Stability analysis of an autocatalytic protein model
NASA Astrophysics Data System (ADS)
Lee, Julian
2016-05-01
A self-regulatory genetic circuit, where a protein acts as a positive regulator of its own production, is known to be the simplest biological network with a positive feedback loop. Although at least three components—DNA, RNA, and the protein—are required to form such a circuit, stability analysis of the fixed points of this self-regulatory circuit has been performed only after reducing the system to a two-component system, either by assuming a fast equilibration of the DNA component or by removing the RNA component. Here, stability of the fixed points of the three-component positive feedback loop is analyzed by obtaining eigenvalues of the full three-dimensional Hessian matrix. In addition to rigorously identifying the stable fixed points and saddle points, detailed information about the system can be obtained, such as the existence of complex eigenvalues near a fixed point.
Stability Analysis for Car Following Model Based on Control Theory
NASA Astrophysics Data System (ADS)
Meng, Xiang-Pei; Li, Zhi-Peng; Ge, Hong-Xia
2014-05-01
Stability analysis is one of the key issues in car-following theory. The stability analysis with Lyapunov function for the two velocity difference car-following model (for short, TVDM) is conducted and the control method to suppress traffic congestion is introduced. Numerical simulations are given and results are consistent with the theoretical analysis.
Surrogate models for efficient stability analysis of brake systems
NASA Astrophysics Data System (ADS)
Nechak, Lyes; Gillot, Frédéric; Besset, Sébastien; Sinou, Jean-Jacques
2015-07-01
This study assesses capacities of the global sensitivity analysis combined together with the kriging formalism to be useful in the robust stability analysis of brake systems, which is too costly when performed with the classical complex eigenvalues analysis (CEA) based on finite element models (FEMs). By considering a simplified brake system, the global sensitivity analysis is first shown very helpful for understanding the effects of design parameters on the brake system's stability. This is allowed by the so-called Sobol indices which discriminate design parameters with respect to their influence on the stability. Consequently, only uncertainty of influent parameters is taken into account in the following step, namely, the surrogate modelling based on kriging. The latter is then demonstrated to be an interesting alternative to FEMs since it allowed, with a lower cost, an accurate estimation of the system's proportions of instability corresponding to the influent parameters.
Discrete time modeling and stability analysis of TCP Vegas
NASA Astrophysics Data System (ADS)
You, Byungyong; Koo, Kyungmo; Lee, Jin S.
2007-12-01
This paper presents an analysis method for TCP Vegas network model with single link and single source. Some papers showed global stability of several network models, but those models are not a dual problem where dynamics both exist in sources and links such as TCP Vegas. Other papers studied TCP Vegas as a dual problem, but it did not fully derive an asymptotic stability region. Therefore we analyze TCP Vegas with Jury's criterion which is necessary and sufficient condition. So we use state space model in discrete time and by using Jury's criterion, we could find an asymptotic stability region of TCP Vegas network model. This result is verified by ns-2 simulation. And by comparing with other results, we could know our method performed well.
[Analysis of the stability and adaptability of near infrared spectra qualitative analysis model].
Cao, Wu; Li, Wei-jun; Wang, Ping; Zhang, Li-ping
2014-06-01
The stability and adaptability of model of near infrared spectra qualitative analysis were studied. Method of separate modeling can significantly improve the stability and adaptability of model; but its ability of improving adaptability of model is limited. Method of joint modeling can not only improve the adaptability of the model, but also the stability of model, at the same time, compared to separate modeling, the method can shorten the modeling time, reduce the modeling workload; extend the term of validity of model, and improve the modeling efficiency. The experiment of model adaptability shows that, the correct recognition rate of separate modeling method is relatively low, which can not meet the requirements of application, and joint modeling method can reach the correct recognition rate of 90%, and significantly enhances the recognition effect. The experiment of model stability shows that, the identification results of model by joint modeling are better than the model by separate modeling, and has good application value. PMID:25358155
Stability analysis of within-host parasite models with delays.
Iggidr, Abderrahman; Mbang, Joseph; Sallet, Gauthier
2007-09-01
We provide a global analysis of systems of within-host parasitic infections. The systems studied have parallel classes of different length of latently infected target cells. These systems can also be thought as systems arising from within-host parasitic systems with distributed continuous delays. We compute the basic reproduction ratio R0 for the systems under consideration. If R0< or =1 the parasite is cleared, if R0>1 and if a sufficient condition is satisfied we conclude to the global asymptotic stability (GAS) of the endemic equilibrium. For some generic class of models this condition reduces to R0>1. These results make possible to revisit some parasitic models including intracellular delays and to study their global stability. PMID:17383688
Lattice Boltzmann equation linear stability analysis: Thermal and athermal models
NASA Astrophysics Data System (ADS)
Siebert, D. N.; Hegele, L. A., Jr.; Philippi, P. C.
2008-02-01
Although several thermal lattice Boltzmann models have been proposed, this method has not yet been shown to be able to describe nonisothermal fully compressible flows in a satisfactory manner, mostly due to the presence of important deviations from the advection-diffusion macroscopic equations and also due to numerical instabilities. In this context, this paper presents a linear stability analysis for some lattice Boltzmann models that were recently derived as discrete forms of the continuous Boltzmann equation [P. C. Philippi, L. A. Hegele, Jr., L. O. E. dos Santos, and R. Surmas, Phys. Rev. E 63, 056702 (2006)], in order to investigate the sources of instability and to find, for each model, the upper and lower limits for the macroscopic variables, between which it is possible to ensure a stable behavior. The results for two-dimensional (2D) lattices with 9, 17, 25, and 37 velocities indicate that increasing the order of approximation of the lattice Boltzmann equation enhances stability. Results are also presented for an athermal 2D nine-velocity model, the accuracy of which has been improved with respect to the standard D2Q9 model, by adding third-order terms in the lattice Boltzmann equation.
A Coupled Aeroelastic Model for Launch Vehicle Stability Analysis
NASA Technical Reports Server (NTRS)
Orr, Jeb S.
2010-01-01
A technique for incorporating distributed aerodynamic normal forces and aeroelastic coupling effects into a stability analysis model of a launch vehicle is presented. The formulation augments the linear state-space launch vehicle plant dynamics that are compactly derived as a system of coupled linear differential equations representing small angular and translational perturbations of the rigid body, nozzle, and sloshing propellant coupled with normal vibration of a set of orthogonal modes. The interaction of generalized forces due to aeroelastic coupling and thrust can be expressed as a set of augmenting non-diagonal stiffness and damping matrices in modal coordinates with no penalty on system order. While the eigenvalues of the structural response in the presence of thrust and aeroelastic forcing can be predicted at a given flight condition independent of the remaining degrees of freedom, the coupled model provides confidence in closed-loop stability in the presence of rigid-body, slosh, and actuator dynamics. Simulation results are presented that characterize the coupled dynamic response of the Ares I launch vehicle and the impact of aeroelasticity on control system stability margins.
Models and Stability Analysis of Boiling Water Reactors
John Dorning
2002-04-15
We have studied the nuclear-coupled thermal-hydraulic stability of boiling water reactors (BWRs) using a model that includes: space-time modal neutron kinetics based on spatial w-modes; single- and two-phase flow in parallel boiling channels; fuel rod heat conduction dynamics; and a simple model of the recirculation loop. The BR model is represented by a set of time-dependent nonlinear ordinary differential equations, and is studied as a dynamical system using the modern bifurcation theory and nonlinear dynamical systems analysis. We first determine the stability boundary (SB) - or Hopf bifurcation set- in the most relevant parameter plane, the inlet-subcooling-number/external-pressure-drop plane, for a fixed control rod induced external reactivity equal to the 100% rod line value; then we transform the SB to the practical power-flow map used by BWR operating engineers and regulatory agencies. Using this SB, we show that the normal operating point at 100% power is very stable, that stability of points on the 100% rod line decreases as the flow rate is reduced, and that operating points in the low-flow/high-power region are least stable. We also determine the SB that results when the modal kinetics is replaced by simple point reactor kinetics, and we thereby show that the first harmonic mode does not have a significant effect on the SB. However, we later show that it nevertheless has a significant effect on stability because it affects the basin of attraction of stable operating points. Using numerical simulations we show that, in the important low-flow/high-power region, the Hopf bifurcation that occurs as the SB is crossed is subcritical; hence, growing oscillations can result following small finite perturbations of stable steady-states on the 100% rod line at points in the low-flow/high-power region. Numerical simulations are also performed to calculate the decay ratios (DRs) and frequencies of oscillations for various points on the 100% rod line. It is determined that the U.S. NRC requirement of DR is not rigorously satisfied in the low-flow/high-power region; hence, this region should be avoided during normal startup and shutdown operations. The frequency of oscillation is shown to decrease as the flow rate is reduced. Moreover, the simulation frequency of 0.5Hz determined in the low-flow/high-power region is consistent with those observed during actual instability incidents. Additional numerical simulations show that in the low-flow/high-power region, for the same initial conditions, the use of point kinetics leads to damped oscillations, whereas the model that includes the modal neutron kinetics equations results in growing nonlinear oscillations.
Stability analysis of the Euler discretization for SIR epidemic model
Suryanto, Agus
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.
Slope Stability Analysis Using Radial Slices: A Mathematical Model
NASA Astrophysics Data System (ADS)
Kumar, Gyan Prakash; Das, Adarsha; Rai, Rajesh; Jaiswal, Ashok
2015-10-01
In this paper, a mathematical model has been formulated for calculating the factor of safety of a slope. Corresponding computer code has also been developed. Limit equilibrium method (moment equilibrium) has been adopted for calculating the net resulting driving and resisting forces. The probable slip circle region has been divided into radial slices for the simulation process. In this approach, the inter-slice shear forces are zero. Thus, the calculation process becomes simpler as compared to that with vertical slices. The slope stability analyses were done. Validation of the present program was done with existing limit equilibrium based methods. Various models were prepared and analysed with varying geometry and soil strength parameters. These models were also analysed with other limit equilibrium methods like Bishop, Janbu and Spencer method. The results were found to be in agreement with the results of other limit equilibrium methods for the same dump soil properties and slope parameters.
Stability analysis of two-dimensional models of three-dimensional convection
Greenside, H.S.; Cross, M.C.
1984-12-01
Analytical and numerical methods are used to study the linear stability of spatially periodic solutions for various two-dimensional equations which model thermal convection in fluids. This analysis suggests new model equations that will be useful for investigating questions such as wave number selection, pattern formation, and the onset of turbulence in large aspect ratio Rayleigh-Benard systems. In particular, we construct a nonrelaxational model that has stability boundaries similar to those calculated for intermediate Prandtl number fluids.
Stability analysis of two-dimensional models of three-dimensional convection
Greenside, H.S.; Cross, M.C.
1985-04-01
Analytical and numerical methods are used to study the linear stability of spatially periodic solutions for various two-dimensional equations which model thermal convection in fluids. This analysis suggests new model equations that will be useful for investigating questions such as wave-number selection, pattern formation, and the onset of turbulence in large-aspect-ratio Rayleigh-Benard systems. In particular, we construct a nonrelaxational model that has stability boundaries similar to those calculated for intermediate Prandtl-number fluids.
Stability analysis of a stochastic logistic model with infinite delay
NASA Astrophysics Data System (ADS)
Liu, Meng; Fan, Dejun; Wang, Ke
2013-09-01
This report is concerned with a stochastic logistic equation with infinite delay. We establish the sufficient conditions for global asymptotical stability of the zero solution and the positive equilibrium. Some classical results are improved and extended. Several numerical simulations are introduced to illustrate the main results.
Floquet stability analysis of the longitudinal dynamics of two hovering model insects.
Wu, Jiang Hao; Sun, Mao
2012-09-01
Because of the periodically varying aerodynamic and inertial forces of the flapping wings, a hovering or constant-speed flying insect is a cyclically forcing system, and, generally, the flight is not in a fixed-point equilibrium, but in a cyclic-motion equilibrium. Current stability theory of insect flight is based on the averaged model and treats the flight as a fixed-point equilibrium. In the present study, we treated the flight as a cyclic-motion equilibrium and used the Floquet theory to analyse the longitudinal stability of insect flight. Two hovering model insects were considered-a dronefly and a hawkmoth. The former had relatively high wingbeat frequency and small wing-mass to body-mass ratio, and hence very small amplitude of body oscillation; while the latter had relatively low wingbeat frequency and large wing-mass to body-mass ratio, and hence relatively large amplitude of body oscillation. For comparison, analysis using the averaged-model theory (fixed-point stability analysis) was also made. Results of both the cyclic-motion stability analysis and the fixed-point stability analysis were tested by numerical simulation using complete equations of motion coupled with the Navier-Stokes equations. The Floquet theory (cyclic-motion stability analysis) agreed well with the simulation for both the model dronefly and the model hawkmoth; but the averaged-model theory gave good results only for the dronefly. Thus, for an insect with relatively large body oscillation at wingbeat frequency, cyclic-motion stability analysis is required, and for their control analysis, the existing well-developed control theories for systems of fixed-point equilibrium are no longer applicable and new methods that take the cyclic variation of the flight dynamics into account are needed. PMID:22491980
NASA Astrophysics Data System (ADS)
Li, Zhipeng; Li, Wenzhong; Xu, Shangzhi; Qian, Yeqing
2015-02-01
This paper presents an extended intelligent driver traffic flow model, in which the power of the considered vehicle is strengthened in proportion to that of the immediately preceding vehicle. We analyze the stability against a small perturbation by use of the linear stability method for the proposed traffic flow model on a single lane under open boundary condition, with the finding that the traffic flow stability can be improved by increasing the proportion of the direct power cooperation of the preceding vehicle. The participation of forward power cooperation can help to stabilize the traffic flow and suppress the traffic jams. In addition, the simulations under open boundary single lane are conducted to validate the correctness on theoretical deduction, which shows that numerical results in large-wave and short-wave stability are in good agreement with those of theoretical analysis.
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.
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
Stability and Bifurcation Analysis of a Three-Species Food Chain Model with Delay
NASA Astrophysics Data System (ADS)
Pal, Nikhil; Samanta, Sudip; Biswas, Santanu; Alquran, Marwan; Al-Khaled, Kamel; Chattopadhyay, Joydev
In the present paper, we study the effect of gestation delay on a tri-trophic food chain model with Holling type-II functional response. The essential mathematical features of the proposed model are analyzed with the help of equilibrium analysis, stability analysis, and bifurcation theory. Considering time-delay as the bifurcation parameter, the Hopf-bifurcation analysis is carried out around the coexisting equilibrium. The direction of Hopf-bifurcation and the stability of the bifurcating periodic solutions are determined by applying the normal form theory and center manifold theorem. We observe that if the magnitude of the delay is increased, the system loses stability and shows limit cycle oscillations through Hopf-bifurcation. The system also shows the chaotic dynamics via period-doubling bifurcation for further enhancement of time-delay. Our analytical findings are illustrated through numerical simulations.
NASA Astrophysics Data System (ADS)
Andronova, Nataliia G.; Schlesinger, Michael E.
1992-04-01
The 'cause-and-effect analysis' (CEA) technique is applied to investigate the stability of mathematical models of geophysical phenomena. It is shown that the ith coefficient of p(lambda) is equal to -PL sup (i), the ith order loop effect of the graph analog of matrix B - I, where I is the identity matrix. The classical conditions for stability for both discrete process (DP) and continuous process (CP) systems are then reformulated in terms of the PL sup (i) determined from the graph analog of the system. The use of the result graph analog stability conditions is illustrated by application to two CP systems, the Chapman photochemical cycle and an energy balance climate model, and to a DP system, a finite-differenced differential equation. CEA stability analysis elucidates the interactions among a system's internal variables and thus determines the cause of an instability and facilitates modification of the system to make it stable.
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.
Perturbation and Stability Analysis of the Multi-Anticipative Intelligent Driver Model
NASA Astrophysics Data System (ADS)
Chen, Xi-Qun; Xie, Wei-Jun; Shi, Jing; Shi, Qi-Xin
This paper discusses three kinds of IDM car-following models that consider both the multi-anticipative behaviors and the reaction delays of drivers. Here, the multi-anticipation comes from two ways: (1) the driver is capable of evaluating the dynamics of several preceding vehicles, and (2) the autonomous vehicles can obtain the velocity and distance information of several preceding vehicles via inter-vehicle communications. In this paper, we study the stability of homogeneous traffic flow. The linear stability analysis indicates that the stable region will generally be enlarged by the multi-anticipative behaviors and reduced by the reaction delays. The temporal amplification and the spatial divergence of velocities for local perturbation are also studied, where the results further prove this conclusion. Simulation results also show that the multi-anticipative behaviors near the bottleneck will lead to a quicker backwards propagation of oscillations.
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.
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)
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.
Global stability analysis of an SIR epidemic model with demographics and time delay on networks
NASA Astrophysics Data System (ADS)
Wang, Jianrong; Wang, Jianping; Liu, Maoxing; Li, Youwen
2014-09-01
In this paper, a susceptible-infected-recovery (SIR) epidemic model is governed with demographics and time delay on networks. Firstly, the basic reproduction number R0 is derived dependent on birth rate, death rate, recovery rate and transmission rate. The disease-free equilibrium of the model is stable when R0≤1 and unstable when R0>1. Secondly, based on a Jacobian matrix calculated along with the disease-free equilibrium, we find that the system does not occur Hopf branch under the disease-free equilibrium. Thirdly, the global asymptotic stability of a disease-free equilibrium and a unique endemic equilibrium are proved by structuring two Lyapunov functions. Finally, numerical simulations are performed to illustrate the analysis results.
Stability analysis of carbon nanotube probes for an atomic force microscope via a continuum model
NASA Astrophysics Data System (ADS)
Wang, Q.; Varadan, V. K.
2005-12-01
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 complete mechanics analysis on the global and local buckling of both single-walled nanotubes (SWNT) and double-walled nanotubes (DWNT) via an elastic beam model. A cantilever beam model under a tilted compressive load for possible global buckling or local buckling instability of the CNT probe is employed, since a CNT probe interacts with the surface of a probe at an angle relative to the surface normal. A discrete beam model is employed to propose a mechanism of local buckling instability for beam structures. Based on this model, the development of kink instability of CNT is revealed and studied. A benchmark study on the size effect of the CNT on the critical axial force is carefully made for SWNT and DWNT probes. In addition, the global buckling load of CNT under horizontal axial force can be recovered from the current results on local instability by setting a zero tilted angle, and the predicted results are compared with those from a model considering the van der Waals effect to demonstrate the great feasibility of the proposed local instability model for global buckling analysis use. It is hoped this research may provide a benchmark study on a practical and novel design for effective AFM probes with CNT.
Stability analysis, non-linear pulsations and mass loss of models for 55 Cygni (HD 198478)
NASA Astrophysics Data System (ADS)
Yadav, Abhay Pratap; Glatzel, Wolfgang
2016-04-01
55 Cygni is a variable supergiant. Recent observational studies revealed that this star pulsates in pressure, gravity and strange modes. The pulsations seem to be associated with episodes of mass loss. In this paper we present a theoretical study of stellar models with parameters close to that of 55 Cygni. A linear non-adiabatic stability analysis with respect to radial perturbations is performed and the evolution of instabilities into the non-linear regime is followed by numerical simulation. Our study indicates that the mass of 55 Cygni lies below 28 M⊙. As the final consequence of the instabilities the non-linear simulations revealed finite amplitude pulsations with periods consistent with the observations. The non-linear results also indicate a connection between pulsations and mass loss and allow for an estimate of the mean mass-loss rate. It is consistent with the observed values.
The Stability Analysis for an Extended Car Following Model Based on Control Theory
NASA Astrophysics Data System (ADS)
Ge, Hong-Xia; Meng, Xiang-Pei; Zhu, Ke-Qiang; Cheng, Rong-Jun
2014-08-01
A new method is proposed to study the stability of the car-following model considering traffic interruption probability. The stability condition for the extended car-following model is obtained by using the Lyapunov function and the condition for no traffic jam is also given based on the control theory. Numerical simulations are conducted to demonstrate and verify the analytical results. Moreover, numerical simulations show that the traffic interruption probability has an influence on driving behavior and confirm the effectiveness of the method on the stability of traffic flow.
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…
The improvement of OPC accuracy and stability by the model parameters' analysis and optimization
NASA Astrophysics Data System (ADS)
Chung, No-Young; Choi, Woon-Hyuk; Lee, Sung-Ho; Kim, Sung-Il; Lee, Sun-Yong
2007-10-01
The OPC model is very critical in the sub 45nm device because the Critical Dimension Uniformity (CDU) is so tight to meet the device performance and the process window latitude for the production level. The OPC model is generally composed of an optical model and a resist model. Each of them has physical terms to be calculated without any wafer data and empirical terms to be fitted with real wafer data to make the optical modeling and the resist modeling. Empirical terms are usually related to the OPC accuracy, but are likely to be overestimated with the wafer data and so those terms can deteriorate OPC stability in case of being overestimated by a small cost function. Several physical terms have been used with ideal value in the optical property and even weren't be considered because those parameters didn't give a critical impact on the OPC accuracy, but these parameters become necessary to be applied to the OPC modeling at the low k1 process. Currently, real optic parameter instead of ideal optical parameter like the laser bandwidth, source map, pupil polarization including the phase and intensity difference start to be measured and those real measured value are used for the OPC modeling. These measured values can improve the model accuracy and stability. In the other hand these parameters can make the OPC model to overcorrect the process proximity errors without careful handling. The laser bandwidth, source map, pupil polarization, and focus centering for the optical modeling are analyzed and the sample data weight scheme and resist model terms are investigated, too. The image blurring by actual laser bandwidth in the exposure system is modeled and the modeling result shows that the extraction of the 2D patterns is necessary to get a reasonable result due to the 2D patterns' measurement noise in the SEM. The source map data from the exposure machine shows lots of horizontal and vertical intensity difference and this phenomenon must come from the measurement noise because this huge intensity difference can't be caused by the scanner system with respect to the X-Y intensity difference specification in the scanner. Therefore this source map should be well organized for the OPC modeling and a manipulated source map improves the horizontal and vertical mask bias and even OPC convergence. The focus parameter which is critical for the process window OPC and ORC should be matched to the tilted Bossung plot which is caused by uncorrectable aberration to predict the CD change in the through focus with a new devised method. Pupil polarization data can be applied into the OPC modeling and this parameter is also used for the unpolarized source and the polarized source and specially this parameter helps Apodization loss to be 0 and is evaluated for the effect into the modeling. With the analysis and optimization about the model parameters the robust model is achieved in the sub 45nm device node.
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.
Zhang, Zhaoyan; Neubauer, Juergen; Berry, David A
2007-10-01
In an investigation of phonation onset, a linear stability analysis was performed on a two-dimensional, aeroelastic, continuum model of phonation. The model consisted of a vocal fold-shaped constriction situated in a rigid pipe coupled to a potential flow which separated at the superior edge of the vocal fold. The vocal fold constriction was modeled as a plane-strain linear elastic layer. The dominant eigenvalues and eigenmodes of the fluid-structure-interaction system were investigated as a function of glottal airflow. To investigate specific aerodynamic mechanisms of phonation onset, individual components of the glottal airflow (e.g., flow-induced stiffness, inertia, and damping) were systematically added to the driving force. The investigations suggested that flow-induced stiffness was the primary mechanism of phonation onset, involving the synchronization of two structural eigenmodes. Only under conditions of negligible structural damping and a restricted set of vocal fold geometries did flow-induced damping become the primary mechanism of phonation onset. However, for moderate to high structural damping and a more generalized set of vocal fold geometries, flow-induced stiffness remained the primary mechanism of phonation onset. PMID:17902864
Linear stability analysis of self-excited vibrations in drilling using an infinite dimensional model
NASA Astrophysics Data System (ADS)
Aarsnes, Ulf Jakob F.; Aamo, Ole Morten
2016-01-01
This paper deals with predicting the occurrence of self-excited vibrations during drilling. Previous work postulates that these are due to the coupling between the distributed drill string system and the regenerative effect in the bit-rock interaction law. We use a previously developed distributed model and the linearized bit-rock interaction law to derive a graphical condition for stability based on the Nyquist stability criterion.
Monte Carlo analysis of critical phenomenon of the Ising model on memory stabilizer structures
Viteri, C. Ricardo; Tomita, Yu; Brown, Kenneth R.
2009-10-15
We calculate the critical temperature of the Ising model on a set of graphs representing a concatenated three-bit error-correction code. The graphs are derived from the stabilizer formalism used in quantum error correction. The stabilizer for a subspace is defined as the group of Pauli operators whose eigenvalues are +1 on the subspace. The group can be generated by a subset of operators in the stabilizer, and the choice of generators determines the structure of the graph. The Wolff algorithm, together with the histogram method and finite-size scaling, is used to calculate both the critical temperature and the critical exponents of each structure. The simulations show that the choice of stabilizer generators, both the number and the geometry, has a large effect on the critical temperature.
Tailings dams stability analysis using numerical modelling of geotechnical and geophysical data
NASA Astrophysics Data System (ADS)
Mihai, S.; Zlagnean, M.; Oancea, I.; Petrescu, A.
2009-04-01
Methods for monitoring seepage and detecting internal erosion are essential for the safety evaluation of embankment dams. Internal erosion is one of the major reasons for embankment dam failures, and there are thousands of large tailings dams and waste-rock dumps in the world that may pe considered as hotspots for environmental impact. In this research the geophysical survey works were performed on Cetatuia 2 tailings dam. Electrical resistivity imaging (ERI) method was able to detect spatially anomalous zones inside the embankment dam. These anomalies are the results of internal erosion phenomena which may progressing inside the dam and is difficult to detect by conventional methods. Data aquired by geophysical survey together with their interpretations were used in the numerical model for slope stability assessment. The final results show us the structural weakness induced by the presence of internal erosion elements especially for seismic loading case. This research methodology may be also available for tailings dam monitoring purposes. Electrical Rezistivity Imaging (ERI) was performed on Cetatuia 2 dam at the Uranium Milling Plant Feldioara, in order to map areas with lateral and vertical changes in resistivity. The electrodes are connected to an automated computer operated switch box that selects the 4 electrodes to be used. A computer controls the switch box and the measuring device, and runs a program that selects the electrodes, makes the measurement, and stores the measurement. For inversion processing procedures was used Res2Din software. The measured resistivity were plotted by the pseudo section contouring method. There are five resistivity pseudosections obtained from the Cetatuia 2 tailings dam during the october 2007 measurements. Four transversal profiles trans1 to trans4 are perpendicular to the berms and the longitudinal one long1 is placed along dam's crest. The high resistivities near the berms surfaces corresponds to unsaturated fill materials and the low resistivities near the crest correspond to water saturated material. The resistivities values greater then 80 ohm.m may be explained by some error obtained for that inversion model. Profiles trans3 and trans4 were measured on perpendicular directions to berm alignment and show two distinct zones. The upward low resistivities zone correspond to water saturated materials especially from the compacted clay dam's core and the downward high resistivities zone belongs to unsaturated fill materials. The boundary between high and low resistivity at the depth of about 5 to 7 meters shows the groundwater level. The continuation of the high resistivity zones towards the end of the profile trans3, which is different from other profiles is probably due to the presence of dry coarse materials in shallow depth correspondingly to sandy clay. The sand fractions from the clay matrix may be affected by internal erosional phenomena, due to seepage currents that overpassed the material critical gradient. In this case the relative high resistivities values were considered as a presumptive erosional pattern. This profile was considered for the slope stability finite element modelling. The profile long1 which is placed along dam's crest is the longest profiles and extends up to nearly 420 m. The boundary between high and low resistivity at the depth of about 4 to 8 meters shows the groundwater across the dam core. The central part of the profile (about meter 200) shows the same relative high resistivities that occurred on transversal profile trans3. Resistivity data was used for building the 3D electrical resistivity model. The water saturated materials have locations very close to dam's crest (resistivity values usually lower then 10 ohm.m) and on both dam's arms. The groundwater levels were confirmed by the piezometric measurements. Electrical Rezistivity Imaging method had the possibility to show the most important disturbant elements that in certain conditions may weak the dam's state of safety. This study considered the SSR (Shear Strength Reduction) technique for slope stability numerical modelling. In the SSR finite element technique, elasto-plastic strength is assumed for dam's materials and shear strengths are progressively reduced until collapse occurs. Numerical modelling was performed on the most critical profile choosed through analysis of geophysical and geotechnical informational volume achieved by insitu or in laboratory tests. Finite element analysis were considered in two situations: first, before geophysical investigations and second considering the whole informational of data achieved. Both situations were analysed in static and pseudo-static conditions. The factor of safety before geophysical investigations is high enough to describe a stable state of stability even for the seismic load. The total displacement distributions were modified by the presence of internal erosional element giving a high state of instability, especially for the pseudo-static case. These analysis using the finite element method prove the importance of structural disturbance elements that may occure inside the dam body produced by internal erosional processes.
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)
Zhao, Xiaomei; Orosz, Gábor
2014-05-01
In day-to-day traffic assignment problems travelers’ past experiences have important impact on their cost prediction which influences their route choice and consequently the arising flow patterns in the network. Many travelers execute the same trip in every few days, not daily, which leads to time delays in the system. In this paper, we propose a nonlinear, discrete-time model with driver experience delay. The linear stability of the stochastic user equilibrium is analyzed by studying the eigenvalues of the Jacobian matrix of the system while the nonlinear oscillations arising at the bifurcations are investigated by normal form calculations, numerical continuation and simulation. The methods are demonstrated on a two-route example. By applying rigorous analysis we show that the linearly unstable parameter domain as well as the period of arising oscillations increase with the delay. Moreover, delays and nonlinearities result in an extended domain of bistability where the stochastic user equilibrium coexists with stable and unstable oscillations. This study explains the influence of initial conditions on the dynamics of transportation networks and may provide guidance for network design and management.
Corrado, Cesare; Lassoued, Jamila; Mahjoub, Moncef; Zemzemi, Njib
2016-02-01
In this paper we show the numerical stability of the Proper Orthogonal Decomposition (POD) reduced order method used in cardiac electrophysiology applications. The difficulty of proving the stability comes from the fact that we are interested in the bidomain model, which is a system of degenerate parabolic equations coupled to a system of ODEs representing the cell membrane electrical activity. The proof of the stability of this method is based on a priori estimates controlling the gap between the reduced order solution and the Galerkin finite element one. We present some numerical simulations confirming the theoretical results. We also combine the POD method with a time splitting scheme allowing a faster solving of the bidomain problem and show numerical results. Finally, we conduct numerical simulation in 2D illustrating the stability of the POD method in its sensitivity to the ionic model parameters. We also perform 3D simulation using a massively parallel code. We show the computational gain using the POD reduced order model. We also show that this method has a better scalability than the full finite element method. PMID:26723278
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.
Linear stability analysis of first-order delayed car-following models on a ring
NASA Astrophysics Data System (ADS)
Lassarre, Sylvain; Roussignol, Michel; Tordeux, Antoine
2012-09-01
The evolution of a line of vehicles on a ring is modeled by means of first-order car-following models. Three generic models describe the speed of a vehicle as a function of the spacing ahead and the speed of the predecessor. The first model is a basic one with no delay. The second is a delayed car-following model with a strictly positive parameter for the driver and vehicle reaction time. The last model includes a reaction time parameter with an anticipation process by which the delayed position of the predecessor is estimated. Explicit conditions for the linear stability of homogeneous configurations are calculated for each model. Two methods of calculus are compared: an exact one via Hopf bifurcations and an approximation by second-order models. The conditions describe stable areas for the parameters of the models that we interpret. The results notably show that the impact of the reaction time on the stability can be palliated by the anticipation process.
NASA Astrophysics Data System (ADS)
Chen, H. M.; Zhao, Z. Y.; Choo, L. Q.; Sun, J. P.
2016-02-01
Rock cavern stability has a close relationship with the uncertain geological parameters, such as the in situ stress, the joint configurations, and the joint mechanical properties. Therefore, the stability of the rock cavern should be studied with variable geological conditions. In this paper, the coupled hydro-mechanical model, which is under the framework of the discontinuous deformation analysis, is developed to study the underground cavern stability when considering the hydraulic pressure after excavation. Variable geological conditions are taken into account to study their impacts on the seepage rate and the cavern stability, including the in situ stress ratio, joint spacing, and joint dip angle. In addition, the two cases with static hydraulic pressure and without hydraulic pressure are also considered for the comparison. The numerical simulations demonstrate that the coupled approach can capture the cavern behavior better than the other two approaches without the coupling effects.
NASA Astrophysics Data System (ADS)
Hanasoge, Aravind M.
Vehicle-guideway interaction studies of Magnetically Levitated (Maglev) vehicles indicate that structural flexibility can adversely affect the overall stability and performance of such systems. This is one of the reasons why guideways are generally made very rigid. This in turn leads to increased cost of the overall system since guideway construction forms a significant portion of the overall cost. In this dissertation, the influence of structural flexibility on the stability of Electromagnetic Suspension (EMS) Maglev systems is studied. It is shown how inherently unstable and flexible structure EMS Maglev systems can achieve guaranteed stability by using collocated actuators and sensors, along with de-centralized Proportional plus Derivative (PD) controllers. These results are valid even in the presence of Track/Guideway flexibility. A detailed dynamic model is developed for the EMS Maglev demonstration system (Test Bogie) currently under research and development at Old Dominion University (ODU). This model incorporates structural dynamics with flexible modes of vibration, non-linear electrodynamics, feedback controllers, discrete time implementation, noise filters and disturbance inputs. This model is validated via real time experimental testing. The model thus validated is used for simulation case studies involving levitation and lateral disturbance, lateral control, and centralized control.
The beam delivery modeling and error sources analysis of beam stabilization system for lithography
NASA Astrophysics Data System (ADS)
Wang, Jun; Huang, Lihua; Hou, Liying; He, Guojun; Ren, Bingqiang; Zeng, Aijun; Huang, Huijie
2013-12-01
Beam stabilization system is one of the most important units for lithography, which can accomplish displacement and pointing detection and control and includes beam measurement unit(BMU) and beam steering unit(BSU). Our group has set up a beam stabilization system and verified preliminarily beam stabilization algorithm of precise control beam position and angle. In the article, we establish beam delivery mathematic model and analyze the system inherent error. This shows that the reason why image rotation effect arises at the output plane of beam stabilization is the fast steering mirror (FSM) rotation of BSU in the process of beam stabilization. Two FSMs rotation around 45o axis of FSM make the most contribution to image rotation which rotates 1.414 mrad as two FSMs rotation angle difference changes 1 mrad. It is found that error sources include three key points: FSM accuracy; measurement noise and beam translation by passing through of beam splitters changing as the ambient temperature changing. FSM accuracy leads to the maximum 13.2μm displacement error and 24.49μrad angle error. Measurement inaccuracy as a result of 5μm measurement noise results in the maximum 0.126mm displacement error and 57.2μrad angle error. Beam translation errors can be negligible if temperature is unchanged. We have achieved beam stability of about 15.5μrad for angle and 28μm for displacement (both 1σ) after correcting 2mm initial displacement deviation and 5mrad initial angle deviation with regard to the system rebuilt due to practical requirements.
Stability analysis of a phase-field model of gravity-driven unsaturated flow through porous media.
Cueto-Felgueroso, Luis; Juanes, Ruben
2009-03-01
The formation of preferential flow paths during infiltration of water into homogeneous, dry soil is an important phenomenon whose explanation and prediction have remained elusive under the standard theories of multiphase flow in porous media. We have recently proposed a macroscopic phase-field model of unsaturated flow in porous media, which explains why such fingering occurs [L. Cueto-Felgueroso and R. Juanes, Phys. Rev. Lett. 101, 244504 (2008)]. Here we present a linear stability analysis of the proposed model for constant-flux infiltration, which allows a quantitative description of the wetting front instability. The present analysis stresses the critical role of the initial water saturation and applied flux ratio in the asymptotic stability of the system, as well as in the transient growth of perturbations, which is consistent with the experimental evidence. The trends in the frequency and growth factor of the most unstable modes predicted by our analysis are also in quantitative agreement with experimental measurements. PMID:19392043
Stability analysis of ecomorphodynamic equations
NASA Astrophysics Data System (ADS)
Bärenbold, F.; Crouzy, B.; Perona, P.
2016-02-01
In order to shed light on the influence of riverbed vegetation on river morphodynamics, we perform a linear stability analysis on a minimal model of vegetation dynamics coupled with classical one- and two-dimensional Saint-Venant-Exner equations of morphodynamics. Vegetation is modeled as a density field of rigid, nonsubmerged cylinders and affects flow via a roughness change. Furthermore, vegetation is assumed to develop following a logistic dependence and may be uprooted by flow. First, we perform the stability analysis of the reduced one-dimensional framework. As a result of the competitive interaction between vegetation growth and removal through uprooting, we find a domain in the parameter space where originally straight rivers are unstable toward periodic longitudinal patterns. For realistic values of the sediment transport parameter, the dominant longitudinal wavelength is determined by the parameters of the vegetation model. Bed topography is found to adjust to the spatial pattern fixed by vegetation. Subsequently, the stability analysis is repeated for the two-dimensional framework, where the system may evolve toward alternate or multiple bars. On a fixed bed, we find instability toward alternate bars due to flow-vegetation interaction, but no multiple bars. Both alternate and multiple bars are present on a movable, vegetated bed. Finally, we find that the addition of vegetation to a previously unvegetated riverbed favors instability toward alternate bars and thus the development of a single course rather than braiding.
NASA Astrophysics Data System (ADS)
Alessi, Roberto; Pham, Kim
2016-02-01
This paper presents a variational framework for the three-dimensional macroscopic modelling of superelastic shape memory alloys in an isothermal setting. Phase transformation is accounted through a unique second order tensorial internal variable, acting as the transformation strain. Postulating the total strain energy density as the sum of a free energy and a dissipated energy, the model depends on two material scalar functions of the norm of the transformation strain and a material scalar constant. Appropriate calibration of these material functions allows to render a wide range of constitutive behaviours including stress-softening and stress-hardening. The quasi-static evolution problem of a domain is formulated in terms of two physical principles based on the total energy of the system: a stability criterion, which selects the local minima of the total energy, and an energy balance condition, which ensures the consistency of the evolution of the total energy with respect to the external loadings. The local phase transformation laws in terms of Kuhn-Tucker relations are deduced from the first-order stability condition and the energy balance condition. The response of the model is illustrated with a numerical traction-torsion test performed on a thin-walled cylinder. Evolutions of homogeneous states are given for proportional and non-proportional loadings. Influence of the stress-hardening/softening properties on the evolution of the transformation domain is emphasized. Finally, in view of an identification process, the issue of stability of homogeneous states in a multi-dimensional setting is answered based on the study of second-order derivative of the total energy. Explicit necessary and sufficient conditions of stability are provided.
Stability analysis of a multibody system model for coupled slosh-vehicle dynamics
NASA Astrophysics Data System (ADS)
Nichkawde, Chetan; Harish, P. M.; Ananthkrishnan, N.
2004-08-01
The coupled slosh-vehicle dynamics of a rigid body in planar atmospheric flight carrying a sloshing liquid is considered as a multibody system with the sloshing motion modelled as a simple pendulum. The coupled, non-linear equations for the four-degree-of-freedom multibody system are derived using the method of Lagrangian dynamics. Careful non-dimensionalization reveals two crucial parameters that determine the extent of coupling between the rigid body and slosh modes, and also two important frequency parameters. Using a two-parameter continuation method, critical combinations of these four parameters for which the coupled slosh-vehicle dynamics can become unstable are computed. Results are displayed in the form of neutral stability curves (stability boundaries) in parameter space, and an analytical expression incorporating the four parameters that represents the neutral stability curves is obtained. Reduced-order linearized models and key transfer functions are derived in an effort to understand the instability phenomenon. Physically, the sloshing motion is seen to induce a static instability, sometimes called tumbling, in the vehicle pitch dynamics, depending on the slosh mass fraction and the location of the slosh pendulum hinge point above the rigid vehicle center of mass.
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, α, β(0) and β(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 of a model gene network links aging, stress resistance, and negligible senescence
Kogan, Valeria; Molodtsov, Ivan; Menshikov, Leonid I.; Reis, Robert J. Shmookler; Fedichev, Peter
2015-01-01
Several animal species are considered to exhibit what is called negligible senescence, i.e. they do not show signs of functional decline or any increase of mortality with age. Recent studies in naked mole rat and long-lived sea urchins showed that these species do not alter their gene-expression profiles with age as much as other organisms do. This is consistent with exceptional endurance of naked mole rat tissues to various genotoxic stresses. We conjectured, therefore, that the lifelong transcriptional stability of an organism may be a key determinant of longevity. We analyzed the stability of a simple genetic-network model and found that under most common circumstances, such a gene network is inherently unstable. Over a time it undergoes an exponential accumulation of gene-regulation deviations leading to death. However, should the repair systems be sufficiently effective, the gene network can stabilize so that gene damage remains constrained along with mortality of the organism. We investigate the relationship between stress-resistance and aging and suggest that the unstable regime may provide a mathematical basis for the Gompertz “law” of aging in many species. At the same time, this model accounts for the apparently age-independent mortality observed in some exceptionally long-lived animals. PMID:26316217
Kogan, Valeria; Molodtsov, Ivan; Menshikov, Leonid I; Shmookler Reis, Robert J; Fedichev, Peter
2015-01-01
Several animal species are considered to exhibit what is called negligible senescence, i.e. they do not show signs of functional decline or any increase of mortality with age. Recent studies in naked mole rat and long-lived sea urchins showed that these species do not alter their gene-expression profiles with age as much as other organisms do. This is consistent with exceptional endurance of naked mole rat tissues to various genotoxic stresses. We conjectured, therefore, that the lifelong transcriptional stability of an organism may be a key determinant of longevity. We analyzed the stability of a simple genetic-network model and found that under most common circumstances, such a gene network is inherently unstable. Over a time it undergoes an exponential accumulation of gene-regulation deviations leading to death. However, should the repair systems be sufficiently effective, the gene network can stabilize so that gene damage remains constrained along with mortality of the organism. We investigate the relationship between stress-resistance and aging and suggest that the unstable regime may provide a mathematical basis for the Gompertz "law" of aging in many species. At the same time, this model accounts for the apparently age-independent mortality observed in some exceptionally long-lived animals. PMID:26316217
Fedorov, Alexey V.; Fedorov, Alexey
2015-01-14
The central goal of this research project was to understand the mechanisms of decadal and multi-decadal variability of the Atlantic Meridional Overturning Circulation (AMOC) as related to climate variability and abrupt climate change within a hierarchy of climate models ranging from realistic ocean models to comprehensive Earth system models. Generalized Stability Analysis, a method that quantifies the transient and asymptotic growth of perturbations in the system, is one of the main approaches used throughout this project. The topics we have explored range from physical mechanisms that control AMOC variability to the factors that determine AMOC predictability in the Earth system models, to the stability and variability of the AMOC in past climates.
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.
A simplified spatial model for BWR stability
Berman, Y.; Lederer, Y.; Meron, E.
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)
Stability analysis of an HIV/AIDS epidemic model with treatment
NASA Astrophysics Data System (ADS)
Cai, Liming; Li, Xuezhi; Ghosh, Mini; Guo, Baozhu
2009-07-01
An HIV/AIDS epidemic model with treatment is investigated. The model allows for some infected individuals to move from the symptomatic phase to the asymptomatic phase by all sorts of treatment methods. We first establish the ODE treatment model with two infective stages. Mathematical analyses establish that the global dynamics of the spread of the HIV infectious disease are completely determined by the basic reproduction number [real]0. If [real]0<=1, the disease-free equilibrium is globally stable, whereas the unique infected equilibrium is globally asymptotically stable if [real]0>1. Then, we introduce a discrete time delay to the model to describe the time from the start of treatment in the symptomatic stage until treatment effects become visible. The effect of the time delay on the stability of the endemically infected equilibrium is investigated. Moreover, the delay model exhibits Hopf bifurcations by using the delay as a bifurcation parameter. Finally, numerical simulations are presented to illustrate the results.
Implementation of a Single-Stage-To-Orbit (SSTO) model for stability and control analysis
NASA Technical Reports Server (NTRS)
Ingalls, Stephen A.
1995-01-01
Three NASA centers: Marshall Space Flight Center (MSFC), Langley Research Center (LaRC), and Johnson Space Center (JSC) are currently involved in studying a family of single-stage- and two-stage-to-orbit (SSTO/TSTO) vehicles to serve as the next generation space transportation system (STS). A rocketed winged-body is the current focus. The configuration (WB001) is a vertically-launched, horizontally-landing system with circular cross-section. Preliminary aerodynamic data was generated by LaRC and is a combination of wind-tunnel data, empirical methods, and Aerodynamic Preliminary Analysis System-(APAS) generated values. JSC's efforts involve descent trajectory design, stability analysis, and flight control system synthesis. Analysis of WB001's static stability indicates instability in 'tuck' (C(sub mu) less than 0: Mach = 0.30, alpha greater than 3.25 deg; Mach = 0.60, alpha greater than 8.04), an unstable dihedral effects (C(sub l(beta)) greater than 0: Mach = 30,alpha less than 12 deg.; Mach = 0.60, alpha less than 10.00 deg.), and, most significantly, an unstable weathercock stability derivative, C(sub n(beta)), at all angles of attack and subsonic Mach numbers. Longitudinal trim solutions for Mach = 0.30 and 0.60 indicate flight path angle possibilities ranging from around 12 (M = 0.30) to slightly over 20 degrees at Mach = 0.60. Trim angles of attack increase from 6.24 at Mach 0.60 and 10,000 feet to 17.7 deg. at Mach 0.30, sea-level. Lateral trim was attempted for a design cross-wind of 25.0 knots. The current vehicle aerodynamic and geometric characteristics will only yield a lateral trim solution at impractical tip-fin deflections (approximately equal to 43 deg.) and bank angles (21 deg.). A study of the lateral control surfaces, tip-fin controllers for WB001, indicate increased surface area would help address these instabilities, particularly the deficiency in C(sub n(beta)), but obviously at the expense of increased vehicle weight. Growth factors of approximately 7 were determined using a design C(sub n(beta)) of 0.100/radian (approximate subsonic values for the orbiter).
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.
MAP stability, design, and analysis
NASA Technical Reports Server (NTRS)
Ericsson-Jackson, A. J.; Andrews, S. F.; O'Donnell, J. R., Jr.; Markley, F. L.
1998-01-01
The Microwave Anisotropy Probe (MAP) is a follow-on to the Differential Microwave Radiometer (DMR) instrument on the Cosmic Background Explorer (COBE) spacecraft. The design and analysis of the MAP attitude control system (ACS) have been refined since work previously reported. The full spacecraft and instrument flexible model was developed in NASTRAN, and the resulting flexible modes were plotted and reduced with the Modal Significance Analysis Package (MSAP). The reduced-order model was used to perform the linear stability analysis for each control mode, the results of which are presented in this paper. Although MAP is going to a relatively disturbance-free Lissajous orbit around the Earth-Sun L(2) Lagrange point, a detailed disturbance-torque analysis is required because there are only a small number of opportunities for momentum unloading each year. Environmental torques, including solar pressure at L(2), aerodynamic and gravity gradient during phasing-loop orbits, were calculated and simulated. Thruster plume impingement torques that could affect the performance of the thruster modes were estimated and simulated, and a simple model of fuel slosh was derived to model its effect on the motion of the spacecraft. In addition, a thruster mode linear impulse controller was developed to meet the accuracy requirements of the phasing loop burns. A dynamic attitude error limiter was added to improve the performance of the ACS during large attitude slews. The result of this analysis is a stable ACS subsystem that meets all of the mission's requirements.
MAP Stability, Design and Analysis
NASA Technical Reports Server (NTRS)
Ericsson -Jackson, A.J.; Andrews, S. F.; ODonnell, J. R., Jr.; Markley, F. L.
1998-01-01
The Microwave Anisotropy Probe (MAP) is a follow-on to the Differential Microwave Radiometer (DMR) instrument on the Cosmic Background Explorer (COBE) spacecraft. The design and analysis of the MAP attitude control system (ACS) have been refined since work previously reported. The full spacecraft and instrument flexible model was developed in NASTRAN, and the resulting flexible modes were plotted and reduced with the Modal Significance Analysis Package (MSAP). The reduced-order model was used to perform the linear stability analysis for each control mode, the results of which are presented in this paper. Although MAP is going to a relatively disturbance-free Lissajous orbit around the Earth-Sun L2 Lagrange point, a detailed disturbance-torque analysis is required because there are only a small number of opportunities for momentum unloading each year. Environmental torques, including solar pressure at L2, and aerodynamic and gravity gradient during phasing-loop orbits, were calculated and simulated. A simple model of fuel slosh was derived to model its effect on the motion of the spacecraft. In addition, a thruster mode linear impulse controller was developed to meet the accuracy requirements of the phasing loop burns. A dynamic attitude error limiter was added to improve the performance of the ACS during large attitude slews. The result of this analysis is a stable ACS subsystem that meets all of the mission's requirements.
Stability analysis and optimal control of an epidemic model with awareness programs by media.
Misra, A K; Sharma, Anupama; Shukla, J B
2015-12-01
The impact of awareness campaigns and behavioral responses on epidemic outbreaks has been reported at times. However, to what extent does the provision of awareness and behavioral changes affect the epidemic trajectory is unknown, but important from the public health standpoint. To address this question, we formulate a mathematical model to study the effect of awareness campaigns by media on the outbreak of an epidemic. The awareness campaigns are treated as an intervention for the emergent disease. These awareness campaigns divide the whole populations into two subpopulation; aware and unaware, by inducing behavioral changes amongst them. The awareness campaigns are included explicitly as a separate dynamic variable in the modeling process. The model is analyzed qualitatively using stability theory of differential equations. We have also identified an optimal implementation rate of awareness campaigns so that disease can be controlled with minimal possible expenditure on awareness campaigns, using optimal control theory. The control setting is investigated analytically using optimal control theory, and the numerical solutions illustrating the optimal regimens under various assumptions are also shown. PMID:26551557
Stability analysis of multi-group deterministic and stochastic epidemic models with vaccination rate
NASA Astrophysics Data System (ADS)
Wang, Zhi-Gang; Gao, Rui-Mei; Fan, Xiao-Ming; Han, Qi-Xing
2014-09-01
We discuss in this paper a deterministic multi-group MSIR epidemic model with a vaccination rate, the basic reproduction number ℛ0, a key parameter in epidemiology, is a threshold which determines the persistence or extinction of the disease. By using Lyapunov function techniques, we show if ℛ0 is greater than 1 and the deterministic model obeys some conditions, then the disease will prevail, the infective persists and the endemic state is asymptotically stable in a feasible region. If ℛ0 is less than or equal to 1, then the infective disappear so the disease dies out. In addition, stochastic noises around the endemic equilibrium will be added to the deterministic MSIR model in order that the deterministic model is extended to a system of stochastic ordinary differential equations. In the stochastic version, we carry out a detailed analysis on the asymptotic behavior of the stochastic model. In addition, regarding the value of ℛ0, when the stochastic system obeys some conditions and ℛ0 is greater than 1, we deduce the stochastic system is stochastically asymptotically stable. Finally, the deterministic and stochastic model dynamics are illustrated through computer simulations.
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.
Stability analysis of free piston Stirling engines
NASA Astrophysics Data System (ADS)
Bégot, Sylvie; Layes, Guillaume; Lanzetta, François; Nika, Philippe
2013-03-01
This paper presents a stability analysis of a free piston Stirling engine. The model and the detailed calculation of pressures losses are exposed. Stability of the machine is studied by the observation of the eigenvalues of the model matrix. Model validation based on the comparison with NASA experimental results is described. The influence of operational and construction parameters on performance and stability issues is exposed. The results show that most parameters that are beneficial for machine power seem to induce irregular mechanical characteristics with load, suggesting that self-sustained oscillations could be difficult to maintain and control.
NASA Astrophysics Data System (ADS)
Pei, Xin; Pan, Yan; Wang, Haixin; Wong, S. C.; Choi, Keechoo
2016-05-01
Car-following models, which describe the reactions of the driver of a following car to the changes of the leading car, are essential for the development of traffic flow theory. A car-following model with a stochastic memory effect is considered to be more realistic in modeling drivers' behavior. Because a gamma-distributed memory function has been shown to outperform other forms according to empirical data, in this study, we thus focus on a car-following model with a gamma-distributed memory effect; analytical and numerical studies are then conducted for stability analysis. Accordingly, the general expression of undamped and stability points is achieved by analytical study. The numerical results show great agreement with the analytical results: introducing the effect of the driver's memory causes the stable regions to weaken slightly, but the metastable region is obviously enlarged. In addition, a numerical study is performed to further analyze the variation of the stable and unstable regions with respect to the different profiles of gamma distribution.
NASA Technical Reports Server (NTRS)
Smith, Arthur F.
1985-01-01
Results of static stability wind tunnel tests of three 62.2 cm (24.5 in) diameter models of the Prop-Fan are presented. Measurements of blade stresses were made with the Prop-Fans mounted on an isolated nacelle in an open 5.5 m (18 ft) wind tunnel test section with no tunnel flow. The tests were conducted in the United Technology Research Center Large Subsonic Wind Tunnel. Stall flutter was determined by regions of high stress, which were compared with predictions of boundaries of zero total viscous damping. The structural analysis used beam methods for the model with straight blades and finite element methods for the models with swept blades. Increasing blade sweep tends to suppress stall flutter. Comparisons with similar test data acquired at NASA/Lewis are good. Correlations between measured and predicted critical speeds for all the models are good. The trend of increased stability with increased blade sweep is well predicted. Calculated flutter boundaries generaly coincide with tested boundaries. Stall flutter is predicted to occur in the third (torsion) mode. The straight blade test shows third mode response, while the swept blades respond in other modes.
Alcantara, Jan Harold M; Lao, Angelyn R; Ruivivar, Leonor A
2016-04-26
The proteolytic breakdown of the amyloid precursor protein (APP) by secretases is a complex cellular process that results in the formation of neurotoxic Aβ peptides, causative of neurodegeneration in Alzheimer's disease (AD). Processing involves monomeric and dimeric forms of APP that are transported through distinct cellular compartments where the various secretases reside. Amyloidogenic processing is also influenced by modifiers such as sorting receptor-related protein (SORLA), an inhibitor of APP breakdown and a major AD risk factor. This paper analyzed the temporal behavior of a mathematical model describing APP processing under the influence of SORLA, by performing a stability analysis of the mathematical model. We found one biochemically meaningful equilibrium point ξ. By means of linearization, Hartman-Grobman theorem, and Routh-Hurwitz test, it was shown that ξ is a locally asymptotically stable equilibrium point. The region of attraction of ξ was approximated by using the fluctuation lemma. An immediate consequence of the stability analysis of the reduced system to the temporal behavior of the solutions of the original system was also obtained. The biological implications of these results for the dynamic behavior of the activity of APP and secretases under SORLA's influence were established. PMID:26980455
NASA Astrophysics Data System (ADS)
Banshchikov, A. V.; Chaikin, S. V.
2015-09-01
Applying Lyapunov's approach to the investigation of the stability of the motion according to first order approximation equations, the regions are singled out in the space of the inputed parameters where the stability, instability, or gyroscopic stabilization of relative equilibriums of a prolate axisymmetric orbital gyrostat with a constant gyrostatic moment vector are ensured. In particular, the result concerning instability and impossibility of gyroscopic stabilization of one in two existing equilibrium classes of the system have been formulated. The investigation was carried out using the LinModel software package and the symbolic—numerical modeling functions of the Mathematica Computer Algebra System.
NASA Astrophysics Data System (ADS)
Zhang, L.; Liu, Y. R.; Yang, Q.
2015-03-01
Reinforcement measures are often used in high-arch dams with complicated geological foundations. The geomechanical model test is an effective method to study the global stability of arch dams and to evaluate the reinforcement effects of foundation treatments. The block masonry technique was developed to simulate the jointed rock mass, tectonic discontinuities, and reinforcement measures. A tailor-made low-strength binder and small blocks were developed to simulate the strength and deformation of the jointed rock mass and discontinuities, respectively. We applied this technique to geomechanical model tests of the Dagangshan arch dam with and without foundation reinforcements. A rupture test was conducted, and the stress and displacement distribution of the dam and abutments were recorded; the failure mechanisms and processes were explored. The reinforcement effects of the foundation treatment were evaluated by comparing the test results of the models with and without foundation reinforcements. Our analysis indicates that foundation reinforcements can improve the stress distribution, decrease deformation, prevent slides, reduce fault movement, and improve the global stability of high-arch dams.
Global stability analysis for cosmological models with nonminimally coupled scalar fields
NASA Astrophysics Data System (ADS)
Skugoreva, Maria A.; Toporensky, Alexey V.; Vernov, Sergey Yu.
2014-09-01
We explore dynamics of cosmological models with a nonminimally coupled scalar field evolving on a spatially flat Friedmann-Lemaître-Robertson-Walker background. We consider cosmological models including the Hilbert-Einstein curvature term and the N degree monomial of the scalar field nonminimally coupled to gravity. The potential of the scalar field is the n degree monomial or polynomial. We describe several qualitatively different types of dynamics depending on values of power indices N and n. We identify that three main possible pictures correspond to n
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 Δ' 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 Δ' calculation. Work supported in part by the US DOE under DE-AC05-00OR22725 and DE-FC02-04ER54698.
Hernández-Cortés, Pedro; Galindo-Moreno, Pablo; Catena, Andrés; Ortega-Oller, Inmaculada; Salas-Pérez, José; Gómez-Sánchez, Rafael; Aguilar, Mariano; Aguilar, David
2014-01-01
Objective. This study was designed to explore relationships of resonance frequency analysis (RFA)—assessed implant stability (ISQ values) with bone morphometric parameters and bone quality in an ex vivo model of dental implants placed in human femoral heads and to evaluate the usefulness of this model for dental implant studies. Material and Methods. This ex vivo study included femoral heads from 17 patients undergoing surgery for femoral neck fracture due to osteoporosis (OP) (n = 7) or for total prosthesis joint replacement due to severe hip osteoarthrosis (OA) (n = 10). Sixty 4.5 × 13 mm Dentsply Astra implants were placed, followed by RFA. CD44 immunohistochemical analysis for osteocytes was also carried out. Results. As expected, the analysis yielded significant effects of femoral head type (OA versus OA) (P < 0.001), but not of the implants (P = 0.455) or of the interaction of the two factors (P = 0.848). Bonferroni post hoc comparisons showed a lower mean ISQ for implants in decalcified (50.33 ± 2.92) heads than in fresh (66.93 ± 1.10) or fixated (70.77 ± 1.32) heads (both P < 0.001). The ISQ score (fresh) was significantly higher for those in OA (73.52 ± 1.92) versus OP (67.13 ± 1.09) heads. However, mixed linear analysis showed no significant association between ISQ scores and morphologic or histomorphometric results (P > 0.5 in all cases), and no significant differences in ISQ values were found as a function of the length or area of the cortical layer (both P > 0.08). Conclusion. Although RFA-determined ISQ values are not correlated with morphometric parameters, they can discriminate bone quality (OP versus OA). This ex vivo model is useful for dental implant studies. PMID:24995307
NASA Astrophysics Data System (ADS)
Cheng, Yung-Chang; Lee, Sen-Yung; Chen, Hsing-Hao
2009-07-01
A heuristic nonlinear creep model is used to derive the nonlinear coupled differential equations of motion of a high-speed railway vehicle traveling on a curved track. The vehicle dynamics are modeled using a 21 degree-of-freedom (21-DOF) system which takes account of the lateral displacement and yaw angle of each wheelset, the lateral displacement, vertical displacement, roll angle and yaw angle of the truck frames, and the lateral displacement, vertical displacement, roll angle, pitch angle and yaw angle of the car body. To analyze the respective effects of the major system parameters on the vehicle dynamics, the 21-DOF system is reduced to 20-DOF, 14-DOF and 6-DOF models, respectively, by excluding designated subsets of the system parameters. The validity of the analytical models and the numerical solution procedure is confirmed by comparing the result obtained using the 6-DOF model for the critical velocity of a railway vehicle traveling on a tangent track with the solution presented in the literature. In general, the results obtained in this study show that the critical hunting speed derived using the 6-DOF or 14-DOF model is generally higher than that evaluated using the 20-DOF model. In addition, the critical hunting speed evaluated via the heuristic nonlinear creep model is lower than that derived using a linear creep model.
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 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. 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)
Stability analysis of the Biot/squirt models for wave propagation in saturated porous media
NASA Astrophysics Data System (ADS)
Liu, Jiawei; Yong, Wen-An
2016-01-01
This work is concerned with the Biot/squirt (BISQ) models for wave propagation in saturated porous media. We show that the models allow exponentially exploding solutions, as time goes to infinity, when the characteristic squirt-flow coefficient is negative or has a non-zero imaginary part. We also show that the squirt-flow coefficient does have non-zero imaginary parts for some experimental parameters or for low angular frequencies. Because the models are linear, the existence of such exploding solutions indicates instability of the BISQ models. This result, for the first time, provides a theoretical explanation of the well-known empirical observation that BISQ model is not reliable (not consistent with Gassmann's formula) at low frequencies. It calls on a reconsideration of the widely used BISQ theory. On the other hand, we demonstrate that the 3-D isotropic BISQ model is stable when the squirt-flow coefficient is positive. In particular, the original Biot model is unconditionally stable where the squirt-flow coefficient is 1.
Global stability analysis of a delayed susceptible-infected-susceptible epidemic model.
Paulhus, Calah; Wang, Xiang-Sheng
2015-01-01
We study a susceptible-infected-susceptible model with distributed delays. By constructing suitable Lyapunov functionals, we demonstrate that the global dynamics of this model is fully determined by the basic reproductive ratio R0. To be specific, we prove that if R0 ? 1, then the disease-free equilibrium is globally asymptotically stable. On the other hand, if R0>1, then the endemic equilibrium is globally asymptotically stable. It is remarkable that the model dynamics is independent of the probability of immunity lost. PMID:24978018
Spectral stability of unitary network models
NASA Astrophysics Data System (ADS)
Asch, Joachim; Bourget, Olivier; Joye, Alain
2015-08-01
We review various unitary network models used in quantum computing, spectral analysis or condensed matter physics and establish relationships between them. We show that symmetric one-dimensional quantum walks are universal, as are CMV matrices. We prove spectral stability and propagation properties for general asymptotically uniform models by means of unitary Mourre theory.
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 analysis of a simplified model of a fluidized bed combustor
Trevino, C. ); Herrera, C. ); Garcia-Ybarra, P. )
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.
A Mathematical Model of Protectant and Curative Fungicide Application and its stability analysis
NASA Astrophysics Data System (ADS)
Anggriani, N.; Istifadah, N.; Hanifah, M.; Supriatna, A. K.
2016-01-01
In this paper we introduce a mathematical model for fungicide application with effect of protectant and curatives factor. We show the value of the Basic Reproduction Number (R0) of the fungal disease, which is computed from the largest eigen value of the next generation matrix of the model. The result show that in the region where R0 greater than one there is only one single stable endemic equilibrium. However, in region where R0 less than one some parameters affect the number of posibble equilibria. Some numerical simulation are also given to illustrate our analytical results.
Cosmological Models and Stability
NASA Astrophysics Data System (ADS)
Andersson, Lars
Principles in the form of heuristic guidelines or generally accepted dogma play an important role in the development of physical theories. In particular, philosophical considerations and principles figure prominently in the work of Albert Einstein. As mentioned in the talk by Jiří Bičák at this conference, Einstein formulated the equivalence principle, an essential step on the road to general relativity, during his time in Prague 1911-1912. In this talk, I would like to discuss some aspects of cosmological models. As cosmology is an area of physics where "principles" such as the "cosmological principle" or the "Copernican principle" play a prominent role in motivating the class of models which form part of the current standard model, I will start by comparing the role of the equivalence principle to that of the principles used in cosmology. I will then briefly describe the standard model of cosmology to give a perspective on some mathematical problems and conjectures on cosmological models, which are discussed in the later part of this paper.
Ghag, G; Ghosh, P; Mauro, A; Rangachari, V; Vaidya, A
2013-11-01
Protein misfolding and concomitant aggregation towards amyloid formation is the underlying biochemical commonality among a wide range of human pathologies. Amyloid formation involves the conversion of proteins from their native monomeric states (intrinsically disordered or globular) to well-organized, fibrillar aggregates in a nucleation-dependent manner. Understanding the mechanism of aggregation is important not only to gain better insight into amyloid pathology but also to simulate and predict molecular pathways. One of the main impediments in doing so is the stochastic nature of interactions that impedes thorough experimental characterization and the development of meaningful insights. In this study, we have utilized a well-known intermediate state along the amyloid-? peptide aggregation pathway called protofibrils as a model system to investigate the molecular mechanisms by which they form fibrils using stability and perturbation analysis. Investigation of protofibril aggregation mechanism limits both the number of species to be modeled (monomers, and protofibrils), as well as the reactions to two (elongation by monomer addition, and protofibril-protofibril lateral association). Our new model is a reduced order four species model grounded in mass action kinetics. Our prior study required 3200 reactions, which makes determining the reaction parameters prohibitively difficult. Using this model, along with a linear perturbation argument, we rigorously determine stable ranges of rate constants for the reactions and ensure they are physically meaningful. This was accomplished by finding the ranges in which the perturbations dieout in a five-parameter sweep, which includes the monomer and protofibril equilibrium concentrations and three of the rate constants. The results presented are a proof-of-concept method in determining meaningful rate constants that can be used as a bonafide way for determining accurate rate constants for other models involving complex biological reactions such as amyloid aggregation. PMID:25018569
Jacobi stability analysis of the Lorenz system
NASA Astrophysics Data System (ADS)
Harko, Tiberiu; Ho, Chor Yin; Leung, Chun Sing; Yip, Stan
2015-06-01
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 nontrivial testing object for studying nonlinear 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 nonlinear 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 nonlinear 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.
Pedro, Sansao A; Abelman, Shirley; Ndjomatchoua, Frank T; Sang, Rosemary; Tonnang, Henri E Z
2014-01-01
This paper investigates a RVF epidemic model by qualitative analysis and numerical simulations. Qualitative analysis have been used to explore the stability dynamics of the equilibrium points while visualization techniques such as bifurcation diagrams, Poincaré maps, maxima return maps and largest Lyapunov exponents are numerically computed to confirm further complexity of these dynamics induced by the seasonal forcing on the mosquitoes oviposition rates. The obtained results show that ordinary differential equation models with external forcing can have rich dynamic behaviour, ranging from bifurcation to strange attractors which may explain the observed fluctuations found in RVF empiric outbreak data, as well as the non deterministic nature of RVF inter-epidemic activities. Furthermore, the coexistence of the endemic equilibrium is subjected to existence of certain number of infected Aedes mosquitoes, suggesting that Aedes have potential to initiate RVF epidemics through transovarial transmission and to sustain low levels of the disease during post epidemic periods. Therefore we argue that locations that may serve as RVF virus reservoirs should be eliminated or kept under control to prevent multi-periodic outbreaks and consequent chains of infections. The epidemiological significance of this study is: (1) low levels of birth rate (in both Aedes and Culex) can trigger unpredictable outbreaks; (2) Aedes mosquitoes are more likely capable of inducing unpredictable behaviour compared to the Culex; (3) higher oviposition rates on mosquitoes do not in general imply manifestation of irregular behaviour on the dynamics of the disease. Finally, our model with external seasonal forcing on vector oviposition rates is able to mimic the linear increase in livestock seroprevalence during inter-epidemic period showing a constant exposure and presence of active transmission foci. This suggests that RVF outbreaks partly build upon RVF inter-epidemic activities. Therefore, active RVF surveillance in livestock is recommended. PMID:25271641
Pedro, Sansao A.; Abelman, Shirley; Ndjomatchoua, Frank T.; Sang, Rosemary; Tonnang, Henri E. Z.
2014-01-01
This paper investigates a RVF epidemic model by qualitative analysis and numerical simulations. Qualitative analysis have been used to explore the stability dynamics of the equilibrium points while visualization techniques such as bifurcation diagrams, Poincaré maps, maxima return maps and largest Lyapunov exponents are numerically computed to confirm further complexity of these dynamics induced by the seasonal forcing on the mosquitoes oviposition rates. The obtained results show that ordinary differential equation models with external forcing can have rich dynamic behaviour, ranging from bifurcation to strange attractors which may explain the observed fluctuations found in RVF empiric outbreak data, as well as the non deterministic nature of RVF inter-epidemic activities. Furthermore, the coexistence of the endemic equilibrium is subjected to existence of certain number of infected Aedes mosquitoes, suggesting that Aedes have potential to initiate RVF epidemics through transovarial transmission and to sustain low levels of the disease during post epidemic periods. Therefore we argue that locations that may serve as RVF virus reservoirs should be eliminated or kept under control to prevent multi-periodic outbreaks and consequent chains of infections. The epidemiological significance of this study is: (1) low levels of birth rate (in both Aedes and Culex) can trigger unpredictable outbreaks; (2) Aedes mosquitoes are more likely capable of inducing unpredictable behaviour compared to the Culex; (3) higher oviposition rates on mosquitoes do not in general imply manifestation of irregular behaviour on the dynamics of the disease. Finally, our model with external seasonal forcing on vector oviposition rates is able to mimic the linear increase in livestock seroprevalence during inter-epidemic period showing a constant exposure and presence of active transmission foci. This suggests that RVF outbreaks partly build upon RVF inter-epidemic activities. Therefore, active RVF surveillance in livestock is recommended. PMID:25271641
Solar array switching unit stability analysis
Fleck, G.W.
1984-08-01
TRW is currently developing solar array switching unit (SASU) technology for output power regulation of large solar arrays. A model is developed which is used to explain the interaction of the SASU and constant power type loads. The stability criteria for the SASU concept is defined and a stability analysis is formulated. The formation developed is a time-domain simulation which utilizes numerical techniques to solve the nonlinear differential equations involved. Verification tests were performed and are presented for the analysis technique developed.
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.
Cage stability analysis for SSME HPOTP bearings
NASA Technical Reports Server (NTRS)
Merriman, T. L.; Kannel, J. W.
1988-01-01
A numerical model of cage motion (CAGEDYN) was used to analyze the stability of bearing cages in the Space Shuttle main engine (SSME) high pressure oxygen turbopump (HPOTP). The stability of existing bearing geometries, as well as perturbations of these geometries, was analyzed for various operating conditions. Results of the analyses show that some combinations of operating parameters, exacerbated by the sparse lubrication that exist in the HPOTP bearings, can cause unstable cage oscillations. Frequencies of cage oscillations were predicted by the CAGEDYN numerical model by Fourier analysis of predicted cage motions. Under conditions that cause unstable cage motion, high frequency oscillations were predicted that could cause premature cage failures.
Modeling of shallow stabilization ponds
Babarutsi, S.; Marchand, P.; Safieddine, T.
1999-07-01
A two-dimensional hydrodynamic model is used to simulate shallow stabilization ponds. The model computes the flow field and the concentration distribution of a conservative tracer in the entire area of a pond. The location and the size of the dead zones, the bypassing, and the recirculating areas are also determined by the model. The numerical results are in good agreement with the experimental data obtained in the laboratory.
Liapunov stability analysis of spinning flexible spacecraft.
NASA Technical Reports Server (NTRS)
Barbera, F. J.; Likins, P.
1973-01-01
The attitude stability of a class of spinning flexible spacecraft in a force-free environment is analyzed. The spacecraft is modeled as a rigid core having attached to it a flexible appendage idealized as a collection of elastically interconnected particles. Liapunov stability theorems are employed with the Hamiltonian of the system, constrained through the angular momentum integral so as to admit complete damping, used as a testing function. The Hamiltonian is written in terms of modal coordinates as interpreted by the hybrid coordinate formulation, thus allowing truncation to a level amenable to literal stability analysis. Testing functions are constructed for a spacecraft with an arbitrary (discretized) appendage, and closed form stability criteria are generated for the first mode of a restricted appendage model lying in a plane which contains the center of mass and is orthogonal to the spin axis. The criteria are (except for idealized cases on the stability boundary line in the parameter space) both necessary and sufficient for stability for any spacecraft characterized by the planar appendage model, such as a spacecraft containing solar panels and/or radial booms.
NASA Astrophysics Data System (ADS)
Havaej, Mohsen; Coggan, John; Stead, Doug; Elmo, Davide
2016-04-01
Rock slope geometry and discontinuity properties are among the most important factors in realistic rock slope analysis yet they are often oversimplified in numerical simulations. This is primarily due to the difficulties in obtaining accurate structural and geometrical data as well as the stochastic representation of discontinuities. Recent improvements in both digital data acquisition and incorporation of discrete fracture network data into numerical modelling software have provided better tools to capture rock mass characteristics, slope geometries and digital terrain models allowing more effective modelling of rock slopes. Advantages of using improved data acquisition technology include safer and faster data collection, greater areal coverage, and accurate data geo-referencing far exceed limitations due to orientation bias and occlusion. A key benefit of a detailed point cloud dataset is the ability to measure and evaluate discontinuity characteristics such as orientation, spacing/intensity and persistence. This data can be used to develop a discrete fracture network which can be imported into the numerical simulations to study the influence of the stochastic nature of the discontinuities on the failure mechanism. We demonstrate the application of digital terrestrial photogrammetry in discontinuity characterization and distinct element simulations within a slate quarry. An accurately geo-referenced photogrammetry model is used to derive the slope geometry and to characterize geological structures. We first show how a discontinuity dataset, obtained from a photogrammetry model can be used to characterize discontinuities and to develop discrete fracture networks. A deterministic three-dimensional distinct element model is then used to investigate the effect of some key input parameters (friction angle, spacing and persistence) on the stability of the quarry slope model. Finally, adopting a stochastic approach, discrete fracture networks are used as input for 3D distinct element simulations to better understand the stochastic nature of the geological structure and its effect on the quarry slope failure mechanism. The numerical modelling results highlight the influence of discontinuity characteristics and kinematics on the slope failure mechanism and the variability in the size and shape of the failed blocks.
ERIC Educational Resources Information Center
Lash, Andrea; Makkonen, Reino; Tran, Loan; Huang, Min
2016-01-01
This study, undertaken at the request of the Nevada Department of Education, examined the stability over years of teacher-level growth scores from the Student Growth Percentile (SGP) model, which many states and districts have selected as a measure of effectiveness in their teacher evaluation systems. The authors conducted a generalizability study…
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.
Global Stability Analysis for Linear Dynamics
NASA Astrophysics Data System (ADS)
Morzyński, 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.
Liquid rocket spray combustion stability analysis
NASA Technical Reports Server (NTRS)
Litchford, Ron J.; Jeng, San-Mou
1992-01-01
A computational approach to the analysis of spray combustion stability in liquid rocket combustors is proposed which is based on the unsteady quasi-two-dimensional Euler equations with interphase source terms derived from a Lagrangian treatment of the combusting spray. Based on a preliminary evaluation, the computational methodology presented here is a promising research tool and a potential design/development aid for investigating the stability characteristics of liquid rocket engines. The method is characterized by low numerical noise; the Lagrangian treatment of the spray offers improved flexibility for the direct modeling of spray combustion.
NASA Astrophysics Data System (ADS)
Iwasaki, Toshiki; Shimizu, Yasuyuki; Kimura, Ichiro
2016-06-01
A number of numerical models have been proposed to understand and simulate fluvial river morphodynamics; however, it is somewhat unclear whether all the models are able to consistently simulate flow-bed instability phenomena. This study investigates the sensitivity of free bar morphology in rivers to secondary flow models used in depth-averaged models using linear stability analyses and numerical simulations. Both the linear analyses and numerical simulations suggest that under certain hydraulic conditions, an equilibrium-type secondary flow model, which has been widely used in river morphodynamic models, fails to generate a finite wavelength and bar mode, allowing the inception of bars of infinitely short scale and infinitely high mode. Using a nonequilibrium-type secondary flow model avoids the unphysical formation of these incipient free bars, and gives better solutions regarding finite amplitude bars. Since free bars are essential, intrinsic river morphological features, the findings of this study can be applied to a wide range of river morphodynamic calculations.
Beg, Ilyas; Minton, Allen P; Hassan, Imtaiyaz; Islam, Asimul; Ahmad, Faizan
2015-06-16
The reversible thermal denaturation of apo α-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.
NASA Technical Reports Server (NTRS)
Charlton, Eric F.
1998-01-01
Aerodynamic analysis are performed using the Lockheed-Martin Tactical Aircraft Systems (LMTAS) Splitflow computational fluid dynamics code to investigate the computational prediction capabilities for vortex-dominated flow fields of two different tailless aircraft models at large angles of attack and sideslip. These computations are performed with the goal of providing useful stability and control data to designers of high performance aircraft. Appropriate metrics for accuracy, time, and ease of use are determined in consultations with both the LMTAS Advanced Design and Stability and Control groups. Results are obtained and compared to wind-tunnel data for all six components of forces and moments. Moment data is combined to form a "falling leaf" stability analysis. Finally, a handful of viscous simulations were also performed to further investigate nonlinearities and possible viscous effects in the differences between the accumulated inviscid computational and experimental data.
NASA Astrophysics Data System (ADS)
Guo, Hui-Jun; Huang, Wei; Liu, Xi; Gao, Pan; Zhuo, Shi-Yi; Xin, Jun; Yan, Cheng-Feng; Zheng, Yan-Qing; Yang, Jian-Hua; Shi, Er-Wei
2014-09-01
Polytype stability is very important for high quality SiC single crystal growth. However, the growth conditions for the 4H, 6H and 15R polytypes are similar, and the mechanism of polytype stability is not clear. The kinetics aspects, such as surface-step nucleation, are important. The kinetic Monte Carlo method is a common tool to study surface kinetics in crystal growth. However, the present lattice models for kinetic Monte Carlo simulations cannot solve the problem of the competitive growth of two or more lattice structures. In this study, a competitive lattice model was developed for kinetic Monte Carlo simulation of the competition growth of the 4H and 6H polytypes of SiC. The site positions are fixed at the perfect crystal lattice positions without any adjustment of the site positions. Surface steps on seeds and large ratios of diffusion/deposition have positive effects on the 4H polytype stability. The 3D polytype distribution in a physical vapor transport method grown SiC ingot showed that the facet preserved the 4H polytype even if the 6H polytype dominated the growth surface. The theoretical and experimental results of polytype growth in SiC suggest that retaining the step growth mode is an important factor to maintain a stable single 4H polytype during SiC growth.
Absolute stability analysis of attitude control systems for large boosters.
NASA Technical Reports Server (NTRS)
Siljak, D. D.; Seltzer, S. M.
1971-01-01
A method for performing an absolute stability analysis of attitude control systems for large launch vehicles is presented. Absolute stability of these systems is shown to be of a limited extent. The regions of absolute stability are computed by using a quadratic Liapunov function. The function is chosen to provide additional information about the exponential property of absolute stability. A system model is used to illustrate the method.
Dynamic Analysis of Power System Voltage Stability.
NASA Astrophysics Data System (ADS)
Gebreselassie, Assefa
This thesis investigates the effects of loads and voltage regulators on the dynamic voltage stability of power systems. The analysis focuses on the interactions of machine flux dynamics with loads and voltage control devices. The results are based on eigenvalue analysis of the linearized models and time simulation of the nonlinear models, using models from the Power System Toolbox, a Matlab -based package for the simulation and small signal analysis of nonlinear power systems. The voltage stability analysis results are developed using a single machine single load system with typical machine and network parameters and the NPCC 10-machine system. Dynamic models for generators, exciters and loads are used. The generator is modeled with a pair of poles and one damper circuit in both the d-axis and the q-axis. Saturation effects are included in the model. The IEEE Type DC1 DC commutator exciter model is used for all the exciters. Five different types of loads: constant impedance, constant current, constant power, a first order induction motor model (slip model) and a third order induction motor model (slip-flux model) are considered. The modes of instability and the stability limits of the different representation of loads are examined for two different operating modes of the exciters. The first, when all the exciters are on automatic control and the second when some exciters are on manual control. Modal participation factors are used to determine the characteristics of the critical modes. The characteristics of the unstable modes are verified by performing time simulation of the nonlinear models. Oscillatory and non-oscillatory instabilities are experienced by load buses when all the exciters are on automatic control and some exciters are on manual control respectively, for loads which are predominantly constant power and induction motors. It is concluded that the mode of instability does not depend on the type of loads but on the operating condition of the exciters. However, the severity of instability depends on the type of loads. Hence in dynamic voltage analysis, to arrive at a meaningful conclusion, the operating conditions of the exciters and the exact load composition should be taken into account.
Massively Parallel Linear Stability Analysis with P_ARPACK for 3D Fluid Flow Modeled with MPSalsa
Lehoucq, R.B.; Salinger, A.G.
1998-10-13
We are interested in the stability of three-dimensional fluid flows to small dkturbances. One computational approach is to solve a sequence of large sparse generalized eigenvalue problems for the leading modes that arise from discretizating the differential equations modeling the flow. The modes of interest are the eigenvalues of largest real part and their associated eigenvectors. We discuss our work to develop an effi- cient and reliable eigensolver for use by the massively parallel simulation code MPSalsa. MPSalsa allows simulation of complex 3D fluid flow, heat transfer, and mass transfer with detailed bulk fluid and surface chemical reaction kinetics.
NASA Astrophysics Data System (ADS)
Yan, Zhi-zhong; Wei, Chun-qiu; Zheng, Hui; Zhang, Chuanzeng
2016-05-01
In this paper, a meshless radial basis function (RBF) collocation method is developed to calculate the phononic band structures taking account of different interface models. The present method is validated by using the analytical results in the case of perfect interfaces. The stability is fully discussed based on the types of RBFs, the shape parameters and the node numbers. And the advantages of the proposed RBF method compared to the finite element method (FEM) are also illustrated. In addition, the influences of the spring-interface model and the three-phase model on the wave band gaps are investigated by comparing with the perfect interfaces. For different interface models, the effects of various interface conditions, length ratios and density ratios on the band gap width are analyzed. The comparison results of the two models show that the weakly bonded interface has a significant effect on the properties of phononic crystals. Besides, the band structures of the spring-interface model have certain similarities and differences with those of the three-phase model.
The stability of colorectal cancer mathematical models
NASA Astrophysics Data System (ADS)
Khairudin, Nur Izzati; Abdullah, Farah Aini
2013-04-01
Colorectal cancer is one of the most common types of cancer. To better understand about the kinetics of cancer growth, mathematical models are used to provide insight into the progression of this natural process which enables physicians and oncologists to determine optimal radiation and chemotherapy schedules and develop a prognosis, both of which are indispensable for treating cancer. This thesis investigates the stability of colorectal cancer mathematical models. We found that continuous saturating feedback is the best available model of colorectal cancer growth. We also performed stability analysis. The result shows that cancer progress in sequence of genetic mutations or epigenetic which lead to a very large number of cells population until become unbounded. The cell population growth initiate and its saturating feedback is overcome when mutation changes causing the net per-capita growth rate of stem or transit cells exceed critical threshold.
NASA Astrophysics Data System (ADS)
Feng, Xiao-Li; Li, Yu-Xiao; Gu, Jian-Zhong; Zhuo, Yi-Zhong
2009-10-01
The relaxation property of both Eigen model and Crow-Kimura model with a single peak fitness landscape is studied from phase transition point of view. We first analyze the eigenvalue spectra of the replication mutation matrices. For sufficiently long sequences, the almost crossing point between the largest and second-largest eigenvalues locates the error threshold at which critical slowing down behavior appears. We calculate the critical exponent in the limit of infinite sequence lengths and compare it with the result from numerical curve fittings at sufficiently long sequences. We find that for both models the relaxation time diverges with exponent 1 at the error (mutation) threshold point. Results obtained from both methods agree quite well. From the unlimited correlation length feature, the first order phase transition is further confirmed. Finally with linear stability theory, we show that the two model systems are stable for all ranges of mutation rate. The Eigen model is asymptotically stable in terms of mutant classes, and the Crow-Kimura model is completely stable.
NASA Astrophysics Data System (ADS)
Wang, Jinliang; Liu, Shengqiang
2015-01-01
We investigate an in-host model with general incidence and removal rate, as well as distributed delays in virus infections and in productions. By employing Lyapunov functionals and LaSalle's invariance principle, we define and prove the basic reproductive number R0 as a threshold quantity for stability of equilibria. It is shown that if R0 > 1 , then the infected equilibrium is globally asymptotically stable, while if R0 ⩽ 1 , then the infection free equilibrium is globally asymptotically stable under some reasonable assumptions. Moreover, n + 1 distributed delays describe (i) the time between viral entry and the transcription of viral RNA, (ii) the n - 1 -stage time needed for activated infected cells between viral RNA transcription and viral release, and (iii) the time necessary for the newly produced viruses to be infectious (maturation), respectively. The model can describe the viral infection dynamics of many viruses such as HIV-1, HCV and HBV.
Stability Analysis of Flow Past a Wingtip
NASA Astrophysics Data System (ADS)
Edstrand, Adam; Schmid, Peter; Taira, Kunihiko; Cattafesta, Louis
2015-11-01
Trailing vortices are commonly associated with diminished aircraft performance by increasing induced drag and producing a wake hazard on following aircraft. Previously, stability analyses have been performed on the Batchelor vortex (Heaton et al., 2009), which models a far field axisymmetric vortex, and airfoil wakes (Woodley & Peake, 1997). Both analyses have shown various instabilities present in these far field vortex-wake flows. This complicates the design of control devices by excluding consideration of near field interactions between the wake and vortex shed from the wing. In this study, we perform temporal and spatial bi-global stability analyses on the near field wake of the flow field behind a NACA0012 wing computed from direct numerical simulation at a chord Reynolds number of 1000. The results identify multiple instabilities including a vortex instability, wake instability, and mixed instability that includes interaction between the wake and vortex. As these modes exhibit wave packets, we perform a wave packet analysis (Obrist & Schmid, 2010), which enables the prediction of spatial mode structures at low computational cost. Furthermore, a bi-global parabolized stability analysis is performed, highlighting disparities between the parallel and parabolized analysis. ONR Grant N00014010824 and NSF PIRE Grant OISE-0968313.
Stability Analysis of ISS Medications
NASA Technical Reports Server (NTRS)
Wotring, V. E.
2014-01-01
It is known that medications degrade over time, and that extreme storage conditions will hasten their degradation. The temperature and humidity conditions of the ISS have been shown to be within the ideal ranges for medication storage, but the effects of other environmental factors, like elevated exposure to radiation, have not yet been evaluated. Current operational procedures ensure that ISS medications are re-stocked before expiration, but this may not be possible on long duration exploration missions. For this reason, medications that have experienced long duration storage on the ISS were returned to JSC for analysis to determine any unusual effects of aging in the low- Earth orbit environment. METHODS Medications were obtained by the JSC Pharmacy from commercial distributors and were re-packaged by JSC pharmacists to conserve up mass and volume. All medication doses were part of the ISS crew medical kit and were transported to the International Space Station (ISS) via NASA's Shuttle Transportation System (Space Shuttle). After 568 days of storage, the medications were removed from the supply chain and returned to Earth on a Dragon (SpaceX) capsule. Upon return to Earth, medications were transferred to temperature and humidity controlled environmental chambers until analysis. Nine medications were chosen on the basis of their availability for study. The medications included several of the most heavily used by US crewmembers: 2 sleep aids, 2 antihistamines/decongestants, 3 pain relievers, an antidiarrheal and an alertness medication. Each medication was available at a single time point; analysis of the same medication at multiple time points was not possible. Because the samples examined in this study were obtained opportunistically from medical supplies, there were no control samples available (i.e. samples aged for a similar period of time on the ground); a significant limitation of this study. Medications were analyzed using the HPLC/MS methods described in the United States Pharmacopeia (USP) to measure the amount of intact active ingredient, identify degradation products and measure their amounts. Some analyses were conducted by an independent analytical laboratory, but certain (Schedule) medications could not be shipped to their facility and were analyzed at JSC. RESULTS Nine medications were analyzed with respect to active pharmaceutical ingredient (API) and degradant amounts. Results were compared to the USP requirements for API and degradants/impurities content for every FDA-approved medication. One medication met USP requirements at 5 months after its expiration date. Four of the nine (44% of those tested) medications tested met USP requirements up to 8 months post-expiration. Another 3 medications (33% of those tested) met USP guidelines 2-3 months before expiration. One medication, a compound classed by the FDA as a dietary supplement and sometimes used as a sleep aid, failed to meet USP requirements at 11 months post-expiration. CONCLUSION Analysis of each medication at a single time point provides limited information on the stability of a medication stored in particular conditions; it is not possible to predict how long a medication may be safe and effective from these data. Notwithstanding, five of the nine medications tested (56%) met USP requirements for API and degradants/impurities at least 5 months past expiration dates. The single compound that failed to meet USP requirements is not regulated as strictly as prescription medications are during manufacture; it is unknown if this medication would have met the requirements prior to flight. Notably, it was the furthest beyond its expiration date. Only more comprehensive analysis of flight-aged samples compared to appropriate ground controls will permit determination of spaceflight effects on medication stability.
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.
NASA Astrophysics Data System (ADS)
Collier, A.; Lao, L. L.; Abla, G.; Chu, M. S.; Prater, R.; Smith, S. P.; St. John, H. E.; Guo, W.; Li, G.; Pan, C.; Ren, Q.; Park, J. M.; Bisai, N.; Srinivasan, R.; Sun, A. P.; Liu, Y.; Worrall, M.
2010-11-01
This presentation summarizes several useful applications provided by the IMFIT integrated modeling framework to support DIII-D and EAST research. IMFIT is based on Python and utilizes modular task-flow architecture with a central manager and extensive GUI support to coordinate tasks among component modules. The kinetic-EFIT application allows multiple time-slice reconstructions by fetching pressure profile data directly from MDS+ or from ONETWO or PTRANSP. The stability application analyzes a given reference equilibrium for stability limits by performing parameter perturbation studies with MHD codes such as DCON, GATO, ELITE, or PEST3. The transport task includes construction of experimental energy and momentum fluxes from profile analysis and comparison against theoretical models such as MMM95, GLF23, or TGLF.
Aeromechanical stability analysis of COPTER
NASA Technical Reports Server (NTRS)
Yin, Sheng K.; Yen, Jing G.
1988-01-01
A plan was formed for developing a comprehensive, second-generation system with analytical capabilities for predicting performance, loads and vibration, handling qualities, aeromechanical stability, and acoustics. This second-generation system named COPTER (COmprehensive Program for Theoretical Evaluation of Rotorcraft) is designed for operational efficiency, user friendliness, coding readability, maintainability, transportability, modularity, and expandability for future growth. The system is divided into an executive, a data deck validator, and a technology complex. At present a simple executive, the data deck validator, and the aeromechanical stability module of the technology complex were implemented. The system is described briefly, the implementation of the technology module is discussed, and correlation data presented. The correlation includes hingeless-rotor isolated stability, hingeless-rotor ground-resonance stability, and air-resonance stability of an advanced bearingless-rotor in forward flight.
Transition prediction using three dimensional stability analysis
NASA Technical Reports Server (NTRS)
Malik, M. R.
1980-01-01
Several methods of transition prediction by linear stability analysis are compared. The spectral stability analysis code SALLY is used to analyze flows over laminar flow control wings. It is shown that transition by the envelope method and a new modified wave packet method are comparable in reliability but that the envelope method is more efficient computationally.
Analysis of cavern and well stability at the West Hackberry SPR site using a full-dome model.
Sobolik, Steven R.
2015-08-01
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 repressurization 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 feet 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.
Stability analysis and stabilization strategies for linear supply chains
NASA Astrophysics Data System (ADS)
Nagatani, Takashi; Helbing, Dirk
2004-04-01
Due to delays in the adaptation of production or delivery rates, supply chains can be dynamically unstable with respect to perturbations in the consumption rate, which is known as “bull-whip effect”. Here, we study several conceivable production strategies to stabilize supply chains, which is expressed by different specifications of the management function controlling the production speed in dependence of the stock levels. In particular, we will investigate, whether the reaction to stock levels of other producers or suppliers has a stabilizing effect. We will also demonstrate that the anticipation of future stock levels can stabilize the supply system, given the forecast horizon τ is long enough. To show this, we derive linear stability conditions and carry out simulations for different control strategies. The results indicate that the linear stability analysis is a helpful tool for the judgement of the stabilization effect, although unexpected deviations can occur in the non-linear regime. There are also signs of phase transitions and chaotic behavior, but this remains to be investigated more thoroughly in the future.
Power System Transient Stability Analysis through a Homotopy Analysis Method
Wang, Shaobu; Du, Pengwei; Zhou, Ning
2014-04-01
As an important function of energy management systems (EMSs), online contingency analysis plays an important role in providing power system security warnings of instability. At present, N-1 contingency analysis still relies on time-consuming numerical integration. To save computational cost, the paper proposes a quasi-analytical method to evaluate transient stability through time domain periodic solutions’ frequency sensitivities against initial values. First, dynamic systems described in classical models are modified into damping free systems whose solutions are either periodic or expanded (non-convergent). Second, because the sensitivities experience sharp changes when periodic solutions vanish and turn into expanded solutions, transient stability is assessed using the sensitivity. Third, homotopy analysis is introduced to extract frequency information and evaluate the sensitivities only from initial values so that time consuming numerical integration is avoided. Finally, a simple case is presented to demonstrate application of the proposed method, and simulation results show that the proposed method is promising.
The stability of input structures in a supply-driven input-output model: A regional analysis
Allison, T.
1994-06-01
Disruptions in the supply of strategic resources or other crucial factor inputs often present significant problems for planners and policymakers. The problem may be particularly significant at the regional level where higher levels of product specialization mean supply restrictions are more likely to affect leading regional industries. To maintain economic stability in the event of a supply restriction, regional planners may therefore need to evaluate the importance of market versus non-market systems for allocating the remaining supply of the disrupted resource to the region`s leading consuming industries. This paper reports on research that has attempted to show that large short term changes on the supply side do not lead to substantial changes in input coefficients and do not therefore mean the abandonment of the concept of the production function as has been suggested (Oosterhaven, 1988). The supply-driven model was tested for six sectors of the economy of Washington State and found to yield new input coefficients whose values were in most cases close approximations of their original values, even with substantial changes in supply. Average coefficient changes from a 50% output reduction in these six sectors were in the vast majority of cases (297 from a total of 315) less than +2.0% of their original values, excluding coefficient changes for the restricted input. Given these small changes, the most important issue for the validity of the supply-driven input-output model may therefore be the empirical question of the extent to which these coefficient changes are acceptable as being within the limits of approximation.
NASA Technical Reports Server (NTRS)
Wong, R. C.; Owen, H. A., Jr.; Wilson, T. G.; Rodriguez, G. E.
1980-01-01
Small-signal modeling techniques are used in a system stability analysis of a breadboard version of a complete functional electrical power system. The system consists of a regulated switching dc-to-dc converter, a solar-cell-array simulator, a solar-array EMI filter, battery chargers and linear shunt regulators. Loss mechanisms in the converter power stage, including switching-time effects in the semiconductor elements, are incorporated into the modeling procedure to provide an accurate representation of the system without requiring frequency-domain measurements to determine the damping factor. The small-signal system model is validated by the use of special measurement techniques which are adapted to the poor signal-to-noise ratio encountered in switching-mode systems. The complete electrical power system with the solar-array EMI filter is shown to be stable over the intended range of operation.
Stability analysis of cylindrical Vlasov equilibria
Short, R W
1980-02-01
A method is presented for the fully kinetic, nonlocal stability analysis of cylindrically symmetric equilibria. Applications to the lower hybrid drift instability and the modes associated with a finite-width relativistic E-layer are discussed.
Nodal analysis for reactor kinetics and stability. [PWR; BWR
Park, J.K.; Becker, M.; Park, G.C.
1983-07-01
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 distribution, since that methodology is general and includes various commonly used nodal methods as special cases. Cross sections are correlated as functions of void fraction and exposure. A computer program investigating thermo-hydrodynamic stability, NUFREQ has been modified to accommodate general spatial kinetics models with an improved thermal-hydraulics model. Stability analyses have been performed for density wave oscillations for a representative operating BWR system. Spatial coupling effects on the stability margins were found to be significant.
Ciarletta, P.; Foret, L.; Ben Amar, M.
2011-01-01
Cutaneous melanoma is disproportionately lethal despite its relatively low incidence and its potential for cure in the early stages. The aim of this study is to foster understanding of the role of microstructure on the occurrence of morphological changes in diseased skin during melanoma evolution. The authors propose a biomechanical analysis of its radial growth phase, investigating the role of intercellular/stromal connections on the initial stages of epidermis invasion. The radial growth phase of a primary melanoma is modelled within the multi-phase theory of mixtures, reproducing the mechanical behaviour of the skin layers and of the epidermal–dermal junction. The theoretical analysis takes into account those cellular processes that have been experimentally observed to disrupt homeostasis in normal epidermis. Numerical simulations demonstrate that the loss of adhesiveness of the melanoma cells both to the basal laminae, caused by deregulation mechanisms of adherent junctions, and to adjacent keratynocytes, consequent to a downregulation of E-cadherin, are the fundamental biomechanical features for promoting tumour initiation. Finally, the authors provide the mathematical proof of a long wavelength instability of the tumour front during the early stages of melanoma invasion. These results open the perspective to correlate the early morphology of a growing melanoma with the biomechanical characteristics of its micro-environment. PMID:20656740
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.
NASA Astrophysics Data System (ADS)
Naguib, Ibrahim A.; Darwish, Hany W.
2012-02-01
A comparison between support vector regression (SVR) and Artificial Neural Networks (ANNs) multivariate regression methods is established showing the underlying algorithm for each and making a comparison between them to indicate the inherent advantages and limitations. In this paper we compare SVR to ANN with and without variable selection procedure (genetic algorithm (GA)). To project the comparison in a sensible way, the methods are used for the stability indicating quantitative analysis of mixtures of mebeverine hydrochloride and sulpiride in binary mixtures as a case study in presence of their reported impurities and degradation products (summing up to 6 components) in raw materials and pharmaceutical dosage form via handling the UV spectral data. For proper analysis, a 6 factor 5 level experimental design was established resulting in a training set of 25 mixtures containing different ratios of the interfering species. An independent test set consisting of 5 mixtures was used to validate the prediction ability of the suggested models. The proposed methods (linear SVR (without GA) and linear GA-ANN) were successfully applied to the analysis of pharmaceutical tablets containing mebeverine hydrochloride and sulpiride mixtures. The results manifest the problem of nonlinearity and how models like the SVR and ANN can handle it. The methods indicate the ability of the mentioned multivariate calibration models to deconvolute the highly overlapped UV spectra of the 6 components' mixtures, yet using cheap and easy to handle instruments like the UV spectrophotometer.
Solar Dynamic Power System Stability Analysis and Control
NASA Technical Reports Server (NTRS)
Momoh, James A.; Wang, Yanchun
1996-01-01
The objective of this research is to conduct dynamic analysis, control design, and control performance test of solar power system. Solar power system consists of generation system and distribution network system. A bench mark system is used in this research, which includes a generator with excitation system and governor, an ac/dc converter, six DDCU's and forty-eight loads. A detailed model is used for modeling generator. Excitation system is represented by a third order model. DDCU is represented by a seventh order system. The load is modeled by the combination of constant power and constant impedance. Eigen-analysis and eigen-sensitivity analysis are used for system dynamic analysis. The effects of excitation system, governor, ac/dc converter control, and the type of load on system stability are discussed. In order to improve system transient stability, nonlinear ac/dc converter control is introduced. The direct linearization method is used for control design. The dynamic analysis results show that these controls affect system stability in different ways. The parameter coordination of controllers are recommended based on the dynamic analysis. It is concluded from the present studies that system stability is improved by the coordination of control parameters and the nonlinear ac/dc converter control stabilize system oscillation caused by the load change and system fault efficiently.
Stability analysis of zigzag boron nitride nanoribbons
Rai, Hari Mohan Late, Ravikiran; Saxena, Shailendra K.; Kumar, Rajesh; Sagdeo, Pankaj R.; Jaiswal, Neeraj K.; Srivastava, Pankaj
2015-05-15
We have explored the structural stability of bare and hydrogenated zigzag boron nitride nanoribbons (ZBNNRs). In order to investigate the structural stability, we calculate the cohesive energy for bare, one-edge and both edges H-terminated ZBNNRs with different widths. It is found that the ZBNNRs with width Nz=8 are energetically more favorable than the lower-width counterparts (Nz<8). Bare ZBNNRs have been found energetically most stable as compared to the edge terminated ribbons. Our analysis reveals that the structural stability is a function of ribbon-width and it is not affected significantly by the type of edge-passivation (one-edge or both-edges)
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.
Stability/Instability Analysis of Rotating Machinery
NASA Technical Reports Server (NTRS)
Powers, Richard W.
1987-01-01
Numerical index of stability calculated for nonlinear system. Technique for determining rotor stability or instability from analysis of measurements adapted for use with computer simulations of rotor motion. Involves calculation of log decrement or increment of vibration amplitude. Applicable to rotors mounted in loose bearings and to similar problems in which load-versus-deflection characteristics nonlinear. Developed for assessments of vibrational characteristics of turbopump rotors, technique also usable with such mechanisms as high-speed ball bearings.
Stability analysis of unsteady ablation fronts
NASA Astrophysics Data System (ADS)
Betti, R.; McCrory, R. L.; Verdon, C. P.
1993-11-01
The linear stability analysis of unsteady ablation fronts is carried out for a semi-infinite uniform medium. For a laser accelerated target, it is shown that a properly selected modulation of the laser intensity can lead to the dynamic stabilization or growth-rate reduction of a large portion of the unstable spectrum. The theory is in qualitative agreement with the numerical results obtained by using the two-dimensional hydrodynamic code orchid.
Stability analysis of unsteady ablation fronts
Betti, R.; McCrory, R.L.; Verdon, C.P.
1993-08-01
The linear stability analysis of unsteady ablation fronts, is carried out for a semi-infinite uniform medium. For a laser accelerated target, it is shown that a properly selected modulation of the laser intensity can lead to the dynamic stabilization or growth-rate reduction of a large portion of the unstable spectrum. The theory is in qualitative agreement with the numerical results obtained by using the two-dimensional hydrodynamic code ORCHID.
Stability analysis of unsteady ablation fronts
Betti, R.; McCrory, R.L.; Verdon, C.P. )
1993-11-08
The linear stability analysis of unsteady ablation fronts is carried out for a semi-infinite uniform medium. For a laser accelerated target, it is shown that a properly selected modulation of the laser intensity can lead to the dynamic stabilization or growth-rate reduction of a large portion of the unstable spectrum. The theory is in qualitative agreement with the numerical results obtained by using the two-dimensional hydrodynamic code ORCHID.
Stability analysis of unsteady ablation fronts
NASA Astrophysics Data System (ADS)
Betti, R.; McCrory, R. L.; Verdon, C. P.
1993-08-01
The linear stability analysis of unsteady ablation fronts is carried out for a semi-infinite uniform medium. For a laser accelerated target, it is shown that a properly selected modulation of the laser intensity can lead to the dynamic stabilization or growth-rate reduction of a large portion of the unstable spectrum. The theory is in qualitative agreement with the numerical results obtained by using the two-dimensional hydrodynamic code ORCHID.
Voltage stability analysis in the new deregulated environment
NASA Astrophysics Data System (ADS)
Zhu, Tong
Nowadays, a significant portion of the power industry is under deregulation. Under this new circumstance, network security analysis is more critical and more difficult. One of the most important issues in network security analysis is voltage stability analysis. Due to the expected higher utilization of equipment induced by competition in a power market that covers bigger power systems, this issue is increasingly acute after deregulation. In this dissertation, some selected topics of voltage stability analysis are covered. In the first part, after a brief review of general concepts of continuation power flow (CPF), investigations on various matrix analysis techniques to improve the speed of CPF calculation for large systems are reported. Based on these improvements, a new CPF algorithm is proposed. This new method is then tested by an inter-area transaction in a large inter-connected power system. In the second part, the Arnoldi algorithm, the best method to find a few minimum singular values for a large sparse matrix, is introduced into the modal analysis for the first time. This new modal analysis is applied to the estimation of the point of voltage collapse and contingency evaluation in voltage security assessment. Simulations show that the new method is very efficient. In the third part, after transient voltage stability component models are investigated systematically, a novel system model for transient voltage stability analysis, which is a logical-algebraic-differential-difference equation (LADDE), is offered. As an example, TCSC (Thyristor controlled series capacitors) is addressed as a transient voltage stabilizing controller. After a TCSC transient voltage stability model is outlined, a new TCSC controller is proposed to enhance both fault related and load increasing related transient voltage stability. Its ability is proven by the simulation.
Moduli stabilization in stringy ISS models
Nakayama, Yu; Nakayama, Yu; Yamazaki, Masahito; Yanagida, T.T.
2007-09-28
We present a stringy realization of the ISS metastable SUSY breaking model with moduli stabilization. The mass moduli of the ISS model is stabilized by gauging of a U(1) symmetry and its D-term potential. The SUSY is broken both by F-terms and D-terms. It is possible to obtain de Sitter vacua with a vanishingly small cosmological constant by an appropriate fine-tuning of flux parameters.
The nu Andromedae System: Models and Stability
NASA Technical Reports Server (NTRS)
Stepinski, Tomasz F.; Malhotra, Renu; Black, David C.
2000-01-01
Radial velocity observations of the F8 V star nu Andromedae taken at Lick and at Whipple Observatories have revealed evidence of three periodicities in the line-of-sight velocity of the star. These periodicities have been interpreted as evidence for at least three low-mass companions (LMCs) revolving around nu Andromedae. The mass and orbital parameters inferred for these companions raise questions about the dynamical stability of the system. We report here results from our independent analysis of the published radial velocity data, as well as new unpublished data taken at Lick Observatory. Our results confirm the finding of three periods in the data. Our best fits to the data, on the assumption that these periods arise from the gravitational perturbations of companions in Keplerian orbits, are also generally in agreement but with some differences from the earlier findings. We find that the available data do not constrain well the orbital eccentricity of the middle companion in a three-companion model of the data. We also find that in order for our best-fit model to the Lick data to be dynamically stable over the lifetime of the star (approximately 2 billion years), the system must have a mean inclination to the plane of the sky greater than 13 deg. The corresponding minimum inclination for the best fit to the Whipple data set is 19 deg. These values imply that the maximum mass for the outer companion can be no greater than about 20 Jupiter masses. Our analysis of the stability of the putative systems also places constraints on the relative inclinations of the orbital planes of the companions. We comment on global versus local (i.e., method of steepest descent) means of finding best-fit orbits from radial velocity data sets.
Wang, Zhiyuan; Sun, Z. Z.
2014-02-14
The stationary-state solutions of magnetization dynamics under a spin-polarized current that was polarized in an arbitrary direction were investigated by solving the Landau-Lifshitz-Gilbert-Slonczewski equation for a single-domain magnet. Taking into consideration the uniaxial magnetic anisotropy, the equilibrium directions of the magnetization vectors were analytically obtained by solving an algebraic cubic equation. It was found that one to three pairs of magnetization equilibrium states existed, depending on the current intensity and the direction of the spin polarization. By numerically analyzing the stabilities of these equilibrium states, the threshold switching current for the reversing the magnetic vector was obtained under different current polarization configurations, which may be useful for use in future spintronics devices.
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.
Advanced stability analysis for laminar flow control
NASA Technical Reports Server (NTRS)
Orszag, S. A.
1981-01-01
Five classes of problems are addressed: (1) the extension of the SALLY stability analysis code to the full eighth order compressible stability equations for three dimensional boundary layer; (2) a comparison of methods for prediction of transition using SALLY for incompressible flows; (3) a study of instability and transition in rotating disk flows in which the effects of Coriolis forces and streamline curvature are included; (4) a new linear three dimensional instability mechanism that predicts Reynolds numbers for transition to turbulence in planar shear flows in good agreement with experiment; and (5) a study of the stability of finite amplitude disturbances in axisymmetric pipe flow showing the stability of this flow to all nonlinear axisymmetric disturbances.
Sand Bank Weakly Nonlinear Stability Analysis
NASA Astrophysics Data System (ADS)
Tambroni, N.; Blondeaux, P.
2006-12-01
In the continental shelf, tidal currents often give rise to large scale periodic bed forms named sand banks. Sand banks are long ridges (length of the order of several tens of kilometers) with a spacing (crest to crest distance) up to 10 km and a height up to several tens of meters. Their crests are almost aligned with the tidal currents, forming small positive or negative angles. Although reliable models based on linear stability analyses exist to predict the main geometrical characteristics of the sand banks as they start to appear, little is known on the morphodynamic processes that shape and maintain these bed forms in equilibrium conditions. A weakly nonlinear analysis is a powerful tool to investigate the equilibrium configuration attained by unstable bottom perturbations when the parameters of the problem are close to the critical values. However difficulties arise to apply a weakly nonlinear analysis of sand bank dynamics because the linear approaches predict infinite wavelengths of the most unstable mode close to the critical conditions. Here we first revisit the linear approach of Hulscher et al. (1993, Cont. Shelf Res. 13). In particular the time development of small amplitude bottom perturbations forced by tidal currents is studied using a different parameterization of both the bed shear stress and the sediment transport predictor which provides vanishing values of the sediment transport rate when the bottom shear stress is smaller than a critical value and accounts for the deviation of the sediment transport rate from the depth averaged velocity. With these improvements, both clockwise and counterclockwise sand banks are predicted. Moreover the wavelength of the most unstable mode close to the critical conditions turns out to be finite. This result opens the possibility to carry out a weakly nonlinear stability analysis. Then the time development of the most unstable mode is studied for values of the parameters close to the marginal conditions. The analysis provides estimates of the sand bank equilibrium amplitude and predicts equilibrium profiles characterized by crests sharper than the troughs, a feature often observed in field surveys.
Stability analysis of spacecraft power systems
NASA Technical Reports Server (NTRS)
Halpin, S. M.; Grigsby, L. L.; Sheble, G. B.; Nelms, R. M.
1990-01-01
The problems in applying standard electric utility models, analyses, and algorithms to the study of the stability of spacecraft power conditioning and distribution systems are discussed. Both single-phase and three-phase systems are considered. Of particular concern are the load and generator models that are used in terrestrial power system studies, as well as the standard assumptions of load and topological balance that lead to the use of the positive sequence network. The standard assumptions regarding relative speeds of subsystem dynamic responses that are made in the classical transient stability algorithm, which forms the backbone of utility-based studies, are examined. The applicability of these assumptions to a spacecraft power system stability study is discussed in detail. In addition to the classical indirect method, the applicability of Liapunov's direct methods to the stability determination of spacecraft power systems is discussed. It is pointed out that while the proposed method uses a solution process similar to the classical algorithm, the models used for the sources, loads, and networks are, in general, more accurate. Some preliminary results are given for a linear-graph, state-variable-based modeling approach to the study of the stability of space-based power distribution networks.
Global stability analysis of electrified jets
NASA Astrophysics Data System (ADS)
Rivero-Rodriguez, Javier; Pérez-Saborid, Miguel
2014-11-01
Electrospinning is a common process used to produce micro and nano polymeric fibers. In this technique, the whipping mode of a very thin electrified jet generated in an electrospray device is nhanced in order to increase its elongation. In this work, we use a theoretical Eulerian model that describes the kinematics and dynamics of the midline of the jet, its radius and convective velocity. The model equations result from balances of mass, linear and angular momentum applied to any differential slice of the jet together with constitutive laws for viscous forces and moments, as well as appropriate expressions for capillary and electrical forces. As a first step towards computing the complete nonlinear, transient dynamics of the electrified jet, we have performed a global stability analysis of the forementioned equations and compared the results with experimental data obtained by Guillaume et al. [2011] and Guerrero-Millán et al. [2014]. The support of the Ministry of Science and Innovation of Spain (Project DPI 2010-20450-C03-02) is acknowledged.
Stability analysis in tachyonic potential chameleon cosmology
Farajollahi, H.; Salehi, A.; Tayebi, F.; Ravanpak, A. E-mail: a.salehi@guilan.ac.ir E-mail: aravanpak@guilan.ac.ir
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.
HVDC models used in stability studies
Johnson, B.K.
1989-04-01
A new generation of detailed models for HVDC systems has recently been applied in power system stability programs. These models represent the high speed dynamics of the converter controllers as well as the L/R dynamics of the dc transmission. Older dc models such as those described in reference which are based upon pseudo-steady state relationships are however still in general use. The latter models remain popular since they require a minimum of data and significantly less computer resources than the detailed models. The following questions therefore need to be answered concerning the two types of models: (1) To what extent is simulation accuracy impacted by using the older HVDC model. (2) Is the difference in precision significant compared to other uncertainties which are inherent in stability calculations. This paper addresses these questions and also considers a third type of HVDC model described in Appendix I which relieves some of the assumptions associated with the pseudo steady state models.
Stock market stability: Diffusion entropy analysis
NASA Astrophysics Data System (ADS)
Li, Shouwei; Zhuang, Yangyang; He, Jianmin
2016-05-01
In this article, we propose a method to analyze the stock market stability based on diffusion entropy, and conduct an empirical analysis of Dow Jones Industrial Average. Empirical results show that this method can reflect the volatility and extreme cases of the stock market.
Wang, Jinliang; Zhang, Ran; Kuniya, Toshikazu
2015-01-01
In this paper, an Susceptible-Vaccines-Exposed-Infectious-Recovered model with continuous age-structure in the exposed and infectious classes is investigated. These two ages are assumed to have arbitrary distributions that are represented by age-specific rates leaving the exposed and the infectious classes. We investigate the global dynamics of this model in the sense of basic reproduction number via constructing Lyapunov functions. The asymptotic smoothness of solutions and uniform persistence of the system is shown from reformulating the system as a system of Volterra integral equations. PMID:25689314
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".
Temperature dependent stability model for graphene nanoribbon interconnects
NASA Astrophysics Data System (ADS)
Chanu, Waikhom Mona; Das, Debaprasad
2016-04-01
In this paper, a temperature dependent equivalent circuit model for graphene nanoribbon (GNR) interconnects is proposed. The stability analysis of GNR interconnects is performed using this proposed model and its performance is compared with respect to that of the copper based interconnects. The analysis is performed for different interconnect systems for 16nm ITRS technology node. With increase in the length of interconnects, the relative stability increases. GNR interconnect shows less increase of resistance with the increase in temperature as compared to Cu interconnects.
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.
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 a Uniformly Heated Channel with Supercritical Water
Ortega Gomez, T.; Class, A.; Schulenberg, T.; Lahey, R.T. Jr.
2006-07-01
The thermal-hydraulic stability of a uniformly heated channel at supercritical water pressure has been investigated to help understand the system instability phenomena which may occur in Supercritical Water Nuclear Reactors (SCWR). We have extended the modeling approach often used for Boiling Water Nuclear Reactor (BWR) stability analysis to supercritical pressure operation conditions. We have shown that Ledinegg excursive instabilities and pressure-drop oscillations (PDO) will not occur in supercritical water systems. The linear stability characteristics of a typical uniformly heated channel were computed by evaluating the eigenvalues of the model. An analysis of non-linear instability phenomena was also performed in the time domain and the dynamic bifurcations were evaluated. (authors)
Stability analysis of automobile driver steering control
NASA Technical Reports Server (NTRS)
Allen, R. W.
1981-01-01
In steering an automobile, the driver must basically control the direction of the car's trajectory (heading angle) and the lateral deviation of the car relative to a delineated pathway. A previously published linear control model of driver steering behavior which is analyzed from a stability point of view is considered. A simple approximate expression for a stability parameter, phase margin, is derived in terms of various driver and vehicle control parameters, and boundaries for stability are discussed. A field test study is reviewed that includes the measurement of driver steering control parameters. Phase margins derived for a range of vehicle characteristics are found to be generally consistent with known adaptive properties of the human operator. The implications of these results are discussed in terms of driver adaptive behavior.
NASA Astrophysics Data System (ADS)
Borisov, M.; Dimitrova, N.
2011-11-01
We consider an ecological model for biodegradation of toxic substances in aquatic and atmospheric biotic systems. The model, which is described by a nonlinear system of four ordinary differential equations, is known to be experimentally validated. We compute the equilibrium points of the model and study their asymptotic stability. The Maple package BifTools is used to calculate one- and two-parameter bifurcations of the equilibrium points.
Stabilization of thermal lattice Boltzmann models
McNamara, G.R.; Garcia, A.L.; Alder, B.J.
1995-10-01
A three-dimensional thermal lattice-Boltzmann model with two relaxation times to separately control viscosity and thermal diffusion is developed. Numerical stability of the model is significantly improved using Lax-Wendroff advection to provide an adjustable time step. Good agreement with a conventional finite-difference Navier-Stokes solver is obtained in modeling compressible Rayleigh-Benard convection when boundary conditions are treated similarly.
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.
Stability Analysis of the Slowed-Rotor Compound Helicopter Configuration
NASA Technical Reports Server (NTRS)
Floros, Matthew W.; Johnson, Wayne
2007-01-01
The stability and control of rotors at high advance ratio are considered. Teetering, articulated, gimbaled, and rigid hub types are considered for a compound helicopter (rotor and fixed wing). Stability predictions obtained using an analytical rigid flapping blade analysis, a rigid blade CAMRAD II model, and an elastic blade CAMRAD II model are compared. For the flapping blade analysis, the teetering rotor is the most stable, showing no instabilities up to an advance ratio of 3 and a Lock number of 18. A notional elastic blade model of a teetering rotor is unstable at an advance ratio of 1.5, independent of pitch frequency. Analysis of the trim controls and blade flapping shows that for small positive collective pitch, trim can be maintained without excessive control input or flapping angles.
Stability Analysis of the Slowed-Rotor Compound Helicopter Configuration
NASA Technical Reports Server (NTRS)
Johnson, Wayne; Floros, Matthew W.
2004-01-01
The stability and control of rotors at high advance ratio are considered. Teetering, articulated, gimbaled, and rigid hub types are considered for a compound helicopter (rotor and fixed wing). Stability predictions obtained using an analytical rigid flapping blade analysis, a rigid blade CAMRAD II model, and an elastic blade CAMRAD II model are compared. For the flapping blade analysis, the teetering rotor is the most stable, 5howing no instabilities up to an advance ratio of 3 and a Lock number of 18. With an elastic blade model, the teetering rotor is unstable at an advance ratio of 1.5. Analysis of the trim controls and blade flapping shows that for small positive collective pitch, trim can be maintained without excessive control input or flapping angles.
Analysis of Stabilization Mechanisms in Lifted Flames
NASA Astrophysics Data System (ADS)
Navarro-Martinez, S.; Kronenburg, A.
2009-12-01
Flame stabilization and the mechanisms that govern the dynamics at the flame base have been subject to numerous studies in recent years. Recent results using a combined Large Eddy Simulation-Conditional Moment Closure (LES-CMC) approach to model the turbulent flow field and the turbulence-chemistry interactions has been successful in predicting flame ignition and stabilization by auto-ignition, but LES-CMCs capability of the accurate modelling of the competition between turbulent quenching and laminar and turbulent flame propagation at the anchor point has not been resolved. This paper will consolidate LES-CMC results by analysing a wide range of lifted flame geometries with different prevailing stabilization mechanisms. The simulations allow a clear distinction of the prevailing stabilization mechanisms for the different flames, LES-CMC accurately predicts the competition between turbulence and chemistry during the auto-ignition process, however, the dynamics of the extinction process and turbulent flame propagation are not well captured. The averaging process inherent in the CMC methods does not allow for an instant response of the transported conditionally averaged reactive species to the changes in the flow conditions and any response of the scalars will therefore be delayed. Stationary or quasi-stationary conditions, however, can be well predicted for all flame configurations.
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.
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.
Stability analysis for a multi-camera photogrammetric system.
Habib, Ayman; Detchev, Ivan; Kwak, Eunju
2014-01-01
Consumer-grade digital cameras suffer from geometrical instability that may cause problems when used in photogrammetric applications. This paper provides a comprehensive review of this issue of interior orientation parameter variation over time, it explains the common ways used for coping with the issue, and describes the existing methods for performing stability analysis for a single camera. The paper then points out the lack of coverage of stability analysis for multi-camera systems, suggests a modification of the collinearity model to be used for the calibration of an entire photogrammetric system, and proposes three methods for system stability analysis. The proposed methods explore the impact of the changes in interior orientation and relative orientation/mounting parameters on the reconstruction process. Rather than relying on ground truth in real datasets to check the system calibration stability, the proposed methods are simulation-based. Experiment results are shown, where a multi-camera photogrammetric system was calibrated three times, and stability analysis was performed on the system calibration parameters from the three sessions. The proposed simulation-based methods provided results that were compatible with a real-data based approach for evaluating the impact of changes in the system calibration parameters on the three-dimensional reconstruction. PMID:25196012
Stability Analysis for a Multi-Camera Photogrammetric System
Habib, Ayman; Detchev, Ivan; Kwak, Eunju
2014-01-01
Consumer-grade digital cameras suffer from geometrical instability that may cause problems when used in photogrammetric applications. This paper provides a comprehensive review of this issue of interior orientation parameter variation over time, it explains the common ways used for coping with the issue, and describes the existing methods for performing stability analysis for a single camera. The paper then points out the lack of coverage of stability analysis for multi-camera systems, suggests a modification of the collinearity model to be used for the calibration of an entire photogrammetric system, and proposes three methods for system stability analysis. The proposed methods explore the impact of the changes in interior orientation and relative orientation/mounting parameters on the reconstruction process. Rather than relying on ground truth in real datasets to check the system calibration stability, the proposed methods are simulation-based. Experiment results are shown, where a multi-camera photogrammetric system was calibrated three times, and stability analysis was performed on the system calibration parameters from the three sessions. The proposed simulation-based methods provided results that were compatible with a real-data based approach for evaluating the impact of changes in the system calibration parameters on the three-dimensional reconstruction. PMID:25196012
DYNAMIC LANDSCAPES, STABILITY AND ECOLOGICAL MODELING
The image of a ball rolling along a series of hills and valleys is an effective heuristic by which to communicate stability concepts in ecology. However, the dynamics of this landscape model have little to do with ecological systems. Other landscape representations, however, are ...
Stability Analysis for HIFiRE Experiments
NASA Technical Reports Server (NTRS)
Li, Fei; Choudhari, Meelan M.; Chang, Chau-Lyan; White, Jeffery A.; Kimmel, Roger; Adamczak, David; Borg, Matthew; Stanfield, Scott; Smith, Mark S.
2012-01-01
The HIFiRE-1 flight experiment provided a valuable database pertaining to boundary layer transition over a 7-degree half-angle, circular cone model from supersonic to hypersonic Mach numbers, and a range of Reynolds numbers and angles of attack. This paper reports selected findings from the ongoing computational analysis of the measured in-flight transition behavior. Transition during the ascent phase at nearly zero degree angle of attack is dominated by second mode instabilities except in the vicinity of the cone meridian where a roughness element was placed midway along the length of the cone. The growth of first mode instabilities is found to be weak at all trajectory points analyzed from the ascent phase. For times less than approximately 18.5 seconds into the flight, the peak amplification ratio for second mode disturbances is sufficiently small because of the lower Mach numbers at earlier times, so that the transition behavior inferred from the measurements is attributed to an unknown physical mechanism, potentially related to step discontinuities in surface height near the locations of a change in the surface material. Based on the time histories of temperature and/or heat flux at transducer locations within the aft portion of the cone, the onset of transition correlated with a linear N-factor, based on parabolized stability equations, of approximately 13.5. Due to the large angles of attack during the re-entry phase, crossflow instability may play a significant role in transition. Computations also indicate the presence of pronounced crossflow separation over a significant portion of the trajectory segment that is relevant to transition analysis. The transition behavior during this re-entry segment of HIFiRE-1 flight shares some common features with the predicted transition front along the elliptic cone shaped HIFiRE-5 flight article, which was designed to provide hypersonic transition data for a fully 3D geometric configuration. To compare and contrast the crossflow dominated transition over the HIFiRE-1 and HIFiRE-5 configurations, this paper also analyzes boundary layer instabilities over a subscale model of the HIFiRE-5 flight configuration that was tested in the Mach 6 quiet tunnel facility at Purdue University.
Stability analysis of White Oak Dam
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.
Stability of Ensemble Models Predicts Productivity of Enzymatic Systems
Theisen, Matthew K.; Lafontaine Rivera, Jimmy G.; Liao, James C.
2016-01-01
Stability in a metabolic system may not be obtained if incorrect amounts of enzymes are used. Without stability, some metabolites may accumulate or deplete leading to the irreversible loss of the desired operating point. Even if initial enzyme amounts achieve a stable steady state, changes in enzyme amount due to stochastic variations or environmental changes may move the system to the unstable region and lose the steady-state or quasi-steady-state flux. This situation is distinct from the phenomenon characterized by typical sensitivity analysis, which focuses on the smooth change before loss of stability. Here we show that metabolic networks differ significantly in their intrinsic ability to attain stability due to the network structure and kinetic forms, and that after achieving stability, some enzymes are prone to cause instability upon changes in enzyme amounts. We use Ensemble Modelling for Robustness Analysis (EMRA) to analyze stability in four cell-free enzymatic systems when enzyme amounts are changed. Loss of stability in continuous systems can lead to lower production even when the system is tested experimentally in batch experiments. The predictions of instability by EMRA are supported by the lower productivity in batch experimental tests. The EMRA method incorporates properties of network structure, including stoichiometry and kinetic form, but does not require specific parameter values of the enzymes. PMID:26963521
Aggregation in ecosystem models and model stability
NASA Astrophysics Data System (ADS)
Giricheva, Evgeniya
2015-05-01
Using a multimodal approach to research ecosystems improves usage of available information on an object. This study presents several models of the Bering Sea ecosystem. The ecosystem is considered as a closed object, that is, the influence of the environment is not provided. We then add the links with the external medium in the models. The models differ in terms of the degree and method of grouping components. Our method is based on the differences in habitat and food source of groups, which allows us to determine the grouping of species with a greater effect on system dynamics. In particular, we determine whether benthic fish aggregation or pelagic fish aggregation can change the consumption structure of some groups of species, and consequently, the behavior of the entire model system.
Wilde, Juray de . E-mail: Guray.Marin@UGent.be; Vierendeels, Jan; Heynderickx, Geraldine J.; Marin, Guy B.
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.
A consistent orbital stability analysis for the GJ 581 system
Joiner, David A.; Sul, Cesar; Kress, Monika E.; Dragomir, Diana; Kane, Stephen R.
2014-06-20
We apply a combination of N-body modeling techniques and automated data fitting with Monte Carlo Markov Chain uncertainty analysis of Keplerian orbital models to RV data to determine long-term stability of the planetary system GJ 581. We find that while there are stability concerns with the four-planet model as published by Forveille et al., when uncertainties in the system are accounted for, particularly stellar jitter, the hypothesis that the four-planet model is gravitationally unstable is not statistically significant. Additionally, the system including proposed planet g by Vogt et al. also shows some stability concerns when eccentricities are allowed to float in the orbital fit, yet when uncertainties are included in the analysis, the system including planet g also cannot be proven to be unstable. We present revised reduced χ{sup 2} values for Keplerian astrocentric orbital fits assuming four-planet and five-planet models for GJ 581 under the condition that best fits must be stable, and we find no distinguishable difference by including planet g in the model. Additionally, we present revised orbital element estimates for each, assuming uncertainties due to stellar jitter under the constraint of the system being gravitationally stable.
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.
Shapes and stability of algebraic nuclear models
NASA Technical Reports Server (NTRS)
Lopez-Moreno, Enrique; Castanos, Octavio
1995-01-01
A generalization of the procedure to study shapes and stability of algebraic nuclear models introduced by Gilmore is presented. One calculates the expectation value of the Hamiltonian with respect to the coherent states of the algebraic structure of the system. Then equilibrium configurations of the resulting energy surface, which depends in general on state variables and a set of parameters, are classified through the Catastrophe theory. For one- and two-body interactions in the Hamiltonian of the interacting Boson model-1, the critical points are organized through the Cusp catastrophe. As an example, we apply this Separatrix to describe the energy surfaces associated to the Rutenium and Samarium isotopes.
Stability analysis and future singularity of the m{sup 2} R □{sup -2} R model of non-local gravity
Dirian, Yves; Mitsou, Ermis E-mail: ermis.mitsou@unige.ch
2014-10-01
We analyse the classical stability of the model proposed by Maggiore and Mancarella, where gravity is modified by a term ∼ m{sup 2} R □{sup -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.
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.
Closed-loop stability of pharmacokinetic-pharmacodynamic models.
Wada, D R
1997-12-01
In automatic feedback control of intravenous drug infusions, convergence to the setpoint is an important objective. This paper examines the stability of pharmacokinetic-pharmacodynamic models of patient response regulated with proportional integral feedback. The model consists of three components: linear compartmental pharmacokinetics, a first-order lag, and sigmoidal static pharmacodynamics. The permitted pharmacokinetic models obey the principle of detailed balance and admit drug administration into and sampling from the same compartment. Convergence to the setpoint occurs if the reset time of the controller is greater than the maximum possible time constant of the first-order lag. The convergence analysis uses standard Popov stability theory and takes advantage of the little known fact that many pharmacokinetic models possess poles and zeros that alternate on the negative real axis. PMID:9348740
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 of the plasma sheet using Hall magnetohydrodynamics
NASA Astrophysics Data System (ADS)
Lee, D.-Y.
1999-09-01
Linear stability analysis of the plasma sheet configuration is performed using Hall magnetohydrodynamics, which is more appropriate than the strict ideal MHD for the stressed current sheet during the substorm growth phase. By adding the Hall term in Ohm's law we study the impact of the error involved in assuming perfect conductivity on the stability. The ballooning-like mode with large perpendicular wavenumber is considered, and its basic eigenmode equations are derived. The ballooning instability is currently one of the strong candidates for causing the substorm onset. Numerical computations of the eigenmode equations are carried out for some model equilibria. It is found that the Hall-MHD effect is not so significant in determining the ballooning stability, as the result is not much different from that of ideal MHD: (1) The ballooning instability is rather easily triggered in the model where the field lines are not too much stretched but the plasma beta still exceeds some critical value, which depends on the situation; (2) The ballooning mode, however, seems to be stabilized in the very stretched field models and is not destabilized by adding the Hall-MHD effect in such models. The result implies that the ballooning stability in the plasma sheet seems to be much more dependent on equilibrium properties such as the field shape than on the physical formulation. It is further suggested that extensive field modeling and subsequent tests for the ballooning mode are a high priority in future in order to establish a firm connection between ballooning instability and the substorm onset.
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.
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.
Modelling Hydrodynamic Stability in Electrochemical Cells
NASA Astrophysics Data System (ADS)
Pontes, J.; Mangiavacchi, N.; Rabello dos Anjos, G.; Barcia, O. E.; Mattos, O. R.; Tribollet, B.
2008-10-01
We review the key points concerning the linear stability of the classical von Kármán's solution of rotating disk flow, modified by the coupling, through the fluid viscosity, with concentration field of a chemical species. The results were recently published by Mangiavacchi et al. (Phys. Fluids, 19: 114109, 2007) and refer to electrochemical cells employing iron rotating disk electrodes, which dissolve in the 1 M H2SO4 solution of the electrolyte. Polarization curves obtained in such cells present a current instability at the beginning of the region where the current is controlled by the the hydrodynamics. The onset of the instability occurs in a range of potentials applied to the cell and disappear above and below this range. Dissolution of the iron electrode gives rise to a thin concentration boundary layer, with thickness of about 4% of the thickness of the hydrodynamic boundary layer. The concentration boundary layer increases the interfacial fluid viscosity, diminishes the diffusion coefficient and couples both fields, with a net result of affecting the hydrodynamic of the problem. Since the current is proportional to the interfacial concentration gradient of the chemical species responsible by the ions transport, the instability of the coupled fields can lead to the current instability observed in the experimental setups. This work presents the results of the linear stability analysis of the coupled fields and the first results concerning the Direct Numerical Simulation, currently undertaken in our group. The results show that small increases of the interfacial viscosity result in a significant reduction of the stability of modes existing in similar configurations, but with constant viscosity fluids. Upon increasing the interfacial viscosity, a new unstable region emerges, in a range of Reynolds numbers much smaller than the lower limit of the unstable region previously known. Though the growth rate of modes in the previously known region is larger than the one of modes in the new region, the amplitude of the concentration unstable modes in this one is very large when compared to the amplitude of the associated hydrodynamic unstable modes. In addition concentration modes are always confined in a rather thin region, leading to the existence of large interfacial concentration gradient. Concentration modes in the new unstable region seem thus, to have a combination of properties sufficient to drive detectable current oscillations. The numerical experiments show that a progressive increase in the interfacial viscosity initially reduces the stability of the flow, but an increase beyond a certain limit restores the stability properties of constant viscosity flows.
Stability of earthquake clustering models: criticality and branching ratios.
Zhuang, Jiancang; Werner, Maximilian J; Harte, David S
2013-12-01
We study the stability conditions of a class of branching processes prominent in the analysis and modeling of seismicity. This class includes the epidemic-type aftershock sequence (ETAS) model as a special case, but more generally comprises models in which the magnitude distribution of direct offspring depends on the magnitude of the progenitor, such as the branching aftershock sequence (BASS) model and another recently proposed branching model based on a dynamic scaling hypothesis. These stability conditions are closely related to the concepts of the criticality parameter and the branching ratio. The criticality parameter summarizes the asymptotic behavior of the population after sufficiently many generations, determined by the maximum eigenvalue of the transition equations. The branching ratio is defined by the proportion of triggered events in all the events. Based on the results for the generalized case, we show that the branching ratio of the ETAS model is identical to its criticality parameter because its magnitude density is separable from the full intensity. More generally, however, these two values differ and thus place separate conditions on model stability. As an illustration of the difference and of the importance of the stability conditions, we employ a version of the BASS model, reformulated to ensure the possibility of stationarity. In addition, we analyze the magnitude distributions of successive generations of the BASS model via analytical and numerical methods, and find that the compound density differs substantially from a Gutenberg-Richter distribution, unless the process is essentially subcritical (branching ratio less than 1) or the magnitude dependence between the parent event and the direct offspring is weak. PMID:24483388
Stability of earthquake clustering models: Criticality and branching ratios
NASA Astrophysics Data System (ADS)
Zhuang, Jiancang; Werner, Maximilian J.; Harte, David S.
2013-12-01
We study the stability conditions of a class of branching processes prominent in the analysis and modeling of seismicity. This class includes the epidemic-type aftershock sequence (ETAS) model as a special case, but more generally comprises models in which the magnitude distribution of direct offspring depends on the magnitude of the progenitor, such as the branching aftershock sequence (BASS) model and another recently proposed branching model based on a dynamic scaling hypothesis. These stability conditions are closely related to the concepts of the criticality parameter and the branching ratio. The criticality parameter summarizes the asymptotic behavior of the population after sufficiently many generations, determined by the maximum eigenvalue of the transition equations. The branching ratio is defined by the proportion of triggered events in all the events. Based on the results for the generalized case, we show that the branching ratio of the ETAS model is identical to its criticality parameter because its magnitude density is separable from the full intensity. More generally, however, these two values differ and thus place separate conditions on model stability. As an illustration of the difference and of the importance of the stability conditions, we employ a version of the BASS model, reformulated to ensure the possibility of stationarity. In addition, we analyze the magnitude distributions of successive generations of the BASS model via analytical and numerical methods, and find that the compound density differs substantially from a Gutenberg-Richter distribution, unless the process is essentially subcritical (branching ratio less than 1) or the magnitude dependence between the parent event and the direct offspring is weak.
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.
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.
Fully Parallel MHD Stability Analysis Tool
NASA Astrophysics Data System (ADS)
Svidzinski, Vladimir; Galkin, Sergei; Kim, Jin-Soo; Liu, Yueqiang
2014-10-01
Progress on full parallelization of the plasma stability code MARS will be reported. MARS calculates eigenmodes in 2D axisymmetric toroidal equilibria in MHD-kinetic plasma models. It is a powerful tool for studying MHD and MHD-kinetic instabilities and it is widely used by fusion community. Parallel version of MARS is intended for simulations on local parallel clusters. It will be an efficient tool for simulation of MHD instabilities with low, intermediate and high toroidal mode numbers within both fluid and kinetic plasma models, already implemented in MARS. Parallelization of the code includes parallelization of the construction of the matrix for the eigenvalue problem and parallelization of the inverse iterations algorithm, implemented in MARS for the solution of the formulated eigenvalue problem. Construction of the matrix is parallelized by distributing the load among processors assigned to different magnetic surfaces. Parallelization of the solution of the eigenvalue problem is made by repeating steps of the present MARS algorithm using parallel libraries and procedures. Initial results of the code parallelization will be reported. Work is supported by the U.S. DOE SBIR program.
Physics-based stability analysis of MOS transistors
NASA Astrophysics Data System (ADS)
Ferrara, A.; Steeneken, P. G.; Boksteen, B. K.; Heringa, A.; Scholten, A. J.; Schmitz, J.; Hueting, R. J. E.
2015-11-01
In this work, a physics-based model is derived based on a linearization procedure for investigating the electrical, thermal and electro-thermal instability of power metal-oxide-semiconductor (MOS) transistors. The proposed model can be easily interfaced with a circuit or device simulator to perform a failure analysis, making it particularly useful for power transistors. Furthermore, it allows mapping the failure points on a three-dimensional (3D) space defined by the gate-width normalized drain current, drain voltage and junction temperature. This leads to the definition of the Safe Operating Volume (SOV), a powerful frame work for making failure predictions and determining the main root of instability (electrical, thermal or electro-thermal) in different bias and operating conditions. A comparison between the modeled and the measured SOV of silicon-on-insulator (SOI) LDMOS transistors is reported to support the validity of the proposed stability analysis.
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
Stability analysis of an evaporating binary mixture
NASA Astrophysics Data System (ADS)
Machrafi, Hatim; Rednikov, Alexey; Colinet, Pierre; Dauby, Pierre
2008-11-01
Rayleigh-Bénard-Marangoni instabilities in an evaporating binary mixture, consisting of a solvent and a solute of weak concentration, are studied theoretically. Local thermodynamic equilibrium is assumed at the flat gas-liquid interface. Solvent evaporation and air absorption in the liquid are neglected. At a certain height above the interface, the temperature and the concentration are fixed. One of the goals of the study is to track down the effects of this artifact on the results. Non-linear quasi-stationary basic profiles (due to evaporation) of the temperature and the solute concentration in the gas phase are considered, while the temperature distribution in the liquid is assumed to be linear and quasi-stationary. For the solute concentration in the liquid phase, two variants of the reference solution are studied, one just linear and quasi-stationary, whereas the other involves a fully transient non-linear profile. The latter is a more realistic option, given the relatively slow diffusion time in the liquid. A linear stability analysis is then carried out numerically, and illustrated for an aqueous solution of ethyl alcohol.
Flight stability analysis under changes in insect morphology
NASA Astrophysics Data System (ADS)
Noest, Robert; Wang, Z. Jane
2015-11-01
Insect have an amazing ability to control their flight, being able to perform both fast aerial maneuvers and stable hovering. The insect's neural system has developed various mechanism by which it can control these flying feats, but we expect that insect morphology is equally important in facilitating the aerial control. We perform a computational study using a quasi-steady instantaneous flapping flight model which allows us to freely adapt the insect's morphological parameters. We picked a fruit fly as the basis for the body shape and wing motion, and study the effect of changes to the morphology for a range of wing stroke amplitudes. In each case we determine the periodic flight mode, with the period equal to a single wing beat, and do a Floquet stability analysis of the flight. To interpret our results we will compare the changed morphology to related insects. We discuss the implications of the insects location on the stability diagram.
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.
Stability analysis of large electric power systems
Elwood, D.M.
1993-01-01
Modern electric power systems are large and complicated, and, in many regions of the world, the generation and transmission systems are operating near their limits. Ensuring the reliable operation of the power system requires engineers to study the response of the system to various disturbances. The responses to large disturbances are examined by numerically solving the nonlinear differential-algebraic equations describing the power system. The response to small disturbances is typically studied via eigenanalysis. The Electric Power Research Institute (EPRI) recently developed the Extended Transient/Mid-term Stability Program (ETMSP) to study large disturbance stability and the Small Signal Stability Program Package (SSSP) to study small signal stability. The primary objectives of the work described in this report were to (1) explore ways of speeding up ETMSP, especially on mid-term voltage stability problems, (2) explore ways of speeding up the Multi-Area Small-Signal Stability program (MASS), one of the codes in SSSP, and (3) explore ways of increasing the size of problem that can be solved by the Cray version of MASS.
Singular Isothermal Disks. I. Linear Stability Analysis
NASA Astrophysics Data System (ADS)
Shu, Frank H.; Laughlin, Gregory; Lizano, Susana; Galli, Daniele
2000-05-01
As part of a larger effort to understand how binary and single stars form from the collapse of magnetized molecular cloud cores, we perform a global stability analysis of isopedically magnetized, singular isothermal disks (SIDs). The work described here has precedents in earlier studies of disturbances in power-law disks by Zang in 1976, Toomre in 1977, Lynden-Bell & Lemos in 1993, Syer & Tremaine in 1996, and Goodman & Evans in 1999. We find the analytic criteria for the bifurcation of axisymmetric disks into nonaxisymmetric forms with azimuthal periodicities m=1 (eccentric displacements), 2 (oval distortions), 3 (triangular distortions), etc. These bifurcations, which occur at zero frequency, are the compressible and differentially rotating analogs of how the classical sequence of incompressible and uniformly rotating Maclaurin spheroids bifurcate (secularly, under dissipative forces) to become Dedekind ellipsoids with figure axes that remain fixed in space. Like Syer & Tremaine and Lynden-Bell & Lemos, we also find that zero-frequency logarithmic spirals are possible scale-free disturbances, but our interpretation of the existence of such steadily propagating wavetrains is different. We give a dynamical instability interpretation based on the onset of swing amplification by overreflection at the corotation circle of prograde spiral density waves the pattern speeds of which have nonzero and positive values. Our analysis yields identical instability criteria as the global normal-modes treatment of Goodman & Evans, and we tentatively also identify dynamical barred-spiral instabilities as the ``breathing mode'' limit of two-armed ordinary-spiral instabilities. We prove a general ``reciprocity theorem,'' which states that the overreflection factors are identical for spiral density waves launched from cavities interior or exterior to Q-barriers that straddle the corotation circle. This globally valid result supports a unifying interpretation, advocated for many years by C. C. Lin and his colleagues (see, e.g., work by Bertin & Lin): the coexistence of spiral structure in galaxies arising from the instability of internal normal modes in the combined star/gas disk or from driving by external tidal influences associated with the chance passages of companion bodies.
Landslide stability analysis on basis of LIDAR data extraction
NASA Astrophysics Data System (ADS)
Hu, Hui; Fernandez-Steeger, Tomas M.; Dong, Mei; Azzam, Rafig
2010-05-01
Currently, existing contradictory between remediation and acquisition from natural resource induces a series of divergences. With regard to open pit mining, legal regulation requires human to fill back the open pit area with water or recreate new landscape by other materials; on the other hand, human can not help excavating the mining area due to the shortage of power resource. However, to engineering geologists, one coincident problem which takes place not only in filling but also in mining operation should be paid more attention to, i.e. the slope stability analysis within these areas. There are a number of construction activities during remediation or mining process which can directly or indirectly cause slope failure. Lives can be endangered since local failure either while or after remediation; for mining process, slope failure in a bench, which carries a main haul road or is adjacent to human activity area, would be significant catastrophe to the whole mining program. The stability of an individual bench or slope is controlled by several factors, which are geological condition, morphology, climate, excavation techniques and transportation approach. The task which takes the longest time is to collect the morphological data. Consequently, it is one of the most dangerous tasks due to the time consuming in mining field. LIDAR scanning for morphological data collecting can help to skip this obstacle since advantages of LIDAR techniques as follows: • Dynamic range available on the market: from 3 m to beyond 1 km, • Ruggedly designed for demanding field applications, • Compact, easily hand-carried and deployed by a single operator. In 2009, scanning campaigns for 2 open pit quarry have been carried out. The aim for these LIDAR detections is to construct a detailed 3D quarry model and analyze the bench stability to support the filling planning. The 3D quarry surface was built up by using PolyWorks 10.1 on basis of LIDAR data. LIDAR data refining takes an important role during surface construction for further more precise analysis purpose. 3D geological model can be built based on the connection between surface model and geological data like borehole data in GOCAD. Regarding the bench stability analysis, LEM (Limit Equilibrium Method) analysis using Janbu and FEM (Finite Element Method) have been adopted during this analyzing task. A program was developed to convert GOCAD 2D section data directly into the FEM software. The meshed model is then used for stability analysis. In one quarry, 3 cross sections have been extracted on basis of LIDAR original data (original 3 cross sections). To evaluate the advantages of LIDAR data for slope analysis, the results of safety factor (SF) were compared to simplified slope models as they are used normally. The comparison showed that variations of the SF reach up to 9%. Additionally, conservative evaluation demonstrated by SF results based on simplified model is not adaptive for decision making of filling.
Analysis of slope stabilization by soil bioengineering method
NASA Astrophysics Data System (ADS)
Switala, Barbara Maria; Wu, Wei
2013-04-01
The aim of the project is to create a numerical model which will include the impact of vegetation on the slope stability analysis, considering both mechanical and hydrological factors. This will enrich the current knowledge about how roots reinforce the soil layers on the slope and how it influences the increase of shear strength of the soil. This has to be combined together with hydrological effects caused by evapotranspiration: modified soil moisture regime, dissipation of excess pore pressure and established matric suction. Coupled analyses (mechanical and hydrological) are rarely conducted, or only outdated models are used, which leads to overestimation of the additional shear strength of soil. That is why there is a need to support this branch of landslide hazard assessment and develop a new model. This research will help to raise awareness, that soil bioengineering methods of slope stabilization can in some cases be more appropriate and less expensive than traditional methods. As an input to the model, the appropriate slope geometry and soil properties have to be chosen. It is also important to consider different plant types and root properties, as well as different levels of groundwater table. To assess the effect of evapotranspiration it is necessary to know the geographical location of the slope and the weather conditions in the chosen region. The final output of the model, which will help to quantitatively assess the impact of vegetation on the slope stability, is the factor of safety (FOS) for vegetated slope for different types of soil and degrees of saturation. Results may then be compared with different conditions and factors of safety, calculated for the corresponding non-vegetated slope. It will be possible to specify the most favorable and unfavorable conditions. Moreover, the calculations provide also information on changes of cohesion, caused by mechanical and hydrological effects, as well as the change in the friction angle of soil.
Research on Stability Analysis of International Prototype Kilogram
NASA Astrophysics Data System (ADS)
Ren, Xiaoping; Zhang, Yue; Wang, Jian; Ren, Qingxiong; Ren, Qingmao
Today, the kilogram is the last of the seven base units of the International System of Units (SI) which is based on a physical artifact. The demands of modern mass metrology have led to an increasing focus on the surface stability and analysis of mass standard. Methods for evaluating the correlation between the measured mass values of the prototypes of the kilogram includes: collection of historical calibration data for kilogram prototypes, setting up a model for deterministic and random changes in the mass of a kilogram prototype (relative to the IPK), adjustment of parameters in a model using historical calibration data, and prediction of future mass values of a kilogram prototype using model and adjusted parameters.
Analysis and prediction of longitudinal stability of airplanes
NASA Technical Reports Server (NTRS)
Gilruth, R R; White, M D
1941-01-01
An analysis has been made of the longitudinal stability characteristics of 15 airplanes as determined in flight. In the correlation of satisfactory and unsatisfactory characteristics with determined values, the derivative that expresses the ratio of static-restoring moments to elevator-control moments was found to represent most nearly the stability characteristics appreciated by the pilots. The analysis was extended to study the effects of various design features on the observed stability characteristics. Design charts and data are included that show the effects on longitudinal stability of relative positions of wing and tail, fuselage size and location, engine nacelles, and horizontal-tail arrangements.
NASA Technical Reports Server (NTRS)
Friedmann, P. P.; Venkatesan, C.
1985-01-01
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.
NASA Astrophysics Data System (ADS)
Dasgupta, Sambarta
Transient stability and sensitivity analysis of power systems are problems of enormous academic and practical interest. These classical problems have received renewed interest, because of the advancement in sensor technology in the form of phasor measurement units (PMUs). The advancement in sensor technology has provided unique opportunity for the development of real-time stability monitoring and sensitivity analysis tools. Transient stability problem in power system is inherently a problem of stability analysis of the non-equilibrium dynamics, because for a short time period following a fault or disturbance the system trajectory moves away from the equilibrium point. The real-time stability decision has to be made over this short time period. However, the existing stability definitions and hence analysis tools for transient stability are asymptotic in nature. In this thesis, we discover theoretical foundations for the short-term transient stability analysis of power systems, based on the theory of normally hyperbolic invariant manifolds and finite time Lyapunov exponents, adopted from geometric theory of dynamical systems. The theory of normally hyperbolic surfaces allows us to characterize the rate of expansion and contraction of co-dimension one material surfaces in the phase space. The expansion and contraction rates of these material surfaces can be computed in finite time. We prove that the expansion and contraction rates can be used as finite time transient stability certificates. Furthermore, material surfaces with maximum expansion and contraction rate are identified with the stability boundaries. These stability boundaries are used for computation of stability margin. We have used the theoretical framework for the development of model-based and model-free real-time stability monitoring methods. Both the model-based and model-free approaches rely on the availability of high resolution time series data from the PMUs for stability prediction. The problem of sensitivity analysis of power system, subjected to changes or uncertainty in load parameters and network topology, is also studied using the theory of normally hyperbolic manifolds. The sensitivity analysis is used for the identification and rank ordering of the critical interactions and parameters in the power network. The sensitivity analysis is carried out both in finite time and in asymptotic. One of the distinguishing features of the asymptotic sensitivity analysis is that the asymptotic dynamics of the system is assumed to be a periodic orbit. For asymptotic sensitivity analysis we employ combination of tools from ergodic theory and geometric theory of dynamical systems.
Nonlinear Stability of Weak Detonation Wavesfor a Combustion Model
NASA Astrophysics Data System (ADS)
Liu, Tai-Ping; Yu, Shih-Hsien
We show that the weak detonation waves for a combustion model of Rosales-Majda are nonlinearly stable. Because of the strongly nonlinear nature of the wave, usual stability analysis of weakly nonlinear nature does not apply. The chemical switch on-off is the main feature of nonlinearity. In particular, the propagation of the wave depends sensitively on the tail behaviour of the flow in front of it. Unlike the strong detonation waves, a weak detonation is supersonic and there is the separation of the gas waves from the reacting front. As a consequence, the reacting front needs to be traced.
Visual optimality and stability analysis of 3DCT scan positions.
Amirkhanov, Artem; Heinzl, Christoph; Reiter, Michael; Gröller, Eduard
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 identifies potentially good or bad placements of a specimen and regions of a specimen, which cause the major portion of artefacts. The tool can be used for a preliminary analysis of the specimen before CT scanning, in order to determine the optimal way of placing the object. The analysis includes: penetration lengths, placement stability and an investigation in Radon space. Novel visualization techniques are applied to the simulation data. A stability widget is presented for determining the placement parameters' robustness. The performance and the comparison of results provided by the tool compared with real world data is demonstrated using two specimens. PMID:20975189
Linear stability analysis for hydrothermal alteration of kimberlitic rocks
NASA Astrophysics Data System (ADS)
Afanasyev, Andrey; Belyaeva, Ekaterina
2016-04-01
The influx of groundwater into hot kimberlite deposits results in the reaction of water with olivine-rich rocks. The products of the reaction are serpentine and release of latent heat. The rise of temperature due to the heat release increases the rate of the reaction. Under certain conditions, this self-speeding up of the reaction can result in instabilities associated with a significantly higher final serpentinisation in slightly warmer regions of the kimberlite deposit. We conduct linear stability analysis of serpentinisation in an isolated volume of porous kimberlitic rocks saturated with water and an inert gas. There is a counteracting interplay between the heat release tending to destabilise the uniform distribution of parameters and the heat conduction tending to stabilise it by smoothing out temperature perturbations. We determine the critical spatial scale separating the parameters where one phenomenon dominates over another. The perturbations of longer-than-critical length grow, whereas the perturbations of shorter-than-critical length fade. The analytical results of the linear stability analysis are supported by direct numerical simulations using a full nonlinear model. Keywords: Hydrothermal systems, volcaniclastic deposits, phase transitions, instability analysis, numerical solutions
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.
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.
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.
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.
CFD Based Computations of Flexible Helicopter Blades for Stability Analysis
NASA Technical Reports Server (NTRS)
Guruswamy, Guru P.
2011-01-01
As a collaborative effort among government aerospace research laboratories an advanced version of a widely used computational fluid dynamics code, OVERFLOW, was recently released. This latest version includes additions to model flexible rotating multiple blades. In this paper, the OVERFLOW code is applied to improve the accuracy of airload computations from the linear lifting line theory that uses displacements from beam model. Data transfers required at every revolution are managed through a Unix based script that runs jobs on large super-cluster computers. Results are demonstrated for the 4-bladed UH-60A helicopter. Deviations of computed data from flight data are evaluated. Fourier analysis post-processing that is suitable for aeroelastic stability computations are performed.
NASA Technical Reports Server (NTRS)
Fitzjerrell, D. G.
1974-01-01
A general study of the stability of nonlinear as compared to linear control systems is presented. The analysis is general and, therefore, applies to other types of nonlinear biological control systems as well as the cardiovascular control system models. Both inherent and numerical stability are discussed for corresponding analytical and graphic methods and numerical methods.
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.
Wellbore stability analysis in carbonate reservoir considering anisotropic behaviour
NASA Astrophysics Data System (ADS)
Alves, Jos; 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.
Space Shuttle Main Engine real time stability analysis
NASA Astrophysics Data System (ADS)
Kuo, F. Y.
1993-06-01
The Space Shuttle Main Engine (SSME) is a reusable, high performance, liquid rocket engine with variable thrust. The engine control system continuously monitors the engine parameters and issues propellant valve control signals in accordance with the thrust and mixture ratio commands. A real time engine simulation lab was installed at MSFC to verify flight software and to perform engine dynamic analysis. A real time engine model was developed on the AD100 computer system. This model provides sufficient fidelity on the dynamics of major engine components and yet simplified enough to be executed in real time. The hardware-in-the-loop type simulation and analysis becomes necessary as NASA is continuously improving the SSME technology, some with significant changes in the dynamics of the engine. The many issues of interfaces between new components and the engine can be better understood and be resolved prior to the firing of the engine. In this paper, the SSME real time simulation Lab at the MSFC, the SSME real time model, SSME engine and control system stability analysis, both in real time and non-real time is presented.
Space Shuttle Main Engine real time stability analysis
NASA Technical Reports Server (NTRS)
Kuo, F. Y.
1993-01-01
The Space Shuttle Main Engine (SSME) is a reusable, high performance, liquid rocket engine with variable thrust. The engine control system continuously monitors the engine parameters and issues propellant valve control signals in accordance with the thrust and mixture ratio commands. A real time engine simulation lab was installed at MSFC to verify flight software and to perform engine dynamic analysis. A real time engine model was developed on the AD100 computer system. This model provides sufficient fidelity on the dynamics of major engine components and yet simplified enough to be executed in real time. The hardware-in-the-loop type simulation and analysis becomes necessary as NASA is continuously improving the SSME technology, some with significant changes in the dynamics of the engine. The many issues of interfaces between new components and the engine can be better understood and be resolved prior to the firing of the engine. In this paper, the SSME real time simulation Lab at the MSFC, the SSME real time model, SSME engine and control system stability analysis, both in real time and non-real time is presented.
Global Stability Analysis of Jet Diffusion Flames
NASA Astrophysics Data System (ADS)
Moreno-Boza, D.; Coenen, W.; Sevilla, A.; Sánchez, A. L.
2014-11-01
This work investigates the global stability of axisymmetric laminar jet diffusion flames at moderately large Reynolds numbers, including effects of buoyancy, temperature increase due to chemical reaction and air coflow. The ultimate objective is to clarify the two different types of instabilities observed in experiments, as well as the connection of these instabilities with the phenomenon of diffusion-flame flickering. Quasi-isobaric conditions corresponding to low-Mach-number jets are considered and stability results regarding hot and light jets are also described. The limit of infinitely fast chemical reaction is used in the development, which assumes also a unity value of the fuel Lewis number, thereby enabling a simplified description of the temperature and composition fields in terms of a single mixture-fraction variable. A finite-element method is developed to integrate the steady equations of continuity, momentum and mixture fraction, which determine the basic steady flame structure as well as the associated perturbed equations that determine its 2D global stability.
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.
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.
Ageostrophic linear stability analysis of the Labrador Current
NASA Astrophysics Data System (ADS)
Thomsen, S.; Eden, C.
2012-12-01
The water mass transformation process in the Labrador Sea during winter plays an important role for the Atlantic meridional overturning circulation and the global climate system. The Labrador Sea Water (LSW) is exported within the deep Labrador Current (LC) after the convection process. LSW takes up large amounts of atmospheric tracer gases as CO2 and oxygen, and is thus one of the major agent for ventilation of the abyssal ocean. It is shown that enhanced eddy kinetic energy (EKE) along the LC shows up in a 1/12 ocean model simulation during the transformation process. Moored in-situ measurements within the LC also show enhanced EKE levels during winter. This instability processes within the LC is important as it might alter the water mass properties of the (LSW) by frontal mixing processes during the water mass transformation and export within the LC. The frontal instability process, which lead to enhanced EKE along the LC during winter is investigated using ageostrophic linear stability analysis. Dense and weakly stratified water masses produced during the wintertime transformation process lead to weaker stratification and a strengthening of the lateral density gradients within the LC. Weak stratification and enhanced vertical shear result in low Richardson numbers and the growth rate of baroclinic waves increases significantly within the shelf break LC during winter. Rapid frontogenesis along the whole LC sets in resulting in enhance EKE. During the rest of the year strong stratification and weak vertical shear leads to larger Richardson numbers and smaller growth rates. Ageostrophic linear stability analysis shows that a geostrophic interior mode has similar wavelengths as the first wavelike disturbances in the model simulations. A shallow mode with lateral scales O (1 km) is also predicted, which can be associated with mixed layer instabilities and submesoscale variability but remains unresolved by the model simulation.
Sensitivity analysis of hydrodynamic stability operators
NASA Technical Reports Server (NTRS)
Schmid, Peter J.; Henningson, Dan S.; Khorrami, Mehdi R.; Malik, Mujeeb R.
1992-01-01
The eigenvalue sensitivity for hydrodynamic stability operators is investigated. Classical matrix perturbation techniques as well as the concept of epsilon-pseudoeigenvalues are applied to show that parts of the spectrum are highly sensitive to small perturbations. Applications are drawn from incompressible plane Couette, trailing line vortex flow and compressible Blasius boundary layer flow. Parametric studies indicate a monotonically increasing effect of the Reynolds number on the sensitivity. The phenomenon of eigenvalue sensitivity is due to the non-normality of the operators and their discrete matrix analogs and may be associated with large transient growth of the corresponding initial value problem.
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. PMID:19566267
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.
Electroweak absolute, meta-, and thermal stability in neutrino mass models
NASA Astrophysics Data System (ADS)
Lindner, Manfred; Patel, Hiren H.; Radovčić, Branimir
2016-04-01
We analyze the stability of the electroweak vacuum in neutrino mass models containing right-handed neutrinos or fermionic isotriplets. In addition to considering absolute stability, we place limits on the Yukawa couplings of new fermions based on metastability and thermal stability in the early Universe. Our results reveal that the upper limits on the neutrino Yukawa couplings can change significantly when the top quark mass is allowed to vary within the experimental range of uncertainty in its determination.
Adjoint sensitivity analysis of hydrodynamic stability in cyclonic flows
NASA Astrophysics Data System (ADS)
Guzman Inigo, Juan; Juniper, Matthew
2015-11-01
Cyclonic separators are used in a variety of industries to efficiently separate mixtures of fluid and solid phases by means of centrifugal forces and gravity. In certain circumstances, the vortex core of cyclonic flows is known to precess due to the instability of the flow, which leads to performance reductions. We aim to characterize the unsteadiness using linear stability analysis of the Reynolds Averaged Navier-Stokes (RANS) equations in a global framework. The system of equations, including the turbulence model, is linearised to obtain an eigenvalue problem. Unstable modes corresponding to the dynamics of the large structures of the turbulent flow are extracted. The analysis shows that the most unstable mode is a helical motion which develops around the axis of the flow. This result is in good agreement with LES and experimental analysis, suggesting the validity of the approach. Finally, an adjoint-based sensitivity analysis is performed to determine the regions of the flow that, when altered, have most influence on the frequency and growth-rate of the unstable eigenvalues.
Stability analysis of discrete-time recurrent neural networks.
Barabanov, N E; Prokhorov, D V
2002-01-01
We address the problem of global Lyapunov stability of discrete-time recurrent neural networks (RNNs) in the unforced (unperturbed) setting. It is assumed that network weights are fixed to some values, for example, those attained after training. Based on classical results of the theory of absolute stability, we propose a new approach for the stability analysis of RNNs with sector-type monotone nonlinearities and nonzero biases. We devise a simple state-space transformation to convert the original RNN equations to a form suitable for our stability analysis. We then present appropriate linear matrix inequalities (LMIs) to be solved to determine whether the system under study is globally exponentially stable. Unlike previous treatments, our approach readily permits one to account for non-zero biases usually present in RNNs for improved approximation capabilities. We show how recent results of others on the stability analysis of RNNs can be interpreted as special cases within our approach. We illustrate how to use our approach with examples. Though illustrated on the stability analysis of recurrent multilayer perceptrons, the approach proposed can also be applied to other forms of time-lagged RNNs. PMID:18244432
Structural Stability of Mathematical Models of National Economy
NASA Astrophysics Data System (ADS)
Ashimov, Abdykappar A.; Sultanov, Bahyt T.; Borovskiy, Yuriy V.; Adilov, Zheksenbek M.; Ashimov, Askar A.
2011-12-01
In the paper we test robustness of particular dynamic systems in a compact regions of a plane and a weak structural stability of one dynamic system of high order in a compact region of its phase space. The test was carried out based on the fundamental theory of dynamical systems on a plane and based on the conditions for weak structural stability of high order dynamic systems. A numerical algorithm for testing the weak structural stability of high order dynamic systems has been proposed. Based on this algorithm we assess the weak structural stability of one computable general equilibrium model.
NASA Astrophysics Data System (ADS)
Wu, Sangwook
2016-04-01
The three transmembrane and the four transmembrane helix models are suggested for human vitamin K epoxide reductase (VKOR). In this study, we investigate the stability of the human three transmembrane/four transmembrane VKOR models by employing a coarse-grained normal mode analysis and molecular dynamics simulation. Based on the analysis of the mobility of each transmembrane domain, we suggest that the three transmembrane human VKOR model is more stable than the four transmembrane human VKOR model.
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.
Analysis of emulsion stability in acrylic dispersions
NASA Astrophysics Data System (ADS)
Ahuja, Suresh
2012-02-01
Emulsions either micro or nano permit transport or solubilization of hydrophobic substances within a water-based phase. Different methods have been introduced at laboratory and industrial scales: mechanical stirring, high-pressure homogenization, or ultrasonics. In digital imaging, toners may be formed by aggregating a colorant with a latex polymer formed by batch or semi-continuous emulsion polymerization. Latex emulsions are prepared by making a monomer emulsion with monomer like Beta-carboxy ethyl acrylate (β-CEA) and stirring at high speed with an anionic surfactant like branched sodium dodecyl benzene sulfonates , aqueous solution until an emulsion is formed. Initiator for emulsion polymerization is 2-2'- azobis isobutyramide dehydrate with chain transfer agent are used to make the latex. If the latex emulsion is unstable, the resulting latexes produce a toner with larger particle size, broader particle size distribution with relatively higher latex sedimentation, and broader molecular weight distribution. Oswald ripening and coalescence cause droplet size to increase and can result in destabilization of emulsions. Shear thinning and elasticity of emulsions are applied to determine emulsion stability.
Linear Stability Analysis of an Acoustically Vaporized Droplet
NASA Astrophysics Data System (ADS)
Siddiqui, Junaid; Qamar, Adnan; Samtaney, Ravi
2015-11-01
Acoustic droplet vaporization (ADV) is a phase transition phenomena of a superheat liquid (Dodecafluoropentane, C5F12) droplet to a gaseous bubble, instigated by a high-intensity acoustic pulse. This approach was first studied in imaging applications, and applicable in several therapeutic areas such as gas embolotherapy, thrombus dissolution, and drug delivery. High-speed imaging and theoretical modeling of ADV has elucidated several physical aspects, ranging from bubble nucleation to its subsequent growth. Surface instabilities are known to exist and considered responsible for evolving bubble shapes (non-spherical growth, bubble splitting and bubble droplet encapsulation). We present a linear stability analysis of the dynamically evolving interfaces of an acoustically vaporized micro-droplet (liquid A) in an infinite pool of a second liquid (liquid B). We propose a thermal ADV model for the base state. The linear analysis utilizes spherical harmonics (Ynm, of degree m and order n) and under various physical assumptions results in a time-dependent ODE of the perturbed interface amplitudes (one at the vapor/liquid A interface and the other at the liquid A/liquid B interface). The perturbation amplitudes are found to grow exponentially and do not depend on m. Supported by KAUST Baseline Research Funds.
Stability over time: Is behavior analysis a trait psychology?
Vyse, Stuart
2004-01-01
Historically, behavior analysis and trait psychology have had little in common; however, recent developments in behavior analysis bring it closer to one of the core assumptions of the trait approach: the stability of behavior over time and, to a lesser extent, environments. The introduction of the concept of behavioral momentum and, in particular, the development of molar theories have produced some common features and concerns. Behavior-analytic theories of stability provide improved explanations of many everyday phenomena and make possible the expansion of behavior analysis into areas that have been inadequately addressed. ImagesFigure 1 PMID:22478416
New Method Developed for Aeroelastic Stability Analysis
NASA Technical Reports Server (NTRS)
1996-01-01
The development of advanced-design ultrahigh bypass ratio engines has led to renewed interest in the study of the flutter of bladed disks. Previously, two fundamental approaches were used in flutter calculations: frequency domain analysis and time-domain analysis. With the development of time-marching computational fluid dynamics (CFD) flow solvers, both approaches have been used with equal ease. In the present work at the NASA Lewis Research Center, substantial computational savings have been achieved by applying a numerical eigensolver to a nonlinear, time-marching fluid-structure interaction system solver for flutter prediction.
Stability analysis of offshore wind farm and marine current farm
NASA Astrophysics Data System (ADS)
Shawon, Mohammad Hasanuzzaman
Renewable energy has been playing an important role to meet power demand and 'Green Energy' market is getting bigger platform all over the world in the last few years. Due to massive increase in the prices of fossil fuels along with global warming issues, energy harvesting from renewable energy sources has received considerable interest, nowadays, where extensive researches are going on to ensure optimum use of renewable sources. In order to meet the increasing demand of electricity and power, integration of renewable energy is getting highest priorities around the world. Wind is one of the most top growing renewable energy resources and wind power market penetration is expected to reach 3.35 percent by 2013 from its present market of about 240 GW. A wind energy system is the most environmental friendly, cost effective and safe among all renewable energy resources available. Another promising form of renewable energy is ocean energy which covers 70 % of the earth. Ocean energy can be tapped from waves, tides and thermal elements. Offshore Wind farm (OWF) has already become very popular for large scale wind power integration with the onshore grid. Recently, marine current farm (MCF) is also showing good potential to become mainstream energy sources and already successfully commissioned in United Kingdom. However, squirrel cage induction generator (SCIG) has the stability problem similar to synchronous generator especially during fault location to restore the electromagnetic torque. Series dynamic braking resistor (SDBR) has been known as a useful mean to stabilize fixed speed wind generator system. On the other hand, doubly fed induction generator (DFIG) has the capability of coupling the control of active and reactive power and to provide necessary reactive power demand during grid fault conditions. Series dynamic braking resistor (SDBR) can also be employed with DFIG to limit the rotor over current. An integration of wind and tidal energy represents a new-trend for large electric energy production using offshore wind generators and marine current generators, respectively. Thus DFIG based offshore wind farm can be an economic solution to stabilize squirrel cage induction generator based marine current farm without installing any addition FACTS devices. This thesis first focuses on the stabilization of fixed speed IG based marine current farm using SDBR. Also stabilization of DFIG based variable speed wind farm utilizing SDBR is studied in this work. Finally a co-operative control strategy is proposed where DFIG is controlled in such a way that it can even provide necessary reactive power demand of induction generator, so that additional cost of FACTS devices can be avoided. In that way, the DFIGs of the offshore wind farm (OWF) will actively compensate the reactive power demand of adjacent IGs of the marine current farm (MCF) during grid fault. Detailed modeling and control scheme for the proposed system are demonstrated considering some realistic scenarios. The power system small signal stability analysis is also carried out by eigenvalue analysis for marine current generator topology, wind turbine generator topology and integrated topology. The relation between the modes and state variables are discussed in light of modal and sensitivity analyses. The results of theoretical analyses are verified by MATLAB/SIMULINK and laboratory standard power system simulator PSCAD/EMTDC.
Stability analysis of a bilayer contained within a cylindrical tube
NASA Astrophysics Data System (ADS)
Song, Yuanyuan
Airways in the lung are coated with a liquid bilayer consisting of a serous layer adjacent to a more viscous mucus layer which is contiguous with the air core. An instability due to surface tension at the interfaces may lead to the formation of a liquid plug that blocks the passage of air. This is known as airway closure. A stability analysis is carried out for the case when a Newtonian and immiscible liquid bilayer coats a compliant tube in the presence of an insoluble surfactant monolayer at the mucus-gas interface. A surface active material such as surfactant lowers the surface tension and also generates a surface stress at the interface, both of which are stabilizing, while the wall compliance may accelerate the formation of the liquid bridge. A system of nonlinear coupled equations for the deflections of the interfaces and the surfactant concentration is derived by using an extended lubrication theory analysis. A linear stability study using normal modes is conducted by linearizing the nonlinear evolution equations. A linear eigenvalue problem for the perturbation amplitudes is obtained. Non-trivial solutions are obtained provided the determinant of a linear system is singular. A fourth order polynomial for the growth rate of the disturbances is derived, whose coefficients depend on the wavenumber of the perturbation, the wall characteristics, the Marangoni number, the thickness of the bilayer, the aspect thickness ratio, the viscosity ratio of two liquid layers, and the surface tension ratio. Both stabilizing and destabilizing effects of various system parameters are investigated. A classical lubrication theory model is also derived for cases where a bilayer coats a rigid tube with insoluble surfactant along the liquid-gas interface, and a bilayer coating in a compliant tube with a clean liquid-gas interface. Results serve as a validation of the extended lubrication theory model. The accuracy of the extended lubrication theory model as the bilayer thickness increases is tested by considering a more general approach that is valid for arbitrary bilayer thickness. A system of two Orr-Sommerfeld equations is obtained using this more general approach, and together with the boundary conditions yields an eigenvalue problem for the growth rate. Validations and comparisons with lubrication theory models (both extended and classical ones) are provided. The nonlinear evolution equations are also solved numerically beyond the linear regime for the case of a bilayer coating a compliant tube together with surfactant along the mucus-gas interface in the last part of this thesis. These equations are solved numerically using the method of lines. Numerical results show that the closure time, that is the time requires for a liquid plug to form, goes up with Marangoni number. It is well known that for a single layer, the closure time can increase by a factor of four or five due to surfactant which immobilizes the gas-liquid interface. However, for a bilayer, surfactant may delay closure by a factor of twenty or more.
Aeroelastic Stability of Rotor Blades Using Finite Element Analysis
NASA Technical Reports Server (NTRS)
Chopra, I.; Sivaneri, N.
1982-01-01
The flutter stability of flap bending, lead-lag bending, and torsion of helicopter rotor blades in hover is investigated using a finite element formulation based on Hamilton's principle. The blade is divided into a number of finite elements. Quasi-steady strip theory is used to evaluate the aerodynamic loads. The nonlinear equations of motion are solved for steady-state blade deflections through an iterative procedure. The equations of motion are linearized assuming blade motion to be a small perturbation about the steady deflected shape. The normal mode method based on the coupled rotating natural modes is used to reduce the number of equations in the flutter analysis. First the formulation is applied to single-load-path blades (articulated and hingeless blades). Numerical results show very good agreement with existing results obtained using the modal approach. The second part of the application concerns multiple-load-path blades, i.e. bearingless blades. Numerical results are presented for several analytical models of the bearingless blade. Results are also obtained using an equivalent beam approach wherein a bearingless blade is modelled as a single beam with equivalent properties. Results show the equivalent beam model.
Modeling and stability of segmented reflector telescopes - A decentralized approach
NASA Technical Reports Server (NTRS)
Ryaciotaki-Boussalis, Helen A.; Ih, Che-Hang Charles
1990-01-01
The decentralization of a segmented reflector telescope based on a finite-element model of its structure is considered. The decentralization of the system at the panel level is considered. Each panel is originally treated as an isolated subsystem so that the controller design is performed independently at the local level, and then applied to the composite system for stability analysis. The panel-level control laws were designed by means of pole placement using local output feedback. Simulation results show a better 1000:1 vibration attenuation in panel position when compared to the open-loop system. It is shown that the overall closed-loop system is exponentially stable provided that certain conditions are met. The advantage to the decentralized approach is that the design is performed in terms of the low-dimensionality subsystems, thus drastically reducing the design computational complexities.
Kinematic Analysis of a Posterior-stabilized Knee Prosthesis
Zhao, Zhi-Xin; Wen, Liang; Qu, Tie-Bing; Hou, Li-Li; Xiang, Dong; Bin, Jia
2015-01-01
Background: The goal of total knee arthroplasty (TKA) is to restore knee kinematics. Knee prosthesis design plays a very important role in successful restoration. Here, kinematics models of normal and prosthetic knees were created and validated using previously published data. Methods: Computed tomography and magnetic resonance imaging scans of a healthy, anticorrosive female cadaver were used to establish a model of the entire lower limbs, including the femur, tibia, patella, fibula, distal femur cartilage, and medial and lateral menisci, as well as the anterior cruciate, posterior cruciate, medial collateral, and lateral collateral ligaments. The data from the three-dimensional models of the normal knee joint and a posterior-stabilized (PS) knee prosthesis were imported into finite element analysis software to create the final kinematic model of the TKA prosthesis, which was then validated by comparison with a previous study. The displacement of the medial/lateral femur and the internal rotation angle of the tibia were analyzed during 0–135° flexion. Results: Both the output data trends and the measured values derived from the normal knee's kinematics model were very close to the results reported in a previous in vivo study, suggesting that this model can be used for further analyses. The PS knee prosthesis underwent an abnormal forward displacement compared with the normal knee and has insufficient, or insufficiently aggressive, “rollback” compared with the lateral femur of the normal knee. In addition, a certain degree of reverse rotation occurs during flexion of the PS knee prosthesis. Conclusions: There were still several differences between the kinematics of the PS knee prosthesis and a normal knee, suggesting room for improving the design of the PS knee prosthesis. The abnormal kinematics during early flexion shows that the design of the articular surface played a vital role in improving the kinematics of the PS knee prosthesis. PMID:25591565
Bifurcation analysis of axial flow compressor stability
NASA Technical Reports Server (NTRS)
Mccaughan, F. E.
1990-01-01
With a one-mode truncation it is possible to reduce the Moore-Greitzer model for compressor instability to a set of three ordinary differential equations. These are approached from the point of view of bifurcation theory. Most of the bifurcations emerge from a degenerate Takens-Bogdanov bifurcation point. The bifurcation sets are completed using the numerical branch tracking scheme AUTO. Despite the severity of the truncation, the agreement with experimental results is excellent.
Stability analysis of axial reflection symmetric spacetime
NASA Astrophysics Data System (ADS)
Sharif, M.; Bhatti, M. Zaeem Ul Haq
2016-01-01
In this paper, we explore instability regions of non-static axial reflection symmetric spacetime with anisotropic source in the interior. We impose linear perturbation on the Einstein field equations and dynamical equations to establish the collapse equation. The effects of different physical factors like energy density and anisotropic stresses on the instability regions are studied under Newtonian and post-Newtonian limits. We conclude that stiffness parameter has a significant role in this analysis while the reflection terms increase instability ranges of non-static axial collapse.
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
Advances in Computational Stability Analysis of Composite Aerospace Structures
Degenhardt, R.; Araujo, F. C. de
2010-09-30
European aircraft industry demands for reduced development and operating costs. Structural weight reduction by exploitation of structural reserves in composite aerospace structures contributes to this aim, however, it requires accurate and experimentally validated stability analysis of real structures under realistic loading conditions. This paper presents different advances from the area of computational stability analysis of composite aerospace structures which contribute to that field. For stringer stiffened panels main results of the finished EU project COCOMAT are given. It investigated the exploitation of reserves in primary fibre composite fuselage structures through an accurate and reliable simulation of postbuckling and collapse. For unstiffened cylindrical composite shells a proposal for a new design method is presented.
Analysis of Human Body Bipedal Stability for Neuromotor Disabilities
NASA Astrophysics Data System (ADS)
Baritz, Mihaela; Cristea, Luciana; Rogozea, Liliana; Cotoros, Diana; Repanovici, Angela
2009-04-01
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 setup used to record the human body behavior in postural stability for persons with neuro-motors disabilities. The results and the conclusions are presented in the final part of the paper and also in the future work meant to establish the computer analysis for rehabilitation neuromotor disabilities.
Advances in Computational Stability Analysis of Composite Aerospace Structures
NASA Astrophysics Data System (ADS)
Degenhardt, R.; de Araújo, F. C.
2010-09-01
European aircraft industry demands for reduced development and operating costs. Structural weight reduction by exploitation of structural reserves in composite aerospace structures contributes to this aim, however, it requires accurate and experimentally validated stability analysis of real structures under realistic loading conditions. This paper presents different advances from the area of computational stability analysis of composite aerospace structures which contribute to that field. For stringer stiffened panels main results of the finished EU project COCOMAT are given. It investigated the exploitation of reserves in primary fibre composite fuselage structures through an accurate and reliable simulation of postbuckling and collapse. For unstiffened cylindrical composite shells a proposal for a new design method is presented.
Ballooning mode stability in the Hall-magnetohydrodynamics model
Torasso, R.; Hameiri, Eliezer
2005-03-01
The governing equations of the ballooning modes are derived within the Hall-magneto-hydrodynamics (HMHD) model and given a standard Hamiltonian form, which is then used to derive sufficient conditions for stability. In most cases, ideal magnetohydrodynamics (MHD) stability implies HMHD stability, as is the case for tokamak configurations if the pressure is a monotone increasing function of density and the entropy is monotone decreasing. The same result holds for general MHD plasmas with constant entropy and for incompressible plasmas. However, in the case of (compressible) closed-line systems such as the field-reversed configuration, or in a typical magnetospheric magnetic field, MHD ballooning stability does not guarantee HMHD stability. For the explicitly solvable configuration of the Z pinch it is in fact shown that the plasma can be MHD stable but HMHD unstable.
Stabilizing model predictive control for constrained nonlinear distributed delay systems.
Mahboobi Esfanjani, R; Nikravesh, S K Y
2011-04-01
In this paper, a model predictive control scheme with guaranteed closed-loop asymptotic stability is proposed for a class of constrained nonlinear time-delay systems with discrete and distributed delays. A suitable terminal cost functional and also an appropriate terminal region are utilized to achieve asymptotic stability. To determine the terminal cost, a locally asymptotically stabilizing controller is designed and an appropriate Lyapunov-Krasoskii functional of the locally stabilized system is employed as the terminal cost. Furthermore, an invariant set for locally stabilized system which is established by using the Razumikhin Theorem is used as the terminal region. Simple conditions are derived to obtain terminal cost and terminal region in terms of Bilinear Matrix Inequalities. The method is illustrated by a numerical example. PMID:21232739
Stability analysis of the pulmonary liquid bilayer.
NASA Astrophysics Data System (ADS)
Halpern, David; Grotberg, James
2010-11-01
The lung consists of liquid-lined compliant airways that convey air to and from the alveoli where gas exchange takes place. Because the airways are coated with a bilayer consisting of a mucus layer on top of a periciliary fluid layer, a surface tension instability can generate flows within the bilayer and induce the formation of liquid plugs that block the passage of air. This is a problem for example with premature neonates whose lungs do not produce sufficient quantities of surfactant and suffer from respiratory distress syndrome. To study this instability a system of coupled nonlinear evolution equations are derived using lubrication theory for the thicknesses of the two liquid layers which are assumed to be Newtonian. A normal mode analysis is used to investigate the initial growth of the disturbances, and reveals how the grow rate is affected by the ratio of viscosities ?, film thicknesses ? and surface tensions ? of the two layers which can change by disease. Numerical solutions of the evolution equations show that there is a critical bilayer thickness ?c above which closure occurs, and that a more viscous and thicker layer compared to the periciliary layer closes more slowly. However, ?cis weakly dependent on ?, ? and ?. We also examine the potential impact of wall shear stress and normal stress on cell damage. This work is funded by NIH HL85156.
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.
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.
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
Stability and failure analysis of steering tie-rod
NASA Astrophysics Data System (ADS)
Jiang, GongFeng; Zhang, YiLiang; Xu, XueDong; Ding, DaWei
2008-11-01
A new car in operation of only 8,000 km, because of malfunction, resulting in lost control and rammed into the edge of the road, and then the basic vehicle scrapped. According to the investigation of the site, it was found that the tie-rod of the car had been broken. For the subjective analysis of the accident and identifying the true causes of rupture of the tierod, a series of studies, from the angle of theory to experiment on the bended broken tie-rod, were conducted. The mechanical model was established; the stability of the defective tie-rod was simulated based on ANSYS software. Meanwhile, the process of the accident was simulated considering the effect of destabilization of different vehicle speed and direction of the impact. Simultaneously, macro graphic test, chemical composition analysis, microstructure analysis and SEM analysis of the fracture were implemented. The results showed that: 1) the toughness of the tie-rod is at a normal level, but there is some previous flaws. One quarter of the fracture surface has been cracked before the accident. However, there is no relationship between the flaw and this incident. The direct cause is the dynamic instability leading to the large deformation of impact loading. 2) The declining safety factor of the tie-rod greatly due to the previous flaws; the result of numerical simulation shows that previous flaw is the vital factor of structure instability, on the basis of the comparison of critical loads of the accident tie-rod and normal. The critical load can decrease by 51.3% when the initial defect increases 19.54% on the cross-sectional area, which meets the Theory of Koiter.
An Efficient and Configurable Preprocessing Algorithm to Improve Stability Analysis.
Sesia, Ilaria; Cantoni, Elena; Cernigliaro, Alice; Signorile, Giovanna; Fantino, Gianluca; Tavella, Patrizia
2016-04-01
The Allan variance (AVAR) is widely used to measure the stability of experimental time series. Specifically, AVAR is commonly used in space applications such as monitoring the clocks of the global navigation satellite systems (GNSSs). In these applications, the experimental data present some peculiar aspects which are not generally encountered when the measurements are carried out in a laboratory. Space clocks' data can in fact present outliers, jumps, and missing values, which corrupt the clock characterization. Therefore, an efficient preprocessing is fundamental to ensure a proper data analysis and improve the stability estimation performed with the AVAR or other similar variances. In this work, we propose a preprocessing algorithm and its implementation in a robust software code (in MATLAB language) able to deal with time series of experimental data affected by nonstationarities and missing data; our method is properly detecting and removing anomalous behaviors, hence making the subsequent stability analysis more reliable. PMID:26540679
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.
Stability Analysis and the Stabilisation of Flexural Toppling Failure
NASA Astrophysics Data System (ADS)
Amini, Mehdi; Majdi, Abbas; Aydan, Ömer
2009-10-01
Flexural toppling is a mode of failure that may occur in a wide range of layered rock strata in both rock slopes and large underground excavations. Whenever rock mass is composed of a set of parallel discontinuities dipping steeply against the excavated face plane, the rock mass will have the potential of flexural toppling failure as well. In such cases, the rock mass behaves like inclined superimposed cantilever beams that bend under their own weight while transferring the load to the underlying strata. If the bending stress exceeds the rock column’s tensile strength, flexural toppling failure will be initiated. Since the rock columns are “statically indeterminate,” thus, their factors of safety may not be determined solely by equations of equilibrium. The paper describes an analytical model with a sequence of inclined superimposed cantilever rock columns with a potential of flexural topping failure. The model is based on the principle of compatibility equations and leads to a new method by which the magnitudes and points of application of intercolumn forces are determined. On the basis of the proposed model, a safety factor for each rock column can be computed independently. Hence, every rock column will have a unique factor of safety. The least factor of safety that exists in any rock column is selected as the rock mass representative safety factor based on which simple equations are proposed for a conservative rock mass stability analysis and design. As a result, some new relations are established in order to design the length, cross-sectional area and pattern of fully grouted rock bolts for the stabilisation of such rock mass. Finally, the newly proposed equations are compared with the results of existing experimental flexural toppling failure models (base friction and centrifuge tests) for further verification.
The stability of axisymmetric galaxy models with anisotropic dispersions
NASA Astrophysics Data System (ADS)
de Zeeuw, T.; Franx, M.; Meys, J.; Brink, K.; Habing, H.
Axisymmetric models constructed by means of Schwarzschild's (1979) self-consistent method are discussed, with attention also given to the stability of the models. Use is made of van Albada's axisymmetric N-body program (van Albada and van Gorkum, 1977) in order to test the stability of the equilibrium models in the presence of axisymmetric perturbations. It is found that models that have a local radial velocity dispersion below a certain critical value are unstable to such perturbations. It is suspected that a generalized stability criterion for the local anisotropic velocity dispersion may exist, analogous to the result for infinitely thin disks. This stability depends only on the orbits that constitute the model and not on the fraction of retrograde stars in each orbit. The models that are stable in the presence of axisymmetric perturbations may still be unstable to barlike perturbations. Since this instability depends on the total angular momentum of the model, the fraction of retrograde stars is important. Using Vandervoort's (1982) refinement of the Ostriker-Peebles (Ostriker and Peebles, 1973) criterion, it is found that some of the models should be stable even if all stars are direct but that other models can be made stable only when a fraction of the stars is retrograde.
Stability investigations of airfoil flow by global analysis
NASA Technical Reports Server (NTRS)
Morzynski, Marek; Thiele, Frank
1992-01-01
As the result of global, non-parallel flow stability analysis the single value of the disturbance growth-rate and respective frequency is obtained. This complex value characterizes the stability of the whole flow configuration and is not referred to any particular flow pattern. The global analysis assures that all the flow elements (wake, boundary and shear layer) are taken into account. The physical phenomena connected with the wake instability are properly reproduced by the global analysis. This enhances the investigations of instability of any 2-D flows, including ones in which the boundary layer instability effects are known to be of dominating importance. Assuming fully 2-D disturbance form, the global linear stability problem is formulated. The system of partial differential equations is solved for the eigenvalues and eigenvectors. The equations, written in the pure stream function formulation, are discretized via FDM using a curvilinear coordinate system. The complex eigenvalues and corresponding eigenvectors are evaluated by an iterative method. The investigations performed for various Reynolds numbers emphasize that the wake instability develops into the Karman vortex street. This phenomenon is shown to be connected with the first mode obtained from the non-parallel flow stability analysis. The higher modes are reflecting different physical phenomena as for example Tollmien-Schlichting waves, originating in the boundary layer and having the tendency to emerge as instabilities for the growing Reynolds number. The investigations are carried out for a circular cylinder, oblong ellipsis and airfoil. It is shown that the onset of the wake instability, the waves in the boundary layer, the shear layer instability are different solutions of the same eigenvalue problem, formulated using the non-parallel theory. The analysis offers large potential possibilities as the generalization of methods used till now for the stability analysis.
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...
GEOTECHNICAL ANALYSIS FOR REVIEW OF DIKE STABILITY (GARDS). TECHNICAL MANUAL
The structure and capabilities of a user-friendly, interactive computer program developed for the stability analysis of dikes (GARDS) are described. The program was developed under the sponsorship of the U.S. Environmental Protection Agency and therefore emphasizes Hazardous Wast...
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.
Stability and optimization in structured population models on graphs.
Colombo, Rinaldo M; Garavello, Mauro
2015-04-01
We prove existence and uniqueness of solutions, continuous dependence from the initial datum and stability with respect to the boundary condition in a class of initial--boundary value problems for systems of balance laws. The particular choice of the boundary condition allows to comprehend models with very different structures. In particular, we consider a juvenile-adult model, the problem of the optimal mating ratio and a model for the optimal management of biological resources. The stability result obtained allows to tackle various optimal management/control problems, providing sufficient conditions for the existence of optimal choices/controls. PMID:25811440
Stability of differential susceptibility and infectivity epidemic models
Bonzi, B.; Fall, A. A.; Iggidr, Abderrahman; Sallet, Gauthier
2011-01-01
We introduce classes of differential susceptibility and infectivity epidemic models. These models address the problem of flows between the different susceptible, infectious and infected compartments and differential death rates as well. We prove the global stability of the disease free equilibrium when the basic reproduction ratio ≤ 1 and the existence and uniqueness of an endemic equilibrium when > 1. We also prove the global asymptotic stability of the endemic equilibrium for a differential susceptibility and staged progression infectivity model, when > 1. Our results encompass and generalize those of [18, 22]. AMS Subject Classification : 34A34,34D23,34D40,92D30 PMID:20148330
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…
A Robustly Stabilizing Model Predictive Control Algorithm
NASA Technical Reports Server (NTRS)
Ackmece, A. Behcet; Carson, John M., III
2007-01-01
A model predictive control (MPC) algorithm that differs from prior MPC algorithms has been developed for controlling an uncertain nonlinear system. This algorithm guarantees the resolvability of an associated finite-horizon optimal-control problem in a receding-horizon implementation.
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
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.
On stability and persistence of some oligopoly models.
Ahmed, E; Hegazi, A S
2003-01-01
A dynamic oligopoly model is given. Its steady state and stability and the bounds of its basin of attraction are studied. Delay (memory) is then introduced. Oligopoly is then reformulated using Smale's game which is more realistic than ordinary games since it takes memory into consideration. Persistence is studied for some oligopoly models. PMID:12876444
Stability analysis of impulsive functional systems of fractional order
NASA Astrophysics Data System (ADS)
Stamova, Ivanka; Stamov, Gani
2014-03-01
In this paper, a class of impulsive fractional functional differential systems is investigated. Sufficient conditions for stability of the zero solution are proved, extending the corresponding theory of impulsive functional differential equations. The investigations are carried out by using the comparison principle, coupled with the Lyapunov function method. We apply our results to an impulsive single species model of Lotka-Volterra type.
Limitations of Deterministic Modelling of Slope Stability on Volcanic Edifices
NASA Astrophysics Data System (ADS)
Burrell, R. V.; Pinkerton, H.; Binley, A.
2004-12-01
The conditions leading to the 18 May 1980 sector collapse of Mount St Helens have been the subject of a number of detailed investigations. Preservation of the initial failure plane(s) allowed Voight et al. (1983) and Donnadieu et al. (2001) to undertake back analyses and determine a range of possible failure conditions. While the models proposed offer major insights into potential failure mechanisms, we will demonstrate that deterministic analyses are of limited usefulness because many of the model parameters, such as cohesion, internal friction and pore pressure, are very poorly constrained. This creates problems of non-uniqueness in the solution. An alternative approach involves a series of Monte Carlo simulations to identify potential combinations of parameters that will produce the observed failure plane. Initial input ranges are specified for each parameter and the predetermined model is run repeatedly, with the parameter values for each model selected at random from within the input ranges. The interaction between parameters can be examined in detail, providing a better understanding of the potential failure conditions. This approach, which has been tested initially on a theoretical slope with predetermined failure conditions, highlights the fact that it is impossible to generate a unique model that fits the data when the slope has poorly defined strength parameters. This has clear implications for the validity of commonly used deterministic approaches. This probabilistic back analysis approach has been used to reanalyse the conditions that led to the May 18 collapse on Mount St Helens. Donnadieu, F., Merle, O., and Besson, J.C., 2001, Volcanic edifice stability during cryptodome intrusion, Bulletin of Volcanology, vol 63, p61-72. Voight, B., Janda, R.J., Glicken, H., and Douglass, P.M., 1983, Nature and Mechanics of the Mount St-Helens Rockslide-Avalanche of 18 May 1980, Geotechnique, vol 33, p243-273.
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.
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
A modal aeroelastic analysis combining structural and aerodynamic models is applied to counterrotating propfans to evaluate their structural integrity for wind-tunnel testing. The aeroelastic analysis code is an extension of the 2D analysis code called the Aeroelastic Stability and Response of Propulsion Systems. Rotational speed and freestream Mach number are the parameters for calculating the stability of the two blade designs with a modal method combining a finite-element structural model with 2D steady and unsteady cascade aerodynamic models. The model demonstrates convergence to the least stable aeroelastic mode, describes the effects of a nonuniform inflow, and permits the modification of geometry and rotation. The analysis shows that the propfan designs are suitable for the wind-tunnel test and confirms that the propfans should be flutter-free under the range of conditions of the testing.
Sensitivity Analysis of Dynamic Stability Indicators in Power Systems
Nguyen, Tony B.; Pai, M. A.
2006-01-01
Real time stability evaluation and preventive scheduling in power systems offers many challenges in a stressed power system. Through fast simulation of contingencies in real time it is possible to extract suitable information from the data and develop reliable metrics or indices to evaluate proximity of the system to an unstable condition. In this chapter we review the recent applications of the trajectory sensitivity analysis (TSA) technique in developing such indicators. Trajectory sensitivities can be used to compute critical parameters such as clearing time of circuit breakers, tie line flow, etc. in a power system by developing suitable norms for ease of interpretation. Alternatively it can be used along with the notion of Principal Singular Surfaces (PSS) to detect mode of instability (MOI). The TSA technique has the advantage that model complexity is not a limitation and the sensitivities are computed numerically. Suitable metrics are developed from these sensitivities. In addition to computing critical parameters, the TSA technique can be extended to do preventive rescheduling. A brief discussion of other applications of TSA is included as well as future areas of research.
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.
Linear stability analysis of three-dimensional compressible boundary layers
NASA Technical Reports Server (NTRS)
Malik, Mujeeb R.; Orszag, Steven A.
1987-01-01
A compressible stability analysis computer code is developed. The code uses a matrix finite-difference method for local eigenvale solution when a good guess for the eigenvalue is available and is significantly more computationally efficient than the commonly used inital-value approach. The local eigenvalue search procedure also results in eigenfunctions and, at little extra work, group velocities. A globally convergent eigenvalue procedure is also developed that may be used when no guess for the eigenvalue is available. The global problem is formulated in such a way that no unstable spurious modes appear so that the method is suitable for use in a black-box stability code. Sample stability calculations are presented for the boundary layer profiles of an LFC swept wing.
Experimental bifurcation analysis of an impact oscillator-Determining stability
NASA Astrophysics Data System (ADS)
Bureau, Emil; Schilder, Frank; Elmegrd, Michael; Santos, Ilmar F.; Thomsen, Jon J.; Starke, Jens
2014-10-01
We propose and investigate three different methods for assessing stability of dynamical equilibrium states during experimental bifurcation analysis, using a control-based continuation method. The idea is to modify or turn off the control at an equilibrium state and study the resulting behavior. As a proof of concept the three methods are successfully implemented and tested for a harmonically forced impact oscillator with a hardening spring nonlinearity, and controlled by electromagnetic actuators. We show that under certain conditions it is possible to quantify the instability in terms of finite-time Lyapunov exponents. As a special case we study an isolated branch in the bifurcation diagram brought into existence by a 1:3 subharmonic resonance. On this isola it is only possible to determine stability using one of the three methods, which is due to the fact that only this method guarantees that the equilibrium state can be restored after measuring stability.
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.
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 a 213 kN (48,000 lbf) Liquid Oxygen (LOX)/RP-1 combustor with a 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 have been incorporated into ROCCID, and ten of them, which have options for triplet injectors, were examined in this study. Calculations using different combinations of analysis models, with little or no anchoring, were carried out on a test matrix of operating conditions 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.
Foerdedal, H.; Midttun, O.; Sjoeblom, J.; Kvalheim, O.M.; Schildberg, Y.; Volle, J.L.
1996-09-01
The electrically induced coalescence of water-in-oil emulsions stabilized by interfacially active fractions from crude oils has been studied by means of time domain dielectric spectroscopy at high electric fields. The experiments were designed with a 2{sup 7-3} reduced factorial design. Regression analysis clearly shows that the choice of organic solvent and the amount of asphaltenes, as well as the interplay between these variables, are the most significant parameters for determining the stability of these emulsions. It should be pointed out that the asphaltenes were the only surface active fraction tested. No interplay between, for instance, asphaltenes and resins was investigated. The nonlinearity found in the regression analysis is explained by different aggregation states of asphaltenes in aliphatic and aromatic solvents. The influence of the variables upon the emulsion stability is discussed.
The beauty of simple adaptive control and new developments in nonlinear systems stability analysis
NASA Astrophysics Data System (ADS)
Barkana, Itzhak
2014-12-01
Although various adaptive control techniques have been around for a long time and in spite of successful proofs of stability and even successful demonstrations of performance, the eventual use of adaptive control methodologies in practical real world systems has met a rather strong resistance from practitioners and has remained limited. Apparently, it is difficult to guarantee or even understand the conditions that can guarantee stable operations of adaptive control systems under realistic operational environments. Besides, it is difficult to measure the robustness of adaptive control system stability and allow it to be compared with the common and widely used measure of phase margin and gain margin that is utilized by present, mainly LTI, controllers. Furthermore, customary stability analysis methods seem to imply that the mere stability of adaptive systems may be adversely affected by any tiny deviation from the pretty idealistic and assumably required stability conditions. This paper first revisits the fundamental qualities of customary direct adaptive control methodologies, in particular the classical Model Reference Adaptive Control, and shows that some of their basic drawbacks have been addressed and eliminated within the so-called Simple Adaptive Control methodology. Moreover, recent developments in the stability analysis methods of nonlinear systems show that prior conditions that were customarily assumed to be needed for stability are only apparent and can be eliminated. As a result, sufficient conditions that guarantee stability are clearly stated and lead to similarly clear proofs of stability. As many real-world applications show, once robust stability of the adaptive systems can be guaranteed, the added value of using Add-On Adaptive Control along with classical Control design techniques is pushing the desired performance beyond any previous limits.
The beauty of simple adaptive control and new developments in nonlinear systems stability analysis
Barkana, Itzhak
2014-12-10
Although various adaptive control techniques have been around for a long time and in spite of successful proofs of stability and even successful demonstrations of performance, the eventual use of adaptive control methodologies in practical real world systems has met a rather strong resistance from practitioners and has remained limited. Apparently, it is difficult to guarantee or even understand the conditions that can guarantee stable operations of adaptive control systems under realistic operational environments. Besides, it is difficult to measure the robustness of adaptive control system stability and allow it to be compared with the common and widely used measure of phase margin and gain margin that is utilized by present, mainly LTI, controllers. Furthermore, customary stability analysis methods seem to imply that the mere stability of adaptive systems may be adversely affected by any tiny deviation from the pretty idealistic and assumably required stability conditions. This paper first revisits the fundamental qualities of customary direct adaptive control methodologies, in particular the classical Model Reference Adaptive Control, and shows that some of their basic drawbacks have been addressed and eliminated within the so-called Simple Adaptive Control methodology. Moreover, recent developments in the stability analysis methods of nonlinear systems show that prior conditions that were customarily assumed to be needed for stability are only apparent and can be eliminated. As a result, sufficient conditions that guarantee stability are clearly stated and lead to similarly clear proofs of stability. As many real-world applications show, once robust stability of the adaptive systems can be guaranteed, the added value of using Add-On Adaptive Control along with classical Control design techniques is pushing the desired performance beyond any previous limits.
Absolute stability analysis of attitude control systems for large boosters.
NASA Technical Reports Server (NTRS)
Seltzer, S. M.; Siljak, D. D.
1972-01-01
A method for performing absolute stability analyses of attitude control systems for large launch vehicles is presented. Absolute stability of these systems is shown in a finite region of the state space. The regions are computed by using the Lur'e-Postnikov Liapunov function. This function is chosen to provide additional information about the exponential property of absolute stability. Significant advantages of the method proposed in this paper are: it is independent of the order of the system; algebraic operations involved in the computations are relatively simple and convenient for machine implementation; and the obtained results are valid not only for a particular nonlinearity but also for an entire class of nonlinear characteristics that satisfy certain general conditions. A system model representing the Saturn V launch vehicle is used to illustrate the method.
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.
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 a stability valve system for extending the dynamic range of a supersonic inlet
NASA Technical Reports Server (NTRS)
Webb, J. A., Jr.; Dustin, M. O.
1975-01-01
A stability valve system designed for a full-scale, flight, supersonic, mixed-compression inlet was modeled dynamically by using analog computer techniques. The system uses poppet valves mounted in the inlet cowl to bypass airflow and augments the inlet shock position control system by preventing unstarts caused by high-frequency perturbations. The model was used as a design aid to investigate the effects of varying both the physical configurations of the valve and the flight and wind tunnel conditions. Results of the analysis indicate that the stability valve will provide a bandpass operation of 1 hertz to 17 hertz.
Stability and Control Analysis of the F-15B Quiet Spike Aircraft
NASA Technical Reports Server (NTRS)
McWherter, Shaun; Moua,Cheng; Gera, Joseph; Cox, Timothy H.
2007-01-01
The primary objective of the Quiet Spike flight research program was the aerodynamic and structural proof-of-concept of a telescoping, 24 ft, sonic-boom suppressing nose boom on a F-15B aircraft. The program goal was to collect flight data for model validation up to 1.8 Mach. In the area of stability and controls the primary concern was to assess the effect of the spike on the stability, controllability and handling qualities of the aircraft. The primary goal of this test philosophy was maintaining safety of flight. Two main issues are discussed in this paper: the stability and controls approach and analysis in the presence of uncertain spike influenced aerodynamics on the F-15B aircraft flight dynamics; and the analysis of F-15B flight dynamics implications due to spike induced air flow in the vicinity of air data and angle-of-attack sensors. Also addressed are flight test implications based on the analysis
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.
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 analysis of explicit guidance laws for space launch vehicles with varying thrust integrals
NASA Astrophysics Data System (ADS)
Song, Eun-Jung; Cho, Sang-bum; Park, Chang-Su; Roh, Woong-Rae; Joh, Miok
2011-07-01
In this study, a stability analysis of the explicit guidance laws for space launch vehicles is performed with consideration of varying thrust integrals. Among various forms of explicit guidance, linear tangent guidance in its general form is selected and six different acceleration profiles are considered for this numerical experiment. A linear system modeling which includes all of the significant dynamic elements of a space launcher is performed to analyze the effect of the characteristics of thrust integrals on stability margins. Numerical results show that in an aspect of guidance stability, it is advantageous to have thrust integrals derived from increasing acceleration profiles, such as constant thrust case, which may be considered in the development of propulsion systems. Finally, time-domain simulation with the original nonlinear models is performed to verify the approach and the result shows that the nonlinear dynamics of the system is conserved well in the linear model.
Stability analysis of quasi-brittle materials - creep under multiaxial loading
NASA Astrophysics Data System (ADS)
Challamel, Noël; Lanos, Christophe; Casandjian, Charles
2006-03-01
The aim of this paper is to develop a simple time-dependent Continuum Damage Mechanics model applied to quasi-brittle materials such as rock or concrete. The three-dimensional constitutive visco-damage model describes phenomena like relaxation, creep and rate-dependent loading using a unified framework. A material stability analysis devoted to creep tests highlights a general creep stress stability domain. This convex domain is connected to the property of the associated time-independent Continuum Damage Mechanics model. More particularly, the boundary of this domain in the creep stress space coincides with the invertibility condition of the constitutive matrix considering infinitely slow loading. Phenomenon as creep failure under high-sustained load is explained quite simply within stability theory. Creep failure appears as the manifestation of a saddle-node bifurcation phenomenon.
Ajbar, A
2001-04-01
The stability characteristics of a continuous bioreactor with cell recycle for biodegradation of mixed wastes are investigated. The system involves a pure culture of Pseudomonas putida and media containing phenol and glucose as carbon and energy sources. The model growth kinetics for the two substitutable substrates were experimentally validated in a previous study. The stability analysis carried out using elementary principles of bifurcation theory shows rich dynamics characteristics of the reactor model, including steady-state multiplicity and hysteresis. The effect of the bioreactor operating parameters on the stability behavior of the model is discussed. Practical criteria are also derived for the safe operation of the unit and to prevent the occurrence of wash-out conditions. PMID:11268840
Bounded Linear Stability Analysis - A Time Delay Margin Estimation Approach for Adaptive Control
NASA Technical Reports Server (NTRS)
Nguyen, Nhan T.; Ishihara, Abraham K.; Krishnakumar, Kalmanje Srinlvas; Bakhtiari-Nejad, Maryam
2009-01-01
This paper presents a method for estimating time delay margin for model-reference adaptive control of systems with almost linear structured uncertainty. The bounded linear stability analysis method seeks to represent the conventional model-reference adaptive law by a locally bounded linear approximation within a small time window using the comparison lemma. The locally bounded linear approximation of the combined adaptive system is cast in a form of an input-time-delay differential equation over a small time window. The time delay margin of this system represents a local stability measure and is computed analytically by a matrix measure method, which provides a simple analytical technique for estimating an upper bound of time delay margin. Based on simulation results for a scalar model-reference adaptive control system, both the bounded linear stability method and the matrix measure method are seen to provide a reasonably accurate and yet not too conservative time delay margin estimation.
NASA Astrophysics Data System (ADS)
Zhang, Tie-Yan; Zhao, Yan; Xie, Xiang-Peng
2012-12-01
This paper is concerned with the problem of stability analysis of nonlinear Roesser-type two-dimensional (2D) systems. Firstly, the fuzzy modeling method for the usual one-dimensional (1D) systems is extended to the 2D case so that the underlying nonlinear 2D system can be represented by the 2D Takagi—Sugeno (TS) fuzzy model, which is convenient for implementing the stability analysis. Secondly, a new kind of fuzzy Lyapunov function, which is a homogeneous polynomially parameter dependent on fuzzy membership functions, is developed to conceive less conservative stability conditions for the TS Roesser-type 2D system. In the process of stability analysis, the obtained stability conditions approach exactness in the sense of convergence by applying some novel relaxed techniques. Moreover, the obtained result is formulated in the form of linear matrix inequalities, which can be easily solved via standard numerical software. Finally, a numerical example is also given to demonstrate the effectiveness of the proposed approach.
Stability Modeling of DIII-D Discharges with Transport Barriers
NASA Astrophysics Data System (ADS)
Lao, L. L.; Ferron, J. R.; Lin-Liu, Y. R.; Strait, E. J.; Turnbull, A. D.; Taylor, T. S.; Murakami, M.
1999-11-01
The stability of DIII--D discharges with transport barriers is systematically studied by modeling the pressure profiles using a hyperbolic tangent representation with various radii, widths, and amplitudes. The q profiles are modeled using a spline representation with varying q(0), q_min, and ρ_q_min. The equilibria are computed using the EFIT and the TOQ codes based on the parameters from a strongly shaped high triangurality DIII--D long pulse high performance discharge. Stability against the ideal low n=1 and 2 modes is evaluated using the GATO code with a conducting wall at 1.5 a. The results show that the stability improves with increasing transport barrier width and radius but varies weakly with q(0). When the transport barriers are L--mode like and have narrow widths in the plasma core, the stability is limited by the n=1 mode. When they are H--mode like and have large widths extending toward the edge, the stability is limited by the n=2 mode.
Stability of a general SEIV epidemic model with time delay
NASA Astrophysics Data System (ADS)
Hikal, M. M.; El-Sheikh, M. M. A.
2013-10-01
An SEIV epidemic model with a general nonlinear incidence rate, vaccination and time delay in treatment is considered. Sufficient conditions for the time delay to keep the stability of the endemic equilibria are given. A numerical simulations is given to illustrate our results.
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.
Estimation of dynamic stability parameters from drop model flight tests
NASA Technical Reports Server (NTRS)
Chambers, J. R.; Iliff, K. W.
1981-01-01
The overall remotely piloted drop model operation, descriptions, instrumentation, launch and recovery operations, piloting concept, and parameter identification methods are discussed. Static and dynamic stability derivatives were obtained for an angle attack range from -20 deg to 53 deg. It is indicated that the variations of the estimates with angle of attack are consistent for most of the static derivatives, and the effects of configuration modifications to the model were apparent in the static derivative estimates.
Linearized stability analysis and design of a flyback dc-dc boost regulator.
NASA Technical Reports Server (NTRS)
Wester, G. W.
1973-01-01
Analytic expressions for the small-signal power-stage describing functions of a switched dc-dc boost regulator are derived from an approximate continuous circuit model which is developed by a time-averaging technique. Closed-loop stability is attained through the design of frequency compensation of the loop gain. Open- and closed-loop regulator output impedances are derived from the linearized models for the given configuration. The analysis and design are compared with and confirmed by breadboard measurements.
Theoretical modelling of the feedback stabilization of external MHD modes in toroidal geometry
NASA Astrophysics Data System (ADS)
Chance, M. S.; Chu, M. S.; Okabayashi, M.; Turnbull, A. D.
2002-03-01
A theoretical framework for understanding the feedback mechanism for stabilization of external MHD modes has been formulated. Efficient computational tools - the GATO stability code coupled with a substantially modified VACUUM code - have been developed to effectively design viable feedback systems against these modes. The analysis assumed a thin resistive shell and a feedback coil structure accurately modelled in θ and phi, albeit with only a single harmonic variation in phi. Time constants and induced currents in the enclosing resistive shell are calculated. An optimized configuration based on an idealized model has been computed for the DIII-D device. Up to 90% of the effectiveness of an ideal wall can be achieved.
Stability analysis of underground mining openings with complex geometry
NASA Astrophysics Data System (ADS)
Cała, Marek; Stopkowicz, Agnieszka; Kowalski, Michał; Blajer, Mateusz; Cyran, Katarzyna; D'obyrn, Kajetan
2016-03-01
Stability of mining openings requires consideration of a number of factors, such as: geological structure, the geometry of the underground mining workings, mechanical properties of the rock mass, changes in stress caused by the influence of neighbouring workings. Long-term prediction and estimation of workings state can be analysed with the use of numerical methods. Application of 3D numerical modelling in stability estimation of workings with complex geometry was described with the example of Crystal Caves in Wieliczka Salt Mine. Preservation of the Crystal Caves reserve is particularly important in view of their unique character and the protection of adjacent galleries which are a part of tourist attraction included in UNESCO list. A detailed 3D model of Crystal Caves and neighbouring workings was built. Application of FLAC3D modelling techniques enabled indication of the areas which are in danger of stability loss. Moreover, the area in which protective actions should be taken as well as recommendations concerning the convergence monitoring were proposed.
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
NASA Astrophysics Data System (ADS)
Corsini, A.; Rispoli, F.; Sheard, A. G.; Tezduyar, T. E.
2012-12-01
The paper illustrates how a computational fluid mechanic technique, based on stabilized finite element formulations, can be used in analysis of noise reduction devices in axial fans. Among the noise control alternatives, the study focuses on the use of end-plates fitted at the blade tips to control the leakage flow and the related aeroacoustic sources. The end-plate shape is configured to govern the momentum transfer to the swirling flow at the blade tip. This flow control mechanism has been found to have a positive link to the fan aeroacoustics. The complex physics of the swirling flow at the tip, developing under the influence of the end-plate, is governed by the rolling up of the jet-like leakage flow. The RANS modelling used in the computations is based on the streamline-upwind/Petrov-Galerkin and pressure-stabilizing/Petrov-Galerkin methods, supplemented with the DRDJ stabilization. Judicious determination of the stabilization parameters involved is also a part of our computational technique and is described for each component of the stabilized formulation. We describe the flow physics underlying the design of the noise control device and illustrate the aerodynamic performance. Then we investigate the numerical performance of the formulation by analysing the inner workings of the stabilization operators and of their interaction with the turbulence model.
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.
Thermodynamic stability and kinetic foldability of a lattice protein model
NASA Astrophysics Data System (ADS)
Li, Jie; Wang, Jun; Zhang, Jian; Wang, Wei
2004-04-01
By using serial mutations, i.e., a residue replaced by 19 kinds of naturally occurring residues, the stability of native conformation and folding behavior of mutated sequences are studied. The 3×3×3 lattice protein model with two kinds of interaction potentials between the residues, namely the original Miyazawa and Jernigan (MJ) potentials and the modified MJ potentials (MMJ), is used. Effects of various sites in the mutated sequences on the stability and foldability are characterized through the Z-score and the folding time. It is found that the sites can be divided into three types, namely the hydrophobic-type (H-type), the hydrophilic-type (P-type) and the neutral-type (N-type). These three types of sites relate to the hydrophobic core, the hydrophilic surface and the parts between them. The stability of the native conformation for the serial mutated sequences increases (or decreases) as the increasing in the hydrophobicity of the mutated residues for the H-type sites (or the P-type sites), while varies randomly for the N-type sites. However, the foldability of the mutated sequences is not always consistent with the thermodynamic stability, and their relationship depends on the site types. Since the hydrophobic tendency of the MJ potentials is strong, the ratio between the number of the H-type sites and the number of the P-type sites is found to be 1:2. Differently, for the MJJ potentials it is found that such a ratio is about 1:1 which is relevant to that of real proteins. This suggests that the modification of the MJ potentials is rational in the aspect of thermodynamic stability. The folding of model proteins with the MMJ potentials is fast. However, the relationship between the foldability and the thermodynamic stability of the mutated sequences is complex.
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.
Calibration and Stability Analysis of the VLP-16 Laser Scanner
NASA Astrophysics Data System (ADS)
Glennie, C. L.; Kusari, A.; Facchin, A.
2016-03-01
We report on a calibration and stability analysis of the Velodyne VLP-16 LiDAR scanner. The sensor is evaluated for long-term stability, geometric calibration and the effect of temperature variations. To generalize the results, three separate VLP-16 sensors were examined. The results and conclusions from the analysis of each of the individual sensors was similar. We found that the VLP-16 showed a consistent level of performance, in terms of range bias and noise level over the tested temperature range from 0-40 °C. A geometric calibration was able to marginally improve the accuracy of the VLP-16 point cloud (by approximately 20%) for a single collection, however the temporal stability of the geometric calibration negated this accuracy improvement. Overall, it was found that there is some long-term walk in the ranging observations from individual lasers within the VLP-16, which likely causes the instability in the determination of geometric calibration parameters. However, despite this range walk, the point cloud delivered from the VLP-16 sensors tested showed an accuracy level within the manufacturer specifications of 3 cm RMSE, with an overall estimated RMSE of range residuals between 22 mm and 27 mm.
Real-time Stability Analysis for Disruption Avoidance in ITER
NASA Astrophysics Data System (ADS)
Glasser, Alexander; Kolemen, Egemen; Glasser, Alan
2015-11-01
ITER is intended to operate at plasma parameters approaching the frontier of achievable stability limits. And yet, plasma disruptions at ITER must be kept to a bare minimum to avoid damage to its plasma-facing structures. These competing goals necessitate real-time plasma stability analysis and feedback control at ITER. This work aims to develop a mechanism for real-time analysis of a large and virulent class of disruptions driven by the rapid growth of ideal MHD unstable modes in tokamak equilibria. Such modes will be identified by a parallelized, low-latency implementation of A.H. Glasser's well-tested DCON (Direct Criterion of Newcomb) code, which measures the energetics of modes in the bulk plasma fluid, as well as M.S. Chance's VACUUM code, which measures the same in the vacuum between the plasma and tokamak chamber wall. Parallelization of these codes is intended to achieve a time-savings of 40x, thereby reducing latency to a timescale of order 100ms and making the codes viable for ideal MHD stability control at ITER. The hardware used to achieve this parallelization will be an Intel Xeon Phi server with 77 cores (308 threads). Supported by the US DOE under DE-AC02-09CH11466.
Plutonium Finishing Plant (PFP) Stabilization & Packaging Equipment Hazard Analysis
BRAUN, D.J.
2001-08-10
A hazard analysis was performed to identify and evaluate hazards associated with the installation and subsequent operation of the Plutonium Stabilization and Packaging Equipment (SPE) at the Plutonium Finishing Plant (PFP). The SPE is designed to handle the packaging of Pu oxide, mixed Pu-uranium oxides, and Pu metals. This document provides the methodology used in the hazard analysis and the corresponding results. The Hazards and Operability Study (HazOp) technique was used in identifying the hazards associated with the SPE. The scope of the HazOp includes transporting the PFP convenience cans from the storage vaults to the SPE room, preparing and packaging of the material into 3013 packages using the SPE, and transport of the 3013 packages to the non-destructive analysis (NDA) lab or storage vault. The HazOp analysis also included construction activities associated with the modifications of the support utilities for the SPE, and the installation of support trailers.
Stability of differential susceptibility and infectivity epidemic models.
Bonzi, B; Fall, A A; Iggidr, A; Sallet, G
2011-01-01
We introduce classes of differential susceptibility and infectivity epidemic models. These models address the problem of flows between the different susceptible, infectious and infected compartments and differential death rates as well. We prove the global stability of the disease free equilibrium when the basic reproduction ratio R0≤1 and the existence and uniqueness of an endemic equilibrium when R0>1. We also prove the global asymptotic stability of the endemic equilibrium for a differential susceptibility and staged progression infectivity model, when R0>1. Our results encompass and generalize those of Hyman and Li (J Math Biol 50:626-644, 2005; Math Biosci Eng 3:89-100, 2006). PMID:20148330
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.
Dynamic Response and Stability Analysis of AN Automatic Ball Balancer for a Flexible Rotor
NASA Astrophysics Data System (ADS)
Chung, J.; Jang, I.
2003-01-01
Dynamic stability and time responses are studied for an automatic ball balancer of a rotor with a flexible shaft. The Stodola-Green rotor model, of which the shaft is flexible, is selected for analysis. This rotor model is able to include the influence of rigid-body rotations due to the shaft flexibility on dynamic responses. Applying Lagrange's equation to the rotor with the ball balancer, the non-linear equations of motion are derived. Based on the linearized equations, the stability of the ball balancer around the balanced equilibrium position is analyzed. On the other hand, the time responses computed from the non-linear equations are investigated. This study shows that the automatic ball balancer can achieve the balancing of a rotor with a flexible shaft if the system parameters of the balancer satisfy the stability conditions for the balanced equilibrium position.
Anisotropic stress and stability in modified gravity models
Saltas, Ippocratis D.; Kunz, Martin
2011-03-15
The existence of anisotropic stress of a purely geometrical origin seems to be a characteristic of higher order gravity models, and has been suggested as a probe to test these models observationally, for example, in weak lensing experiments. In this paper, we seek to find a class of higher order gravity models of f(R,G) type that would give us a zero anisotropic stress and study the consequences for the viability of the actual model. For the special case of a de Sitter background, we identify a subclass of models with the desired property. We also find a direct link between anisotropic stress and the stability of the model as well as the presence of extra degrees of freedom, which seems to be a general feature of higher order gravity models. Particularly, setting the anisotropic stress equal to zero for a de Sitter background leads to a singularity that makes it impossible to reach the de Sitter evolution.
Riepema, Karel; Bakker, Douwe; Gordon, Stephen V.
2015-01-01
Johne’s Disease (JD) is a chronic enteritis of ruminants caused by Mycobacterium avium subspecies paratuberculosis (MAP). Current disease control strategies are hampered by the lack of sensitive and specific diagnostic modalities. Therefore, novel diagnostic and prognostic tools are needed, and circulating microRNAs (miRNAs) may hold potential in this area. The aims of this study were twofold: (i) to address the stability of miRNA in bovine sera from biobanked samples, and (ii) to assess the potential of miRNAs as biomarkers for JD disease progression. To address these aims we used bovine sera from an experimental MAP infection model that had been stored at -20°C for over a decade, allowing us to also assess the stability of miRNA profiles in biobanked serum samples through comparison with fresh sera. Approximately 100–200 intact miRNAs were identified in each sample with 83 of these being consistently detected across all 57 samples. The miRNA profile of the biobanked sera stored at -20°C for over 10 years was highly similar to the profile of <1 year-old sera stored at -80°C, with an overlap of 73 shared miRNAs. IsomiR analysis also indicated a distinct bovine serum-specific isomiR profile as compared to previously reported bovine macrophage miRNA profiles. To explore the prognostic potential of miRNA profiles cattle defined as seropositive for anti-MAP antibodies (n = 5) were compared against seronegative cattle (n = 7). No significant differential expressed miRNAs were detected at either the early (6 months) or late (43, 46 and 49 months) intervals (FDR≤0.05, fold-change≥1.5) across seropositive or seronegative animals. However, comparing pre-infection sera to the early and late time-points identified increased miR-29a and miR-92b abundance (2-fold) that may be due to blood-cell population changes over time (P<0.001). In conclusion our study has demonstrated that bovine circulating miRNAs retain their integrity under long-term sub-optimal storage temperatures opening the way for increased miRNA analyses from biobanked samples for a range of infectious and non-infectious diseases. PMID:26675426
Shaughnessy, Ronan G; Farrell, Damien; Riepema, Karel; Bakker, Douwe; Gordon, Stephen V
2015-01-01
Johne's Disease (JD) is a chronic enteritis of ruminants caused by Mycobacterium avium subspecies paratuberculosis (MAP). Current disease control strategies are hampered by the lack of sensitive and specific diagnostic modalities. Therefore, novel diagnostic and prognostic tools are needed, and circulating microRNAs (miRNAs) may hold potential in this area. The aims of this study were twofold: (i) to address the stability of miRNA in bovine sera from biobanked samples, and (ii) to assess the potential of miRNAs as biomarkers for JD disease progression. To address these aims we used bovine sera from an experimental MAP infection model that had been stored at -20°C for over a decade, allowing us to also assess the stability of miRNA profiles in biobanked serum samples through comparison with fresh sera. Approximately 100-200 intact miRNAs were identified in each sample with 83 of these being consistently detected across all 57 samples. The miRNA profile of the biobanked sera stored at -20°C for over 10 years was highly similar to the profile of <1 year-old sera stored at -80°C, with an overlap of 73 shared miRNAs. IsomiR analysis also indicated a distinct bovine serum-specific isomiR profile as compared to previously reported bovine macrophage miRNA profiles. To explore the prognostic potential of miRNA profiles cattle defined as seropositive for anti-MAP antibodies (n = 5) were compared against seronegative cattle (n = 7). No significant differential expressed miRNAs were detected at either the early (6 months) or late (43, 46 and 49 months) intervals (FDR≤0.05, fold-change≥1.5) across seropositive or seronegative animals. However, comparing pre-infection sera to the early and late time-points identified increased miR-29a and miR-92b abundance (2-fold) that may be due to blood-cell population changes over time (P<0.001). In conclusion our study has demonstrated that bovine circulating miRNAs retain their integrity under long-term sub-optimal storage temperatures opening the way for increased miRNA analyses from biobanked samples for a range of infectious and non-infectious diseases. PMID:26675426
Carreón-Calderón, Bernardo
2012-10-14
Stability analysis is generally used to verify that the solution to phase equilibrium calculations corresponds to a stable state (minimum of the free energy). In this work, tangent plane distance analysis for stability of macroscopic mixtures is also used for analyzing the nucleation process, reconciling thus this analysis with classical nucleation theories. In the context of the revised nucleation theory, the driving force and the nucleation work are expressed as a function of the Lagrange multiplier corresponding to the mole fraction constraint from the minimization problem of stability analysis. Using a van der Waals fluid applied to a ternary mixture, Lagrange multiplier properties are illustrated. In particular, it is shown how the Lagrange multiplier value is equal to one on the binodal and spinodal curves at the same time as the driving force of nucleation vanishes on these curves. Finally, it is shown that, on the spinodal curve, the nucleation work from the revised and generalized nucleation theories are characterized by two different local minima from stability analysis, irrespective of any interfacial tension models. PMID:23061836
Enumeration and stability analysis of simple periodic orbits in β-Fermi Pasta Ulam lattice
Sonone, Rupali L. Jain, Sudhir R.
2014-04-24
We study the well-known one-dimensional problem of N particles with a nonlinear interaction. The special case of quadratic and quartic interaction potential among nearest neighbours is the β-Fermi-Pasta-Ulam model. We enumerate and classify the simple periodic orbits for this system and find the stability zones, employing Floquet theory. Such stability analysis is crucial to understand the transition of FPU lattice from recurrences to globally chaotic behavior, energy transport in lower dimensional system, dynamics of optical lattices and also its impact on shape parameter of bio-polymers such as DNA and RNA.
Stability and L2 performance analysis of stochastic delayed neural networks.
Chen, Yun; Zheng, Wei Xing
2011-10-01
This brief focuses on the robust mean-square exponential stability and L(2) performance analysis for a class of uncertain time-delay neural networks perturbed by both additive and multiplicative stochastic noises. New mean-square exponential stability and L(2) performance criteria are developed based on the delay partition Lyapunov-Krasovskii functional method and generalized Finsler lemma which is applicable to stochastic systems. The analytical results are established without involving any model transformation, estimation for cross terms, additional free-weighting matrices, or tuning parameters. Numerical examples are presented to verify that the proposed approach is both less conservative and less computationally complex than the existing ones. PMID:21843984
Stability analysis of position and force control problems for robot arms
NASA Technical Reports Server (NTRS)
Wen, John T.; Murphy, Steve
1990-01-01
A stability analysis for robot manipulators under the influence of external forces is presented. Several control objectives are considered: rejecting the external force as a source of disturbance, complying to the external force as a generalized mass-spring-damper system, and actively controlling the external force when a dynamic model for the environment is available. An explanation of instability is given for the case in which the environment has flexibility and the gains are inappropriately chosen. When the environment is stiff in the force control subspace, robust stability can be achieved via the integral force feedback.
A versatile FACTS device model for powerflow and stability simulations
Arabi, S.; Kundur, P.
1996-11-01
While early FACTs devices consisted mainly of thyristor-controlled/switched RLC/transformer components, the newer generation is based on the self-commutated voltage-sourced converter. The variety of devices and applications, and the changing nature of the technology, call for versatile modelling capabilities at different levels of detail. This paper describes a model conceived as a coordinated and interconnected set of controllable shunt and series elements. For each device, functional characteristics, typical settings and controls, and simulation examples are presented. The model is capable of representing virtually any FACTS device for powerflow and all types of stability simulations.
Game Theoretical Analysis on Cooperation Stability and Incentive Effectiveness in Community Networks
Liu, Yi; Qian, Depei; Zhang, Han; Cai, Jihong
2015-01-01
Community networks, the distinguishing feature of which is membership admittance, appear on P2P networks, social networks, and conventional Web networks. Joining the network costs money, time or network bandwidth, but the individuals get access to special resources owned by the community in return. The prosperity and stability of the community are determined by both the policy of admittance and the attraction of the privileges gained by joining. However, some misbehaving users can get the dedicated resources with some illicit and low-cost approaches, which introduce instability into the community, a phenomenon that will destroy the membership policy. In this paper, we analyze on the stability using game theory on such a phenomenon. We propose a game-theoretical model of stability analysis in community networks and provide conditions for a stable community. We then extend the model to analyze the effectiveness of different incentive policies, which could be used when the community cannot maintain its members in certain situations. Then we verify those models through a simulation. Finally, we discuss several ways to promote community network’s stability by adjusting the network’s properties and give some proposal on the designs of these types of networks from the points of game theory and stability. PMID:26551649
Song, Kaida; Wang, Rui; Liu, Yi; Qian, Depei; Zhang, Han; Cai, Jihong
2015-01-01
Community networks, the distinguishing feature of which is membership admittance, appear on P2P networks, social networks, and conventional Web networks. Joining the network costs money, time or network bandwidth, but the individuals get access to special resources owned by the community in return. The prosperity and stability of the community are determined by both the policy of admittance and the attraction of the privileges gained by joining. However, some misbehaving users can get the dedicated resources with some illicit and low-cost approaches, which introduce instability into the community, a phenomenon that will destroy the membership policy. In this paper, we analyze on the stability using game theory on such a phenomenon. We propose a game-theoretical model of stability analysis in community networks and provide conditions for a stable community. We then extend the model to analyze the effectiveness of different incentive policies, which could be used when the community cannot maintain its members in certain situations. Then we verify those models through a simulation. Finally, we discuss several ways to promote community network's stability by adjusting the network's properties and give some proposal on the designs of these types of networks from the points of game theory and stability. PMID:26551649
Gumus, Koray; Crockett, Charlene Hong; Rao, Kavita; Yeu, Elizabeth; Weikert, Mitchell P.; Shirayama, Mariko; Hada, Shigeki
2011-01-01
Purpose. To evaluate tear film stability in patients with tear dysfunction and an asymptomatic control group by using the novel, noninvasive Tear Stability Analysis System (TSAS). Methods. In this prospective case–control study, 45 patients with dysfunctional tear syndrome (DTS) were stratified into three groups (1, 2, and 3/4) based on clinical severity, with higher scores indicating more severe symptoms; 25 asymptomatic control subjects were evaluated. TSAS measurements were performed with the RT-7000 Auto Refractor-Keratometer (Tomey Corporation, Nagoya, Japan). Images of ring mires projected onto the cornea every second for 6 seconds were captured and analyzed. Focal changes in brightness were calculated as numerical ring breakup (RBU) values, and the elapsed time when the cumulative values (RBU sum) exceeded a threshold was defined as the ring breakup time (RBUT). Results. RBUTs in the DTS groups were all significantly lower than those in the control subjects, with the lowest values found in DTS 3/4. RBUT was significantly shorter in DTS 3/4 than in DTS 1 (P < 0.001). The change in RBU sum over a 6-second period in the DTS groups combined or between the individual groups was statistically significant (P < 0.001), as was the difference between the 1- and 6-second values. For distinguishing between asymptomatic controls and DTS, the sensitivity and specificity of a 5.0-second RBUT cutoff were 82.0% and 60.0%, respectively. Conclusions. The TSAS may be a useful, noninvasive instrument for evaluating tear stability and for classifying DTS severity. PMID:20631241
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 stability index for detonation waves in Majdas model for reacting flow
NASA Astrophysics Data System (ADS)
Lyng, Gregory; Zumbrun, Kevin
2004-07-01
Using Evans function techniques, we develop a stability index for weak and strong detonation waves analogous to that developed for shock waves in [SIAM J. Math. Anal. 32 (2001) 929; Commun. Pure Appl. Math. 51 (7) (1998) 797], yielding useful necessary conditions for stability. Here, we carry out the analysis in the context of the Majda model, a simplified model for reacting flow; the method is extended to the full Navier-Stokes equations of reacting flow in [G. Lyng, One dimensional stability of detonation waves, Doctoral Thesis, Indiana University, 2002; G. Lyng, K. Zumbrun, Stability of detonation waves, Preprint, 2003]. The resulting stability condition is satisfied for all nondegenerate, i.e., spatially exponentially decaying, weak and strong detonations of the Majda model in agreement with numerical experiments of [SIAM J. Sci. Statist. Comput. 7u (1986) 1059] and analytical results of [Commun. Math. Phys. 204 (3) (1999) 551; Commun. Math. Phys. 202 (3) (1999) 547] for a related model of Majda and Rosales. We discuss also the role in the ZND limit of degenerate, subalgebraically decaying weak detonation and (for a modified, bump-type ignition function) deflagration profiles, as discussed in [SIAM J. Math. Anal. 24 (1993) 968; SIAM J. Appl. Math. 55 (1995) 175] for the full equations.
Control sensitivity indices for stability analysis of HVdc systems
Nayak, O.B.; Gole, A.M.; Chapman, D.G.; Davies, J.B.
1995-10-01
This paper presents a new concept called the ``Control Sensitivity Index`` of CSI, for the stability analysis of HVdc converters connected to weak ac systems. The CSI for a particular control mode can be defined as the ratio of incremental changes in the two system variables that are most relevant to that control mode. The index provides valuable information on the stability of the system and, unlike other approaches, aids in the design of the controller. It also plays an important role in defining non-linear gains for the controller. This paper offers a generalized formulation of CSI and demonstrates its application through an analysis of the CSI for three modes of HVdc control. The conclusions drawn from the analysis are confirmed by a detailed electromagnetic transients simulation of the ac/dc system. The paper concludes that the CSI can be used to improve the controller design and, for an inverter in a weak ac system, the conventional voltage control mode is more stable than the conventional {gamma} control mode.
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
Higgs-radion mixing in stabilized brane world models
NASA Astrophysics Data System (ADS)
Boos, Edward E.; Bunichev, Viacheslav E.; Perfilov, Maxim A.; Smolyakov, Mikhail N.; Volobuev, Igor P.
2015-11-01
We consider a quartic interaction of the Higgs and Goldberger-Wise fields, which connects the mechanism of the extra dimension size stabilization with spontaneous symmetry breaking on our brane and gives rise to a coupling of the Higgs field to the radion and its KK tower. We estimate a possible influence of this coupling on the Higgs-radion mixing and study restrictions on model parameters from the LHC data.
Thermal Stability Analysis for Superconducting Coupling Coil in MICE
Wu, Hong; Wang, Li; Pan, Heng; Guo, XingLong; Green, M.A.
2010-06-28
The superconducting coupling coil to be used in the Muon Ionization Cooling Experiment (MICE) with inner radius of 750 mm, length of 285 mm and thickness of 110.4 mm will be cooled by a pair of 1.5 W at 4.2 K cryo-coolers. When the coupling coil is powered to 210 A, it will produce about 7.3 T peak magnetic field at the conductor and it will have a stored energy of 13 MJ. A key issue for safe operation of the coupling coil is the thermal stability of the coil during a charge and discharge. The magnet and its cooling system are designed for a rapid discharge where the magnet is to be discharged in 5400 seconds. The numerical simulation for the thermal stability of the MICE coupling coil has been done using ANSYS. The analysis results show that the superconducting coupling coil has a good stability and can be charged and discharged safely.
Architectural stability analysis of the rotary-laser scanning technique
NASA Astrophysics Data System (ADS)
Xue, Bin; Yang, Xiaoxia; Zhu, Jigui
2016-03-01
The rotary-laser scanning technique is an important method in scale measurements due to its high accuracy and large measurement range. This paper first introduces a newly designed measurement station which is able to provide two-dimensional measurement information including the azimuth and elevation by using the rotary-laser scanning technique, then presents the architectural stability analysis of this technique by detailed theoretical derivations. Based on the designed station, a validation using both experiment and simulation is presented in order to verify the analytic conclusion. The results show that the architectural stability of the rotary-laser scanning technique is only affected by the two scanning angles' difference. And the difference which brings the best architectural stability can be calculated by using pre-calibrated parameters of the two laser planes. This research gives us an insight into the rotary-laser scanning technique. Moreover, the measurement accuracy of the rotary-laser scanning technique can be further improved based on the results of the study.
Graph theory and stability analysis of protein complex interaction networks.
Huang, Chien-Hung; Chen, Teng-Hung; Ng, Ka-Lok
2016-04-01
Protein complexes play an essential role in many biological processes. Complexes can interact with other complexes to form protein complex interaction network (PCIN) that involves in important cellular processes. There are relatively few studies on examining the interaction topology among protein complexes; and little is known about the stability of PCIN under perturbations. We employed graph theoretical approach to reveal hidden properties and features of four species PCINs. Two main issues are addressed, (i) the global and local network topological properties, and (ii) the stability of the networks under 12 types of perturbations. According to the topological parameter classification, we identified some critical protein complexes and validated that the topological analysis approach could provide meaningful biological interpretations of the protein complex systems. Through the Kolmogorov-Smimov test, we showed that local topological parameters are good indicators to characterise the structure of PCINs. We further demonstrated the effectiveness of the current approach by performing the scalability and data normalization tests. To measure the robustness of PCINs, we proposed to consider eight topological-based perturbations, which are specifically applicable in scenarios of targeted, sustained attacks. We found that the degree-based, betweenness-based and brokering-coefficient-based perturbations have the largest effect on network stability. PMID:26997661
NASA Technical Reports Server (NTRS)
Sevart, F. D.; Patel, S. M.; Wattman, W. J.
1972-01-01
Testing and evaluation of stability augmentation systems for aircraft flight control were conducted. The flutter suppression system analysis of a scale supersonic transport wing model is described. Mechanization of the flutter suppression system is reported. The ride control synthesis for the B-52 aeroelastic model is discussed. Model analyses were conducted using equations of motion generated from generalized mass and stiffness data.
Stability analysis of restricted non-static axial symmetry
Sharif, M.; Bhatti, M. Zaeem Ul Haq E-mail: mzaeem.math@gmail.com
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.
Stability of functions in Boolean models of gene regulatory networks
NASA Astrophysics Data System (ADS)
Rämö, Pauli; Kesseli, Juha; Yli-Harja, Olli
2005-09-01
Boolean networks are used to model large nonlinear systems such as gene regulatory networks. We will present results that can be used to understand how the choice of functions affects the network dynamics. The so called bias-map and its fixed points depict much of the function's dynamical role in the network. We define the concept of stabilizing functions and show that many Post and canalizing functions are also stabilizing functions. Boolean networks constructed using the same type of stabilizing functions are always stable regardless of the average in-degree of network functions. We derive the number of all stabilizing functions and find it to be much larger than the number of Post and canalizing functions. We also discuss the implementation of functions and apply the presented results to biological data that give an approximation of the distribution of regulatory functions in eucaryotic cells. We find that the obtained theoretical results on the number of active genes are biologically plausible. Finally, based on the presented results, we discuss why canalizing and Post regulatory functions seem to be common in cells.
Stability of spiky solution of Keller-Segel's minimal chemotaxis model
NASA Astrophysics Data System (ADS)
Chen, Xinfu; Hao, Jianghao; Wang, Xuefeng; Wu, Yaping; Zhang, Yajing
2014-11-01
A huge volume of research has been done for the simplest chemotaxis model (Keller-Segel's minimal model) and its variants, yet, some of the basic issues remain unresolved until now. For example, it is known that the minimal model has spiky steady states that can be used to model the important cell aggregation phenomenon, but the stability of monotone spiky steady states was not shown. In this paper, we derive, first formally and then rigorously, the asymptotic expansion of these monotone steady states, and then we use this fine information on the spike to prove its local asymptotic stability. Moreover, we obtain the uniqueness of such steady states. We expect that the new ideas and techniques for rigorous asymptotic expansion and spectrum analysis presented in this paper will be useful in attacking and hence stimulating research on other more sophisticated chemotaxis models.
Climate stability and sensitivity in some simple conceptual models
NASA Astrophysics Data System (ADS)
Bates, J. Ray
2012-02-01
A theoretical investigation of climate stability and sensitivity is carried out using three simple linearized models based on the top-of-the-atmosphere energy budget. The simplest is the zero-dimensional model (ZDM) commonly used as a conceptual basis for climate sensitivity and feedback studies. The others are two-zone models with tropics and extratropics of equal area; in the first of these (Model A), the dynamical heat transport (DHT) between the zones is implicit, in the second (Model B) it is explicitly parameterized. It is found that the stability and sensitivity properties of the ZDM and Model A are very similar, both depending only on the global-mean radiative response coefficient and the global-mean forcing. The corresponding properties of Model B are more complex, depending asymmetrically on the separate tropical and extratropical values of these quantities, as well as on the DHT coefficient. Adopting Model B as a benchmark, conditions are found under which the validity of the ZDM and Model A as climate sensitivity models holds. It is shown that parameter ranges of physical interest exist for which such validity may not hold. The 2 × CO2 sensitivities of the simple models are studied and compared. Possible implications of the results for sensitivities derived from GCMs and palaeoclimate data are suggested. Sensitivities for more general scenarios that include negative forcing in the tropics (due to aerosols, inadvertent or geoengineered) are also studied. Some unexpected outcomes are found in this case. These include the possibility of a negative global-mean temperature response to a positive global-mean forcing, and vice versa.
Stability Analysis of a Rock Column in Seismic Conditions
NASA Astrophysics Data System (ADS)
Barbero, M.; Barla, G.
2010-11-01
The stability of a rock column located on a high conglomerate cliff in Roverino, near Ventimiglia, in north-western Italy, has been analysed by continuum and discontinuum modelling, in both static and seismic conditions. The rock column, which is 40 m high and nearly 36,000 m3 in volume, exposes the residential area below the cliff, housing more than 4,000 people, to a high risk level. As the area is located in a seismic region with estimated peak acceleration between 0.24 and 0.28 g, the stability analyses were carried out in both static and seismic conditions. Continuum and discontinuum modelling of the rock mass was carried out by using the finite difference methods and the distinct element methods. It is shown that both methods are effective in describing the modes of instability of the rock column in static conditions. On the contrary, a convincing description of the rock column response induced by earthquake excitation is achieved by discontinuum modelling.
Bakr, Brandon W; Sherrill, C David
2016-04-21
Rational design of catalysts would be aided by a better understanding of how non-covalent interactions stabilize transition states. Here, we apply the newly-developed Functional-Group Symmetry-Adapted Perturbation Theory (F-SAPT) to quantify non-covalent interactions in transition states of the proline-catalyzed intermolecular aldol reaction between benzaldehyde and cyclohexanone, according to the Houk-List mechanism [Bahmanyar et al., J. Am. Chem. Soc., 2003, 125, 2475]. A recent re-examination of this organocatalytic reaction by Rzepa and co-workers [Armstrong et al., Chem. Sci., 2014, 5, 2057] used electron density analysis to identify three key non-covalent interactions thought to influence stereoselectivity: (1) a favorable electrostatic interaction (originally identified by Houk and List) between the NCH(δ+) group of the enamine intermediate and the (δ-)O[double bond, length as m-dash]C of benzaldehyde; (2) a C-H/π interaction between the cyclohexene group of the enamine intermediate and the benzaldehyde phenyl ring; (3) a stabilizing contact between an ortho-hydrogen of the phenyl and an oxygen of the carboxylic acid group of the enamine. These three interactions have been directly computed using F-SAPT, which confirms the stabilizing interaction between an ortho-hydrogen and the carboxylic acid in the (S,S) and (R,S) transition state stereoisomers. F-SAPT analysis also finds stabilizing dispersion and electrostatic interactions due to a C-H/π interaction between the cyclohexene and phenyl groups in the (S,S) and (R,R) transition states. However, unfavorable exchange-repulsion cancels the attractive terms that favor these stereoisomers. Surprisingly, the interaction thought to be most important for stereoselectivity, the NCH(δ+)(δ-)O[double bond, length as m-dash]C interaction, is actually found to be repulsive due to the negative charge on the nitrogen. Hence, our results indicate that geometric analysis and/or density-based analysis does not necessarily produce a reliable picture of non-covalent stabilization. As confirmed by high-level coupled-cluster computations, intermolecular interaction energies are strongest for the (R,R) transition states, which are not the experimentally favored products. This suggests that at least for this reaction, stereoselectivity is also strongly dependent on the energy required to distort the reacting molecules into the transition state geometry. PMID:27020417
Qualitative analysis of the stability of a continuous vermicomposting system.
Hu, Enzhu; Liu, Hong
2012-12-01
A mathematical model was established to describe ecological relationships in a continuous vermicomposting system. The distributions of organic matter, microbes and earthworms on non-dimensional specific growth rates were simulated. The range of specific growth rates were visualized utilizing three-dimensional reconstruction technology. The stability of a vermicomposting system was not influenced by the initial concentrations of microbes and earthworms, only their species. The coordinates of the stable point depended on the dilution rate and initial amount of organic matter. The method described could be help for establishing a stable continuous vermicomposting system. PMID:23127841
Fuzzy Current-Mode Control and Stability Analysis
NASA Technical Reports Server (NTRS)
Kopasakis, George
2000-01-01
In this paper a current-mode control (CMC) methodology is developed for a buck converter by using a fuzzy logic controller. Conventional CMC methodologies are based on lead-lag compensation with voltage and inductor current feedback. In this paper the converter lead-lag compensation will be substituted with a fuzzy controller. A small-signal model of the fuzzy controller will also be developed in order to examine the stability properties of this buck converter control system. The paper develops an analytical approach, introducing fuzzy control into the area of CMC.
Estimation of dynamic stability parameters from drop model flight tests
NASA Technical Reports Server (NTRS)
Chambers, J. R.; Iliff, K. W.
1981-01-01
A recent NASA application of a remotely-piloted drop model to studies of the high angle-of-attack and spinning characteristics of a fighter configuration has provided an opportunity to evaluate and develop parameter estimation methods for the complex aerodynamic environment associated with high angles of attack. The paper discusses the overall drop model operation including descriptions of the model, instrumentation, launch and recovery operations, piloting concept, and parameter identification methods used. Static and dynamic stability derivatives were obtained for an angle-of-attack range from -20 deg to 53 deg. The results of the study indicated that the variations of the estimates with angle of attack were consistent for most of the static derivatives, and the effects of configuration modifications to the model (such as nose strakes) were apparent in the static derivative estimates. The dynamic derivatives exhibited greater uncertainty levels than the static derivatives, possibly due to nonlinear aerodynamics, model response characteristics, or additional derivatives.
GIS modelling of slope stability in Phewa Tal watershed, Nepal
NASA Astrophysics Data System (ADS)
Rowbotham, David N.; Dudycha, Douglas
1998-12-01
Hazards are an inherent but dangerous and costly element of mountainous environments. Conventional maps of mountain hazards provide useful inventories of hazardous sites but provide little insight into the operation of the hazards. Furthermore, this approach tends to rely heavily on subjective interpretation of the landscape, which means that the results can not be replicated or transferred to other areas. Thus, alternative approaches employing the quantitative capabilities of geographic information systems (GIS) to model and predict slope stability are receiving increasing attention. This paper reports on the use of a diverse GIS database, compiled primarily from existing maps and aerial photographs, to construct a regional model of slope stability in Phewa Tal watershed, Nepal. An integral part of the research was to explore an alternative approach to the commonly used grid cell approach by employing geomorphometrically significant terrain units. The terrain units employed were created by generating line networks representing local maxima and minima extracted from elevation and curvature surfaces. One of the chief benefits of applying GIS technology in this research was the ability to georeference all of the attribute data to these terrain units. In doing so, it allowed the database to be exported into an external statistical package, where the terrain units could be statistically explored as the basic analytical unit. The application of a variety of statistical techniques resulted in logistic regression being selected as the most useful. Logistic regression successfully predicted terrain units as being either stable or unstable at a rate of approximately 90% concordance with a conventionally produced map of slope stability. The statistical probabilities of terrain unit stability were imported back into the GIS to produce a map of predicted slope stability that compared well with the conventional map of slope stability. The findings of this research suggest that the use of geomorphometrically significant terrain units extracted from a digital elevation model (DEM) are an efficient alternative to approaches using regular grid cells. In particular, the terrain units facilitated the use of logistic regression, and significantly decreased the amount of computing costs. Finally, this research also suggests that important information can be gathered from existing information sources, such as maps, aerial photographs, and written documents, thereby limiting the need for costly and time consuming field work at the reconnaissance level. Based on this latter finding, other information sources, such as satellite imagery, should be examined.
Robust Stability Analysis of the Space Launch System Control Design: A Singular Value Approach
NASA Technical Reports Server (NTRS)
Pei, Jing; Newsome, Jerry R.
2015-01-01
Classical stability analysis consists of breaking the feedback loops one at a time and determining separately how much gain or phase variations would destabilize the stable nominal feedback system. For typical launch vehicle control design, classical control techniques are generally employed. In addition to stability margins, frequency domain Monte Carlo methods are used to evaluate the robustness of the design. However, such techniques were developed for Single-Input-Single-Output (SISO) systems and do not take into consideration the off-diagonal terms in the transfer function matrix of Multi-Input-Multi-Output (MIMO) systems. Robust stability analysis techniques such as H(sub infinity) and mu are applicable to MIMO systems but have not been adopted as standard practices within the launch vehicle controls community. This paper took advantage of a simple singular-value-based MIMO stability margin evaluation method based on work done by Mukhopadhyay and Newsom and applied it to the SLS high-fidelity dynamics model. The method computes a simultaneous multi-loop gain and phase margin that could be related back to classical margins. The results presented in this paper suggest that for the SLS system, traditional SISO stability margins are similar to the MIMO margins. This additional level of verification provides confidence in the robustness of the control design.
Study of nonlinear system stability using eigenvalue analysis: Gyroscopic motion
NASA Astrophysics Data System (ADS)
Shabana, Ahmed A.; Zaher, Mohamed H.; Recuero, Antonio M.; Rathod, Cheta
2011-11-01
General computational multibody system (MBS) algorithms allow for the linearization of the highly nonlinear equations of motion at different points in time in order to obtain the eigenvalue solution. This eigenvalue solution of the linearized equations is often used to shed light on the system stability at different configurations that correspond to different time points. Different MBS algorithms, however, employ different sets of orientation coordinates, such as Euler angles and Euler parameters, which lead to different forms of the dynamic equations of motion. As a consequence, the forms of the linearized equations and the eigenvalue solution obtained strongly depend on the set of orientation coordinates used. This paper addresses this fundamental issue by examining the effect of the use of different orientation parameters on the linearized equations of a gyroscope. The nonlinear equations of motion of the gyroscope are formulated using two different sets of orientation parameters: Euler angles and Euler parameters. In order to obtain a set of linearized equations that can be used to define the eigenvalue solution, the algebraic equations that describe the MBS constraints are systematically eliminated leading to a nonlinear form of the equations of motion expressed in terms of the system degrees of freedom. Because in MBS applications the generalized forces can be highly nonlinear and can depend on the velocities, a state space formulation is used to solve the eigenvalue problem. It is shown in this paper that the independent state equations formulated using Euler angles and Euler parameters lead to different eigenvalue solutions. This solution is also different from the solution obtained using a form of the Newton-Euler matrix equation expressed in terms of the angular accelerations and angular velocities. A time-domain solution of the linearized equations is also presented in order to compare between the solutions obtained using two different sets of orientation parameters and also to shed light on the important issue of using the eigenvalue analysis in the study of MBS stability. The validity of using the eigenvalue analysis based on the linearization of the nonlinear equations of motion in the study of the stability of railroad vehicle systems, which have known critical speeds, is examined. It is shown that such an eigenvalue analysis can lead to wrong conclusions regarding the stability of nonlinear systems.
Thermohaline Circulation Stability: A Box Model Study. Part I: Uncoupled Model.
NASA Astrophysics Data System (ADS)
Lucarini, Valerio; Stone, Peter H.
2005-02-01
A thorough analysis of the stability of the uncoupled Rooth interhemispheric three-box model of thermohaline circulation (THC) is presented. The model consists of a northern high-latitude box, a tropical box, and a southern high-latitude box, which correspond to the northern, tropical, and southern Atlantic Ocean, respectively. Restoring boundary conditions are adopted for the temperature variables, and flux boundary conditions are adopted for the salinity variables. This paper examines how the strength of THC changes when the system undergoes forcings that are analogous to those of global warming conditions by applying the equilibrium state perturbations to the moisture and heat fluxes into the three boxes. In each class of experiments, using suitably defined metrics, the authors determine the boundary dividing the set of forcing scenarios that lead the system to equilibria characterized by a THC pattern similar to the present one from those that drive the system to equilibria with a reversed THC. Fast increases in the moisture flux into the northern high-latitude box are more effective than slow increases in leading the THC to a breakdown, while the increases of moisture flux into the southern high-latitude box strongly inhibit the breakdown and can prevent it, as in the case of slow increases in the Northern Hemisphere. High rates of heat flux increase in the Northern Hemisphere destabilize the system more effectively than low ones; increases in the heat fluxes in the Southern Hemisphere tend to stabilize the system.
NASA Astrophysics Data System (ADS)
Ramanujam, G.; Bert, C. W.
1983-06-01
The objective of this paper is to provide a theoretical foundation to predict many aspects of dynamic behavior of flywheel systems when spin-tested with a quill shaft support and driven by an air turbine. Theoretical analyses for the following are presented: (1) determination of natural frequencies (or for brevity critical speeds of various orders), (2) Routh-type stability analysis to determine the stability limits (i.e., the speed range within which small perturbations attenuate rather than cause catastrophic failure), and (3) forced whirling analysis to estimate the response of major components of the system to flywheel mass eccentricity and initial tilt. For the first and third kinds of analyses, two different mathematical models of the generic system are investigated. One is a seven-degree-of-freedom lumped parameter analysis, while the other is a combined distributed and lumped parameter analysis.
Stability Analysis of Flow Induced by the Traveling Magnetic Field
NASA Technical Reports Server (NTRS)
Mazuruk, Konstantin
2003-01-01
Re-circulating flow in molten metal columns can be conveniently induced by the axisymmetric traveling magnetic field. A number of applications can benefit from this technique, such as mixing under microgravity environment, or.crysta1 growth from metallic melts. For small magnetic field excitations, the flow is laminar and stationary. As the imposed field increases, a more complex flow will set up in the cylindrical column. Conditions for stable laminar flow are of importance for practical applications. In this work, a linear stability analysis is performed in order to determine the onset of the bifurcation in the system. Here the analysis is restricted to the axisymmetric modes and the low-frequency regime.
Stability Analysis of Flow Induced by the Traveling Magnetic Field
NASA Technical Reports Server (NTRS)
Mazuruk, Konstantin
2003-01-01
Re-circulating flow in molten metal columns can be conveniently induced by the axisymmetric traveling magnetic field. A number of applications can benefit from this technique, such as mixing under microgravity environment, or crysta1 growth from metallic melts. For small magnetic field excitations, the flow is laminar and stationary. As the imposed field increases, a more complex flow will set up in the cylindrical column. Conditions for stable laminar flow are of importance for practical applications. In this work, a linear stability analysis is performed in order to determine the onset of the bifurcation in the system. Here the analysis is restricted to the axisymmetric modes and the low-frequency regime.
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.
Stability analysis and controller design in microbial continuous culture with discrete time delay.
Zhu, Xi; Gao, Jinggui; Feng, Enmin; Xiu, Zhilong; Jin, Sheng
2013-01-01
In this paper, stability analysis and controller design in microbial continuous culture with discrete time delay are studied. The dissimilation process of glycerol to 1,3-propanediol cannot avoid the disturbances caused by time delay. Time delay can limit and degrade the achievable performance of controlled systems, and even induce instability. Based on the biodynamic model, some properties of its solutions are discussed. In addition, we investigate how the time-delay affects the stability of the system. A linear matrix inequalities method is applied to find a feedback controller to ensure the stability of the closed-loop system. The simulation results indicate that this controller might be feasible for continuous bioprocess control. PMID:23586672
Stability analysis of position and force control problems for robot arms
NASA Technical Reports Server (NTRS)
Wen, John T.; Murphy, Steve
1990-01-01
Stability issues involving the control of a robot arm under the influence of external forces are discussed. Several different scenarios are considered: position control with the external force as an unmodeled disturbance, compliant control for a bounded external force in some subspace, and compliant control for a force due to the interaction with an environment whose dynamical behavior can be modeled. In each of these cases, a stability analysis using the Lyapunov method is presented. An explanation of instability is put forth for the case in which the environment has flexibility and the gains are inappropriately chosen. When the environment is stiff in the force control subspace, robust stability can be achieved with the integral force feedback.
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
Ant colony optimization analysis on overall stability of high arch dam basis of field monitoring.
Lin, Peng; 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
NASA Astrophysics Data System (ADS)
Chanda, Sandip; De, Abhinandan
2015-07-01
A social welfare optimization technique has been proposed in this paper with a developed state space based model and bifurcation analysis to offer substantial stability margin even in most inadvertent states of power system networks. The restoration of the power market dynamic price equilibrium has been negotiated in this paper, by forming Jacobian of the sensitivity matrix to regulate the state variables for the standardization of the quality of solution in worst possible contingencies of the network and even with co-option of intermittent renewable energy sources. The model has been tested in IEEE 30 bus system and illustrious particle swarm optimization has assisted the fusion of the proposed model and methodology.
Wavelet modeling and prediction of the stability of states: the Roman Empire and the European Union
NASA Astrophysics Data System (ADS)
Yaroshenko, Tatyana Y.; Krysko, Dmitri V.; Dobriyan, Vitalii; Zhigalov, Maksim V.; Vos, Hendrik; Vandenabeele, Peter; Krysko, Vadim A.
2015-09-01
How can the stability of a state be quantitatively determined and its future stability predicted? The rise and collapse of empires and states is very complex, and it is exceedingly difficult to understand and predict it. Existing theories are usually formulated as verbal models and, consequently, do not yield sharply defined, quantitative prediction that can be unambiguously validated with data. Here we describe a model that determines whether the state is in a stable or chaotic condition and predicts its future condition. The central model, which we test, is that growth and collapse of states is reflected by the changes of their territories, populations and budgets. The model was simulated within the historical societies of the Roman Empire (400 BC to 400 AD) and the European Union (1957-2007) by using wavelets and analysis of the sign change of the spectrum of Lyapunov exponents. The model matches well with the historical events. During wars and crises, the state becomes unstable; this is reflected in the wavelet analysis by a significant increase in the frequency ω (t) and wavelet coefficients W (ω, t) and the sign of the largest Lyapunov exponent becomes positive, indicating chaos. We successfully reconstructed and forecasted time series in the Roman Empire and the European Union by applying artificial neural network. The proposed model helps to quantitatively determine and forecast the stability of a state.
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
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.
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.
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.
Genome-wide analysis of long noncoding RNA stability
Clark, Michael B.; Johnston, Rebecca L.; Inostroza-Ponta, Mario; Fox, Archa H.; Fortini, Ellen; Moscato, Pablo; Dinger, Marcel E.; Mattick, John S.
2012-01-01
Transcriptomic analyses have identified tens of thousands of intergenic, intronic, and cis-antisense long noncoding RNAs (lncRNAs) that are expressed from mammalian genomes. Despite progress in functional characterization, little is known about the post-transcriptional regulation of lncRNAs and their half-lives. Although many are easily detectable by a variety of techniques, it has been assumed that lncRNAs are generally unstable, but this has not been examined genome-wide. Utilizing a custom noncoding RNA array, we determined the half-lives of ?800 lncRNAs and ?12,000 mRNAs in the mouse Neuro-2a cell line. We find only a minority of lncRNAs are unstable. LncRNA half-lives vary over a wide range, comparable to, although on average less than, that of mRNAs, suggestive of complex metabolism and widespread functionality. Combining half-lives with comprehensive lncRNA annotations identified hundreds of unstable (half-life < 2 h) intergenic, cis-antisense, and intronic lncRNAs, as well as lncRNAs showing extreme stability (half-life > 16 h). Analysis of lncRNA features revealed that intergenic and cis-antisense RNAs are more stable than those derived from introns, as are spliced lncRNAs compared to unspliced (single exon) transcripts. Subcellular localization of lncRNAs indicated widespread trafficking to different cellular locations, with nuclear-localized lncRNAs more likely to be unstable. Surprisingly, one of the least stable lncRNAs is the well-characterized paraspeckle RNA Neat1, suggesting Neat1 instability contributes to the dynamic nature of this subnuclear domain. We have created an online interactive resource (http://stability.matticklab.com) that allows easy navigation of lncRNA and mRNA stability profiles and provides a comprehensive annotation of ?7200 mouse lncRNAs. PMID:22406755
Postural Stability Analysis with Inertial Measurement Units in Alzheimer's Disease
Gago, Miguel F.; Fernandes, Vitor; Ferreira, Jaime; Silva, Hélder; Rocha, Luís; Bicho, Estela; Sousa, Nuno
2014-01-01
Background The cause of frequent falls in patients with Alzheimer's disease (AD) is still not well understood. Nevertheless, balance control and sensory organization are known to be critical for moving safely and adapting to the environment. Methods We evaluated postural stability in 20 AD patients (11 fallers and 9 nonfallers) and 16 healthy controls with an inertial measurement unit (triaxial accelerometers and gyroscopes) attached to the center of mass (COM) in different balance conditions (Romberg on flat surface and frontward/backward-inclined surface, with or without visual suppression) in a motor lab. Results In AD patients, the group of fallers showed a different kinetic pattern of postural stability characterized by higher vulnerability to visual suppression, higher total/maximal displacement and a mediolateral/anteroposterior range of sway, and a consequent need for more corrections of COM pitch and roll angles. Conclusion Further studies are needed to consolidate the normative values of the discriminatory kinetic variables with the potential of inclusion in a multifactorial analysis of the risk of falls. Nevertheless, these results highlight signs of impairment of central postural control in AD, which may require early therapeutic intervention. PMID:24575114
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.
Bifurcation analysis of aircraft pitching motions near the stability boundary
NASA Technical Reports Server (NTRS)
Hui, W. H.; Tobak, M.
1984-01-01
Bifuraction theory is used to analyze the nonlinear dynamic stability characteristics of an aircraft subject to single degree of freedom pitching-motion perturbations about a large mean angle of attack. The requisite aerodynamic information in the equations of motion is represented in a form equivalent to the response to finite-amplitude pitching oscillations about the mean angle of attack. This information is deduced from the case of infinitesimal-amplitude oscillations. The bifurcation theory analysis reveals that when the mean angle of attack is increased beyond a critical value at which the aerodynamic damping vanishes, new solutions representing finite-amplitude periodic motions bifurcate from the previously stable steady motion. The sign of a simple criterion, cast in terms of aerodynamic properties, determines whether the bifurcating solutions are stable (supercritical) or unstable (subcritical). For flat-plate airfoils flying at supersonic/hypersonic speed, the bifurcation is subcritical, implying either that exchanges of stability between steady and periodic motion are accompanied by hysteresis phenomena, or that potentially large aperiodic departures from steady motion may develop.
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).
NASA Astrophysics Data System (ADS)
Antinoro, Chiara; Arnone, Elisa; Noto, Leonardo V.
2015-04-01
The mechanisms of rainwater infiltration causing slope instability had been analyzed and reviewed in many scientific works. Rainwater infiltration into unsaturated soil increases the degree of saturation, hence affecting the shear strength properties and thus the probability of slope failure. It has been widely proved that the shear strength properties change with the soil water suction in unsaturated soils; therefore, the accuracy to predict the relationship between soil water content and soil water suction, parameterized by the soil-water characteristic curve, has significant effects on the slope stability analysis. The aim of this study is to investigate how the characterization of SWRC of differently structured unsaturated soils affects the slope stability on a simple infinite slope. In particular, the unimodal and bimodal distributions of the soil pore size were compared. Samples of 40 soils, highly different in terms of structure and texture, were collected and used to calibrate two bimodal SWRCs, i.e. Ross and Smettem (1993) and Dexter et al., (2008). The traditional unimodal van Genuchten (1980) model was also applied for comparison. Slope stability analysis was conducted in terms of Factor of Safety (FS) by applying the infinite slope model for unsaturated soils. In the used formulation, the contribution of the suction effect is tuned by a parameter 'chi' in a rate proportional to the saturation conditions. Different parameterizations of this term were also compared and analyzed. Results indicated that all three SWRC models showed good overall performance in fitting the sperimental SWRCs. Both the RS and DE models described adequately the water retention data for soils with a bimodal behavior confirmed from the analysis of pore size distribution, but the best performance was obtained by DE model confirmed. In terms of FS, the tree models showed very similar results as soil moisture approached to the saturated condition; however, within the residual zone, the DE model denoted an anomalous behavior depending on the used formulation for the 'chi' parameter, with decreasing FS as soil moisture decreases.
Absolute Stability Analysis of a Phase Plane Controlled Spacecraft
NASA Technical Reports Server (NTRS)
Jang, Jiann-Woei; Plummer, Michael; Bedrossian, Nazareth; Hall, Charles; Jackson, Mark; Spanos, Pol
2010-01-01
Many aerospace attitude control systems utilize phase plane control schemes that include nonlinear elements such as dead zone and ideal relay. To evaluate phase plane control robustness, stability margin prediction methods must be developed. Absolute stability is extended to predict stability margins and to define an abort condition. A constrained optimization approach is also used to design flex filters for roll control. The design goal is to optimize vehicle tracking performance while maintaining adequate stability margins. Absolute stability is shown to provide satisfactory stability constraints for the optimization.
The global stability of an SIRS model with infection age.
Chen, Yuming; Yang, Junyuan; Zhang, Fengqin
2014-06-01
Infection age is an important factor affecting the transmission of infectious diseases. In this paper, we consider an SIRS model with infection age, which is described by a mixed system of ordinary differential equations and partial differential equations. The expression of the basic reproduction number R0 is obtained. If R0≤1 then the model only has the disease-free equilibrium, while if R0>1 then besides the disease-free equilibrium the model also has an endemic equilibrium. Moreover, if R0<1 then the disease-free equilibrium is globally asymptotically stable otherwise it is unstable; if R0>1 then the endemic equilibrium is globally asymptotically stable under additional conditions. The local stability is established through linearization. The global stability of the disease-free equilibrium is shown by applying the fluctuation lemma and that of the endemic equilibrium is proved by employing Lyapunov functionals. The theoretical results are illustrated with numerical simulations. PMID:24506548
SOSlope 3D: implementing root reinforcement and preferential flow in slope stability modeling
NASA Astrophysics Data System (ADS)
Schwarz, M.; Cohen, D.
2013-12-01
The quantification of root reinforcement represents a key issue in different area of engineering (slope stability, soil protection, silviculture/tree stability, hydraulic). Between all the effects of plants (direct and indirect) on the physical and chemical soil processes, the mechanical effect of roots is considered particularly important for slope stability. The study of root reinforcement is faced with the high complexity of interactions of processes and factors at different spatio-temporal scales. In particular, the hierarchical spatial heterogeneity of vegetation and its effects on soil processes represent a big challenge for quantitative up-scaling methods. The objective of this contribution is to contextualize the complexity of the root-soil interactions in view of slope stability problems, to review the recent scientific contributions in the quantification of root reinforcement, and to discuss the practical meaning of recent research results. In the presentation of an up-scaling framework for the implementation of root reinforcement and preferential flow in slope stability analysis, the following arguments will be discussed: tensile force and pullout force of single roots, apparent elasticity of single roots, strain loading approach for the characterization of root bundle mechanics, meaning of root diameter distribution on root reinforcement, spatial heterogeneity of root distribution, hydro-mechanical and rheological properties of rooted soil under tension and compression, and triggering mechanism of shallow landslides. The above-mentioned factors and processes build up the modules implemented in a numerical model for slope stability calculations, the SOSlope model. The SOSlope model is characterized by the use of a spring-block framework (with 1x1 m cell grid), a strain step loading approach for the redistribution of forces, and the implementation of a spatial distribution of root at the hill slope scale. The results of simulations performed with the SOSlope model serve as background for the discussion on the role of root reinforcement for protection forests management and bioengineering applications.
Analysis of cavern stability at the Bryan Mound SPR site.
Ehgartner, Brian L.; Sobolik, Steven Ronald
2009-04-01
This report presents computational analyses that simulate the structural response of caverns at the Strategic Petroleum Reserve Bryan Mound site. The cavern field comprises 20 caverns. Five caverns (1, 2, 4, and 5; 3 was later plugged and abandoned) were acquired from industry and have unusual shapes and a history dating back to 1946. The other 16 caverns (101-116) 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 3-D geomechanics model of the site that predicts deformations, strains, and stresses. Future leaching scenarios due 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 result in this report is relevant to caverns 1, 2, and 5. The caverns have non-cylindrical shapes and have potential regions where the surrounding salt may be damaged during workover procedures. During a workover the normal cavern operating pressure is lowered to service a well. At this point the wellhead pressures are atmospheric. When the workover is complete, the cavern is repressurized. The resulting elastic stresses are sufficient to cause tension and large deviatoric stresses at several locations. With time, these stresses relax to a compressive state due to salt creep. However, the potential for salt damage and fracturing exists. The analyses predict tensile stresses at locations with sharp-edges in the wall geometry, or in the case of cavern 5, in the neck region between the upper and lower lobes of the cavern. The effects do not appear to be large-scale, however, so the only major impact is the potential for stress-induced salt falls in cavern 5, potentially leading to hanging string damage. Caverns 1 and 2 have no significant issues regarding leachings due to drawdowns; cavern 5 may require a targeted leaching of the neck region to improve cavern stability and lessen hanging string failure potential. The remaining caverns have no significant issues regarding cavern stability and may be safely enlarged during subsequent oil drawdowns. Well strains are significant and consequently future remedial actions may be necessary. Well strains certainly suggest the need for appropriate monitoring through a well-logging program. Subsidence is currently being monitored; there are no issues identified regarding damage from surface subsidence or horizontal strain to surface facilities.
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.
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.
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.
Assessment of sampling stability in ecological applications of discriminant analysis
Williams, B.K.; Titus, K.
1988-01-01
A simulation study was undertaken to assess the sampling stability of the variable loadings in linear discriminant function analysis. A factorial design was used for the factors of multivariate dimensionality, dispersion structure, configuration of group means, and sample size. A total of 32,400 discriminant analyses were conducted, based on data from simulated populations with appropriate underlying statistical distributions. A review of 60 published studies and 142 individual analyses indicated that sample sizes in ecological studies often have met that requirement. However, individual group sample sizes frequently were very unequal, and checks of assumptions usually were not reported. The authors recommend that ecologists obtain group sample sizes that are at least three times as large as the number of variables measured.
Stability analysis and numerical simulation of simplified solid rocket motors
NASA Astrophysics Data System (ADS)
Boyer, G.; Casalis, G.; Estivalèzes, 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.
Stability analysis of three species food chain with competition
NASA Astrophysics Data System (ADS)
Abadi, Savitri, D.
2015-03-01
We study a food chain system that consists of 1 prey and 2 predators populations. The prey population grows logistically while the predators apply different Holling functional responses. The first predator preys on the prey following Holling type II functional response and the second predator preys on both the prey and the first predator following Holling type II and III functional responses, respectively. The study starts with the stability analysis of critical points of the systems. Then, by using normal form and centre manifold method the information about other nontrivial solutions due to bifurcation including possible limit cycles appearance is obtained. The results are confirmed by numerical simulation using MatCont and biological interpretation of the results are also presented.
Coupled three-dimensional aeroelastic stability analysis of bladed disks
Gerolymos, G.A. )
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 of the Planetary System Orbiting Upsilon Andromedae
NASA Technical Reports Server (NTRS)
Lissauer, Jack J.; Rivera, Eugenio J.; DeVincenzi, Donald (Technical Monitor)
2000-01-01
We present results of long-term numerical orbital integrations designed to test the stability of the three-planet system orbiting Upsilon Andromedae and short-term integrations to test whether mutual perturbations among the planets can be used to determine planetary masses. Our initial conditions are based on the latest fits to the radial velocity data obtained by the planet-search group at Lick Observatory. The new fits result in significantly more stable systems than did the initially announced planetary parameters. An analytic analysis of the star and the two outer planets shows that this subsystem is Hill stable up to five. Our integrations involving all three planets show that the system is stable for at least 100 Myr for up to four. In our simulations, we still see a secular resonance between the outer two planets and in some cases large oscillations in the eccentricity of the inner planet.
NASA Astrophysics Data System (ADS)
Kamiński, 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.
On the stability of equilibrium for a reformulated foreign trade model of three countries
NASA Astrophysics Data System (ADS)
Dassios, Ioannis K.; Kalogeropoulos, Grigoris
2014-06-01
In this paper, we study the stability of equilibrium for a foreign trade model consisting of three countries. As the gravity equation has been proven an excellent tool of analysis and adequately stable over time and space all over the world, we further enhance the problem to three masses. We use the basic Structure of Heckscher-Ohlin-Samuelson model. The national income equals consumption outlays plus investment plus exports minus imports. The proposed reformulation of the problem focus on two basic concepts: (1) the delay inherited in our economic variables and (2) the interaction effect along the three economies involved. Stability and stabilizability conditions are investigated while numerical examples provide further insight and better understanding. Finally, a generalization of the gravity equation is somehow obtained for the model.
Stability analysis and area spectrum of three-dimensional Lifshitz black holes
NASA Astrophysics Data System (ADS)
Cuadros-Melgar, Bertha; de Oliveira, Jeferson; Pellicer, C. E.
2012-01-01
In this work, we probe the stability of a z=3 three-dimensional Lifshitz black hole by using scalar and spinorial perturbations. We found an analytical expression for the quasinormal frequencies of the scalar probe field, which perfectly agree with the behavior of the quasinormal modes obtained numerically. The results for the numerical analysis of the spinorial perturbations reinforce the conclusion of the scalar analysis, i.e., the model is stable under scalar and spinor perturbations. As an application we found the area spectrum of the Lifshitz black hole, which turns out to be equally spaced.
Camporeale, Carlo; Ridolfi, Luca
2012-06-01
A novel hydrodynamic-driven stability analysis is presented for surface patterns on speleothems, i.e., secondary sedimentary cave deposits, by coupling fluid dynamics to the geochemistry of calcite precipitation or dissolution. Falling film theory provides the solution for the flow-field and depth perturbations, the latter being crucial to triggering patterns known as crenulations. In a wide range of Reynolds numbers, the model provides the dominant wavelengths and pattern celerities, in fair agreement with field data. The analysis of the phase velocity of ridges on speleothems has a potential as a proxy of past film flow rates, thus suggesting a new support for paleoclimate analyses. PMID:23004000
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.
Nonlinear Speed Control Scheme and Its Stability Analysis for SI Engines
NASA Astrophysics Data System (ADS)
Zhang, Jiangyan; Shen, Tielong; Marino, Riccardo
For international combustion engines, due to the combustion cyclic nature, the intake-to-power stroke delay is inherent that causes additional difficulties in control design and validation phases. In this paper, a nonlinear speed control scheme is proposed based on the proportional feedback control method. From the consideration of improving the transient performance, a reference model is introduced to design the feedback controller. Then, the speed controller is formulated as a designed feedback control law connecting with a model-based feedforward compensation. The asymptotic convergence to the desired speed is guaranteed under the presented conditions of the feedback gains, which include the cases of using a speed-depended gain function and a constant gain, respectively. For the stability analysis of the proposed delayed control system, an initial method is presented via Lyapunov-Krasovskii functional stability theorem. Experimental results on the transition speed control are shown to demonstrate the control scheme.
Densmore, Jeffery D; Warsa, James S; Lowrie, Robert B; Morel, Jim E
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.
NASA Astrophysics Data System (ADS)
Densmore, Jeffery D.; Warsa, James S.; Lowrie, Robert B.; Morel, Jim E.
2009-09-01
The Fokker-Planck equation is a widely used approximation for modeling the Compton scattering of photons in high energy density applications. In this paper, we perform a stability analysis of three implicit time discretizations for the Compton-Scattering Fokker-Planck equation. Specifically, we examine (i) a Semi-Implicit (SI) scheme that employs backward-Euler differencing but evaluates temperature-dependent coefficients at their beginning-of-time-step values, (ii) a Fully Implicit (FI) discretization that instead evaluates temperature-dependent coefficients at their end-of-time-step values, and (iii) a Linearized Implicit (LI) scheme, which is developed by linearizing the temperature dependence of the FI discretization within each time step. Our stability analysis shows that the FI and LI schemes are unconditionally stable and cannot generate oscillatory solutions regardless of time-step size, whereas the SI discretization can suffer from instabilities and nonphysical oscillations for sufficiently large time steps. With the results of this analysis, we present time-step limits for the SI scheme that prevent undesirable behavior. We test the validity of our stability analysis and time-step limits with a set of numerical examples.
Computational Modeling and Finite Element Analysis.
Goel, Vijay K; Nyman, Edward
2016-04-01
Computational modeling with finite element analysis (FEA) is an integral component of medical device design and development. Researchers assess dimensions and stability of the experimental device; test load sharing, stresses, and strains; and analyze failures and modifications. The most important step in FEA is validation of the model. Testing should include decompression and stabilization procedures simulated in the finite element model (FEM). Prerequisites of quality FEA include a solid understanding of morphology and material properties of the model, a firm grasp of the effects of loads on body structures, and the work of a skilled bioengineer who can translate the ideas of surgeons into an appropriate FEM. With today's modern techniques-computed tomography/magnetic resonance imaging, etc.-the bioengineer moves from scan to FEM in just weeks. PMID:27015076
On the stability of a soft-wall model
Gherghetta, T.; Setzer, N.
2010-10-01
We investigate the stability and fluctuations of a soft-wall model that has an asymptotically anti-de Sitter metric and a scalar field that has an asymptotically power-law dependence in the conformal coordinate. By imposing UV boundary conditions, the soft-wall mass scale can be fixed to be near the TeV scale and causes the radion to no longer be massless. A hierarchy between the weak scale and the Planck scale can be generated for various particle spectrum behavior, although natural values only occur for a gravitational sector containing scalar fields that act like unparticles. In addition, if bulk standard model fields have nonstandard couplings to the gravitational sector, then a discrete particle spectrum can be realized in the nongravitational sector. This allows for the possibility of an unparticle solution to the hierarchy problem.
NASA Astrophysics Data System (ADS)
Camera, C.; Apuani, T.; Masetti, M.
2013-02-01
The aim of this work was to understand and reproduce the hydrological dynamics of a slope, which was terraced using dry-stone retaining walls and its response to these processes in terms of stability at the slope scale. The slope studied is located in Valtellina (northern Italy), near the village of Tresenda, and in the last 30 yr has experienced several soil slip/debris flow events. In 1983 alone, such events caused the death of 18 people. Direct observation of the events of 1983 enabled the principal triggering cause of these events to be recognized in the formation of an overpressure at the base of a dry-stone wall, which caused its failure. To perform the analyses it is necessary to include the presence of dry-stone walls, considering the importance they have in influencing hydrological and geotechnical processes at the slope scale. This requires a very high resolution DEM (1 m × 1 m because the walls are from 0.60 m to 1.0 m wide) that has been appositely derived. A hydrogeological raster-based model, which takes into account both the unsaturated and saturated flux components, was applied. This was able to identify preferential infiltration zones and was rather precise in the prediction of maximum groundwater levels, providing valid input for the distributed stability analysis. Results of the hydrogeological model were used for the successive stability analysis. Sections of terrace were identified from the downslope base of a retaining wall to the top of the next downslope retaining wall. Within each section a global method of equilibrium was applied to determine its safety factor. The stability model showed a general tendency to overestimate the amount of unstable areas. An investigation of the causes of this unexpected behavior was, therefore, also performed in order to progressively improve the reliability of the model.
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.
Analysis of a Major Electric Grid -- Stability and Adaptive Protection
NASA Astrophysics Data System (ADS)
Alanzi, Sultan
Protective systems of the electric grid are designed to detect and mitigate the effects of faults and other disturbances that may occur. Distance relays are used extensively for the detection of faults on transmission lines. Out-of-step relays are used for generator protection to detect loss of synchronism conditions that result from disturbances on the electric grid. Also, when a disturbance occurs and generators may tend to lose synchronism with each other, it is beneficial to separate the overall system into several independent systems that can remain stable. Unfortunately there have been cases, such as the 2003 Northeast blackout where the operation of protective relays, namely the zone 3 distance relay used for transmission line protection, contributed to the cascading effect of the blackout. It is the objective of this dissertation to propose adaptive relays for both distance protection of transmission lines and out-of-step protection of generators. By being adaptive, the relays are made aware of the system operating conditions and can adjust its settings accordingly. Inputs to the adaptive logic can come from system or environmental conditions. As a result of this effort, a new distance relay operating characteristic is proposed, referred to as a mushroom relay, which is a combination of a quadrilateral relay and a Mho relay. Also, a new criterion for determining if a power swing following a disturbance is stable or unstable is proposed. Distance protection of transmission lines is very important when discussing system responses to faults and disturbances. Distance relays are very common worldwide and although they offer great protection, there are limitations that need to be addressed. Parallel line operations (infeed effect) and the loadability limits are among the limitations that lead to improper response of relays. An Adaptive Distance Relays (ADR) offer great benefits to the protection scheme as their settings can be changed in accordance with prefault system conditions. This dissertation introduces a combination of quadrilateral and mho characteristics to create a distance relay with a mushroom shape in R-X diagrams. This new relay offers larger protective reach with a lower limitation on loadability. When major disturbances occur, the power balance between load and generation might be disturbed causing the generators to lose synchronism (to be out-of-step) with each other. Out-of-step protection against power swings is essential to provide supervising signals for distance relays to mitigate the effects of the disturbance. A new R-X criterion is proposed to identify out-of-step conditions for large and complex power systems, such as KEG. A proposed Adaptive Out-of-Step Relay (AOSR) will monitor power system conditions and adjust the relay reach accordingly for better power swing classification. When unstable swings are detected, controllable tripping signals are initiated and system separation will create small subsystems or islands of the power system. These smaller systems will be created to achieve a balance of load and available generation. The electric power system chosen to study and to illustrate the criteria for the proposed adaptive relays was that of the country of Kuwait. The small oil-rich country of Kuwait has been dealing with an electric energy crisis that started summer 2006. With a dry dessert climate and intensely hot summers, the 3.6 million residents of Kuwait depend on continuously operated A/C units for living. This is the major reason why the peak load in a summer month reaches almost 11,000 MW while the peak load in a winter month does not exceed 5,000 MW. The Kuwait Electric Grid (KEG) is modelled and analyzed using Power Analytics' software known as PaladinRTM DesignBase(TM). Performance studies produce data to examine distance and out-of-step protection. Power Flow (PF), Short Circuit Analysis (SCA), and Transient Stability Analysis (TSA) are used to verify the model of KEG. These studies are the starting point when studying any large power system in order to investigate how the system operates during normal conditions and during abnormal conditions due to disturbances. Simulations showed that KEG is highly stressed, as major disturbances would cause instability.
Mode switching and linear stability analysis of resonant acoustic flows
NASA Astrophysics Data System (ADS)
Panickar, Praveen
Resonant acoustic flows occur in a wide variety of practical, aerospace-related applications and are a rich source of complex flow-physics. The primary concern associated with these types of flows is the high-amplitude fluctuating pressures associated with the resonant tones that could lead to sonic fatigue failure of sensitive components in the vicinity of such flows. However, before attempting to devise methods to suppress the resonant tones, it is imperative to understand the physics governing these flows in the hope that such an understanding will lead to more robust and effective suppression techniques. To this end, an in-depth study of various resonant acoustic flows was undertaken in this thesis, the main aim being to bring about a better understanding of such flows by revealing physically relevant information. Starting with the resonant acoustic mechanism in underexpanded jets from two-dimensional nozzles, it was shown that, for a variety of flow situations (geometries, shock-cell structures and orientations) in such jets, the nonlinear interaction density acted as a faithful precursor to a, hitherto unpredictable, spanwise instability mode switch. Following this, a study of the occurrence of, previously undocumented and theoretically unexpected, helical instabilities in subsonic impinging jets was undertaken. Using metrics from linear stability analysis, it was shown that the presence of the helical modes was justified. The results from this study on impinging jets are directly applicable to modern Stationary Take-Off and Vertical Landing (STOVL) aircraft that have twin, closely spaced exhausts. Finally, a novel technique that yielded dramatic suppression of resonant acoustic tones using high frequency excitation, in subsonic flows over open cavities, was investigated. Linear stability calculations of the experimentally measured baseline and excited velocity profiles showed that the instability of the high frequency excitation corresponded to a spatially decaying mode, which in turn lead to the resonance suppression associated with this mechanism. The experimental results showed good agreement with linear stability calculations for the measured mean velocity profiles. It is hoped that the work presented in this thesis will further the understanding of resonant acoustic flows and provide insights that can lead to better control techniques in the future.
Analysis and stability of aldehydes and terpenes in electropolished canisters
NASA Astrophysics Data System (ADS)
Batterman, Stuart A.; Zhang, Guo-Zheng; Baumann, Melissa
Aldehydes and terpenes are important classes of polar VOC contaminants for which few sampling and analysis methods have been validated. This study reports on the analysis, stability and recovery of seven aldehydes (butanal, pentanal, hexanal, heptanal, octanal, nonanal and benzaldehyde) and four terpenes ( α-pinene, β-pinene, limonene and 3-carene) prepared at trace levels (3-5 ppb) and stored in electropolished stainless-steel canisters. Humidified air, humidified N 2, and dry air were used to dilute three sets of canisters. A series of samples was withdrawn from each canister over a period of 16 days, and concentrations were determined by cryogenic preconcentration, gas chromatography and mass spectrometry. The VOCs were easily separated, but butanal and pentanal had high detection limits relative to the other compounds. While measurements were reproducible, concentrations decreased considerably in the first hour (19% in the humidified air-filled canister set), and losses continued over the measurement period, although at a slower rate. The estimated half-lives of aldehydes and terpenes were 18 d in humidified air-filled canisters, 24 d in humidified N 2, and 6 d in dry air. Loss mechanisms and analytical considerations for the target compounds are discussed. Like other VOCs, the collection and storage of aldehydes and terpenes in canisters require humidification; however; the absolute accuracy of samples and standards of mixtures of aldehydes and terpenes stored in canisters may be limited.
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.
Proton stability and light Z' inspired by string derived models
Faraggi, Alon E.; Mehta, Viraf M.
2011-10-15
Proton stability is one of the most perplexing puzzles in particle physics. While the renormalizable standard model forbids proton decay mediating operators due to accidental global symmetries, many of its extensions introduce such dimension four, five and six operators. Furthermore, it is, in general, expected that quantum gravity only respects local gauge, or discreet, symmetries. String theory provides the arena to study particle physics in a consistent framework of perturbative quantum gravity. An appealing proposition, in this context, is that the dangerous operators are suppressed by an Abelian gauge symmetry, which is broken near the TeV scale. A viable U(1) symmetry should also be anomaly free, be family universal, and allow the generation of fermion masses via the Higgs mechanism. We discuss such U(1) symmetries that arise in quasirealistic free fermionic heterotic-string derived models. Ensuring that the U(1) symmetry is anomaly free at the low scale requires that the standard model spectrum is augmented by additional states that are compatible with the charge assignments in the string models. We construct such string-inspired models and discuss some of their phenomenological implications.
Kinetic Analysis of Haloacetonitrile Stability in Drinking Waters.
Yu, Yun; Reckhow, David A
2015-09-15
Haloacetonitriles (HANs) are an important class of drinking water disinfection byproducts (DBPs) that are reactive and can undergo considerable transformation on time scales relevant to system distribution (i.e., from a few hours to a week or more). The stability of seven mono-, di-, and trihaloacetonitriles was examined under a variety of conditions including different pH levels and disinfectant doses that are typical of drinking water distribution systems. Results indicated that hydroxide, hypochlorite, and their protonated forms could react with HANs via nucleophilic attack on the nitrile carbon, forming the corresponding haloacetamides (HAMs) and haloacetic acids (HAAs) as major reaction intermediates and end products. Other stable intermediate products, such as the N-chloro-haloacetamides (N-chloro-HAMs), may form during the course of HAN chlorination. A scheme of pathways for the HAN reactions was proposed, and the rate constants for individual reactions were estimated. Under slightly basic conditions, hydroxide and hypochlorite are primary reactants and their associated second-order reaction rate constants were estimated to be 6 to 9 orders of magnitude higher than those of their protonated conjugates (i.e., neutral water and hypochlorous acid), which are much weaker but more predominant nucleophiles at neutral and acidic pHs. Developed using the estimated reaction rate constants, the linear free energy relationships (LFERs) summarized the nucleophilic nature of HAN reactions and demonstrated an activating effect of the electron withdrawing halogens on nitrile reactivity, leading to decreasing HAN stability with increasing degree of halogenation of the substituents, while subsequent shift from chlorine to bromine atoms has a contrary stabilizing effect on HANs. The chemical kinetic model together with the reaction rate constants that were determined in this work can be used for quantitative predictions of HAN concentrations depending on pH and free chlorine contact times (CTs), which can be applied as an informative tool by drinking water treatment and system management engineers to better control these emerging nitrogenous DBPs, and can also be significant in making regulatory decisions. PMID:26275044
Stability analysis and controller synthesis for hybrid dynamical systems.
Heemels, W P M H; De Schutter, B; Lunze, J; Lazar, M
2010-11-13
Wherever continuous and discrete dynamics interact, hybrid systems arise. This is especially the case in many technological systems in which logic decision-making and embedded control actions are combined with continuous physical processes. Also for many mechanical, biological, electrical and economical systems the use of hybrid models is essential to adequately describe their behaviour. To capture the evolution of these systems, mathematical models are needed that combine in one way or another the dynamics of the continuous parts of the system with the dynamics of the logic and discrete parts. These mathematical models come in all kinds of variations, but basically consist of some form of differential or difference equations on the one hand and automata or other discrete-event models on the other hand. The collection of analysis and synthesis techniques based on these models forms the research area of hybrid systems theory, which plays an important role in the multi-disciplinary design of many technological systems that surround us. This paper presents an overview from the perspective of the control community on modelling, analysis and control design for hybrid dynamical systems and surveys the major research lines in this appealing and lively research area. PMID:20921005
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.
Laboratory and modelling studies on the atmospheric stability of levoglucosan
NASA Astrophysics Data System (ADS)
Tilgner, Andreas; Hoffmann, Dirk; Iinuma, Yoshiteru; Herrmann, Hartmut
2010-05-01
Aerosol particles are known to influence important atmospheric processes such as cloud formation and the solar radiation budget. Therefore, much effort is spend to characterise and locate the sources of atmospheric particles. Source apportionment studies using molecular tracer compounds are a common approach to distinguish between different sources. The anhydromonosaccharide levoglucosan (1,6-anhydro-β-D-glucopyranose) is an widely used and very specific tracer compound for particle emissions from natural and anthropogenic biomass combustion processes. Levoglucosan is formed in large quantities during the pyrolysis of cellulose at temperatures above 300° C. Even if levoglucosan is widely used in source apportionment studies only few studies investigated the atmospheric stability of this tracer compound so far. Furthermore, oxidation processes by free radicals in aqueous particles are not yet considered as a potential sink reaction for this highly water soluble compound. Therefore, detailed kinetic studies on the reactivity of levoglucosan towards three important atmospheric free radicals (OH, NO3 and SO4-) in aqueous solutions were performed for the first time using the laser flash photolysis technique. Laboratory studies on the stability of levoglucosan were done both in the presence and absence of other water soluble reaction partners. The results obtained in the different experiments will be presented, compared and discussed. Furthermore, the experimental data were implemented into the parcel model SPACCIM (Spectral Aerosol Cloud Chemistry Interaction Model; Wolke et al., 2005) in order to study the degradation fluxes of levoglucosan in cloud droplets and aqueous particles considering a detailed microphysics and multiphase chemistry. The model calculations, performed under different conditions (summer, winter, with cloud passages, without cloud passages, different relative humidity and iron contents), show that levoglucosan can be oxidised readily by OH radicals in the tropospheric aqueous phase. Mean degradation fluxes of about 7.2 ng m-3 h-1 in summer and 4.7 ng m-3 h-1 in winter were calculated. The detailed results of the model calculations will be presented and the influence of the different model scenarios on the calculated degradation fluxes discussed. Model calculations demonstrate that under certain atmospheric conditions the oxidation of levoglucosan can be as fast as that of other atmospherically relevant organic compounds and it may not be as stable as previously thought in the atmosphere particularly under high relative humidity conditions. References: Wolke, R.; Sehili, A. M.; Simmel, M.; Knoth, O.; Tilgner, A.; Herrmann, H. SPACCIM: A parcel model with detailed microphysics and complex multiphase chemistry. Atmos. Environ. 2005, 39, 4375-4388.
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.
Movement stability under uncertain internal models of dynamics.
Crevecoeur, F; McIntyre, J; Thonnard, J-L; Lefèvre, P
2010-09-01
Sensory noise and feedback delay are potential sources of instability and variability for the on-line control of movement. It is commonly assumed that predictions based on internal models allow the CNS to anticipate the consequences of motor actions and protect the movements from uncertainty and instability. However, during motor learning and exposure to unknown dynamics, these predictions can be inaccurate. Therefore a distinct strategy is necessary to preserve movement stability. This study tests the hypothesis that in such situations, subjects adapt the speed and accuracy constraints on the movement, yielding a control policy that is less prone to undesirable variability in the outcome. This hypothesis was tested by asking subjects to hold a manipulandum in precision grip and to perform single-joint, discrete arm rotations during short-term exposure to weightlessness (0 g), where the internal models of the limb dynamics must be updated. Measurements of grip force adjustments indicated that the internal predictions were altered during early exposure to the 0 g condition. Indeed, the grip force/load force coupling reflected that the grip force was less finely tuned to the load-force variations at the beginning of the exposure to the novel gravitational condition. During this learning period, movements were slower with asymmetric velocity profiles and target undershooting. This effect was compared with theoretical results obtained in the context of optimal feedback control, where changing the movement objective can be directly tested by adjusting the cost parameters. The effect on the simulated movements quantitatively supported the hypothesis of a change in cost function during early exposure to a novel environment. The modified optimization criterion reduces the trial-to-trial variability in spite of the fact that noise affects the internal prediction. These observations support the idea that the CNS adjusts the movement objective to stabilize the movement when internal models are uncertain. PMID:20554851
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
Stability analysis of a backfilled room-and-pillar mine
Tesarik, D.R.; Seymour, J.B.; Yanske, T.R.; McKibbin, R.W.
1995-12-31
Displacement and stress changes in cemented backfill and ore pillars at the Buick Mine, near Boss, MO, were monitored by engineers from the US Bureau of Mines and The Doe Run Co., St. Louis, MO. A test area in this room-and-pillar mine was backfilled to provide support when remnant ore pillars were mined. Objectives of this research were to evaluate the effect of backfill on mine stability, observe backfill conditions during pillar removal, and calibrate a numerical model to be used to design other areas of the mine. Relative vertical displacements in the backfill were measured with embedment strain gauges and vertical extensometers. Other types of instruments used were earth pressure cells (to identify loading trends in the backfill), borehole extensometers (to measure relative displacement changes in the mine roof and support pillars), and biaxial stressmeters (to measure stress changes in several support pillars and abutments). Two- and three-dimensional numeric codes were used to model the study area. With information from these codes and the installed instruments, two failed pillars were identified and rock mass properties were estimated.
Transport Analysis of the Kinetically Stabilized Tandem Mirror
NASA Astrophysics Data System (ADS)
Pratt, J.; Kim, J.-H.; Horton, W.; Wong, H. V.; Fowler, T. K.
2004-11-01
We undertake a transport study for the Kinetically Stabilized Tandem Mirror (KSTM), an attractive magnetic confinement device for achieving a steady-state fusion burning experiment. For an MHD stable system, we investigate three different radial transport models with Bohm, gyroBohm, and ETG scaling. Numerical coefficients in the models are consistent with tokamak and stellarator databases, thus providing a conservative transport estimate. The well-known confinement improvement at high ? and steep ?-gradient is taken into account. The plug mirrors create an ambipolar potential that controls end losses, whereas radial losses are driven by drift wave turbulence, which also lowers the electron temperature via the ETG effect. We solve the radial transport equations using Pastukhov-type power and particle losses, with mirror ratio R=9 and with large density ratio between plug and central cell regions in order to achieve an ion potential ?i ? 2.3 Te = 6 Ti for high axial confinement. Profiles and total energy confinement times are calculated for a proof-of-principle experiment (L=7 m,B=0.28 T, R=1 m) and for a test reactor facility (L = 30 m to 80 m, B=3 T, R= 1 m). Work supported by DOE grant DE-FG02-04ER5474.
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.
In situ vitrification: application analysis for stabilization of transuranic waste
Oma, K.H.; Farnsworth, R.K.; Rusin, J.M.
1982-09-01
The in situ vitrification process builds upon the electric melter technology previously developed for high-level waste immobilization. In situ vitrification converts buried wastes and contaminated soil to an extremely durable glass and crystalline waste form by melting the materials, in place, using joule heating. Once the waste materials have been solidified, the high integrity waste form should not cause future ground subsidence. Environmental transport of the waste due to water or wind erosion, and plant or animal intrusion, is minimized. Environmental studies are currently being conducted to determine whether additional stabilization is required for certain in-ground transuranic waste sites. An applications analysis has been performed to identify several in situ vitrification process limitations which may exist at transuranic waste sites. Based on the process limit analysis, in situ vitrification is well suited for solidification of most in-ground transuranic wastes. The process is best suited for liquid disposal sites. A site-specific performance analysis, based on safety, health, environmental, and economic assessments, will be required to determine for which sites in situ vitrification is an acceptable disposal technique. Process economics of in situ vitrification compare favorably with other in-situ solidification processes and are an order of magnitude less than the costs for exhumation and disposal in a repository. Leachability of the vitrified product compares closely with that of Pyrex glass and is significantly better than granite, marble, or bottle glass. Total release to the environment from a vitrified waste site is estimated to be less than 10/sup -5/ parts per year. 32 figures, 30 tables.
NASA Astrophysics Data System (ADS)
Tanahashi, Seitaro; Itamiya, Keietsu
This paper proposes a new analytical method for stability and control performance of a robust model reference adaptive control system (MRACS). In the past studies, the following analytical policy has been adopted, that is, deriving tight and quantitative conditions for a stable robust MRACS is not important since those conditions depend on unknown factors such as the transfer characteristic of the controlled object. As a result, the most important things about stability and control performance disappear in algebraic calculations based on many inequalities. Naturally, it is not easy to answer the following questions. How is the stabilization of a robust MRACS achieved? What can we prepare for design of a robust MRACS which has a sufficient stability margin and a better control performance? The motivation of this paper is to answer these questions. For the purpose, this paper defines a desired system for the model reference control, and uses an analytical model parameterized with the desired controller parameters. Especially in a main loop analysis, a certain equivalent feedback system is derived, and the stability of a robust MRACS is explained with an expanded notion of the L2 stability. According to this method, it is possible to understand stabilization of a robust MRACS. Furthermore, some useful findings for design of a robust MRACS can be obtained from the results of analysis and a numerical simulation.
NASA Astrophysics Data System (ADS)
Firmansyah; Feranie, S.; Tohari, Adrin; Latief, F. D. E.
2016-01-01
Mitigation of landslide hazard requires the knowledge of landslide run-out distance. This paper presents the application of slope stability analysis and center of mass approach to predict the run-out distance of a rotational landslide model with different soil types. The Morgenstern-Price method was used to estimate the potential sliding zone and volume of landslide material. The center of mass approach used a simple Coulomb friction model to determine the run-out distance. Results of the slope stability analysis showed that the soil unit weight can influence the depth of sliding zone, and the volume of unstable material. The slope model of silty sand and gravel would have the largest volume of unstable mass. From the Coulomb friction analysis, this slope model has higher run-out distance and velocity than other slope models. Thus, the run-out distance will be influenced by soil type and the dimension of unstable soil mass.
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 (AγR) 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.
Continuum modeling of the equilibrium and stability of animal flocks
NASA Astrophysics Data System (ADS)
Mecholsky, Nicholas A.; Ott, Edward; Antonsen, Thomas M.; Guzdar, Parvez
2012-03-01
Groups of animals often tend to arrange themselves in flocks that have characteristic spatial attributes and temporal dynamics. Using a dynamic continuum model for a flock of individuals, we find equilibria of finite spatial extent where the density goes continuously to zero at a well-defined flock edge, and we discuss conditions on the model that allow for such solutions. We also demonstrate conditions under which, as the flock size increases, the interior density in our equilibria tends to an approximately uniform value. Motivated by observations of starling flocks that are relatively thin in a direction transverse to the direction of flight, we investigate the stability of infinite, planar-sheet flock equilibria. We find that long-wavelength perturbations along the sheet are unstable for the class of models that we investigate. This has the conjectured consequence that sheet-like flocks of arbitrarily large transverse extent relative to their thickness do not occur. However, we also show that our model admits approximately sheet-like, pancake-shaped, three-dimensional ellipsoidal equilibria with definite aspect ratios (transverse length-scale to flock thickness) determined by anisotropic perceptual/response characteristics of the flocking individuals, and we argue that these pancake-like equilibria are stable to the previously mentioned sheet instability.
A study of aeroelastic stability for the model support system of the National Transonic Facility
NASA Technical Reports Server (NTRS)
Strganac, Thomas W.
1988-01-01
Oscillations of wind-tunnel models have been observed during testing in the National Transonic Facility. These oscillations have been the subject of an extensive investigation. As a part of this effort, a study of the aeroelastic stability of the model support structure has been performed. This structure is mathematically modelled as a wing and conventional flutter analysis is performed. The math model implemented both experimentally and numerically obtained modal characteristics. A technique for illustrating the flutter boundary for wind tunnels is demonstrated. Results indicate that the classical flutter boundary is well above the operating envelope of the facility. However, the analysis indicates a damping-dependent instability is present which is inherent in the design. One possible modification in the design has been evaluated which eliminates the predicted instability.
A Note on Local Stability Conditions for Two Types of Monetary Models with Recursive Utility
NASA Astrophysics Data System (ADS)
Miyazaki, Kenji; Utsunomiya, Hitoshi
2009-09-01
This note explores local stability conditions for money-in-utility-function (MIUF) and transaction-costs (TC) models with recursive utility. Although Chen et al. [Chen, B.-L., M. Hsu, and C.-H. Lin, 2008, Inflation and growth: impatience and a qualitative equivalent, Journal of Money, Credit, and Banking, Vol. 40, No. 6, 1310-1323] investigated the relationship between inflation and growth in MIUF and TC models with recursive utility, they conducted only a comparative static analysis in a steady state. By establishing sufficient conditions for local stability, this note proves that impatience should be increasing in consumption and real balances. Increasing impatience, although less plausible from an empirical point of view, receives more support from a theoretical viewpoint.
Analytical mass leaching model for contaminated soil and soil stabilized waste
Shackelford, C.D.; Glade, M.J.
1997-03-01
An analytical model for evaluating mass leaching from contaminated soil or soil stabilized waste is presented. The model is based on mass transport due to advection, dispersion, and retardation and can be used to evaluate the suitability and/or efficiency of soil washing solutions based on the results of column leaching studies. The model differs from more traditional models for column leaching studies in that the analysis is based on the cumulative mass of leachate instead of leachate concentration. A cumulative mass basis for leaching eliminates the requirement for determination of instantaneous effluent concentrations in the more traditional column leaching approach thereby allowing for the collection of relatively large effluent volumes. The cumulative masses of three heavy metals -- Cd, Pb, and Zn -- leached from two specimens of soil mixed with fly ash are analyzed with the mass leaching model to illustrate application and limitation of the model.
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
Epidemic spreading and global stability of an SIS model with an infective vector on complex networks
NASA Astrophysics Data System (ADS)
Kang, Huiyan; Fu, Xinchu
2015-10-01
In this paper, we present a new SIS model with delay on scale-free networks. The model is suitable to describe some epidemics which are not only transmitted by a vector but also spread between individuals by direct contacts. In view of the biological relevance and real spreading process, we introduce a delay to denote average incubation period of disease in a vector. By mathematical analysis, we obtain the epidemic threshold and prove the global stability of equilibria. The simulation shows the delay will effect the epidemic spreading. Finally, we investigate and compare two major immunization strategies, uniform immunization and targeted immunization.
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.
NASA Technical Reports Server (NTRS)
Fay, John F.
1990-01-01
A calculation is made of the stability of various relaxation schemes for the numerical solution of partial differential equations. A multigrid acceleration method is introduced, and its effects on stability are explored. A detailed stability analysis of a simple case is carried out and verified by numerical experiment. It is shown that the use of multigrids can speed convergence by several orders of magnitude without adversely affecting stability.
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.
Stabilizing l1-norm prediction models by supervised feature grouping.
Kamkar, Iman; Gupta, Sunil Kumar; Phung, Dinh; Venkatesh, Svetha
2016-02-01
Emerging Electronic Medical Records (EMRs) have reformed the modern healthcare. These records have great potential to be used for building clinical prediction models. However, a problem in using them is their high dimensionality. Since a lot of information may not be relevant for prediction, the underlying complexity of the prediction models may not be high. A popular way to deal with this problem is to employ feature selection. Lasso and l1-norm based feature selection methods have shown promising results. But, in presence of correlated features, these methods select features that change considerably with small changes in data. This prevents clinicians to obtain a stable feature set, which is crucial for clinical decision making. Grouping correlated variables together can improve the stability of feature selection, however, such grouping is usually not known and needs to be estimated for optimal performance. Addressing this problem, we propose a new model that can simultaneously learn the grouping of correlated features and perform stable feature selection. We formulate the model as a constrained optimization problem and provide an efficient solution with guaranteed convergence. Our experiments with both synthetic and real-world datasets show that the proposed model is significantly more stable than Lasso and many existing state-of-the-art shrinkage and classification methods. We further show that in terms of prediction performance, the proposed method consistently outperforms Lasso and other baselines. Our model can be used for selecting stable risk factors for a variety of healthcare problems, so it can assist clinicians toward accurate decision making. PMID:26689771
Escobar, D.; Ahedo, E.
2015-10-15
The linear stability of the Hall thruster discharge is analysed against axial-azimuthal perturbations in the low frequency range using a time-dependent 2D code of the discharge. This azimuthal stability analysis is spatially global, as opposed to the more common local stability analyses, already afforded previously (D. Escobar and E. Ahedo, Phys. Plasmas 21(4), 043505 (2014)). The study covers both axial and axial-azimuthal oscillations, known as breathing mode and spoke, respectively. The influence on the spoke instability of different operation parameters such as discharge voltage, mass flow, and thruster size is assessed by means of different parametric variations and compared against experimental results. Additionally, simplified models are used to unveil and characterize the mechanisms driving the spoke. The results indicate that the spoke is linked to azimuthal oscillations of the ionization process and to the Bohm condition in the transition to the anode sheath. Finally, results obtained from local and global stability analyses are compared in order to explain the discrepancies between both methods.
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.
Crack stability analysis of low alloy steel primary coolant pipe
Tanaka, T.; Kameyama, M.; Urabe, Y.
1997-04-01
At present, cast duplex stainless steel has been used for the primary coolant piping of PWRs in Japan and joints of dissimilar material have been applied for welding to reactor vessels and steam generators. For the primary coolant piping of the next APWR plants, application of low alloy steel that results in designing main loops with the same material is being studied. It means that there is no need to weld low alloy steel with stainless steel and that makes it possible to reduce the welding length. Attenuation of Ultra Sonic Wave Intensity is lower for low alloy steel than for stainless steel and they have advantageous inspection characteristics. In addition to that, the thermal expansion rate is smaller for low alloy steel than for stainless steel. In consideration of the above features of low alloy steel, the overall reliability of primary coolant piping is expected to be improved. Therefore, for the evaluation of crack stability of low alloy steel piping to be applied for primary loops, elastic-plastic future mechanics analysis was performed by means of a three-dimensioned FEM. The evaluation results for the low alloy steel pipings show that cracks will not grow into unstable fractures under maximum design load conditions, even when such a circumferential crack is assumed to be 6 times the size of the wall thickness.
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 σci, 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 σci is relatively small, the relation between F and σci is nonlinear, but when σci is relatively large, the relation is linear; with the increase of mi, F decreases first and then increases. PMID:25147838
Design of multiple axis robotic platform for postural stability analysis.
Kharboutly, Haissam; Ma, Jianting; Benali, Abderraouf; Thoumie, Philippe; Pasqui, Viviane; Bouzit, Mourad
2015-01-01
This paper presents the design and implementation of IsiMove, a new dynamic posturography platform. It allows the evaluation of the static and dynamic balance of a human placed on a force plate. IsiMove is a robotic platform open kinematic with four degrees of freedom: anteroposterior tilt, mediolateral tilt, vertical rotation, and horizontal translation. It is capable of measuring the displacement of the center of pressure over time, with a resolution of 0.1 mm for each foot and support a human of about 120 kg. IsiMove can generate various types of balance perturbations based on parameters such as direction, amplitude, frequency and shape. In this paper, we will give a description of the mechanisms that constitute our platform. First, the technical specifications of the hardware and software architecture will be presented. Then, we will provide details related to extensive experimental evaluations of the platform in both static and dynamic condition as well as result of postural stability analysis with healthy subjects and stroke patients. PMID:24951702
Implications of stability analysis for heat transfer at Yucca Mountain
Ross, B.; Yiqiang Zhang; Ning Lu
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.
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.
Escobar, D.; Ahedo, E.
2014-04-15
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.
Stability analysis of uncertain fuzzy Hopfield neural networks with time delays
NASA Astrophysics Data System (ADS)
Syed Ali, M.; Balasubramaniam, P.
2009-06-01
In this paper, the global stability problem of uncertain Takagi-Sugeno (T-S) fuzzy Hopfield neural networks with time delays (TSFHNNs) is considered. A novel LMI-based stability criterion is obtained by using Lyapunov functional theory to guarantee the asymptotic stability of TSFHNNs. Here, we choose a generalized Lyapunov functional and introduce a parameterized model transformation with free weighting matrices to it, in order to obtain generalized stability region. In fact, these techniques lead to generalized and less conservative stability condition that guarantee the wide stability region. The proposed stability conditions are demonstrated with four numerical examples. Comparison with other stability conditions in the literature shows our conditions are the more powerful ones to guarantee the widest stability region.
A new free-surface stabilization algorithm for geodynamical modelling: Theory and numerical tests
NASA Astrophysics Data System (ADS)
Andrés-Martínez, Miguel; Morgan, Jason P.; Pérez-Gussinyé, Marta; Rüpke, Lars
2015-09-01
The surface of the solid Earth is effectively stress free in its subaerial portions, and hydrostatic beneath the oceans. Unfortunately, this type of boundary condition is difficult to treat computationally, and for computational convenience, numerical models have often used simpler approximations that do not involve a normal stress-loaded, shear-stress free top surface that is free to move. Viscous flow models with a computational free surface typically confront stability problems when the time step is bigger than the viscous relaxation time. The small time step required for stability (< 2 Kyr) makes this type of model computationally intensive, so there remains a need to develop strategies that mitigate the stability problem by making larger (at least ∼10 Kyr) time steps stable and accurate. Here we present a new free-surface stabilization algorithm for finite element codes which solves the stability problem by adding to the Stokes formulation an intrinsic penalization term equivalent to a portion of the future load at the surface nodes. Our algorithm is straightforward to implement and can be used with both Eulerian or Lagrangian grids. It includes α and β parameters to respectively control both the vertical and the horizontal slope-dependent penalization terms, and uses Uzawa-like iterations to solve the resulting system at a cost comparable to a non-stress free surface formulation. Four tests were carried out in order to study the accuracy and the stability of the algorithm: (1) a decaying first-order sinusoidal topography test, (2) a decaying high-order sinusoidal topography test, (3) a Rayleigh-Taylor instability test, and (4) a steep-slope test. For these tests, we investigate which α and β parameters give the best results in terms of both accuracy and stability. We also compare the accuracy and the stability of our algorithm with a similar implicit approach recently developed by Kaus et al. (2010). We find that our algorithm is slightly more accurate and stable for steep slopes, and also conclude that, for longer time steps, the optimal α controlling factor for both approaches is ∼2/3, instead of the 1/2 Crank-Nicolson parameter inferred from a linearized accuracy analysis. This more-implicit value coincides with the velocity factor for a Galerkin time discretization applied to our penalization term using linear shape functions in time.
Hydrodynamic Stability Analysis of Particle-Laden Solid Rocket Motors
NASA Astrophysics Data System (ADS)
Elliott, T. S.; Majdalani, J.
2014-11-01
Fluid-wall interactions within solid rocket motors can result in parietal vortex shedding giving rise to hydrodynamic instabilities, or unsteady waves, that translate into pressure oscillations. The oscillations can result in vibrations observed by the rocket, rocket subsystems, or payload, which can lead to changes in flight characteristics, design failure, or other undesirable effects. For many years particles have been embedded in solid rocket propellants with the understanding that their presence increases specific impulse and suppresses fluctuations in the flowfield. This study utilizes a two dimensional framework to understand and quantify the aforementioned two-phase flowfield inside a motor case with a cylindrical grain perforation. This is accomplished through the use of linearized Navier-Stokes equations with the Stokes drag equation and application of the biglobal ansatz. Obtaining the biglobal equations for analysis requires quantification of the mean flowfield within the solid rocket motor. To that end, the extended Taylor-Culick form will be utilized to represent the gaseous phase of the mean flowfield while the self-similar form will be employed for the particle phase. Advancing the mean flowfield by quantifying the particle mass concentration with a semi-analytical solution the finalized mean flowfield is combined with the biglobal equations resulting in a system of eight partial differential equations. This system is solved using an eigensolver within the framework yielding the entire spectrum of eigenvalues, frequency and growth rate components, at once. This work will detail the parametric analysis performed to demonstrate the stabilizing and destabilizing effects of particles within solid rocket combustion.
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...
Lech, Frederik J; Wierenga, Peter A; Gruppen, Harry; Meinders, Marcel B J
2015-03-10
Foam lamellae are the smallest structural elements in foam. Such lamellae can experimentally be studied by analysis of thin liquid films in glass cells. These thin liquid films usually have to be stabilized against rupture by surface active substances, such as proteins or low molecular weight surfactants. However, horizontal thin liquid films of pure water with a radius of 100 μm also show remarkable stability when created in closed Sheludko cells. To understand thin film stability of surfactant-free films, the drainage behavior and rupture times of films of water and NaCl solutions were determined. The drainage was modeled with an extended Derjaguin-Landau-Verwey-Overbeek (DLVO) model, which combines DLVO and hydrophobic contributions. Good correspondence between experiment and theory is observed, when hydrophobic interactions are included, with fitted values for surface potential (ψ(0,water)) of -60 ± 5 mV, hydrophobic strength (B(hb,water)) of 0.22 ± 0.02 mJ/m(2), and a range of the hydrophobic interaction (λ(hb, water)) of 15 ± 1 nm in thin liquid films. In addition, Vrij's rupture criterion was successfully applied to model the stability regions and rupture times of the films. The films of pure water are stable over long time scales (hours) and drain to a final thickness >40 nm if the concentration of electrolytes is low (resistivity 18.2 MQ). With increasing amounts of ions (NaCl) the thin films drain to <40 nm thickness and the rupture stability of the films is reduced from hours to seconds. PMID:25689104
Primary posterior stabilized total knee arthroplasty: analysis of different instrumentation
2014-01-01
Background Intercondylar femoral bone removal during posterior stabilized (PS) total knee arthroplasty (TKA) makes many cruciate substituting implant designs less appealing than cruciate retaining implants. Bone stock conservation is considered fundamental in the prevision of future revision surgeries. The purpose of this study was to compare the quantity of intercondylar bone removable during PS housing preparation using three contemporary PS TKA instrumentations. Method We compared different box cutting jigs which were utilized for the PS housing of three popular PS knee prostheses. The bone removal area from every PS box cutting jig was three-dimensionally measured. Results Independently from the implant size, the cutting jig for a specific PS TKA always resected significantly less bone than the others: this difference was statistically significant, especially for small- to medium-sized total knee femoral components. Conclusion This study does not establish a clinical relevance of removing more or less bone at primary TKA, but suggests that if a PS design is indicated, it is preferable to select a model which possibly resects less distal femoral bone. PMID:25037275
Stability and bifurcation analyses of reduced-order models of forced and natural circulation BWRs
NASA Astrophysics Data System (ADS)
Zhou, Quan
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 and characteristics of oscillations were studied in the frequency domain and using the Poincare-Andronov-Hopf Bifurcation (PAH-B) theorem. Results show that both supercritical and subcritical bifurcations may occur along the stability boundary in different parts of the parameter space. Moreover, it was found that although the conjugate pair of eigenvalues with the largest real part determines linear stability of the system, a second pair, with the second largest real part, is also important in determining the phase characteristics (in-phase vs. out-of-phase) of the oscillations. Numerical integrations have also been carried out, and confirm the results of stability and bifurcation analyses. In the second part of this dissertation, a new reduced-order model has been developed for the natural circulation BWRs. Water saturation enthalpy in this model depends on local pressure, allowing simulation and analysis of the flashing phenomenon. The core and riser are discretized into nodes. ODES for flow enthalpy, water saturation enthalpy, steam quality and flow velocity are derived for each node using the classical weighted residual approach. Two different nodalization schemes have been developed and implemented. Neither scheme was found to be superior to the other for all applications. The model was validated by comparing the results with experimental data reported in the literature for the SIRIUS natural circulation loop and with data measured in experiments carried out on the natural circulation Dodewaard reactor. Results show that both, supercritical or subcritical, bifurcations may occur along the stability boundary in different parts of the parameter space. It is hoped that results of this study are of value in demonstrating the safety features of current BWRs, and in improved design of future natural circulation BWR systems.
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.
Harp, Dylan R.
2015-05-15
MATK provides basic functionality to facilitate model analysis within the Python computational environment. Model analysis setup within MATK includes: - define parameters - define observations - define model (python function) - define samplesets (sets of parameter combinations) Currently supported functionality includes: - forward model runs - Latin-Hypercube sampling of parameters - multi-dimensional parameter studies - parallel execution of parameter samples - model calibration using internal Levenberg-Marquardt algorithm - model calibration using lmfit package - model calibration using levmar package - Markov Chain Monte Carlo using pymc package MATK facilitates model analysis using: - scipy - calibration (scipy.optimize) - rpy2 - Python interface to R
Electrical transient stability and underfrequency load shedding analysis for a large pump station
Shilling, S.R.
1997-01-01
Electrical transients from faults, loss of generation, and load swings can disrupt pump station operations. Isolated stations with no utility tie, and those with weak utility ties, are especially at risk. Relative to this problem, the following four main issues are addressed: (1) analyze the methods that use high-speed underfrequency load shedding to maintain system stability and preserve station operations; (2) analyze combustion gas turbine generator and diesel generator transient responses, as they pertain to the electrical engineer; (3) discuss system component modeling and the use of low voltage circuit switching devices to shed loads; (4) compare two computer analysis program outputs for underfrequency load shedding responses.
Electrical transient stability and underfrequency load shedding analysis for a large pump station
Shilling, S.R.
1995-12-31
Electrical transients from faults, loss of generation, and load swings can disrupt pump station operations. Isolated stations with no utility tie and those with weak utility ties are especially at risk. Relative to this problem, the following four main issues are addressed: (1) Analyze the methods that use high-speed underfrequency load shedding to maintain system stability and preserve station operations. (2) Analyze combustion gas turbine generator and diesel generator transient responses, as they pertain to the Electrical Engineer. (3) Discuss system component modeling and the use of low voltage circuit switching devices to shed loads. (4) Compare two computer analysis program outputs for underfrequency load shedding responses.
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.
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.
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.
Stability analysis of multiple time-delayed system.
Zheng, Da; Ren, Zhengyun; Fang, Jian-An
2008-10-01
A general class of linear time-invariant systems with time delays is studied. A number of methodologies have been suggested to assess the stability in the parametric domain of time delay or coefficient. This study offers an exact, structured and robust methodology to determine the stability regions of uncertain parameters in both time-delay space and coefficient space. The Rekasius transformation is used as a connection between time-delay space and coefficient space. An explicit analytical expression in terms of the system parameters which reveals the stability regions(pockets) in the domain of time delay and coefficient is presented. The method starts with the determination of all possible values of uncertain parameters which result in purely imaginary characteristic roots. In addition, some special stability boundaries are also discussed. After generating stability boundaries in parametric space, the two-step determination procedure is proposed to determine the actual stability regions. Such an approach can be used to determine the stability regions of any uncertain parameters of any retarded time-delay system. A complete example case study is also provided. PMID:18589418
Stability analysis for linear systems with time delays
NASA Technical Reports Server (NTRS)
Barker, L. K.; Whitesides, J. L.
1977-01-01
Time delays in the mathematical description of a physical system occur whenever the system is affected not only by conditions at the present time, but also by conditions which have occurred in the past. The tau-decomposition method, as refined by Lee and Hsu, is a method for studying the effects of time delay on the stability of retarded dynamical systems. In this paper, the method is extended to examine the stability and relative stability of: (1) retarded systems with many time delays; and (2) a class of neutral systems with one delay. Applications are included which illustrate the power of the technique.
Parametric analysis of a predator-prey system stabilized by a top predator.
Morozov, Andrew Y; Li, Bai-Lian
2006-08-01
We present a complete parametric analysis of a predator-prey system influenced by a top predator. We study ecosystems with abundant nutrient supply for the prey where the prey multiplication can be considered as proportional to its density. The main questions we examine are the following: (1) Can the top predator stabilize such a system at low densities of prey? (2) What possible dynamic behaviors can occur? (3) Under which conditions can the top predation result in the system stabilization? We use a system of two nonlinear ordinary differential equations with the density of the top predator as a parameter. The model is investigated with methods of qualitative theory of ODEs and the theory of bifurcations. The existence of 12 qualitatively different types of dynamics and complex structure of the parametric space are demonstrated. Our studies of phase portraits and parametric diagrams show that a top predator can be an important factor leading to stabilization of the predator-prey system with abundant nutrient supply. Although the model here is applied to the plankton communities with fish (or carnivorous zooplankton) as the top trophic level, the general form of the equations allows applications of our results to other ecological systems. PMID:16767445
NASA Astrophysics Data System (ADS)
Wang, Qianfeng; Zhou, Kefa; Sun, Li; Chen, Limou; Ou, Yang; Li, Guangyu; Qin, Yanfang; Wang, Jinlin
2011-02-01
In order to evaluate quantitatively the landscape stability of arid areas, a study area was selected in Yuli county of the middle and lower reaches of Tarim river. Remote sensing image data are the main data sources, the image data are processed by the support of RS and GIS technology. The study extracted 11 indices of landscape stability by FRAGSTATS software, and the standard matrix of these indices data are got using Z-Score method, then the comprehensive evaluation model of landscape stability is constructed by principal component analysis method. The study results showed that the range of comprehensive evaluation scores of Yuli's ecological landscape stability is 1.736, which indicated there is a great variation in ecological landscape stability of study area. The stability declines as the following order: forest land - water area- grass land- cultivated land - buildup land -unused land. The landscape stability is always the key scientific issues which should be solved urgently, the study on landscape stability has important theoretical and practical significance.
NASA Astrophysics Data System (ADS)
Stoll, John C.
1995-05-01
The performance of an unaided attitude determination system based on GPS interferometry is examined using linear covariance analysis. The modelled system includes four GPS antennae onboard a gravity gradient stabilized spacecraft, specifically the Air Force's RADCAL satellite. The principal error sources are identified and modelled. The optimal system's sensitivities to these error sources are examined through an error budget and by varying system parameters. The effects of two satellite selection algorithms, Geometric and Attitude Dilution of Precision (GDOP and ADOP, respectively) are examined. The attitude performance of two optimal-suboptimal filters is also presented. Based on this analysis, the limiting factors in attitude accuracy are the knowledge of the relative antenna locations, the electrical path lengths from the antennae to the receiver, and the multipath environment. The performance of the system is found to be fairly insensitive to torque errors, orbital inclination, and the two satellite geometry figures-of-merit tested.
Analysis of relationship between stability and flow parameters in a BWR
Upadhyaya, B.R.; Kitamura, M.
1980-01-01
Results of quantitative analysis of mutual relationship between the BWR stability and channel steam velocity are presented. The stability parameter, defined by the damping ratio, and the steam velocity are estimated by analysis of neutron noise data from local power range monitor (LPRM) detector signals. These parameters are treated as varying randomly as a function of time.
40 CFR 1065.190 - PM-stabilization and weighing environments for gravimetric analysis.
Code of Federal Regulations, 2010 CFR
2010-07-01
... 40 Protection of Environment 32 2010-07-01 2010-07-01 false PM-stabilization and weighing environments for gravimetric analysis. 1065.190 Section 1065.190 Protection of Environment ENVIRONMENTAL... § 1065.190 PM-stabilization and weighing environments for gravimetric analysis. (a) This...
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...
NASA Technical Reports Server (NTRS)
Kayten, Gerald G
1945-01-01
The analysis of results of wind-tunnel stability and control tests of powered airplane models in terms of the flying qualities of full-scale airplanes is advocated. In order to indicated the topics upon which comments are considered desirable in the report of a wind-tunnel stability and control investigation and to demonstrate the nature of the suggested analysis, the present NACA flying-qualities requirements are discussed in relation to wind-tunnel tests. General procedures for the estimation of flying qualities from wind-tunnel tests are outlined.
Bifurcation analysis of parametrically excited bipolar disorder model
NASA Astrophysics Data System (ADS)
Nana, Laurent
2009-02-01
Bipolar II disorder is characterized by alternating hypomanic and major depressive episode. We model the periodic mood variations of a bipolar II patient with a negatively damped harmonic oscillator. The medications administrated to the patient are modeled via a forcing function that is capable of stabilizing the mood variations and of varying their amplitude. We analyze analytically, using perturbation method, the amplitude and stability of limit cycles and check this analysis with numerical simulations.
NASA Astrophysics Data System (ADS)
Wehner, W.; Schuster, E.
2012-07-01
Suppression of magnetic islands driven by the neoclassical tearing mode (NTM) is necessary for efficient and sustained operation of tokamak fusion reactors. Compensating for the lack of bootstrap current, due to the pressure profile flattening in the magnetic island, by a localized electron cyclotron current drive (ECCD) has been proved experimentally as an effective method to stabilize NTMs. The effectiveness of this method is limited in practice by the uncertainties in the width of the island, the relative position between the island and the beam, and the ECCD power threshold for NTM stabilization. Heuristic search and suppress algorithms have been proposed and shown effective in improving the alignment of the ECCD beam with the island, using only an estimate of the island width. Making use of this estimate, real-time, non-model-based, extremum-seeking optimization algorithms have also been proposed not only for beam steering but also for power modulation in order to minimize the island-beam misalignment and the time required for NTM stabilization. A control-oriented dynamic model for the effect of ECCD on the magnetic island is proposed in this work to enable both control design and performance analysis of these minimum-seeking type of controllers. The model expands previous work by including the impact of beam modulation parameters such as the island-beam phase mismatch and the beam duty-cycle on the island width dynamics.
NASA Astrophysics Data System (ADS)
van Beek, L. P. H.; Bogaard, T. A.; van Asch, Th. W.
2003-04-01
Contrary to the beneficial mechanical effect of root reinforcement, the hydrological influence of vegetation are neither exclusively positive or negative with regards to slope stability. The net effect of vegetation on the hillslope scale is consequently difficult to establish and experimental data to test relevant hypotheses at the hillslope scale are thinly sown. Notwithstanding the limited amount of field data, eco-engineers, planners and decision makers need reliable information to evaluate the possible hydrological effects of changes in the vegetation cover or management strategies. Physically-based modelling can provide a solution to this problem by rigorous evaluation of the influence of the various hydrological processes that are related to vegetation. The proposed approach establishes the hydrological influence of vegetation on slope stability by means of a sensitivity analysis. The input for the sensitivity analysis is specified by an idealised slope. This slope is based on several existing slopes subject to landsliding and considers a range of typical soil, slope and vegetation conditions. This allows for the identification of those conditions under which vegetation may have a positive, hydrological influence on slope stability by attenuation of the hydrological response after potentially triggering events. However, uncertainty is introduced by the models themselves since they are merely approximations of reality. Moreover, the natural variability in input data and the way in which these data are treated will affect the reliability of the model outcome. These effects of uncertainty on the model outcome must be assessed before it can be applied with confidence in the decision making process. In order to study the effects of uncertainty, several transient 2-D hydrological models of varying complexity have been applied to the idealised slope (water balance approach and FEM). Data from the idealised slope have been used to specify conditions that range from transient and spatially distributed to steady-state and lumped. This results in a range of complexity and detail at which the hydrological influence of vegetation is modelled. The results are used to define what level of model complexity is warranted by readily available data and to establish to which extent uncertainty affects the reliability of the model outcome. This hydrological modelling approach in eco-engineering is part of the EU-funded ECOSLOPES project which studies the effects of vegetation on the mechanical and hydrological aspects on slope stability.
Physical and numerical model of colloidal silica injection for passive site stabilization
Gallagher, Patricia M.; Finsterle, Stefan
2004-08-01
Passive site stabilization is a new technology proposed for nondisruptive mitigation of liquefaction risk at developed sites susceptible to liquefaction. This technology is based on the concept of slow injection of stabilizing materials at the edge of a site and delivery of the stabilizer to the target location, using the natural or augmented groundwater flow. In this research, a box model was used to investigate the ability to uniformly deliver colloidal silica stabilizer to loose sands using low-head injection and extraction wells. Five injection wells and two extraction wells were used to deliver stabilizer in a generally uniform pattern to the loose sand formation. Numerical modeling was used to identify the key parameters affecting stabilizer migration and to determine their effective values for the box experiment. In our modeling approach, the stabilizer is treated as a miscible fluid, the viscosity of which is a function of time and concentration of the stabilizer in the pore water. Inverse modeling techniques are employed to reproduce data from the laboratory experiment for the determination of soil and stabilizer properties. While the details of the stabilizer distribution were difficult to reproduce with the simplified conceptual model employed in this study, the overall system behavior was well captured, providing confidence that numerical simulation is a useful tool for designing centrifuge model tests, pilot tests, and eventually field stabilizer-injection projects.
Stability analysis of bridged cracks in brittle matrix composites
NASA Technical Reports Server (NTRS)
Ballarini, Roberto; Muju, Sandeep
1991-01-01
The bridging of matrix cracks by fibers is an important toughening mechanism in fiber reinforced brittle matrix composites. This paper presents the results of a nonlinear finite element analysis of the Mode-I propagation of a bridged matrix crack in a finite size specimen. The composite is modeled as an orthotropic continuum and the bridging due to the fibers is modeled as a distribution of tractions which resist crack opening. A critical stress intensity factor criterion is employed for matrix crack propagation while a critical crack opening condition is used for fiber failure. The structural response of the specimen (load-deflection curves) as well as the stress intensity factor of the propagating crack are calculated for various constituent properties and specimen configurations for both tensile and bending loading. By controlling the length of the bridged crack results are obtained which highlight the transition from stable to unstable behavior of the propagating crack.
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 ...
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.
Experimentation and Modeling of Jet A Thermal Stability in a Heated Tube
NASA Technical Reports Server (NTRS)
Khodabandeh, Julia W.
2005-01-01
High performance aircraft typically use hydrocarbon fuel to regeneratively cool the airframe and engine components. As the coolant temperatures increase, the fuel may react with dissolved oxygen forming deposits that limit the regenerative cooling system performance. This study investigates the deposition of Jet A using a thermal stability experiment and computational fluid dynamics (CFD) modeling. The experimental portion of this study is performed with a high Reynolds number thermal stability (HiRets) tester in which fuel passes though an electrically heated tube and the fuel outlet temperature is held constant. If the thermal stability temperature of the fuel is exceeded, deposits form and adhere to the inside of the tube creating an insulating layer between the tube and the fuel. The HiRets tester measures the tube outer wall temperatures near the fuel outlet to report the effect of deposition occurring inside the tube. Final deposits are also estimated with a carbon burn off analysis. The CFD model was developed and used to simulate the fluid dynamics, heat transfer, chemistry, and transport of the deposit precursors. The model is calibrated to the experiment temperature results and carbon burn-off deposition results. The model results show that the dominant factor in deposition is the heated wall temperature and that most of the deposits are formed in the laminar sublayer. The models predicted a 7.0E-6 kilograms per square meter-sec deposition rate, which compared well to the carbon burn-off analysis deposition rate of 1.0E-6 kilograms per square meter-sec.
Robust stability analysis of genetic regulatory network with time delays.
Liu, Pin-Lin
2013-05-01
The robust asymptotic stability problem of genetic regulatory networks with time delays is investigated by Lyapunov functional approach and linear matrix inequality techniques (LMIs). Stability criteria for the delayed genetic regulatory networks are expressed as a set of LMIs, yielding much less conservative analytic results. New criteria with reduced conservatism are obtained and they involve less matrix parameters than the existing ones. Finally, three numerical examples are presented to illustrate effectiveness and less conservative results. PMID:23433548
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; Tomnek, 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.
Limits of stability of the extended water model
NASA Astrophysics Data System (ADS)
Van Royen, Eddy; Meijer, Paul H. E.
1986-12-01
In this paper we report the metastable states of the extended water model. The framework of the computations is explained in detail; the constrained or “observed” variables are determined as function of the nonobserved order parameters, or cluster variables, and the susceptibility is expressed in terms of the Hessian of the free energy with respect to these constrained variables. Since the Hessian is of the fourth order in this model, there are different possibilities for it to be zero, each associated with different spinodal. The analysis of this problem was done and examples are given. The procedure used is compared with Gibbs original work on the equilibrium of heterogeneous substances.
Vortex stability in a multi-layer quasi-geostrophic model: application to Mediterranean Water eddies
NASA Astrophysics Data System (ADS)
Carton, Xavier; Sokolovskiy, Mikhail; Mnesguen, Claire; Aguiar, Ana; Meunier, Thomas
2014-12-01
The stability of circular vortices to normal mode perturbations is studied in a multi-layer quasi-geostrophic model. The stratification is fitted on the Gulf of Cadiz where many Mediterranean Water (MW) eddies are generated. Observations of MW eddies are used to determine the parameters of the reference experiment; sensitivity tests are conducted around this basic case. The objective of the study is two-fold: (a) determine the growth rates and nonlinear evolutions of unstable perturbations for different three-dimensional (3D) velocity structures of the vortices, (b) check if the different structure of our idealized vortices, mimicking MW cyclones and anticyclones, can induce different stability properties in a model that conserves parity symmetry, and apply these results to observed MW eddies. The linear stability analysis reveals that, among many 3D distributions of velocity, the observed eddies are close to maximal stability, with instability time scales longer than 100 days (these time scales would be less than 10 days for vertically more sheared eddies). The elliptical deformation is most unstable for realistic eddies (the antisymmetric one dominates for small eddies and the triangular one for large eddies); the antisymmetric mode is stronger for cyclones than for anticyclones. Nonlinear evolutions of eddies with radii of about 30 km, and elliptically perturbed, lead to their re-organization into 3D tripoles; smaller eddies are stable and larger eddies break into 3D dipoles. Horizontally more sheared eddies are more unstable and sustain more asymmetric instabilities. In summary, few differences were found between cyclone and anticyclone stability, except for strong horizontal velocity shears.
NASA Astrophysics Data System (ADS)
Kolarik, Roman; Zatloukal, Martin
2011-07-01
In this work, a stable numerical scheme for the film blowing stability analysis, considering the variational principle based film blowing model, non-isothermal processing conditions and non-Newtonian behavior of the polymer, has been proposed and used with the aim to reveal the effect of flow activation energy, heat transfer coefficient, mass flow rate and melt temperature on the film blowing stability. It has been found that the model predictions are in good agreement with the corresponding experimental data taken from the open literature.
Energy Science and Technology Software Center (ESTSC)
2015-05-15
MATK provides basic functionality to facilitate model analysis within the Python computational environment. Model analysis setup within MATK includes: - define parameters - define observations - define model (python function) - define samplesets (sets of parameter combinations) Currently supported functionality includes: - forward model runs - Latin-Hypercube sampling of parameters - multi-dimensional parameter studies - parallel execution of parameter samples - model calibration using internal Levenberg-Marquardt algorithm - model calibration using lmfit package - modelmore » calibration using levmar package - Markov Chain Monte Carlo using pymc package MATK facilitates model analysis using: - scipy - calibration (scipy.optimize) - rpy2 - Python interface to R« less
Traffic stability of a car-following model considering driver’s desired velocity
NASA Astrophysics Data System (ADS)
Zhang, Geng; Sun, Di-Hua; Liu, Wei-Ning; Liu, Hui
2015-07-01
In this paper, a new car-following model is proposed by considering driver’s desired velocity according to Transportation Cyber Physical Systems. The effect of driver’s desired velocity on traffic flow has been investigated through linear stability theory and nonlinear reductive perturbation method. The linear stability condition shows that driver’s desired velocity effect can enlarge the stable region of traffic flow. From nonlinear analysis, the Burgers equation and mKdV equation are derived to describe the evolution properties of traffic density waves in the stable and unstable regions respectively. Numerical simulation is carried out to verify the analytical results, which reveals that traffic congestion can be suppressed efficiently by taking driver’s desired velocity effect into account.
NASA Technical Reports Server (NTRS)
Tangler, J. L.; Wohlfeld, R. M.; Miley, S. J.
1973-01-01
Schlieren methods of flow visualization and hot-wire anemometry for velocity measurements were used to investigate the wakes generated by hovering model propellers and rotors. The research program was directed toward investigating (1) the stability of the tip vortex, (2) the effects produced by various tip shapes on performance and tip vortex characteristics, and (3) the shock formation and noise characteristics associated with various tip shapes. A free-wake analysis was also conducted for comparison with the vortex stability experimental results. Schlieren photographs showing wake asymmetry, interaction, and instability are presented along with a discussion of the effects produced by the number of blades, collective pitch, and tip speed. Two hot-wire anemometer techniques, used to measure the maximum circumferential velocity in the tip vortex, are discussed.
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 alloy systems. Consistency between the experimental results and the present model predictions provide a more rigorous criterion for investigating thermal stabilization. However, other possible contributions for grain growth stabilization should still be considered.
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.
NASA Astrophysics Data System (ADS)
Lazar, A.; Stegner, A.; Heifetz, E.
2012-04-01
The stability of axisymmetric oceanic-like vortices to inertial perturbations is investigated by means of linear stability analysis, taking into account the thickness and the stratification of the thermocline, as well as the vertical eddy viscosity. The model considers different types of circular barotropic vortices in a linearly stratified shallow layer confined with rigid lids. In this case the aspect ratio (thermocline height to vortex radius ratio) should be added to the parameters that control the stability for columnar vortices, which are the stratification, and the Ekman and Rossby numbers. We show that for strong stratification the Burger number (the radius of the vortex in relation to the Rossby radius of deformation) replaces the aspect ratio and the stratification parameter, and then only three parameters are needed. Numerical analysis reveals that if the intensity of the vortex is characterized by the vortex Rossby number, then for monotonic and non-isolated vortices, the instability is not sensitive to the vorticity profile. This allows extending our analytical solutions for the Rankine vortex to a wide variety of oceanic cases, including results such as the analytic dispersion relation, and the marginal stability criterion. This criterion suits oceanic conditions better than the generalized Rayleigh criterion, which is only valid for non-dissipative and non-stratified eddies. Comparison with literature oceanographic data shows that our criterion allows for cases that seem to contradict the common oceanographic hypothesis for inertial instability: 1. Intense submesoscale anticyclones may be stable even with a core region of negative absolute vorticity; and on the other hand, 2. mesoscale vortices can be unstable. We corroborate our findings with large-scale laboratory experiments, performed at the LEGI-Coriolis platform.
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...
Thermohaline Circulation Stability: A Box Model Study. Part II: Coupled Atmosphere-Ocean Model.
NASA Astrophysics Data System (ADS)
Lucarini, Valerio; Stone, Peter H.
2005-02-01
A thorough analysis of the stability of a coupled version of an interhemispheric three-box model of thermohaline circulation (THC) is presented. This study follows a similarly structured analysis of an uncoupled version of the same model presented in Part I of this paper. The model consists of a northern high-latitude box, a tropical box, and a southern high-latitude box, which can be thought of as corresponding to the northern, tropical, and southern Atlantic Ocean, respectively. This paper examines how the strength of THC changes when the system undergoes forcings representing global warming conditions.Since a coupled model is used, a direct representation of the radiative forcing is possible because the main atmospheric physical processes responsible for freshwater and heat fluxes are formulated separately. Each perturbation to the initial equilibrium is characterized by the total radiative forcing realized, by the rate of increase, and by the north-south asymmetry. Although only weakly asymmetric or symmetric radiative forcings are representative of physically reasonable conditions, general asymmetric forcings are considered in order to get a more complete picture of the mathematical properties of the system. The choice of suitably defined metrics makes it possible to determine the boundary dividing the set of radiative forcing scenarios that lead the system to equilibria characterized by a THC pattern similar to the present one, from those that drive the system to equilibria where the THC is reversed. This paper also considers different choices for the atmospheric transport parameterizations and for the ratio between the high-latitude and tropical radiative forcing. It is generally found that fast forcings are more effective than slow forcings in disrupting the present THC pattern, forcings that are stronger in the northern box are also more effective in destabilizing the system, and very slow forcings do not destabilize the system whatever their asymmetry, unless the radiative forcings are very asymmetric and the atmospheric transport is a relatively weak function of the meridional temperature gradient. In this latter case some relevant hysteresis graphs of the system are presented. The changes in the strength of the THC are primarily forced by changes in the latent heat transport in the hemisphere because of its sensitivity to temperature, which arises from the Clausius-Clapeyron relation.
Applied Modeling of Surface Fluxes under Different Stability Regimes.
NASA Astrophysics Data System (ADS)
Mohan, Manju; Siddiqui, T. A.
1998-10-01
In this study various surface layer parameters, fluxes, and eddy diffusivity profiles have been estimated by making use of routine meteorological data for both unstable and stable conditions. Several empirical relationships for estimating turbulence parameters are tested with data. The estimation schemes are discussed at length for both stability conditions. Routine meteorological observations have been used for the computations of net radiation, sensible heat flux, friction velocity, scaling temperature in the surface layer, Monin-Obukhov length, and eddy diffusivity profiles. These parameters are important and are used for the estimation of input parameters for air quality models for predicting ground-level concentrations. Special emphasis has been given to stable conditions by using recent formulations for turbulence parameters and their verification with data. Two recent schemes have been compared. About 153 h of data have been selected from the field experiments sponsored by the Electric Power Research Institute around the Kincaid Power Plant in 1980-81 for the validation of net radiation, friction velocity, and Monin-Obukhov length. Several statistical techniques have been used to assess the performance of the schemes. Based on the statistical measures, the chosen parameterization schemes are judged to perform well.
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.
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)
GraTeLPy: graph-theoretic linear stability analysis
2014-01-01
Background A biochemical mechanism with mass action kinetics can be represented as a directed bipartite graph (bipartite digraph), and modeled by a system of differential equations. If the differential equations (DE) model can give rise to some instability such as multistability or Turing instability, then the bipartite digraph contains a structure referred to as a critical fragment. In some cases the existence of a critical fragment indicates that the DE model can display oscillations for some parameter values. We have implemented a graph-theoretic method that identifies the critical fragments of the bipartite digraph of a biochemical mechanism. Results GraTeLPy lists all critical fragments of the bipartite digraph of a given biochemical mechanism, thus enabling a preliminary analysis on the potential of a biochemical mechanism for some instability based on its topological structure. The correctness of the implementation is supported by multiple examples. The code is implemented in Python, relies on open software, and is available under the GNU General Public License. Conclusions GraTeLPy can be used by researchers to test large biochemical mechanisms with mass action kinetics for their capacity for multistability, oscillations and Turing instability. PMID:24572152
A combined conceptual model for the effects of fissure-induced infiltration on slope stability
NASA Astrophysics Data System (ADS)
van Beek, L. P. H.; van Asch, Th. W. J.
In humid and subhumid Mediterranean environments the disruption of the vegetation cover by in particular shallow landslides limits the area in which erodible material is exposed to overland flow. On short temporal scales the hydrological system that allows for the generation of critical pore pressures or soil moisture conditions on the potential shear surface determines the occurrence of these landslides. Hence the relative contribution of landsliding to land degradation processes can be quantified in terms of its magnitude and frequency through a semiphysical hillslope model that links the relevant hydrological processes to a stability analysis. For the development of such a combined model for hydrology and slope stability a conceptualization of the process system is needed. Through the implementation of the resulting model in a GIS environment the effect of topography, to which the occurrence of landslides is intrinsically linked, can be incorporated. In addition, the spatial variation of hydrological and geomechanical parameters can be incorporated in the model. This is important since the occurrence and extent of shallow landslides is directly dependent on the net rainfall input in the hydrological system, as defined by the land cover of the area. In this paper a conceptual model is presented that combines a description of the hydrology with an assessment of the slope stability. The conceptual framework of this model is based on field observations in the Alcoy area (SE Spain). In this area shallow landslides occur on steep, unsaturated slopes in marly deposits of Miocene age, at the boundary between regolith and bedrock (1-2 m depth). Given the low matric permeability of the marl it has been assumed that preferential flow along distinct sets of fissures by-passing slower matric percolation might account for the observed response time of landslides to rainfall events. The fissures in the regolith are either relict primary bedrock structures (discontinuities) or are formed by weathering, creep and shear; they are supplied with water by subsurface flow through the more permeable rootzone. With the combined slope stability model, which is programmed in the meta-language embedded in the PCRaster GIS package, a sensitivity analysis has been performed to assess the impact of fissure flow on the occurrence of landslides in a small catchment of 1.2 km2 near Alcoy.
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.
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.
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/.
Strength Analysis of Coconut Fiber Stabilized Earth for Farm Structures
NASA Astrophysics Data System (ADS)
Enokela, O. S.; P. O, Alada
2012-07-01
Investigation of the strength characteristic of soil from alluvial deposit of River Benue in makurdi stabilized with coconut fiber as a stabilizer was carried as local building material for farm structure. Processed coconut fibers were mixed with the soil at four different mix ratios of 1% fiber, 2% fiber, 3% fiber and 4% fiber by percentage weight with 0% fiber as control. Compaction test and compressive strength were carried out on the various stabilizing ratio. From the compaction test, the correlation between the maximum dry density and optimum moisture content is a second order polynomial with a coefficient of 63% obtained at1.91kg/m3and 20.0% respectively while the compressive strength test shows an optimum failure load of 8.62N/mm2 at 2%fibre:100% soil mix ratio at 2.16 maximum dry density.
Perturbed Stability Analysis of External Ideal MHD Modes
NASA Astrophysics Data System (ADS)
Comer, K. J.; Callen, J. D.; Hegna, C. C.; Garstka, G. D.; Turnbull, A. D.; Garofalo, A. M.; Cowley, S. C.
2002-11-01
Traditionally, numerical parameter scans are performed to study the effects of equilibrium shaping and profiles on long wavelength ideal MHD instabilities. Previously, we introduced a new perturbative technique to more efficiently explore these dependencies: changes in delta-W due to small equilibrium variations are found using a perturbation of the energy principle rather than with an eigenvalue-solver instability code. With this approach, the stability properties of similar equilibria can be efficiently explored without generating complete numerical results for every set of parameters (which is time-intensive for accurate representations of several configurations). Here, we apply this approach to toroidal geometry using GATO (an ideal MHD stability code) and experimental equilibria. In particular, we explore ideal MHD stability of external kink modes in the spherical tokamak Pegasus and resistive wall modes in DIII-D.
MHD Stability Analysis of Reversed Shear Discharges in Alcator C-Mod
NASA Astrophysics Data System (ADS)
Ramos, J. J.; Hubbard, A.; in, Y.; Porkolab, M.; Snipes, J.; Wolfe, S. M.; Bondeson, A.; Martynov, A.
1997-11-01
Reversed magnetic shear experiments have been carried out in Alcator C-mod by applying early ICRF heating during the current ramp-up phase. A detailed MHD stability analysis of these configurations is presented here. The purpose of this work is to find a theoretical explanation for the observed bursts of MHD activity as detected by the ECE and magnetic diagnostics. MHD equilibrium models of the experimental plasmas are generated with the EFIT code, and their linear stability is investigated with the KINX code for ideal modes and the MARS code for resistive modes. MHD stability results are sensitive to equilibrium details that cannot be resolved with the available diagnostics of pressure and current profiles, therefore different possible equilibrium reconstructions must be considered. Resistive single tearing modes with resonant surfaces in the cold plasma region near the edge seem to provide the best interpretation of experimental data. However, if the edge current density gradient is sufficiently large, ideal surface kink instabilities can also be excited.
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.
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.
Stability analysis of non-inertial thin film flow over a heterogeneously heated porous substrate
NASA Astrophysics Data System (ADS)
Kumawat, Tara Chand; Tiwari, Naveen
2016-02-01
The dynamics and linear stability of a gravity drive thin film flowing over non-uniformly heated porous substrate are studied. A governing equation for the evolution of film-thickness is derived within the lubrication approximation. Darcy-Brinkman equation is used to model flow in the porous medium along with a tangential stress-jump condition at the interface of the porous layer and the fluid film. A temperature profile is imposed at the solid wall to model an embedded heater beneath the porous layer. At the upstream edge of the heater, an opposing thermocapillary stress at the liquid-air interface leads to the formation of a thermocapillary ridge. The ridge becomes unstable beyond a critical Marangoni number leading to the formation of rivulets that are periodic in the spanwise direction. Increase in the values of parameters such as Darcy number, stress jump coefficient, and porosity is shown to have stabilizing effect on the film dynamics. The critical Marangoni number is shown to increase monotonically with Darcy number for various values of porosity. At large values of stress-jump coefficient, a non-monotonic variation in critical Marangoni number versus Darcy number is shown. A correlation is developed numerically for the ratio of critical Marangoni number at large Darcy number to that for a non-porous substrate as a function of porosity and thickness of the porous substrate. A transient growth analysis is carried out followed by non-linear stability analysis. The non-modal growth is found to be negligible thus indicating that the eigenvalues are physically determinant.
F-111 natural laminar flow glove flight test data analysis and boundary layer stability analysis
NASA Technical Reports Server (NTRS)
Runyan, L. J.; Navran, B. H.; Rozendaal, R. A.
1984-01-01
An analysis of 34 selected flight test data cases from a NASA flight program incorporating a natural laminar flow airfoil into partial wing gloves on the F-111 TACT airplane is given. This analysis determined the measured location of transition from laminar to turbulent flow. The report also contains the results of a boundary layer stability analysis of 25 of the selected cases in which the crossflow (C-F) and Tollmien-Schlichting (T-S) disturbance amplification factors are correlated with the measured transition location. The chord Reynolds numbers for these cases ranges from about 23 million to 29 million, the Mach numbers ranged from 0.80 to 0.85, and the glove leading-edge sweep angles ranged from 9 deg to 25 deg. Results indicate that the maximum extent of laminar flow varies from 56% chord to 9-deg sweep on the upper surface, and from 51% chord at 16-deg sweep to 6% chord at 25-deg sweep on the lower. The results of the boundary layer stability analysis indicate that when both C-F and T-S disturbances are amplified, an interaction takes place which reduces the maximum amplification factor of either type of disturbance that can be tolerated without causing transition.
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...
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.
Nonlinear global stability analysis of compressor stall phenomena
NASA Technical Reports Server (NTRS)
Razavi, H.
1985-01-01
Compressor stall phenomena are analyzed from the point of view of nonlinear control theory, based on bifurcation-catastrophe techniques. This new approach appears promising and offers insight into such well-known compressor instability problems as surge and rotating stall and suggests strategies for recovery. Three interlocking dynamic nonlinear state space models are developed. It is shown that the problem of rotating stall can be viewed as an induced bifurcation of solution of the unstalled model. Hysteresis effects are shown to exist in the stall/recovery process. Surge cycles are observed for some critical parameter values. The oscillatory behavior is seen to be due to development of limit cycles, generated by Hopf bifurcation of solutions. More specifically, it is observed that at certain critical values of parameters, a family of stable limit cycles with growning and then diminishing amplitudes is generated, then giving rise to an unstable family of limit cycles. This unstable family in turn bifurcates into other unstable families. To further illustrate the utility of the methodology, some partial computation of domains is carried out, and parameter sensitivity analysis is performed.
Stability analysis of nonlinear systems with slope restricted nonlinearities.
Liu, Xian; Du, Jiajia; Gao, Qing
2014-01-01
The problem of absolute stability of Lur'e systems with sector and slope restricted nonlinearities is revisited. Novel time-domain and frequency-domain criteria are established by using the Lyapunov method and the well-known Kalman-Yakubovich-Popov (KYP) lemma. The criteria strengthen some existing results. Simulations are given to illustrate the efficiency of the results. PMID:24592160
Stability Analysis of Nonlinear Systems with Slope Restricted Nonlinearities
Du, Jiajia
2014-01-01
The problem of absolute stability of Lur'e systems with sector and slope restricted nonlinearities is revisited. Novel time-domain and frequency-domain criteria are established by using the Lyapunov method and the well-known Kalman-Yakubovich-Popov (KYP) lemma. The criteria strengthen some existing results. Simulations are given to illustrate the efficiency of the results. PMID:24592160
Application of historical channel stability analysis to instream flow studies
Kondolf, G.M.; Sale, M.J.
1985-01-01
Evaluation of the long-term stability of river channels is an important component of instream flow assessments because significant instability may invalidate the results of habitat simulation, especially when the variation of habitat over time is to be examined. Procedures are described for reconnaissance-level studies of river channel dynamics, with emphasis on the use of readily available historical records.
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 of the analytical solution of Penna model of biological aging.
Magdoń-Maksymowicz, M S
2008-11-01
There are some analytical solutions of the Penna model of biological aging; here, we discuss the approach by Coe et al. (Phys. Rev. Lett. 89, 288103, 2002), based on the concept of self-consistent solution of a master equation representing the Penna model. The equation describes transition of the population distribution at time t to next time step (t + 1). For the steady state, the population n(a, l, t) at age a and for given genome length l becomes time-independent. In this paper we discuss the stability of the analytical solution at various ranges of the model parameters--the birth rate b or mutation rate m. The map for the transition from n(a, l, t) to the next time step population distribution n(a + 1, l, t + 1) is constructed. Then the fix point (the steady state solution) brings recovery of Coe et al. results. From the analysis of the stability matrix, the Lyapunov coefficients, indicative of the stability of the solutions, are extracted. The results lead to phase diagram of the stable solutions in the space of model parameters (b, m, h), where h is the hunt rate. With increasing birth rate b, we observe critical b (0) below which population is extinct, followed by non-zero stable single solution. Further increase in b leads to typical series of bifurcations with the cycle doubling until the chaos is reached at some b (c). Limiting cases such as those leading to the logistic model are also discussed. PMID:18941823
Charles Reece; Edward Daly; G. Davis; William Hicks; Timothy Rothgeb; H. Phillips; Joseph Preble; Haipeng Wang; Genfa Wu
2008-02-12
During initial testing of the prototype cavities incorporated into the developmental cryomodule Renascence severe thermal stability issues were encountered during CW operation. Additional diagnostic instrumentation was added. This enabled identification of an unanticipated thermal impedance between the HOM coupler probe feedthrough assembly and the cavity beamtube. Subsequent detailed FE analysis successfully modeled the situation and indicated the need for alternate cooling path for the couplers on those cavities. HOM damping was measured to be adequate employing only two of the four HOM couplers. The two pickup probes on the couplers at the input power coupler side of each cavity were removed, the remaining HOM probe feedthroughs were heat stationed to two-phase helium supply piping, and a novel heat sink was added to station both the inner and outer conductors of the remaining HOM rf cables. The characterization measurements, analysis, modifications, and resulting performance are presented.
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.
Stabilized plane and axisymmetric Lobatto finite element models
NASA Astrophysics Data System (ADS)
Hu, Y. C.; Sze, K. Y.; Zhou, Y. X.
2015-11-01
High order elements are renowned for their high accuracy and convergence. Among them, Lobatto spectral finite elements are commonly used in explicit dynamic analyses as their mass matrices when evaluated by the Lobatto integration rule are diagonal. While there are numerous advanced first and second order elements, advanced high order elements are rarely seen. In this paper, generic stabilization schemes are devised for the reduced integrated plane and axisymmetric elements. Static and explicit dynamic tests are considered for evaluating the relatively merits of the stabilized and conventional elements. The displacement errors of the stabilized elements are less than those of the conventional Lobatto elements. When the material is nearly incompressible, the stabilized elements are also more accurate in terms of the energy error norm. This advantage is of practical importance for bio-tissue and hydrated soil analyses.
Katipoglu-Yazan, Tugce
2015-01-01
The objective of the study was to investigate the achievable limits of aerobic sludge stabilization applied on waste-activated sludge generated in domestic, tannery, and pharmaceutical wastewater treatment plants. Stabilization study involved monitoring of conventional parameters and model evaluation of oxygen uptake rate and particulate components of waste sludge. Multi-component biomass approach was adopted based on death-regeneration mechanism. The results showed that sludge stabilization efficiency ranged between 25% and 30%, which was closely related to the fate of different particulate fractions of biomass, that is, viable biomass, hydrolysable particulates, and microbial metabolic products. Model calibration exercises yield in rate coefficient ranges of 0.18-0.32/day for biomass decay and 0.60-0.65/day for hydrolysis of non-biomass components. Degradation rates of particulate metabolic products were estimated as 0.035, 0.04, and 0.01/day for domestic, tannery, and pharmaceutical sludge, respectively. Relatively low degradation rates compared to conventional biological treatment processes confirmed reduced microbial activity in the course of aerobic stabilization. PMID:25687597
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.
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.
Coalbed methane modeling analysis
Covatch, G.L.; Layne, A.W.; Salamy, S.P.
1985-12-01
Systems analyses or the Department of Energy's (DOE) Coalbed Methane Project (CMP) were performed at the Morgantown Energy Technology Center (METC). In the analyses, both reservoir and stimulation models were evaluated using data from US Steel's Oak Grove Coal Degasification Field. In the first part of the study two reservoir models designed for predicting methane and water production from coalbeds, WELL2D and ARRAY, were evaluated. WELL2D is a two-dimensional, single-well, radial flow model; ARRAY is a two-dimensional, multiwell production model. In the evaluation, the models were used to history match the actual production of the individual wells. The resultant information was then factored into a full-field simulation of the Oak Grove Field. This report summarizes the technical approaches used in the two models, their installation onto the DOE/METC computer system, and gives the results from their evaluation. In the second part of the study, three stimulation models were evaluated to determine their applicability to the CMP. The stimulation models, OSUFRAC (generalized hydraulic fracture), ORUFRAC1 (stress contrast hydraulic fracture model), and TUFRAC (hydraulic fracture proppant placement model), were designed for hydraulic fracturing of homogeneous reservoirs. A summary of the technical approach used in each model and the results of the analyses are presented. 11 refs., 27 figs., 12 tabs.
Stability of the rate, state and temperature dependent friction model and its applications
NASA Astrophysics Data System (ADS)
Singh, Arun K.; Singh, Trilok N.
2016-04-01
In this paper, we study stability of the rate, state and temperature friction (RSTF) model. The Segall and Rice approach is used to model heat transfer at the sliding interface with its surroundings. The effect of pore pressure is not considered in the model to avoid the complex expression for critical stiffness. Linear stability analysis of the spring-mass sliding system is carried out with the ageing law under the quasistatic conditions in order to determine the critical stiffness above which sliding behaviour changes from unstable to stable or vice versa. Our numerical simulations establish that critical stiffness of the heated surface may increase or decrease from corresponding to the critical stiffness of the unheated surface depending on the relative values of two contradictory parameters related with velocity effect and temperature effect. Parametric studies are also carried out to understand shear velocity and temperature of the sliding surface dependence of steady friction. The RSTF model is also used to study the gravity induced failure of a creeping rock slope and the results are justified.
Stability and invariant manifolds of a generalized Beddington host-parasitoid model.
Kapçak, Sinan; Ufuktepe, Ünal; Elaydi, Saber
2013-01-01
We will investigate the stability and invariant manifolds of a new discrete host-parasitoid model. It is a generalization of the Beddington-Nicholson-Bailey model. Our study establishes analytically, for the first time, the stability of the coexistence fixed point. PMID:24303904
Mechanical Analysis of the Effects of Cephalic Trim on Lower Lateral Cartilage Stability
Oliaei, Sepehr; Manuel, Cyrus; Protsenko, Dmitriy; Hamamoto, Ashley; Chark, Davin; Wong, Brian
2014-01-01
Objective To determine how mechanical stability changes in the lower lateral cartilage (LLC) after varying degrees of cephalic resection in a porcine cartilage nasal tip model. Methods Alar cartilage was harvested from fresh porcine crania (n=14) and sectioned to precisely emulate a human LLC in size and dimension. Flexural mechanical analysis was performed both before and after cephalic trims of 0 (control), 4, and 6 mm. Cantilever deformation tests were performed on the LLC models at 3 locations (4, 6, and 8 mm from the midline), and the integrated reaction force was measured. An equivalent elastic modulus of the crura was calculated assuming that the geometry of the LLC model approximated a modified single cantilever beam. A 3-dimensional finite element model was used to model the stress distribution of the prescribed loading conditions for each of the 3 types of LLC widths. Results A statistically significant decrease (P=.02) in the equivalent elastic modulus of the LLC model was noted at the most lateral point at 8 mm and only when 4 mm of the strut remained (P=05). The finite element model revealed that the greatest internal stresses was at the tip of the nose when tissue was flexed 8 mm from the midline. Conclusion Our results provide the mechanical basis for suggested clinical guidelines stating that a residual strut of less than 6 mm can lead to suboptimal cosmetic results owing to poor structural support of the overlying skin soft-tissue envelope by an overly resected LLC. PMID:22250265
Stability of landsat-4 thematic mapper outgassing models
Micijevic, E.; Chander, G.
2006-01-01
Oscillations in radiometric gains of the short wave infrared (SWIR) bands in Landsat-4 (L4) and Landsat-5 (L5) Thematic Mappers (TMs) are observed through an analysis of detector responses to the Internal Calibrator (IC) pulses. The oscillations are believed to be caused by an interference effect due to a contaminant film buildup on the window of the cryogenically cooled dewar that houses these detectors. This process of contamination, referred to as outgassing effects, has been well characterized using an optical thin-film model that relates detector responses to the accumulated film thickness and its growth rate. The current models for L4 TM are based on average detector responses to the second brightest IC lamp and have been derived from three data sets acquired during different times throughout the instrument's lifetime. Unlike in L5 TM outgassing characterization, it was found that the L4 TM responses to all three IC lamps can be used to provide accurate characterization and correction for outgassing effects. The analysis of single detector responses revealed an up to five percent difference in the estimated oscillating periods and also indicated a gradual variation of contaminant growth rate over the focal plane.
40 CFR 1065.190 - PM-stabilization and weighing environments for gravimetric analysis.
Code of Federal Regulations, 2013 CFR
2013-07-01
... 40 Protection of Environment 34 2013-07-01 2013-07-01 false PM-stabilization and weighing environments for gravimetric analysis. 1065.190 Section 1065.190 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY (CONTINUED) AIR POLLUTION CONTROLS ENGINE-TESTING PROCEDURES Equipment Specifications § 1065.190 PM-stabilization and...
ERIC Educational Resources Information Center
Jose, Anita; O'Leary, K. Daniel; Moyer, Anne
2010-01-01
Cohabitation with a romantic partner has become common in recent decades. This meta-analysis examined the link between premarital cohabitation and marital stability (k = 16) and marital quality (k = 12). Cohabitation had a significant negative association with both marital stability and marital quality. The negative predictive effect on marital
Stability and Change in Work Values: A Meta-Analysis of Longitudinal Studies
ERIC Educational Resources Information Center
Jin, Jing; Rounds, James
2012-01-01
A meta-analysis of longitudinal studies was conducted to investigate stability and change in work values across the life span. Both rank-order stability and mean-level change were investigated using an integrative classification for intrinsic, extrinsic, social and status work values (Ross, Schwartz, & Surkis, 1999). Results of rank-order…
ERIC Educational Resources Information Center
Jose, Anita; O'Leary, K. Daniel; Moyer, Anne
2010-01-01
Cohabitation with a romantic partner has become common in recent decades. This meta-analysis examined the link between premarital cohabitation and marital stability (k = 16) and marital quality (k = 12). Cohabitation had a significant negative association with both marital stability and marital quality. The negative predictive effect on marital…
Linearized stability analysis of gravastars in noncommutative geometry
NASA Astrophysics Data System (ADS)
Lobo, Francisco S. N.; Garattini, Remo
2013-12-01
In this work, we find exact gravastar solutions in the context of noncommutative geometry, and explore their physical properties and characteristics. The energy density of these geometries is a smeared and particle-like gravitational source, where the mass is diffused throughout a region of linear dimension due to the intrinsic uncertainty encoded in the coordinate commutator. These solutions are then matched to an exterior Schwarzschild spacetime. We further explore the dynamical stability of the transition layer of these gravastars, for the specific case of β = M 2/ α < 1.9, where M is the black hole mass, to linearized spherically symmetric radial perturbations about static equilibrium solutions. It is found that large stability regions exist and, in particular, located sufficiently close to where the event horizon is expected to form.
Linear MHD Stability Analysis of the SSPX Spheromak
NASA Astrophysics Data System (ADS)
Jayakumar, R.; Cohen, B. I.; Hooper, E. B.; Lodestro, L. L.; McLean, H. S.; Pearlstein, L. D.; Wood, R.; Turnbull, A. D.; Sovinec, C.
2007-11-01
Good correlation between the toroidal mode numbers of measured magnetic fluctuations in high temperature SSPX plasmas and presence of low-order rational surfaces in the reconstructed q profiles, suggests that the quality of magnetic surfaces in SSPX is sufficiently good for applying standard linear MHD stability analyses. Previously we have reported on benchmarking the code NIMROD against GATO, with good agreement in growth rates for ideal-MHD internal kinks and an external kinks with no current on open field lines (for equilibria imported from the code Corsica). Recent stability analyses also show that presence of low order rational surfaces causes internal modes to become unstable. We will report on the progress in applying these tools for assessing beta limits in SSPX, using NIMROD analyses including current on open field lines and for comparison with experiments.