or chaos phenomenon will appear for relatively large h. Both analytical and numerical results show that the discrete SIR model has a richer dynamical behavior than its continuous counterpart.
Stability Analysis and Breast Tumor Classification from 2D ARMA Models of Ultrasound Images
Bouaynaya, Nidhal
Stability Analysis and Breast Tumor Classification from 2D ARMA Models of Ultrasound Images A. Abdulsadda, N. Bouaynaya, and K. Iqbal Abstract-- Two-dimensional (2D) autoregressive moving av- erage (ARMA properties of these models have not been examined. In this paper, we investigate the stability of 2D ARMA
Algebraic geometrization of the Kuramoto model: Equilibria and stability analysis.
Mehta, Dhagash; Daleo, Noah S; Dörfler, Florian; Hauenstein, Jonathan D
2015-05-01
Finding equilibria of the finite size Kuramoto model amounts to solving a nonlinear system of equations, which is an important yet challenging problem. We translate this into an algebraic geometry problem and use numerical methods to find all of the equilibria for various choices of coupling constants K, natural frequencies, and on different graphs. We note that for even modest sizes (N???10-20), the number of equilibria is already more than 100?000. We analyze the stability of each computed equilibrium as well as the configuration of angles. Our exploration of the equilibrium landscape leads to unexpected and possibly surprising results including non-monotonicity in the number of equilibria, a predictable pattern in the indices of equilibria, counter-examples to conjectures, multi-stable equilibrium landscapes, scenarios with only unstable equilibria, and multiple distinct extrema in the stable equilibrium distribution as a function of the number of cycles in the graph. PMID:26026315
Distributed nonlinear modeling and stability analysis of axial compressor stall and surge
Catherine A. Mansoux; Daniel L. Gysling; Joga D. Setiawan; James D. Paduano
1994-01-01
This paper presents a nonlinear formulation of the Moore-Greitzer rotating stall model that is suitable for control analysis and design. The model is validated by comparing stall inception experiments to simulated stall inception transients. The shape of the nonlinear compressor characteristic is shown to be a primary determinant of stall inception transient behavior. A Lyapunov stability analysis procedure is then
Stability analysis and bifurcations of SEPIC DC-DC converter using a discrete-time model
Mohamed B. Debbat; Abdelali El Aroudi; Roberto Giral; Luis Martinez-Salamero
2002-01-01
In this work, stability analysis and bifurcations of a SEPIC dc-dc converter, operating in the continuous conduction mode (CCM) and under current-programmed control is carried out by means of a discrete-time model. Large-signal model is built, and its corresponding linearised version is performed in order to study the stability of the nominal (1-periodic orbit) operating regime. Varying the reference current,
Bifurcation and stability analysis of a two step model for monitoring anaerobic digestion processes$
Paris-Sud XI, Université de
Bifurcation and stability analysis of a two step model for monitoring anaerobic digestion processes in simulation. Keywords: Anaerobic digestion, biotechnology, steady state analysis, $ This work was supported the phenomenologic behavior of anaerobic digestion systems following the idea that all the available information
[Stability analysis of allelopathic effects of Panax notoginseng on main crops by AMMI model].
Zhang, Zi-long; Hou, Jun-ling; Wang, Wen-quan
2015-01-01
This paper is aimed to study the differences of allelopathic effects of Panax notoginseng under different allelopathic chemicals resources and selection of appropriate rotation crops. The additive main effects and multiplicative interaction ( AMMI) model had been used to evaluate the stability of allelopathic effects of P. notoginseng on the varieties of corn, wheat and rice properly. The model could use not only to evaluate the stability of non-regional trial data but also explore the interaction between the rotation crop genotypes and donor substances more efficiently. Meanwhile, correspondence analysis can be used in the AMMI to evaluate genotype stability and donor substances. Ejingza No. 1 (g6) had stronger allelopathic effects with high stability, but Yunrui No. 1 (g9) which was appropriate rotation crop genotype, had weaker allelopathic effects with high stability. These findings will aid in choosing appropriate rotation crops and establishing proper rotation system. PMID:26080543
Stability Analysis of a Simplified Yet Complete Model for Chronic Myelegenous Leukemia
Stability Analysis of a Simplified Yet Complete Model for Chronic Myelegenous Leukemia Marie Doumic is of value in understanding the dynamics of hematopoiesis and of chronic myelogenous leukemia leukemia, model simplification. 1 INRIA Paris-Rocquencourt, BANG, BP105, F78153 LeChesnay Cedex. Email
Stability Analysis of a Simplified Yet Complete Model for Chronic Myelogenous Leukemia
Perthame, Benoit
Stability Analysis of a Simplified Yet Complete Model for Chronic Myelogenous Leukemia Marie Doumic and of chronic myelogenous leukemia, and it presents the advantage of having fewer parameters, which makes, hematopoiesis, chronic myelogenous leukemia, model simplification. 1 INRIA Paris-Rocquencourt, BANG, BP105, F
A moving-boundary nodal model for the analysis of the stability of boiling channels
Veronica B. Garea; Donald A. Drew; Richard T. Lahey
1999-01-01
A moving-boundary nodal model has been derived for the linear and non-linear stability analysis of boiling channels. This model is based on the integration of the conservation (partial differential) equations in space and an approximation of the integral with a weighted average of the integrated variable evaluated at the boundaries of the nodes. The resulting system of ODEs has been
LEONID ENGELSON
This paper proposes an analytical method for stability analysis of traffic flows in a traffic network with an advanced traveller information system. The presented model describes within-day development of queues when drivers affected by real-time traffic information choose their paths en route. The model reduces to a system of differential equations with delays and discontinuous right hand sides. Equilibrium points
A model-based approach to stability analysis of autonomic-cardiac regulation.
Ataee, Pedram; Hahn, Jin-Oh; Dumont, Guy A; Noubari, Hossein A; Boyce, W Thomas
2015-06-01
This paper presents a model-based approach to analyze the stability of autonomic-cardiac regulation. In the proposed approach, a low-order lumped parameter model of autonomic-cardiac regulation is used to derive the system equilibria based on the measurements of heart rate and blood pressure, and then the stability margin associated with the equilibria is quantified via the Lyapunov?s stability analysis method. A unique strength of the proposed approach is that it provides a quantitative measure of autonomic-cardiac stability via a computationally efficient analysis. Therefore, by integrating it with system identification techniques to derive autonomic-cardiac regulation model tuned to each individual, the proposed approach is able to assess subject-specific autonomic-cardiac stability. Indeed, our initial in-silico investigation showed that the proposed approach could estimate the system equilibria accurately, and the associated stability margin behaved consistently with widely accepted physiologic knowledge. The proposed approach may be useful in identifying physiological conditions that can lead to instability in autonomic-cardiac regulation, quantifying the margin of stability and distance to instability related to autonomic-cardiac regulation, and developing interventions to prevent autonomic-cardiac instability. PMID:25898226
MHD Stability Analysis of Axisymmetric Surface Current Model Tokamaks Close to the Spheromak Regime
Toshihisa Honma; Masafumi Kito; Ikuo Kaji; Ichiro Fukai
1984-01-01
In the toroidal coordinates, a stability analysis is presented for very low-aspect-ratio tokamaks with circular cross section which is described by a surface current model (SCM) of axisymmetric equilibria. The energy principle determining the stability of plasma is treated without any expansion of aspect ratio. Numerical results show that, owing to the occurrence of the non-axisymmetric (n{=}1) unstable modes, there
Analytical modeling of the input admittance of an electric drive for stability analysis purposes
NASA Astrophysics Data System (ADS)
Girinon, S.; Baumann, C.; Piquet, H.; Roux, N.
2009-07-01
Embedded electric HVDC distribution network are facing difficult issues on quality and stability concerns. In order to help to resolve those problems, this paper proposes to develop an analytical model of an electric drive. This self-contained model includes an inverter, its regulation loops and the PMSM. After comparing the model with its equivalent (abc) full model, the study focuses on frequency analysis. The association with an input filter helps in expressing stability of the whole assembly by means of Routh-Hurtwitz criterion.
A Motorcycle Model for Stability and Control Analysis
ROBIN S. SHARP; DAVID J. N. LIMEBEER
2001-01-01
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
Stability analysis of carbon nanotube probes for an atomic force microscope via a continuum model
Q. Wang; V. K. Varadan
2005-01-01
A continuum model is employed in the stability analysis of carbon nanotubes (CNT) in the application in atomic force microscope (AFM) probes. Current experimental results have observed instability of CNT in the applications in AFM probes. However, a complete study and understanding of the instability of CNT has not yet been conducted so far. The research in the paper provides
A thyristor controlled series compensation model for power system stability analysis
J. J. Paserba; N. W. Miller; E. V. Larsen; R. J. Piwko
1995-01-01
Thyristor-controlled series compensation (TCSC) is expected to be applied in transmission systems to achieve a number of benefits. To ensure best use of this new controller, planning engineers require analysis capability tailored to the specific performance characteristics of the TCSC. This paper presents a model for TCSC which is applicable for typical transient and oscillatory stability studies. Also included is
A TwoWay Analysis of Covariance Model for Classification of Stability Data \\Lambda
New York at Stoney Brook, State University of
the degradation of the drug product by testing various batches of the product at several time points. CurrentlyA TwoWay Analysis of Covariance Model for Classification of Stability Data \\Lambda Hongshik Ahn, 1 Assessment National Center for Toxicological Research Food and Drug Administration Jefferson, AR 72079 U
Stability Analysis of a Model of Atherosclerotic Plaque Growth
Reddy, Sushruth; Seshaiyer, Padmanabhan
2015-01-01
Atherosclerosis, the formation of life-threatening plaques in blood vessels, is a form of cardiovascular disease. In this paper, we analyze a simplified model of plaque growth to derive physically meaningful results about the growth of plaques. In particular, the main results of this paper are two conditions, which express that the immune response increases as LDL cholesterol levels increase and that diffusion prevails over inflammation in a healthy artery. PMID:25883675
Global stability analysis for SEIS models with n latent classes.
Bame, Napoleon; Bowong, Samuel; Mbang, Joseph; Sallet, Gauthier; Tewa, Jean-Jules
2008-01-01
We compute the basic reproduction ratio of a SEIS model with n classes of latent individuals and bilinear incidence. The system exhibits the traditional behaviour. We prove that if R(0) < or = 1, then the disease-free equilibrium is globally asymptotically stable on the nonnegative orthant and if R (0) > 1, an endemic equilibrium exists and is globally asymptotically stable on the positive orthant. PMID:18193929
Sensitivity analysis and calibration of a coupled hydrological/slope stability model (TRIGRS)
NASA Astrophysics Data System (ADS)
Zieher, Thomas; Rutzinger, Martin; Perzl, Frank; Meißl, Gertraud
2014-05-01
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
A stability analysis of a conduit flow model for lava dome eruptions
M. Nakanishi; T. Koyaguchi
2008-01-01
Periodic variations in magma discharge rate and ground deformation have been commonly observed during lava dome eruptions. We performed a stability analysis of a conduit flow model by Barmin et al. [Barmin, A., Melnik, O., Sparks, R.S.J., 2002. Periodic behavior in lava dome eruptions. Earth and Planetary Science Letters 199 (1-2), 173–184], in which the periodic variations in magma flow
MHD Stability Analysis of Axisymmetric Surface Current Model Tokamaks Close to the Spheromak Regime
NASA Astrophysics Data System (ADS)
Honma, Toshihisa; Kito, Masafumi; Kaji, Ikuo; Fukai, Ichiro
1984-05-01
In the toroidal coordinates, a stability analysis is presented for very low-aspect-ratio tokamaks with circular cross section which is described by a surface current model (SCM) of axisymmetric equilibria. The energy principle determining the stability of plasma is treated without any expansion of aspect ratio. Numerical results show that, owing to the occurrence of the non-axisymmetric (n{=}1) unstable modes, there exists no MHD-stable ideal SCM spheromak characterized by zero external toroidal vacuum field. Instead, a stable spheromak-type plasma which comes to the ideal SCM spheromak is provided by the configuration with a very weak external toroidal field. Close to the spheromak regime (1.0
Mohammand Narimani; Hak-Keung Lam
2010-01-01
This paper presents stability analysis of polynomial fuzzy-model-based (FMB) control systems using the sum-of-squares (SOS) approach. Recently, stability analysis of the polynomial fuzzy-control systems, which is a generalized form of the well-known Takagi-Sugeno (T-S) FMB control systems, has been reported in the form of SOS-based stability conditions. Lack of information on the relations between membership functions and premise variables, in
NASA Technical Reports Server (NTRS)
Bansal, P. N.; Arseneaux, P. J.; Smith, A. F.; Turnberg, J. E.; Brooks, B. M.
1985-01-01
Results of dynamic response and stability wind tunnel tests of three 62.2 cm (24.5 in) diameter models of the Prop-Fan, advanced turboprop, are presented. Measurements of dynamic response were made with the rotors mounted on an isolated nacelle, with varying tilt for nonuniform inflow. One model was also tested using a semi-span wing and fuselage configuration for response to realistic aircraft inflow. Stability tests were performed using tunnel turbulence or a nitrogen jet for excitation. Measurements are compared with predictions made using beam analysis methods for the model with straight blades, and finite element analysis methods for the models with swept blades. Correlations between measured and predicted rotating blade natural frequencies for all the models are very good. The IP dynamic response of the straight blade model is reasonably well predicted. The IP response of the swept blades is underpredicted and the wing induced response of the straight blade is overpredicted. Two models did not flutter, as predicted. One swept blade model encountered an instability at a higher RPM than predicted, showing predictions to be conservative.
NASA Technical Reports Server (NTRS)
Venkatesan, C.; Friedmann, P. P.
1984-01-01
Hybrid Heavy Lift Airship (HHLA) is a proposed candidate vehicle aimed at providing heavy lift capability at low cost. This vehicle consists of a buoyant envelope attached to a supporting structure to which four rotor systems, taken from existing helicopters are attached. Nonlinear equations of motion capable of modelling the dynamics of this coupled multi-rotor/support frame/vehicle system have been developed. Using these equations of motion the aeroelastic and aeromechanical stability analysis is performed aimed at identifying potential instabilities which could occur for this type of vehicle. The coupling between various blade, supporting structure and rigid body modes is identified. Furthermore, the effects of changes in buoyancy ratio (Buoyant lift/total weight) on the dynamic characteristics of the vehicle are studied. The dynamic effects found are of considerable importance for the design of such vehicles. The analytical model developed is also useful for studying the aeromechanical stability of single rotor and tandem rotor coupled rotor/fuselage systems.
Haldar, Krishnendu 1978-
2012-12-06
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...
Stability analysis of an e-SEIAR model with point-to-group worm propagation
NASA Astrophysics Data System (ADS)
Wang, Fangwei; Zhang, Yunkai; Wang, Changguang; Ma, Jianfeng
2015-03-01
Internet worms have drawn significant attention due to their enormous threats to the Internet. The main goal of this paper is to explore the interaction dynamics between a malicious worm and an benign worm, using a mathematical model, namely e-SEIAR. The e-SEIAR model takes two important network environment factors into consideration: point-to-group worm propagation mode and benign worms. Furthermore, some related dynamics properties are studied, along with the analysis of how to combat the worm prevalence based on the stability of equilibria. Simulation results show that the performance of our proposed models is effective in combating such worms, in terms of decreasing the number of hosts infected by the malicious worm and reducing the malicious worm propagation speed. Based on our simulations, we believe there is great potential for an effective method to use benign worms to combat malicious worms in some point-to-group applications.
NASA Astrophysics Data System (ADS)
Georgiou, K.; Tang, J.; Riley, W. J.; Torn, M. S.
2014-12-01
Soil organic matter (SOM) decomposition is regulated by biotic and abiotic processes. Feedback interactions between such processes may act to dampen oscillatory responses to perturbations from equilibrium. Indeed, although biological oscillations have been observed in small-scale laboratory incubations, the overlying behavior at the plot-scale exhibits a relatively stable response to disturbances in input rates and temperature. Recent studies have demonstrated the ability of microbial models to capture nonlinear feedbacks in SOM decomposition that linear Century-type models are unable to reproduce, such as soil priming in response to increased carbon input. However, these microbial models often exhibit strong oscillatory behavior that is deemed unrealistic. The inherently nonlinear dynamics of SOM decomposition have important implications for global climate-carbon and carbon-concentration feedbacks. It is therefore imperative to represent these dynamics in Earth System Models (ESMs) by introducing sub-models that accurately represent microbial and abiotic processes. In the present study we explore, both analytically and numerically, four microbe-enabled model structures of varying levels of complexity. The most complex model combines microbial physiology, a non-linear mineral sorption isotherm, and enzyme dynamics. Based on detailed stability analysis of the nonlinear dynamics, we calculate the system modes as functions of model parameters. This dependence provides insight into the source of state oscillations. We find that feedback mechanisms that emerge from careful representation of enzyme and mineral interactions, with parameter values in a prescribed range, are critical for both maintaining system stability and capturing realistic responses to disturbances. Corroborating and expanding upon the results of recent studies, we explain the emergence of oscillatory responses and discuss the appropriate microbe-enabled model structure for inclusion in ESMs.
NASA Astrophysics Data System (ADS)
Conway, Sheila Ruth
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.
NASA Astrophysics Data System (ADS)
Haldar, Krishnendu
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.
Abdelhamid Dokhane; Dieter Hennig; Rizwan-uddin; Rakesh Chawla
2007-01-01
The system code RAMONA, as well as a recently developed BWR reduced order model (ROM), are employed for the stability analysis of a specific operational point of the Leibstadt nuclear power plant. This has been done in order to assess the ROM’s applicability and limitations in a quantitative manner.In the context of a detailed local bifurcation analysis carried out using
Stability analysis of a viscoelastic model for ion-irradiated silicon
Scott A. Norris
2012-01-12
To study the effect of stress within the thin amorphous film generated atop Si irradiated by Ar+, we model the film as a viscoelastic medium 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. 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 beam stress at normal incidence is unlikely to be a source of instability at any energy, supporting recent theories attributing hexagonal ordered dots to the effects of composition. In addition, 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 should greatly simplify future analytical studies of highly nonplanar surface evolution, in which the beam-injected stress is considered to be an important effect.
Stability analysis of the lambda-model during fast elbow movements.
Li, Lan; Kuanyi, Zhu
2007-01-01
In control, stability insures the reproducibility of motions and the robustness to external and internal perturbations. In this short paper, the stability of the lambda-model during fast elbow movements is analyzed, and the operation regions of the unmeasurably descending commands are calculated to guarantee the stabilizing ability of the motor control system. In this system, the elbow is modeled as a pair of antagonist muscles around the hinge joint in the horizontal plane. Both extensor and flexor muscles are described by a Hill-type muscle model. The muscle activation is produced by the physiological lambda version of the equilibrium point hypothesis (EPH). Conditions for global stability are calculated analytically by the Lyapunov theory and contraction theory. The results suggest that to guarantee the stability, the descending commands R, C and mu from central nervous system (CNS) must be tuned to the muscle properties, the muscle geometry and the geometric properties of the linkage system. PMID:18003220
Sontag, Eduardo
Stabilization and Robustness Analysis for a Chemostat Model with Two Species and Monod Growth Rates of the two species of organism; the dilution rate D(·) and the input nutrient concentration sin species chemostat model with one limiting substrate. We design feedback controllers so that an equilibrium
ERIC Educational Resources Information Center
Rhatigan, Deborah L.; Moore, Todd M.; Stuart, Gregory L.
2005-01-01
This investigation examined relationship stability among 60 women court-mandated to violence interventions by applying a general model (i.e., Rusbult's 1980 Investment Model) to predict intentions to leave current relationships. As in past research, results showed that Investment Model predictions were supported such that court-mandated women who…
Safe distance car-following model including backward-looking and its stability analysis
NASA Astrophysics Data System (ADS)
Yang, Da; Jin, Peter Jing; Pu, Yun; Ran, Bin
2013-03-01
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.
NASA Technical Reports Server (NTRS)
Tesch, W. A.; Moszee, R. H.; Steenken, W. G.
1976-01-01
NASA developed stability and frequency response analysis techniques were applied to a dynamic blade row compression component stability model to provide a more economic approach to surge line and frequency response determination than that provided by time-dependent methods. This blade row model was linearized and the Jacobian matrix was formed. The clean-inlet-flow stability characteristics of the compressors of two J85-13 engines were predicted by applying the alternate Routh-Hurwitz stability criterion to the Jacobian matrix. The predicted surge line agreed with the clean-inlet-flow surge line predicted by the time-dependent method to a high degree except for one engine at 94% corrected speed. No satisfactory explanation of this discrepancy was found. The frequency response of the linearized system was determined by evaluating its Laplace transfer function. The results of the linearized-frequency-response analysis agree with the time-dependent results when the time-dependent inlet total-pressure and exit-flow function amplitude boundary conditions are less than 1 percent and 3 percent, respectively. The stability analysis technique was extended to a two-sector parallel compressor model with and without interstage crossflow and predictions were carried out for total-pressure distortion extents of 180 deg, 90 deg, 60 deg, and 30 deg.
NASA Astrophysics Data System (ADS)
Tomoyuki Kimoto,; Tatsuya Uezu,; Masato Okada,
2010-06-01
Miyashita found that the long-term memory of visual stimuli is stored in the monkey’s inferior temporal cortex and that the temporal correlation in terms of the learning order of visual stimuli is converted into spatial correlation in terms of the firing rate patterns of the neuron group. To explain Miyashita’s findings, Griniasty et al. [Neural Comput. 5 (1993) 1] and Amit et al. [J. Neurosci. 14 (1994) 6435] proposed the attractor neural network model, and the Amit model has been examined only for the stable state acquired by storing memory patterns in a fixed sequence. In the real world, however, the learning order has statistical continuity but it also has randomness, and the stability of the state changes depending on the statistical properties of learning order when memory patterns are stored randomly. In addition, it is preferable for the stable state to become an appropriate attractor that reflects the relationship between memory patterns by the statistical properties of the learning order. In this study, we examined the dependence of the stable state on the statistical properties of the learning order without modifying the Amit model. The stable state was found to change from the correlated attractor to the Hopfield or Mp attractor, which is the mixed state with all memory patterns when the rate of random learning increases. Furthermore, we found that if the statistical properties of the learning order change, the stable state can change to an appropriate attractor reflecting the relationship between memory patterns.
NASA Technical Reports Server (NTRS)
Acree, C. W., Jr.
1993-01-01
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.
Dudásová, Dorota; Rune Flĺten, Geir; Sjöblom, Johan; Řye, Gisle
2009-09-15
The transmission profiles of one- to three-component particle suspension mixtures were analyzed by multivariate methods such as principal component analysis (PCA) and partial least-squares regression (PLS). The particles mimic the solids present in oil-field-produced water. Kaolin and silica represent solids of reservoir origin, whereas FeS is the product of bacterial metabolic activities, and Fe(3)O(4) corrosion product (e.g., from pipelines). All particles were coated with crude oil surface active components to imitate particles in real systems. The effects of different variables (concentration, temperature, and coating) on the suspension stability were studied with Turbiscan LAb(Expert). The transmission profiles over 75 min represent the overall water quality, while the transmission during the first 15.5 min gives information for suspension behavior during a representative time period for the hold time in the separator. The behavior of the mixed particle suspensions was compared to that of the single particle suspensions and models describing the systems were built. The findings are summarized as follows: silica seems to dominate the mixture properties in the binary suspensions toward enhanced separation. For 75 min, temperature and concentration are the most significant, while for 15.5 min, concentration is the only significant variable. Models for prediction of transmission spectra from run parameters as well as particle type from transmission profiles (inverse calibration) give a reasonable description of the relationships. In ternary particle mixtures, silica is not dominant and for 75 min, the significant variables for mixture (temperature and coating) are more similar to single kaolin and FeS/Fe(3)O(4). On the other hand, for 15.5 min, the coating is the most significant and this is similar to one for silica (at 15.5 min). The model for prediction of transmission spectra from run parameters gives good estimates of the transmission profiles. Although the model for prediction of particle type from transmission parameters is able to predict some particles, further improvement is required before all particles are consistently correctly classified. Cross-validation was done for both models and estimation errors are reported. PMID:19560152
Stability analysis of fourth-order charge-pump PLLs using linearized discrete-time models
Chia-Yu Yao; Chun-Te Hsu; Chih-Chun Hsieh
2007-01-01
In this paper, we derive state equations for linearized discrete-time models of fourth-order charge-pump phase-locked loops. We solve the differential equations of the loop filter by using the initial conditions and the boundary conditions in a period. The solved equations are linearized and rearranged as discrete-time state equations for checking stability conditions. Some behavioral simulations are performed to verify the
Bifurcation analysis and dynamic stability
Washburn, R.B. Jr.; Mehra, R.K.
1980-01-01
Using tools of bifurcation analysis, we examine the long-term behavior of implicit differential equations which are defined by simultaneous ordinary differential equations and implicit algebraic equations. The analysis shows how certain nonlinearities can make the long term behavior of such dynamic systems sensitive to very small amplitude uncertainties and noise. This sensitivity makes the long term behavior practically unpredictable. At the same time the analysis suggests simple stochastic models in case of such unpredictable behavior. Implicit differential equations are often used in modeling the dynamic behavior of electric power systems. Our analysis indicates essential limitations on the ability of such models to predict long term behavior of the system, and it suggests ways to improve the ability of these models to describe important features of long term behavior. This analysis of implicit differential equations has significant implications for the study of the long term dynamic stability of power systems. The analysis also sheds light on the origin and significance of multiple solutions of the load flow equations.
Stability Analysis of a Simplified Yet Complete Model for Chronic Myelegenous Leukemia
Jauffret, Marie Doumic; Perthame, Benoît
2009-01-01
We analyze the asymptotic behavior of a partial differential equation (PDE) model for hematopoiesis. This PDE model is derived from the original agent-based model formulated by (Roeder et al., Nat. Med., 2006), and it describes the progression of blood cell development from the stem cell to the terminally differentiated state. To conduct our analysis, we start with the PDE model of (Kim et al, JTB, 2007), which coincides very well with the simulation results obtained by Roeder et al. We simplify the PDE model to make it amenable to analysis and justify our approximations using numerical simulations. An analysis of the simplified PDE model proves to exhibit very similar properties to those of the original agent-based model, even if for slightly different parameters. Hence, the simplified model is of value in understanding the dynamics of hematopoiesis and of chronic myelogenous leukemia, and it presents the advantage of having fewer parameters, which makes comparison with both experimental data and alternative...
A simplified spatial model for BWR stability
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
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)
Global stability analysis - a key enabler in reduced order models and flow control
NASA Astrophysics Data System (ADS)
Morzy?ski, M.; Stankiewicz, W.; Thiele, F.; Noack, B. R.; Tadmor, G.
2012-01-01
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).
Stability analysis of a mathematical model in a microcosm with piecewise constant arguments.
Oztürk, I; Bozkurt, F; Gurcan, F
2012-12-01
In this paper, we have modeled a population density of a bacteria species in a microcosm by using a differential equation, [Formula in text] where t ? 0, the parameters r, ?, ?(0) and ?(1) denote positive numbers ann [t] denotes the integer part of [Formula in text]. First, to obtain the local and global behaviors, the boundedness character and the periodic nature of the population density for bacteria, discrete solutions of differential Eq. (A) is investigated. Examinations of the stability characterization of (A) show that increasing of the population growth rate decreases the local stability of the positive equilibrium point. Due to this result we need to consider a second approximation to obtain stability of population density. This can be performed at low density by incorporating an Allee function to (A) at time t. For the theoretical results obtained here we give an example by taking some parameter values from experimental data of bacteria populations [8] and show that the experimental and theoretical results for both models with and without Allee effect are in good agreement. PMID:22954716
Stability analysis using a geometrically nonlinear assumed strain solid shell element model
Chahngmin Cho; Hoon C. Park; Sung W. Lee
1998-01-01
A solid shell element model with six degrees of freedom per node is applied to buckling and postbuckling analysis of geometrically nonlinear shell structures. The present model allows changes in the thickness direction and does not require rotational angles or parameters for the description of the kinematics of deformation. The finite element model is constructed based on the assumed strain
Cairoli, Andrea; Piovani, Duccio; Jensen, Henrik Jeldtoft
2014-12-31
We propose a new procedure to monitor and forecast the onset of transitions in high-dimensional complex systems. We describe our procedure by an application to the tangled nature model of evolutionary ecology. The quasistable configurations of the full stochastic dynamics are taken as input for a stability analysis by means of the deterministic mean-field equations. Numerical analysis of the high-dimensional stability matrix allows us to identify unstable directions associated with eigenvalues with a positive real part. The overlap of the instantaneous configuration vector of the full stochastic system with the eigenvectors of the unstable directions of the deterministic mean-field approximation is found to be a good early warning of the transitions occurring intermittently. PMID:25615342
Nodal analysis for reactor kinetics and stability
1981-01-01
General space kinetics models have been developed for more accurate stability analysis utilizing nodal analysis, a commonly used technique for analyzing power distributions in large power reactors. Kinetics parameters for use in these kinetics models have been properly derived by utilizing self-consistent nodal data and power distributions. The procedure employed in the nodal code SIMULATE has been utilized for power
Jerez, S; Chen, B
2015-06-01
In order to analyze theoretically the dynamics of osteoblast and osteoclast cells in the bone remodeling process we first consider a simplified Komarova model. The existence of periodic solutions, which is consistent with the biophysical phenomenon, has been observed only numerically for the general model. By a stability analysis of the simplified model we provide sufficient conditions to obtain existence and uniqueness of positive periodic solutions. Considering recent biological evidence about the participation of another cells like osteocytes in the regulation of bone remodeling, we incorporate to the simplified model a new term as a way to model the signaling of external agents in the remodeling process. Finally, we demonstrate that this new model has stable positive non-periodic solutions. All the theoretical results are accompanied by computational simulations. PMID:25784536
A dynamic model describing heterotrophic culture of Chlorella and its stability analysis.
Zhang, Yan; Ma, Wanbiao; Yan, Hai; Takeuchi, Yasuhiro
2011-10-01
Chlorella is an important species of microorganism, which includes about 10 species. Chlorella USTB01 is a strain of microalga which is isolated from Qinghe River in Beijing and has strong ability in the utilization of organic compounds and was identified as Chlorella sp. (H. Yan et al, Isolation and heterotrophic culture of Chlorella sp., J. Univ. Sci. Tech. Beijing, 2005, 27:408-412). In this paper, based on the standard Chemostat models and the experimental data on the heterotrophic culture of Chlorella USTB01, a dynamic model governed by differential equations with three variables (Chlorella, carbon source and nitrogen source) is proposed. For the model, there always exists a boundary equilibrium, i.e. Chlorella-free equilibrium. Furthermore, under additional conditions, the model also has the positive equilibria, i.e., the equilibira for which Chlorella, carbon source and nitrogen source are coexistent. Then, local and global asymptotic stability of the equilibria of the model have been discussed. Finally, the parameters in the model are determined according to the experimental data, and numerical simulations are given. The numerical simulations show that the trajectories of the model fit the trends of the experimental data well. PMID:21936603
PrimeSupplier Cross-Program Impact Analysis and Supplier Stability Indicator Simulation Model
NASA Technical Reports Server (NTRS)
Calluzzi, Michael
2009-01-01
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.
Shuttle wing panel stability analysis
NASA Technical Reports Server (NTRS)
Balderes, T.; Mason, P. W.; Ranalli, E.; Zalesak, J.; Levy, A.
1975-01-01
The use of the NASTRAN program in the shuttle wing stability analysis is described, and details of the actual structure, the finite element idealization, and the NASTRAN results are given. A comparison of the NASTRAN results with those obtained with another computer program and with hand generated results indicates good agreement. An alternate approach for solving eigenvalue problems is illustrated and shows a considerable savings in computer time. Some emphasis is placed on the relationship of the NASTRAN analysis in the design process bringing out more clearly the contribution of the results and showing the importance of the mode plots. A deficiency in the NASTRAN plate elements when used to model structures made up of intersecting plates is discussed.
NASA Technical Reports Server (NTRS)
Wolfgang, R.; Natarajan, T.; Day, J.
1987-01-01
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.
Rajagopal, K.R.
1993-07-01
In the previous report the linearized stability equations for the flow of granular materials down an inclined plane, modeled by the kinetic constitutive theory [cf Richman & Marciniec (1990)] were derived. Here, we use the approximate solution of Richman & Marciniec (1990) as the base solution for the linearized stability analysis. The governing equations obtained are solved numerically to obtain the marginal stability curves which are presented in this report.
NASA Astrophysics Data System (ADS)
Esmaieli, Kamran; Hadjigeorgiou, John; Grenon, Martin
2013-11-01
The longevity of ore pass systems is an important consideration in underground mines. This is controlled to a degree by the structural stability of an ore pass which can be compromised by changes in the stress regime and the degree of fracturing of the rock mass. A failure mechanism specific to ore pass systems is damage on the ore pass wall by impact load or wear by material flow. Structural, stress and material flow-induced failure mechanisms interact with severe repercussions, although in most cases one mechanism is more dominant. This paper aims to provide a better understanding of the interaction of ore pass failure mechanisms in an operating mine. This can provide an aid in the design of ore pass systems. A two-stage numerical approach was used for the back analysis of an ore pass at Brunswick mine in Canada. The first stage in the analysis relied on a 3D boundary element analysis to define the stress regime in the vicinity of the ore pass. The second stage used a synthetic rock mass (SRM) model, constructed from a discrete fracture network, generated from quantitative rock mass field data. The fracture network geometry was introduced into a bonded particle model, in a particle flow code (PFC). Subsequently, the ore pass was excavated within the SRM model. A stability analysis quantified the extent of rock mass failure around the ore pass due to the interaction of pre-existing fractures and the failure of the intact rock bridges between these fractures. The resulting asymmetric failure patterns along the length of the ore pass were controlled to a large degree by the in situ fractures. The influence of particle flow impact was integrated into the model by projecting a discrete rock fragment against the ore pass walls represented by the SRM model. The numerical results illustrated that material impact on ore pass walls resulted in localised damage and accelerated the stress-induced failure.
Clifton Ellis; Hassan Nouri; Rade Ciric; B. Miedzinsky
2007-01-01
Synchronous machines, that is, practically all generators together with synchronous motors and synchronous compensators, are the most important power system components in the analysis of electromechanical and electromagnetic dynamics in power systems. Power system modelling (PSM) in general is an area of ongoing interest in the transmission management and control systems community. Continual development is driven by the traditional task
Guangming Lv; Xiaomeng Sun; Jian Wang
2011-01-01
n Abstract-In this paper, we improved the standard algorithm for telescopic boom by finite element method. The structure vibration stability of telescopic boom is obtained through model analysis, and then by comparison and analysis, the precise model was established. Thus through an example, we have tested and verified the characteristics of the telescopic boom that is easy to contended, and
Voltage stability evaluation using modal analysis
B. Gao; G. K. Morison; P. Kundur
1992-01-01
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
Stability analysis of an acoustically levitated disk
Junhui Hu; Kentaro Nakamura; Sadayuki Ueha
2003-01-01
In this paper, a model is developed for the stability analysis of an acoustically levitated disk on the basis of analyzing eddy acoustic streaming and acoustic viscous stress. In the model, the effect of the acoustic streaming outside the boundary layer that is on the surface of the levitated disk is properly taken into account. Also, the calculation of sound
Analysis of Chatter Stability in Facing
NASA Astrophysics Data System (ADS)
Kebdani, S.; Sahli, A.; Rahmani, O.; Boutchicha, D.; Belarbi, A.
This study attempts to develop a chatter model for predicting chatter stability conditions in hard turning. A linear model is developed by introducing non-uniform load distribution on a tool tip to account for the flank wear effect. Stability analysis based on the root locus method and the harmonic balance method is conducted to determine a critical stability parameter. To validate the model, a series of experiment is carried out to determine the stability limits as well as certain characteristic parameters for facing and straight turning. Chatter in hard turning has the feature that the critical stability limits increase very rapidly when the cutting speed is higher than 13 rev sec-1 for all feed directions. The main contributions of the study are threefold. First, chatter-free cutting conditions are predicted and can be used as a guideline for designing tools and machines. Second, the characteristics of chatter in hard turning, which is observed for the first time, helps to broaden our physical understanding of the interactions between the tool and the workpiece in hard turning. Third, experimental stability limits for different flank wear can contribute to lead more reasonable ways to consider the flank wear effect in chatter models of hard turning. Based on these contributions, the proposed linear chatter model will support to improve the productivity in many manufacturing processes. In addition, the chatter experimental data will be useful to develop other chatter models in hard turning.
NASA Technical Reports Server (NTRS)
Sevart, F. D.
1971-01-01
An analytical and mechanization study was conducted for two flutter stability augmentation systems. One concept uses only the wing trailing edge control surface. Another concept uses leading and trailing edge control surfaces operating simultaneously. The combined use of leading and trailing edge control surfaces should improve the surface coupling (controllability) with vertical bending and torsional structural modes and decrease the coupling between bending and torsional modes. The study was directed toward stability augmentation systems characteristics for the supersonic transport aircraft.
G. C. Park; M. Podowski; M. Becker; Lahey R. T. Jr
1983-01-01
A state-of-the-art one-dimensional thermal-hydraulic model has been developed to be used for the linear analysis of nuclear-coupled density-wave oscillations in a boiling water nuclear reactor (BWR). The model accounts for phasic slip, distributed spacers, subcooled boiling, space\\/time-dependent power distributions and distributed heated wall dynamics. In addition to a parallel channel stability analysis, a detailed model was derived for the BWR
1983-01-01
A state-of-the-art one-dimensional thermal-hydraulic model has been developed to be used for the linear analysis of nuclear-coupled density-wave oscillations in a boiling water nuclear reactor (BWR). The model accounts for phasic slip, distributed spacers, subcooled boiling, space\\/time-dependent power distributions and distributed heated wall dynamics. In addition to a parallel channel stability analysis, a detailed model was derived for the BWR
Energy function analysis for power system stability
M. A. Pai
1989-01-01
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.
Jacobi stability analysis of the Lorenz system
Tiberiu Harko; Chor Yin Ho; Chun Sing Leung; Stan Yip
2015-04-11
We perform the study of the stability of the Lorenz system by using the Jacobi stability analysis, or the Kosambi-Cartan-Chern (KCC) theory. The Lorenz model plays an important role for understanding hydrodynamic instabilities and the nature of the turbulence, also representing a non-trivial testing object for studying non-linear effects. The KCC theory represents a powerful mathematical method for the analysis of dynamical systems. In this approach we describe the evolution of the Lorenz system in geometric terms, by considering it as a geodesic in a Finsler space. By associating a non-linear connection and a Berwald type connection, five geometrical invariants are obtained, with the second invariant giving the Jacobi stability of the system. The Jacobi (in)stability is a natural generalization of the (in)stability of the geodesic flow on a differentiable manifold endowed with a metric (Riemannian or Finslerian) to the non-metric setting. In order to apply the KCC theory we reformulate the Lorenz system as a set of two second order non-linear differential equations. The geometric invariants associated to this system (nonlinear and Berwald connections), and the deviation curvature tensor, as well as its eigenvalues, are explicitly obtained. The Jacobi stability of the equilibrium points of the Lorenz system is studied, and the condition of the stability of the equilibrium points is obtained. Finally, we consider the time evolution of the components of the deviation vector near the equilibrium points.
NASA Astrophysics Data System (ADS)
Tsamopoulos, John; Karapetsas, George
2013-11-01
It is well known that during extrusion of viscoelastic fluids various flow instabilities may arise resulting in a distorted free surface. In order to investigate the factors generating these instabilities we perform a linear stability analysis at zero Reynolds number around the steady solution of the cylindrical or planar stick-slip flow for a viscoelastic fluid following the PTT model. The stick-slip flow is an important special case of the extrudate swell problem, since the latter reduces to it in the limit of infinite surface tension. We will show that the flow becomes unstable as the Weissenberg number increases above a critical value, due to a Hopf bifurcation suggesting that the flow will become periodic in time. Both the critical value of the Weissenberg number and the frequency of the instability depend strongly on the rheological parameters of the viscoelastic model. The elasticity alone can be responsible for the appearance of instabilities in the extrusion process of viscoelastic fluids and the often used assumptions of wall slip or compressibility, although they might be present, are not required. Finally, the mechanisms that produce these instabilities are examined through energy analysis of the disturbance flow. It is well known that during extrusion of viscoelastic fluids various flow instabilities may arise resulting in a distorted free surface. In order to investigate the factors generating these instabilities we perform a linear stability analysis at zero Reynolds number around the steady solution of the cylindrical or planar stick-slip flow for a viscoelastic fluid following the PTT model. The stick-slip flow is an important special case of the extrudate swell problem, since the latter reduces to it in the limit of infinite surface tension. We will show that the flow becomes unstable as the Weissenberg number increases above a critical value, due to a Hopf bifurcation suggesting that the flow will become periodic in time. Both the critical value of the Weissenberg number and the frequency of the instability depend strongly on the rheological parameters of the viscoelastic model. The elasticity alone can be responsible for the appearance of instabilities in the extrusion process of viscoelastic fluids and the often used assumptions of wall slip or compressibility, although they might be present, are not required. Finally, the mechanisms that produce these instabilities are examined through energy analysis of the disturbance flow. The authors would like to acknowledge the financial support by the General Secretariat of Research and Technology of Greece under the Action ``Supporting Postdoctoral Researchers'' (Grant No: PE8/906), and under the ``Excellence Program'' (Grant No: 1918)
Modeling and Analysis for Tearing Mode Stability in DIII-D Hybrid Discharges
NASA Astrophysics Data System (ADS)
Kim, Kyungjin; Park, J. M.; Murakami, M.; La Haye, R. J.; Na, Yong-Su; DIII-D Team
2014-10-01
Plasma rotation in DIII-D hybrid scenario plasmas is found to change the stability of tearing modes (TMs) in a profound manner. It is important to understand the onset threshold and the evolution of TMs for developing a high-performance steady-state fusion reactor. The modified Rutherford equation (MRE) estimates the growth rate of an island and is used to analyze the TM stability. The change in TM stability was investigated in hybrid plasmas with various conditions including rotation, normalized beta, q profile, and so on. The measured island width is larger in low q95 cases and increased as plasma rotation was reduced. The island width calculated by MRE with TM stability index ?' assumed from its poloidal mode number, -m/r, showed a good agreement during high rotation, but could not be matched to the experimental island width at lower rotation. Simulations of TMs using resistive MHD codes such as NIMROD and PEST3 will also be presented and compared with experiments to determine the possibility for predicting TM onset by ?' calculation. Work supported in part by the US DOE under DE-AC05-00OR22725 and DE-FC02-04ER54698.
NASA Astrophysics Data System (ADS)
Curtaz, M.; Ferrero, A. M.; Roncella, R.; Segalini, A.; Umili, G.
2014-03-01
Several high-altitude slope instability phenomena, involving rock blocks of different volumes, have been observed in recent years. The increase in these phenomena could be correlated to climatic variations and to a general increase in temperature that has induced both ice melting with consequent water seepage and glacial lowering, with a consequent loss of support of the rock face. The degradation of the high-altitude thermal layer, which is known as "permafrost", can determine the formation of highly fractured rock slopes where instabilities can concentrate. The present research has developed a methodology to improve the understanding and assessment of rock slope stability conditions in high mountain environments where access is difficult. The observed instabilities are controlled by the presence of discontinuities that can determine block detachments. Consequently, a detailed survey of the rock faces is necessary, both in terms of topography and geological structure, and in order to locate the discontinuities on the slope to obtain a better geometric reconstruction and subsequent stability analysis of the blocky rock mass. Photogrammetric surveys performed at different times allow the geostructure of the rock mass to be determined and the rock block volumes and detachment mechanisms to be estimated, in order to assess the stability conditions and potential triggering mechanisms. Photogrammetric surveys facilitate both the characterisation of the rock mass and the monitoring of slope instabilities over time. The methodology has been applied in a case study pertaining to the North Face of Aiguilles Marbrées in the Mont Blanc massif, which suffers from frequent instability phenomena. A slope failure that occurred in 2007 has been back-analysed using both the limit equilibrium method (LEM) and 3D distinct element modelling (DEM). The method has been supported and validated with traditional in situ surveys and measurements of the discontinuity orientation and other rock mass features.
Global Stability Analysis for Linear Dynamics
NASA Astrophysics Data System (ADS)
Morzy?ski, Marek; Noack, Bernd R.; Tadmor, Gilead
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.
Modeling of a self-excited pulse combustor and stability analysis
Yanying Xu; Ming Zhai; Peng Dong; Fei Wang; Qunyi Zhu
2011-01-01
The major bottleneck for popularization and utilization of the conventional mechanical valve pulse combustors is the self-priming mode of gas supply. An aerodynamic valve (as against mechanical valve) self-excited pulse combustor of the Helmholtz-type with continuous supply of gas and air was designed and a mathematical model was established in this paper. The theoretical model employed well-stirred reactor model and
Dorota Dudášová; Geir Rune Flĺten; Johan Sjöblom; Gisle Řye
2009-01-01
The transmission profiles of one- to three-component particle suspension mixtures were analyzed by multivariate methods such as principal component analysis (PCA) and partial least-squares regression (PLS). The particles mimic the solids present in oil-field-produced water. Kaolin and silica represent solids of reservoir origin, whereas FeS is the product of bacterial metabolic activities, and Fe3O4 corrosion product (e.g., from pipelines). All
Stability analysis of a simplified model of a fluidized bed combustor
Trevino, C. (Div. de Estudios de Posgrado, Facultad de Ingenieria, UNAM (MX)); Herrera, C. (Instituto de Investigaciones Electricas, Departamento Mecanico, A.P. 5-849 (MX)); Garcia-Ybarra, P. (Universidad Nacional de Educacion a Distancia, Departamento de Fisica Experimental, Madrid (ES))
1990-06-01
The transient behavior of a simplified two-phase model of a fluidized bed combustor is analyzed in this article. The chemical reaction assumed was only the heterogeneous reaction C + 1/2 O{sub 2} {r arrow} CO, which is also assumed to be controlled by diffusion. A set of nonlinear perturbation equations, around the steady-state solution, have been obtained. The corresponding set of linearized equations are then solved, obtaining the stable and unstable regions in the parametric space. The system proves to be always stable for the possible parametric set of the present model.
The Existence and Stability Analysis of the Equilibria in Dengue Disease Infection Model
NASA Astrophysics Data System (ADS)
Anggriani, N.; Supriatna, A. K.; Soewono, E.
2015-06-01
In this paper we formulate an SIR (Susceptible - Infective - Recovered) model of Dengue fever transmission with constant recruitment. We found a threshold parameter K0, known as the Basic Reproduction Number (BRN). This model has two equilibria, disease-free equilibrium and endemic equilibrium. By constructing suitable Lyapunov function, we show that the disease- free equilibrium is globally asymptotic stable whenever BRN is less than one and when it is greater than one, the endemic equilibrium is globally asymptotic stable. Numerical result shows the dynamic of each compartment together with effect of multiple bio-agent intervention as a control to the dengue transmission.
Stability and Asymptotic Analysis of a Fluid-Particle Interaction Model
Goudon, Thierry
: gravity settling processes or centrifugal forces. These procedures find their applications modelling Diesel engines or rocket propulsors [45, 46]. In what follows, we describe a single specie forces can be produced by a great deal of relevant physical mechanisms: gravity, centrifugal, electric
Elaiw, A M
2015-12-01
In this paper, we propose and analyse a virus dynamics model with humoral immune response including latently infected cells. The incidence rate is given by Beddington-DeAngelis functional response. We have derived two threshold parameters, the basic infection reproduction number [Formula: see text] and the humoral immune response activation number [Formula: see text] which completely determined the basic and global properties of the virus dynamics model. By constructing suitable Lyapunov functions and applying LaSalle's invariance principle we have proven that if [Formula: see text], then the infection-free equilibrium is globally asymptotically stable (GAS), if [Formula: see text], then the chronic-infection equilibrium without humoral immune response is GAS, and if [Formula: see text], then the chronic-infection equilibrium with humoral immune response is globally asymptotically stable. These results are further illustrated by numerical simulations. PMID:26145479
Stability analysis of a new model for floating caliper disk brake
T. Jearsiripongkul; G. Chakraborty; P. Hagedorn
2002-01-01
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:
Algebraic Approaches to Stability Analysis of Biological Systems
Paris-Sud XI, Université de
Algebraic Approaches to Stability Analysis of Biological Systems Wei Niu and Dongming Wang Abstract. In this paper, we improve and extend the approach of Wang and Xia for stability analysis of biological systems system, triangular decomposition. 1. Introduction Many biological networks can be modeled by dynamical
Stability regions for maintaining efficiency in data envelopment analysis
Lawrence M. Seiford; Joe Zhu
1998-01-01
This paper develops a procedure for performing a sensitivity analysis of the efficient decision making units (DMUs) within the Charnes et al. (CCR) [European Journal of Operational Research 2 (1978) 429–444] model of data envelopment analysis (DEA). The procedure yields an exact `input stability region' and `output stability region' within which the efficiency of a specific efficient DMU remains unchanged.
Frequency-dependent nodal analysis of boiling water reactor stability
J. K. Park; M. Becker; G. C. Park
1983-01-01
A general spatial kinetics model has been developed for boiling water reactor (BWR) stability analysis utilizing nodal analysis, a commonly used technique for analyzing power distributions in large power reactors. Kinetics parameters for use in the kinetics equations have been derived by utilizing self-consistent nodal data and power distribution. Spatial coupling effects on the stability margin have been analyzed for
Enhanced rotor modeling tailored for rub dynamic stability analysis and simulation
NASA Technical Reports Server (NTRS)
Davis, R. R.
1989-01-01
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.
NASA Technical Reports Server (NTRS)
Jordan, Keith J.
1998-01-01
This report documents results from the NASA-Langley sponsored Euler Technology Assessment Study conducted by Lockheed-Martin Tactical Aircraft Systems (LMTAS). The purpose of the study was to evaluate the ability of the SPLITFLOW code using viscous and inviscid flow models to predict aerodynamic stability and control of an advanced fighter model. The inviscid flow model was found to perform well at incidence angles below approximately 15 deg, but not as well at higher angles of attack. The results using a turbulent, viscous flow model matched the trends of the wind tunnel data, but did not show significant improvement over the Euler solutions. Overall, the predictions were found to be useful for stability and control design purposes.
NASA Astrophysics Data System (ADS)
Anggriani, N.; Putri, L. Nurul; Supriatna, A. K.
2015-03-01
Many plants could not escape from diseases caused by fungi. The use of fungicide can help to reduce the spread of the fungi but if it used continuously with the same dosage, the fungi would be invulnerable to fungicide eventually. Hence, it is critical to know the appropriate level of fungicide application and its impact on the dynamics of the plants. In this paper we use an explicit model of fungal outbreaks of plant by taking into account a curative factor including the dynamic of fungicides itself. Granting of fungicide on crops is useful to control the infected plants as well as protecting the vulnerable plants. Optimal control is used to find out how many doses of the appropriate fungicide should be used to cure infected plants. Optimal control is obtained by applying Pontryagin's Minimum Principle. We found that the presence of appropriate level of fungicide speeds up the reduction of infected plants as well as accelerates the growth of healthy plants.
NASA Astrophysics Data System (ADS)
Rötzer, K.; Montzka, C.; Bogena, H.; Wagner, W.; Kerr, Y. H.; Kidd, R.; Vereecken, H.
2014-11-01
Since soil moisture is an important influencing factor of the hydrological cycle, knowledge of its spatio-temporal dynamics is crucial for climate and hydrological modeling. In recent years several soil moisture data products from satellite information have become available with global coverage and sub-monthly resolution. Since the remote sensing of soil moisture is an indirect measurement method and influenced by a large number of factors (e.g. atmospheric correction, vegetation, soil roughness, etc.), a comprehensive validation of the resulting soil moisture products is required. However, the coarse spatial resolution of these products hampers the comparison with point-scale in situ measurements. Therefore, upscaling of in situ to the scale of the satellite data is needed. We present the validation results of the soil moisture products of the years 2010-2012 retrieved from the Soil Moisture and Ocean Salinity (SMOS) and the Advanced Scatterometer (ASCAT) for the Rur and Erft catchments in western Germany. For the upscaling of in situ data obtained from three test sites of the Terrestrial Environmental Observatories (TERENO) initiative we used the hydrological model WaSiM ETH. Correlation of the SMOS product to modeled and upscaled soil moisture resulted in a mean correlation coefficient of 0.28 whereas for ASCAT a correlation coefficient of 0.50 was obtained. However, for specific regions the SMOS product showed similar correlation coefficients as the ASCAT product. While for ASCAT correlation was mainly dependent on topography and vegetation, SMOS was also influenced by radiofrequency interferences in our study area. Both products show dry biases as compared to the soil moisture reference. However, while SMOS showed relatively constant bias values, ASCAT bias is variable throughout the year. As an additional validation method we performed a temporal stability analysis of the retrieved spatio-temporal soil moisture data. Through investigation of mean relative differences of soil moisture for every pixel, their standard deviations and their rankings, we analyzed the temporal persistence of spatial patterns. Our results show high standard deviations for both SMOS and ASCAT soil moisture products as compared to modeled soil moisture, indicating a lower temporal persistence. The consistence of ranks of mean relative differences was low for SMOS and relative ASCAT soil moisture compared to modeled soil moisture, while ASCAT soil moisture, converted to absolute values, showed higher rank consistence.
Multidimensional nodal analysis of boiling water reactor stability
1985-01-01
A computer program, NUFREQ-3D, was developed for boiling water reactor stability analysis. The code, which incorporates sophisticated thermal-hydraulic model coupled with a space dependent nodal neutronic model, is able to evaluate the system stabilities in terms of state variables such as inlet flow rate, power density, and system pressure. The detailed full 3-D representation was developed for more accurate stability
Stability analysis of a polymer coating process
NASA Astrophysics Data System (ADS)
Kallel, A.; Hachem, E.; Demay, Y.; Agassant, J. F.
2015-05-01
A new coating process involving a short stretching distance (1 mm) and a high draw ratio (around 200) is considered. The resulting thin molten polymer film (around 10 micrometers) is set down on a solid primary film and then covered by another solid secondary film. In experimental studies, periodical fluctuation in the thickness of the coated layer may be observed. The processing conditions markedly influence the onset and the development of these defects and modeling will help our understanding of their origins. The membrane approach which has been commonly used for cast film modeling is no longer valid and two dimensional time dependent models (within the thickness) are developed in the whole domain (upstream die and stretching path). A boundary-value problem with a free surface for the Stokes equations is considered and stability of the free surface is assessed using two different numerical strategies: a tracking strategy combined with linear stability analysis involving computation of leading eigenvalues, and a Level Set capturing strategy coupled with transient stability analysis.
Beg, Ilyas; Minton, Allen P; Hassan, Md Imtaiyaz; Islam, Asimul; Ahmad, Faizan
2015-06-16
The reversible thermal denaturation of apo ?-lactalbumin and lysozyme was monitored via measurement of changes in absorbance and ellipticity in the presence of varying concentrations of seven mono- and oligosaccharides: glucose, galactose, fructose, sucrose, trehalose, raffinose, and stachyose. The temperature dependence of the unfolding curves was quantitatively accounted for by a two-state model, according to which the free energy of unfolding is increased by an amount that is independent of temperature and depends linearly upon the concentration of added saccharide. The increment of added unfolding free energy per mole of added saccharide was found to depend approximately linearly upon the extent of oligomerization of the saccharide. The relative strength of stabilization of different saccharide oligomers could be accounted for by a simplified statistical-thermodynamic model attributing the stabilization effect to volume exclusion deriving from steric repulsion between protein and saccharide molecules. PMID:26000826
NASA Technical Reports Server (NTRS)
Sevart, F. D.; Patel, S. M.
1973-01-01
Testing and evaluation of a stability augmentation system for aircraft flight control were performed. The flutter suppression system and synthesis conducted on a scale model of a supersonic wing for a transport aircraft are discussed. Mechanization and testing of the leading and trailing edge surface actuation systems are described. The ride control system analyses for a 375,000 pound gross weight B-52E aircraft are presented. Analyses of the B-52E aircraft maneuver load control system are included.
Adjoint Equations in Stability Analysis
NASA Astrophysics Data System (ADS)
Luchini, Paolo; Bottaro, Alessandro
2014-01-01
The objective of this article is to review some developments in the use of adjoint equations in hydrodynamic stability theory. Adjoint-based sensitivity analysis finds both analytical and numerical applications much beyond those originally imagined. It can be used to identify optimal perturbations, pinpoint the most receptive path to break down, select the most destabilizing base-flow defect in a nominally stable configuration, and map the structural sensitivity of an oscillator. We focus on two flow cases more closely: the noise-amplifying instability of a boundary layer and the global mode occurring in the wake of a cylinder. For both cases, the clever interpretation and use of direct and adjoint modes provide key insight into the process of the transition to turbulence.
Stability analysis and future singularity of the $m^2 R \\Box^{-2} R$ model of non-local gravity
Yves Dirian; Ermis Mitsou
2014-12-02
We analyse the classical stability of the model proposed by Maggiore and Mancarella, where gravity is modified by a term $\\sim m^2 R \\Box^{-2} R$ to produce the late-time acceleration of the expansion of the universe. Our study takes into account all excitations of the metric that can potentially drive an instability. There are some subtleties in identifying these modes, as a non-local field theory contains dynamical fields which yet do not correspond to degrees of freedom. Since some of them are ghost-like, we clarify the impact of such modes on the stability of the solutions of interest that are the flat space-time and cosmological solutions. We then find that flat space-time is unstable under scalar perturbations, but the instability manifests itself only at cosmological scales, i.e. out of the region of validity of this solution. It is therefore the stability of the FLRW solution which is relevant there, in which case the scalar perturbations are known to be well-behaved by numerical studies. By finding the analytic solution for the late-time behaviour of the scale factor, which leads to a big rip singularity, we argue that the linear perturbations are bounded in the future because of the domination of Hubble friction. In particular, this effect damps the scalar ghost perturbations which were responsible for destabilizing Minkowski space-time. Thus, the model remains phenomenologically viable.
A stability analysis of polymerization fronts
NASA Astrophysics Data System (ADS)
Comissiong, Donna M. G.
Frontal Polymerization (FP) is a process of converting monomer into polymer via a localized zone that propagates through the monomer. It bears a strong resemblance to self-propagating high-temperature synthesis (SHS), which uses combustion waves to synthesize desired inorganic materials. The reaction front propagates through the coupling of thermal diffusion and the Arrhenius reaction kinetics of the exothermic polymerization process. This thesis utilizes a moving free-boundary model to describe free-radical FP. The focus of attention here is the self-sustaining wave which travels through the reaction vessel as polymer molecules are being formed. Numerical and analytical techniques are used to determine one-dimensional traveling waves, and stability analysis (linear and weakly nonlinear) of the reaction front is performed. It is then possible to suggest ways to curb instabilities in the propagating reaction front. After our initial analysis, we account for autoacceleration and determine its effect on frontal stability. In an effort to facilitate the propagation of weakly exothermic fronts, we consider a one-dimensional polymerization wave in a sandwich-type two-layer setting. First one layer is reactive while the other is considered to be inert. Heat exchange between layers is possible, and the effect this has on frontal stability is investigated. Next, we allow both layers to be reactive, thus further enhancing inter-layer heat exchange. We comment on the effect that the second reactive layer has on the basic state of the system. Finally, two future research directions are presented in detail. One of our goals is to determine how the propagating front is affected by bulk polymerization at the far end of the reaction vessel. This is an important aspect to be studied in greater depth and incorporated into existing FP models, since bulk reactions can influence the speed and long-term stability of the reaction front. We end with a theoretical discussion for the manufacture of polymer-dispersed liquid crystal films via FP.
Rajagopal, K.R.
1992-12-31
The flow of granular materials down an inclined plane is modeled by the Richman & Marciniec (1990) in which, they consider a kinetic constitutive theory that includes the effects of particle transport and collisions. Richman & Marciniec (1990) obtained closed form solution for the granular temperature profile, by replacing the volume fraction by its depth-averaged value in the balance equation`s, and thereby from constitutive relations for the normal and shear stresses they obtained the volume fraction and velocity profiles. Here, we use the model proposed by Richman & marciniec (1990) to study the linearized stability for the flow of granular materials down an inclined plane. The governing equations are obtained from the conservation of mass, balance of linear momentum and balance of energy. The basic flow equations and the order of {epsilon} equations are derived, but we intend to use the approximate solution of Richman & Marciniec (1990) as the base solution for the linearized stability analysis.
Slope stability analysis of Valles Marineris, Mars
NASA Astrophysics Data System (ADS)
Vittorio De Blasio, Fabio; Battista Crosta, Giovanni; Castellanza, Riccardo; Utili, Stefano
2013-04-01
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.
Stability analysis of intershaft squeeze film dampers
NASA Astrophysics Data System (ADS)
El-Shafei, A.
1991-08-01
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, it was determined both theoretically and experimentally that the intershaft squeeze film damper was unstable above the engine's first critical speed. In this paper, a stability analysis of rotors incorporating intershaft squeeze film dampers is performed. A rotor model consisting of two Jeffcott rotors with two intershaft squeeze film dampers is investigated. Examining the system characteristic equation for the conditions at which the roots indicate an ever growing unstable motion results in the stability conditions. The cause of the instability is identified as the rotation of the oil in the damper clearance. The oil rotation adds energy to the forward whirl of the rotor system above the critical speed and thus causes the instability. Below the critical speed the oil film removes energy from the forward rotor whirl. It is also shown that the backward whirl of the rotor system is always stable. Several proposed configurations of intershaft squeeze film dampers are discussed, and it is shown that the intershaft dampers are stable supercritically only with a configuration in which the oil film does not rotate.
Stability analysis for dynamical neural network systems
S. Lam; Y. S. Hung
1994-01-01
In this paper, the small gain theorem is used to establish a criterion for the stability of a feedback system containing a feedforward neural network. A method for the determination of the gain of a piecewise-linear feedforward neural network is introduced and applied to the stability analysis for a control system consisting of a LTI SISO system with a dynamic
Computer Aided Transient Stability Analysis
Nihad M. Al-Rawi; Afaneen Anwar; Ahmed Muhsin Abdul-Majeed
2007-01-01
A program for handling and improving the transient stability of the Iraqi Super Grid electrical network was developed. The idea was demonstrated by applying it to the outages of the main generating units. The methodology was built upon a state of increasing power transfer through the healthy portion of network during disturbances. There were three parts concerned; the first part
Vacuum Stability of Standard Model^{++}
Luis A. Anchordoqui; Ignatios Antoniadis; Haim Goldberg; Xing Huang; Dieter Lust; Tomasz R. Taylor; Brian Vlcek
2013-01-23
The latest results of the ATLAS and CMS experiments point to a preferred narrow Higgs mass range (m_h \\simeq 124 - 126 GeV) in which the effective potential of the Standard Model (SM) develops a vacuum instability at a scale 10^{9} -10^{11} GeV, with the precise scale depending on the precise value of the top quark mass and the strong coupling constant. Motivated by this experimental situation, we present here a detailed investigation about the stability of the SM^{++} vacuum, which is characterized by a simple extension of the SM obtained by adding to the scalar sector a complex SU(2) singlet that has the quantum numbers of the right-handed neutrino, H", and to the gauge sector an U(1) that is broken by the vacuum expectation value of H". We derive the complete set of renormalization group equations at one loop. We then pursue a numerical study of the system to determine the triviality and vacuum stability bounds, using a scan of 10^4 random set of points to fix the initial conditions. We show that, if there is no mixing in the scalar sector, the top Yukawa coupling drives the quartic Higgs coupling to negative values in the ultraviolet and, as for the SM, the effective potential develops an instability below the Planck scale. However, for a mixing angle -0.35 \\alt \\alpha \\alt -0.02 or 0.01 \\alt \\alpha \\alt 0.35, with the new scalar mass in the range 500 GeV \\alt m_{h"} \\alt 8 TeV, the SM^{++} ground state can be absolutely stable up to the Planck scale. These results are largely independent of TeV-scale free parameters in the model: the mass of the non-anomalous U(1) gauge boson and its branching fractions.
Stabilization of the full model compression system
MingQing Xiao
1998-01-01
Stability of compression systems is a major concern in the study of aerodynamics. This paper considers feedback stabilization for compressor systems based on Moore-Greitzer PDE model (1986) with general compressor characteristics. The formulation and discussion of the model is completely in the framework of distributed parameter systems. The asymptotic behavior of the full model is characterized by using semigroup theory
John B. Collings; Grand Forks
1995-01-01
The non-linear behavior of a differential equations-based predator-prey model, incorporating a spatial refuge protecting a\\u000a consant proportion of prey and with temperature-dependent parameters chosen appropriately for a mite interaction on fruit\\u000a trees, is examined using the numerical bifurcation code AUTO 86. The most significant result of this analysis is the existence\\u000a of a temperature interval in which increasing the amount
Global stability for cholera epidemic models.
Tian, Jianjun Paul; Wang, Jin
2011-07-01
Cholera is a water and food borne infectious disease caused by the gram-negative bacterium, Vibrio cholerae. Its dynamics are highly complex owing to the coupling among multiple transmission pathways and different factors in pathogen ecology. Although various mathematical models and clinical studies published in recent years have made important contribution to cholera epidemiology, our knowledge of the disease mechanism remains incomplete at present, largely due to the limited understanding of the dynamics of cholera. In this paper, we conduct global stability analysis for several deterministic cholera epidemic models. These models, incorporating both human population and pathogen V. cholerae concentration, constitute four-dimensional non-linear autonomous systems where the classical Poincaré-Bendixson theory is not applicable. We employ three different techniques, including the monotone dynamical systems, the geometric approach, and Lyapunov functions, to investigate the endemic global stability for several biologically important cases. The analysis and results presented in this paper make building blocks towards a comprehensive study and deeper understanding of the fundamental mechanism in cholera dynamics. PMID:21513717
Stability determination of steric-stabilized nanoparticles - Numerical and experimental analysis
NASA Astrophysics Data System (ADS)
Olatunji, Olakunle; Tomas, Jürgen
2013-06-01
Particle sedimentation is an essential tool for determining the stability behaviour of colloidal dispersions. In this study, we derive new analytical equations of motion for estimating the settling velocity-time function of particles sedimenting in colloidal dispersions under uniformly accelerated sedimentation model. The stability behaviour of spherically shaped TiO2 nanoparticles synthesized by reproducible sol-gel process and steric-stabilized by commercial surfactant Brij 30 were analysed both numerically and experimentally. Our newly derived analytical equation was used for the numerical analysis while experimentally a multiple light scattering analysis was applied. We show in the study that increase in solid volume fraction means decrease in porosity within the colloidal dispersion system and dispersion stability estimated by particle sedimentation rate is accurate.
NASA Astrophysics Data System (ADS)
Karapetsas, George; Tsamopoulos, John
2013-09-01
During extrusion of viscoelastic fluids various flow instabilities may arise resulting in a distorted free surface. In order to investigate the factors generating these instabilities we performed a linear stability analysis at zero Reynolds number around the steady solution of the cylindrical or planar stick-slip flow for a viscoelastic fluid following the affine exponential Phan-Thien Tanner (PTT) model. Stick-slip flow is an important special case of the extrudate swell problem, since the latter reduces to it in the limit of infinite surface tension but avoids the complications of a free-boundary flow. The linear stability analysis is performed for various values of the rheological parameters of the PTT model in order to determine the effects of all material properties. It is found that the flow becomes unstable as the Weissenberg number increases above a critical value, due to a Hopf bifurcation suggesting that the flow will become periodic in time. Both the critical value of the Weissenberg number and the frequency of the instability depend strongly on the rheological parameters of the viscoelastic model. The corresponding eigenvectors indicate that the perturbed flow field has a spatially periodic structure, initiated at the rim of the die, extending for up to 5-7 die gaps downstream, but confined close to the surface of the extrudate, in qualitative agreement with existing experiments. This suggests that instability is generated by the combination of the singularity in the velocity and stress fields at the die lip and the strong extension that the extruded polymer undergoes near its surface. The elasticity alone can be responsible for the appearance of instabilities in the extrusion process of viscoelastic fluids and the often used assumptions of wall slip or compressibility, although they might be present, are not required. Finally, the mechanisms that produce these instabilities are examined through energy analysis of the disturbance flow.
Developments in Cylindrical Shell Stability Analysis
NASA Technical Reports Server (NTRS)
Knight, Norman F., Jr.; Starnes, James H., Jr.
1998-01-01
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.
ASTROP2 users manual: A program for aeroelastic stability analysis of propfans
NASA Technical Reports Server (NTRS)
Narayanan, G. V.; Kaza, K. R. V.
1991-01-01
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.
STABILITY ANALYSIS OF ACTIVE FACE SEALS
The work discusses selected problems of stability of two most commonly used non-contacting seal types, i.e. FMR and FMS, including the control signals. A control system is described and its mathematical model presented. Applying the Routh-Hurwitz criterion the stability conditions are given and the critical angular velocities of the shaft determined. The influence of the seal and controller parameters on
Performance and Stability Analysis of a Shrouded-Fan UAV
de Divitiis, Nicola
2009-01-01
This paper deals with the estimation of the performance and stability for a shrouded-fan unmanned rotorcraft whose mission profile also prescribes the flight in ground effect. The not so simple estimation of the aerodynamic coefficients and of the thrust in the various situations makes the performance calculation and the stability analysis difficult tasks. This is due to the strong interaction between the fan flow and shroud that causes quite different flow structures about the airframe depending on flight conditions. A further difficulty is related to the ground effect which produces substantial modifications in the rotor thrust and aerodynamic coefficients. To evaluate performance and stability, two models have been developed. One determines the aerodynamic coefficients of the shroud, whereas the other one calculates thrust and moment of the rotors system. Both models take into account the mutual interference between fan flow and fuselage and ground effect. Performance and stability are then discussed with ...
Aeroelastic stability analysis of a Darrieus wind turbine
D. Popelka
1982-01-01
An aeroelastic stability analysis was developed for predicting flutter instabilities on vertical axis wind turbines. The analytical model and mathematical formulation of the problem are described as well as the physical mechanism that creates flutter in Darrieus turbines. Theoretical results are compared with measured experimental data from flutter tests of the Sandia 2 Meter turbine. Based on this comparison, the
Quantitative analysis on stability for deep foundation pit support structure
Zhiyang Yuan; Dajun Zhao
2011-01-01
The size of the reliability index can reflect the stability of excavation. This paper analyzes the engineering structure that is derived the reliability index, and the engineering model of structural reliability methods. The different types of supporting structure are taken into account, including the additional load, earth pressure, a variety of loads, the analysis of the main failure mode of
Sensitivity and stability of efficiency classifications in Data Envelopment Analysis
Abraham Charnes; John J. Rousseau; John H. Semple
1996-01-01
A new technique for assessing the sensitivity and stability of efficiency classifications in Data Envelopment Analysis (DEA) is presented. Here developed for the ratio (CCR) model, this technique extends easily to other DEA variants. An organization's input-outut vector serves as the center for a cell within which the organization's classification remains unchanged under perturbations of the data. For the l1,
Nonlinear Systems: Analysis, Stability and Control Spring 2007
Sastry, S. Shankar
. 2. Simple Nonlinear Models Planar Dynamical Systems Chapter 2 of textbook. 1. Phase Plane TechniquesNonlinear Systems: Analysis, Stability and Control Outline EECS 222 Spring 2007 Linear vs. Nonlinear Chapter 1 of textbook. 1. Nonlinear Phenomena: Multiple Equilibria, Limit Cycles, Complex Dynamics
Aeroelastic stability analysis of flexible overexpanded rocket nozzle
NASA Astrophysics Data System (ADS)
Bekka, N.; Sellam, M.; Chpoun, A.
2015-05-01
The aim of this paper is to present a new aeroelastic stability model taking into account the viscous effects for a supersonic nozzle flow in overexpanded regimes. This model is inspired by the Pekkari model which was developed initially for perfect fluid flow. The new model called the "Modified Pekkari Model" (MPM) considers a more realistic wall pressure profile for the case of a free shock separation inside the supersonic nozzle using the free interaction theory of Chapman. To reach this objective, a code for structure computation coupled with aerodynamic excitation effects is developed that allows the analysis of aeroelastic stability for the overexpanded nozzles. The main results are presented in a comparative manner using existing models (Pekkari model and its extended version) and the modified Pekkari model developed in this work.
Stress transducer interpretation analysis and stability data
E. C. Francis; R. E. Thompson
1984-01-01
A semi-conductor strain gage transducer was developed for use in measuring stress in solid propellant grain rocket motors. The requirements for survival and performance are such that the sensor has direct use as a general pressure transducer especially where small size and high reliability are a requirement. The design work, gage interpretation analysis and some long-term stability results are summarized.
Stability Analysis of an Encapsulated Microbubble against Gas Diffusion
Katiyar, Amit; Sarkar, Kausik
2009-01-01
Linear stability analysis is performed for a mathematical model of diffusion of gases from an encapsulated microbubble. It is an Epstein-Plesset model modified to account for encapsulation elasticity and finite gas permeability. Although, bubbles, containing gases other than air is considered, the final stable bubble, if any, contains only air, and stability is achieved only when the surrounding medium is saturated or oversaturated with air. In absence of encapsulation elasticity, only a neutral stability is achieved for zero surface tension, the other solution being unstable. For an elastic encapsulation, different equilibrium solutions are obtained depending on the saturation level and whether the surface tension is smaller or higher than the elasticity. For an elastic encapsulation, elasticity can stabilize the bubble. However, imposing a non-negativity condition on the effective surface tension (consisting of reference surface tension and the elastic stress) leads to an equilibrium radius which is only neutrally stable. If the encapsulation can support net compressive stress, it achieves actual stability. The linear stability results are consistent with our recent numerical findings. Physical mechanisms for the stability or instability of various equilibriums are provided. PMID:20005522
Stability Analysis of the Impoundment of Ash
NASA Astrophysics Data System (ADS)
Slávik, Ivan
2013-03-01
An impoundment is an engineering construction used for the safe deposition of unexploitable waste from industrial and mining facilities. In terms of the legislative requirements of the Slovak Republic, a "Measurements Project" must be developed for each impoundment. In this document the prerequisites for the safe operation of an impoundment, the limit and critical values of the monitored phenomena and the facts influencing the safety of the impoundment and the area endangered by such a site are also defined. The safety and stability of an impoundment are verified according to a "Measurements Project" by considering stability at regular time intervals. This contribution presents, in the form of a parametric study, a stability analysis of an ash impoundment. The stability analysis provides an example of the utilization of an information database of the results of the regular monitoring of the geotechnical properties of the materials forming the impoundment's body and the surrounding rock mass. The stability of the impoundment is expressed for a recent state - without a continuous water level in its body and, at the same time, for a hypothetical limit and critical water level according to the valid "Handling Regulations".
Stability analysis in tachyonic potential chameleon cosmology
Farajollahi, H.; Salehi, A.; Tayebi, F.; Ravanpak, A., E-mail: hosseinf@guilan.ac.ir, E-mail: a.salehi@guilan.ac.ir, E-mail: ftayebi@guilan.ac.ir, E-mail: aravanpak@guilan.ac.ir [Department of Physics, University of Guilan, Rasht (Iran, Islamic Republic of)
2011-05-01
We study general properties of attractors for tachyonic potential chameleon scalar-field model which possess cosmological scaling solutions. An analytic formulation is given to obtain fixed points with a discussion on their stability. The model predicts a dynamical equation of state parameter with phantom crossing behavior for an accelerating universe. We constrain the parameters of the model by best fitting with the recent data-sets from supernovae and simulated data points for redshift drift experiment generated by Monte Carlo simulations.
Aeroelastic stability analysis of a Darrieus wind turbine
Popelka, D.
1982-02-01
An aeroelastic stability analysis has been developed for predicting flutter instabilities on vertical axis wind turbines. The analytical model and mathematical formulation of the problem are described as well as the physical mechanism that creates flutter in Darrieus turbines. Theoretical results are compared with measured experimental data from flutter tests of the Sandia 2 Meter turbine. Based on this comparison, the analysis appears to be an adequate design evaluation tool.
A renormalisation group method. IV. Stability analysis
Slade, Gordon
in the critical dimension d = 4. The results in this paper include: proof of stability of the interaction of the general renormalisation group step in the fifth paper in the series. 1 Introduction This paper,5], and the n-component ||4 spin model [7], in the critical dimension d = 4. In both cases, logarithmic
Stability analysis of heat exchanger dynamics
Tiejun Zhang; John T. Wen; Juan Catano; Rongliang Zhou
2009-01-01
In the study of vapor compression cycle, momentum balance equation is often ignored in the heat exchanger model. In this paper, we investigate the effect of the momentum balance through a systematic study of the open loop stability of a heat exchanger. We consider 1-D fluid flow in a pipe in four cases of increasing complexity the most general case
Stability analysis and \\mu-synthesis control of brake systems
Lignon, Sylvain; Jezequel, Louis
2008-01-01
The concept of friction-induced brake vibrations, commonly known as judder, is investigated. Judder vibration is based on the class of geometrically induced or kinematic constraint instability. After presenting the modal coupling mechanism and the associated dynamic model, a stability analysis as well as a sensitivity analysis have been conducted in order to identify physical parameters for a brake design avoiding friction-induced judder instability. Next, in order to reduce the size of the instability regions in relation to possible system parameter combinations, robust stability via \\mu-synthesis is applied. By comparing the unstable regions between the initial and controlled brake system, some general indications emerge and it appears that robust stability via \\mu-synthesis has some effect on the instability of the brake system.
Nonlinear aerostatic stability analysis of suspension bridges
Virote Boonyapinyo; Yingsak Lauhatanon; Panitan Lukkunaprasit
2006-01-01
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
Thomas R. Weicht; Daryl L. Moorhead
2004-01-01
The nematode ( Scottnema lindsayae) is one of the most common soil invertebrates in the soils of the McMurdo Dry Valleys, Antarctica. A stage-structured population model developed for S. lindsayae was modified to include the effects of anhydrobiosis resulting from soil moisture limitations. Model results indicated that anhydrobiosis lowered temperature requirements needed to establish stable populations by buffering mortality at
A Renormalisation Group Method. IV. Stability Analysis
NASA Astrophysics Data System (ADS)
Brydges, David C.; Slade, Gordon
2015-05-01
This paper is the fourth in a series devoted to the development of a rigorous renormalisation group method for lattice field theories involving boson fields, fermion fields, or both. The third paper in the series presents a perturbative analysis of a supersymmetric field theory which represents the continuous-time weakly self-avoiding walk on . We now present an analysis of the relevant interaction functional of the supersymmetric field theory, which permits a nonperturbative analysis to be carried out in the critical dimension . The results in this paper include: proof of stability of the interaction, estimates which enable control of Gaussian expectations involving both boson and fermion fields, estimates which bound the errors in the perturbative analysis, and a crucial contraction estimate to handle irrelevant directions in the flow of the renormalisation group. These results are essential for the analysis of the general renormalisation group step in the fifth paper in the series.
A renormalisation group method. IV. Stability analysis
David C. Brydges; Gordon Slade
2014-11-25
This paper is the fourth in a series devoted to the development of a rigorous renormalisation group method for lattice field theories involving boson fields, fermion fields, or both. The third paper in the series presents a perturbative analysis of a supersymmetric field theory which represents the continuous-time weakly self-avoiding walk on $\\mathbb{Z}^d$. We now present an analysis of the relevant interaction functional of the supersymmetric field theory, which permits a nonperturbative analysis to be carried out in the critical dimension $d = 4$. The results in this paper include: proof of stability of the interaction, estimates which enable control of Gaussian expectations involving both boson and fermion fields, estimates which bound the errors in the perturbative analysis, and a crucial contraction estimate to handle irrelevant directions in the flow of the renormalisation group. These results are essential for the analysis of the general renormalisation group step in the fifth paper in the series.
NASA Astrophysics Data System (ADS)
Borlace, S.; Cai, W.; Santoso, A.
2012-12-01
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.
NASA Astrophysics Data System (ADS)
Tassi, E.; Ratiu, T. S.; Lazzaro, E.
2012-12-01
We analyze the collisionless and inviscid limit of a reduced fluid model for tokamak plasma dynamics. We show that the model under consideration possesses a noncanonical Hamiltonian structure with four infinite families of Casimir invariants. Sufficient conditions for energy stability are derived and formulated in terms of requirements on the current, electron pressure, and parallel ion velocity gradients, as well as on the ion temperature. In particular, the stability condition requires a gradient of the parallel flow in the presence of ion temperature and a negative upper bound on the current gradient, in the presence of pressure gradients and/or parallel velocity gradients. Examples of stable configurations are derived.
Stability analysis of White Oak Dam
NONE
1995-04-11
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.
NASA Astrophysics Data System (ADS)
Godey, Cyril; Balakireva, Irina V.; Coillet, Aurélien; Chembo, Yanne K.
2014-06-01
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.
Finite Element Modeling for Temperature Stabilization of Gated Hall Sensors
Paris-Sud XI, Université de
Finite Element Modeling for Temperature Stabilization of Gated Hall Sensors B. Jouault1,2 , L, France Abstract Using finite element analysis, we have calculated the Hall voltage of gated Hall sensors of Applied Physics 104, 5 (2008) 053705" DOI : 10.1063/1.2968436 #12;I. INTRODUCTION Hall effect sensors
Application of TRACE\\/PARCS to BWR stability analysis
Yunlin Xu; Thomas Downar; R. Walls; K. Ivanov; J. Staudenmeier; J. March-Lueba
2009-01-01
The work described here is the validation of TRACE\\/PARCS for Boiling Water Reactor stability analysis. A stability methodology was previously developed, verified, and validated using data from the OECD Ringhals stability benchmark. The work performed here describes the application of TRACE\\/PARCS to all the stability test points from cycle 14 of the Ringhals benchmark. The benchmark points from cycle 14
Juanes, Ruben
This paper presents the application of adaptive rational spectral methods to the linear stability analysis of nonlinear fourth-order problems. Our model equation is a phase-field model of infiltration, but the proposed ...
Shenping Li; Ramon Pons; Yizhou Zhang
1994-01-01
In this paper, we 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, we 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
Linear stability analysis of dynamical quadratic gravity
NASA Astrophysics Data System (ADS)
Ayzenberg, Dimitry; Yagi, Kent; Yunes, Nicolás
2014-02-01
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.
A New Method for Transient Stability Analysis
NASA Astrophysics Data System (ADS)
Yorino, Naoto; Saito, Takeshi; Kamei, Yoshifumi; Sasaki, Hiroshi
This paper proposes a brand new method for transient stability analysis in power systems. The proposed method directly computes the critical trajectory for a given contingency to obtain the critical condition of the studied system. Although the method may be useful for general nonlinear dynamic systems, it is applied to the problem of obtaining a controlling UEP, unstable equilibrium point, which provides inevitable information for the energy function methods to assess transient stability. Namely, the proposed method effectively yields a critical trajectory on PEBS together with the controlling UEP, thus improving the conventional BCU method. The effectiveness of the proposed method is demonstrated in 3-machine 9-bus system and 6-machine 30-bus system.
Lukasz Bratek
2004-09-03
Linear stability analysis of the whole spectrum of static hedgehog solutions of the Skyrme model on the three-sphere of radius L is carried out. It turns out that only solutions that in the limit of infinite L tend to skyrmions (localized at the poles) are linearly stable. The other solutions are unstable and, for a given solution, the number of instabilities, for L sufficiently large, is equal to the index of a harmonic map to which this solution tends pointwise in the limit of infinite L. Solutions which tends pointwise to harmonic maps and which in addition have a definite parity, undergo a transition by +1 in the number of instabilities as L grows. Due to the instability, new solutions, with spontaneously broken reflection symmetry, appeare by bifurcations. In the case of the 1-skyrmion this critical phenomenon can be fully described analytically. As a result, in some neighbourhood of critical radius at which 1-skyrmion bifurcates from the identity solution, one gets unique series expansions for the profile of the 1-skyrmion and for its energy, though the series coefficients, due to nonlinearity, are not known in general form. To the author's best knowledge the series were not given in literature so far. A similar mechanism of spontaneous breaking of parity is also observed when other solutions appear by bifurcations from symmetric solutions.
Sorensen, J.M.; Healzer, J.M.; Ostenso, A.L.
1988-03-01
The EPRI reactor analysis support package (RASP) system consists of computer codes, documentation, linkage software, and support methodology and training that utilities can use in-house to perform a wide range of nuclear plant safety analyses. As part of the RASP development project, this study devised a specialized methodology for BWR reload fuel licensing as required by NRC. Each plant and fuel design must meet criteria for total-plant core-reactivity and channel-hydrodynamic stability. The current vendor methodology for BWR stability analysis has been reviewed, and a transformation code to compute the required stability parameters (decay ratio and natural frequency) using RETRAN time history results has been developed. Several analyses for each of the three different stability criteria to validate the methodology and demonstrate its application were performed. Utilities that have already established control and primary system models with RETRAN will be able to use this new methodology to perform stability analyses as well. With this technique, RETRAN provides the capability for total-plant stability analysis in the real-time domain; with Fourier transform methods, the code provides the key parameters for core-reactivity and channel-hydrodynamic stability analysis.
M. Amabili; A. Rivola
1997-01-01
The steady-state response and stability of the single degree of freedom (sdof) model of a pair of low contact ratio spur gears are studied. In the proposed model, a time-varying stiffness of the meshing tooth pairs and a viscous damping proportional to the meshing stiffness are considered. Gear errors of each meshing tooth pair are also included. A continuous closed-form
STABILITY ANALYSIS OF THE ITER TF CONDUCTOR
Savoldi Richard, L.; Zanino, R. [Dipartimento di Energetica, Politecnico Torino, I-10129 (Italy)
2008-03-16
The stability analysis of the reference Nb{sub 3}Sn conductor for the International Thermonuclear Experimental Reactor (ITER) Toroidal Field (TF) coils is performed using the Mithrandir code. From the point of view of the temperature margin, the most critical conductor in the winding pack, as well as the most critical location along it, is identified by a Vincenta code analysis, which also provides the initial and boundary conditions for the stability study. With this approach, the 1D Mithrandir analysis can be restricted to the most critical conductor, using a much finer grid than Vincenta, in order to capture the details of normal zone initiation and possible recovery to SC state. Two different disturbances are considered: one short in space and time (0.01 m, 1 ms), simulating a disturbance of mechanical nature, the other longer (3 m, 100 ms), corresponding to AC losses (plasma disruption). Both disturbances are applied to the superconducting cable at end-of-burn, in the reference ITER inductive operation scenario. The grid-independence of the results was verified first. Since the results are strongly influenced by the choice of the heat transfer coefficient between strands and helium, this effect has been also parametrically investigated. In all cases, the computed minimum quench energies turn out to be above the level of the expected disturbances.
Positive complexity–stability relations in food web models without foraging adaptation
Boris Kartascheff; Christian Guill; Barbara Drossel
2009-01-01
May's [1972. Will a large complex system be stable? Nature 238, 413–414] local stability analysis of random food web models showed that increasing network complexity leads to decreasing stability, a result that is contradictory to earlier empirical findings. Since this seminal work, research of complexity–stability relations became one of the most challenging issues in theoretical ecology. We investigate conditions for
Stability analysis of nonlinear muscle dynamics using contraction theory
Bizzi, Emilio
Stability analysis of nonlinear muscle dynamics using contraction theory Andrew G. Richardson1 the interactions between different physiological feedback mech- anisms. Contraction theory provides tools for analyzing the stability of nonlinear distributed control systems. Here we use contraction the- ory
Thermodynamic modeling of natural zeolite stability
Chipera, S.J.; Bish, D.L.
1997-06-01
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.
Potential of GIS in 3-dimensional slope stability analysis of landslide site
M K Kalra; Jitendar Kumar
The stability analysis of any landslide site requires determining the balance between the triggering and the resisting forces acting within the soil mass. Models exist that consider the shape of slip plane, the interslice forces, effect of groundwater position, position of external loads etc. Most of these models evaluate the stability along any longitudinal section of the slope i.e. 2-Dimensional
MODEL-BASED NETWORKED CONTROL SYSTEMS - STABILITY
Luis A. Montestruque; Panos J. Antsaklis
2002-01-01
1. ABSTRACT In this report the control of continuous linear plants where the state sensor is connected to a linear controller\\/actuator via a network is addressed. The work focuses on reducing the network usage using knowledge of the plant dynamics. Specifically, the controller uses an explicit model of the plant that approximates the plant dynamics and makes possible stabilization of
Bounded Linear Stability Margin Analysis of Nonlinear Hybrid Adaptive Control
NASA Technical Reports Server (NTRS)
Nguyen, Nhan T.; Boskovic, Jovan D.
2008-01-01
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.
Wilde, Juray de [Laboratorium voor Petrochemische Techniek, Ghent University, Krijgslaan 281, Blok S5, B-9000 Ghent (Belgium) and Fluid Mechanics Laboratory, Department of Fluid, Heat and Combustion Mechanics, Ghent University, St.-Pietersnieuwstraat 41, B-9000 Ghent (Belgium)]. E-mail: Guray.Marin@UGent.be; Vierendeels, Jan [Fluid Mechanics Laboratory, Department of Fluid, Heat and Combustion Mechanics, Ghent University, St.-Pietersnieuwstraat 41, B-9000 Ghent (Belgium); Heynderickx, Geraldine J. [Laboratorium voor Petrochemische Techniek, Ghent University, Krijgslaan 281, Blok S5, B-9000 Ghent (Belgium); Marin, Guy B. [Laboratorium voor Petrochemische Techniek, Ghent University, Krijgslaan 281, Blok S5, B-9000 Ghent (Belgium)
2005-07-20
Simultaneous solution algorithms for Eulerian-Eulerian gas-solid flow models are presented and their stability analyzed. The integration algorithms are based on dual-time stepping with fourth-order Runge-Kutta in pseudo-time. The domain is solved point or plane wise. The discretization of the inviscid terms is based on a low-Mach limit of the multi-phase preconditioned advection upstream splitting method (MP-AUSMP). The numerical stability of the simultaneous solution algorithms is analyzed in 2D with the Fourier method. Stability results are compared with the convergence behaviour of 3D riser simulations. The impact of the grid aspect ratio, preconditioning, artificial dissipation, and the treatment of the source terms is investigated. A particular advantage of the simultaneous solution algorithms is that they allow a fully implicit treatment of the source terms which are of crucial importance for the Eulerian-Eulerian gas-solid flow models and their solution. The numerical stability of the optimal simultaneous solution algorithm is analyzed for different solids volume fractions and gas-solid slip velocities. Furthermore, the effect of the grid resolution on the convergence behaviour and the simulation results is investigated. Finally, simulations of the bottom zone of a pilot-scale riser with a side solids inlet are experimentally validated.
Stress transducer interpretation analysis and stability data
NASA Astrophysics Data System (ADS)
Francis, E. C.; Thompson, R. E.
1984-02-01
A semi-conductor strain gage transducer was developed for use in measuring stress in solid propellant grain rocket motors. The requirements for survival and performance are such that the sensor has direct use as a general pressure transducer especially where small size and high reliability are a requirement. The design work, gage interpretation analysis and some long-term stability results are summarized. Design of this reliable stress transducer for embedment in a solid propellant rocket motor has utilized finite element structural analysis to minimize the stress disturbance above the transducer body and to reduce diaphragm interaction with the nonlinear viscoelastic solid propellant. Minimizing the interaction between solid propellant and transducer diaphragm required that the transducer body and flexural diaphragm be much stiffer than conventional pressure transducers.
Stability Analysis of DM-Ice17
NASA Astrophysics Data System (ADS)
Pierpoint, Zachary; DM-Ice Collaboration
2015-04-01
DM-Ice17, a 17 kg sodium iodide prototype detector for the proposed DM-Ice experiment, was deployed in the Antarctic Ice at the geographic South Pole in December 2010, and has been in operation since January 2011. I will present a stability analysis of three years of data, with a focus on sources of noise and time-dependent effects that could mimic or obfuscate a dark matter modulation. Due to the small mass of the detector, the analysis does not significantly probe dark matter regions of interest but does provide further evidence that the Antarctic ice provides an ideal location for dark matter annual modulation searches. On behalf of the DM-Ice Collaboration.
On the stability of a nonlinear maturity structured model of cellular proliferation
Paris-Sud XI, Université de
On the stability of a nonlinear maturity structured model of cellular proliferation Mostafa Adimy model, Blood production system, Delay depending on the maturity, Global stability, Instability. 1 Introduction and motivation This paper is devoted to the analysis of a maturity structured model which involves
Stabilization control of a hovering model insect: lateral motion
NASA Astrophysics Data System (ADS)
Zhang, Yan-Lai; Sun, Mao
2011-10-01
Our previous study shows that the lateral disturbance motion of a model drone fly does not have inherent stability (passive stability), because of the existence of an unstable divergence mode. But drone flies are observed to fly stably. Constantly active control must be applied to stabilize the flight. In this study, we investigate the lateral stabilization control of the model drone fly. The method of computational fluid dynamics is used to compute the lateral control derivatives and the techniques of eigenvalue and eigenvector analysis and modal decomposition are used for solving the equations of motion. Controllability analysis shows that although inherently unstable, the lateral disturbance motion is controllable. By feeding back the state variables (i.e. lateral translation velocity, yaw rate, roll rate and roll angle, which can be measured by the sensory system of the insect) to produce anti-symmetrical changes in stroke amplitude and/or in angle of attack between the left and right wings, the motion can be stabilized, explaining why the drone flies can fly stably even if the flight is passively unstable.
Truck Roll Stability Data Collection and Analysis
Stevens, SS
2001-07-02
The principal objective of this project was to collect and analyze vehicle and highway data that are relevant to the problem of truck rollover crashes, and in particular to the subset of rollover crashes that are caused by the driver error of entering a curve at a speed too great to allow safe completion of the turn. The data are of two sorts--vehicle dynamic performance data, and highway geometry data as revealed by vehicle behavior in normal driving. Vehicle dynamic performance data are relevant because the roll stability of a tractor trailer depends both on inherent physical characteristics of the vehicle and on the weight and distribution of the particular cargo that is being carried. Highway geometric data are relevant because the set of crashes of primary interest to this study are caused by lateral acceleration demand in a curve that exceeds the instantaneous roll stability of the vehicle. An analysis of data quality requires an evaluation of the equipment used to collect the data because the reliability and accuracy of both the equipment and the data could profoundly affect the safety of the driver and other highway users. Therefore, a concomitant objective was an evaluation of the performance of the set of data-collection equipment on the truck and trailer. The objective concerning evaluation of the equipment was accomplished, but the results were not entirely positive. Significant engineering apparently remains to be done before a reliable system can be fielded. Problems were identified with the trailer to tractor fiber optic connector used for this test. In an over-the-road environment, the communication between the trailer instrumentation and the tractor must be dependable. In addition, the computer in the truck must be able to withstand the rigors of the road. The major objective--data collection and analysis--was also accomplished. Using data collected by instruments on the truck, a ''bad-curve'' database can be generated. Using this database, instrumented vehicles would not need roadside beacons. The speed, acceleration, and roll stability of the vehicle could be determined prior to entering a curve, and a warning issued, if appropriate, for curves that have been characterized in the database. Thus, the analysis indicates that the data can be effectively used to provide a timely warning of rollover risk.
Stability analysis and synthesis of fuzzy singularly perturbed systems
Huaping Liu; Fuchun Sun; Zengqi Sun
2005-01-01
In this paper, we investigate the stability analysis and synthesis problems for both continuous-time and discrete-time fuzzy singularly perturbed systems. For continuous-time case, both the stability analysis and synthesis can be parameterized in terms of a set of linear matrix inequalities (LMIs). For discrete-time case, only the analysis problem can be cast in LMIs, while the derived stability conditions for
Stability analysis of singularly perturbed systems via vector Lyapunov methods
Z. Retchkiman; G. Silva
1996-01-01
The aim of this paper consists of providing a more general and flexible methodology for the stability analysis of nonlinear singularly perturbed systems. Starting from slow and fast comparison principles, for each subsystem, a two-time scale comparison principle is constructed for the full-order singularly perturbed system to conclude its stability. The technique results natural and appropriate for studying stability for
Decentralized, Cooperative Control of Multivehicle Systems: Design and Stability Analysis
Weitz, Lesley A.
2010-01-16
This dissertation addresses the design and stability analysis of decentralized, cooperative control laws for multivehicle systems. Advances in communication, navigation, and surveillance systems have enabled greater autonomy ...
O. Rodriguez; A. Medina
2002-01-01
This paper describes a methodology for the efficient stability analysis of the synchronous machine. The state space phase coordinates model of the synchronous machine incorporates the effects of time-varying and inter-spatial harmonic inductances. The dynamics of the synchronous machine are represented by a set of ordinary differential equations (ODEs). The machine behaviour is analyzed under severe unbalanced operation conditions. The
Stability analysis of constrained multibody systems
NASA Astrophysics Data System (ADS)
Ider, S. K.; Amirouche, F. M. L.
1990-09-01
Automated algorithms for the dynamic analysis and simulation of constrained multibody systems usually assume the rows of the constraint Jacobian matrix to be linearly independent. But during the motion, at instantaneous configurations, the Jacobian matrix may become less than full rank resulting in singularities. This occurs when the closed-loop goes from 3D to 2D type of configuration. In this paper the linearly dependent rows are identified by an uptriangular decomposition process. The corresponding constraint equations are modified so that the singularities in the numerical procedure are avoided. The conditions for the validity of the modified equations are described. Furthermore, the constraint equations expressed in accelerations are modified by Baumgarte's approach to stabilize the accumulation of the numerical errors during integration. A computational procedure based on Kane's equations is presented. Two and three-link robotic manipulators will be simulated at singular configurations to illustrate the use of the modified constraints.
Analysis of Brace Stiffness Influence on Stability of the Truss
NASA Astrophysics Data System (ADS)
Krajewski, M.; Iwicki, P.
2015-02-01
The paper is devoted to the numerical and experimental research of stability of a truss with side elastic supports at the top chord. The structure is a model of a real roof truss scaled by factor 1/4. The linear buckling analysis and non-linear static analysis were carried out. The buckling length factor for the compressed top chord was calculated and the limit load for the imperfect truss shell model with respect to brace stiffness was obtained. The relation between brace normal force and loading of the truss is presented. The threshold stiffness of braces necessary to obtain the maximum buckling load was found. The truss load bearing capacity obtained from numerical analysis was compared with Eurocode 3 requirements.
Stability analysis of steady states for surface diffusion equation in a bounded domain
Ishii, Hitoshi
. . Stability analysis of steady states for surface diffusion equation in a bounded domain Yoshihito Kohsaka (Muroran Institute of Technology) joint work with H. Garcke and K. Ito Mathematical diffusion 30 July, 2010 1 / 19 #12;Model ˘ˇ¤Ł¦Ą §©¨ ˇŁ¦Ą §¨ ¨ ˘ˇŁ Ą¤Ł §¦Ł ¨© ¨© ¨Ą© Along
Melaku Mihret; Olorunfemi Ojo; Meharegzi Abreham
2011-01-01
A new generalized model for stability analysis based on a small signal modeling is proposed, for matrix converter fed induction motor drive system. This approach considers the analysis when the drive system operates at unity as well as non-unity input power factor at the source side. With the help of this model, different factors which affect the matrix converter stability
Decentralized, cooperative control of multivehicle systems: Design and stability analysis
NASA Astrophysics Data System (ADS)
Weitz, Lesley Anne
2009-12-01
This dissertation addresses the design and stability analysis of decentralized, cooperative control laws for multivehicle systems. Advances in communication, navigation, and surveillance systems have enabled greater autonomy in multivehicle systems, and there is a shift toward decentralized, cooperative systems for computational efficiency and robustness. In a decentralized control scheme, control inputs are determined onboard each vehicle; therefore, decentralized controllers are more efficient for large numbers of vehicles, and the system is more robust to communication failures and reconfiguration. The design of decentralized, cooperative control laws is explored for a nonlinear vehicle model that can be represented in a double-integrator form. Cooperative controllers are functions of spacing errors with respect to other vehicles in the system, where the communication structure defines the information that is available to each vehicle. Control inputs are selected to achieve internal stability, or zero steady-state spacing errors, between vehicles in the system. Closed-loop equations of motion for the cooperative system can be written in a structural form, where damping and stiffness matrices contain control gains acting on the velocity and positions of the vehicles, respectively. The form of the stiffness matrix is determined by the communication structure, where different communication structures yield different control forms. Communication structures are compared using two structural analysis tools: modal cost and frequency-response functions, which evaluate the response of the multivehicle systems to disturbances. The frequency-response information is shown to reveal the string stability of different cooperative control forms. The effects of time delays in the feedback states of the cooperative control laws on system stability are also investigated. Closed-loop equations of motion are modeled as delay differential equations, and two stability notions are presented: delay-independent and delay-dependent stability. Lastly, two additional cooperative control forms are investigated. The first control form spaces vehicles along an arbitrary path, where distances between vehicles are constant for a given spacing parameter. This control form shows advantages over spacing vehicles using control laws designed in an inertial frame. The second control form employs a time-based spacing scheme, which spaces vehicles at constant-time intervals at a desired endpoint. The stability of these control forms is presented.
Stability analysis of holographic dark energy in Brans-Dicke cosmology
NASA Astrophysics Data System (ADS)
Farajollahi, H.; Sadeghi, J.; Pourali, M.
2012-10-01
We study stability formulation of holographic dark energy in Brans-Dicke theory. The model is constrained with observations. The results verifies the cosmic acceleration in near past. With the stability analysis we find that the universe transits from quintessence to phantom state in near future while approaching a stable state.
Stability analysis of the accretion line
NASA Technical Reports Server (NTRS)
Soker, Noam
1990-01-01
The stability of the flow along the accretion line in the Bondi-Hoyle-Lyttleton-type accretion flow is studied. The WKB approximation is used to analyze short wavelength linear perturbations of the axisymmetric steady state flow. The viscosity terms in the gasdynamical equations are included in the analysis. The radial modes are studied both in two- and three-dimensional accretion flow. Since a displaced accretion line cannot be defined in three-dimensional flow, the tangential modes are only analyzed in the two-dimensional flow. The analysis of the perturbed gasdynamical equations are made simpler as a result of the radial and tangential modes being decoupled in the linear regime. As was shown before, the three-dimensional accretion flow is unstable against radial modes. The two-dimensional accretion flow is found to be unstable against tangential modes, as well as against radial modes. Using typical numerical parameters which are in common use, the wavelength which gives the maximum growth rate of a small perturbation is found to be about 0.5 r(a), where r(a) is the accretion radius.
Stability and Bifurcation Analysis of Coupled Fitzhugh-Nagumo Oscillators
William Hanan; Dhagash Mehta; Guillaume Moroz; Sepanda Pouryahya
2010-01-29
Neurons are the central biological objects in understanding how the brain works. The famous Hodgkin-Huxley model, which describes how action potentials of a neuron are initiated and propagated, consists of four coupled nonlinear differential equations. Because these equations are difficult to deal with, there also exist several simplified models, of which many exhibit polynomial-like non-linearity. Examples of such models are the Fitzhugh-Nagumo (FHN) model, the Hindmarsh-Rose (HR) model, the Morris-Lecar (ML) model and the Izhikevich model. In this work, we first prescribe the biologically relevant parameter ranges for the FHN model and subsequently study the dynamical behaviour of coupled neurons on small networks of two or three nodes. To do this, we use a computational real algebraic geometry method called the Discriminant Variety (DV) method to perform the stability and bifurcation analysis of these small networks. A time series analysis of the FHN model can be found elsewhere in related work[15].
Theory and modelling of nanocarbon phase stability.
Barnard, A. S.
2006-01-01
The transformation of nanodiamonds into carbon-onions (and vice versa) has been observed experimentally and has been modeled computationally at various levels of sophistication. Also, several analytical theories have been derived to describe the size, temperature and pressure dependence of this phase transition. However, in most cases a pure carbon-onion or nanodiamond is not the final product. More often than not an intermediary is formed, known as a bucky-diamond, with a diamond-like core encased in an onion-like shell. This has prompted a number of studies investigating the relative stability of nanodiamonds, bucky-diamonds, carbon-onions and fullerenes, in various size regimes. Presented here is a review outlining results of numerous theoretical studies examining the phase diagrams and phase stability of carbon nanoparticles, to clarify the complicated relationship between fullerenic and diamond structures at the nanoscale.
Robustness for slope stability modelling under deep uncertainty
NASA Astrophysics Data System (ADS)
Almeida, Susana; Holcombe, Liz; Pianosi, Francesca; Wagener, Thorsten
2015-04-01
Landslides can have large negative societal and economic impacts, such as loss of life and damage to infrastructure. However, the ability of slope stability assessment to guide management is limited by high levels of uncertainty in model predictions. Many of these uncertainties cannot be easily quantified, such as those linked to climate change and other future socio-economic conditions, restricting the usefulness of traditional decision analysis tools. Deep uncertainty can be managed more effectively by developing robust, but not necessarily optimal, policies that are expected to perform adequately under a wide range of future conditions. Robust strategies are particularly valuable when the consequences of taking a wrong decision are high as is often the case of when managing natural hazard risks such as landslides. In our work a physically based numerical model of hydrologically induced slope instability (the Combined Hydrology and Stability Model - CHASM) is applied together with robust decision making to evaluate the most important uncertainties (storm events, groundwater conditions, surface cover, slope geometry, material strata and geotechnical properties) affecting slope stability. Specifically, impacts of climate change on long-term slope stability are incorporated, accounting for the deep uncertainty in future climate projections. Our findings highlight the potential of robust decision making to aid decision support for landslide hazard reduction and risk management under conditions of deep uncertainty.
Wellbore stability analysis during the production of a carbonate reservoir
NASA Astrophysics Data System (ADS)
Alves, J.-L.; Coehlo, L.; Baud, P.; Guevara Junior, N.
2009-04-01
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.
Dynamic flight stability of a hovering model dragonfly.
Liang, Bin; Sun, Mao
2014-05-01
The longitudinal dynamic flight stability of a model dragonfly at hovering flight is studied, using the method of computational fluid dynamics to compute the stability derivatives and the techniques of eigenvalue and eigenvector analysis for solving the equations of motion. Three natural modes of motion are identified for the hovering flight: one unstable oscillatory mode, one stable fast subsidence mode and one stable slow subsidence mode. The flight is dynamically unstable owing to the unstable oscillatory mode. The instability is caused by a pitch-moment derivative with respect to horizontal velocity. The damping force and moment derivatives (with respect to horizontal and vertical velocities and pitch-rotational velocity, respectively) weaken the instability considerably. The aerodynamic interaction between the forewing and the hindwing does not have significant effect on the stability properties. The dragonfly has similar stability derivatives, hence stability properties, to that of a one-wing-pair insect at normal hovering, but there are differences in how the derivatives are produced because of the highly inclined stroke plane of the dragonfly. PMID:24486234
Zacharias, M; Sklenar, H
1997-12-01
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. PMID:9414214
Hassan Ali Kojori; J. Douglas Lavers; Shashi B. Dewan
1993-01-01
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
Kahler stabilized, modular invariant heterotic string models
Gaillard, Mary K.; Gaillard, Mary K.; Nelson, Brent D.
2007-03-19
We review the theory and phenomenology of effective supergravity theories based on orbifold compactifications of the weakly-coupled heterotic string. In particular, we consider theories in which the four-dimensional theory displays target space modular invariance and where the dilatonic mode undergoes Kahler stabilization. A self-contained exposition of effective Lagrangian approaches to gaugino condensation and heterotic string theory is presented, leading to the development of the models of Binétruy, Gaillard and Wu. Various aspects of the phenomenology of this class of models are considered. These include issues of supersymmetry breaking and superpartner spectra, the role of anomalous U(1) factors, issues of flavor and R-parity conservation, collider signatures, axion physics, and early universe cosmology. For the vast majority of phenomenological considerations the theories reviewed here compare quite favorably to other string-derived models in the literature. Theoretical objections to the framework and directions for further research are identified and discussed.
Stability analysis of a nonlinear rotating blade with torsional vibrations
NASA Astrophysics Data System (ADS)
Wang, Fengxia; Zhang, Wei
2012-12-01
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.
NASA Technical Reports Server (NTRS)
Friedmann, P. P.; Venkatesan, C.
1984-01-01
The aeromechanical stability of a helicopter in ground resonance was analyzed, by incorporating five different aerodynamic models in the coupled rotor/fuselage analysis. The sensitivity of the results to changes in aerodynamic modelling was carefully examined. The theoretical results were compared with experimental data and useful conclusions are drawn regarding the role of aerodynamic modeling on this aeromechanical stability problem. The aerodynamic model which provided the best all around correlation with the experimental data was identified.
Static and dynamic stability analysis of the space shuttle vehicle-orbiter
NASA Technical Reports Server (NTRS)
Chyu, W. J.; Cavin, R. K.; Erickson, L. L.
1978-01-01
The longitudinal static and dynamic stability of a Space Shuttle Vehicle-Orbiter (SSV Orbiter) model is analyzed using the FLEXSTAB computer program. Nonlinear effects are accounted for by application of a correction technique in the FLEXSTAB system; the technique incorporates experimental force and pressure data into the linear aerodynamic theory. A flexible Orbiter model is treated in the static stability analysis for the flight conditions of Mach number 0.9 for rectilinear flight (1 g) and for a pull-up maneuver (2.5 g) at an altitude of 15.24 km. Static stability parameters and structural deformations of the Orbiter are calculated at trim conditions for the dynamic stability analysis, and the characteristics of damping in pitch are investigated for a Mach number range of 0.3 to 1.2. The calculated results for both the static and dynamic stabilities are compared with the available experimental data.
Topological Tools For The Analysis Of Active Region Filament Stability
NASA Astrophysics Data System (ADS)
DeLuca, Edward E.; Savcheva, A.; van Ballegooijen, A.; Pariat, E.; Aulanier, G.; Su, Y.
2012-05-01
The combination of accurate NLFFF models and high resolution MHD simulations allows us to study the changes in stability of an active region filament before a CME. Our analysis strongly supports the following sequence of events leading up to the CME: first there is a build up of magnetic flux in the filament through flux cancellation beneath a developing flux rope; as the flux rope develops a hyperbolic flux tube (HFT) forms beneath the flux rope; reconnection across the HFT raises the flux rope while adding addition flux to it; the eruption is triggered when the flux rope becomes torus-unstable. The work applies topological analysis tools that have been developed over the past decade and points the way for future work on the critical problem of CME initiation in solar active regions. We will present the uses of this approach, current limitations and future prospects.
Modelling and stability of a hydro plant with two surge tanks
C. D. Vournas; G. Papaioannou
1995-01-01
This paper deals with the modelling and the stability analysis of a hydroelectric power plant with two surge tanks placed upstream and downstream of the turbine. The interaction of the two surge tanks is investigated and the system is simulated for the case of sudden opening or closure of the turbine gates. The stability of the frequency control loop is
Load-Factor Stability Analysis of Embankments on Saturated Soil Deposits
Young-Kyo Seo; Colby C. Swan
2001-01-01
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
Stability analysis of PWM feedback control systems with PID regulators
M. LA CAVA; G. PALETTA; C. PICARDI
1984-01-01
Stability analysis is of great significance in those feedback control systems in which the power amplifier is operated as a pulse-modulator device, since under these circumstances the whole control system is highly non-linear. Stability in PWM feedback control systems with a proportional type regulator has been amply described in the literature. Only recently, however, have such studies been extended to
Borehole stability analysis at the Coporo-1 well, Colombia
Arias, Henry
2000-01-01
Coporo-1 is an 18,000-ft dry hole located in the tectonically active foothills of the Eastern Cordillera of Colombia. A mechanical stability analysis allowed explaining most of the drilling stability-related problems and elaborating an optimal mud...
Parallel power system transient stability analysis on hypercube multiprocessors
S. Y. Lee; N. D. Chiang; K. G. Lee; B. Y. Ku
1991-01-01
With the growth in size and complexity of interconnected power systems the simulation of power system equations in the time domain for stability assessment is becoming more time-consuming or too expensive. There is always considerable incentive to find better computation schemes. The authors develop an efficient and fast computation scheme for transient stability analysis on a hypercube multiprocessor. In order
Stability analysis of an adaptive controller for robotic manipulators
Nader Sadegh; R. Horowitz
1987-01-01
The stability analysis of an adaptive control scheme for robotic manipulators, originally introduced by Horowitz and Tomizuka (1980), is presented in this paper. In the previous stability proof it was assumed that the manipulator parameter variation is negligible compared with the speed of adaptation. It is shown that this key assumption can be removed by introducing two modifications in the
GE simplified boiling water reactor stability analysis in time domain
NASA Astrophysics Data System (ADS)
Lu, Shanlai
1997-12-01
General Electric Simplified Boiling Water Reactor (SBWR) was designed as a next generation light water reactor. It uses natural circulation to remove the heat from the reactor core. Because of this unique in-vessel circulation feature, SBWR is expected to exhibit different stability behaviors. The main emphasis of this thesis is to study the SBWR stability behavior in the time domain. The best-estimate BWR accident/transient analysis computer code, TRAC-BF1, is employed to analyze the SBWR stability behavior. A detailed TRAC-BF1 SBWR model has been developed, which has the capability to model the in-vessel natural circulation and the reactor core kinetics. The model is used to simulate three slow depressurization processes. The simulation results show that the reactor is stable under low pressure and nominal downcomer water level conditions. However, when the downcomer water level is raised to about 19.2 m above the bottom of the reactor vessel, an unstable power oscillation is observed. The identified power oscillation is further analyzed using TRAC-BF1 1-D kinetics and the new TRAC-BF1 3-D kinetics code developed in this thesis. The effects of different time step sizes and vessel model nodalizations are examined. It is found that the power oscillation is in-phase and has a frequency of 0.3 HZ. In order to further explore the physical instabilty initiation mechanisms, a simplified dynamic model consisting of six simple differential equations is developed. The simplified model is able to predict the dominant physical phenomenon identified by the TRAC-BF1 analysis. The results indicate that the system instability is possibly caused by the steam separator hydro-static head oscillation under the high water level condition. In order to explore the higher order spacial effect of power oscillation, a 3-D reactor core kinetics code is coupled with the TRAC-BF1 computer code in the PVM parallel processing environment. A new coupling scheme and a multiple time step marching technique are developed. The new TRAC-BF1 3-D code package is examined using LMW standard benchmark problem. It is then successfully used to study the possible SBWR power oscillation.
Simplified model and stabilization of SSFP sequences.
Le Roux, Patrick
2003-07-01
Steady-state free precession (SSFP) is used today in a form similar to other rapid sequences like fast spin echo (FSE) where a large longitudinal magnetization is present at the beginning of the train of excitations. This results in a transient behavior which impedes any measurement before the steady state is established. Several solutions have been proposed to stabilize the signals more quickly. Starting from a simplified model of signal generation, and by a suitable change of reference frame, this paper justifies theoretically the linear ramp-up proposed by Nishimura and Vasanawala (p. 301, 8th Annual Proceedings of ISMRM, 2000, Denver). This linear ramp-up can be generalized into a one giving less oscillatory residues. The solution is efficient in the sense that it does not require nutation angles larger than the one used during the stabilized period. Also, this solution is robust because it scales up or down nicely and is thus insensitive to B(1) variations. PMID:12852904
Wellbore stability analysis in carbonate reservoir considering anisotropic behaviour
NASA Astrophysics Data System (ADS)
Alves, José; Guevara, Nestor; Coelho, Lucia; Baud, Patrick
2010-05-01
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.
Large-signal stability analysis of PWM converters
Huynh, P.T. [Philips Labs., Briarcliff Manor, NY (United States); Cho, B.H. [Seoul National Univ. (Korea, Republic of). Dept. of Electrical Engineering
1995-12-31
Investigation of the effects of existing nonlinearities on the stability of PWM converters is performed. The bilinear structure, the duty cycle saturation, and the opamp saturation are the principal nonlinearities in PWM converters. These nonlinearities are incorporated in the large-signal analytical models of PWM converters, and the basic input-output stability theory is applied to analyze their stability. Design and optimization of the small-signal loop gains to counteract the undesirable nonlinear effects are also discussed.
A linear thermal stability analysis of discretized fluid equations
NASA Astrophysics Data System (ADS)
Miyamoto, Yoshiaki; Ito, Junshi; Nishizawa, Seiya; Tomita, Hirofumi
2015-06-01
The effects of discretization on the equations, and their solutions, describing Rayleigh-Bénard convection are studied through linear stability analysis and numerical integration of the discretized equations. Linear stability analyses of the discretized equations were conducted in the usual manner except that the assumed solution contained discretized components (e.g., spatial grid interval in the x direction, ). As the resolution became infinitely high (), the solutions approached those obtained from the continuous equations. The wavenumber of the maximum growth rate increased with increasing until the wavenumber reached a minimum resolvable resolution, . Therefore, the discretization of equations tends to reproduce higher-wavenumber structures than those predicted by the continuous equations. This behavior is counter intuitive and opposed to the expectation of leading to blurred simulated convection structures. However, when the analysis is conducted for discretized equations that are not combined into a single equation, as is the case for practically solved numerical models, the maximum growing wavenumber rather tends to decrease with increasing as intuitively expected. The degree of the decrease depends on the discretization accuracy of the first-order differentials. When the accuracy of the discretization scheme is of low order, the wavenumber monotonically decreases with increasing . On the other hand, when higher-order schemes are used for the discretization, the wavenumber does increase with increasing , a similar trend to that in the case of the single-discretized equation for smaller.
STATCOM Modeling for Voltage and Angle Stability Studies
Claudio A. Canizares; Massimo Pozzi; Sandro Corsi; Edvina Uzunovic
2003-01-01
This paper proposes and validates models to accurately represent STATic Syn- chronous Shunt COMpensators (STATCOM) in voltage and angle stability studies of powers systems. The proposed STATCOM stability models are justified based on the basic operational characteristics of this Flexible AC Transmission System (FACTS) controller for both phase and PWM control strategies. These models are first validated by means of
STATCOM modeling for voltage and angle stability studies
Claudio A. Cańizares; Massimo Pozzi; Sandro Corsi; Edvina Uzunovic
2003-01-01
This paper proposes and validates models to accurately represent static synchronous shunt compensators (STATCOM) in voltage and angle stability studies of powers systems. The proposed STATCOM stability models are justified based on the basic operational characteristics of this flexible AC transmission system (FACTS) controller for both phase and PWM control strategies. These models are first validated by means of EMTP
Stability and phase error analysis of FDTD in dispersive dielectrics
Peter G. Petropoulos
1994-01-01
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
Exact and Volterra analysis of synchronous machine stability
F. FALLSIDE; J. WADDINGTON
1970-01-01
The stability of unsaturated, round-rotor synchronous machines is investigated from a mathematical model which includes winding resistance, leakage reactance and iron loss. Under certain conditions an exact boundary can be obtained and very close agreement is obtained between it and experimental results. The effect on stability of varying the machine loading is demonstrated.When stator resistance and iron loss are neglected
Perturbative stability of SFT-based cosmological models
NASA Astrophysics Data System (ADS)
Galli, Federico; Koshelev, Alexey S.
2011-05-01
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.
Perturbative stability of SFT-based cosmological models
Federico Galli; Alexey S. Koshelev
2011-06-14
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.
Perturbative stability of SFT-based cosmological models
Galli, Federico
2010-01-01
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 demonstrate 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.
Seismic Stability Analysis of a Himalayan Rock Slope
NASA Astrophysics Data System (ADS)
Latha, Gali Madhavi; Garaga, Arunakumari
2010-11-01
The seismic slope stability analysis of the right abutment of a railway bridge proposed at about 350 m above the ground level, crossing a river and connecting two huge hillocks in the Himalayas, India, is presented in this paper. The rock slopes are composed of highly jointed rock mass and the joint spacing and orientation are varying at different locations. Seismic slope stability analysis of the slope under consideration is carried out using both pseudo-static approach and time response approach as the site is located in seismic zone V as per the earth quake zonation maps of India. Stability of the slope is studied numerically using program FLAC. The results obtained from the pseudo-static analysis are presented in the form of Factor of Safety (FOS) and the results obtained from the time response analysis of the slope are presented in terms of horizontal and vertical displacements along the slope. The results obtained from both the analyses confirmed the global stability of the slope as the FOS in case of pseudo-static analysis is above 1.0 and the displacements observed in case of time response analysis are within the permissible limits. This paper also presents the results obtained from the parametric analysis performed in the case of time response analysis in order to understand the effect of individual parameters on the overall stability of the slope.
Methods of stability analysis in nonlinear mechanics
Warnock, R.L.; Ruth, R.D.; Gabella, W.; Ecklund, K.
1989-01-01
We review our recent work on methods to study stability in nonlinear mechanics, especially for the problems of particle accelerators, and compare our ideals to those of other authors. We emphasize methods that (1) show promise as practical design tools, (2) are effective when the nonlinearity is large, and (3) have a strong theoretical basis. 24 refs., 2 figs., 2 tabs.
White Oak Dam stability analysis. Volume I
Ahmed, S.B.
1994-01-01
A parametric study was conducted to evaluate the stability of the White Oak Dam (WOD) embankment and foundation. Slope stability analyses were performed for the upper and lower bound soil properties at three sections of the dam using the PCSTABL4 computer program. Minimum safety factors were calculated for the applicable seismic and static loading conditions. Liquefaction potential of the dam embankment and foundation solid during the seismic event was assessed by using simplified procedures. The WOD is classified as a low hazard facility and the Evaluation Basis Earthquake (EBE) is defined as an earthquake with a magnitude of m{sub b} = 5.6 and a Peak Ground Accelerator (PGA) of 0.13 g. This event is approximately equivalent to a Modified Mercalli Intensity of VI-VIII. The EBE is used to perform the seismic evaluation for slope stability and liquefaction potential. Results of the stability analyses and the liquefaction assessment lead to the conclusion that the White Oak Dam is safe and stable for the static and the seismic events defined in this study. Ogden Environmental, at the request of MMES, has checked and verified the calculations for the critical loading conditions and performed a peer review of this report. Ogden has determined that the WOD is stable under the defined static and seismic loading conditions and the embankment materials are in general not susceptible to liquefaction.
Stability Analysis of a Symmetrical Induction Machine
ROBERT H. NELSON; THOMAS A. LIPO; PAUL C. KRAUSE
1969-01-01
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
Huang, Xun
Lateral Stability Analysis of Hypersonic Vehicle under Pressure Fluctuation by Solving Mathieu's Republic of China Two recent test failures of Hypersonic Technology Vehicle 2 impose a strike in dynamic analysis of hypersonic vehicles. To demonstrate the idea, a hypersonic model is imagined
Development of long-term stability models for ring laser gyros
P. B. Reddy; A. Dushman
1977-01-01
Time series analysis (TSA) techniques are applied to the modeling of ring laser gyro (RLG) long-term stability data. Results are presented for two sets of bias stability data: one for an RLG which exhibited drift rate performance of roughly 0.03 degree\\/hour, and the other for an RLG in the 0.004 degree\\/hour area. The approach taken to time series analysis is
Decoupled stability analysis of power systems with slow and fast dynamics
Othman, H.A.
1988-01-01
This thesis deals with the stability analysis of large-scale power systems with strong and weak interconnections. The system dynamical model belongs to the class of two-time-scale, nonlinear, singularly perturbed systems. Through a near-identity coordinate transformation, the slow and fast dynamics are partially decoupled, allowing for independent stability studies in the slow and fast subspaces. The decoupled subsystems can be physically interpreted as smaller-size power systems. On a higher hierarchy, a weighted sum of the Lyapunov functions of the decoupled slow and fast subsystems is used as a Lyapunov function for the original two-time-scale system, thus accounting for the effect of the small coupling terms. Two case studies confirm the improved accuracy of the decoupled stability-analysis method as compared to that for the system-wide stability-analysis methods.
Stability analysis of rotor-bearing systems via Routh-Hurwitz criterion
Abd Alla El-Marhomy; Nasar Eldin Abdel-Sattar
2004-01-01
A method of analysis is developed for studying the whirl stability of rotor-bearing systems without the need to solve the governing differential-equations of motion of such systems. A mathematical model, comprised of an axially-symmetric appendage at the mid-span of a spinning shaft mounted on two dissimilar eight-coefficient bearings, is used to illustrate the method. Sufficient conditions for asymptotic stability of
GLOBAL STABILITY IN CHEMOSTAT-TYPE COMPETITION MODELS WITH NUTRIENT RECYCLING
Ruan, Shigui
GLOBAL STABILITY IN CHEMOSTAT-TYPE COMPETITION MODELS WITH NUTRIENT RECYCLING SHIGUI RUAN AND XUE- type competition models with nutrient recycling. In the first model the recycling is instantaneous, whereas in the second, the recycling is delayed. They carried out the equilibrium analysis and obtained
A stability model for the advanced series compensator (ASC)
S. G. Jalali; R. A. Hedin; M. Pereira; K. Sadek
1996-01-01
This paper develops an accurate and general stability model for the ASC. The model is valid for both the capacitive and inductive regions of the ASC operation. It is accurate in that the instantaneous voltage and current waveforms and also the fundamental component of the capacitor voltage (needed for stability) are determined every half-cycle by solving the differential equations of
Model format for a vaccine stability report and software solutions
Jinho Shin; Timothy Schofield
2009-01-01
A session of the International Association for Biologicals Workshop on Stability Evaluation of Vaccine, a Life Cycle Approach was devoted to a model format for a vaccine stability report, and software solutions. Presentations highlighted the utility of a model format that will conform to regulatory requirements and the ICH common technical document. However, there need be flexibility to accommodate individual
Stability and Convergence Analysis for FluidStructure
Thompson, Lonny L.
acoustic energy in the finite domain\\Omega plus the radiation energy absorbed through the artificial `nonconservative'. The purpose of this Chap ter is to prove through a rigorous analysis that the proposed spacetime]. In this work, the stability and convergence analysis of the timediscontinuous Galerkin/leastsquares method
Robust Stability Analysis for a Class of Extended Linearization Systems
NASA Astrophysics Data System (ADS)
Nazari, Sam
We consider analysis of nonlinear systems that can be brought into a state dependent representation known as extended linearization. Under this formulation, conventional linear analysis techniques may be adapted to study the stability, optimality, and robustness properties of nonlinear systems. When subject to system uncertainty, estimating the radius of stability for systems under extended linearization is difficult since the closed-loop system equations are not available explicitly. A method for obtaining the upper bound for the radius of stability in this class of systems is proposed. It is shown that the stability radius around a suitable domain can be obtained by computing the largest singular value of an overvalued matrix with special properties. Additionally, a property of extended linearization is that it relies on a non-unique factorization of the system dynamics to bring the nonlinear system into a psuedo- linear form referred to as the State Dependent Coefficient (SDC) parametrization. Under system uncertainty, each SDC parametrization will produce its own radius of stability in a region of interest in the state space. We propose a method to obtain the SDC parametrization which results in the maximum radius of stability for the original nonlinear system in the region of interest. It is shown that the problem of obtaining the maximum radius of stability from a hyperplane of SDC parametrizations can be reduced to constrained minimization of the spectral norm of a comparison system.
Stability analysis of ultrasound thick-shell contrast agents
Lu, Xiaozhen; Chahine, Georges L.; Hsiao, Chao-Tsung
2012-01-01
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. PMID:22280568
Dynamic stability margin analysis on SRAM
Ho, Yenpo
2009-05-15
s e xWUxA =? where x m , m=1,2, ?, are all equilibria of any order in )( s e xA? . 29 Fig. 3-6 An Example of Phase Portrait for an SRAM. 3.4.2.2 The Stable Manifold and Stability Boundary Theorem for SRAM In particular case, from Fig. 3-6...? The Static Random Access Memory cell (SRAM) is often constructed by two cross-coupled inverters (labeled Q1 Q2 Q3 and Q4) and two access transistors, labeled Q5 and Q6 from Fig. 2-1. [41] The access transistor acts as transmission gate allowing...
Global stability analysis of multitime-scale neural networks
Zhanshan Wang; Enlin Zhang; Huaguang Zhang; Zhengyun Ren
Global asymptotic stability problem is studied for a class of recurrent neural networks with multitime scale. The concerned\\u000a network involves two coupling terms, i.e., long-term memory and short-term memory, which leads to the difficulty to the dynamics\\u000a analysis, especially for the case of multiple time varying delays. Some novel stability criteria are proposed on the basis\\u000a of linear matrix inequality
System model of an image stabilization system
NASA Astrophysics Data System (ADS)
Carmona, Manuel; Gómez, José María.; Roma, David; Casas, Albert; López, Manel; Bosch, José; Herms, Atilŕ; Sabater, Josep; Volkmer, Reiner; Heidecke, Frank; Maue, Thorsten; Nakai, Eiji; Schmidt, Wolfgang
2014-08-01
The Polarimetric and Helioseismic Imager (PHI) instrument is part of the remote instruments for the ESA Solar Orbiter (SO), which is scheduled to launch in 2017. PHI captures polarimetric images from the Sun to better understand our nearest star, the Sun. A set of images is acquired with different polarizations, and afterwards is processed to extract the Stokes parameters. As Stokes parameters require the subtraction of the image values, in order to get the desired quality it is necessary to have good contrast in the image and very small displacements between them. As a result an Image Stabilization System (ISS) is required. This paper is focused in the behavior and the main characteristics of this system. This ISS is composed of a camera, a tip-tilt mirror and a control system. The camera is based on a STAR1000 sensor that includes a 10 bits resolution high-speed Analog-to-Digital Converter (ADC). The control system includes a Correlation Tracking (CT) algorithm that determines the necessary corrections. The tip-tilt mirror is moved based on this corrections to minimize the effects of the spacecraft (S/C) drift and jitter with respect to the Sun. Due to its stringent requirements, a system model has been developed in order to verify that the required parameters can be satisfied. The results show that the ISS is feasible, although the margins are very small.
NASA Astrophysics Data System (ADS)
Kukillaya, R.; Proctor, J.; Holmes, P.
2009-06-01
We describe a hierarchy of models for legged locomotion, emphasizing relationships among feedforward (preflexive) stability, maneuverability, and reflexive feedback. We focus on a hexapedal geometry representative of insect locomotion in the ground plane that includes a neural central pattern generator circuit, nonlinear muscles, and a representative proprioceptive sensory pathway. Although these components of the model are rather complex, neglect of leg mass yields a neuromechanical system with only three degrees of freedom, and numerical simulations coupled with a Poincaré map analysis shows that the feedforward dynamics is strongly stable, apart from one relatively slow mode and a neutral mode in body yaw angle. These modes moderate high frequency perturbations, producing slow heading changes that can be corrected by a stride-to-stride steering strategy. We show that the model's response to a lateral impulsive perturbation closely matches that of a cockroach subject to a similar impulse. We also describe preliminary studies of proprioceptive leg force feedback, showing how a reflexive pathway can reinforce the preflexive stability inherent in the system.
Modeling, model simplification and stability robustness with aeroelastic vehicles
NASA Technical Reports Server (NTRS)
Schmidt, David K.; Newman, Brett
1988-01-01
The linearization and simplification of a nonlinear, literal model for flexible aircraft is highlighted. Areas of model fidelity that are critical if the model is to be used for control system synthesis are developed, and several simplification techniques that can deliver the necessary model fidelity are discussed. These techniques include both numerical and analytical approaches. An analytical approach, based on first-order sensitivity theory is shown to lead not only to excellent numerical results, but also to closed-form analytical expressions for key system dynamic properties such as the pole/zero factors of the vehicle transfer-function matrix. The analytical results are expressed in terms of vehicle mass properties, vibrational characteristics, and rigid-body and aeroelastic stability derivatives, thus leading to the underlying causes for critical dynamic characteristics.
Dynamic stability margin analysis on SRAM
Ho, Yenpo
2009-05-15
bifurcation theory. The state flipping requires a minimum noise current (Icritical) and time (Tcritical). This work derives Icritical analytically for simple L1 model and provides design insight using a level one circuit model, and also provides numerical...
AC system stability analysis and assessment for Shipboard Power Systems
Qi, Li
2006-04-12
algorithm, in which time step size varies automatically due to the truncation error of the former step [14]- [17]. EUROSTAG allows the simulation of all dynamics with one invariant complete model except for fast electromagnetic transients [14]. In many... [2]. According to the time frames of dynamics, power system stability can be divided into steady-state, dynamic, or small signal and transient and long-term stability. The main physical nature of instability in power systems could be angle...
Dagan Bakun-Mazor; Yossef H. Hatzor; William S. Dershowitz
2009-01-01
This paper examines the significance of mechanical layering for “blocky” rock mass deformation around underground openings excavated through sedimentary rocks. The analysis is based on an integration of geologically based discrete fracture models (“geoDFN”), which incorporate “mechanical layering”, with the numerical discrete element method—the discontinuous deformation analysis (DDA). We begin with addressing limitations of classical solutions for mine roof stability
Stability Analysis and Stabilization of Nonlinear Systems via Locally Defined Density Functions
NASA Astrophysics Data System (ADS)
Masubuchi, Izumi
This paper considers local stability analysis of nonlinear systems with deriving a positively invariant set based on the Rantzer's stability theory by using density functions. We define a notion of locally defined density functions around an equilibrium that give monotonously increasing positive measures near the equilibrium of a nonlinear system. Under certain assumptions, it is shown that some level set of a locally defined density function is a positively invariant set where almost all of the system trajectories converge to the equilibrium. We also mention an SOS (sum-of-squares) formulation for synthesis of a nonlinear gain via locally defined density functions.
Stability analysis of refrigeration systems for electronics cooling
Tiejun Zhang; John T. Wen; Juan Catano; Rongliang Zhou; Greg Michna; Yoav Peles; Michael K. Jensen
2009-01-01
In modeling studies of vapor compression cycles, the momentum balance equation is usually ignored in the dynamic heat exchanger models. However, in micro-scale heat exchangers, significant pressure drop has been observed. In this paper, we investigate the effects of the momentum balance through a systematic study of the open loop stability of a heat exchanger. We consider 1D compressible fluid
Reliability based analysis of the crosswind stability of railway vehicles
A. Carrarini
2007-01-01
The computational models used to assess the crosswind stability of railway vehicles by multibody simulation (MBS) are affected by large uncertainties. Especially, the aerodynamic loads acting on the vehicle are difficult to model and the respective parameters cannot be easily acquired. Such uncertainties are usually neglected in the safety norms even though their effects on the risk assessment can be
Postural stability of two biped models via Lyapunov second method
H. Hemami; V. Cvetkovic
1977-01-01
In biped locomotion, postural stability about vertical stance is of practical significance. Three problems related to postural stability are discussed here. Estimates of the region in the vicinity of vertical stance, where the biped model with linear feedback is stable, are derived. A method of designing nonlinear feedback is developed in which the combination of linear and nonlinear feedback provides
Models and Feedback Stabilization of Open Quantum Systems
Pierre Rouchon
2015-01-08
At the quantum level, feedback-loops have to take into account measurement back-action. We present here the structure of the Markovian models including such back-action and sketch two stabilization methods: measurement-based feedback where an open quantum system is stabilized by a classical controller; coherent or autonomous feedback where a quantum system is stabilized by a quantum controller with decoherence (reservoir engineering). We begin to explain these models and methods for the photon box experiments realized in the group of Serge Haroche (Nobel Prize 2012). We present then these models and methods for general open quantum systems.
Model format for a vaccine stability report and software solutions.
Shin, Jinho; Southern, James; Schofield, Timothy
2009-11-01
A session of the International Association for Biologicals Workshop on Stability Evaluation of Vaccine, a Life Cycle Approach was devoted to a model format for a vaccine stability report, and software solutions. Presentations highlighted the utility of a model format that will conform to regulatory requirements and the ICH common technical document. However, there need be flexibility to accommodate individual company practices. Adoption of a model format is premised upon agreement regarding content between industry and regulators, and ease of use. Software requirements will include ease of use and protections against inadvertent misspecification of stability design or misinterpretation of program output. PMID:19720545
Kinematic analysis of rope skipper's stability
NASA Astrophysics Data System (ADS)
Ab Ghani, Nor Atikah; Rambely, Azmin Sham
2014-06-01
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.
Nonlinear analysis for image stabilization in IR imaging system
NASA Astrophysics Data System (ADS)
Xie, Zhan-lei; Lu, Jin; Luo, Yong-hong; Zhang, Mei-sheng
2009-07-01
In order to acquire stabilization image for IR imaging system, an image stabilization system is required. Linear method is often used in current research on the system and a simple PID controller can meet the demands of common users. In fact, image stabilization system is a structure with nonlinear characters such as structural errors, friction and disturbances. In up-grade IR imaging system, although conventional PID controller is optimally designed, it cannot meet the demands of higher accuracy and fast responding speed when disturbances are present. To get high-quality stabilization image, nonlinear characters should be rejected. The friction and gear clearance are key factors and play an important role in the image stabilization system. The friction induces static error of system. When the system runs at low speed, stick-slip and creeping induced by friction not only decrease resolution and repeating accuracy, but also increase the tracking error and the steady state error. The accuracy of the system is also limited by gear clearance, and selfexcited vibration is brought on by serious clearance. In this paper, effects of different nonlinear on image stabilization precision are analyzed, including friction and gear clearance. After analyzing the characters and influence principle of the friction and gear clearance, a friction model is established with MATLAB Simulink toolbox, which is composed of static friction, Coulomb friction and viscous friction, and the gear clearance non-linearity model is built, providing theoretical basis for the future engineering practice.
STABILITY OF CLUSTER SOLUTIONS IN A TRITROPHIC FOOD CHAIN MODEL
Wei, Jun-cheng
STABILITY OF CLUSTER SOLUTIONS IN A TRITROPHIC FOOD CHAIN MODEL JUNCHENG WEI AND MATTHIAS WINTER Abstract. We study a tritrophic food chain model which is based on Schnakenberg type kinetics. This model] for which there is only one prey and one predator. In this food chain model there is one predator feeding
Analysis of Stability, Response and LQR Controller Design of a Small Scale Helicopter Dynamics
Dharmayanda, Hardian Reza; Lee, Young Jae; Sung, Sangkyung
2008-01-01
This paper presents how to use feedback controller with helicopter dynamics state space model. A simplified analysis is presented for controller design using LQR of small scale helicopters for axial and forward flights. Our approach is simple and gives the basic understanding about how to develop controller for solving the stability of linear helicopter flight dynamics.
Technological Forecasting---Model Selection, Model Stability, and Combining Models
Nigel Meade; Towhidul Islam
1998-01-01
The paper identifies 29 models that the literature suggests are appropriate for technological forecasting. These models are divided into three classes according to the timing of the point of inflexion in the innovation or substitution process. Faced with a given data set and such a choice, the issue of model selection needs to be addressed. Evidence used to aid model
NASA Astrophysics Data System (ADS)
Ehrmann, Andrea; Blachowicz, Tomasz; Zghidi, Hafed
2015-05-01
Modelling hysteresis behaviour, as it can be found in a broad variety of dynamical systems, can be performed in different ways. An elementary approach, applied for a set of elementary cells, which uses only two possible states per cell, is the Ising model. While such Ising models allow for a simulation of many systems with sufficient accuracy, they nevertheless depict some typical features which must be taken into account with proper care, such as meta-stability or the externally applied field sweeping speed. This paper gives a general overview of recent results from Ising models from the perspective of a didactic model, based on a 2D spreadsheet analysis, which can be used also for solving general scientific problems where direct next-neighbour interactions take place.
Weakly dispersive hydraulic flows in a contraction --Nonlinear stability analysis
Ee, Bernard Kuowei
Weakly dispersive hydraulic flows in a contraction -- Nonlinear stability analysis Bernard K. Ee hydraulic solutions of the forced Korteweg de-Vries equation is investigated here. For numerical convenience is destabilized by a hydraulic instability in which superexponential growth occurs prior to satura- tion
Bank stability analysis for fluvial erosion and mass failure
Technology Transfer Automated Retrieval System (TEKTRAN)
The central objective of this study was to highlight the differences in magnitude between mechanical and fluvial streambank erosional strength with the purpose of developing a more comprehensive bank stability analysis. Mechanical erosion and ultimately failure signifies the general movement or coll...
Stability analysis for a semiconductor laser in an external cavity
B. Tromborg; J. Osmundsen; H. Olesen
1984-01-01
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
A Practical Method for the Direct Analysis of Transient Stability
T. Athay; R. Podmore; S. Virmani
1979-01-01
This paper describes the development and evaluation of an analytical method for the direct determination of transient stability. The method developed is based on the analysis of transient energy and accounts for the nature of the system disturbance as well as for the effects of transfer conductances onsystenmbehavior. It has been evaluated on a 10 generator 39 bus system and
Analysis of Human Body Bipedal Stability for Neuromotor Disabilities
Mihaela Baritz; Luciana Cristea; Liliana Rogozea; Diana Cotoros; Angela Repanovici
2009-01-01
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
Stability Analysis of Networked Control Systems with Unknown Inputs
Sun, Dengfeng
Stability Analysis of Networked Control Systems with Unknown Inputs Ahmad F Taha, Ahmed Elmahdi# , Jitesh H. Panchal and Dengfeng Sun Abstract-- Unknown Input Observers (UIO) use the known plant's inputs and outputs to generate state estimates for plants with unknown inputs. In many cases, the UIO's inputs
Phasor measurement placement for voltage stability analysis of power systems
L. Mili; T. Baldwin; R. Adapa
1990-01-01
The use of real-time phasor measurements for voltage stability analysis of power systems is considered. Two schemes of phasor measurement unit (PMU) placement have been investigated. In the first scheme, PMUs are used as pilot points for the secondary voltage control of a power system. Several criteria for pilot point selections are reviewed and assessed. In the second scheme, the
Stability analysis of a reinforced carbon carbon shell
NASA Technical Reports Server (NTRS)
Agan, W. E.; Jordan, B. M.
1977-01-01
This paper presents the development of a stability analysis for the nose cap of the NASA Space Shuttle Orbiter. Stability is evaluated by the differential stiffness analysis of the NASTRAN finite-element computer code, addressing those nonstandard characteristics in the nose cap such as nonuniform curvature, asymmetrical and nonuniform loads, support fixity, and various combinations of membrane and bending stresses. A full-sized nose cap, thinner than production, was statically tested and stability analyzed. The failing load level correlated to within 30%. The region and mode of buckling that occurred during test was accurately predicted by analysis. The criterion for predicting instability is based on the behavior of the nonlinear deflections. The deflections are nonlinear elastic in that the stresses are well within the elastic range of the material, but the geometry-load relationship produces nonlinear deflections. The load-deflection relationship is well defined by differential stiffness analysis up to the zero-slope portion of the curve, the point of neutral stability or where the shell 'snaps through' just prior to general instability.
Prediction of the biochar carbon stability by thermal analysis
NASA Astrophysics Data System (ADS)
Méndez, Ana; Cely, Paola; Plaza, César; Paz-Ferreiro, Jorge; Gascó, Gabriel
2015-04-01
Thermal analysis (DTA, DSC, TG and dTG) has been used for decades to characterize carbonaceous materials used as fuels (oil, coal). Our research group has used these techniques for the characterisation of different biochars in order to assess proportions of labile and recalcitrant organic matter and to study the evolution of soil organic matter in soils amended with biochar. Thermal analysis could be used to determine the proximate analysis, i.e., the percentage of humidity, volatile matter and fixed carbon or to calculate the thermostability index, previously identified as a reliable parameter for evaluating the level of stability of organic matter in organic wastes and biochar. Relationship between the stability of biochar, the raw material and the pyrolysis conditions could be established by thermal analysis techniques.
Energy-Casimir stability of hybrid Vlasov-MHD models
Cesare Tronci; Emanuele Tassi; Philip J. Morrison
2014-10-07
Different variants of hybrid kinetic-fluid models are considered for describing the interaction of a bulk fluid plasma obeying MHD and an energetic component obeying a kinetic theory. Upon using the Vlasov kinetic theory for energetic particles, two planar Vlasov-MHD models are compared in terms of their stability properties. This is made possible by the Hamiltonian structures underlying the considered hybrid systems, whose infinite number of invariants makes the energy-Casimir method effective for determining stability. Equilibrium equations for the models are obtained from a variational principle and in particular a generalized hybrid Grad-Shafranov equation follows for one of the considered models. The stability conditions are then derived and discussed with particular emphasis on kinetic particle effects on classical MHD stability.
Rotorcraft Dynamics Models for a Comprehensive Analysis
Wayne Johnson
Recent developments of the dynamics models for the comprehensive analysis CAMRAD II are described, specifically advanced models of the geometry and material for the beam component, and a force balance method for calculating section loads. Calculations are compared with measurements for beams undergoing large deflection. Bearingless rotor stability and bending loads calculations are compared with the results from a full-scale
C. A. Canizares
2000-01-01
This paper presents transient stability and power flow models of thyristor controlled reactor (TCR) and voltage sourced inverter (VSI) based flexible AC transmission system (FACTS) controllers. Models of the static VAr compensator (SVC), the thyristor controlled series compensator (TCSC), the static VAr compensator (STATCOM), the static synchronous source series compensator (SSSC), and the unified power flow controller (UPFC) appropriate for
Thermal analysis and test of SUNLITE reference cavity for laser frequency stabilization
NASA Technical Reports Server (NTRS)
Amundsen, R. M.
1992-01-01
SUNLITE is a space-based experiment which uses a reference cavity to provide a stable frequency reference for a terahertz laser oscillator. Thermal stability of the cavity is a key factor in attaining a stable narrow-linewidth laser beam. This paper describes the thermal stability requirements on the cavity design and detailed thermal analysis performed, as well as thermal testing that was performed on a prototype. Analytical thermal models were correlated to the test data and additional modeling of the current design is presented. Suggestions for improving similar high-precision thermal tests are given.
Nonlinear aeroelastic stability analysis of wind turbine blade with bending-bending-twist coupling
NASA Astrophysics Data System (ADS)
Liu, Tingrui; Ren, Yongsheng; Yang, Xinghua
2013-10-01
In this study, the nonlinear aeroelastic stability of wind turbine blade with bending-bending-twist coupling has been investigated for composite thin-walled structure with pretwist angle. The aerodynamic model used here is the differential dynamic stall nonlinear ONERA model. The nonlinear aeroelastic equations are reduced to ordinary equations by Galerkin method, with the aerodynamic force decomposition by strip theory. The nonlinear resulting equations are solved by a time-marching approach, and are linearized by small perturbation about the equilibrium point. The nonlinear aeroelastic stability characteristics are investigated through eigenvalue analysis, nonlinear time domain response, and linearized time domain response.
Analysis of the stability of hemoglobin S double strands.
Mu, X Q; Makowski, L; Magdoff-Fairchild, B
1998-01-01
The deoxyhemoglobin S (deoxy-HbS) double strand is the fundamental building block of both the crystals of deoxy-HbS and the physiologically relevant fibers present within sickle cells. To use the atomic-resolution detail of the hemoglobin-hemoglobin interaction known from the crystallography of HbS as a basis for understanding the interactions in the fibers, it is necessary to define precisely the relationship between the straight double strands in the crystal and the twisted, helical double strands in the fibers. The intermolecular contact conferring the stability of the double strand in both crystal and fiber is between the beta6 valine on one HbS molecule and residues near the EF corner of an adjacent molecule. Models for the helical double strands were constructed by a geometric transformation from crystal to fiber that preserves this critical interaction, minimizes distortion, and makes the transformation as smooth as possible. From these models, the energy of association was calculated over the range of all possible helical twists of the double strands and all possible distances of the double strands from the fiber axis. The calculated association energies reflect the fact that the axial interactions decrease as the distance between the double strand and the fiber axis increases, because of the increased length of the helical path taken by the double strand. The lateral interactions between HbS molecules in a double strand change relatively little between the crystal and possible helical double strands. If the twist of the fiber or the distance between the double strand and the fiber axis is too great, the lateral interaction is broken by intermolecular contacts in the region around the beta6 valine. Consequently, the geometry of the beta6 valine interaction and the residues surrounding it severely restricts the possible helical twist, radius, and handedness of helical aggregates constructed from the double strands. The limitations defined by this analysis establish the structural basis for the right-handed twist observed in HbS fibers and demonstrates that for a subunit twist of 8 degrees, the fiber diameter cannot be more than approximately 300 A, consistent with electron microscope observations. The energy of interaction among HbS molecules in a double strand is very slowly varying with helical pitch, explaining the variable pitch observed in HbS fibers. The analysis results in a model for the HbS double strand, for use in the analysis of interactions between double strands and for refinement of models of the HbS fibers against x-ray diffraction data. PMID:9449367
Stability analysis through bifurcation theory, 1
NASA Astrophysics Data System (ADS)
Guicheteau, P.
1993-06-01
This communication is the first part of the three papers which are presented by the author in the same AGARD Lecture Series (LS 191). It aims at the study of asymptotic solutions of non-linear differential equations depending on parameters. The first part is devoted to a brief presentation of the basis of Bifurcation Theory which is limited to the non-linear phenomena observed by the author when he analyzed high performance aircraft behavior. In particular, complex bifurcations and chaotic motions are not treated. Numerical procedures developed to use results from Bifurcation Theory are presented. Then, some remarks are stated to establish a connection between asymptotic and quasi-stationary behavior. Finally, a methodology dedicated to the analysis of non-linear systems is proposed.
Climate stability for a Sellers-type model. [atmospheric diffusive energy balance model
NASA Technical Reports Server (NTRS)
Ghil, M.
1976-01-01
We study a diffusive energy-balance climate model governed by a nonlinear parabolic partial differential equation. Three positive steady-state solutions of this equation are found; they correspond to three possible climates of our planet: an interglacial (nearly identical to the present climate), a glacial, and a completely ice-covered earth. We consider also models similar to the main one studied, and determine the number of their steady states. All the models have albedo continuously varying with latitude and temperature, and entirely diffusive horizontal heat transfer. The diffusion is taken to be nonlinear as well as linear. We investigate the stability under small perturbations of the main model's climates. A stability criterion is derived, and its application shows that the 'present climate' and the 'deep freeze' are stable, whereas the model's glacial is unstable. A variational principle is introduced to confirm the results of this stability analysis. For a sufficient decrease in solar radiation (about 2%) the glacial and interglacial solutions disappear, leaving the ice-covered earth as the only possible climate.
Fluid Dynamic and Stability Analysis of a Thin Liquid Sheet
NASA Technical Reports Server (NTRS)
McMaster, Matthew S.
1992-01-01
Interest in thin sheet flows has recently been renewed due to their potential application in space radiators. Theoretical and experimental studies of the fluid dynamics and stability of thin liquid sheet flows have been carried out in this thesis. A computer program was developed to determine the cross-sectional shape of the edge cylinder given the cross-sectional area of the edge cylinder. A stability analysis was performed on a non-planer liquid sheet. A study was conducted to determine the effects of air resistance on the sheet.
Modelling the growth and stabilization of cerebral aneurysms.
Watton, Paul N; Ventikos, Yiannis; Holzapfel, Gerhard A
2009-06-01
Experimental and theoretical guidance is needed to understand how the collagen fabric evolves during the development of aneurysms. In this paper, we model the development of an aneurysm as a cylindrical/spherical membrane subject to 1D enlargement; these conceptual models reflect the development of fusiform and saccular cerebral aneurysms. The mechanical response is attributed to the elastin and collagen. We introduce variables which define the elastin and collagen fibre concentration; these evolve to simulate growth/atrophy of the constituents. A hypothetical aneurysm model is analysed: collagen stretch is constant, elastin degrades and collagen fibre concentration can adapt to maintain mechanical equilibrium. An analytic expression for the rate of evolution of the fibre concentration is derived. The functional form is dependent on (i) the current collagen fibre concentration, (ii) the deviations in the collagen fibre stretch from the attachment stretch, (iii) the rate of change of fibre stretch, (iv) the rate of loss of elastin and (v) the ratio of load borne by elastinous and collagenous constituents. Finally, numerical examples of aneurysm development are considered. Suitable candidates for the fibre concentration evolution equations are identified that yield stabilization of the aneurysm even when there is complete loss of elastin. This theoretical analysis provides the basis for the development of physiologically realistic models of aneurysm development. PMID:19234094
Modeling sawtooth stabilization by energetic ions from neutral beam injection
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
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.
String Stability Analysis of Adaptive Cruise Controlled Vehicles Chi-Ying LIANG and Huei PENG
Peng, Huei
1/30 String Stability Analysis of Adaptive Cruise Controlled Vehicles Chi-Ying LIANG and Huei PENG Key Words: Adaptive Cruise Control, String Stability, String Stability Margin, Optimal ACC Design) 647-3170 #12;2/30 ABSTRACT A framework for string-stability analysis is formulated in this paper
Stability in a Nonlinear Population Maturation Model Stephane Mischler
Mischler, Stéphane
Stability in a Nonlinear Population Maturation Model St´ephane Mischler Laboratoire de Math 60637, USA November 26, 2004 Abstract. We consider models for population structured by maturation/maturation which is also illustrated on the simpler McKendrick-Von Foerster model. The nonlinear variants
Stability analysis of agegraphic dark energy in Brans-Dicke cosmology
NASA Astrophysics Data System (ADS)
Farajollahi, H.; Sadeghi, J.; Pourali, M.; Salehi, A.
2012-05-01
Stability analysis of agegraphic dark energy in Brans-Dicke theory is presented in this paper. We constrain the model parameters with the observational data and thus the results become broadly consistent with those expected from experiment. Stability analysis of the model without best fitting shows that universe may begin from an unstable state passing a saddle point and finally become stable in future. However, with the best fitted model, There is no saddle intermediate state. The agegraphic dark energy in the model by itself exhibits a phantom behavior. However, contribution of cold dark matter on the effective energy density modifies the state of the universe from phantom phase to quintessence one. The statefinder diagnosis also indicates that the universe leaves an unstable state in the past, passes the LCDM state and finally approaches the sable state in future.
Effect of model selection on combustor performance and stability predictions using ROCCID
NASA Technical Reports Server (NTRS)
Giuliani, James E.; Klem, Mark D.
1992-01-01
The ROCket Combustor Interactive Design (ROCCID) methodology is an interactive computer program that combines previously developed combustion analysis models to calculate the combustion performance and stability of liquid rocket engines. Test data from 213 kN (48,000 lbf) Liquid Oxygen (LOX)/RP-1 combustor with an O-F-O (oxidizer-fuel-oxidizer) triplet injector were used to characterize the predictive capabilities of the ROCCID analysis models for this injector/propellant configuration. Thirteen combustion performance and stability models were incorporated into ROCCID, and ten of them, which have options for triplet injectors, were examined. Calculations using different combinations of analysis models, with little or no anchoring, were carried out on a test matrix of operating combinations matching those of the test program. Results of the computer analyses were compared to test data, and the ability of the model combinations to correctly predict combustion stability or instability was determined. For the best model combination(s), sensitivity of the calculations to fuel drop size and mixing efficiency was examined. Error in the stability calculations due to uncertainty in the pressure interaction index (N) was examined. The recommended model combinations for this O-F-O triplet LOX/RP-1 configuration are proposed.
The Stability of Radiatively Cooling Jets I. Linear Analysis
NASA Technical Reports Server (NTRS)
Hardee, Philip E.; Stone, James M.
1997-01-01
The results of a spatial stability analysis of a two-dimensional slab jet, in which optically thin radiative cooling is dynamically important, are presented. We study both magnetized and unmagnetized jets at external Mach numbers of 5 and 20. We model the cooling rate by using two different cooling curves: one appropriate to interstellar gas, and the other to photoionized gas of reduced metallicity. Thus, our results will be applicable to both protostellar (Herbig-Haro) jets and optical jets from active galactic nuclei. We present analytical solutions to the dispersion relations in useful limits and solve the dispersion relations numerically over a broad range of perturbation frequencies. We find that the growth rates and wavelengths of the unstable Kelvin-Helmholtz (K-H) modes are significantly different from the adiabatic limit, and that the form of the cooling function strongly affects the results. In particular, if the cooling curve is a steep function of temperature in the neighborhood of the equilibrium state, then the growth of K-H modes is reduced relative to the adiabatic jet. On the other hand, if the cooling curve is a shallow function of temperature, then the growth of K-H modes can be enhanced relative to the adiabatic jet by the increase in cooling relative to heating in overdense regions. Inclusion of a dynamically important magnetic field does not strongly modify the important differences between an adiabatic jet and a cooling jet, provided the jet is highly supermagnetosonic and not magnetic pressure-dominated. In the latter case, the unstable modes behave more like the transmagnetosonic magnetic pressure-dominated adiabatic limit. We also plot fluid displacement surfaces associated with the various waves in a cooling jet in order to predict the structures that might arise in the nonlinear regime. This analysis predicts that low-frequency surface waves and the lowest order body modes will be the most effective at producing observable features in the jet.
Positive complexity-stability relations in food web models without foraging adaptation.
Kartascheff, Boris; Guill, Christian; Drossel, Barbara
2009-07-01
May's [1972. Will a large complex system be stable? Nature 238, 413-414] local stability analysis of random food web models showed that increasing network complexity leads to decreasing stability, a result that is contradictory to earlier empirical findings. Since this seminal work, research of complexity-stability relations became one of the most challenging issues in theoretical ecology. We investigate conditions for positive complexity-stability relations in the niche, cascade, nested hierarchy, and random models by evaluating the network robustness, i.e., the fraction of surviving species after population dynamics. We find that positive relations between robustness and complexity can be obtained when resources are large, Holling II functional response is used and interaction strengths are weighted with the number of prey species, in order to take foraging efforts into account. In order to obtain these results, no foraging dynamics needs to be included. However, the niche model does not show positive complexity-stability relations under these conditions. By comparing to empirical food web data, we show that the niche model has unrealistic distributions of predator numbers. When this distribution is randomized, positive complexity-stability relations can be found also in the niche model. PMID:19318109
Preliminary hazards analysis of thermal scrap stabilization system. Revision 1
Lewis, W.S.
1994-08-23
This preliminary analysis examined the HA-21I glovebox and its supporting systems for potential process hazards. Upon further analysis, the thermal stabilization system has been installed in gloveboxes HC-21A and HC-21C. The use of HC-21C and HC-21A simplified the initial safety analysis. In addition, these gloveboxes were cleaner and required less modification for operation than glovebox HA-21I. While this document refers to glovebox HA-21I for the hazards analysis performed, glovebox HC-21C is sufficiently similar that the following analysis is also valid for HC-21C. This hazards analysis document is being re-released as revision 1 to include the updated flowsheet document (Appendix C) and the updated design basis (Appendix D). The revised Process Flow Schematic has also been included (Appendix E). This Current revision incorporates the recommendations provided from the original hazards analysis as well. The System Design Description (SDD) has also been appended (Appendix H) to document the bases for Safety Classification of thermal stabilization equipment.
Stability of finite difference models containing two boundaries or interfaces
NASA Technical Reports Server (NTRS)
Trefethen, L. N.
1984-01-01
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.
Why allometric scaling enhances stability in food web models
Boris Kartascheff; Lotta Heckmann; Barbara Drossel; Christian Guill
2010-01-01
It has recently been shown that the incorporation of allometric scaling into the dynamic equations of food web models enhances\\u000a network stability if predators are assigned a higher body mass than their prey. We investigate the underlying mechanisms leading\\u000a to this stability increase. The dynamic equations can be written such that allometric scaling influences these equations at\\u000a three places: the
Entropically-Stabilized Self-Compactification in Model Colloidal Systems
Juyong Park; Alexei V. Tkachenko
2003-04-15
We discuss the phenomenon of spontaneous self-compactification in a model colloidal system, proposed in a recent work on DNA-mediated self-assembly. We focus on the effect of thermal fluctuations on the stability of membrane-like self-assembled phase with in-plane square order. Surprisingly, the fluctuations are shown to enhance the stability of this quasi-2D phase with respect to transition to alternative 3D structures.
Stability Modeling and Comparative Study of Series Vectorial Compensators
Juan Miguel Gonzalez; Claudio A. Canizares; Juan M. Ramirez
2010-01-01
Complete stability analyses, including voltage, small perturbation and transient stability studies, and the associated models and controls of a series vectorial compensator (SVeC) are presented in this paper. It is also shown through detailed simulations that the SVeC is a competitive device against series power-flow controllers and it might be a better option for similar purposes where space and costs
Chooi, Wai Hon; Zhou, Ruijie; Yeo, Suan Siong; Zhang, Feng; Wang, Dong-An
2013-06-01
Gene expression study is widely used to obtain information of the cell activities and phenotypes. To quantify gene expression, measurement of the mRNA copy number is commonly done by quantitative RT-PCR (RT-qPCR). However, proper reference gene is needed for different tissues to normalize the expression level of different genes accurately. In this study, reference gene determination was done for three-dimensional (3D) artificial tissue constructs in hydrogel. Porcine synovium-derived mesenchymal stem cells (SMSCs) and rabbit chondrocytes were cultured in both alginate and agarose hydrogels to set up four different 3D culture systems to form the artificial tissue constructs. The gene expression levels of candidate genes were determined by RT-qPCR and then analyzed by geNorm, Bestkeeper, and Normfinder. For porcine SMSCs, PPIA, and TBP were selected for tissue in alginate scaffold whereas HPRT and TBP were selected for the agarose scaffold system. On the other hand, HPRT, PPIA, and RPL18 were the stable reference genes for rabbit chondrocytes in alginate scaffold while TBP, RPL5, and RPL18 were selected for rabbit chondrocytes in agarose scaffold. This study has further indicated that suitable reference genes are different for each tissue and study purpose. The reference genes are expressed in different stability when a scaffold of different material is used. PMID:23054629
Exposure Analysis Modeling System
The Exposure Analysis Modeling System (EXAMS) is an interactive software application for formulating aquatic ecosystem models and evaluating the fate, transport, and exposure concentrations of synthetic organic chemicals including pesticides, industrial materials, and leachates f...
Stability analysis for liquid-bridging induced contact
NASA Astrophysics Data System (ADS)
Fan, H.; Wang, G. F.
2003-03-01
Microscale contact between two solid surfaces induced by liquid-bridging force was studied in this article. Attention was placed on configurational stability of the liquid between the two contacting bodies. By examining the solutions for describing the shape of the liquid under equilibrium, it was found that these solutions become physically infeasible as the volume of the liquid vanishes. A linear stability analysis was carried out by perturbing the relevant equilibrium configurations and examining the change of the free energy of the system under consideration. The analysis leads to the conclusion that the equilibrium shape of the liquid, that bridges two solids in contact, may become unstable under certain conditions. As its volume diminishes, the liquid may break into smaller droplets.
Mechanisms and models of postural stability and control.
Iqbal, Kamran
2011-01-01
Though simple in appearance, postural stabilization is a complex neuromuscular task requiring coordination among multiple joints. Mechanisms of postural stability and control in the body include supraspinal processes responsible for anticipatory postural adjustments (APA) and internal model control, lower level motor servo, and passive viscoelasticity of the musculo-tendon complex (MTC). Nevertheless, active control mechanisms may have limited effectiveness due to intrinsic delays in the reflex pathways and muscle low-pass characteristics. The use of control-oriented mathematical models, aided by analytical methods, help provide insight into neuro-physiology. Control of balance in human upright standing is particularly well suited for modeling, and is also a popular experimental paradigm. This paper examines neuro-physiological basis of postural stability and control in the background of popular biomechanic and neuroscientific models. PMID:22256156
The Stability of Social Desirability: A Latent Change Analysis.
Haberecht, Katja; Schnuerer, Inga; Gaertner, Beate; John, Ulrich; Freyer-Adam, Jennis
2015-08-01
Social desirability has been shown to be stable in samples with higher school education. However, little is known about the stability of social desirability in more heterogeneous samples differing in school education. This study aimed to investigate the stability of social desirability and which factors predict interindividual differences in intraindividual change. As part of a randomized controlled trial, 1,243 job seekers with unhealthy alcohol use were systematically recruited at three job agencies. A total of 1,094 individuals (87.8%) participated in at least one of two follow-ups (6 and 15 months after baseline) and constitute this study's sample. The Social Desirability Scale-17 was applied. Two latent change models were conducted: Model 1 tested for interindividual differences in intraindividual change of social desirability between both follow-ups; Model 2 included possible predictors (age, sex, education, current employment status) of interindividual differences in intraindividual change. Model 1 revealed a significant decrease of social desirability over time. Model 2 revealed school education to be the only significant predictor of change. These findings indicate that stability of social desirability may depend on school education. It may not be as stable in individuals with higher school education as in individuals with lower education. PMID:25041464
Comprehensive gait analysis in posterior-stabilized knee arthroplasty
Stephen A. Wilson; Peter D. McCann; Robert S. Gotlin; H. K. Ramakrishnan; Mary E. Wootten; John N. Insall
1996-01-01
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)
NASA Technical Reports Server (NTRS)
Oberg, C. L.
1974-01-01
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.
Stability in a Nonlinear Population Maturation Model St ephane Mischler
Ryzhik, Lenya
Stability in a Nonlinear Population Maturation Model St#19;ephane Mischler Laboratoire de Math#19 University of Chicago, Chicago IL 60637, USA May 14, 2002 Abstract. We consider models for population structured by maturation/maturation speed pro- posed by Rotenberg. It is a variant of transport equations
On global stability of the scalar Chaboche models
M. Brokate; D. Rachinskii
2005-01-01
We present global stability conditions for systems of differential equations, which arise as models of multisurface stress–strain laws of the so-called nonlinear kinematic hardening type and include the scalar stop operator. In addition, we analyze some properties of the models, in particular, monotonicity and contracting properties, and consider periodic solutions in case of periodic inputs.
Von-Neumann stability analysis of FDTD methods in complex Brigitte BidegarayFesquet
Bidegaray, Brigitte
Von-Neumann stability analysis of FDTD methods in complex media Brigitte Bid-mail: Brigitte.Bidegaray@imag.fr Abstract -- The stability analysis of Finite DifferenceTime Difference (FDTDtime domain (FDTD) approaches and their stability analysis. Examples of such coupled sys- tems and associated
NASA Astrophysics Data System (ADS)
Grandy, Stuart; Wieder, Will; Kallenbach, Cynthia; Tiemann, Lisa
2014-05-01
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.
NSDL National Science Digital Library
National Centers for Environmental Prediction, National Oceanic and Atmospheric Administration
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.
Mechanical models for insect locomotion: stability and parameter studies
NASA Astrophysics Data System (ADS)
Schmitt, John; Holmes, Philip
2001-08-01
We extend the analysis of simple models for the dynamics of insect locomotion in the horizontal plane, developed in [Biol. Cybern. 83 (6) (2000) 501] and applied to cockroach running in [Biol. Cybern. 83 (6) (2000) 517]. The models consist of a rigid body with a pair of effective legs (each representing the insect’s support tripod) placed intermittently in ground contact. The forces generated may be prescribed as functions of time, or developed by compression of a passive leg spring. We find periodic gaits in both cases, and show that prescribed (sinusoidal) forces always produce unstable gaits, unless they are allowed to rotate with the body during stride, in which case a (small) range of physically unrealistic stable gaits does exist. Stability is much more robust in the passive spring case, in which angular momentum transfer at touchdown/liftoff can result in convergence to asymptotically straight motions with bounded yaw, fore-aft and lateral velocity oscillations. Using a non-dimensional formulation of the equations of motion, we also develop exact and approximate scaling relations that permit derivation of gait characteristics for a range of leg stiffnesses, lengths, touchdown angles, body masses and inertias, from a single gait family computed at ‘standard’ parameter values.
An Alternative Interpretation of Three Stability Models.
ERIC Educational Resources Information Center
Wilcox, Rand R.
1979-01-01
Wilcox has described three probability models which characterize a single test item in terms of a population of examinees (ED 156 718). This note indicates indicates that similar models can be derived which characterize a single examinee in terms of an item domain. A numerical illustration is given. (Author/JKS)
Longitudinal Measurement Models in Evaluation Research: Examining Stability and Change.
ERIC Educational Resources Information Center
Pitts, Steven C.; And Others
1996-01-01
An introduction is provided to the use of confirmatory factor analysis to test measurement invariance and stability in longitudinal research. The approach is illustrated through examples representing one or two constructs in one to three measurement waves. Basic issues in establishing measurement invariance are discussed. (SLD)
Generalized Kinetic Theory of Electrons and Phonons: Models, Equilibrium, Stability
A. Rossani; A. M. Scarfone
2003-03-18
In the present paper our aim is to introduce some models for the generalization of the kinetic theory of electrons and phonons (KTEP), as well as to study equilibrium solutions and their stability for the generalized KTEP (GKTEP) equations. We consider a couple of models, relevant to non standard quantum statistics, which give rise to inverse power law decays of the distribution function with respect to energy. In the case of electrons in a phonon background, equilibrium and stability are investigated by means of Lyapounov theory. Connections with thermodynamics are pointed out.
CP violation and moduli stabilization in heterotic models
Giedt, Joel
2002-04-01
The role of moduli stabilization in predictions for CP violation is examined in the context of four-dimensional effective supergravity models obtained from the weakly coupled heterotic string. They point out that while stabilization of compactification moduli has been studied extensively, the determination of background values for other scalar by dynamical means has not been subjected to the same degree of scrutiny. These other complex scalars are important potential sources of CP violation and they show in a simple model how their background values (including complex phases) may be determined from the minimization of the supergravity scalar potential, subject to the constraint of vanishing cosmological constant.
Progress Toward the Analysis of the Kinetic Stabilizer Concept
Post, R F; Byers, J A; Cohen, R H; Fowler, T K; Ryutov, D D; Tung, L S
2005-02-08
The Kinetic Stabilizer (K-S) concept [1] represents a means for stabilizing axisymmetric mirror and tandem-mirror (T-M) magnetic fusion systems against MHD interchange instability modes. Magnetic fusion research has given us examples of axisymmetric mirror confinement devices in which radial transport rates approach the classical ''Spitzer'' level, i.e. situations in which turbulence if present at all, is at too low a level to adversely affect the radial transport [2,3,4]. If such a low-turbulence condition could be achieved in a T-M system it could lead to a fusion power system that would be simpler, smaller, and easier to develop than one based on closed-field confinement, e.g., the tokamak, where the transport is known to be dominated by turbulence. However, since conventional axisymmetric mirror systems suffer from the MHD interchange instability, the key to exploiting this new opportunity is to find a practical way to stabilize this mode. The K-S represents one avenue to achieving this goal. The starting point for the K-S concept is a theoretical analysis by Ryutov [5]. He showed that a MHD-unstable plasma contained in an axisymmetric mirror cell can be MHD-stabilized by the presence of a low-density plasma on the expanding field lines outside the mirrors. If this plasma communicates well electrically with the plasma in the then this exterior plasma can stabilize the interior, confined, plasma. This stabilization technique was conclusively demonstrated in the Gas Dynamic Trap (GDT) experiment [6] at Novosibirsk, Russia, at mirror-cell plasma beta values of 40 percent. The GDT operates in a high collisionality regime. Thus the effluent plasma leaking through the mirrors, though much lower in density than that of the confined plasma, is still high enough to satisfy the stabilization criterion. This would not, however, be the case in a fusion T-M with axisymmetric plug and central cell fields. In such a case the effluent plasma would be far too low in density to stabilize the plasmas in the plug cells and the central cell. The K-S resolves this dilemma by employing ion beams injected up the magnetic gradient in the ''expander'' region outside the outermost mirror in such a way that as they are compressed, stagnated, and reflected they form a ''stabilizer'' plasma in the expander. Preliminary calculations [1] showed that the power required to maintain the stabilizer beams would be orders of magnitude less than the fusion power generated. This report reviews those calculations and describes additional theoretical and computational work in progress, aimed at confirming and extending the analysis of the K-S concept as applied to axisymmetric tandem mirror systems.
A model study of articulated mat stability
Sasaki, Tetsu
1990-01-01
characteristics were established by measuring the following parameters: wave height, wave runup& wave rundown, uplifting force, slide-up force, and slide-down force. All three disturbing forces: uplifting force, slide-up force, and slide-down forces were... measured by strain gages insta'led in instrumented blocks. All together, 243 experimental conditions were exanfined by varying incident wave height, wave period, instrumented block depth, model revetment slope, and permeability of the model revetment...
Modelling and transient stability of large wind farms
Vladislav Akhmatov; Hans Knudsen; Arne Hejde Nielsen; Jřrgen Kaas Pedersen; Niels Kjřlstad Poulsen
2003-01-01
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
Application of Quotient Rings for Stability Analysis in Chemical Systems
NASA Astrophysics Data System (ADS)
Sauerbrei, Sonja; Sensse, Anke; Eiswirth, Markus
2011-04-01
Concepts from algebraic geometry (polynomial rings) can be used to determine analytically the stationary solutions in chemical reactions systems, more generally, systems of ordinary differential equations of polynomial form. The stability analysis via the Jacobian matrix often leads to complicated expressions which can hardly be analyzed. It is shown that these expressions can be simplified by forming quotient rings of the corresponding polynomial ring. The coefficients in the characteristic equation of the Jacobian can be represented by the normal forms obtained by generating the quotient rings so that their sign changes in dependence of a kinetic parameter and, hence, the stability can be determined. The procedure is illustrated using a well-known surface reaction.
Consistency Stability, Convergence Of Stirling Engine Models
L. Bauwans
1990-01-01
Stirling engine modeling can be diided into two main steps. First, an idealization of the engine that can be translated into a complete and unique mathematical problem must be chosen. Then, a computer code that provides a numerical, approximate solution to that problem must be written. The solution Is meaningful if the error due to its approximate nature can be
Stabilizing a Bicycle: A Modeling Project
ERIC Educational Resources Information Center
Pennings, Timothy J.; Williams, Blair R.
2010-01-01
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…
Stability in a Nonlinear Population Maturation Model
Stephane Mischler; Lenya Ryzhik
We consider models for population structured by maturation\\/maturation speed proposed by Rotenberg. It is a variant of transport equations for age-structured populations which presents particu- larly interesting mathematical diculties. It allows to introduce more stochasticity in the birth process and in the aging phenomena. We present a new method for studying the time asymptotics which is also illustrated on the
Computational analysis of a stability robustness margin for structured real-parameter perturbations
NASA Technical Reports Server (NTRS)
Wedell, Evan; Chuang, C.-H.; Wie, Bong
1989-01-01
An efficient computational method is presented for stability robustness analysis with structured real-parameter perturbations. A generic model of a class of uncertain dynamical systems is used as an example. The parameter uncertainty is characterized by a real scalar, epsilon. Multilinearity of the closed-loop characteristic polynomial is exploited to permit application of the mapping theorem to calculate the stability robustness margin. It is found that sensitive geometry of the stability boundary in the epsilon, omega-plane renders problematic the calculation of the minimum epsilon as a function of omega. This difficulty is avoided by calculating the minimum distance to the image of the uncertainty domain over omega as a function of epsilon. It is also shown that a certain class of uncertain dynamical systems has the required multilinearity property and are thus amenable to the proposed technique.
Per Arne Rikvold
2007-01-01
We compare and contrast the long-time dynamical properties of two individual-based models of biological coevolution. Selection\\u000a occurs via multispecies, stochastic population dynamics with reproduction probabilities that depend nonlinearly on the population\\u000a densities of all species resident in the community. New species are introduced through mutation. Both models are amenable\\u000a to exact linear stability analysis, and we compare the analytic results
Doubly-fed induction machine models for stability assessment of wind farms
Markus A. Poller
2003-01-01
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
Stability analysis for a semiconductor laser in an external cavity
Tromborg, B.; Olesen, H.; Osmundsen, J.H.
1984-09-01
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.
Ant Colony Optimization Analysis on Overall Stability of High Arch Dam Basis of Field Monitoring
Liu, Xiaoli; Chen, Hong-Xin; Kim, Jinxie
2014-01-01
A dam ant colony optimization (D-ACO) analysis of the overall stability of high arch dams on complicated foundations is presented in this paper. A modified ant colony optimization (ACO) model is proposed for obtaining dam concrete and rock mechanical parameters. A typical dam parameter feedback problem is proposed for nonlinear back-analysis numerical model based on field monitoring deformation and ACO. The basic principle of the proposed model is the establishment of the objective function of optimizing real concrete and rock mechanical parameter. The feedback analysis is then implemented with a modified ant colony algorithm. The algorithm performance is satisfactory, and the accuracy is verified. The m groups of feedback parameters, used to run a nonlinear FEM code, and the displacement and stress distribution are discussed. A feedback analysis of the deformation of the Lijiaxia arch dam and based on the modified ant colony optimization method is also conducted. By considering various material parameters obtained using different analysis methods, comparative analyses were conducted on dam displacements, stress distribution characteristics, and overall dam stability. The comparison results show that the proposal model can effectively solve for feedback multiple parameters of dam concrete and rock material and basically satisfy assessment requirements for geotechnical structural engineering discipline. PMID:25025089
A Three-Dimensional Unsteady CFD Model of Compressor Stability
NASA Technical Reports Server (NTRS)
Chima, Rodrick V.
2006-01-01
A three-dimensional unsteady CFD code called CSTALL has been developed and used to investigate compressor stability. The code solved the Euler equations through the entire annulus and all blade rows. Blade row turning, losses, and deviation were modeled using body force terms which required input data at stations between blade rows. The input data was calculated using a separate Navier-Stokes turbomachinery analysis code run at one operating point near stall, and was scaled to other operating points using overall characteristic maps. No information about the stalled characteristic was used. CSTALL was run in a 2-D throughflow mode for very fast calculations of operating maps and estimation of stall points. Calculated pressure ratio characteristics for NASA stage 35 agreed well with experimental data, and results with inlet radial distortion showed the expected loss of range. CSTALL was also run in a 3-D mode to investigate inlet circumferential distortion. Calculated operating maps for stage 35 with 120 degree distortion screens showed a loss in range and pressure rise. Unsteady calculations showed rotating stall with two part-span stall cells. The paper describes the body force formulation in detail, examines the computed results, and concludes with observations about the code.
On the stability of steady states in a granuloma model
NASA Astrophysics Data System (ADS)
Friedman, Avner; Lam, King-Yeung
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.
Stability and Control Analysis of the F-15B Quiet SpikeTM Aircraft
NASA Technical Reports Server (NTRS)
McWherter, Shaun C.; Moua, Cheng M.; Gera, Joseph; Cox, Timothy H.
2009-01-01
The primary purpose of the Quiet Spike(TradeMark) flight research program was to analyze the aerodynamic, structural, and mechanical proof-of-concept of a large multi-stage telescoping nose spike installed on the National Aeronautics and Space Administration Dryden Flight Research Center (Edwards, California) F-15B airplane. This report describes the preflight stability and control analysis performed to assess the effect of the spike on the stability, controllability, and handling qualities of the airplane; and to develop an envelope expansion approach to maintain safety of flight. The overall flight test objective was to collect flight data to validate the spike structural dynamics and loads model up to Mach 1.8. Other objectives included validating the mechanical feasibility of a morphing fuselage at operational conditions and determining the near-field shock wave characterization. The two main issues relevant to the stability and control objectives were the effects of the spike-influenced aerodynamics on the F-15B airplane flight dynamics, and the air data and angle-of-attack sensors. The analysis covered the sensitivity of the stability margins, and the handling qualities due to aerodynamic variation and the maneuvering limitations of the F-15B Quiet Spike configuration. The results of the analysis and the implications for the flight test program are also presented.
George, Glyn
through its equilibrium position with angular speed vo, then the initial conditions are ( ) ( ) o 0 0 0ENGI 9420 Lecture Notes 4 - Stability Analysis Page 4.01 4. Stability Analysis for Non-linear Ordinary Differential Equations A pair of simultaneous first order homogeneous linear ordinary differential
George, Glyn
equilibrium position with angular speed vo, then the initial conditions are ( ) ( ) o 0 0 0 , 0 t d x x v v dtENGI 9420 Lecture Notes 4 - Stability Analysis Page 4.01 4. Stability Analysis for Non-linear Ordinary Differential Equations A pair of simultaneous first order homogeneous linear ordinary differential
Stability analysis of restricted non-static axial symmetry
NASA Astrophysics Data System (ADS)
Sharif, M.; Haq Bhatti, M. Zaeem Ul
2013-11-01
This paper aims to investigate the instability of very restricted class of non-static axially symmetric spacetime with anisotropic matter configuration. The perturbation scheme is established for the Einstein field equations and conservation laws. The instability range in the Newtonian and post-Newtonian regions are explored by constructing the collapse equation in this scenario. It is found that the adiabatic index plays an important role in the stability analysis which depends upon the physical parameters i.e., energy density and anisotropic pressure of the fluid distribution.
NASA Astrophysics Data System (ADS)
Poletkin, K.; Lu, Z.; den Hartogh, B.; Wallrabe, U.; Badilita, V.
2014-11-01
We present a linear analytical model coupled with experimental analysis to discuss stability of a levitated proof mass (PM) in a micromachined inductive suspension (MIS), which has been previously introduced and characterized. The model is a function of the MIS geometry, describes the dynamics of a levitated disk-shaped PM near the equilibrium point, and predicts conditions for stable levitation. The experimental setup directly measures the lateral component of the Lorentz force, which has a stabilization role in the MIS structure, as well as the vertical levitation force. The experimental setup is further used to derive mechanical parameters such as stiffness values relative to lateral, vertical and angular displacements, proven to be in excellent agreement with the values predicted by the analytical model.
Choi, Min-Hyung
Numerical Stability and Convergence Analysis of Geometric Constraint Enforcement in Dynamic constraint enforcement using Lagrange Multipliers is one of the popular methods to control the behavior a guideline to choose a proper constraint enforcement method. In addition, the numerical stability
Modelling of turbulent diffusion flames stabilized on a bluff body
Chang E. Lee; Ok Y. Yang; Yoshiaki Onuma
1992-01-01
The present authors previously proposed a modification of the k-epsilon turbulence model in the modeling of jet diffusion flames to represent the so-called laminarization phenomenon, caused by combustion in the low-turbulence region, and recently found, in experiments on diffusion flames stabilized on a bluff body, that this phenomenon also exerts an important influence on the structure of these flames with
The Predictive Performance and Stability of Six Species Distribution Models
Huang, Min-Yi; Fan, Wei-Yi; Wang, Zhi-Gao
2014-01-01
Background Predicting species’ potential geographical range by species distribution models (SDMs) is central to understand their ecological requirements. However, the effects of using different modeling techniques need further investigation. In order to improve the prediction effect, we need to assess the predictive performance and stability of different SDMs. Methodology We collected the distribution data of five common tree species (Pinus massoniana, Betula platyphylla, Quercus wutaishanica, Quercus mongolica and Quercus variabilis) and simulated their potential distribution area using 13 environmental variables and six widely used SDMs: BIOCLIM, DOMAIN, MAHAL, RF, MAXENT, and SVM. Each model run was repeated 100 times (trials). We compared the predictive performance by testing the consistency between observations and simulated distributions and assessed the stability by the standard deviation, coefficient of variation, and the 99% confidence interval of Kappa and AUC values. Results The mean values of AUC and Kappa from MAHAL, RF, MAXENT, and SVM trials were similar and significantly higher than those from BIOCLIM and DOMAIN trials (p<0.05), while the associated standard deviations and coefficients of variation were larger for BIOCLIM and DOMAIN trials (p<0.05), and the 99% confidence intervals for AUC and Kappa values were narrower for MAHAL, RF, MAXENT, and SVM. Compared to BIOCLIM and DOMAIN, other SDMs (MAHAL, RF, MAXENT, and SVM) had higher prediction accuracy, smaller confidence intervals, and were more stable and less affected by the random variable (randomly selected pseudo-absence points). Conclusions According to the prediction performance and stability of SDMs, we can divide these six SDMs into two categories: a high performance and stability group including MAHAL, RF, MAXENT, and SVM, and a low performance and stability group consisting of BIOCLIM, and DOMAIN. We highlight that choosing appropriate SDMs to address a specific problem is an important part of the modeling process. PMID:25383906
Synchronized clusters in coupled map networks: Stability analysis
Sarika Jalan; R. E. Amritkar; Chin-Kun Hu
2003-07-22
We study self-organized (s-) and driven (d-) synchronization in coupled map networks for some simple networks, namely two and three node networks and their natural generalization to globally coupled and complete bipartite networks. We use both linear stability analysis and Lyapunov function approach for this study and determine stability conditions for synchronization. We see that most of the features of coupled dynamics of small networks with two or three nodes, are carried over to the larger networks of the same type. The phase diagrams for the networks studied here have features very similar to the different kinds of networks studied in Ref. \\cite{sarika-REA2}. The analysis of the dynamics of the difference variable corresponding to any two nodes shows that when the two nodes are in driven synchronization, all the coupling terms cancel out whereas when they are in self-organized synchronization, the direct coupling term between the two nodes adds an extra decay term while the other couplings cancel out.
Postburn roof stability analysis for the TONO CRIP UCG burn
Taylor, L.M.; Sutherland, H.J.; Kuszmaul, J.S.
1986-01-01
During the Ninth Annual Underground Coal Gasification Symposium, Sutherland, Hommert, Taylor, and Benzley presented a preburn prediction for the burn, roof fall and surface subsidence for the TONO CRIP UCG site in Washington state. That burn has now been completed and postburn measurements of cavity sizes have become available. In this manuscript the authors show that the preburn predictions are, in general, in good agreement with the postburn examination of the burn site. Discrepancies between the predictions and the measurements are shown to arise for two reasons. The first is that the burn sequence analyzed in the prediction was not allowed during the course of the experiment due to experimental difficulties. The second reason is that the stratigraphic section analyzed in the preburn predictions is slightly different form that observed above the burn. To clarify the discrepancies, the roof stability of the measured burn cavity is analyzed using the two analysis schemes that were used in the preburn analysis.
Validation of IVA Computer Code for Flow Boiling Stability Analysis
Ivanov Kolev, Nikolay [Framatome-ANP, PO Box 3220, D-91058, Erlangen (Germany)
2006-07-01
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 of the oscillations are used for comparison. The comparison demonstrates the capability of the code to successfully simulate such class of processes. (author)
Stability analysis for spatial attrition with n forces
NASA Astrophysics Data System (ADS)
González, Eduardo; Villena, Marcelo J.
2012-09-01
Close combat between two forces can be modelled through a set of two coupled partial differential equations, of second order in space and first order in time. That problem has been studied and shows a way to find stable solutions by means of a careful selection of the discretization both in time and space and through the use of a simple transformation. The results are generalized here for more interacting forces. It is found that the eigenvalues of the matrix that represent the system dynamics together with the time step size shape up the stability coefficients.
NASA Astrophysics Data System (ADS)
Kami?ski, M.; Szafran, J.
2015-05-01
The main purpose of this work is to verify the influence of the weighting procedure in the Least Squares Method on the probabilistic moments resulting from the stability analysis of steel skeletal structures. We discuss this issue also in the context of the geometrical nonlinearity appearing in the Stochastic Finite Element Method equations for the stability analysis and preservation of the Gaussian probability density function employed to model the Young modulus of a structural steel in this problem. The weighting procedure itself (with both triangular and Dirac-type) shows rather marginal influence on all probabilistic coefficients under consideration. This hybrid stochastic computational technique consisting of the FEM and computer algebra systems (ROBOT and MAPLE packages) may be used for analogous nonlinear analyses in structural reliability assessment.
Parallel processing for efficient 3D slope stability modelling
NASA Astrophysics Data System (ADS)
Marchesini, Ivan; Mergili, Martin; Alvioli, Massimiliano; Metz, Markus; Schneider-Muntau, Barbara; Rossi, Mauro; Guzzetti, Fausto
2014-05-01
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.
NASA Astrophysics Data System (ADS)
Lambert, Carolyn; Suneeta, Vardarajan
2012-10-01
We analyze the stability of the Euclidean Witten black hole (the cigar soliton in mathematics literature) under first-order renormalization group (Ricci) flow of the world-sheet sigma model. This analysis is from the target space point of view. We find that the Witten black hole has no unstable normalizable perturbative modes in a linearized mode analysis in which we consider circularly symmetric perturbations. Finally, we discuss a result from mathematics that implies the existence of a nonnormalizable mode of the Witten black hole under which the geometry flows to the sausage solution studied by Fateev, Onofri and Zamolodchikov.
Densmore, Jeffery D. [Computational Physics and Methods Group, Los Alamos National Laboratory, P.O. Box 1663, MS D409, Los Alamos, NM 87545 (United States)], E-mail: jdd@lanl.gov; Warsa, James S. [Computational Physics and Methods Group, Los Alamos National Laboratory, P.O. Box 1663, MS D409, Los Alamos, NM 87545 (United States)], E-mail: warsa@lanl.gov; Lowrie, Robert B. [Computational Physics and Methods Group, Los Alamos National Laboratory, P.O. Box 1663, MS D409, Los Alamos, NM 87545 (United States)], E-mail: lowrie@lanl.gov; Morel, Jim E. [Department of Nuclear Engineering, Texas A and M University, 3133 TAMU, College Station, TX 77843 (United States)], E-mail: morel@tamu.edu
2009-09-01
The Fokker-Planck equation is a widely used approximation for modeling the Compton scattering of photons in high energy density applications. In this paper, we perform a stability analysis of three implicit time discretizations for the Compton-Scattering Fokker-Planck equation. Specifically, we examine (i) a Semi-Implicit (SI) scheme that employs backward-Euler differencing but evaluates temperature-dependent coefficients at their beginning-of-time-step values, (ii) a Fully Implicit (FI) discretization that instead evaluates temperature-dependent coefficients at their end-of-time-step values, and (iii) a Linearized Implicit (LI) scheme, which is developed by linearizing the temperature dependence of the FI discretization within each time step. Our stability analysis shows that the FI and LI schemes are unconditionally stable and cannot generate oscillatory solutions regardless of time-step size, whereas the SI discretization can suffer from instabilities and nonphysical oscillations for sufficiently large time steps. With the results of this analysis, we present time-step limits for the SI scheme that prevent undesirable behavior. We test the validity of our stability analysis and time-step limits with a set of numerical examples.
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
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.
Aeroelastic stability analyses of two counter rotating propfan designs for a cruise missile model
NASA Technical Reports Server (NTRS)
Mahajan, Aparajit J.; Lucero, John M.; Mehmed, Oral; Stefko, George L.
1992-01-01
Aeroelastic stability analyses were performed to insure structural integrity of two counterrotating propfan blade designs for a NAVY/Air Force/NASA cruise missile model wind tunnel test. This analysis predicted if the propfan designs would be flutter free at the operating conditions of the wind tunnel test. Calculated stability results are presented for the two blade designs with rotational speed and Mach number as the parameters. A aeroelastic analysis code ASTROP2 (Aeroelastic Stability and Response of Propulsion Systems - 2 Dimensional Analysis), developed at LeRC, was used in this project. The aeroelastic analysis is a modal method and uses the combination of a finite element structural model and two dimensional steady and unsteady cascade aerodynamic models. This code was developed to analyze single rotation propfans but was modified and applied to counterrotating propfans for the present work. Modifications were made to transform the geometry and rotation of the aft rotor to the same reference frame as the forward rotor, to input a non-uniform inflow into the rotor being analyzed, and to automatically converge to the least stable aeroelastic mode.
Stability analysis of an impacting T-junction pipe flow
NASA Astrophysics Data System (ADS)
Chen, Kevin; Rowley, Clarence; Stone, Howard
2013-11-01
The flow through a T-shaped pipe bifurcation (with the inlet at the bottom of the ``T'') is a common occurrence in both natural and man-made systems, including blood vessels, industrial pipe networks, and microfluidic channels. Despite the ubiquitous nature of the geometry, many questions about the flow physics remain. We analyze the stability of Navier-Stokes equilibria by executing numerical continuation on the Reynolds number (based on the average inlet velocity), using a combination of linear extrapolation and the Newton-GMRES algorithm. We find that the qualitative nature of the equilibria's local bifurcations is highly sensitive to the grid resolution. On a sufficiently resolved grid, a rapid succession of supercritical Hopf bifurcations begins at Re ~ 550 . Visualizations of the neutrally stable eigenmodes reveal the physical nature of the instabilities. We also compare equilibria computed with different radii of curvature at the square corners of the ``T.'' Next, a wavemaker analysis reveals the locations in the T-junction where the stability is most sensitive to localized changes in the dynamics, e.g., via a change in geometry. The flow through a T-shaped pipe bifurcation (with the inlet at the bottom of the ``T'') is a common occurrence in both natural and man-made systems, including blood vessels, industrial pipe networks, and microfluidic channels. Despite the ubiquitous nature of the geometry, many questions about the flow physics remain. We analyze the stability of Navier-Stokes equilibria by executing numerical continuation on the Reynolds number (based on the average inlet velocity), using a combination of linear extrapolation and the Newton-GMRES algorithm. We find that the qualitative nature of the equilibria's local bifurcations is highly sensitive to the grid resolution. On a sufficiently resolved grid, a rapid succession of supercritical Hopf bifurcations begins at Re ~ 550 . Visualizations of the neutrally stable eigenmodes reveal the physical nature of the instabilities. We also compare equilibria computed with different radii of curvature at the square corners of the ``T.'' Next, a wavemaker analysis reveals the locations in the T-junction where the stability is most sensitive to localized changes in the dynamics, e.g., via a change in geometry. This work was supported by the NSF GRFP.
Thermal Stability of Nanocrystalline Alloys by Solute Additions and A Thermodynamic Modeling
NASA Astrophysics Data System (ADS)
Saber, Mostafa
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
Local Analysis of Inverse Problems: H\\"{o}lder Stability and Iterative Reconstruction
de Hoop, Maarten V; Scherzer, Otmar
2011-01-01
We consider a class of inverse problems defined by a nonlinear map from parameter or model functions to the data. We assume that solutions exist. The space of model functions is a Banach space which is smooth and uniformly convex; however, the data space can be an arbitrary Banach space. We study sequences of parameter functions generated by a nonlinear Landweber iteration and conditions under which these strongly converge, locally, to the solutions within an appropriate distance. We express the conditions for convergence in terms of H\\"{o}lder stability of the inverse maps, which ties naturally to the analysis of inverse problems.
NASA Astrophysics Data System (ADS)
Hegner, Benedikt
2011-12-01
We review the options for performing user analyses at CMS. In this text we put the CMS physics analysis software framework and other tools in the context of a bigger picture of performing data analysis. The flow of physics data through layers of skimming is briefly described, and the user options for analyzing objects on local computing resources or laptop discussed in turn. We present the first experiences with this model obtained after the recent start of the LHC physics programme.
Modeling and Simulation of a Helicopter Slung Load Stabilization Device
NASA Technical Reports Server (NTRS)
Cicolani, Luigi S.; Ehlers, George E.
2002-01-01
This paper addresses the problem of simulation and stabilization of the yaw motions of a cargo container slung load. The study configuration is a UH-60 helicopter carrying a 6ft x 6 ft x 8 ft CONEX container. This load is limited to 60 KIAS in operations and flight testing indicates that it starts spinning in hover and that spin rate increases with airspeed. The simulation reproduced the load yaw motions seen in the flight data after augmenting the load model with terms representing unsteady load yaw moment effects acting to reinforce load oscillations, and augmenting the hook model to include yaw resistance at the hook. The use of a vertical fin to stabilize the load is considered. Results indicate that the CONEX airspeed can be extended to 110 kts using a 3x5 ft fin.
A general stability analysis of FIT\\/FDTD applied to lossy dielectrics and lumped elements
Fredrik Edelvik; Rolf Schuhmann; Thomas Weiland
2004-01-01
Stability analysis of the finite-di erence time-domain (FDTD) method is usually performed using von Neumann analysis, where a necessary condition for stability is obtained by requiring the amplitude of discrete Fourier modes defined on the grid to remain bounded. However, this limits the analysis to homogeneous materials, equidistant grids and unbounded domains. A rare situation in practical computations. In this
Hard-core yukawa model for charge-stabilized colloids
Davoudi; Kohandel; Mohammadi; Tanatar
2000-11-01
The hypernetted chain approximation is used to study the phase diagram of a simple hardcore Yukawa model of a charge-stabilized colloids. We calculate the static structure factor, the pair distribution function, and the collective mode energies over a wide range of parameters, and the results are used for studying the freezing transition of the system. The resulting phase diagram is in good agreement with the known estimates and the Monte Carlo simulations. PMID:11102053
Analysis of Faint Glints from Stabilized GEO Satellites
NASA Astrophysics Data System (ADS)
Hall, D.; Kervin, P.
2013-09-01
Ground-based telescopes routinely acquire temporal brightness measurements of satellites in geo-stationary and geo-synchronous orbit that provide valuable characterization information. For instance, GEO satellites that are not stabilized tend to rotate, and produce brightnesses that vary in time with frequencies corresponding to rotation rates. Temporal brightness patterns can also be exploited to characterize stabilized GEO satellites. For example, many operational GEO satellites have solar panels that glint when they reflect sunlight towards an observer in a mirror-like fashion. These well-known solar panel glints can be remarkably bright, often exceeding several stellar magnitudes in amplitude. Measured brightnesses and times of these glints can be exploited to estimate the size, segmentation, and alignment of the solar array, valuable information about the satellite's power generation and consumption capabilities. However, satellites can produce other glints in addition to those originating from solar panels. These glints can be much fainter, with amplitudes as small as 0.2 magnitudes. Several observations of GEO satellites show several such glints occurring during the span of a single night. Furthermore, many of these recur from night to night when observed from a single ground-based site, but with subtle, incremental changes in both peak times and brightnesses. These fainter glints must originate from reflective elements mounted on the satellite's main bus, solar panel structure, or other peripheral structures that might be stationary or moving with respect to the main bus. Our analysis indicates that such glints can be exploited for GEO satellite characterization.
Tool for bonded optical element thermal stability analysis
NASA Astrophysics Data System (ADS)
Klotz, Gregory L.
2011-09-01
An analytical tool is presented which supports the opto-mechanical design of bonded optical elements. Given the mounting requirements from the optical engineer, the alignment stability and optical stresses in bonded optics can be optimized for the adhesive and housing material properties. While a perfectly athermalized mount is desirable, it is not realistic. The tool permits evaluation of element stability and stress over the expected thermal range at nominal, or worst case, achievable assembly and manufacturing tolerances. Selection of the most appropriate mount configuration and materials, which maintain the optical engineer's design, is then possible. The tool is based on a stress-strain analysis using Hooke's Law in the worst case plane through the optic centerline. The optimal bond line is determined for the selected adhesive, housing and given optic materials using the basic athermalization equation. Since a mounting solution is expected to be driven close to an athermalized design, the stress variations are considered linearly related to strain. A review of the equation set, the tool input and output capabilities and formats and an example will be discussed.
Discrete tones around airfoils: a global stability analysis.
NASA Astrophysics Data System (ADS)
Fosas de Pando, Miguel; Schmid, Peter J.; Sipp, Denis
2012-11-01
Airfoil self-noise stems from an interaction between the airfoil surface, the boundary layers and the wake. At moderate Reynolds number and small angles of attack, the acoustic spectrum is dominated by discrete tones correlated to the ringing of coherent structures localized in the vicinity of the trailing edge. Local stability analyses show strong amplification of hydrodynamic instabilities in the frequency range of acoustic tones, suggesting an interplay between sound waves and instabilities. However, owing to the intrinsic limitations of local approaches, a satisfactory explanation of the tonal-noise phenomenon is still missing. We present a global stability analysis of the mean-flow linearized dynamics. Features of the global modes spectrum and of the resolvent norm will be discussed. The least-stable direct modes show a link between the suction-side boundary layer, the near wake dynamics, and acoustic radiation; conversely, the corresponding adjoint modes pinpoint at the pressure side as the location of maximum sensitivity. Although the linearized operator is stable, the resolvent norm shows substantial energy amplification. Finally, the pressure-side, suction-side and wake dynamics will be analyzed in isolation to assess their respective contribution to the overall process. This work was performed using HPC resources from GENCI-CINES (Grant 2012-026451).
Stability analysis of a natural circulation lead-cooled fast reactor
NASA Astrophysics Data System (ADS)
Lu, Qiyue
This dissertation is aimed at nuclear-coupled thermal hydraulics stability analysis of a natural circulation lead cooled fast reactor design. The stability concerns arise from the fact that natural circulation operation makes the system susceptible to flow instabilities similar to those observed in boiling water reactors. In order to capture the regional effects, modal expansion method which incorporates higher azimuthal modes is used to model the neutronics part of the system. A reduced order model is used in this work for the thermal-hydraulics. Consistent with the number of heat exchangers (HXs), the reactor core is divided into four equal quadrants. Each quadrant has its corresponding external segments such as riser, plenum, pipes and HX forming an equivalent 1-D closed loop. The local pressure loss along the loop is represented by a lumped friction factor. The heat transfer process in the HX is represented by a model for the coolant temperature at the core inlet that depends on the coolant temperature at the core outlet and the coolant velocity. Additionally, time lag effects are incorporated into this HX model due to the finite coolant speed. A conventional model is used for the fuel pin heat conduction to couple the neutronics and thermal-hydraulics. The feedback mechanisms include Doppler, axial/radial thermal expansion and coolant density effects. These effects are represented by a linear variation of the macroscopic cross sections with the fuel temperature. The weighted residual method is used to convert the governing PDEs to ODEs. Retaining the first and second modes, leads to six ODEs for neutronics, and five ODEs for the thermal-hydraulics in each quadrant. Three models are developed. These are: 1) natural circulation model with a closed coolant flow path but without coupled neutronics, 2) forced circulation model with constant external pressure drop across the heated channels but without coupled neutronics, 3) coupled system including neutronics with higher modes and thermal-hydraulics. In the second model, the HX and the external flow path are not incorporated and therefore no time delays are considered, and a constant heat source term is assumed. There is no difference among four equivalent loops, and the system is finally described by a set of ODEs. The thermal hydraulics in the first and third models is represented by sets of ODEs with time lags, namely, DDEs, due to external pipes and the HX model. Models 1 and 2 use a constant heat source term rather than coupled neutronics as is the case in model 3. In model 3, the four equivalent loops are linked via modal neutronics. They are represented by twenty-six (six for neutronics; twenty for thermal-hydraulics / five for each loop) equations. Two approaches, one in time domain and the other in frequency domain, are used for stability analyses. For model number 1, based on the characteristic of DDEs, a MATLAB package is used to carry out the stability analysis. Results of the frequency domain analysis are presented in core-height---friction-factor space, dividing the space into stable and unstable regions. Results are also verified in time-domain. For model number 2, eigenvalues of the Jacobian matrix are evaluated for the frequency domain stability analysis. Scenarios including pulse stimulation on coolant velocity, and different friction factors are simulated in the time domain. The third model is studied only in the time domain. Eight different scenarios are simulated. These include system response after different perturbations such as positive or negative reactivity insertion in one or more quadrants. Results show that SUPERSTAR design is very robust, and that the nominal operation points have considerable safety margins. Results also identify regions in design and operation parameter spaces where the reactor becomes less stable or even unstable.
Modeling and Control of Combustion Dynamics in Lean-Premixed Swirl-Stabilized Combustors
Ying Huang; Vigor Yang
2005-01-01
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
Stability of a Resonant System of Conservation Laws Modeling Polymer Flow with Gravitation
NASA Astrophysics Data System (ADS)
Klingenberg, Christian; Risebro, Nils Henrik
2001-03-01
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.
A continuum model for flocking: Obstacle avoidance, equilibrium, and stability
NASA Astrophysics Data System (ADS)
Mecholsky, Nicholas Alexander
The modeling and investigation of the dynamics and configurations of animal groups is a subject of growing attention. In this dissertation, we present a partial-differential-equation based continuum model of flocking and use it to investigate several properties of group dynamics and equilibrium. We analyze the reaction of a flock to an obstacle or an attacking predator. We show that the flock response is in the form of density disturbances that resemble Mach cones whose configuration is determined by the anisotropic propagation of waves through the flock. We investigate the effect of a flock 'pressure' and pairwise repulsion on an equilibrium density distribution. We investigate both linear and nonlinear pressures, look at the convergence to a 'cold' (T ? 0) equilibrium solution, and find regions of parameter space where different models produce the same equilibrium. Finally, we analyze the stability of an equilibrium density distribution to long-wavelength perturbations. Analytic results for the stability of a constant density solution as well as stability regimes for constant density solutions to the equilibrium equations are presented.
Stability analysis of dynamic multilayer neuro identifier Departamento de Control Automatico,
Sontag, Eduardo
Stability analysis of dynamic multilayer neuro identifier Wen Yu Departamento de Control Automatico-line identification. Pas- sivity approach is applied to access several stability properties of the neuro identifier by off-line learn- ing may make the neuro identification algorithm robust stability with respect to any
Author's personal copy Reachability analysis based transient stability design in power systems
Kumar, Ratnesh
algorithm to determine the stability region. Energy function method has also been applied in transient stability assessment. Anthony et al. [7] derived the energy function for machines based on a centerAuthor's personal copy Reachability analysis based transient stability design in power systems
A Global Stability Analysis of Clusters of Galaxies with Conduction and AGN Feedback Heating
NASA Astrophysics Data System (ADS)
Guo, Fulai; Oh, S. Peng; Ruszkowski, M.
2008-12-01
We investigate a series of steady state models of galaxy clusters, in which the hot intracluster gas is efficiently heated by active galactic nucleus (AGN) feedback and thermal conduction, and in which the mass accretion rates are highly reduced compared to those predicted by the standard cooling flow models. We perform a global Lagrangian stability analysis. We show for the first time that the global radial instability in cool core clusters can be suppressed by the AGN feedback mechanism, provided that the feedback efficiency exceeds a critical lower limit. Furthermore, our analysis naturally shows that the clusters can exist in two distinct forms. Globally stable clusters are expected to have either (1) cool cores stabilized by both AGN feedback and conduction or (2) noncool cores stabilized primarily by conduction. Intermediate central temperatures typically lead to globally unstable solutions. This bimodality is consistent with the recent observation by Dunn & Fabian of anticorrelation between the flatness of the temperature profiles and the AGN activity and the observation by Rafferty et al. that the shorter central cooling times tend to correspond to significantly younger AGN X-ray cavities.
Adaptability and stability analysis of the juice yield of yellow passion fruit varieties.
Oliveira, E J; Freitas, J P X; Jesus, O N
2014-01-01
This study analyzed the genotype x environment interaction (GE) for the juice productivity (JuProd) of 12 yellow passion fruit varieties (Passiflora edulis Sims. f. flavicarpa Deg.) using additive main effects and multiplicative interaction (AMMI) model and auxiliary parameters. The experiments were conducted in eight environments of Bahia State, Brazil, using a randomized block design with three replications. Analysis of variance showed significant effects (P ? 0.01) for environments, genotypes, and GE interaction. The first two interaction principal component axes (IPCAs) explained 81.00% of the sum of squares of the GE interaction. The AMMI1 and AMMI2 models showed that varieties 09 and 11 were the most stable. Other parameters, namely, the AMMI stability value (ASV), yield stability (YSI), sustainability, and stability index (StI), indicated that other varieties were more stable. These varying results were certainly a consequence of methodological differences. In contrast, the ranking of varieties for each of the stability parameters showed significant positive correlations (P ? 0.05) between IPCA1 x (ASV, YSI), JuProd x (StI, YSI), YSI x ASV, and StI x YSI. Cluster analysis based on the genotypic profile of the effects of the GE interaction identified three groups that correlated with the distribution of varieties in the AMMI1 biplot. However, the classification of stable genotypes was limited because the association with the productivity was not included in the analysis. Variety 08 showed the most stable and productive behavior, ranking above average in half of the environments, and it should be recommended for use. PMID:25177932
Coupled three-dimensional aeroelastic stability analysis of bladed disks
Gerolymos, G.A. (Univ. Pierre and Marie Curie, Paris (France))
1993-10-01
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.
Stability analysis and numerical simulation of simplified solid rocket motors
NASA Astrophysics Data System (ADS)
Boyer, G.; Casalis, G.; Estivalčzes, J.-L.
2013-08-01
This paper investigates the Parietal Vortex Shedding (PVS) instability that significantly influences the Pressure Oscillations of the long and segmented solid rocket motors. The eigenmodes resulting from the stability analysis of a simplified configuration, namely, a cylindrical duct with sidewall injection, are presented. They are computed taking into account the presence of a wall injection defect, which is shown to induce hydrodynamic instabilities at discrete frequencies. These instabilities exhibit eigenfunctions in good agreement with the measured PVS vortical structures. They are successfully compared in terms of temporal evolution and frequencies to the unsteady hydrodynamic fluctuations computed by numerical simulations. In addition, this study has shown that the hydrodynamic instabilities associated with the PVS are the driving force of the flow dynamics, since they are responsible for the emergence of pressure waves propagating at the same frequency.
Symplectic maps for the n-body problem - Stability analysis
NASA Technical Reports Server (NTRS)
Wisdom, Jack; Holman, Matthew
1992-01-01
The stability of new symplectic n-body maps is examined from the point of view of nonlinear dynamics. The resonances responsible for the principal artifacts are identified. These are resonances between the stepsize and the difference of mean motions between pairs of planets. For larger stepsizes resonant perturbations are evident in the variation of the energy of the system corresponding to these stepsize resonances. It is shown that the principal instability of the method can be predicted and corresponds to the overlap of the stepsize resonances. It is noted that the analysis suggests that other artifacts will occur. For example, the overlap of a stepsize resonance with a resonance of the actual system may also give a region of chaotic behavior that is an artifact. It is pointed out that the fact that the principal artifacts corresponds to a particular set of stepsize resonances suggests that it may be possible to perturbatively remove the effect when the stepsize resonances are nonoverlapping.
Stability analysis of runaway-driven waves in a tokamak
NASA Astrophysics Data System (ADS)
Aleynikov, Pavel; Breizman, Boris
2015-04-01
Runaway electrons (REs) generated during disruption events in tokamaks have to be mitigated to minimize the detrimental impact from their massive losses to the wall, especially in ITER. RE-driven micro-instabilities, such as whistlers and magnetized plasma waves, can cause enhanced RE scattering and thereby alleviate the mitigation problem. This work presents a newly developed ray-tracing code COIN which enables stability analysis of runaway-driven waves in a tokamak. The code uses a standard ray-tracing procedure to calculate a wave-packet trajectory in a realistic plasma equilibrium and integrates the runaway kinetic drive and collisional damping of the wave. This approach captures convective aspects of wave amplification, such as the evolution of the wave vector due to plasma non-uniformity and internal reflection of the wave from the plasma boundary. An illustrative ray-tracing calculation of the instability threshold is presented for ITER-like parameters.
Lv, Baoyi; Xing, Meiyan; Zhao, Chunhui; Yang, Jian; Xiang, Liang
2014-12-01
In this study, fluorescence excitation-emission matrix (EEM) combined with parallel factor analysis (PARAFAC) was employed to trace the behavior of water extractable organic matter and assess the stabilization process during vermicomposting of sewage sludge and cattle dung. Experiments using different mixing ratios of sewage sludge and cattle dung were conducted using Eisenia fetida. The results showed that vermicomposting reduced the DOC, DOC/DON ratio and ammonia, while increased the nitrate content. A three-component model containing two humic-like materials (components 1 and 2) and a protein-like material (component 3) was successfully developed using PARAFAC analysis. Moreover, the initial waste composition had a significant effect on the distribution of each component and the addition of cattle dung improved the stability of sewage sludge in vermicomposting. The PARAFAC results also indicated that protein-like materials were degraded and humic acid-like compounds were evolved during vermicomposting. Pearson correlation analysis showed that components 2 and 3 are more suitable to assess vermicompost maturity than component 1. In all, EEM-PARAFAC can be used to track organic transformation and assess biological stability during the vermicomposting process. PMID:25068534
Modal Voltage Stability Analysis of Multi-infeed HVDC System Considering its Control Systems
NASA Astrophysics Data System (ADS)
Wu, Guohong; Minakawa, Tamotsu; Hayashi, Toshiyuki
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.
A multiloop generalization of the circle criterion for stability margin analysis
NASA Technical Reports Server (NTRS)
Safonov, M. G.; Athans, M.
1979-01-01
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.
ASTROP2 Users Manual: A Program for Aeroelastic Stability Analysis of Propfans
NASA Technical Reports Server (NTRS)
Reddy, T. S. R.; Lucero, John M.
1996-01-01
This manual describes the input data required for using the second version of the ASTROP2 (Aeroelastic STability and Response Of Propulsion systems - 2 dimensional analysis) computer code. In ASTROP2, version 2.0, the program is divided into two modules: 2DSTRIP, which calculates the structural dynamic information; and 2DASTROP, which calculates the unsteady aerodynamic force coefficients from which the aeroelastic stability can be determined. In the original version of ASTROP2, these two aspects were performed in a single program. The improvements to version 2.0 include an option to account for counter rotation, improved numerical integration, accommodation for non-uniform inflow distribution, and an iterative scheme to flutter frequency convergence. ASTROP2 can be used for flutter analysis of multi-bladed structures such as those found in compressors, turbines, counter rotating propellers or propfans. The analysis combines a two-dimensional, unsteady cascade aerodynamics model and a three dimensional, normal mode structural model using strip theory. The flutter analysis is formulated in the frequency domain resulting in an eigenvalue determinant. The flutter frequency and damping can be inferred from the eigenvalues.
On the stability analysis of delayed neural networks systems
Chunhua Feng; Réjean Plamondon
2001-01-01
In this paper, the problems of stability of delayed neural networks are investigated, including the stability of discrete and distributed delayed neural networks. Under the generalization of dropping the Lipschitzian hypotheses for output functions, some stability criteria are obtained by using the Liapunov functional method. We do not assume the symmetry of the connection matrix and we establish that the
Stability Analysis for Variable Frequency Operation of Synchronous Machines
THOMAS A. LIPO; PAUL C. KRAUSE
1968-01-01
A stability study of a synchronous 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, in some cases, machine instability can occur at low operating speeds. Regions of machine stability are established from the results of a digital computer
Snoring: Linear Stability Analysis and In-Vitroexperiments
NASA Astrophysics Data System (ADS)
Aurégan, Y.; Depollier, C.
1995-11-01
A theoretical and experimental study is presented of the aeroelastic instability of the human soft palate, which can explain the occurrence of snoring. The soft palate is modelled by a beam clamped at its leading edge and free at its trailing edge. The continuous and discrete cases are investigated. Only the two first modes of vibration of the soft palate are taken into account. The flow is incompressible, inviscid and one dimensional. Structural damping and flow nonstationarities can be considered. Theory shows that the soft palate loses its stability by flutter and that this instability is mainly controlled by a single dimensionless parameter which can be easily interpreted from a medical point of view. An experimental apparatus which produces sounds very close to human snoring is described. Agreement between theory and experiments is good.
TRACE/PARCS analysis of the OECD/NEA Oskarshamn-2 BWR stability benchmark
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
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)
Paris-Sud XI, UniversitĂ© de
Performances of some reduced bases for the stability analysis of a disc/pads system in sliding of a dynamical system with frictional contact. In the case of brake systems, it is the most frequently employed method to study the propensity of the brake to generate squeal noise. When finite elements models
NASA Astrophysics Data System (ADS)
Zhang, Wei-Ya; Li, Yong-Li; Chang, Xiao-Yong; Wang, Nan
2013-09-01
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.
NASA Astrophysics Data System (ADS)
Escobar, D.; Ahedo, E.
2014-04-01
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.
Reactor dynamics and stability analysis for two gaseous core reactor space power systems
NASA Astrophysics Data System (ADS)
Dugan, Edward T.; Kahook, Samer D.
1992-01-01
Reactor dynamics and system stability studies are performed for two conceptual gaseous core reactor space nuclear power systems. The analysis is conducted using non-linear models which include circulating fuel, point reactor kinetics equations and appropriate thermodynamic, heat transfer and one-dimensional isentropic flow equations. The studies reveal the existence of some unique and very effective inherent reactivity feedback effects such as the vapor fuel density power coefficient that are capable of stabilizing these systems safely and quickly, within a few seconds, even when large positive reactivity insertions are imposed. However, due to the strength of these feedbacks, it is found that external reactivity insertions alone are inadequate for bringing about significant power level changes during normal operations. Additional methods of reactivity control such as changes in the gaseous fuel mass flow rate, or gaseous fuel core inlet pressure are needed to achieve the desired power level control.
Nonlinear flight dynamics and stability of hovering model insects
Liang, Bin; Sun, Mao
2013-01-01
Current analyses on insect dynamic flight stability are based on linear theory and limited to small disturbance motions. However, insects' aerial environment is filled with swirling eddies and wind gusts, and large disturbances are common. Here, we numerically solve the equations of motion coupled with the Navier–Stokes equations to simulate the large disturbance motions and analyse the nonlinear flight dynamics of hovering model insects. We consider two representative model insects, a model hawkmoth (large size, low wingbeat frequency) and a model dronefly (small size, high wingbeat frequency). For small and large initial disturbances, the disturbance motion grows with time, and the insects tumble and never return to the equilibrium state; the hovering flight is inherently (passively) unstable. The instability is caused by a pitch moment produced by forward/backward motion and/or a roll moment produced by side motion of the insect. PMID:23697714
Stability analysis of multiple-robot control systems
NASA Technical Reports Server (NTRS)
Wen, John T.; Kreutz, Kenneth
1989-01-01
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.
Stability Analysis of Large-Scale Incompressible Flow Calculations on Massively Parallel Computers
LEHOUCQ,RICHARD B.; ROMERO,LOUIS; SALINGER,ANDREW G.
1999-10-25
A set of linear and nonlinear stability analysis tools have been developed to analyze steady state incompressible flows in 3D geometries. The algorithms have been implemented to be scalable to hundreds of parallel processors. The linear stability of steady state flows are determined by calculating the rightmost eigenvalues of the associated generalize eigenvalue problem. Nonlinear stability is studied by bifurcation analysis techniques. The boundaries between desirable and undesirable operating conditions are determined for buoyant flow in the rotating disk CVD reactor.
Vacuum Stability and Triviality Analyses of the Renormalizable Coloron Model
R. Sekhar Chivukula; Arsham Farzinnia; Elizabeth H. Simmons
2015-04-12
The renormalizable coloron model is built around a minimally extended color gauge group, which is spontaneously broken to QCD. The formalism introduces massive color-octet vector bosons (colorons), as well as several new scalars and fermions associated with the symmetry breaking sector. In this paper, we examine vacuum stability and triviality conditions within the context of the renormalizable coloron model up to a cutoff energy scale of 100~TeV, by computing the beta-functions of all relevant couplings and determining their running behavior as a function of the renormalization scale. We constrain the parameter space of the theory for four separate scenarios based on differing fermionic content, and demonstrate that the vectorial scenarios are less constrained by vacuum stability and triviality bounds than the chiral scenarios. Our results are summarized in exclusion plots for the separate scenarios, with previous bounds on the model overlaid for comparison. We find that a 100 TeV hadron collider could explore the entire allowed parameter space of the chiral models very effectively.
William D. Rosehart; Claudio A. Cańizares; Victor H. Quintana
2003-01-01
In this paper, detailed generator, exponential load, and static volt-ampere-reactive (VAr) compensator models are incorporated into traditional and voltage-stability-constrained optimal power-flow problems to study the effect that the different models have on costs and system-loadability. The proposed models are compared to typical models by means of a detailed analysis of the results obtained for two IEEE test systems; interior point
NASA Technical Reports Server (NTRS)
Tai, H.; Wilson, J. W.; Maiden, D. L.
2003-01-01
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.
Buffered Aloha with K-Exponential Backoff -- Part I: Stability and Throughput Analysis
Lee, Tony T
2009-01-01
This two-part paper series studies the performance of buffered Aloha networks with K-Exponential Backoff collision resolution algorithms. Part I focuses on stability and throughput analysis and Part II presents the delay analysis. In Part I, the buffered Aloha network is modeled as a multi-queue single-server system. We adopt a widely used approach in packet switching systems to decompose the multi-queue system into independent first-in-first-out (FIFO) queues, which are hinged together by the probability of success of head-of-line (HOL) packets. A unified method is devised to tackle the stability and throughput problems of K-Exponential Backoff with any cutoff phase K. We demonstrate that a network with K-Exponential Backoff can be stabilized if the retransmission factor q is properly selected. The stable region of q is characterized and illustrated via examples of Geometric Retransmission (K=1) and Exponential Backoff (K=infinity). With an increasing number of nodes n, we show that the stable region of Geom...
Stability analysis of two-layer immiscible viscous fluids in an inclined closed tube
Lebovitz, Norman
Stability analysis of two-layer immiscible viscous fluids in an inclined closed tube Zhan Wang densities. A linear analysis of normal mode instability of the interface in an inclined closed tube discussed the linear stability of two-layer Couette and plane Poiseuille flows using a long-wave approach
Transient stability limit conditions analysis using a corrected transient energy function approach
Da-Zhong Fang; T. S. Chung; Yao Zhang; Wennan Song
2000-01-01
This paper addresses the issue in developing tools for transient stability limit conditions analysis in on-line power system operation. Concepts, including corrected potential energy and corrected potential energy boundary surface, are proposed for improving use of hybrid method in transient stability limit conditions analysis. It is shown that the value of corrected transient energy function (CTEF), which is the sum
LONG-TERM STABILITY OF FOOD PATTERNS IDENTIFIED BY USE OF FACTOR ANALYSIS AMONG SWEDISH WOMEN
Technology Transfer Automated Retrieval System (TEKTRAN)
Limited data exist on the reproducibility of food patterns measured using factor analysis, as well as the stability of patterns over time. Our primary objective was to explore the long-term stability of food patterns derived using confirmatory factor analysis among 33,840 women participating in the...
Stability analysis of discrete-time Lur'e systems Carlos A. C. Gonzaga, a
Paris-Sud XI, Université de
Stability analysis of discrete-time Lur'e systems Carlos A. C. Gonzaga, a Marc Jungers, a Jamal functions is proposed for discrete-time linear systems interconnected with a cone bounded nonlinearity, the novel function is considered in the local stability analysis problem of discrete-time Lur'e systems
GMAW process stability evaluation through acoustic emission by time and frequency domain analysis
E. Huanca Cayo; S. C. Absi Alfaro
2009-01-01
Purpose: In the present work was made the comparative analysis in time domain and frequency domain to the acoustical pressure generate by the electric arc to determinate which of the two analysis methods is better to evaluates the stability in GMAW process. Design\\/methodology\\/approach: Welds had been made with the parameters adjusted to get the highest stability. In these conditions, were
Delay-dependent stability analysis of linear systems with time-varying delay
Paris-Sud XI, Université de
Delay-dependent stability analysis of linear systems with time-varying delay Yassine Ariba and Fr´ed´eric Gouaisbaut December 2007 Abstract Stability analysis of linear systems with time-varying delay is inves of linear time delay systems have attracted a lot of attention [5], [13], [14], [17], [9] and references
General stability analysis of synchronized dynamics in coupled systems Yonghong Chen,1,3
Rangarajan, Govindan
General stability analysis of synchronized dynamics in coupled systems Yonghong Chen,1,3 Govindan that enables the analysis of general coupling topologies. This function defines a region of stabil- ity, periodic orbit, or chaotic attractor in arbitrarily coupled dynamical systems maps or ordinary differential
Synchronized clusters in coupled map networks. II. Stability analysis R. E. Amritkar,* Sarika Jalan,
Synchronized clusters in coupled map networks. II. Stability analysis R. E. Amritkar,* Sarika Jalan coupled networks and complete bipartite networks, using both linear stability analysis and Lyapunov study self-organized and driven synchronization in some simple coupled map networks, namely globally
Modal analysis for Liapunov stability of rotating elastic bodies. Ph.D. Thesis. Final Report
NASA Technical Reports Server (NTRS)
Colin, A. D.
1973-01-01
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.
Extensions to the time lag models for practical application to rocket engine stability design
NASA Astrophysics Data System (ADS)
Casiano, Matthew J.
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.
Analysis of cavern stability at the West Hackberry SPR site.
Ehgartner, Brian L.; Sobolik, Steven Ronald
2009-05-01
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.
Modelling and control of a balloon borne stabilized platform
NASA Astrophysics Data System (ADS)
Chingcuanco, Alfredo Ong; Meinhold, Peter R.; Lubin, Philip M.; Tomizuka, Masayoshi
1989-12-01
A balloon-borne, stabilized platform has been developed for a remotely operated altitude-azimuth pointing of a millimeter wave telescope system. A modeling and controller design of the azimuth pointing system of the platform is presented. Simulation results show that the system is capable of continuous operation with pointing rms to better than 0.01 deg. Ground testing results show continuous operation with pointing rms to better than 0.02 deg, while results of the first flight from the National Scientific Balloon Facility (NSBF) at Palestine, Texas show pointing rms better than 0.02 deg.
Wei, Qingkai
2012-01-01
Two recent test failures of Hypersonic Technology Vehicle 2 impose a strike to the increasingly growing enthusiasm, not only on the United States side. It is important to find out the exact failure reason, otherwise a solution is impossible. In this Note, we propose a potential failure reason from the perspective of lateral stability analysis. We argue that the time variant pressure fluctuations, which are normally omitted in classical aircraft dynamics analysis, could not be neglected in dynamic analysis of hypersonic vehicles. To demonstrate the idea, a hypersonic model is imagined in this work and its aerodynamic parameters are estimated using fundamental fluid principles. Pressure fluctuations are thereafter estimated by an empirical formula. A lateral dynamic equation is set up, taking those time variant fluctuations into account. The resulted equation is a Mathieu differential equation. Numerical solutions of this equation show that the inclusion of fluctuation terms generates more complicated dynamics ...
Stability of the scale parameter: Hu-Sawicki model
Jaakko Vainio; Iiro Vilja
2013-03-19
The evolution of the scale parameter in the Hu-Sawicki model is examined. We search the parameter area for instabilities. It turns out the parameter area of physically meaningful evolution is non-existent. For greater stability a stabilising term such as R^2 should be added. With the addition, the area mainly coincides with phantom models. We also find that the evolution of the scale parameter can be examined through a linear expansion and not only in the Hu-Sawicki case. The oscillatory behaviour found in the evolution raises questions of the physicality of the model. The behaviour can also cause current observations of the Hubble parameter to be misleading. This paper has been withdrawn by the authords due to a critical error in equation (10)
Stability and Teller's theorem: Fullerenes in the March model
NASA Astrophysics Data System (ADS)
Clougherty, Dennis P.; Zhu, Xiang
1997-07-01
We study C60 with the use of the March model [N. H. March, Proc. Camb. Philos. Soc. 48, 665 (1952)]. A spherical shell model is invoked to treat the nuclear potential, where the nuclear and core charges are smeared out into a shell of constant surface charge density. The valence electron distribution and the electrostatic potential are efficiently computed by integration of the Thomas-Fermi equation, subject to the shell boundary conditions. Total energy is numerically calculated over a range of shell radii, and the mechanical stability of the model is explored with attention to the constraints of Teller's theorem [E. Teller, Rev. Mod. Phys. 34, 627 (1962)]. The calculated equilibrium radius of the shell is in fair agreement with experiment.
Stability and persistence in ODE models for populations with many stages.
Fan, Guihong; Lou, Yijun; Thieme, Horst R; Wu, Jianhong
2015-08-01
A model of ordinary differential equations is formulated for populations which are structured by many stages. The model is motivated by ticks which are vectors of infectious diseases, but is general enough to apply to many other species. Our analysis identifies a basic reproduction number that acts as a threshold between population extinction and persistence. We establish conditions for the existence and uniqueness of nonzero equilibria and show that their local stability cannot be expected in general. Boundedness of solutions remains an open problem though we give some sufficient conditions. PMID:25974341
General Stability Analysis of Synchronized Dynamics in Coupled Systems
Yonghong Chen; Govindan Rangarajan; Mingzhou Ding
2002-12-27
We consider the stability of synchronized states (including equilibrium point, periodic orbit or chaotic attractor) in arbitrarily coupled dynamical systems (maps or ordinary differential equations). We develop a general approach, based on the master stability function and Gershgorin disc theory, to yield constraints on the coupling strengths to ensure the stability of synchronized dynamics. Systems with specific coupling schemes are used as examples to illustrate our general method.
Modeling genomic data with type attributes, balancing stability and maintainability
Busch, Norbert; Wedemann, Gero
2009-01-01
Background Molecular biology (MB) is a dynamic research domain that benefits greatly from the use of modern software technology in preparing experiments, analyzing acquired data, and even performing "in-silico" analyses. As ever new findings change the face of this domain, software for MB has to be sufficiently flexible to accommodate these changes. At the same time, however, the efficient development of high-quality and interoperable software requires a stable model of concepts for the subject domain and their relations. The result of these two contradictory requirements is increased complexity in the development of MB software. A common means to reduce complexity is to consider only a small part of the domain, instead of the domain as a whole. As a result, small, specialized programs develop their own domain understanding. They often use one of the numerous data formats or implement proprietary data models. This makes it difficult to incorporate the results of different programs, which is needed by many users in order to work with the software efficiently. The data conversions required to achieve interoperability involve more than just type conversion. Usually they also require complex data mappings and lead to a loss of information. Results To address these problems, we have developed a flexible computer model for the MB domain that supports both changeability and interoperability. This model describes concepts of MB in a formal manner and provides a comprehensive view on it. In this model, we adapted the design pattern "Dynamic Object Model" by using meta data and association classes. A small, highly abstract class model, named "operational model," defines the scope of the software system. An object model, named "knowledge model," describes concrete concepts of the MB domain. The structure of the knowledge model is described by a meta model. We proved our model to be stable, flexible, and useful by implementing a prototype of an MB software framework based on the proposed model. Conclusion Stability and flexibility of the domain model is achieved by its separation into two model parts, the operational model and the knowledge model. These parts are connected by the meta model of the knowledge model to the whole domain model. This approach makes it possible to comply with the requirements of interoperability and flexibility in MB. PMID:19327130
Long term voltage stability analysis for small disturbances
Men, Kun
2009-05-15
LIST OF FIGURES...............................................................................................................ix LIST OF TABLES... ................................................................................................................... 113 VITA................................................................................................................................... 117 ix LIST OF FIGURES Page Figure II-1 Dynamic vs. static stability margin...
Bilgili, Ecevit; Afolabi, Afolawemi
2012-12-15
Although polymers and surfactants are commonly used as stabilizers to impart physical stability to the suspensions produced by wet stirred media milling of poorly water-soluble drugs, scant information is available in pharmaceutical literature regarding their impact on the breakage kinetics. We present a combined microhydrodynamics-polymer adsorption analysis to elucidate the roles of stabilizers with a focus on the kinetics. Griseofulvin (GF), a model poorly water-soluble drug, was milled at various concentrations of hydroxypropyl cellulose (HPC) in the presence-absence of sodium dodecyl sulfate (SDS). Particle sizing, scanning electron microscopy, thermal analysis, and rheometry were used to determine the breakage kinetics, adsorption isotherm, and apparent viscosity, which were then used to analyze the aggregation state of the milled suspensions and the microhydrodynamics. In the absence of SDS, an increase in HPC concentration slowed the particle aggregation leading to faster apparent breakage. On the other hand, due to a synergistic stabilizing action of HPC with SDS, lower HPC concentration was needed to stabilize the suspensions, and an optimum HPC concentration for the fastest apparent breakage was identified. The microhydrodynamic analysis quantified, for the first time, the viscous dampening effect of polymers, while only the combined analysis could explain the observed optimum. PMID:23018114
Cardiovascular & Respiratory Modeling, Analysis & Control
Batzel, Jerry
. . . . . . . . . . . . . . . . 36 1.7.3 Sensitivity analysis . . . . . . . . . . . . . . . . . . . 38 2 Respiratory Modeling 45 2Cardiovascular & Respiratory Systems: Modeling, Analysis & Control J. J. Batzel, F. Kappel, D.1 Respiratory Control Physiology . . . . . . . . . . . . . . . . . . 46 2.1.1 General features of respiration
GIS-based modelling of deep-seated slope stability in complex geology
NASA Astrophysics Data System (ADS)
Mergili, Martin; Marchesini, Ivan; Schneider-Muntau, Barbara; Cardinali, Mauro; Fiorucci, Federica; Valigi, Daniela; Santangelo, Michele; Bucci, Francesco; Guzzetti, Fausto
2014-05-01
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.
Joint regression analysis and AMMI model applied to oat improvement
NASA Astrophysics Data System (ADS)
Oliveira, A.; Oliveira, T. A.; Mejza, S.
2012-09-01
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.
Strength analysis of yttria-stabilized tetragonal zirconia polycrystals
Noguchi, K.; Matsuda, Y.; Oishi, M. (Toray Research Center, Inc., Otsu, Shiga 520 (JP)); Masaki, T.; Nakayama, S.; Mizushina, M. (Toray Industries, Inc., Otsu, Shiga 520 (JP))
1990-09-01
This paper reports the tensile strength of Y{sub 2}O{sub 3}-stabilized ZrO{sub 2} polycrystals (Y-TZP) measured by a newly developed tensile testing method with a rectangular bar. The tensile strength of Y-TZP was lower than that of the three-point bend strength, and the shape of the tensile strength distribution was quite different from that of the three-point bend strength distribution. It was difficult to predict the distribution curve of the tensile strength using the data of the three-point bend strength by one-modal Weibull distribution. The distribution of the tensile strength was analyzed by two- or three-modal Weibull distribution coupled with an analysis of fracture origins. The distribution curve of the three-point bend strength which was estimated by multimodal Weibull distribution agreed favorably with that of the measured three-point bend strength values. A two-modal Weibull distribution function was formulated approximately from the distributions of the tensile and three-point bend strengths, and the estimated two-modal Weibull distribution function for the four-point bend strength agreed well with the measured four-point bend strength.
BLSTA: A boundary layer code for stability analysis
NASA Technical Reports Server (NTRS)
Wie, Yong-Sun
1992-01-01
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.
Implications of stability analysis for heat transfer at Yucca Mountain
Ross, B.; Yiqiang Zhang; Ning Lu [Disposal Safety, Inc., Washington, DC (United States)
1993-03-01
An analytical solution has been obtained to the stability problem for an infinite horizontal layer of gas with Its humidity constrained to 100%. Latent heat transfer makes convective heat transfer much more Important for this moist gas than for a dry gas. The critical Rayleigh number for the onset of convective flow in the moist gas, with a lower no-flow boundary at 97{degrees}C and an upper no-flow boundary at 27{degrees}C, is 0.18, much less than the value of 4m{sup 2} for a dry gas. Although the heat source at Yucca Mountain will be finite in extent, the solution for an infinite horizontal layer still gives a useful criterion for the qualitative importance of convective heat transfer. The critical Rayleigh number of 0.18 corresponds to a permeability of 4 {times} 10{sup {minus}12} m{sup 2} if other parameters ate given values measured at Yucca Mountain. This value falls roughly in the middle of the range of measured permeabilities. The analysis also gives a time constant for the onset of convection, which at twice the critical Rayleigh number is 1000 yr. Thus convection will probably make an important contribution, to host transfer at Yucca Mountain if the rock permeability falls in the upper portion of the range of measurements to date, but only at times after a few hundred or thousand years.
Slope Stability Analysis Using Limit Equilibrium Method in Nonlinear Criterion
Lin, Hang; Zhong, Wenwen; Xiong, Wei; Tang, Wenyu
2014-01-01
In slope stability analysis, the limit equilibrium method is usually used to calculate the safety factor of slope based on Mohr-Coulomb criterion. However, Mohr-Coulomb criterion is restricted to the description of rock mass. To overcome its shortcomings, this paper combined Hoek-Brown criterion and limit equilibrium method and proposed an equation for calculating the safety factor of slope with limit equilibrium method in Hoek-Brown criterion through equivalent cohesive strength and the friction angle. Moreover, this paper investigates the impact of Hoek-Brown parameters on the safety factor of slope, which reveals that there is linear relation between equivalent cohesive strength and weakening factor D. However, there are nonlinear relations between equivalent cohesive strength and Geological Strength Index (GSI), the uniaxial compressive strength of intact rock ?ci, and the parameter of intact rock mi. There is nonlinear relation between the friction angle and all Hoek-Brown parameters. With the increase of D, the safety factor of slope F decreases linearly; with the increase of GSI, F increases nonlinearly; when ?ci is relatively small, the relation between F and ?ci is nonlinear, but when ?ci is relatively large, the relation is linear; with the increase of mi, F decreases first and then increases. PMID:25147838
Visual Optimality and Stability Analysis of 3DCT Scan Positions
Artem Amirkhanov; Christoph Heinzl; Michael Reiter; Eduard Gröller
2010-01-01
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
Parallel stability analysis of membrane lamellar structures and foam films
N. G. Ivanova; R. Tsekov
2015-03-20
In the frames of the DLVO theory the root mean square amplitude of capillary waves in a thin liquid film is calculated and its dependence on some important physical parameters is unveiled. Two important models are considered: films with classical interfaces and films between lipid bilayers. The performed numerical analysis demonstrates essential difference in their behavior due to the different elastic properties of the film surfaces. It is shown that the film lifetime is significantly long at some 'magic' film radii.
P. Buyle; E. Van Hese; S. De Rijcke; H. Dejonghe
2006-12-12
We present a method to investigate the radial stability of a spherical anisotropic system that hosts a central supermassive black hole (SBH). Such systems have never been tested before for stability, although high anisotropies have been considered in the dynamical models that were used to estimate the masses of the central putative supermassive black holes. A family of analytical anisotropic spherical Hernquist models with and without a black hole were investigated by means of N-body simulations. A clear trend emerges that the supermassive black hole has a significant effect on the overall stability of the system, i.e. an SBH with a mass of a few percent of the total mass of the galaxy can prevent or reduce the bar instabilities in anisotropic systems. Its mass not only determines the strength of the instability reduction, but also the time in which this occurs. These effects are most significant for models with strong radial anisotropies. Furthermore, our analysis shows that unstable systems with similar SBH but with different anisotropy radii evolve differently: highly radial systems become oblate, while more isotropic models tend to form into prolate structures. In addition to this study, we also present a Monte-Carlo algorithm to generate particles in spherical anisotropic systems.
Bifurcation and Stability Analysis of Aircraft Turning Manoeuvres
James Rankin; Mark Lowenberg
During ground manoeuvres a loss of lateral stability due to the saturation of the main landing gear tyres can cause the aircraft to enter a skid or a spin. The lateral stability is governed not only by aspects of the gear design, such as its geometry and tyre characteris- tics, but also by operational parameters, for example, the weather and
Rank Stability Analysis of Surface and Profile Soil Moisture
Technology Transfer Automated Retrieval System (TEKTRAN)
Although several studies have examined the spatial and rank stability of soil moisture at the surface layer (0-5cm) with the purpose of estimating large scale mean soil moisture, the integration of the rank stability of profile (0-60cm) soil moisture has not been fully considered. This research comb...
STABILITY ANALYSIS OF LINEAR CONTROL SYSTEMS WITH UNCERTAIN PARAMETERS
Latchman, Haniph A.
large deviation theory to study the relationship between "lower moment" stability and almost sure in partial fulfillment of the requirements for the Degree of Doctor of Philosophy Thesis Advisor: Dr. Kenneth investigate the properties of various types of moment stability for stochastic jump linear systems, and use
Stability Analysis of Nonstandard Nonlinear Singularly Perturbed Discrete Systems
Kyun-Sang Park; Jong-Tae Lim
2011-01-01
In this brief, we consider the stability problem of nonstandard nonlinear singularly perturbed discrete systems (NN-SPDSs). Specifically, an NN-SPDS is decomposed into two standard nonlinear SPDSs. Based on the lower order subsystems of the standard nonlinear SPDSs, we analyze the stability of the NN-SPDS.
Stability Analysis of Nonlinear Multiparameter Singularly Perturbed Systems
Hassan K. Khalil
1987-01-01
Asymptotic stability of nonlinear multiparameter singularly perturbed systems is analyzed. Sufficient conditions for existence of a Lyapunov function and uniform asymptotic stability are derived. The new feature of these conditions over earlier results is that there is no restriction on the relative magnitudes of the small singular perturbation parameters. Moreover, the class of systems under consideration can be nonlinear in
Stability Analysis of a Reluctance-Synchronous Machine
THOMAS A. LIPO; PAUL C. KRAUSE
1967-01-01
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
GE simplified boiling water reactor stability analysis in time domain
Shanlai Lu
1997-01-01
General Electric Simplified Boiling Water Reactor (SBWR) was designed as a next generation light water reactor. It uses natural circulation to remove the heat from the reactor core. Because of this unique in-vessel circulation feature, SBWR is expected to exhibit different stability behaviors. The main emphasis of this thesis is to study the SBWR stability behavior in the time domain.
Masanobu UEHIRO; Yan F. RAO; Kenji FUKUDA
1996-01-01
An analytical model is proposed to study the two-phase flow instabilities of in-phase and out-of-phase modes in boiling water reactors. This model, developed for parallel boiling channels with the void-reactivity feedback loop, takes into consideration the interaction between channels with different void fraction variations. Linear stability analysis in the frequency domain is performed to reveal the mechanisms of the instability.
Stability analysis and trend study of a balloon tethered in a wind, with experimental comparisons
NASA Technical Reports Server (NTRS)
Redd, L. T.; Bland, S. R.; Bennett, R. M.
1973-01-01
A stability analysis and trend study for a balloon tethered in a steady wind are presented. The linearized, stability-derivative type analysis includes balloon aerodynamics, buoyancy, mass (including apparent mass), and static forces resulting from the tether cable. The analysis has been applied to a balloon 7.64 m in length, and the results are compared with those from tow tests of this balloon. This comparison shows that the analysis gives reasonable predictions for the damping, frequencies, modes of motion, and stability boundaries exhibited by the balloon. A trend study for the 7.64-m balloon was made to illustrate how the stability boundaries are affected by changes in individual stability parameters. The trends indicated in this study may also be applicable to many other tethered-balloon systems.
Best-estimate plus uncertainty thermal-hydraulic stability analysis of BWRs using TRACG code
Vedovi, J.; Yang, J.; Klebanov, L.; Vreeland, D. G.; Zino, J. F. [GE Hitachi Nuclear Energy Americas, 3901 Castle Hayne, Wilmington, NC 28401 (United States)
2012-07-01
Over the last decade, Boiling Water Reactor (BWR) power up-rates have increased plant rated power output significantly. Subsequent projects have expanded flow domains (e.g. MELLLA+) for operation at these higher power levels. This has resulted in an increase in the power to flow ratio in regions susceptible to reactor thermal-hydraulic instabilities. Since BWRs are susceptible to coupled thermal-hydraulic/nuclear oscillations when operating at these conditions, such oscillations must be prevented or reliably detected and suppressed. The Detect and Suppress Solution - Confirmation Density (DSS-CD) is the most sophisticated GEH BWR instability protection system ever employed. DSS-CD implements algorithms that monitor closely-spaced groups of Local Power Range Monitor (LPRM) detectors to detect periodic behavior typical of reactor instability events. This system is able to detect small, localized power variations in the core, distinguish between true instabilities and plant noise, and trip/scram the reactor while maintaining adequate safety margins. The combination of hardware, software, and system setpoints provides protection against violation of the Safety Limit Minimum Critical Power Ratio (SLMCPR) for anticipated oscillations. To support DSS-CD implementation, the TRACG system code is used to simulate events to confirm the capability of the DSS-CD solution for early oscillation detection and suppression. TRACG is a GEH proprietary version of the Transient Reactor Analysis Code (TRAC). TRACG includes a multi-dimensional, two-fluid model for the reactor thermal-hydraulics and a three-dimensional reactor kinetics model. The models are qualified to simulate a large variety of tests and reactor configurations, including thermal-hydraulic stability events. These features allow for detailed, best-estimate simulation of a wide range of BWR phenomena. A set of integrated TRACG event simulations for reasonably limiting anticipated events can be used to calculate the effect on the Minimum Critical Power Ratio (MCPR) performance. The purpose of the DSS-CD TRACG analysis is to confirm the inherent MCPR margin afforded by the solution design. This paper presents the Best Estimate Plus Uncertainty (BEPU) DSS-CD TRACG methodology and its application to BWR Thermal-Hydraulic (T-H) stability analyses. The statistical Code Scaling, Applicability and Uncertainty (CSAU) methodology (defined in NUREG/CR-5249) is used to calculate the MCPR uncertainty. The TRACG simulation includes a full core individual bundle model in which each fuel bundle is modeled as an individual T-H channel. The complete CSAU analysis of full core individual bundle model is an innovative solution represents the state-of-the-art stability analysis of BWRs and is the first ever full statistical analysis for stability safety analyses. The adoption of BEPU methodologies for stability analyses advances the understanding of the associated physical phenomena and maintains the safety of reactor plant operation in expanded operation domain with up-rated power. (authors)
Lee, S.
2011-05-05
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.
STABILITY AND PRICE SCALING LIMIT OF A HAWKES PROCESS-BASED ORDER BOOK MODEL
Paris-Sud XI, Université de
STABILITY AND PRICE SCALING LIMIT OF A HAWKES PROCESS-BASED ORDER BOOK MODEL AYMEN JEDIDI to order book modelling 15 4.1. Model setup 15 4.2. Stability of the order book 17 4.3. Large scale limit microstructure, and particularly order book modelling, the relevance of these processes comes at least from two
NASA Technical Reports Server (NTRS)
Barwey, D.; Gaonkar, Gopal H.
1994-01-01
The effects of blade and root-flexure elasticity and dynamic stall on the stability of hingeless rotor blades are investigated. The dynamic stall description is based on the ONERA models of lift, drag, and pitching moment. The structural analysis is based on three blade models that range from a rigid flap-lag model to two elastic flap-lag-torsion models, which differ in representing root-flexure elasticity. The predictions are correlated with the measured lag damping of an experimental isolated three-blade rotor; the correlation covers rotor operations from near-zero-thrust conditions in hover to highly stalled, high-thrust conditions in foward flight. That correlation shows sensitivity of lag-damping predictions to structural refinements in blade and root-flexure modeling. Moreover, this sensitivity increases with increasing control pitch angle and advance ratio. For high-advance-ratio and high-thrust conditions, inclusion of dynamic stall generally improves the correlation.
Probability of vacuum stability in type IIB multi-Kähler moduli models
NASA Astrophysics Data System (ADS)
Sumitomo, Yoske; Rummel, Markus
2013-12-01
We study the probability that all eigenvalues of the moduli mass matrix at extremal points are positive in concrete multi-Kähler moduli models of type IIB string theory compactifications in the large volume regime. Our analysis is motivated by the open question if vacua which are uplifted to de Sitter remain stable. We derive a simple analytical condition for the mass matrix to be positive definite, and estimate the corresponding probability in a supersymmetric moduli stabilization model along the lines of KKLT and a non-supersymmetric Large Volume Scenario type of model, given a reasonable range of compactification parameters. Under identical conditions, the probability for the supersymmetric model is moderately higher than that of the Large Volume Scenario type model.
Stabilizing a CFD model of an unstable system through model reduction
Gravdahl, Jan Tommy
Stabilizing a CFD model of an unstable system through model reduction S. Hovland and J. T. Gravdahl of interest from the control community. A nice review of ad- vances made in the intersection between control on a computer, the PDEs are usually discretized using a set of tools known as compu- tational uid dynamics (CFD
Stabilization precision control methods of photoelectric aim-stabilized system
NASA Astrophysics Data System (ADS)
Song, Xiaoru; Chen, Hua; Xue, Yonggang
2015-09-01
To solve the question that photoelectric aim-stabilized system can be controlled with high precision and stability, this paper researches a new photoelectric aim-stabilized control algorithm, analyzes the photoelectric aim-stabilized system architecture, sets up stability control system mathematical model, designs the stability of the photoelectric aim-stabilized LSSVM identification and control system, discusses uncertain factors and calculates the LSSVM parameters by the Chaos theory, gives the predictive controller model by the LSSVM and designs new photoelectric aim-stabilized system. Through the simulation calculation and experimental analysis, new photoelectric aim-stabilized control algorithm was verified; the results show the new photoelectric aim-stabilized control method can meet the demand of high precision control in photoelectric aim-stabilized system.
NASA Astrophysics Data System (ADS)
Faucci, Maria Teresa; Melani, Fabrizio; Mura, Paola
2002-06-01
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.
A multiloop generalization of the circle criterion for stability margin analysis
NASA Technical Reports Server (NTRS)
Safonov, M. G.; Athans, M.
1981-01-01
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.
The stability analysis of rolling motion of hypersonic vehicles and its validations
NASA Astrophysics Data System (ADS)
Ye, YouDa; Zhao, ZhongLiang; Tian, Hao; Zhang, XianFeng
2014-12-01
The stability of the rolling motion of near space hypersonic vehicles with rudder control is studied using method of qualitative analysis of nonlinear differential equations, and the stability criteria of the deflected rolling motions are improved. The outcomes can serve as the basis for further study regarding the influence of pitching and lateral motion on the stability of rolling motion. To validate the theoretical results, numerical simulations were done for the rolling motion of two hypersonic vehicles with typical configurations. Also, wind tunnel experiments for four aircraft models with typical configurations have been done. The results show that: 1) there exist two dynamic patterns of the rolling motion under statically stable condition. The first one is point attractor, for which the motion of aircraft returns to the original state. The second is periodic attractor, for which the aircraft rolls periodically. 2) Under statically unstable condition, there exist three dynamic patterns of rolling motion, namely, the point attractor, periodic attractor around deflected state of rolling motion, and double periodic attractors or chaotic attractors.
2013-01-01
Background Cellular differentiation and reprogramming are processes that are carefully orchestrated by the activation and repression of specific sets of genes. An increasing amount of experimental results show that despite the large number of genes participating in transcriptional programs of cellular phenotypes, only few key genes, which are coined here as reprogramming determinants, are required to be directly perturbed in order to induce cellular reprogramming. However, identification of reprogramming determinants still remains a combinatorial problem, and the state-of-art methods addressing this issue rests on exhaustive experimentation or prior knowledge to narrow down the list of candidates. Results Here we present a computational method, without any preliminary selection of candidate genes, to identify reduced subsets of genes, which when perturbed can induce transitions between cellular phenotypes. The method relies on the expression profiles of two stable cellular phenotypes along with a topological analysis stability elements in the gene regulatory network that are necessary to cause this multi-stability. Since stable cellular phenotypes can be considered as attractors of gene regulatory networks, cell fate and cellular reprogramming involves transition between these attractors, and therefore current method searches for combinations of genes that are able to destabilize a specific initial attractor and stabilize the final one in response to the appropriate perturbations. Conclusions The method presented here represents a useful framework to assist researchers in the field of cellular reprogramming to design experimental strategies with potential applications in the regenerative medicine and disease modelling. PMID:24350678
Stability analysis for acoustic wave propagation in tilted TI media by finite differences
NASA Astrophysics Data System (ADS)
Bakker, Peter M.; Duveneck, Eric
2011-05-01
Several papers in recent years have reported instabilities in P-wave modelling, based on an acoustic approximation, for inhomogeneous transversely isotropic media with tilted symmetry axis (TTI media). In particular, instabilities tend to occur if the axis of symmetry varies rapidly in combination with strong contrasts of medium parameters, which is typically the case at the foot of a steeply dipping salt flank. In a recent paper, we have proposed and demonstrated a P-wave modelling approach for TTI media, based on rotated stress and strain tensors, in which the wave equations reduce to a coupled set of two second-order partial differential equations for two scalar stress components: a normal component along the variable axis of symmetry and a lateral component of stress in the plane perpendicular to that axis. Spatially constant density is assumed in this approach. A numerical discretization scheme was proposed which uses discrete second-derivative operators for the non-mixed second-order derivatives in the wave equations, and combined first-derivative operators for the mixed second-order derivatives. This paper provides a complete and rigorous stability analysis, assuming a uniformly sampled grid. Although the spatial discretization operator for the TTI acoustic wave equation is not self-adjoint, this operator still defines a complete basis of eigenfunctions of the solution space, provided that the solution space is somewhat restricted at locations where the medium is elliptically anisotropic. First, a stability analysis is given for a discretization scheme, which is purely based on first-derivative operators. It is shown that the coefficients of the central difference operators should satisfy certain conditions. In view of numerical artefacts, such a discretization scheme is not attractive, and the non-mixed second-order derivatives of the wave equation are discretized directly by second-derivative operators. It is shown that this modification preserves stability, provided that the central difference operators of the second-order derivatives dominate over the twice applied operators of the first-order derivatives. In practice, it turns out that this is almost the case. Stability of the desired discretization scheme is enforced by slightly weighting down the mixed second-order derivatives in the wave equation. This has a minor, practically negligible, effect on the kinematics of wave propagation. Finally, it is shown that non-reflecting boundary conditions, enforced by applying a taper at the boundaries of the grid, do not harm the stability of the discretization scheme.
Advanced techniques for the analysis of crisis stability, deterrence, and latency
Canavan, G.H.
1997-12-01
Studies on crisis stability, deterrence, and latency are presented in chronological order, which also reflects their logical order of development, captures the main features of stability analysis; relates first strike, crisis, and arms control stability as seen from US and Russian perspective; and addresses questions such as whether uncertainty in damage preference or defense deployment can be destabilizing. It illustrates the problems with alternative metrics, latency and reconstitution, and deep unilateral and proportional force reductions.
NASA Technical Reports Server (NTRS)
Bartels, Robert E.
2011-01-01
Launch vehicles frequently experience a reduced stability margin through the transonic Mach number range. This reduced stability margin is caused by an undamping of the aerodynamics in one of the lower frequency flexible or rigid body modes. Analysis of the behavior of a flexible vehicle is routinely performed with quasi-steady aerodynamic lineloads derived from steady rigid computational fluid dynamics (CFD). However, a quasi-steady aeroelastic stability analysis can be unconservative at the critical Mach numbers where experiment or unsteady computational aeroelastic (CAE) analysis show a reduced or even negative aerodynamic damping. This paper will present a method of enhancing the quasi-steady aeroelastic stability analysis of a launch vehicle with unsteady aerodynamics. The enhanced formulation uses unsteady CFD to compute the response of selected lower frequency modes. The response is contained in a time history of the vehicle lineloads. A proper orthogonal decomposition of the unsteady aerodynamic lineload response is used to reduce the scale of data volume and system identification is used to derive the aerodynamic stiffness, damping and mass matrices. The results of the enhanced quasi-static aeroelastic stability analysis are compared with the damping and frequency computed from unsteady CAE analysis and from a quasi-steady analysis. The results show that incorporating unsteady aerodynamics in this way brings the enhanced quasi-steady aeroelastic stability analysis into close agreement with the unsteady CAE analysis.
ESF SOUTH PORTAL BOX-CUT/HIGHWALL STABILITY ANALYSIS (SCPB:N/A)
Saeed Bonabian
1996-03-28
The main purpose and objective of this analysis is to design a Box-Cut at the ESF South Portal to accommodate the Tunnel Boring Machine's (TBM) exit at the conclusion of the ESF Main Loop construction. The stability of the Highwall and the sidewalls at the Box-Cut are assessed using analytical methods by numerical modeling techniques. A ground reinforcement system for the South Ramp Box-Cut slopes will be recommended. This report summarizes the results of the analyses and provides the details of the recommended ground reinforcement system for the Box-Cut slopes at the South Portal. The reinforcement design details are then incorporated into design output documents for implementation in the field. Method of excavation for the Box-Cut is also discussed and a recommendation is provided in this analysis.
NASA Technical Reports Server (NTRS)
Bertolotti, F. P.; Herbert, TH.
1991-01-01
The application of linearized parabolic stability equations (PSE) to compressible flow is considered. The effect of mean-flow nonparallelism is found to be weak on 2D waves and strong on 3D waves. Results for a single choice of free-stream parameters that corresponds to the atmospheric conditions at 15,000 m above sea level are presented.
Stabilizing effects in spatial parasitoid–host and predator–prey models: a review
Cheryl J. Briggs; Martha F. Hoopes
2004-01-01
We review the literature on spatial host–parasitoid and predator–prey models. Dispersal on its own is not stabilizing and can destabilize a stable local equilibrium. We identify three mechanisms whereby limited dispersal of hosts and parasitoids combined with other features, such as spatial and temporal heterogeneity, can promote increased persistence and stability. The first mechanism, “statistical stabilization”, is simply the statistical
Impulsive exponential stabilization of discrete population growth models with time delays
Yu Zhang; Jitao Sun
2010-01-01
The purpose of this paper is to investigate the impulsive exponential stabilization for the positive equilibrium points of a class of discrete population growth models with time delays. By using Lyapunov functionals, some new exponential stability criteria are given. It is shown that impulses can indeed make unstable equilibrium points exponentially stable, and when the impulses are employed to stabilize
Stability analysis of a variable-speed wind turbine
Bir, G.S.; Wright, A.D.; Butterfield, C.P.
1996-10-01
This paper examines the elastomechanical stability of a four-bladed wind turbine over a specific rotor speed range. Stability modes, frequencies, and dampings are extracted using a specialized modal processor developed at NREL that post-processes the response data generated by the ADAMS simulation code. The processor can analyze a turbine with an arbitrary number of rotor blades and offers a novel capability of isolating stability modes that become locked at a single frequency. Results indicate that over a certain rotor speed range, the tower lateral mode and the rotor regressive in-plane mode coalesce, resulting in a self-excited instability. Additional results show the effect of tower and nacelle parameters on the stability boundaries.
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 ...
Some kanbancontrolled manufacturing systems: a first stability analysis
Seidman, Thomas I.
(410)-455-2438 e-mail: seidman@math.umbc.edu and Instituto de Matem´atica e Estatistica Universidade de we are led to test the efficacy of the kanban structure as a possible stabilizing control mechanism
APPLICATIONS ANALYSIS REPORT: CHEMFIX TECHNOLOGIES, INC., SOLIDIFICATION/STABILIZATION PROCESS
The Chemfix Solidification/Stabilization treatment process was evaluated under EPA's SITE program. he process reduced leaching levels of lead and copper. hysical testing results were acceptable. ppropriate applications and process limitations are discussed in this report....
Relative stability and local curvature analysis in carbon nanotori
NASA Astrophysics Data System (ADS)
Chuang, Chern; Guan, Jie; Witalka, David; Zhu, Zhen; Jin, Bih-Yaw; Tománek, David
2015-04-01
We introduce a concise formalism to characterize nanometer-sized tori based on carbon nanotubes and to determine their stability by combining ab initio density functional calculations with a continuum elasticity theory approach that requires only shape information. We find that the high strain energy in nanotori containing only hexagonal rings is significantly reduced in nanotori containing also other polygons. Our approach allows to determine local curvature and link it to local strain energy, which is correlated with local stability and chemical reactivity.
Nonlocal stability analysis of the MHD Kelvin-Helmholtz instability in a compressible plasma
A. Miura; P. L. Pritchett
1982-01-01
A general stability analysis is given of the Kevin-Helmholtz instability, for the case of sheared MHD flow of finite thickness in a compressible plasma which allows for the arbitrary orientation of the magnetic field, velocity flow, and wave vector in the plane perpendicular to the velocity gradient. The stability problem is reduced to the solution of a single second-order differential
Impact Analysis of Transient Stability Due to Cyber Attack on FACTS Devices
Kundur, Deepa
Impact Analysis of Transient Stability Due to Cyber Attack on FACTS Devices Bo Chen, Karen L attacks can make the system angle or voltage unstable under the proposed attack scenarios. Index Terms--cyber attack, cyber security, smart grids, SVC, STATCOM, FACTS, transient stability, voltage support device I
Frequency analysis of the stability of asteroids in the framework of the restricted, three Cedex 4 (France) (elena@obs-nice.fr) October 16, 2003 Abstract The stability of some asteroids an isoenergetic KAM theorem. More precisely, having fixed a level of energy related to the motion of the asteroid
A theoretical analysis of pitch stability during gliding in flying snakes
Ross, Shane
A theoretical analysis of pitch stability during gliding in flying snakes Farid Jafari1 , Shane D April 2014 Published 22 May 2014 Abstract Flying snakes use their entire body as a continuously morphing and stability of the snakes, resulting from the continuous redistribution of mass and aerodynamic forces
Stability of Li-carbon materials: a molecular modeling study
NASA Astrophysics Data System (ADS)
Nicolau, Dan V.
2004-03-01
Materials with exceptionally high content of carbon are used in technologies with various degrees of added value, from quasi-amorphous materials for carbon electrodes used in e.g. lithium batteries to highly-organized materials comprising e.g. nanotubes and fullerenes. The present study aims to test the feasibility of predicting the properties of carbon based materials using (i) molecular modeling and simulation techniques for prediction of compositional stability; and (ii) experimental data regarding materials used for lithium batteries as validation data. It has been found that a higher H/C atomic ratio has a complex influence on lithium uptake. The decrease of the number of the aromatic rings will limit the number of lithium ions allowed in the pore and the increase in pore flexibility will induce a more energetically favorable mechanism for lithium ions uptake (folding/house-of-cards formation against pore expansion).
A model following variable stability system for the NASA ARC X-14B.
NASA Technical Reports Server (NTRS)
Gallagher, J. T.; Saworotnow, I.; Seemann, R.; Gossett, T. D.
1972-01-01
A description of the basic design concept, hardware design, and flight evaluation of a Variable Stability System (VSS) installed on the NASA ARC X-14B is presented. The NASA ARC X-14B is a twin-engine, single-seated VTOL aircraft. The VSS is unique in that it employs a general purpose airborne digital computer as an integral part of the hybrid model following flight control system. The system design, analysis and testing phases are discussed in the paper from the application of optimal control techniques in the preliminary design of the system, through the flight demonstration of the VSS hardware.
NASA Astrophysics Data System (ADS)
Bayer, Natascha; Rank, Elisabet; Traxler, Lukas; Beckert, Erik; Drauschke, Andreas
2015-03-01
Cataract still remains the leading cause of blindness affecting 20 million people worldwide. To restore the patients vision the natural lens is removed and replaced by an intraocular lens (IOL). In modern cataract surgery the posterior capsular bag is maintained to prevent inflammation and to enable stabilization of the implant. Refractive changes following cataract surgery are attributable to lens misalignments occurring due to postoperative shifts and tilts of the artificial lens. Mechanical eye models allow a preoperative investigation of the impact of such misalignments and are crucial to improve the quality of the patients' sense of sight. Furthermore, the success of sophisticated IOLs that correct high order aberrations is depending on a critical evaluation of the lens position. A new type of an IOL holder is designed and implemented into a preexisting mechanical eye model. A physiological representation of the capsular bag is realized with an integrated film element to guarantee lens stabilization and centering. The positioning sensitivity of the IOL is evaluated by performing shifts and tilts in reference to the optical axis. The modulation transfer function is used to measure the optical quality at each position. Lens stability tests within the holder itself are performed by determining the modulation transfer function before and after measurement sequence. Mechanical stability and reproducible measurement results are guaranteed with the novel capsular bag model that allows a precise interpretation of postoperative lens misalignments. The integrated film element offers additional stabilization during measurement routine without damaging the haptics or deteriorating the optical performance.
Studies of global stability of field-reversed configuration plasmas using a rigid body model
Ji, Hantao
Studies of global stability of field-reversed configuration plasmas using a rigid body model H. Ji stability of field-reversed configuration FRC plasmas has been studied using a simple rigid body model of motion for each global mode is formulated and analyzed using a rigid body model of the FRC plasma
Advanced techniques for the analysis of crisis stability, deterrence, and latency
Canavan, G.H.
1998-12-31
This is the final report of a one-year, Laboratory Directed Research and Development (LDRD) project at Los Alamos National Laboratory (LANL). The principal results of studies on crisis stability, deterrence, and latency are presented in their order of development. They capture the main features of stability analysis; relate first strike, crisis, and arms control stability as seen from US and Russian perspective; and address whether different metrics, uncertain damage preferences, or the deployment of defenses can be destabilizing. The report explores differences between unilateral and proportional force reductions in the region of deep reductions where concern shifts from stability to latency.
Operations and Modeling Analysis
NASA Technical Reports Server (NTRS)
Ebeling, Charles
2005-01-01
The Reliability and Maintainability Analysis Tool (RMAT) provides NASA the capability to estimate reliability and maintainability (R&M) parameters and operational support requirements for proposed space vehicles based upon relationships established from both aircraft and Shuttle R&M data. RMAT has matured both in its underlying database and in its level of sophistication in extrapolating this historical data to satisfy proposed mission requirements, maintenance concepts and policies, and type of vehicle (i.e. ranging from aircraft like to shuttle like). However, a companion analyses tool, the Logistics Cost Model (LCM) has not reached the same level of maturity as RMAT due, in large part, to nonexistent or outdated cost estimating relationships and underlying cost databases, and it's almost exclusive dependence on Shuttle operations and logistics cost input parameters. As a result, the full capability of the RMAT/LCM suite of analysis tools to take a conceptual vehicle and derive its operations and support requirements along with the resulting operating and support costs has not been realized.
Castro Ospina, J.M.
1984-01-01
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/.
The stability of tangential discontinuities
NASA Technical Reports Server (NTRS)
Birmingham, T.
1972-01-01
Intuition regarding the stability of MHD tangential discontinuities of solar wind has been borne out by a linear stability analysis of the MHD equations. In performing the calculation, the model used had no plasma flow and thus corresponded to the solar wind rest frame. The method calculated the change in total energy, plasma plus magnetic, due to the perturbation. This type of stability analysis is analogous to the test of the stability of an equilibrium point in a mechanical potential.
Nonparallel stability of three-dimensional compressible boundary layers. Part 1: Stability analysis
NASA Technical Reports Server (NTRS)
El-Hady, N. M.
1980-01-01
A compressible linear stability theory is presented for nonparallel three-dimensional boundary-layer flows, taking into account the normal velocity component as well as the streamwise and spanwise variations of the basic flow. The method of multiple scales is used to account for the nonparallelism of the basic flow, and equations are derived for the spatial evolution of the disturbance amplitude and wavenumber. The numerical procedure for obtaining the solution of the nonparallel problem is outlined.
James Aweya; Michel Ouellette; Delfin Y. Montuno
2004-01-01
Feedback delays arise in the control of a computer network--from the information transfer process itself and from the processing of control signals at the network nodes. Flow control of data sources in a computer network often results in a time-delayed control problem. Feedback delay reduces the stability of a system. In this paper we discuss how to use the Routh-Hurwitz
Flavor stability analysis of dense supernova neutrinos with flavor-dependent angular distributions
NASA Astrophysics Data System (ADS)
Mirizzi, Alessandro; Serpico, Pasquale Dario
2012-10-01
Numerical simulations of the supernova (SN) neutrino self-induced flavor conversions, associated with the neutrino-neutrino interactions in the deepest stellar regions, have been typically carried out assuming the “bulb model.” In this approximation, neutrinos are taken to be emitted half-isotropically by a common neutrinosphere. In the recent [A. Mirizzi and P. D. Serpico, Phys. Rev. Lett. 108, 231102 (2012)] we have removed this assumption by introducing flavor-dependent angular distributions for SN neutrinos, as suggested by core-collapse simulations. We have found that in this case a novel multiangle instability in the self-induced flavor transitions can arise. In this work we perform an extensive study of this effect, carrying out a linearized flavor stability analysis for different SN neutrino energy fluxes and angular distributions, in both normal and inverted neutrino mass hierarchy. We confirm that spectra of different ? species which cross in angular space (where F?e=F?x and F?Że=F?Żx) present a significant enhancement of the flavor instability, and a shift of the onset of the flavor conversions at smaller radii with respect to the case of an isotropic neutrino emission. We also illustrate how a qualitative (and sometimes quantitative) understanding of the dynamics of these systems follows from a stability analysis.
Bubbles breaking the wall: Two-dimensional stress and stability analysis
NASA Astrophysics Data System (ADS)
Eriksen, Jon Alm; Marks, Benjy; Sandnes, Bjřrnar; Toussaint, Renaud
2015-05-01
Submerged granular material exhibits a wide range of behavior when the saturating fluid is slowly displaced by a gas phase. In confined systems, the moving interface between the invading gas and the fluid/grain mixture can cause beads to jam, and induce intermittency in the dynamics. Here, we study the stability of layers of saturated jammed beads around stuck air bubbles, and the deformation mechanism leading to air channel formations in these layers. We describe a two-dimensional extension of a previous model of the effective stress in the jammed packing. The effect of the tangential stress component on the yield stress is discussed, in particular how arching effects may impact the yield threshold. We further develop a linear stability analysis, to study undulations which develop under certain experimental conditions at the air-liquid interface. The linear analysis gives estimates for the most unstable wavelengths for the initial growth of the perturbations. The estimates correspond well with peak to peak length measurements of the experimentally observed undulations.
This Applications Analysis Report evaluates the solidification/stabilization treatment process of Silicate Technology Corporation (STC) for the on-site treatment of hazardous waste. The STC immobilization technology utilizes a proprietary product (FMS Silicate) to chemically stab...
Software user's manual for stability and transition analysis with the codes LSH and PSH
NASA Astrophysics Data System (ADS)
Herbert, T.; Stuckert, G. K.; Lin, N.
1993-09-01
This manual describes how to use the local linear stability code LSH and the nonlinear Parabolized Stability Equations (PSE) solver PSH for compressible flows. Both codes are adaptable to analysis of different flows over fairly general shapes of bodies. For analysis of a new problem, the user may specify the basic state, the coordinate system, dependent disturbance variables and their boundary conditions to be used for the stability analysis through physics insert files. Once these preliminary steps are completed, different tasks of stability analysis and PSE calculations can be carried out by simple modifications of a few input files. Both codes are highly modular and closely integrated. Output data from LSH can be used directly as initial data for PSH runs. Examples of several insert files and input files of the built-in problems are given to assist the user in setting up a new problem.
This Applications Analysis Report evaluates the Soliditech, Inc., solidification/ stabilization process for the on-site treatment of waste materials. The Soliditech process mixes and chemically treats waste material with Urrichem (a proprietary reagent), additives, pozzolanic mat...
Linear Stability Regime Analysis of the Compressible Reacting Mixing Layer
NASA Technical Reports Server (NTRS)
Day, M. J.; Reynolds, William C.; Mansour, N. N.; Rai, Man Mohan (Technical Monitor)
1995-01-01
Previous investigations have shown that a compressible reacting mixing layer can develop two peaks in the mean density weighted vorticity profile. Linear stability analyses show that at these peaks two distinct 'outer' instability modes appear in addition to the more common central mode, which exists unaccompanied in incompressible nonreacting flows. The present study parametrically analyzes the effects of compressibility, heat release, stoichiometry, and density ratio on the amplification rate and obliquity of each stability mode. The mean profiles used in the spatial stability calculation are generated by self-similar solutions of the compressible boundary layer equations combined with the assumption of infinitely fast chemistry. It is shown that the influence of stoichiometry and density ratio on the peaks of the density weighted vorticity profile determines which modes will dominate. Of particular interest are the conditions where two modes are equally amplified, causing the mixing layer to develop into a 'colayer' structure.
De Santo, Robert James William
1972-01-01
A DYNAMIC STABILITY ANALYSIS OF AN AIRCRAFT PASSING THROUGH THE TRAILING VORTICES OF ANOTHER AIRCRAFT A Thesi~ x ROBERT J. MAE SANTO, JR. Submitted to the Graduate College of Texas A&M University in partial fulfillment of the requirement... for the degree of MASTER OF SCIENCE December 1972 Major Subject: Aerospace Engineering A DYNAMIC STABILITY ANALYSIS OF AN AIRCRAFT PASSING THROUGH THE TRAILING VORTICES OF ANOTHER AIRCRAFT A Thesis by ROBERT J. W. DE SANTO) JR. Approved as to style...
Feedback stabilization of nonaxisymmetric resistive wall modes in tokamaks. II. Control analysis
NASA Astrophysics Data System (ADS)
Fransson, C. M.; Lennartson, B.; Breitholtz, C.; Bondeson, A.; Liu, Y. Q.
2000-10-01
Active feedback of nonaxisymmetric resistive wall modes in tokamaks is investigated using control theory. Control systems are designed to stabilize the resistive wall mode of toroidal mode number n=1 and meet certain performance specifications for a set of test equilibria. The response of the plasma and resistive wall is described by low order rational functions from an electromagnetic model [Y. Q. Liu et al., Phys. Plasmas 7, 3681 (2000)]. Simple coil arrangements are assumed, both for the sensor and feedback coil arrays, and the sensors detect the perturbed poloidal field. The active coils are modeled both as broad strips and as thin wires, and several different controllers: P (proportional), PD (proportional plus derivative) and H? are investigated. An important parameter is the ratio, ?, of control system response time to the resistive wall time, and the analysis shows the restrictions on this ratio for acceptable performance. For an equilibrium that exceeds the no-wall beta limit by 63%, good control with broad strips and a PD controller is possible for ??5.4, while thin-wire coils require ??2.1. H? controllers give some improvement for thin wires and about a factor of 2 increase in ? for broad strips. The upper limit in ? decreases with increasing pressure. A control system designed to stabilize a certain pressure generally works well at lower pressures.
NASA Astrophysics Data System (ADS)
Fazelzadeh, S. A.; Kazemi-Lari, M. A.
2013-02-01
In the present study, the stability of a cantilever column resting on an elastic foundation under the action of a uniformly distributed tangential load is discussed. A Winkler type elastic foundation is considered. Moreover, the effect of a lumped mass located in an arbitrary position on the stability of the system when the column is subjected to a partially distributed follower force is investigated. The equations of motion are obtained using the extended Hamilton's principle and the influences of the lumped mass and applied load are included in the equations using the generalized functions theories. Applying the Ritz technique, the resulting equations are transformed into a general eigenvalue problem. The effects of several design parameters such as foundation elastic modulus, ratio of the lumped mass to the column's mass, position of the lumped mass and the distribution model of the follower force are examined. The validity of the present analysis is confirmed by comparing the results with those obtained in literature and excellent agreement is observed. The numerical results reveal that the load distribution length and model have significant effects on the flutter boundaries of the system.
NASA Astrophysics Data System (ADS)
Marques, Wilson, Jr.; Jacinta Soares, Ana; Pandolfi Bianchi, Miriam; Kremer, Gilberto M.
2015-06-01
A shock wave structure problem, like the one which can be formulated for the planar detonation wave, is analyzed here for a binary mixture of ideal gases undergoing the symmetric reaction {{A}1}+{{A}1}\\rightleftharpoons {{A}2}+{{A}2}. The problem is studied at the hydrodynamic Euler limit of a kinetic model of the reactive Boltzmann equation. The chemical rate law is deduced in this frame with a second-order reaction rate, in a chemical regime such that the gas flow is not far away from the chemical equilibrium. The caloric and the thermal equations of state for the specific internal energy and temperature are employed to close the system of balance laws. With respect to other approaches known in the kinetic literature for detonation problems with a reversible reaction, this paper aims to improve some aspects of the wave solution. Within the mathematical analysis of the detonation model, the equation of the equilibrium Hugoniot curve of the final states is explicitly derived for the first time and used to define the correct location of the equilibrium Chapman–Jouguet point in the Hugoniot diagram. The parametric space is widened to investigate the response of the detonation solution to the activation energy of the chemical reaction. Finally, the mathematical formulation of the linear stability problem is given for the wave detonation structure via a normal-mode approach, when bidimensional disturbances perturb the steady solution. The stability equations with their boundary conditions and the radiation condition of the considered model are explicitly derived for small transversal deviations of the shock wave location. The paper shows how a second-order chemical kinetics description, derived at the microscopic level, and an analytic deduction of the equilibrium Hugoniot curve, lead to an accurate picture of the steady detonation with reversible reaction, as well as to a proper bidimensional linear stability analysis.
V. P. Butseroga; V. B. Red'kin
1972-01-01
The present article is devoted to setting up a mathematical model of a fatigue-testing machine with programmed control of the ampIitude of the load, and to an analysis of its stability. An example of such a system is a T sLU 30 [8] hydraulic re sonance fatigue-testing machine, of which a functional schematic diagram is shown in Fig. 1,
Dynamics of the Heisenberg model and a theorem on stability
NASA Astrophysics Data System (ADS)
Pantelidis, Leonidas
2013-02-01
We consider the general discrete classical Heisenberg model (HM) with z axis anisotropy and external magnetic field and show that its phase space is foliated into a family of invariant manifolds (the leaves) diffeomorphic to (S2)?, where ? is the number of spins. We also show that the flow on each leaf S is Hamiltonian. Subsequently, we focus on the isotropic HM in the absence of external field. We discuss the rotational symmetry of the model and further analyze its phase space structure. We prove that the manifold F of longitudinal fixed points intersects each leaf S orthogonally. For a real local flow with a continuous symmetry, we show that the Lyapunov stability of invariant sets on an invariant subspace can be extended to the whole phase space. This general theorem is the main result of the article. We use it to show that, in the case of the isotropic HM, the ferromagnetic state and the antiferromagnetic state with non-zero total spin are both stable fixed points. The theorem does not apply at total spin zero, and indeed the AF state on an equal-spins leaf is found to be unstable.
STABILITY ANALYSIS OF THE BUTTAHATCHEE RIVER BASIN, MISSISSIPPI AND ALABAMA
Technology Transfer Automated Retrieval System (TEKTRAN)
The overall purpose of this study was to evaluate the stability of the Buttahatchee River and major tributaries, and to determine if observed instabilities were the result of localized or system-wide disturbances. Instabilities in the channel may lead to excessive sediment erosion and deposition, b...
Time-domain Dynamics and Stability Analysis of Optoelectronic Oscillators
Paris-Sud XI, Université de
optimization has led to novel config- urations where this fiber delay line is replaced by a ultrahigh Q because of the temperature-stabilized box containing the optical fiber delay line. Effectively ultrastable radio-frequency signals with unprecedented phase noise performance for aerospace and communication
Sensitivity and Stability Analysis in DEA: Some Recent Developments
W. W. Cooper; Shanling Li; L. M. Seiford; Kaoru Tone; R. M. Thrall; J. Zhu
2001-01-01
This papersurveys recently developed analytical methods for studying thesensitivity of DEA results to variations in the data. The focusis on the stability of classification of DMUs (Decision MakingUnits) into efficient and inefficient performers. Early workon this topic concentrated on developing solution methods andalgorithms for conducting such analyses after it was noted thatstandard approaches for conducting sensitivity analyses in linearprogramming could
Stability analysis of supply chain collaboration for project
Ming-juan Li; Guo-shuang Tian
2011-01-01
In order to ensure supply chain collaboration stability, ant colony optimization algorithm was used to study construction supply chain operational efficiency, to determine the dynamic operational errors of construction supply chain. Neural network and data mining technology were used to forecast the investment risk of construction project, to determine the forecasting errors of construction project investment risk. Rough sets and
Stability analysis of electrical drives fed by matrix converters
D. Casadei; G. Serra; A. Tani; L. Zarri
2002-01-01
Input filters are usually adopted in electrical drives in order to improve the input current quality and to reduce the input voltage distortion. These filters; can determine instabilities, depending on the converter topology and drive control strategy. In this paper the stability of an electrical drive fed by a three-phase to three-phase matrix converter is analyzed considering two different input
Bifurcation and stability analysis of laminar isothermal counterflowing jets
A. G. S ALINGER; J. N. S HADID; T. J. M OUNTZIARIS
2006-01-01
We present a numerical study of the structure and stability of laminar isothermal flows formed by two counterflowing jets of an incompressible Newtonian fluid. We demonstrate that symmetric counterflowing jets with identical mass flow rates exhibit multiple steady states and, in certain cases, time-dependent (periodic) steady states. Two geometric configurations were studied based on the inlet jet shapes: planar and
EXPOSURE ANALYSIS MODELING SYSTEM (EXAMS)
The Exposure Analysis Modeling System (EXAMS), first published in 1982 (EPA-600/3-82-023), provides interactive computer software for formulating aquatic ecosystem models and rapidly evaluating the fate, transport, and exposure concentrations of synthetic organic chemicals--pesti...
Stability of building gene regulatory networks with sparse autoregressive models
Rajapakse, Jagath
Background: Biological networks are constantly subjected to random perturbations, and efficient feedback and compensatory mechanisms exist to maintain their stability. There is an increased interest in building gene ...
Effects of Maximal Sodium and Potassium Conductance on the Stability of Hodgkin-Huxley Model
Wang, Kuanquan; Yuan, Yongfeng; Zhang, Henggui
2014-01-01
Hodgkin-Huxley (HH) equation is the first cell computing model in the world and pioneered the use of model to study electrophysiological problems. The model consists of four differential equations which are based on the experimental data of ion channels. Maximal conductance is an important characteristic of different channels. In this study, mathematical method is used to investigate the importance of maximal sodium conductance g-Na and maximal potassium conductance g-K. Applying stability theory, and taking g-Na and g-K as variables, we analyze the stability and bifurcations of the model. Bifurcations are found when the variables change, and bifurcation points and boundary are also calculated. There is only one bifurcation point when g-Na is the variable, while there are two points when g-K is variable. The (g-Na,??g-K) plane is partitioned into two regions and the upper bifurcation boundary is similar to a line when both g-Na and g-K are variables. Numerical simulations illustrate the validity of the analysis. The results obtained could be helpful in studying relevant diseases caused by maximal conductance anomaly. PMID:25104970
Nuclear-coupled thermal-hydraulic stability analysis of boiling water reactors
NASA Astrophysics Data System (ADS)
Karve, Atul A.
We have studied the nuclear-coupled thermal-hydraulic stability of boiling water reactors (BWRs) using a model we developed from: the space-time modal neutron kinetics equations based on spatial omega-modes, the equations for two-phase flow in parallel boiling channels, the fuel rod heat conduction equations, and a simple model for the recirculation loop. The model is represented as a dynamical system comprised of time-dependent nonlinear ordinary differential equations, and it is studied using stability analysis, modern bifurcation theory, and numerical simulations. We first determine the stability boundary (SB) 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 and then transform the SB to the practical power-flow map. Using this SB, we show that the normal operating point at 100% power is very stable, stability of points on the 100% rod line decreases as the flow rate is reduced, and that points are least stable in the low-flow/high-power region. We also determine the SB when the modal kinetics is replaced by simple point reactor kinetics and show that the first harmonic mode has no significant effect on the SB. Later we carry out the relevant numerical simulations where we first show that the Hopf bifurcation, that occurs as a parameter is varied across the SB is subcritical, and that, in the important low-flow/high-power region, growing oscillations can result following small finite perturbations of stable steady-states on the 100% rod line. Hence, a point on the 100% rod line in the low-flow/high-power region, although stable, may nevertheless be a point at which a BWR should not be operated. Numerical simulations are then done to calculate the decay ratios (DRs) and frequencies of oscillations for various points on the 100% rod line. It is determined that the NRC requirement of DR < 0.75-0.8 is not rigorously satisfied in the low-flow/high-power region and hence these points should be avoided during normal startup and shutdown operations. The frequency of oscillation is shown to decrease as the flow rate is reduced and the frequency of 0.5Hz observed 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 kinetics equations results in growing nonlinear oscillations. Thus, we show that side-by-side out-of-phase growing power oscillations result due to the very important first harmonic mode effect and that the use of point kinetics, which fails to predict these growing oscillations, leads to dramatically nonconservative results. Finally, the effect of a simple recirculation loop model that we develop is studied by carrying out additional stability analyses and additional numerical simulations. It is shown that the loop has a stabilizing effect on certain points on the 100% rod line for time delays equal to integer multiples of the natural period of oscillation, whereas it has a destabilizing effect for half-integer multiples. However, for more practical time delays, it is determined that the overall effect generally is destabilizing.
Stability Analysis of a DiffServ Network Having Two-Level Coloring at the Network Edge and
Massachusetts at Amherst, University of
Stability Analysis of a DiffServ Network Having Two-Level Coloring at the Network Edge stability result for Differentiated Services (DiffServ) networks with heterogeneous TCP flows consisting is stated for sources under TCP-Reno congestion control algorithm. Stability analysis of several DiffServ
The effects of HNE on ovine oxymyoglobin redox stability in a microsome model.
Yin, Shuang; Faustman, Cameron; Tatiyaborworntham, Nantawat; Ramanathan, Ranjith; Sun, Qun
2013-10-01
The effect of 4-hydroxy-2-nonenal (HNE), a secondary lipid oxidation product, on ovine myoglobin (Mb) redox stability was investigated. HNE increased oxymyoglobin (OxyMb) oxidation under all pH/temperature conditions studied. Mono-, di- and tri-HNE adducts were detected by ESI-Q-TOF MS analysis. Sites of adduction, His 120, His 25 and His 65, were determined by ESI-CID-MS/MS analysis. The relationship between ovine Mb (with/without HNE) and lipid oxidation was also studied in a microsome model in the presence of ?-tocopherol. Surprisingly, preincubation of Mb with HNE did not affect subsequent Mb redox stability in the microsome model (P<0.05). Microsomes with elevated concentrations of ?-tocopherol delayed lipid and Mb oxidations relative to controls. HNE-treated ovine Mb caused greater lipid oxidation compared to control ovine Mb in control microsomes (P<0.05). This study demonstrated an interaction between ovine Mb oxidation and lipid oxidation. PMID:23747615
Weston, Ken
Atomistic Modeling of Macromolecular Crowding Predicts Modest Increases in Protein Folding that macromolecular crowding can increase protein folding stability, but depending on details of the models (e.g., how on the effects of macro- molecular crowding on protein folding and binding stability has been reached. Crowders
Globally stabilizing switching controllers for a centrifugal compressor model with spool dynamics
Alexander Leonessa; Wassim M. Haddad; Hua Li
2000-01-01
In this paper we develop a globally stabilizing stability-based switching controller for a three-state lumped parameter centrifugal compressor surge model. The proposed model involves pressure and mass flow compression system dynamics as well as spool dynamics to account for the influence of speed transients on the compression surge dynamics. The proposed nonlinear switching controller architecture involves throttle and compressor torque
Stability analysis of large space structure control systems with delayed input
NASA Technical Reports Server (NTRS)
Reddy, A. S. S. R.; Bainum, Peter M.
1988-01-01
Large space structural systems, due to their inherent flexibility and low mass to area ratio, are represented by large dimensional mathematical models. For implementation of the control laws for such systems a finite amount of time is required to evaluate the control signals; and this time delay may cause instability in the closed loop control system that was previously designed without taking the input delay into consideration. The stability analysis of a simple harmonic oscillator representing the equation of a single mode as a function of delay time is treated analytically and verified numerically. The effect of inherent damping on the delay is also analyzed. The control problem with delayed input is also formulated in the discrete time domain.
Method to assess in vivo knee stability longitudinally in an animal model of ligament injury.
Maitland, M E; Leonard, T; Frank, C B; Shrive, N G; Herzog, W
1998-07-01
The purpose of this study was to develop a method to prospectively quantify passive knee stability in an animal model of joint injury over time. Knee stability is defined here as the amount of translation or rotation of the tibia relative to the femur for a given application of force or moment, respectively. Five animals that had undergone transection of the anterior cruciate ligament and three control animals that had undergone a sham operation were anaesthetized and positioned in a stereotaxic frame. Motion of the tibia relative to the femur was quantified with use of reflective markers secured to modified bone pins and a three-dimensional motion analysis system. External forces and moments in the transverse plane of the tibia were measured with use of force transducers based on a strain-gauge design. Longitudinal measurements of knee stability were made before either sham surgery (control animals) or transection of the ligament (experimental animals), immediately after surgery, and at 2 and 4 months after transection. The results showed that the animals tolerated the procedures well and that systematic measurements could be obtained. The method described here has the practical advantage over cross-sectional experimental designs in that the number of subjects can be decreased while maintaining statistical power and has the further conceptual advantage that individual changes can be accounted for over time. PMID:9747785
Incorporating seepage processes into a streambank stability model
Technology Transfer Automated Retrieval System (TEKTRAN)
Seepage processes are usually neglected in bank stability analyses although they can become a prominent failure mechanism under certain field conditions. This study incorporated the effects of seepage (i.e., seepage gradient forces and seepage erosion undercutting) into the Bank Stability and Toe Er...
Thermal Stability Analysis for a Heliocentric Gravitational Radiation Detection Mission
NASA Technical Reports Server (NTRS)
Folkner, W.; McElroy, P.; Miyake, R.; Bender, P.; Stebbins, R.; Supper, W.
1994-01-01
The Laser Interferometer Space Antenna (LISA) mission is designed for detailed studies of low-frequency gravitational radiation. The mission is currently a candidate for ESA's post-Horizon 2000 program. Thermal noise affects the measurement in at least two ways. Thermal variation of the length of the optical cavity to which the lasers are stabilized introduces phase variations in the interferometer signal, which have to be corrected for by using data from the two arms separately.
Comparative analysis of geo-engineering approaches to climate stabilization
Yu. A. Izrael; A. G. Ryaboshapko; N. N. Petrov
2009-01-01
Geo-engineering approaches to modern climate stabilization, irrelative to the Kyoto Protocol measures, are under consideration.\\u000a Conditionally, these approaches are subdivided into two groups: purposive changes in the Earth radiation balance to compensate\\u000a the greenhouse gas effect and removal of the excessive amount of carbon dioxide from the atmosphere. The first group includes\\u000a such methods as injection of sulfate and other
Studies of iso-alpha-acids: analysis, purification, and stability
Alfi Khatib
2006-01-01
The female cones of hop (Humulus lupulus L.) are added to beer, providing taste and flavour and contributing to the stability of foam. The main constituents of hop related to these properties are generically known as alpha-acids. During the brewing process, these acids are isomerized, resulting in the formation of three pairs of trans-\\/cis-iso-alpha–acids.\\u000a The aim of this thesis project
Nonparallel stability analysis of axisymmetric stagnation-point flow
W. J. Grabowski
1980-01-01
The method of multiple scales has been used to extend linear-stability theory to nonparallel axisymmetric boundary-layer flow in the neighborhood of the stagnation point on a blunt body of revolution. The extended theory includes nonparallel planar effects as well as the effects of such possibly destabilizing three-dimensional mechanisms as the stretching of vortex filaments in the rapidly diverging boundary-layer flow.
Reflectance stability analysis of Spectralon diffuse calibration panels
Carol J. Bruegge; Albert E. Stiegman; Daniel R. Coulter; Robert R. Hale; David J. Diner; Arthur W. Springsteen
1991-01-01
The Multi-angle Imaging SpectroRadiometer (MISR) plans to use deployable diffuse reflectance panels to provide periodic radiometric calibrations of its nine cameras while in-flight. Near-Lambertian reflectance characteristics are desirable to facilitate flat-field camera intercomparisons. Also required is panel spatial and spectral uniformity, and stability with time. Spectralon, a commercially available polytetrafluoroethylene (PTFE) compound, has been baselined in the MISR design. To
Stability analysis of paraplegic standing while wearing an orthosis
Takahiro Kagawa; Hiroshi Fukuda; Yoji Uno
2006-01-01
Paraplegics can maintain a standing posture, called the “C-posture”, while wearing an orthosis. The significant feature of the C-posture is that the body’s center of mass is located behind the hip joint. In this study, we investigate the C-posture mechanism and assess the relationship between posture and stability, the aim being to restore standing function. We first measured the standing
How to model the stability of terraced slopes? The case study of Tresenda (northern Italy)
NASA Astrophysics Data System (ADS)
Camera, Corrado; Apuani, Tiziana; Masetti, Marco
2015-04-01
Terraces are very common morphological features all around the Mediterranean Basin. They have been built to adapt the natural morphology of the territory to the development of anthropogenic activities, particularly agriculture. However, the increasing land abandonment during the last century is leading to soil degradation and stability issues, mainly due to lack of maintenance of these peculiar environments. The objective of this study was to develop a coupled hydrologic-stability model to identify possible triggering areas of superficial landslides during intense rainfall events. The model was tested on a slope uphill of the village of Tresenda, in Northern Italy, which experienced several superficial landslides in the last 35 years. Distributed stability analyses are usually carried out using an infinite slope approach, but in the case of terraces some basic assumptions of this method fail: the parallelism between topographical surface and potential sliding surface and the high ratio between slope length and failure surface depth are the most important examples. In addition, the interest is more on the stability of the terrace system (dry stone retaining wall and backfill soil) and not on soil alone. For these reasons, a stability analysis based on the global method of equilibrium is applied and soft coupled to a well know hydrological model (STARWARS). Sections of terrace, one cell wide, are recognized from the base of a wall to the top of the closest downstream one, and each cell (1 x 1 m2) is considered as a slice. The method of Sarma for circular and non-circular failure is applied. The very fine horizontal resolution (1 m) is crucial to take into consideration the hydrogeological and mechanical properties of dry stone walls (0.6-1.0 m wide). A sensitivity analysis was conducted for saturated water content, initial volumetric water content, the cohesion and friction angle of soil and walls and soil depth. The results of the sensitivity analysis showed that instability never occurs if less than 60% of the soil depth is saturated. In addition, a variation of 10% in the cohesion and friction angle of soil leads to changes in critical acceleration (factor of safety) of 4% and 5%, respectively. On the other hand, a variation of 10% in wall cohesion and friction angle leads to changes in the critical acceleration of around 4% and 1.5%, respectively. The use of a soil depth map with slightly different depths caused a different distribution in the number and location of instabilities. This underlines how this parameter, which is difficult to determine at high resolution, plays a central role in controlling location and volume of potential unstable masses. The model was finally evaluated on historical events and it demonstrated to be a good and reliable instrument to reproduce water levels and localise the most critical area for the triggering of superficial landslides on terraced slopes. In detail, field-measured water levels are modelled with a normalized RMSE of about 10%. Regarding stability, the triggering areas of the two superficial landslides occurred in May 1983 were well reproduced both temporally and spatially.
Analysis of a Precambrian Resonance-Stabilized Day Length
NASA Astrophysics Data System (ADS)
Bartlett, B. C.; Stevenson, D. J.
2014-12-01
Calculations indicate the average rate of decrease of Earth's angular momentum must have been less than its present value in the past; otherwise, the Earth should have a longer day length. Existing stromatolite data suggests the Earth's rotational frequency would have been near that of the atmospheric resonance frequency toward the end of the Precambrian era, approximately 600Ma. The semidiurnal atmospheric tidal torque would have reached a maximum near this day length of 21hr. At this point, the atmospheric torque would have been comparable in magnitude but opposite in direction to the lunar torque, creating a stabilizing effect which could preserve a constant day length while trapped in this resonant state, as suggested by Zahnle and Walker (1987). We examine the hypothesis that this resonant stability was encountered and sustained for a large amount of time during the Precambrian era and was broken by a large and relatively fast increase in global temperature, possibly in the deglaciation period following a snowball event. Computational simulations of this problem were performed, indicating that a persistent increase in temperature larger than around 10K over a period of time less than 107 years will break resonance (though these values vary with Q), but that the resonant stability is not easily broken by random high-amplitude high-frequency atmospheric temperature fluctuation or other forms of thermal noise. Further work also indicates it is possible to escape resonance simply by increasing the lunar tidal torque on the much longer timescale of plate tectonics, particularly for low atmospheric Q-factors, or that resonance could have never formed in the first place, had the lunar torque been very high or Q been very low when the Earth's rotational frequency was near the atmospheric resonance frequency. However, the need to explain the present day length given the current lunar torque favors the interpretation we offer, in which Earth's length of day was stabilized for hundreds of millions of years, escaping this stability in the aftermath of a sudden global temperature change.
Grapentin, Christoph; Barnert, Sabine; Schubert, Rolf
2015-01-01
Perfluorocarbon nanoemulsions (PFC-NE) are disperse systems consisting of nanoscale liquid perfluorocarbon droplets stabilized by an emulsifier, usually phospholipids. Perfluorocarbons are chemically inert and non-toxic substances that are exhaled after in vivo administration. The manufacture of PFC-NE can be done in large scales by means of high pressure homogenization or microfluidization. Originally investigated as oxygen carriers for cases of severe blood loss, their application nowadays is more focused on using them as marker agents in 19F Magnetic Resonance Imaging (19F MRI). 19F is scarce in organisms and thus PFC-NE are a promising tool for highly specific and non-invasive imaging of inflammation via 19F MRI. Neutrophils, monocytes and macrophages phagocytize PFC-NE and subsequently migrate to inflamed tissues. This technique has proven feasibility in numerous disease models in mice, rabbits and mini pigs. The translation to clinical trials in human needs the development of a stable nanoemulsion whose droplet size is well characterized over a long storage time. Usually dynamic light scattering (DLS) is applied as the standard method for determining particle sizes in the nanometer range. Our study uses a second method, analysis of transmission electron microscopy images of cryo-fixed samples (Cryo-TEM), to evaluate stability of PFC-NE in comparison to DLS. Four nanoemulsions of different composition are observed for one year. The results indicate that DLS alone cannot reveal the changes in particle size, but can even mislead to a positive estimation of stability. The combination with Cryo-TEM images gives more insight in the particulate evolution, both techniques supporting one another. The study is one further step in the development of analytical tools for the evaluation of a clinically applicable perfluorooctylbromide nanoemulsion. PMID:26098661
Flexible Launch Vehicle Stability Analysis Using Steady and Unsteady Computational Fluid Dynamics
NASA Technical Reports Server (NTRS)
Bartels, Robert E.
2012-01-01
Launch vehicles frequently experience a reduced stability margin through the transonic Mach number range. This reduced stability margin can be caused by the aerodynamic undamping one of the lower-frequency flexible or rigid body modes. Analysis of the behavior of a flexible vehicle is routinely performed with quasi-steady aerodynamic line loads derived from steady rigid aerodynamics. However, a quasi-steady aeroelastic stability analysis can be unconservative at the critical Mach numbers, where experiment or unsteady computational aeroelastic analysis show a reduced or even negative aerodynamic damping.Amethod of enhancing the quasi-steady aeroelastic stability analysis of a launch vehicle with unsteady aerodynamics is developed that uses unsteady computational fluid dynamics to compute the response of selected lower-frequency modes. The response is contained in a time history of the vehicle line loads. A proper orthogonal decomposition of the unsteady aerodynamic line-load response is used to reduce the scale of data volume and system identification is used to derive the aerodynamic stiffness, damping, and mass matrices. The results are compared with the damping and frequency computed from unsteady computational aeroelasticity and from a quasi-steady analysis. The results show that incorporating unsteady aerodynamics in this way brings the enhanced quasi-steady aeroelastic stability analysis into close agreement with the unsteady computational aeroelastic results.
Stability of a Random Walk Model for Fruiting Body Aggregation in M. xanthus
NASA Astrophysics Data System (ADS)
McKenzie-Smith, G. C.; Schüttler, H. B.; Cotter, C.; Shimkets, L.
2015-03-01
Myxococcus xanthus exhibits the social starvation behavior of aggregation into a fruiting body containing myxospores able to survive harsh conditions. During fruiting body aggregation, individual bacteria follow random walk paths determined by randomly selected runtimes, turning angles, and speeds. We have simulated this behavior in terms of a continuous-time random walk (CTRW) model, re-formulated as a system of integral equations, describing the angle-resolved cell density, R(r, t, ?), at position r and cell orientation angle ? at time t, and angle-integrated ambient cell density ?(r, t). By way of a linear stability analysis, we investigated whether a uniform cell density R0 will be unstable for a small non-uniform density perturbation ?R(r, t, ?). Such instability indicates aggregate formation, whereas stability indicates absence of aggregation. We show that a broadening of CTRW distributions of the random speed and/or random runtimes strongly favors aggregation. We also show that, in the limit of slowly-varying (long-wavelength) density perturbations, the time-dependent linear density response can be approximated by a drift-diffusion model for which we calculate diffusion and drift coefficients as functions of the CTRW model parameters. Funded by the Fungal Genomics and Computational Biology REU at UGA.
Modelling and solutions to the linear stability of a detonation wave in the kinetic frame
M. Pandolfi Bianchi; A. J. Soares
2011-01-01
The analysis of linear stability of a steady detonation wave is formulated for the first time at the kinetic level in the frame of the Boltzmann equation extended to reacting gases. Within this context and for a reversible reaction, the stability problem is carried out, in agreement with most classical papers on gas detonation, through a normal mode approach for
Flame stability monitoring and characterization through digital imaging and spectral analysis
NASA Astrophysics Data System (ADS)
Sun, Duo; Lu, Gang; Zhou, Hao; Yan, Yong
2011-11-01
This paper presents the design, implementation and evaluation of an instrumentation system for the stability monitoring and characterization of combustion flames. The system, incorporating optical sensing, image processing and spectral analysis techniques, is designed to monitor a range of flame characteristic parameters. The stability of the flame is assessed through statistical analysis of the flame parameters obtained. Embedded computer techniques are employed to ensure the compactness and robustness of the system. Experiments were conducted on a gas-fired combustion test rig to evaluate the system. The impact of equivalence ratio on the stability of the gaseous flame is investigated. Further trials were carried out on a 9 MWth heavy-oil-fired combustion test facility. The impact of the swirl vane angle of tertiary air on the oil-fired flames is studied. The results demonstrate the effectiveness of the system for the monitoring and characterization of the flame stability.
Modal and nonmodal stability analysis of electrohydrodynamic flow with and without cross-flow
Zhang, Mengqi; Wu, Jian; Schmid, Peter J; Quadrio, Maurizio
2015-01-01
We report the results of a complete modal and nonmodal linear stability analysis of the electrohydrodynamic flow (EHD) for the problem of electroconvection in the strong injection region. Convective cells are formed by Coulomb force in an insulating liquid residing between two plane electrodes subject to unipolar injection. Besides pure electroconvection, we also consider the case where a cross-flow is present, generated by a streamwise pressure gradient, in the form of a laminar Poiseuille flow. The effect of charge diffusion, often neglected in previous linear stability analyses, is included in the present study and a transient growth analysis, rarely considered in EHD, is carried out. In the case without cross-flow, a non-zero charge diffusion leads to a lower linear stability threshold and thus to a more unstable low. The transient growth, though enhanced by increasing charge diffusion, remains small and hence cannot fully account for the discrepancy of the linear stability threshold between theoretical a...
Langley Stability and Transition Analysis Code (LASTRAC) Version 1.2 User Manual
NASA Technical Reports Server (NTRS)
Chang, Chau-Lyan
2004-01-01
LASTRAC is a general-purposed, physics-based transition prediction code released by NASA for Laminar Flow Control studies and transition research. The design and development of the LASTRAC code is aimed at providing an engineering tool that is easy to use and yet capable of dealing with a broad range of transition related issues. It was written from scratch based on the state-of-the-art numerical methods for stability analysis and modern software technologies. At low fidelity, it allows users to perform linear stability analysis and N-factor transition correlation for a broad range of flow regimes and configurations by using either the linear stability theory or linear parabolized stability equations method. At high fidelity, users may use nonlinear PSE to track finite-amplitude disturbances until the skin friction rise. This document describes the governing equations, numerical methods, code development, detailed description of input/output parameters, and case studies for the current release of LASTRAC.
NASA Technical Reports Server (NTRS)
Joshi, Anjali; Heimdahl, Mats P. E.; Miller, Steven P.; Whalen, Mike W.
2006-01-01
System safety analysis techniques are well established and are used extensively during the design of safety-critical systems. Despite this, most of the techniques are highly subjective and dependent on the skill of the practitioner. Since these analyses are usually based on an informal system model, it is unlikely that they will be complete, consistent, and error free. In fact, the lack of precise models of the system architecture and its failure modes often forces the safety analysts to devote much of their effort to gathering architectural details about the system behavior from several sources and embedding this information in the safety artifacts such as the fault trees. This report describes Model-Based Safety Analysis, an approach in which the system and safety engineers share a common system model created using a model-based development process. By extending the system model with a fault model as well as relevant portions of the physical system to be controlled, automated support can be provided for much of the safety analysis. We believe that by using a common model for both system and safety engineering and automating parts of the safety analysis, we can both reduce the cost and improve the quality of the safety analysis. Here we present our vision of model-based safety analysis and discuss the advantages and challenges in making this approach practical.
Nonlocal stability analysis of the MHD Kelvin-Helmholtz instability in a compressible plasma
A. Miura; P. L. Pritchett
1982-01-01
A general stability analysis is performed for the Kelvin-Helmholtz instability in sheared magnetohydrodynamic flow of finite thickness in a compressible plasma. The analysis allows for arbitrary orientation of the magnetic field Bâ, velocity flow vâ, and wave vector k in the plane perpendicular to the velocity gradient, and no restrictions are imposed on the sound or Alfven Mach numbers. The
Design Analysis Report for 244-AR Interim Stabilization Exhaust Ventilation Ducting
RUTHERFORD, J.
2002-11-21
This report documents the design analysis performed for the exhaust ducting associated with the 244-AR Interim Stabilization Project. The exhaust ducting connects portable exhausters PORO5 and PORO6 to the existing east dog house of the 291-AR filter vault and the vessel ventilation system. This analysis examines loads on the ductwork and ductwork supports.
Modeling of Neoclassical Tearing Mode Stability for Generalized Toroidal Geometry
A.L. Rosenberg; D.A. Gates; A. Pletzer; J.E. Menard; S.E. Kruger; C.C. Hegna; F. Paoletti; S. Sabbagh
2002-08-21
Neoclassical tearing modes (NTMs) can lead to disruption and loss of confinement. Previous analysis of these modes used large aspect ratio, low beta (plasma pressure/magnetic pressure) approximations to determine the effect of NTMs on tokamak plasmas. A more accurate tool is needed to predict the onset of these instabilities. As a follow-up to recent theoretical work, a code has been written which computes the tearing mode island growth rate for arbitrary tokamak geometry. It calls PEST-3 [A. Pletzer et al., J. Comput. Phys. 115, 530 (1994)] to compute delta prime, the resistive magnetohydrodynamic (MHD) matching parameter. The code also calls the FLUXGRID routines in NIMROD [A.H. Glasser et al., Plasma Phys. Controlled Fusion 41, A747 (1999)] for Dnc, DI and DR [C.C. Hegna, Phys. Plasmas 6, 3980 (1999); A.H. Glasser et al., Phys. Fluids 18, 875 (1975)], which are the bootstrap current driven term and the ideal and resistive interchange mode criterion, respectively. In addition to these components, the NIMROD routines calculate alphas-H, a new correction to the Pfirsch-Schlter term. Finite parallel transport effects were added and a National Spherical Torus Experiment (NSTX) [M. Ono et al., Nucl. Fusion 40, 557 (2000)] equilibrium was analyzed. Another program takes the output of PEST-3 and allows the user to specify the rational surface, island width, and amount of detail near the perturbed surface to visualize the total helical flux. The results of this work will determine the stability of NTMs in an spherical torus (ST) [Y.-K.M. Peng et al., Nucl. Fusion 26, 769 (1986)] plasma with greater accuracy than previously achieved.
Stability analysis of the motion along re-entry optimal trajectories
NASA Astrophysics Data System (ADS)
Popescu, M.
1983-10-01
A stability analysis of the equations of motion governing the ricochet re-entry trajectory of a rocket-powered vehicle is presented. The plane case of a vehicle propelled by the time-dependent expulsion of gases is considered, taking the change in mass into account. The zone of stability is defined using a frequency criterion, while the stability domains of the parameters of motion are derived by constructing a Liapunov function. The perturbations of the state variables and their damping-out velocities are estimated.
Avdeev, M V; Bica, D; Vékás, L; Aksenov, V L; Feoktystov, A V; Marinica, O; Rosta, L; Garamus, V M; Willumeit, R
2009-06-01
The structure of ferrofluids (magnetite in decahydronaphtalene) stabilized with saturated mono-carboxylic acids of different chain lengths (lauric, myristic, palmitic and stearic acids) is studied by means of magnetization analysis and small-angle neutron scattering. It is shown that in case of saturated acid surfactants, magnetite nanoparticles are dispersed in the carrier approximately with the same size distribution whose mean value and width are significantly less as compared to the classical stabilization with non-saturated oleic acid. The found thickness of the surfactant shell around magnetite is analyzed with respect to stabilizing properties of mono-carboxylic acids. PMID:19376524
Robust Stability Analysis of the PWM Push-Pull DC–DC Converter
Yogesh V. Hote; D. Roy Choudhury; J. R. P. Gupta
2009-01-01
In this letter, robust stability analysis of the closed-loop pulsewidth modulated push-pull DC-DC converter with a state feedback control is presented using simple frequency-domain conditions based on the Hermite-Biehler theorem. The proposed technique for checking robust stability is efficient, since there is no need to calculate all the uncertain values of the system and hence no need to formulate and
A rule-based expert system for steady-state stability analysis [of power systems
Yuan-Yin Hsu; Chung-Ching Su
1991-01-01
A rule-based expert system is designed for steady-state stability analysis of a power system. In the proposed expert system approach, the key variables which affect steady-state stability most are first identified through discussions with operators and engineers. A number of offline studies (both eigenvalue analyses and time-domain simulations) are also conducted to help identify important system variables. A set of
Stability analysis on single-phase natural circulation in Argonne lead loop facility
Qiao Wu; James J. Sienicki
2003-01-01
One-dimensional linear stability analysis was performed for single-phase lead–bismuth eutectic (LBE) natural circulation. The Nyquist criterion and a root search method were employed to find the linear stability boundary of both forward and backward circulations. It was found that the natural circulations could be linearly unstable in a high Reynolds number region. Increasing loop friction makes a forward circulation more
Stability Analysis for Neural Networks With Time-Varying Interval Delay
Yong He; Guo-ping Liu; David Rees; Min Wu
2007-01-01
This letter is concerned with the stability analysis of neural networks (NNs) with time-varying interval delay. The relationship between the time-varying delay and its lower and upper bounds is taken into account when estimating the upper bound of the derivative of Lyapunov functional. As a result, some improved delay\\/interval-dependent stability criteria for NNs with time-varying interval delay are proposed. Numerical
New approach to the steady state stability analysis of synchronous machines
J. Tamura; T. Murata; I. Takeda; J. Hasegawa; H. Fujiwara
1988-01-01
A novel method for steady state stability analysis of synchronous machines is presented. The method is based on a novel swing equation, which is a second-order, nonlinear differential equation. Two steady-state stability criteria can be derived by evaluating the eigenvalues of a linearized version of the new equation, one of which is for step-out instability and the other for hunting.
Srinivasan, Sathyanarayanan; Dunn, Jeff F.
2011-01-01
Hypoxia-inducible factor-1? (HIF-1?) is a widely studied protein with significant biomedical impact. Care is needed to stabilize HIF-1? protein during sample preparation for Western blot analysis due to its rapid degradation in the presence of oxygen. Enzyme inhibitor cocktails can be complex and expensive. We present a protease inhibitor-free buffer, containing cobalt chloride, which is effective at stabilizing HIF-1?, while being inexpensive, straightforward, convenient, and has potential for widespread application. PMID:21601556
Oxidation stability of methyl esters studied by differential thermal analysis and rancimat
J. Polavka; J. Paligová; J. Cvengroš; P. Simon
2005-01-01
The oxidation stability of methyl esters derived from fresh rapeseed oil and waste frying oil, used as alternative biodiesel\\u000a fuels, both distilled and undistilled, unstabilized and stabilized by pyrogallol and BHT, was studied by differential thermal\\u000a analysis (DTA) under nonisothermal conditions at various heating rates and by the Rancimat test under isothermal conditions\\u000a at 110C. The results obtained by both
Statistical Analysis of Econometric Models
Arnold Zellner
1979-01-01
In this article, a summary of some research bearing on the statistical analysis of econometric models is reviewed. Many estimation, testing, and prediction techniques used in econometrics have just large-sample justifications. Selected Bayesian inference results relating to econometric models are reviewed. On the problem of constructing econometric models, an approach that is a blend of traditional econometric and modern time
Stability analysis of a time-periodic 2-dof MEMS structure
NASA Astrophysics Data System (ADS)
Kniffka, Till Jochen; Welte, Johannes; Ecker, Horst
2012-11-01
Microelectromechanical systems (MEMS) are becoming important for all kinds of industrial applications. Among them are filters in communication devices, due to the growing demand for efficient and accurate filtering of signals. In recent developments single degree of freedom (1-dof) oscillators, that are operated at a parametric resonances, are employed for such tasks. Typically vibration damping is low in such MEM systems. While parametric excitation (PE) is used so far to take advantage of a parametric resonance, this contribution suggests to also exploit parametric anti-resonances in order to improve the damping behavior of such systems. Modeling aspects of a 2-dof MEM system and first results of the analysis of the non-linear and the linearized system are the focus of this paper. In principle the investigated system is an oscillating mechanical system with two degrees of freedom x = [x1x2]T that can be described by Mx+Cx+K1x+K3(x2)x+Fes(x,V(t)) = 0. The system is inherently non-linear because of the cubic mechanical stiffness K3 of the structure, but also because of electrostatic forces (1+cos(?t))Fes(x) that act on the system. Electrostatic forces are generated by comb drives and are proportional to the applied time-periodic voltage V(t). These drives also provide the means to introduce time-periodic coefficients, i.e. parametric excitation (1+cos(?t)) with frequency ?. For a realistic MEM system the coefficients of the non-linear set of differential equations need to be scaled for efficient numerical treatment. The final mathematical model is a set of four non-linear time-periodic homogeneous differential equations of first order. Numerical results are obtained from two different methods. The linearized time-periodic (LTP) system is studied by calculating the Monodromy matrix of the system. The eigenvalues of this matrix decide on the stability of the LTP-system. To study the unabridged non-linear system, the bifurcation software ManLab is employed. Continuation analysis including stability evaluations are executed and show the frequency ranges for which the 2-dof system becomes unstable due to parametric resonances. Moreover, the existence of frequency intervals are shown where enhanced damping for the system is observed for this MEMS. The results from the stability studies are confirmed by simulation results.
Stability and bifurcation analyses of reduced-order models of forced and natural circulation BWRs
Quan Zhou
2006-01-01
In this dissertation, dynamical analyses of the forced and natural circulation BWRs have been separately carried out using stability, bifurcation, and time-domain numerical integration techniques. In the first part of the dissertation, an existing reduced-order BWR model was modified and used for stability and bifurcation analyses of forced-circulation BWRs. An additional parameter to account for core inhomogeneity was introduced. Stability
Stability of GNSS Monumentation: Analysis of Co-Located Monuments in the Plate Boundary Observatory
NASA Astrophysics Data System (ADS)
Blume, F.; Berglund, H. T.; Feaux, K.; Dittmann, S. T.; Walls, C. P.; Austin, K. E.; Mattioli, G. S.
2013-12-01
Geodetic-quality permanent GNSS stations have used a number of different monumentation styles for the purpose of ensuring that the motions of the GNSS antenna reflect those of the Earth's crust while minimizing non-tectonic motions near the surface. Monuments range from simple masts drilled into building roofs or bedrock that cost a few hundred dollars to machine-drilled-braced monuments in soil that cost tens of thousands. Monument stability can depend on their design, the construction techniques used to install them, and the local surface geology where they are installed. Previous studies have separately investigated pairs of identical monuments at a single site, monument type variations using global statistical analysis, and multiple monument styles at a single site. Despite these efforts, the stability of different styles of monumentation in similarly varying geologic conditions has not been adequately determined. Errors in GPS measurements can be dominated by error sources unrelated to the movement of the monument with respect to the Earth's crust, thus making it difficult to isolate monument instability. Contributions from GPS measurement error unrelated to monument stability include, but are not limited to: satellite orbits, satellite clocks, tropospheric delay, and ionospheric delay, antenna phase center variations, near-field multipath, far-field multipath. Installing multiple monuments with small antenna separations at a given test location can help to reduce GPS measurement errors. To increase the understanding of monument stability of various monument styles in diverse geologic conditions UNAVCO has constructed two additional monuments at five existing Plate Boundary Observatory stations during the past year. Deep drilled-braced, short drilled-braced, and single mast type monuments were installed at sites with bedrock at the surface; deep drilled-braced, short driven-braced and pillar type monuments were installed at sites with alluvium or soil at the surface. Sites were selected that comprised a variety of geographic, hydrologic, and geologic conditions. The resulting set of 10-meter spaced monument triangles will yield valuable information regarding the stability of their types in different settings. Data collected from PBO Multi-Monument Experiment are being analyzed using a variety of methods. Each site is characterized using quality-control parameters such as multipath, signal-to-noise and previously determined seasonal variations. High-precision processing by the PBO Analysis Centers with GAMIT and GIPSY software packages using regional and global schemes yield time-series with millimeter-level that determine noise content, overall site stability relative to other PBO sites and differential motions between the individual monuments. Sub-millimeter results from UNAVCO's short-baseline processing efforts will be presented showing further details of monument performance site characterization including the effects of varying elevation cutoff angle and modeling of monument-dependent noise.
The Cosmic No-Hair Theorem and the Nonlinear Stability of Homogeneous Newtonian Cosmological Models
U. Brauer; A. Rendall; O. Reula
1994-03-28
The validity of the cosmic no-hair theorem is investigated in the context of Newtonian cosmology with a perfect fluid matter model and a positive cosmological constant. It is shown that if the initial data for an expanding cosmological model of this type is subjected to a small perturbation then the corresponding solution exists globally in the future and the perturbation decays in a way which can be described precisely. It is emphasized that no linearization of the equations or special symmetry assumptions are needed. The result can also be interpreted as a proof of the nonlinear stability of the homogeneous models. In order to prove the theorem we write the general solution as the sum of a homogeneous background and a perturbation. As a by-product of the analysis it is found that there is an invariant sense in which an inhomogeneous model can be regarded as a perturbation of a unique homogeneous model. A method is given for associating uniquely to each Newtonian cosmological model with compact spatial sections a spatially homogeneous model which incorporates its large-scale dynamics. This procedure appears very natural in the Newton-Cartan theory which we take as the starting point for Newtonian cosmology.
Reflectance stability analysis of Spectralon diffuse calibration panels
NASA Technical Reports Server (NTRS)
Bruegge, Carol J.; Stiegman, Albert E.; Coulter, Daniel R.; Hale, Robert R.; Diner, David J.; Springsteen, Arthur W.
1991-01-01
The Multi-angle Imaging SpectroRadiometer (MISR) plans to use deployable diffuse reflectance panels to provide periodic radiometric calibrations of its nine cameras while in-flight. Near-Lambertian reflectance characteristics are desirable to facilitate flat-field camera intercomparisons. Also required is panel spatial and spectral uniformity, and stability with time. Spectralon, a commercially available polytetrafluoroethylene (PTFE) compound, has been baselined in the MISR design. To assess the suitability of this material, a series of degradation tests were planned and implemented. These included UV vacuum exposure and proton bombardment tests which simulated the exposure levels to be encountered during the mission life. Proton levels are now considered too low to be of concern, but UV vacuum tests demonstrate sensitivity to material contamination. Material investigations have concluded that hydrocarbons are present in the bulk of the material, and that plastic packaging materials can introduce additional surface-layer contamination. It is found however, that these unwanted elements can be eliminated through vacuum pumping at elevated temperatures. Exposure to a UV source, while in vacuum, is again planned for a set of targets which have been vacuum baked. This will assess the stability of the pure PTFE form.
Reflectance stability analysis of Spectralon diffuse calibration panels
NASA Astrophysics Data System (ADS)
Bruegge, Carol J.; Stiegman, Albert E.; Coulter, Daniel R.; Hale, Robert R.; Diner, David J.; Springsteen, Arthur W.
1991-08-01
The Multi-angle Imaging SpectroRadiometer (MISR) plans to use deployable diffuse reflectance panels to provide periodic radiometric calibrations of its nine cameras while in-flight. Near-Lambertian reflectance characteristics are desirable to facilitate flat-field camera intercomparisons. Also required is panel spatial and spectral uniformity, and stability with time. Spectralon, a commercially available polytetrafluoroethylene (PTFE) compound, has been baselined in the MISR design. To assess the suitability of this material, a series of degradation tests were planned and implemented. These included UV vacuum exposure and proton bombardment tests which simulated the exposure levels to be encountered during the mission life. Proton levels are now considered too low to be of concern, but UV vacuum tests demonstrate sensitivity to material contamination. Material investigations have concluded that hydrocarbons are present in the bulk of the material, and that plastic packaging materials can introduce additional surface-layer contamination. It is found however, that these unwanted elements can be eliminated through vacuum pumping at elevated temperatures. Exposure to a UV source, while in vacuum, is again planned for a set of targets which have been vacuum baked. This will assess the stability of the pure PTFE form.
Coupled effects in stability analysis of pile–slope systems
Jinoh Won; Kwangho You; Sangseom Jeong; Sooil Kim
2005-01-01
A numerical comparison of predictions by limit equilibrium analysis and 3D numerical analysis is presented for a slope–pile system. Special attention is given to the coupled analysis based on the explicit-finite-difference code, FLAC 3D. To this end, an internal routine (FISH) was developed to calculate a factor of safety for a pile-reinforced slope according to a shear strength reduction technique.
Enterprise modeling and analysis: an enterprise modeling and analysis toolkit
Dursun Delen; Perakath C. Benjamin
2000-01-01
A fully integrated modeling and analysis toolkit, which facilitates multi-perspective knowledge capturing, sharing and reusing, is necessary for today's enterprises to meet the challenges of the ever more competitive global marketplace. In this paper we present a suite of software tools, designed and developed by Knowledge Based Systems, Inc., that can generate integrated solutions to complicated enterprise analysis including business
Chung, M.; Miskovsky, N.M.; Cutler, P.H.; Feuchtwang, T.E.; Kazes, E.
1987-11-01
An exact mathematical treatment of the problem of an electrically stressed fluid from zero field to the onset of instability gives rise to the nonlinear electrohydrodynamic equations which, in general, are not amenable to analytic solution. To make the problem more tractable, one considers two limiting regimes, the electrohydrostatic (EHS) and the electrohydrodynamic (EHD) limits. In the EHS case, the fields and the velocities are assumed to be small so that quasistatic equilibrium exists and the fluid surface is essentially at rest. In this paper we consider the electrohydrostatic analysis of the equilibrium shape and stability of the electrically stressed fluids. The current work reintroduces the EHS stability criterion due to Zeleny, as well as a new set of equations and numerical procedure for analyzing the stability of an axially symmetric fluid with an arbitrary shaped surface. These are contrasted with a stability criterion, introduced by Taylor, which it is argued, is only an equilibrium condition and not a proper criterion for analyzing the general stability of electrified fluids. The Taylor and Zeleny criteria are applied to fluid sources modeled as simple coordinate surfaces, such as the cone, the cusp, and the hyperboloid. These results lead to a new physical interpretation of the onset of fluid instability in the EHS limit. A set of partial differential equations is derived, whose solution describes the equilibrium shape of a conducting fluid as a function of the applied electric field. Numerical results are presented for the evolution of the equilibrium shapes of several liquid metals as a function of the applied voltage. Values of the critical or breakdown voltage are obtained from these results and found to be in good agreement with experiment. Finally, the EHS analysis indicates that a realistic and accurate treatment of the onset of instability requires fluid flow in a dynamical model.
NASA Astrophysics Data System (ADS)
Vanacker, Veerle; Vanderschaeghe, Michiel; Govers, Gerard; Willems, Edith; Poesen, Jean; Deckers, Jozef; De Bievre, Bert
2003-06-01
In the Ecuadorian Andes, episodic slope movements comprising shallow rotational and translational slides and rapid flows of debris and soil material are common. Consequently, not only considerable financial costs are experienced, but also major ecological and environmental problems arise in a larger geographical area. Sediment production by slope movement on hillslopes directly affects sediment transport and deposition in downstream rivers and dams and morphological changes in the stream channels. In developing countries world-wide, slope movement hazards are growing: increasing population pressure and economic development force more people to move to potentially hazardous areas, which are less suitable for agriculture and rangelands. This paper describes the methods used to determine the controlling factors of slope failure and to build upon the results of the statistical analysis a process-based slope stability model, which includes a dynamic soil wetness index using a simple subsurface flow model. The model provides a time-varying estimate of slope movement susceptibility, by linking land-use data with spatially varying hydrologic (soil conductivity, evapotranspiration, soil wetness) and soil strength properties. The slope stability model was applied to a high Andean watershed (Gordeleg Catchment, 250 ha, southern Ecuadorian Andes) and was validated by calculating the association coefficients between the slope movement susceptibility map of 2000 and the spatial pattern of active slope movements, as measured in the field with GPS. The proposed methodology allows assessment of the effects of past and future land-use change on slope stability. A realistic deforestation scenario was presented: past land-use change includes a gradual fragmentation and clear cut of the secondary forests, as observed over the last four decades (1963-2000), future land-use change is simulated based on a binary logistic deforestation model, whereby it was assumed that future land-use change would continue at the same rate and style as over the last 37 years (1963-2000).