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.
Stability analysis of the ribosome flow model.
Margaliot, Michael; Tuller, Tamir
2012-01-01
Gene translation is a central process in all living organisms. Developing a better understanding of this complex process may have ramifications to almost every biomedical discipline. Recently, Reuveni et al. proposed a new computational model of this process called the ribosome flow model (RFM). In this study, we show that the dynamical behavior of the RFM is relatively simple. There exists a unique equilibrium point e and every trajectory converges to e. Furthermore, convergence is monotone in the sense that the distance to e can never increase. This qualitative behavior is maintained for any feasible set of parameter values, suggesting that the RFM is highly robust. Our analysis is based on a contraction principle and the theory of monotone dynamical systems. These analysis tools may prove useful in studying other properties of the RFM as well as additional intracellular biological processes. PMID:22732691
Linear stability analysis of swirling turbulent flows with turbulence models
NASA Astrophysics Data System (ADS)
Gupta, Vikrant; Juniper, Matthew
2013-11-01
In this paper, we consider the growth of large scale coherent structures in turbulent flows by performing linear stability analysis around a mean flow. Turbulent flows are characterized by fine-scale stochastic perturbations. The momentum transfer caused by these perturbations affects the development of larger structures. Therefore, in a linear stability analysis, it is important to include the perturbations' influence. One way to do this is to include a turbulence model in the stability analysis. This is done in the literature by using eddy viscosity models (EVMs), which are first order turbulence models. We extend this approach by using second order turbulence models, in this case explicit algebraic Reynolds stress models (EARSMs). EARSMs are more versatile than EVMs, in that they can be applied to a wider range of flows, and could also be more accurate. We verify our EARSM-based analysis by applying it to a channel flow and then comparing the results with those from an EVM-based analysis. We then apply the EARSM-based stability analysis to swirling pipe flows and Taylor-Couette flows, which demonstrates the main benefit of EARSM-based analysis. This project is supported by EPSRC and Rolls-Royce through a Dorothy Hodgkin Research Fellowship.
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.
Stability Analysis of a Spinning and Precessing Viscoelastic Rotor Model
NASA Astrophysics Data System (ADS)
Bose, S.; Nandi, A.; Neogy, S.
2013-10-01
The present work deals with stability analysis of a spinning and precessing gyroscopic systems, where the spin axis and precession axis intersect at right angle. The nutation speed is zero, the spin and precession speeds are considered to be uniform and the precession axis is located at one end of the shaft. The properties of the shaft material correspond to a four element type linear viscoelastic model. The shaft disk system is assumed to be axially and torsionally stiff. For analysis, a simple rotor has been considered with the rigid disk placed on a massless viscoelastic shaft at specified locations from one end of the shaft. The governing parametric equations for such a rotor are derived in the simultaneously spinning and precessing frame. A stability analysis is performed considering both two- and four-degree of freedom models. The stability borderlines are computed considering spin and precession speeds as parameters. It is shown that though viscoelastic material may appear attractive for its large material damping, for gyroscopic systems it may lead to unstable vibrations.
Stability and Perturbation Analysis on a Model of Cell Chemotaxis
NASA Astrophysics Data System (ADS)
McCann, Colin; Skupsky, Ron; Losert, Wolfgang; Nossal, Ralph
2006-03-01
Many eukaryotic cells respond with directional movement to spatial and/or temporal gradients of small molecules that bind to cell surface receptors. The computational model of a chemotaxing cell developed in [1], which models cells such as neutrophils or Dictyostelium discoideum, is investigated with regard to stability and response to perturbations. A formal stability analysis finds that, when placed in an initial linear gradient, the model is most sensitive to perturbations at a 60-90 degree offset from the direction of the initial gradient. The model also responds most quickly and strongly to external point sources placed in that direction. These responses hold for all four of the model variants developed in [1]. This suggests that the observed `zigzag' behavior of real cell movement in a gradient may be influenced by the nature of the biochemical reactions that control a cell's chemotactic response. This research was funded in by the National Institutes of Health (NIH) and the National Institute of Standards and Technology (NIST). [1] Skupsky, R., W. Losert, and R.J. Nossal. 2005. ``Distinguishing modes of eukaryotic gradient sensing''. Biophys. J. 89:2806--2823
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 an implicitly defined labor market model
NASA Astrophysics Data System (ADS)
Mendes, Diana A.; Mendes, Vivaldo M.
2008-06-01
Until very recently, the pervasive existence of models exhibiting well-defined backward dynamics but ill-defined forward dynamics in economics and finance has apparently posed no serious obstacles to the analysis of their dynamics and stability, despite the problems that may arise from possible erroneous conclusions regarding theoretical considerations and policy prescriptions from such models. A large number of papers have dealt with this problem in the past by assuming the existence of symmetry between forward and backward dynamics, even in the case when the map cannot be invertible either forward or backwards. However, this procedure has been seriously questioned over the last few years in a series of papers dealing with implicit difference equations and inverse limit spaces. This paper explores the search and matching labor market model developed by Bhattacharya and Bunzel [J. Bhattacharya, H. Bunzel, Chaotic Planning Solution in the Textbook Model of Equilibrium Labor Market Search and Matching, Mimeo, Iowa State University, 2002; J. Bhattacharya, H. Bunzel, Economics Bulletin 5 (19) (2003) 1-10], with the following objectives in mind: (i) to show that chaotic dynamics may still be present in the model for acceptable parameter values, (ii) to clarify some open questions related with the admissible dynamics in the forward looking setting, by providing a rigorous proof of the existence of cyclic and chaotic dynamics through the application of tools from symbolic dynamics and inverse limit theory.
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.
Stability analysis of a holographic dark energy model
NASA Astrophysics Data System (ADS)
Banerjee, Narayan; Roy, Nandan
2015-08-01
The stability of interacting holographic dark energy model is discussed. It is found that for some class of the rate of interaction between dark matter and dark energy, the system has a natural solution where the universe had been decelerating in the beginning but finally settles down to an accelerated phase of expansion.
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 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
2012-01-01
Because of the periodically varying aerodynamic and inertial forces of the flapping wings, a hovering or constant-speed flying insect is a cyclically forcing system, and, generally, the flight is not in a fixed-point equilibrium, but in a cyclic-motion equilibrium. Current stability theory of insect flight is based on the averaged model and treats the flight as a fixed-point equilibrium. In the present study, we treated the flight as a cyclic-motion equilibrium and used the Floquet theory to analyse the longitudinal stability of insect flight. Two hovering model insects were considereda 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 NavierStokes 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
Thillainathan, M; Fernandez, G C
2001-01-01
A user-friendly graphical data analysis to perform stability analysis of genotype x environmental interactions, using Tai's stability model and additive main effects and multiplicative interaction (AMMI) biplots, are presented here. This practical approach integrates statistical and graphical analysis tools available in SAS systems and provides user-friendly applications to perform complete stability analyses without writing SAS program statements or using pull-down menu interfaces by running the SAS macros in the background. By using this macro approach, the agronomists and plant breeders can effectively perform stability analysis and spend more time in data exploration, interpretation of graphs, and output, rather than debugging their program errors. The necessary MACRO-CALL files can be downloaded from the author's home page at http://www.ag.unr.edu/gf. The nature and the distinctive features of the graphics produced by these applications are illustrated by using published data. PMID:11535655
[Stability analysis of allelopathic effects of Panax notoginseng on main crops by AMMI model].
Zhang, Zi-long; Hou, Jun-ling; Wang, Wen-quan
2015-01-01
This paper is aimed to study the differences of allelopathic effects of Panax notoginseng under different allelopathic chemicals resources and selection of appropriate rotation crops. The additive main effects and multiplicative interaction ( AMMI) model had been used to evaluate the stability of allelopathic effects of P. notoginseng on the varieties of corn, wheat and rice properly. The model could use not only to evaluate the stability of non-regional trial data but also explore the interaction between the rotation crop genotypes and donor substances more efficiently. Meanwhile, correspondence analysis can be used in the AMMI to evaluate genotype stability and donor substances. Ejingza No. 1 (g6) had stronger allelopathic effects with high stability, but Yunrui No. 1 (g9) which was appropriate rotation crop genotype, had weaker allelopathic effects with high stability. These findings will aid in choosing appropriate rotation crops and establishing proper rotation system. PMID:26080543
Stability analysis of dynamic collaboration model with control signals on two lanes
NASA Astrophysics Data System (ADS)
Li, Zhipeng; Zhang, Run; Xu, Shangzhi; Qian, Yeqing; Xu, Juan
2014-12-01
In this paper, the influence of control signals on the stability of two-lane traffic flow is mainly studied by applying control theory with lane changing behaviors. We present the two-lane dynamic collaboration model with lateral friction and the expressions of feedback control signals. What is more, utilizing the delayed feedback control theory to the two-lane dynamic collaboration model with control signals, we investigate the stability of traffic flow theoretically and the stability conditions for both lanes are derived with finding that the forward and lateral feedback signals can improve the stability of traffic flow while the backward feedback signals cannot achieve it. Besides, direct simulations are conducted to verify the results of theoretical analysis, which shows that the feedback signals have a significant effect on the running state of two vehicle groups, and the results are same with the theoretical analysis.
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 analysis of predator-prey model on the case of aerosol-cloud-precipitation interactions
NASA Astrophysics Data System (ADS)
Sulistyowati, Rita; Kurniadi, Rizal; Srigutomo, Wahyu
2015-09-01
A preliminary study has been performed on the analysis of the stability of predator-prey models in the case of aerosol-cloud-precipitation interactions which initiated by Koren-Feingold. The model consists of two coupled non-linear differential equations describing the development of a population of cloud drop concentration and cloud depth for precipitation. Stability analysis of the models was conducted to understand the stability behavior of systems interactions. In this paper, the analysis focused on the model without delay. The first step was done by determining the equilibrium point of the model equations which yielded 1 non-trivial equilibrium point and 4 trivial equilibrium point. Nontrivial equilibrium point (0,0) associated with the steady state or the absence of precipitation while the non-trivial equilibrium point shows the oscillation behavior in the formation of precipitation. The next step is linearizing the equation around the equilibrium point and calculating of eigenvalues of Jacobian matrix. Evaluation of the eigen values of characteristic equation determined the type of stability. There are saddle node, star point, unstable node, stable node and center. The results of numerical computations was simulated in the form of phase portrait to support the theoretical calculation. Phase portraits show the characteristic of populations growth of cloud depth and drop cloud. In the next research, this analysis will compared to delay model to determine the effect of time delay on the equilibrium point of the system.
Stability analysis of predator-prey model on the case of aerosol-cloud-precipitation interactions
NASA Astrophysics Data System (ADS)
Sulistyowati, Rita; Kurniadi, Rizal; Srigutomo, Wahyu
2015-09-01
A preliminary study has been performed on the analysis of the stability of predator-prey models in the case of aerosol-cloud-precipitation interactions which initiated by Koren-Feingold. The model consists of two coupled non- linear differential equations describing the development of a population of cloud drop concentration and cloud depth for precipitation. Stability analysis of the models was conducted to understand the stability behavior of systems interactions. In this paper, the analysis focused on the model without delay. The first step was done by determining the equilibrium point of the model equations which yielded 1 non-trivial equilibrium point and 4 trivial equilibrium point. Nontrivial equilibrium point (0,0) associated with the steady state or the absence of precipitation while the non-trivial equilibrium point shows the oscillation behavior in the formation of precipitation. The next step is linearizing the equation around the equilibrium point and calculating of eigenvalues of Jacobian matrix. Evaluation of the eigen values of characteristic equation determined the type of stability. There are saddle node, star point, unstable node, stable node and center. The results of numerical computations was simulated in the form of phase portrait to support the theoretical calculation. Phase portraits show the characteristic of populations growth of cloud depth and drop cloud. In the next research, this analysis will compared to delay model to determine the effect of time delay on the equilibrium point of the system.
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.
Analysis of stability and density waves of traffic flow model in an ITS environment
NASA Astrophysics Data System (ADS)
Li, Z.-P.; Liu, Y.-C.
2006-10-01
By introducing relative velocities of arbitrary number of cars ahead into the full velocity difference models (FVDM), we present a forward looking relative velocity model (FLRVM) of cooperative driving control system. To our knowledge, the model is an improvement over the similar extension in the forward looking optimal velocity models (FLOVM), because it is more reasonable and realistic in implement of incorporating intelligent transportation system in traffic. Then the stability criterion is investigated by the linear stability analysis with finding that new consideration theoretically lead to the improvement of the stability of traffic flow, and the validity of our theoretical analysis is confirmed by direct simulations. In addition, nonlinear analysis of the model shows that the three waves: triangular shock wave, soliton wave and kink-antikink wave appear respectively in stable, metastable and unstable regions. These correspond to the solutions of the Burgers equation, Korteweg-de Vries (KdV) equation and modified Korteweg-de Vries (mKdV) equation.
Sensitivity analysis and calibration of a coupled hydrological/slope stability model (TRIGRS)
NASA Astrophysics Data System (ADS)
Zieher, Thomas; Rutzinger, Martin; Perzl, Frank; Meil, Gertraud
2014-05-01
Shallow landslides potentially endanger human living in mountain regions worldwide. In order to prevent impacts of such gravitational mass movements it is necessary to fully understand the processes involved. Shallow landslides are usually understood as gravitational mass movements of the translational, slope-parallel type comprising of a mixture of earth and debris with a maximum depth of 1-2 m. Depending on the degree of saturation the initial sliding can turn into a flow-like movement. Numerous approaches for modelling shallow landslide susceptibility with different degrees of complexity exist. Regardless of the modelling approach it is crucial to provide sufficient field data, mainly on regolith characteristics. As for the TRIGRS (Transient Rainfall Infiltration and Grid-Based Regional Slope-Stability) model, numerous hydraulic and geotechnical parameters have to be known area-wide. Hence, as spatial interpolation of these input parameters is generally problematic in terms of accuracy, calibrating the model accordingly is a crucial step before conducting any simulations. This study presents a sensitivity analysis and the calibration of the coupled hydrological/slope stability model TRIGRS for a study area in Vorarlberg (Austria). The results of the sensitivity analysis show that in case of the stability model cohesion is the driving parameter while for the hydrological model it is the initial depth of the water table and the saturated hydraulic conductivity. The calibration of the stability model was carried out using a landslide inventory assuming completely saturated conditions. The use of geotechnical parameters extracted from literature for mapped soil types generally lead to unlikely stable conditions. In order to simulate mapped landslide initial areas correctly values for soil cohesion had to be adapted. However, the calibration of the stability model generally supports the assumption of saturated conditions. In absence of meteorological or hydrological data the hydrological model was calibrated using the landslide inventory aiming at saturated conditions for the respective landslide initial zones. Simulations conducted with the calibrated input parameters generally lead to conservatively unstable conditions. However, it has to be noted that the TRIGRS model does not account for effects of vegetation on slope hydrology and stability (e.g. interception or root cohesion). This work has been conducted within C3S-ISLS, which is funded by the Austrian Climate and Energy Fund, 5th ACRP Program. http://www.uibk.ac.at/geographie/lidar/c3s/c3s.html
Wissa, Aimy; Calogero, Joseph; Wereley, Norman; Hubbard, James E; Frecker, Mary
2015-01-01
This paper presents the stability analysis of the leading edge spar of a flapping wing unmanned air vehicle with a compliant spine inserted in it. The compliant spine is a mechanism that was designed to be flexible during the upstroke and stiff during the downstroke. Inserting a variable stiffness mechanism into the leading edge spar affects its structural stability. The model for the spar-spine system was formulated in terms of the well-known Mathieu's equation, in which the compliant spine was modeled as a torsional spring with a sinusoidal stiffness function. Experimental data was used to validate the model and results show agreement within 11%. The structural stability of the leading edge spar-spine system was determined analytically and graphically using a phase plane plot and Strutt diagrams. Lastly, a torsional viscous damper was added to the leading edge spar-spine model to investigate the effect of damping on stability. Results show that for the un-damped case, the leading edge spar-spine response was stable and bounded; however, there were areas of instability that appear for a range of spine upstroke and downstroke stiffnesses. Results also show that there exist a damping ratio between 0.2 and 0.5, for which the leading edge spar-spine system was stable for all values of spine upstroke and downstroke stiffnesses. PMID:26502210
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.
NASA Astrophysics Data System (ADS)
Chen, S.; Al-Muntasheri, G.; Abousleiman, Y. N.
2014-12-01
The critical state concept based bounding surface model is one of the most widely used elastoplastic constitutive models for geomaterials, attributed mainly to its essential feature of allowing plastic deformation to occur for stress points within the bounding surface and thus the capability to represent the realistic non-recoverable behaviour of soils and rocks observed under the cyclic loading. This paper develops an implicit integration algorithm for the bounding surface model, using the standard return mapping approach (elastic predictor-plastic corrector), to obtain the updated stresses for the given strain increments. The formulation of the constitutive integration requires the derivation of a supplementary differential equation to describe the evolution of a key variable, i.e., the ratio between the image stress and the current stress quantities. It is essentially an extension of the integration scheme presented in an earlier work used for the simple bounding surface version of modified Cam Clay associated with a substantially simplified hardening rule. The integration algorithm for the bounding surface model is implemented into the finite element analysis commercial program, ABAQUS, through the material interface of UMAT (user defined material subroutine), and then used for the analysis of wellbore stability problem. The predictions from the ABAQUS simulations are generally in excellent agreement with the available analytical solutions, thus demonstrating the accuracy and robustness of the proposed integration scheme.
Stability analysis, nonlinear pulsations and mass loss of models for 55 Cygni (HD 198478)
NASA Astrophysics Data System (ADS)
Yadav, Abhay Pratap; Glatzel, Wolfgang
2016-01-01
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 nonadiabatic stability analysis with respect to radial perturbations is performed and the evolution of instabilities into the nonlinear 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 nonlinear simulations revealed finite amplitude pulsations with periods consistent with the observations. The nonlinear 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.
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.
Viscous Models of Liquid Bridges with Mode-Coupled Feedback Stress: Stability Analysis
NASA Astrophysics Data System (ADS)
Thiessen, David B.; Marston, Philip L.
2000-11-01
Linear viscous models with varying degrees of approximation are tested to describe liquid bridge dynamics in order to explore the stability of mode-coupled feedback stress. Stabilization of a liquid bridge against the Rayleigh-Plateau instability in effective zero gravity has been demonstrated by applying stress distributions with appropriate phasing to the liquid surface which couple into the lowest order unstable mode of the bridge [M. J. Marr-Lyon et al., Phys. Fluids 121, 986-995 (2000)]. In the experimental demonstrations to date, feedback stress has been applied in direct proportion to the measured mode amplitude. The effect of feedback delay in this case is destabilizing. This is a critical factor for certain technologies. The addition of mode velocity information to the feedback system should allow for greater stability in the presence of feedback delay. Simple models of liquid bridge dynamics are used to study the effects of parameters such as feedback gain and delay on the bridge stability.
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.
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, Gbor
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
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.
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
NASA Astrophysics Data System (ADS)
Yang, Da; Jin, Peter (Jing); Pu, Yun; Ran, Bin
2014-02-01
Real-world traffic flow usually contains a mixture of passenger vehicles (PV) and heavy vehicles (HV). In this paper, the four types of car-truck following combinations are considered: the car-following-car case, car-following-truck case, truck-following-car case and truck-following-truck case. The effect of different combinations on the stability of traffic flow is explored by converting the original Bandos optimal velocity (OV) model to a heterogeneous form. A new linear stability analysis method that can derive the stability criterion of the heterogeneous traffic flow mixed by cars and trucks is introduced. Moreover, the effect of the proportions of the four car-truck following combinations on traffic flow is examined through the trajectory analysis. It concludes that the linear stability of the car-truck mixed traffic flow is determined more by the proportions of the different car-truck following scenarios, rather than the numbers of the cars and trucks. Moreover, cars and trucks can both stabilize and destabilize traffic flow depending on the density of the traffic flow and the parameters of the heterogeneous OV model.
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 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
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.
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.
NASA Astrophysics Data System (ADS)
Markovi?, V. M.; ?upi?, .; Ivanovi?, A.; Kolar-Ani?, Lj.
2011-12-01
Stoichiometric network analysis (SNA) represents a powerful mathematical tool for stability analysis of complex stoichiometric networks. Recently, the important improvement of the method has been made, according to which instability relations can be entirely expressed via reaction rates, instead of thus far used, in general case undefined, current rates. Such an improved SNA methodology was applied to the determination of exact instability conditions of the extended model of the hypothalamic-pituitary-adrenal (HPA) axis, a neuroendocrinological system, whose hormone concentrations exert complex oscillatory evolution. For emergence of oscillations, the Hopf bifurcation condition was utilized. Instability relations predicted by SNA showed good correlation with numerical simulation data of the HPA axis model.
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.
Bifurcation analysis and dynamic stability
Washburn, R.B. Jr.; Mehra, R.K.
1980-01-01
Using tools of bifurcation analysis, we examine the long-term behavior of implicit differential equations which are defined by simultaneous ordinary differential equations and implicit algebraic equations. The analysis shows how certain nonlinearities can make the long term behavior of such dynamic systems sensitive to very small amplitude uncertainties and noise. This sensitivity makes the long term behavior practically unpredictable. At the same time the analysis suggests simple stochastic models in case of such unpredictable behavior. Implicit differential equations are often used in modeling the dynamic behavior of electric power systems. Our analysis indicates essential limitations on the ability of such models to predict long term behavior of the system, and it suggests ways to improve the ability of these models to describe important features of long term behavior. This analysis of implicit differential equations has significant implications for the study of the long term dynamic stability of power systems. The analysis also sheds light on the origin and significance of multiple solutions of the load flow equations.
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).
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.
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.
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
Stochastic stability and instability of model ecosystems
NASA Technical Reports Server (NTRS)
Ladde, G. S.; Siljak, D. D.
1975-01-01
In this work, we initiate a stability study of multispecies communities in stochastic environment by using Ito's differential equations as community models. By applying the direct method of Liapunov, we obtain sufficient conditions for stability and instability in the mean of the equilibrium populations. The conditions are expressed in terms of the dominant diagonal property of community matrices, which is a suitable mechanism for resolving the central problem of 'complexity vs stability' in model ecosystems. As a by-product of this analysis we exhibit important structural properties of the stochastic density-dependent models, and establish tolerance of community stability to a broad class of nonlinear time-varying perturbations.
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.
NASA Technical Reports Server (NTRS)
Sevart, F. D.
1971-01-01
An analytical and mechanization study was conducted for two flutter stability augmentation systems. One concept uses only the wing trailing edge control surface. Another concept uses leading and trailing edge control surfaces operating simultaneously. The combined use of leading and trailing edge control surfaces should improve the surface coupling (controllability) with vertical bending and torsional structural modes and decrease the coupling between bending and torsional modes. The study was directed toward stability augmentation systems characteristics for the supersonic transport aircraft.
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.
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)
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.
Dynamic Simulation and Stability Analysis
NASA Technical Reports Server (NTRS)
Frisch, H. P.; Sanborn, J. A.
1985-01-01
Dynamic Interaction Simulation of Controls and Structure (DISCOS) program developed for dynamic simulation and stability analysis of passive and actively controlled spacecraft. In use of DISCOS, physical system undergoing analysis generally described as cluster of contiguous flexible structures (bodies) that comprise mechanical system, such as spacecraft.
Park, G.C.
1983-01-01
A state-of-the-art one-dimensional thermal-hydraulic model has been developed to be used for the linear analysis of nuclear-coupled density-wave oscillations in a boiling water nuclear reactor (BWR). The model accounts for phasic slip, distributed spacers, subcooled boiling, space/time-dependent power distributions and distributed heated wall dynamics. In addition to a parallel channel stability analysis, a detailed model was derived for the BWR loop analysis of both the natural and forced circulation modes of operation. In its final form, this model constitutes a multi-input, multi-output (MIMO) linear system, which features a general nodal neutron kinetics model. Kinetics parameters for use in the kinetics model have been obtained by utilizing self-consistent nodal data and power distributions. The stability characteristics of a typical BWR/4 has been investigated with the Nyquist criterion. The computer implementation of this mode, NUFREQ-N, was used for the parametric study of a typical BWR/4 and comparison were made with existing in-core and out-of-core data. Also, NUFREQ-N was used to analyze the expected stability characteristics of a typical BWR/4. The parametric results revealed important factors influencing BWR stability margin. It was found that NUFREQ-N generally agreed well with out-of-core data. This was especially true for the predicted power-to-flow transfer function, which is the most important transfer function in thermal-hydraulic stability analysis.
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 Marbres 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.
Hernndez-Corts, Pedro; Galindo-Moreno, Pablo; Catena, Andrs; Ortega-Oller, Inmaculada; Salas-Prez, Jos; Gmez-Snchez, 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.
Stability analysis of sleep apnea time series using identified models: a case study.
Aguirre, Luis Antonio; Souza, Alvaro V P
2004-04-01
This paper investigates the use of identified nonlinear multivariable autonomous models in the classification of breathing patterns of a patient with sleep apnea. Details about the identification procedure are provided and the results reported for the case study at hand suggest that identified models could be useful in computer-based monitoring. PMID:15047435
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.
Dynamic simulation and stability analysis
NASA Technical Reports Server (NTRS)
Frisch, H. P.
1979-01-01
Dynamic Interaction Simulation of Controls and Structure (DISCOS) program was developed for dynamic simulation and stability analysis of passive and actively controlled spacecraft. Program is written in FORTRAN IV for batch execution and requires access to finite-element structures program as NASTRAN for flexible-body input data.
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.
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.
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
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.
Enhanced rotor modeling tailored for rub dynamic stability analysis and simulation
NASA Technical Reports Server (NTRS)
Davis, R. R.
1989-01-01
New methods are presented that allow straightforward application of complex nonlinearities to finite element based rotor dynamic analyses. The key features are: (1) the methods can be implemented with existing finite element or dynamic simulation programs, (2) formulation is general for simple application to a wide range of problems, and (3) implementation is simplified because nonlinear aspects are separated from the linear part of the model. The new techniques are illustrated with examples of inertial nonlinearity and torquewhirl which can be important in rubbing turbomachinery. The sample analyses provide new understanding of these nonlinearities which are discussed.
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, Poincar 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
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.
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.
NASA Astrophysics Data System (ADS)
Sreenivasachar, Kannan
2001-07-01
Unified power flow controller (UPFC) has been the most versatile Flexible AC Transmission System (FACTS) device due to its ability to control real and reactive power flow on transmission lines while controlling the voltage of the bus to which it is connected. UPFC being a multi-variable power system controller it is necessary to analyze its effect on power system operation. To study the performance of the UPFC in damping power oscillations using PSCAD-EMTDC software, a de-coupled control system has been designed for the shunt inverter to control the UPFC bus voltage and the DC link capacitor voltage. The series inverter of a UPFC controls the real power flow in the transmission line. One problem associated with using a high gain PI controller (used to achieve fast control of transmission line real power flow) for the series inverter of a UPFC to control the real power flow in a transmission line is the presence of low damping. This problem is solved in this research by using a fuzzy controller. A method to model a fuzzy controller in PSCAD-EMTDC software has also been described. Further, in order to facilitate proper operation between the series and the shunt inverter control system, a new real power coordination controller has been developed and its performance was evaluated. The other problem concerning the operation of a UPFC is with respect to transmission line reactive power flow control. Step changes to transmission line reactive power references have significant impact on the UPFC bus voltage. To reduce the adverse effect of step changes in transmission line reactive power references on the UPFC bus voltage, a new reactive power coordination controller has been designed. Transient response studies have been conducted using PSCAD-EMTDC software to show the improvement in power oscillation damping with UPFC. These simulations include the real and reactive power coordination controllers. Finally, a new control strategy has been proposed for UPFC. In this proposed control strategy, the shunt inverter controls the DC link capacitor voltage and the transmission line reactive power flow. The series inverter controls the transmission line real power flow and the UPFC bus voltage. PSCAD-EMTDC simulations have been conducted to show the viability of the control strategy in damping power oscillations.
Stability analysis of an acoustically levitated disk.
Hu, Junhui; Nakamura, Kentaro; Ueha, Sadayuki
2003-02-01
In this paper, a model is developed for the stability analysis of an acoustically levitated disk on the basis of analyzing eddy acoustic streaming and acoustic viscous stress. In the model, the effect of the acoustic streaming outside the boundary layer that is on the surface of the levitated disk is properly taken into account. Also, the calculation of sound field and acoustic viscous stress is limited to the range that has a dominant effect on the stability. By this method, we obtain a quite accurate solution of the stability coefficient. For the small horizontal shift of a large levitated disk, the model is verified by the good agreement between the experimental and theoretical results. By means of this model and relevant experiments, some factors that affect the stability of the levitated disk are investigated, and useful guidelines for design and application are obtained. It is found that the range from the edge to the outermost nodal circle of the disk-shaped vibrator has a large effect on the stability of the levitated disk. To stabilize the levitated disk by acoustic viscous force, the distance between the edge and the outermost nodal circle of the vibrator must be larger than a critical value, which is determined by the driving frequency and the sound velocity of the fluid between the levitated disk and the vibrator. When this condition is satisfied, increasing the distance between the edge and the outermost nodal circle leads to a decrease in the stability. It is also found that the property of the fluid between the levitated disk and the vibrator has a large effect on the stability. It is easier to stabilize the levitated disk in steam than in air, but more difficult to do so in carbon dioxide and hydrogen. In addition, theoretical results show that increasing the weight per unit area of the levitated object increases the stability for a given vibrator velocity. The distribution of the acoustic viscous stress and the dependence of the stability coefficient and the holding force on the horizontal shift of the levitated disk, which are obtained by this study, also are useful to a better understanding of the stability of the levitated disk. PMID:12625585
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.
NASA Astrophysics Data System (ADS)
Rtzer, K.; Montzka, C.; Bogena, H.; Wagner, W.; Kerr, Y. H.; Kidd, R.; Vereecken, H.
2014-11-01
Since soil moisture is an important influencing factor of the hydrological cycle, knowledge of its spatio-temporal dynamics is crucial for climate and hydrological modeling. In recent years several soil moisture data products from satellite information have become available with global coverage and sub-monthly resolution. Since the remote sensing of soil moisture is an indirect measurement method and influenced by a large number of factors (e.g. atmospheric correction, vegetation, soil roughness, etc.), a comprehensive validation of the resulting soil moisture products is required. However, the coarse spatial resolution of these products hampers the comparison with point-scale in situ measurements. Therefore, upscaling of in situ to the scale of the satellite data is needed. We present the validation results of the soil moisture products of the years 2010-2012 retrieved from the Soil Moisture and Ocean Salinity (SMOS) and the Advanced Scatterometer (ASCAT) for the Rur and Erft catchments in western Germany. For the upscaling of in situ data obtained from three test sites of the Terrestrial Environmental Observatories (TERENO) initiative we used the hydrological model WaSiM ETH. Correlation of the SMOS product to modeled and upscaled soil moisture resulted in a mean correlation coefficient of 0.28 whereas for ASCAT a correlation coefficient of 0.50 was obtained. However, for specific regions the SMOS product showed similar correlation coefficients as the ASCAT product. While for ASCAT correlation was mainly dependent on topography and vegetation, SMOS was also influenced by radiofrequency interferences in our study area. Both products show dry biases as compared to the soil moisture reference. However, while SMOS showed relatively constant bias values, ASCAT bias is variable throughout the year. As an additional validation method we performed a temporal stability analysis of the retrieved spatio-temporal soil moisture data. Through investigation of mean relative differences of soil moisture for every pixel, their standard deviations and their rankings, we analyzed the temporal persistence of spatial patterns. Our results show high standard deviations for both SMOS and ASCAT soil moisture products as compared to modeled soil moisture, indicating a lower temporal persistence. The consistence of ranks of mean relative differences was low for SMOS and relative ASCAT soil moisture compared to modeled soil moisture, while ASCAT soil moisture, converted to absolute values, showed higher rank consistence.
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.
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)
Iwens, R. P.; Yu, Y.; Triner, J. E.
1975-01-01
Using state variable representation a nonlinear, discrete-time system is derived that models the converter exactly. This system is linearized about its steady state solution, and converter stability, transient response and audio susceptibility are studied. The steady state solution of the converter is stable if and only if all the roots of the linearized system are absolutely less than unity. Excellent agreement with laboratory test data has been observed.
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.
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.
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.
Park, G.C.; Podowski, M.; Becker, M.; Lahey, R.T., Jr.
1983-07-01
A state-of-the-art one-dimensional thermal-hydraulic model has been developed to be used for the linear analysis of nuclear-coupled density-wave oscillations in a boiling water nuclear reactor (BWR). The model accounts for phasic slip, distributed spacers, subcooled boiling, space/time-dependent power distributions and distributed heated wall dynamics. In addition to a parallel channel stability analysis, a detailed model was derived for the BWR loop analysis of both the natural and forced circulation modes of operation. In its final form, this model constitutes a multi-input, multi-output(MIMO) linear system, which features a general nodal neutron kinetics model. The computer implementation of this model, NUFREQ-N, was used for the parametric study of a typical BWR/4 and comparisons were made with existing in-core and out-of-core data. Also, NUFREQ-N was used to analyze the expected stability characteristics of a typical BWR/4.
Li, S.; Pons, R. . Dept. of Fisica); Zhang, Y. . Telecommunications Engineering Dept.)
1994-08-01
In this paper, the authors study a laser using a nonlinear Fabry-Perot etalon as a cavity mirror. First, using the semiclassical laser theory and the differential equation for the lossy nonlinear Fabry-Perot etalon, they develop dynamic equations describing this system for single-mode operation. In this model, the frequency-pulling effect, a finite response time of the nonlinear medium, and a finite-cavity round-trip time of the Fabry-Perot etalon are included. Second, based on this model, they analyze the stability of this laser and give some numerical results. The results show that (1) this system can exist in the stable state and in the unstable state; (2) there are not only saddle-node bifurcations but also Hopf bifurcations; (3) the detuning parameter will effect the characteristics of the bistability and the number and distribution of Hopf bifurcation points.
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 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.
NASA Technical Reports Server (NTRS)
Smith, Arthur F.
1985-01-01
Results of wind tunnel tests at low forward speed for blade dynamic response and stability of three 62.2 cm (24.5 in) diameter models of the Prop-Fan, advanced turboprop, are presented. Measurements of dynamic response were made with the rotors mounted on an isolated nacelle, with varying tilt for nonuniform inflow. Low speed stall flutter tests were conducted at Mach numbers from 0.0 to 0.35. Measurements are compared to Eigen-solution flutter boundaries. Calculated 1P stress response agrees favorably with experiment. Predicted stall flutter boundaries correlate well with measured high stress regions. Stall flutter is significantly reduced by increased blade sweep. Susceptibility to stall flutter decreases rapidly with forward speed.
NASA Astrophysics Data System (ADS)
Chau, K. T.
1999-12-01
This paper further examines the possibility of modelling landslide as a consequence of the unstable slip in a steadily creeping slope when it is subject to perturbations, such as those induced by rainfall and earthquakes. In particular, the one-state variable friction law used in the landslide analysis by Chau is extended to a two-state variable friction law. According to this state variable friction law, the shear strength () along the slip surface depends on the creeping velocity (V) as well as the two state variables (1 and 2), which evolve with the ongoing slip. For translational slides, a system of three coupled non-linear first-order ordinary differential equations is formulated, and a linear stability analysis is applied to study the stability in the neighbourhood of the equilibrium solution of the system. By employing the stability classification of Reyn for three-dimensional space, it is found that equilibrium state (or critical point) of a slope may change from a stable spiral to a saddle spiral with unstable plane focus through a transitional state called converging vortex spiral (i.e. bifurcation occurs), as the non-linear parameters of the slip surface evolve with its environmental changes (such as those induced by rainfall or human activities). If the one-state variable friction law is used in landslide modelling, velocity strengthening (i.e. d
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.
Concrete gravity dam stability analysis
Morris, D.
1992-09-01
Under Federal Energy Regulatory Commission (FERC) guidelines, dam owners must evaluate the stability of their structures every five years. Because traditional approaches typically yield overly conservative stability estimates, EPRI sponsored the development of a computer code, CG-DAMS, to provide more-realistic assessments that reflect site-specific conditions. This finite-element code-which is available in mainframe, workstation, and personal computer versions-can be used to predict crack growth, shear, and stress under a variety of loads.
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.
Slope stability analysis of Valles Marineris, Mars
NASA Astrophysics Data System (ADS)
Vittorio De Blasio, Fabio; Battista Crosta, Giovanni; Castellanza, Riccardo; Utili, Stefano
2013-04-01
Valles Marineris (VM) in the equatorial area of Mars exhibits several gravitational failures which resulted in a series of large landslides up to several hundred cubic kilometers in volume. Questions arise as to forces at play and rock strength in the stability of the walls of VM. In this work we address the stability analysis of the walls of VM by considering the strength of the materials of the chasma walls and the causes of landslides. Using finite element calculations and the limit analysis upper bound method, we explore the range of cohesion and friction angle values associated to realistic failure geometries, and compare predictions with the classical Culmann's wedge model. Our analysis is based both on synthetic, simplified slope profiles and also on the real shape of the walls of VM taken from the MOLA topographic data. Validation of the calibrated cohesion and friction angle values is performed by comparing the computed unstable cross sectional areas with the observed pre- and post-failure profiles and estimated failure surface geometry. This offers a link between rock mass properties, slope geometry and volume of the observed failure. Pseudo-static seismic analyses generated another set of dimensionless charts. Our pseudo-static analyses show that low seismicity events induced by meteoroids impacts compatible with the size of craters could be a cause for some of the observed landslides if poor rock properties for VM is assumed.
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.
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
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.
Bonner, Tara F; Colbrunn, Robb W; Bottros, John J; Mutnal, Amar B; Greeson, Clay B; Klika, Alison K; van den Bogert, Antonie J; Barsoum, Wael K
2015-06-01
The acetabular labrum provides mechanical stability to the hip joint in extreme positions where the femoral head is disposed to subluxation. We aimed to quantify the isolated labrum's stabilizing value. Five human cadaveric hips were mounted to a robotic manipulator, and subluxation potential tests were run with and without labrum. Three-dimensional (3D) kinematic data were quantified using the stability index (Colbrunn et al., 2013, "Impingement and Stability of Total Hip Arthroplasty Versus Femoral Head Resurfacing Using a Cadaveric Robotics Model," J. Orthop. Res., 31(7), pp. 1108-1115). Global and regional stability indices were significantly greater with labrum intact than after total labrectomy for both anterior and posterior provocative positions. In extreme positions, the labrum imparts significant overall mechanical resistance to hip subluxation. Regional stability contributions vary with joint orientation. PMID:25759977
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 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
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.
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. )
1993-11-08
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/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.
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.
Convective instability in sedimentation: Linear stability analysis
NASA Astrophysics Data System (ADS)
Yu, Xiao; Hsu, Tian-Jian; Balachandar, S.
2013-01-01