Science.gov

Sample records for aeromechanical stability analysis

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

    NASA Astrophysics Data System (ADS)

    Liu, Qiang; Chattopadhyay, Aditi

    2000-06-01

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

  2. Aeromechanical stability analysis of a multirotor vehicle model representing a hybrid heavy lift airship (HHLA)

    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.

  3. Application of GRASP to nonlinear analysis of a cantilever beam. [General Rotorcraft Aeromechanical Stability Program

    NASA Technical Reports Server (NTRS)

    Hinnant, Howard E.; Hodges, Dewey H.

    1987-01-01

    The General Rotorcraft Aeromechanical Stability Program (GRASP) was developed to analyze the steady-state and linearized dynamic behavior of rotorcraft in hovering and axial flight conditions. Because of the nature of problems GRASP was created to solve, the geometrically nonlinear behavior of beams is one area in which the program must perform well in order to be of any value. Numerical results obtained from GRASP are compared to both static and dynamic experimental data obtained for a cantilever beam undergoing large displacements and rotations caused by deformation. The correlation is excellent in all cases.

  4. Application of GRASP (General Rotorcraft Aeromechanical Stability Program) to nonlinear analysis of a cantilever beam

    NASA Technical Reports Server (NTRS)

    Hinnant, Howard E.; Hodges, Dewey H.

    1987-01-01

    The General Rotorcraft Aeromechanical Stability Program (GRASP) was developed to analyse the steady-state and linearized dynamic behavior of rotorcraft in hovering and axial flight conditions. Because of the nature of problems GRASP was created to solve, the geometrically nonlinear behavior of beams is one area in which the program must perform well in order to be of any value. Numerical results obtained from GRASP are compared to both static and dynamic experimental data obtained for a cantilever beam undergoing large displacements and rotations caused by deformations. The correlation is excellent in all cases.

  5. Influence of various unsteady aerodynamic models on the aeromechanical stability of a helicopter in ground resonance

    NASA Technical Reports Server (NTRS)

    Friedmann, P. P.; Venkatesan, C.

    1985-01-01

    The aeromechanical stability of a helicopter in ground resonance was analyzed, by incorporating five different aerodynamic models in the coupled rotor/fuselage analysis. The sensitivity of the results to changes in aerodynamic modelling was carefully examined. The theoretical results were compared with experimental data and useful conclusions are drawn regarding the role of aerodynamic modeling on this aeromechanical stability problem. The aerodynamic model which provided the best all around correlation with the experimental data was identified.

  6. Bearingless rotor aeromechanical stability measurements and correlations using nonlinear aerodynamics

    NASA Technical Reports Server (NTRS)

    Wang, James M.; Chopra, Inderjit

    1990-01-01

    The aeromechanical stability of a 1/8th Froude scaled bearingless rotor model was investigated experimentally in a wind tunnel. Both shaft-fixed and shaft-free conditions were examined to study the aeroelastic stability of a bearingless rotor without the incorporation of auxiliary dampers. This wind tunnel investigation generated a set of stability data for four different advance ratios, and a wide range of collective pitch settings. Theoretical analysis was performed using the newly developed University of Maryland Advanced Rotorcraft Code (UMARC). For analysis, the blade is modeled as an elastic beam undergoing flap bending, lag bending, elastic twist, and axial deformation. Blade response is calculated using a finite element method in time. Nonlinear aerodynamic effects are included by using a semiempirical stall modeling. The linearized periodic rotor perturbation equations in the nonrotating frame are solved for stability roots using Floquet transition matrix theory, as well as constant coefficient approximation. The predicted results are compared with the experimental data.

  7. Rotorcraft aeromechanical stability-methodology assessment. Phase 2: Workshop

    NASA Technical Reports Server (NTRS)

    Bousman, William G.

    1990-01-01

    Helicopter rotor aeroelastic and aeromechanical stability predictions for four data sets were made using industry and government stability analyses and compared with data at a workshop held at Ames Research Center, August 2-3, 1988. The present report contains the workshop comparisons.

  8. An experimental investigation of the aeromechanical stability of a hingeless rotor in hover and forward flight

    NASA Technical Reports Server (NTRS)

    Yeager, William T., Jr.; Hamouda, M-Nabil H.; Mantay, Wayne R.

    1987-01-01

    Analysis and testing were conducted in the Langley Transonic Dynamics Tunnel to investigate the aeromechanical stability of a soft inplane hingeless rotor model. Rotor stability data were obtained in hover and in forward flight up to an advance ratio of 0.35. Model rotor parameters evaluated were blade sweep and droop, pre-cone of the blade feathering axis, and blade pitch-flap coupling. Data obtained during these tests are presented without analysis.

  9. Aeromechanics Analysis of a Boundary Layer Ingesting Fan

    NASA Technical Reports Server (NTRS)

    Bakhle, Milind A.; Reddy, T. S. R.; Herrick, Gregory P.; Shabbir, Aamir; Florea, Razvan V.

    2013-01-01

    Boundary layer ingesting propulsion systems have the potential to significantly reduce fuel burn but these systems must overcome the challe nges related to aeromechanics-fan flutter stability and forced response dynamic stresses. High-fidelity computational analysis of the fan a eromechanics is integral to the ongoing effort to design a boundary layer ingesting inlet and fan for fabrication and wind-tunnel test. A t hree-dimensional, time-accurate, Reynolds-averaged Navier Stokes computational fluid dynamics code is used to study aerothermodynamic and a eromechanical behavior of the fan in response to both clean and distorted inflows. The computational aeromechanics analyses performed in th is study show an intermediate design iteration of the fan to be flutter-free at the design conditions analyzed with both clean and distorte d in-flows. Dynamic stresses from forced response have been calculated for the design rotational speed. Additional work is ongoing to expan d the analyses to off-design conditions, and for on-resonance conditions.

  10. General Rotorcraft Aeromechanical Stability Program (GRASP): Theory manual

    NASA Technical Reports Server (NTRS)

    Hodges, Dewey H.; Hopkins, A. Stewart; Kunz, Donald L.; Hinnant, Howard E.

    1990-01-01

    The general rotorcraft aeromechanical stability program (GRASP) was developed to calculate aeroelastic stability for rotorcraft in hovering flight, vertical flight, and ground contact conditions. GRASP is described in terms of its capabilities and its philosophy of modeling. The equations of motion that govern the physical system are described, as well as the analytical approximations used to derive them. The equations include the kinematical equation, the element equations, and the constraint equations. In addition, the solution procedures used by GRASP are described. GRASP is capable of treating the nonlinear static and linearized dynamic behavior of structures represented by arbitrary collections of rigid-body and beam elements. These elements may be connected in an arbitrary fashion, and are permitted to have large relative motions. The main limitation of this analysis is that periodic coefficient effects are not treated, restricting rotorcraft flight conditions to hover, axial flight, and ground contact. Instead of following the methods employed in other rotorcraft programs. GRASP is designed to be a hybrid of the finite-element method and the multibody methods used in spacecraft analysis. GRASP differs from traditional finite-element programs by allowing multiple levels of substructure in which the substructures can move and/or rotate relative to others with no small-angle approximations. This capability facilitates the modeling of rotorcraft structures, including the rotating/nonrotating interface and the details of the blade/root kinematics for various types. GRASP differs from traditional multibody programs by considering aeroelastic effects, including inflow dynamics (simple unsteady aerodynamics) and nonlinear aerodynamic coefficients.

  11. Milestones in Rotorcraft Aeromechanics

    NASA Technical Reports Server (NTRS)

    Johnson, Wayne

    2011-01-01

    The subject of this paper is milestones in rotorcraft aeromechanics. Aeromechanics covers much of what the engineer needs: performance, loads, vibration, stability, flight dynamics, noise. These topics cover many of the key performance attributes, and many of the often-encountered problems in rotorcraft designs. A milestone is a critical achievement, a turning point, an event marking a significant change or stage in development. The milestones identified and discussed include the beginnings of aeromechanics with autogyro analysis, ground resonance, aeromechanics books, unsteady aerodynamics and airloads, nonuniform inflow and wakes, beams and dynamics, comprehensive analysis, computational fluid dynamics, and rotor airloads tests. The focus on milestones limits the scope of the history, but allows the author to acknowledge his choices for key steps in the development of the science and engineering of rotorcraft.

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

    NASA Astrophysics Data System (ADS)

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

    2000-08-01

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

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

    NASA Technical Reports Server (NTRS)

    Venkatesan, C.; Friedmann, P. P.

    1987-01-01

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

  14. Aeromechanical stability of helicopters with composite rotor blades in forward flight

    NASA Technical Reports Server (NTRS)

    Smith, Edward C.; Chopra, Inderjit

    1992-01-01

    The aeromechanical stability, including air resonance in hover, air resonance in forward flight, and ground resonance, of a helicopter with elastically tailored composite rotor blades is investigated. Five soft-inplane hingeless rotor configurations, featuring elastic pitch-lag, pitch-flap and extension-torsion couplings, are analyzed. Elastic couplings introduced through tailored composite blade spars can have a powerful effect on both air and ground resonance behavior. Elastic pitch-flap couplings (positive and negative) strongly affect body, rotor and dynamic inflow modes. Air resonance stability is diminished by elastic pitch-flap couplings in hover and forward flight. Negative pitch-lag elastic coupling has a stabilizing effect on the regressive lag mode in hover and forward flight. The negative pitch-lag coupling has a detrimental effect on ground resonance stability. Extension-torsion elastic coupling (blade pitch decreases due to tension) decreases regressive lag mode stability in both airborne and ground contact conditions. Increasing thrust levels has a beneficial influence on ground resonance stability for rotors with pitch-flap and extension-torsion coupling and is only marginally effective in improving stability of rotors with pitch-lag coupling.

  15. Effects of Inlet Distortion on Aeromechanical Stability of a Forward-Swept High-Speed Fan

    NASA Technical Reports Server (NTRS)

    Herrick, Gregory P.

    2011-01-01

    Concerns regarding noise, propulsive efficiency, and fuel burn are inspiring aircraft designs wherein the propulsive turbomachines are partially (or fully) embedded within the airframe; such designs present serious concerns with regard to aerodynamic and aeromechanic performance of the compression system in response to inlet distortion. Separately, a forward-swept high-speed fan was developed to address noise concerns of modern podded turbofans; however this fan encounters aeroelastic instability (flutter) as it approaches stall. A three-dimensional, unsteady, Navier-Stokes computational fluid dynamics code is applied to analyze and corroborate fan performance with clean inlet flow. This code, already validated in its application to assess aerodynamic damping of vibrating blades at various flow conditions, is modified and then applied in a computational study to preliminarily assess the effects of inlet distortion on aeroelastic stability of the fan. Computational engineering application and implementation issues are discussed, followed by an investigation into the aeroelastic behavior of the fan with clean and distorted inlets.

  16. A computational analysis of the aerodynamic and aeromechanical behavior of the purdue multistage compressor

    NASA Astrophysics Data System (ADS)

    Monk, David James Winchester

    Compressor design programs are becoming more reliant on computational tools to predict and optimize aerodynamic and aeromechanical behavior within a compressor. Recent trends in compressor development continue to push for more efficient, lighter weight, and higher performance machines. To meet these demands, designers must better understand the complex nature of the inherently unsteady flow physics inside of a compressor. As physical testing can be costly and time prohibitive, CFD and other computational tools have become the workhorse during design programs. The objectives of this research were to investigate the aerodynamic and aeromechanical behavior of the Purdue multistage compressor, as well as analyze novel concepts for reducing rotor resonant responses in compressors. Advanced computational tools were utilized to allow an in-depth analysis of the flow physics and structural characteristics of the Purdue compressor, and complement to existing experimental datasets. To analyze the aerodynamic behavior of the compressor a Rolls-Royce CFD code, developed specifically for multistage turbomachinery flows, was utilized. Steady-state computations were performed using the RANS solver on a single-passage mesh. Facility specific boundary conditions were applied to the model, increasing the model fidelity and overall accuracy of the predictions. Detailed investigations into the overall compressor performance, stage performance, and individual blade row performance were completed. Additionally, separation patterns on stator vanes at different loading conditions were investigated by plotting pathlines near the stator suction surfaces. Stator cavity leakage flows were determined to influence the size and extent of stator hub separations. In addition to the aerodynamic analysis, a Rolls-Royce aeroelastic CFD solver was utilized to predict the forced response behavior of Rotor 2, operating at the 1T mode crossing of the Campbell Diagram. This computational tool couples

  17. Aeromechanical stability augmentation using semi-active friction-based lead-lag damper

    NASA Astrophysics Data System (ADS)

    Agarwal, Sandeep

    2005-11-01

    ground resonance problem. In view of the inherent nonlinearity in the system due to friction phenomena, multiblade transformation from rotating frame to nonrotating frame is not useful. Stability analysis of the system is performed in the rotating frame to gain an understanding of the dynamic characteristics of rotor system with attached semi-active friction based lag dampers. This investigation is extended to the ground resonance stability analysis of a comprehensive UH-60 model within the framework of finite element based multibody dynamics formulations. Simulations are conducted to study the performance of several integrated lag dampers ranging from passive to semi-active ones with varying levels of selectivity. Stability analysis is performed for a nominal range of rotor speeds using Prony's method.

  18. Aeromechanical stability of helicopters with a bearingless main rotor. Part 1: Equations of motion

    NASA Technical Reports Server (NTRS)

    Hodges, D. H.

    1978-01-01

    Equations of motion for a coupled rotor-body system were derived for the purpose of studying air and ground resonance characteristics of helicopters that have bearingless main rotors. For the fuselage, only four rigid body degrees of freedom are considered; longitudinal and lateral translations, pitch, and roll. The rotor is assumed to consist of three or more rigid blades. Each blade is joined to the hub by means of a flexible beam segment (flexbeam or strap). Pitch change is accomplished by twisting the flexbeam with the pitch-control system, the characteristics of which are variable. Thus, the analysis is capable of implicitly treating aeroelastic couplings generated by the flexbeam elastic deflections, the pitch-control system, and the angular offsets of the blade and flexbeam. The linearized equations are written in the nonrotating system retaining only the cyclic rotor modes; thus, they comprise a system of homogeneous ordinary differential equations with constant coefficients. All contributions to the linearized perturbation equations from inertia, gravity, quasi-steady aerodynamics, and the flexbeam equilibrium deflections are retained exactly.

  19. Interfacing comprehensive rotorcraft analysis with advanced aeromechanics and vortex wake models

    NASA Astrophysics Data System (ADS)

    Liu, Haiying

    This dissertation describes three aspects of the comprehensive rotorcraft analysis. First, a physics-based methodology for the modeling of hydraulic devices within multibody-based comprehensive models of rotorcraft systems is developed. This newly proposed approach can predict the fully nonlinear behavior of hydraulic devices, and pressure levels in the hydraulic chambers are coupled with the dynamic response of the system. The proposed hydraulic device models are implemented in a multibody code and calibrated by comparing their predictions with test bench measurements for the UH-60 helicopter lead-lag damper. Predicted peak damping forces were found to be in good agreement with measurements, while the model did not predict the entire time history of damper force to the same level of accuracy. The proposed model evaluates relevant hydraulic quantities such as chamber pressures, orifice flow rates, and pressure relief valve displacements. This model could be used to design lead-lag dampers with desirable force and damping characteristics. The second part of this research is in the area of computational aeroelasticity, in which an interface between computational fluid dynamics (CFD) and computational structural dynamics (CSD) is established. This interface enables data exchange between CFD and CSD with the goal of achieving accurate airloads predictions. In this work, a loose coupling approach based on the delta-airloads method is developed in a finite-element method based multibody dynamics formulation, DYMORE. To validate this aerodynamic interface, a CFD code, OVERFLOW-2, is loosely coupled with a CSD program, DYMORE, to compute the airloads of different flight conditions for Sikorsky UH-60 aircraft. This loose coupling approach has good convergence characteristics. The predicted airloads are found to be in good agreement with the experimental data, although not for all flight conditions. In addition, the tight coupling interface between the CFD program, OVERFLOW

  20. Integrated Aeromechanics with Three-Dimensional Solid-Multibody Structures

    NASA Technical Reports Server (NTRS)

    Datta, Anubhav; Johnson, Wayne

    2014-01-01

    A full three-dimensional finite element-multibody structural dynamic solver is coupled to a three-dimensional Reynolds-averaged Navier-Stokes solver for the prediction of integrated aeromechanical stresses and strains on a rotor blade in forward flight. The objective is to lay the foundations of all major pieces of an integrated three-dimensional rotor dynamic analysis - from model construction to aeromechanical solution to stress/strain calculation. The primary focus is on the aeromechanical solution. Two types of three-dimensional CFD/CSD interfaces are constructed for this purpose with an emphasis on resolving errors from geometry mis-match so that initial-stage approximate structural geometries can also be effectively analyzed. A three-dimensional structural model is constructed as an approximation to a UH-60A-like fully articulated rotor. The aerodynamic model is identical to the UH-60A rotor. For preliminary validation measurements from a UH-60A high speed flight is used where CFD coupling is essential to capture the advancing side tip transonic effects. The key conclusion is that an integrated aeromechanical analysis is indeed possible with three-dimensional structural dynamics but requires a careful description of its geometry and discretization of its parts.

  1. Further Results of Soft-Inplane Tiltrotor Aeromechanics Investigation Using Two Multibody Analyses

    NASA Technical Reports Server (NTRS)

    Masarati, Pierangelo; Quaranta, Giuseppe; Piatak, David J.; Singleton, Jeffrey D.

    2004-01-01

    This investigation focuses on the development of multibody analytical models to predict the dynamic response, aeroelastic stability, and blade loading of a soft-inplane tiltrotor wind-tunnel model. Comprehensive rotorcraft-based multibody analyses enable modeling of the rotor system to a high level of detail such that complex mechanics and nonlinear effects associated with control system geometry and joint deadband may be considered. The influence of these and other nonlinear effects on the aeromechanical behavior of the tiltrotor model are examined. A parametric study of the design parameters which may have influence on the aeromechanics of the soft-inplane rotor system are also included in this investigation.

  2. Fundamental Aeronautics Program Subsonic Rotary Wing Project: Aeromechanics Overview

    NASA Technical Reports Server (NTRS)

    Norman, Thomas

    2012-01-01

    The following presentation will cover the topic of Aeromechanics. This includes, the organization of the SRW project, as well as, the Aeromechanic task areas and corresponding facilities including ARC, GRC, and LARC. This presentation will also be covering Aeromechanics highlights like rotorcraft icing, Apache Active Twist Rotor and many more. Furthermore, near-term plans will also be discussed.

  3. Design optimization and uncertainty quantification for aeromechanics forced response of a turbomachinery blade

    NASA Astrophysics Data System (ADS)

    Modgil, Girish A.

    Gas turbine engines for aerospace applications have evolved dramatically over the last 50 years through the constant pursuit for better specific fuel consumption, higher thrust-to-weight ratio, lower noise and emissions all while maintaining reliability and affordability. An important step in enabling these improvements is a forced response aeromechanics analysis involving structural dynamics and aerodynamics of the turbine. It is well documented that forced response vibration is a very critical problem in aircraft engine design, causing High Cycle Fatigue (HCF). Pushing the envelope on engine design has led to increased forced response problems and subsequently an increased risk of HCF failure. Forced response analysis is used to assess design feasibility of turbine blades for HCF using a material limit boundary set by the Goodman Diagram envelope that combines the effects of steady and vibratory stresses. Forced response analysis is computationally expensive, time consuming and requires multi-domain experts to finalize a result. As a consequence, high-fidelity aeromechanics analysis is performed deterministically and is usually done at the end of the blade design process when it is very costly to make significant changes to geometry or aerodynamic design. To address uncertainties in the system (engine operating point, temperature distribution, mistuning, etc.) and variability in material properties, designers apply conservative safety factors in the traditional deterministic approach, which leads to bulky designs. Moreover, using a deterministic approach does not provide a calculated risk of HCF failure. This thesis describes a process that begins with the optimal aerodynamic design of a turbomachinery blade developed using surrogate models of high-fidelity analyses. The resulting optimal blade undergoes probabilistic evaluation to generate aeromechanics results that provide a calculated likelihood of failure from HCF. An existing Rolls-Royce High Work Single

  4. An Assessment of the State-of-the-art in Multidisciplinary Aeromechanical Analyses

    NASA Technical Reports Server (NTRS)

    Datta, Anubhav; Johnson, Wayne

    2008-01-01

    This paper presents a survey of the current state-of-the-art in multidisciplinary aeromechanical analyses which integrate advanced Computational Structural Dynamics (CSD) and Computational Fluid Dynamics (CFD) methods. The application areas to be surveyed include fixed wing aircraft, turbomachinery, and rotary wing aircraft. The objective of the authors in the present paper, together with a companion paper on requirements, is to lay out a path for a High Performance Computing (HPC) based next generation comprehensive rotorcraft analysis. From this survey of the key technologies in other application areas it is possible to identify the critical technology gaps that stem from unique rotorcraft requirements.

  5. Comprehensive rotorcraft analysis methods

    NASA Technical Reports Server (NTRS)

    Stephens, Wendell B.; Austin, Edward E.

    1988-01-01

    The development and application of comprehensive rotorcraft analysis methods in the field of rotorcraft technology are described. These large scale analyses and the resulting computer programs are intended to treat the complex aeromechanical phenomena that describe the behavior of rotorcraft. They may be used to predict rotor aerodynamics, acoustic, performance, stability and control, handling qualities, loads and vibrations, structures, dynamics, and aeroelastic stability characteristics for a variety of applications including research, preliminary and detail design, and evaluation and treatment of field problems. The principal comprehensive methods developed or under development in recent years and generally available to the rotorcraft community because of US Army Aviation Research and Technology Activity (ARTA) sponsorship of all or part of the software systems are the Rotorcraft Flight Simulation (C81), Dynamic System Coupler (DYSCO), Coupled Rotor/Airframe Vibration Analysis Program (SIMVIB), Comprehensive Analytical Model of Rotorcraft Aerodynamics and Dynamics (CAMRAD), General Rotorcraft Aeromechanical Stability Program (GRASP), and Second Generation Comprehensive Helicopter Analysis System (2GCHAS).

  6. A Closed-Loop Optimal Neural-Network Controller to Optimize Rotorcraft Aeromechanical Behaviour. Volume 1; Theory and Methodology

    NASA Technical Reports Server (NTRS)

    Leyland, Jane Anne

    2001-01-01

    Given the predicted growth in air transportation, the potential exists for significant market niches for rotary wing subsonic vehicles. Technological advances which optimise rotorcraft aeromechanical behaviour can contribute significantly to both their commercial and military development, acceptance, and sales. Examples of the optimisation of rotorcraft aeromechanical behaviour which are of interest include the minimisation of vibration and/or loads. The reduction of rotorcraft vibration and loads is an important means to extend the useful life of the vehicle and to improve its ride quality. Although vibration reduction can be accomplished by using passive dampers and/or tuned masses, active closed-loop control has the potential to reduce vibration and loads throughout a.wider flight regime whilst requiring less additional weight to the aircraft man that obtained by using passive methads. It is ernphasised that the analysis described herein is applicable to all those rotorcraft aeromechanical behaviour optimisation problems for which the relationship between the harmonic control vector and the measurement vector can be adequately described by a neural-network model.

  7. Rotorcraft aeroelastic stability

    NASA Technical Reports Server (NTRS)

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

    1988-01-01

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

  8. A Higher Harmonic Optimal Controller to Optimise Rotorcraft Aeromechanical Behaviour

    NASA Technical Reports Server (NTRS)

    Leyland, Jane Anne

    1996-01-01

    Three methods to optimize rotorcraft aeromechanical behavior for those cases where the rotorcraft plant can be adequately represented by a linear model system matrix were identified and implemented in a stand-alone code. These methods determine the optimal control vector which minimizes the vibration metric subject to constraints at discrete time points, and differ from the commonly used non-optimal constraint penalty methods such as those employed by conventional controllers in that the constraints are handled as actual constraints to an optimization problem rather than as just additional terms in the performance index. The first method is to use a Non-linear Programming algorithm to solve the problem directly. The second method is to solve the full set of non-linear equations which define the necessary conditions for optimality. The third method is to solve each of the possible reduced sets of equations defining the necessary conditions for optimality when the constraints are pre-selected to be either active or inactive, and then to simply select the best solution. The effects of maneuvers and aeroelasticity on the systems matrix are modelled by using a pseudo-random pseudo-row-dependency scheme to define the systems matrix. Cases run to date indicate that the first method of solution is reliable, robust, and easiest to use, and that it was superior to the conventional controllers which were considered.

  9. A Tribute to Professor Rene H. Miller - A Pioneer in Aeromechanics and Rotary Wing Flight Transportation

    NASA Technical Reports Server (NTRS)

    Friedmann, Peretz P.; Johnson, Wayne; Scully, Michael P.

    2011-01-01

    Rene H. Miller (May 19, 1916 January 28, 2003), Emeritus H. N. Slater Professor of Flight Transportation, was one of the most influential pioneers in rotary wing aeromechanics as well as a visionary whose dream was the development of a tilt-rotor based short haul air transportation system. This paper pays a long overdue tribute to his memory and to his extraordinary contributions.

  10. Computational investigations of axial and radial flow compressor aeromechanics

    NASA Astrophysics Data System (ADS)

    Ramakrishnan, Kishore

    The focus of this research is aeromechanics issues in advanced compressors of the type used in modern day high thrust-to-weight ratio aircraft gas turbine engines. The driving factor for the studies undertaken is the High Cycle Fatigue (HCF) failure of gas turbine blades. HCF is a key technology issue in the development and endurance of gas turbine engines that arises primarily due to resonant response of turbomachine blading to unsteady aerodynamic excitation. Because it is a truly coupled nonlinear fluid-structure problem, predicting HCF requires a unified approach to modeling both the fluid and the structure. Considering the serious nature of HCF and the inadequacy of lower order design systems to accurately predict blade vibratory stress, the need to develop advanced predictive tools is pressing. The first aspect of this research therefore addresses the development of a turbomachinery coupled fluid-structure interaction tool to predict flow-induced blade vibration. To this end, the TAM-ALE3D solver is further developed as a derivative of the ALE3D code of Lawrence Livermore National Laboratory. In the second aspect of this research, TAM-ALE3D is validated by predicting viscous blade row unsteady aerodynamics and the modal properties of the stator vane in the baseline configuration of the Purdue Transonic Compressor. It is then used to predict the vane vibratory response excited by rotor wakes at resonance, with the resulting stresses in the range expected. For radial flow compressors, a very limited knowledge base exists on the unsteady aerodynamic and aeroelastic mechanisms that result in HCF. The bulk of this research is thus directed at the understanding of these fundamental unsteady phenomena using TAM-ALE3D as an investigative tool. The energy transfer from the downstream diffuser generated forcing function to the impeller blading is addressed by means of unsteady aerodynamic and aeroelastic analyses. From these computational investigations, the details of

  11. Stability analysis of ecomorphodynamic equations

    NASA Astrophysics Data System (ADS)

    Bärenbold, F.; Crouzy, B.; Perona, P.

    2016-02-01

    In order to shed light on the influence of riverbed vegetation on river morphodynamics, we perform a linear stability analysis on a minimal model of vegetation dynamics coupled with classical one- and two-dimensional Saint-Venant-Exner equations of morphodynamics. Vegetation is modeled as a density field of rigid, nonsubmerged cylinders and affects flow via a roughness change. Furthermore, vegetation is assumed to develop following a logistic dependence and may be uprooted by flow. First, we perform the stability analysis of the reduced one-dimensional framework. As a result of the competitive interaction between vegetation growth and removal through uprooting, we find a domain in the parameter space where originally straight rivers are unstable toward periodic longitudinal patterns. For realistic values of the sediment transport parameter, the dominant longitudinal wavelength is determined by the parameters of the vegetation model. Bed topography is found to adjust to the spatial pattern fixed by vegetation. Subsequently, the stability analysis is repeated for the two-dimensional framework, where the system may evolve toward alternate or multiple bars. On a fixed bed, we find instability toward alternate bars due to flow-vegetation interaction, but no multiple bars. Both alternate and multiple bars are present on a movable, vegetated bed. Finally, we find that the addition of vegetation to a previously unvegetated riverbed favors instability toward alternate bars and thus the development of a single course rather than braiding.

  12. A comparison of theory and experiment for coupled rotor-body stability of a hingeless rotor model in hover under simulated vacuum conditions

    NASA Technical Reports Server (NTRS)

    Bousman, William G.

    1988-01-01

    Two cases were selected for correlation from an experiment that examined the aeromechanical stability of a small-scale model rotor that used tantalum rods instead of blades to simulate vacuum conditions. The first case involved body roll freedom only while the second case included body pitch and roll degrees of freedom together. Analyses from Hughes Helicopters and the U.S. Army Aeromechanics Laboratory were compared with the data and the correlations ranged from poor to good.

  13. 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.

  14. Stability Analysis of ISS Medications

    NASA Technical Reports Server (NTRS)

    Wotring, V. E.

    2014-01-01

    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.

  15. Process Improvement Through Tool Integration in Aero-Mechanical Design

    NASA Technical Reports Server (NTRS)

    Briggs, Clark

    2010-01-01

    Emerging capabilities in commercial design tools promise to significantly improve the multi-disciplinary and inter-disciplinary design and analysis coverage for aerospace mechanical engineers. This paper explores the analysis process for two example problems of a wing and flap mechanical drive system and an aircraft landing gear door panel. The examples begin with the design solid models and include various analysis disciplines such as structural stress and aerodynamic loads. Analytical methods include CFD, multi-body dynamics with flexible bodies and structural analysis. Elements of analysis data management, data visualization and collaboration are also included.

  16. Transition prediction using three dimensional stability analysis

    NASA Technical Reports Server (NTRS)

    Malik, M. R.

    1980-01-01

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

  17. High beta and second stability region transport and stability analysis

    SciTech Connect

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

    1992-09-01

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

  18. Stability analysis of dynamic thin shells

    NASA Astrophysics Data System (ADS)

    Lobo, Francisco S. N.; Crawford, Paulo

    2005-11-01

    We analyse the stability of generic spherically symmetric thin shells to linearized perturbations around static solutions. We include the momentum flux term in the conservation identity, deduced from the 'ADM' constraint and the Lanczos equations. Following the Ishak Lake analysis, we deduce a master equation which dictates the stable equilibrium configurations. Considering the transparency condition, we study the stability of thin shells around black holes, showing that our analysis is in agreement with previous results. Applying the analysis to traversable wormhole geometries, by considering specific choices for the form function, we deduce stability regions and find that the latter may be significantly increased by considering appropriate choices for the redshift function.

  19. Analysis of longwall pillar stability

    SciTech Connect

    Mark, C.

    1987-01-01

    This dissertation proposes a new method for longwall pillar design, developed primarily from underground measurements. This dissertation addresses three areas of direct relevance to longwall pillar design: (1) The magnitude, time-of-arrival, and distribution of the abutment loads applied to longwall pillars; (2) The strength and behavior of coal pillars; (3) The relationship between pillar sizing and entry stability, and other factors affecting the roof/pillar/floor interaction during longwall mining. The research focused on two field studies performed in adjacent longwall panels at a West Virginia coal mine. In each study, measurements of pillar stress, pillar deformation, and entry stability were obtained during and after the approach of the longwall face. Other research included detailed reanalyses of field data from other studies, an in-depth comparative study of available longwall pillar design methods, numerical modeling to determine post-development longwall pillar loads, and an evaluation of two index tests used to determine coal strength. The proposed longwall pillar design method incorporates a new approach to estimating abutment loads hat was developed from the research. The method also employs existing empirical pillar strength formulas that were shown to be applicable to longwall pillars. The proposed design method represents an improvement over the existing methods, because it can be used with designs employing combinations of differently sized pillars, and because it can calculate stability factors for the several different service functions of pillars around a longwall.

  20. Aeromechanics and Aeroacoustics Predictions of the Boeing-SMART Rotor Using Coupled-CFD/CSD Analyses

    NASA Technical Reports Server (NTRS)

    Bain, Jeremy; Sim, Ben W.; Sankar, Lakshmi; Brentner, Ken

    2010-01-01

    This paper will highlight helicopter aeromechanics and aeroacoustics prediction capabilities developed by Georgia Institute of Technology, the Pennsylvania State University, and Northern Arizona University under the Helicopter Quieting Program (HQP) sponsored by the Tactical Technology Office of the Defense Advanced Research Projects Agency (DARPA). First initiated in 2004, the goal of the HQP was to develop high fidelity, state-of-the-art computational tools for designing advanced helicopter rotors with reduced acoustic perceptibility and enhanced performance. A critical step towards achieving this objective is the development of rotorcraft prediction codes capable of assessing a wide range of helicopter configurations and operations for future rotorcraft designs. This includes novel next-generation rotor systems that incorporate innovative passive and/or active elements to meet future challenging military performance and survivability goals.

  1. Selected topics on the active control of helicopter aeromechanical and vibration problems

    NASA Technical Reports Server (NTRS)

    Friedmann, Peretz P.

    1994-01-01

    This paper describes in a concise manner three selected topics on the active control of helicopter aeromechanical and vibration problems. The three topics are as follows: (1) the active control of helicopter air-resonance using an LQG/LTR approach; (2) simulation of higher harmonic control (HHC) applied to a four bladed hingeless helicopter rotor in forward flight; and (3) vibration suppression in forward flight on a hingeless helicopter rotor using an actively controlled, partial span, trailing edge flap, which is mounted on the blade. Only a few selected illustrative results are presented. The results obtained clearly indicate that the partial span, actively controlled flap has considerable potential for vibration reduction in helicopter rotors.

  2. Aeromechanical Evaluation of Smart-Twisting Active Rotor

    NASA Technical Reports Server (NTRS)

    Lim, Joon W.; Boyd, D. Douglas, Jr.; Hoffman, Frauke; van der Wall, Berend G.; Kim, Do-Hyung; Jung, Sung N.; You, Young H.; Tanabe, Yasutada; Bailly, Joelle; Lienard, Caroline; Delrieux, Yves

    2014-01-01

    An investigation of Smart-Twisting Active Rotor (STAR) was made to assess potential benefits of the current active twist rotor concept for performance improvement, vibration reduction, and noise alleviation. The STAR rotor is a 40% Mach-scaled, Bo105 rotor with an articulated flap-lag hinge at 3.5%R and no pre-cone. The 0-5 per rev active twist harmonic inputs were applied for various flight conditions including hover, descent, moderate to high speed level flights, and slowed rotor high advance ratio. For the analysis, the STAR partners used multiple codes including CAMRAD II, S4, HOST, rFlow3D, elsA, and their associated software. At the high thrust level in hover, the 0 per rev active twist with 80% amplitude increased figure of merit (FM) by 0.01-0.02 relative to the baseline. In descent, the largest BVI noise reduction was on the order of 2 to 5 dB at the 3 per rev active twist. In the high speed case (mu = 0.35), the 2 per rev actuation was found to be the most effective in achieving a power reduction as well as a vibration reduction. At the 2 per rev active twist, total power was reduced by 0.65% at the 60 deg active twist phase, and vibration was reduced by 47.6% at the 45 deg active twist phase. The use of the 2 per rev active twist appears effective for vibration reduction. In the high advance ratio case (mu = 0.70), the 0 per rev actuation appeared to have negligible impact on performance improvement. In summary, computational simulations successfully demonstrated that the current active twist concept provided a significant reduction of the maximum BVI noise in descent, a significant reduction of the vibration in the high speed case, a small improvement on rotor performance in hover, and a negligible impact on rotor performance in forward flight.

  3. 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.

  4. 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.

  5. Stability analysis of zigzag boron nitride nanoribbons

    SciTech Connect

    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)

  6. 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.

  7. Stability analysis of unsteady ablation fronts

    SciTech Connect

    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.

  8. Stability analysis of unsteady ablation fronts

    SciTech Connect

    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.

  9. 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.

  10. 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.

  11. Advanced stability analysis for laminar flow control

    NASA Technical Reports Server (NTRS)

    Orszag, S. A.

    1981-01-01

    Five classes of problems are addressed: (1) the extension of the SALLY stability analysis code to the full eighth order compressible stability equations for three dimensional boundary layer; (2) a comparison of methods for prediction of transition using SALLY for incompressible flows; (3) a study of instability and transition in rotating disk flows in which the effects of Coriolis forces and streamline curvature are included; (4) a new linear three dimensional instability mechanism that predicts Reynolds numbers for transition to turbulence in planar shear flows in good agreement with experiment; and (5) a study of the stability of finite amplitude disturbances in axisymmetric pipe flow showing the stability of this flow to all nonlinear axisymmetric disturbances.

  12. An experimental investigation on wind turbine aeromechanics and wake interferences among multiple wind turbines

    NASA Astrophysics Data System (ADS)

    Ozbay, Ahmet

    A comprehensive experimental study was conducted to investigate wind turbine aeromechanics and wake interferences among multiple wind turbines sited in onshore and offshore wind farms. The experiments were carried out in a large-scale Aerodynamic/Atmospheric Boundary Layer (AABL) Wind Tunnel available at Iowa State University. An array of scaled three-blade Horizontal Axial Wind Turbine (HAWT) models were placed in atmospheric boundary layer winds with different mean and turbulence characteristics to simulate the situations in onshore and offshore wind farms. The effects of the important design parameters for wind farm layout optimization, which include the mean and turbulence characteristics of the oncoming surface winds, the yaw angles of the turbines with respect to the oncoming surface winds, the array spacing and layout pattern, and the terrain topology of wind farms on the turbine performances (i.e., both power output and dynamic wind loadings) and the wake interferences among multiple wind turbines, were assessed in detail. The aeromechanic performance and near wake characteristics of a novel dual-rotor wind turbine (DRWT) design with co-rotating or counter-rotating configuration were also investigated, in comparison to a conventional single rotor wind turbine (SRWT). During the experiments, in addition to measuring dynamic wind loads (both forces and moments) and the power outputs of the scaled turbine models, a high-resolution Particle Image Velocity (PIV) system was used to conduct detailed flow field measurements (i.e., both free-run and phase-locked flow fields measurements) to reveal the transient behavior of the unsteady wake vortices and turbulent flow structures behind wind turbines and to quantify the characteristics of the wake interferences among the wind turbines sited in non-homogenous surface winds. A miniature cobra anemometer was also used to provide high-temporal-resolution data at points of interest to supplement the full field PIV

  13. Liapunov stability analysis of spinning flexible spacecraft.

    NASA Technical Reports Server (NTRS)

    Barbera, F. J.; Likins, P.

    1973-01-01

    The attitude stability of a class of spinning flexible spacecraft in a force-free environment is analyzed. The spacecraft is modeled as a rigid core having attached to it a flexible appendage idealized as a collection of elastically interconnected particles. Liapunov stability theorems are employed with the Hamiltonian of the system, constrained through the angular momentum integral so as to admit complete damping, used as a testing function. The Hamiltonian is written in terms of modal coordinates as interpreted by the hybrid coordinate formulation, thus allowing truncation to a level amenable to literal stability analysis. Testing functions are constructed for a spacecraft with an arbitrary (discretized) appendage, and closed form stability criteria are generated for the first mode of a restricted appendage model lying in a plane which contains the center of mass and is orthogonal to the spin axis. The criteria are (except for idealized cases on the stability boundary line in the parameter space) both necessary and sufficient for stability for any spacecraft characterized by the planar appendage model, such as a spacecraft containing solar panels and/or radial booms.

  14. Stock market stability: Diffusion entropy analysis

    NASA Astrophysics Data System (ADS)

    Li, Shouwei; Zhuang, Yangyang; He, Jianmin

    2016-05-01

    In this article, we propose a method to analyze the stock market stability based on diffusion entropy, and conduct an empirical analysis of Dow Jones Industrial Average. Empirical results show that this method can reflect the volatility and extreme cases of the stock market.

  15. Stability Analysis of the Impoundment of Ash

    NASA Astrophysics Data System (ADS)

    Slávik, Ivan

    2013-03-01

    An impoundment is an engineering construction used for the safe deposition of unexploitable waste from industrial and mining facilities. In terms of the legislative requirements of the Slovak Republic, a "Measurements Project" must be developed for each impoundment. In this document the prerequisites for the safe operation of an impoundment, the limit and critical values of the monitored phenomena and the facts influencing the safety of the impoundment and the area endangered by such a site are also defined. The safety and stability of an impoundment are verified according to a "Measurements Project" by considering stability at regular time intervals. This contribution presents, in the form of a parametric study, a stability analysis of an ash impoundment. The stability analysis provides an example of the utilization of an information database of the results of the regular monitoring of the geotechnical properties of the materials forming the impoundment's body and the surrounding rock mass. The stability of the impoundment is expressed for a recent state - without a continuous water level in its body and, at the same time, for a hypothetical limit and critical water level according to the valid "Handling Regulations".

  16. 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.

  17. Master stability analysis in transient spatiotemporal chaos.

    PubMed

    Wackerbauer, Renate

    2007-11-01

    The asymptotic stability of spatiotemporal chaos is difficult to determine, since transient spatiotemporal chaos may be extremely long lived. A master stability analysis reveals that the asymptotic state of transient spatiotemporal chaos in the Gray-Scott system and in the Bär-Eiswirth system is characterized by negative transverse Lyapunov exponents on the attractor of the invariant synchronization manifold. The average lifetime of transient spatiotemporal chaos depends on the number of transverse directions that are unstable along a typical excitation cycle. PMID:18233739

  18. CFD analysis of baffle flame stabilization

    NASA Astrophysics Data System (ADS)

    Chen, Yen-Sen; Farmer, Richard C.

    1991-06-01

    A computational fluid dynamics analysis of ignition and combustion in baffle flame stabilized combustors was developed in order to increase the understanding of combustion efficiency and stability. The objectives of this investigation were to develop and verify a computational model of the ignition and combustion of typical augmenter configurations and to generalize the model for application to the combustion occurring in a generic gas turbine engine with augmenters, upstream vitiation, and a downstream chocked nozzle. Triangular bar and cone stabilized flames were simulated. Quasi-global propane and methane kinetics models were employed in the computation. A more detailed methane-air kinetics model was also used. An ignition procedure was devised by initially providing a 1200 K hot spot near the base to start the flame. The recirculation zone lengths of cold and hot flows were well predicted. Time averaged flow quantities were used for data comparisons since the predicted recirculating zones of the reacting flows were unsteady.

  19. A Renormalisation Group Method. IV. Stability Analysis

    NASA Astrophysics Data System (ADS)

    Brydges, David C.; Slade, Gordon

    2015-05-01

    This paper is the fourth in a series devoted to the development of a rigorous renormalisation group method for lattice field theories involving boson fields, fermion fields, or both. The third paper in the series presents a perturbative analysis of a supersymmetric field theory which represents the continuous-time weakly self-avoiding walk on . We now present an analysis of the relevant interaction functional of the supersymmetric field theory, which permits a nonperturbative analysis to be carried out in the critical dimension . The results in this paper include: proof of stability of the interaction, estimates which enable control of Gaussian expectations involving both boson and fermion fields, estimates which bound the errors in the perturbative analysis, and a crucial contraction estimate to handle irrelevant directions in the flow of the renormalisation group. These results are essential for the analysis of the general renormalisation group step in the fifth paper in the series.

  20. Stability analysis of a polymer coating process

    NASA Astrophysics Data System (ADS)

    Kallel, A.; Hachem, E.; Demay, Y.; Agassant, J. F.

    2015-05-01

    A new coating process involving a short stretching distance (1 mm) and a high draw ratio (around 200) is considered. The resulting thin molten polymer film (around 10 micrometers) is set down on a solid primary film and then covered by another solid secondary film. In experimental studies, periodical fluctuation in the thickness of the coated layer may be observed. The processing conditions markedly influence the onset and the development of these defects and modeling will help our understanding of their origins. The membrane approach which has been commonly used for cast film modeling is no longer valid and two dimensional time dependent models (within the thickness) are developed in the whole domain (upstream die and stretching path). A boundary-value problem with a free surface for the Stokes equations is considered and stability of the free surface is assessed using two different numerical strategies: a tracking strategy combined with linear stability analysis involving computation of leading eigenvalues, and a Level Set capturing strategy coupled with transient stability analysis.

  1. Stability analysis of an autocatalytic protein model

    NASA Astrophysics Data System (ADS)

    Lee, Julian

    2016-05-01

    A self-regulatory genetic circuit, where a protein acts as a positive regulator of its own production, is known to be the simplest biological network with a positive feedback loop. Although at least three components—DNA, RNA, and the protein—are required to form such a circuit, stability analysis of the fixed points of this self-regulatory circuit has been performed only after reducing the system to a two-component system, either by assuming a fast equilibration of the DNA component or by removing the RNA component. Here, stability of the fixed points of the three-component positive feedback loop is analyzed by obtaining eigenvalues of the full three-dimensional Hessian matrix. In addition to rigorously identifying the stable fixed points and saddle points, detailed information about the system can be obtained, such as the existence of complex eigenvalues near a fixed point.

  2. 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.

  3. Stability analysis of lattice Boltzmann methods

    SciTech Connect

    Sterling, J.D.; Chen, Shiyi

    1996-01-01

    The lattice Boltzmann equation describes the evolution of the velocity distribution function on a lattice in a manner that macroscopic fluid dynamical behavior is recovered. Although the equation is a derivative of lattice gas automata, it may be interpreted as a Lagrangian finite-difference method for the numerical simulation of the discrete-velocity Boltzmann equation that makes use of a BGK collision operator. As a result, it is not surprising that numericaI instability of lattice Boltzmann methods have been frequently encountered by researchers. We present an analysis of the stability of perturbations of the particle populations linearized about equilibrium values corresponding to a constant-density uniform mean flow. The linear stability depends on the following parameters: the distribution of the mass at a site between the different discrete speeds, the BGK relaxation time, the mean velocity, and the wave-number of the perturbations. This parameter space is too large to compute the complete stability characteristics. We report some stability results for a subset of the parameter space for a 7-velocity hexagonal lattice, a 9-velocity square lattice, and a 15-velocity cubic lattice. Results common to all three lattices are (1) the BGK relaxation time {tau} must be greater than 1/2 corresponding to positive shear viscosity, (2) there exists a maximum stable mean velocity for fixed values of theother parameters, and (3) as {tau} is increased from 1/2 the maximum stable velocity increases monotonically until some fixed velocity is reached which does not change for larger {tau}.

  4. Stability analysis for laminar flow control, part 1

    NASA Technical Reports Server (NTRS)

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

    1977-01-01

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

  5. Truck Roll Stability Data Collection and Analysis

    SciTech Connect

    Stevens, SS

    2001-07-02

    The principal objective of this project was to collect and analyze vehicle and highway data that are relevant to the problem of truck rollover crashes, and in particular to the subset of rollover crashes that are caused by the driver error of entering a curve at a speed too great to allow safe completion of the turn. The data are of two sorts--vehicle dynamic performance data, and highway geometry data as revealed by vehicle behavior in normal driving. Vehicle dynamic performance data are relevant because the roll stability of a tractor trailer depends both on inherent physical characteristics of the vehicle and on the weight and distribution of the particular cargo that is being carried. Highway geometric data are relevant because the set of crashes of primary interest to this study are caused by lateral acceleration demand in a curve that exceeds the instantaneous roll stability of the vehicle. An analysis of data quality requires an evaluation of the equipment used to collect the data because the reliability and accuracy of both the equipment and the data could profoundly affect the safety of the driver and other highway users. Therefore, a concomitant objective was an evaluation of the performance of the set of data-collection equipment on the truck and trailer. The objective concerning evaluation of the equipment was accomplished, but the results were not entirely positive. Significant engineering apparently remains to be done before a reliable system can be fielded. Problems were identified with the trailer to tractor fiber optic connector used for this test. In an over-the-road environment, the communication between the trailer instrumentation and the tractor must be dependable. In addition, the computer in the truck must be able to withstand the rigors of the road. The major objective--data collection and analysis--was also accomplished. Using data collected by instruments on the truck, a ''bad-curve'' database can be generated. Using this database

  6. Bounded Linear Stability Margin Analysis of Nonlinear Hybrid Adaptive Control

    NASA Technical Reports Server (NTRS)

    Nguyen, Nhan T.; Boskovic, Jovan D.

    2008-01-01

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

  7. Power System Transient Stability Analysis through a Homotopy Analysis Method

    SciTech Connect

    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.

  8. Global stability analysis of electrified jets

    NASA Astrophysics Data System (ADS)

    Rivero-Rodriguez, Javier; Pérez-Saborid, Miguel

    2014-11-01

    Electrospinning is a common process used to produce micro and nano polymeric fibers. In this technique, the whipping mode of a very thin electrified jet generated in an electrospray device is nhanced in order to increase its elongation. In this work, we use a theoretical Eulerian model that describes the kinematics and dynamics of the midline of the jet, its radius and convective velocity. The model equations result from balances of mass, linear and angular momentum applied to any differential slice of the jet together with constitutive laws for viscous forces and moments, as well as appropriate expressions for capillary and electrical forces. As a first step towards computing the complete nonlinear, transient dynamics of the electrified jet, we have performed a global stability analysis of the forementioned equations and compared the results with experimental data obtained by Guillaume et al. [2011] and Guerrero-Millán et al. [2014]. The support of the Ministry of Science and Innovation of Spain (Project DPI 2010-20450-C03-02) is acknowledged.

  9. Electrostatic Analysis of The Nucleosome Stability

    NASA Astrophysics Data System (ADS)

    Fenley, Andrew; Adams, David; Onufriev, Alexey

    2007-03-01

    The wrapping and unwrapping of the DNA around the histone octomer of a nucleosome core particle (NCP) plays a vital role in many cellular processes, such as transcription, replication, and cell differentiation. The exact mechanisms underlying the associated transitions in the NCP are still not well understood. We present a simple, two-state electrostatic model of the NCP that agrees with a number of experiments and suggests mechanisms that could initiate DNA unwrapping in vivo. We present and discuss a 2D phase diagram of the system as a function of ambient salt concentration and the net charge of the histone octomer. The model also predicts the free energy of a NCP at physiological conditions. The stability of the system is strongly dependent on the charge of the histone octomer, hinting at possible modes of control in in vivo (acetylation and/or pH changes). The model permits analytical solutions in the low and high salt limits. The analysis of these solutions suggests simple physical mechanisms behind the observed folding and unfolding behavior at environmental solvent conditions.

  10. Survey of Army/NASA rotorcraft aeroelastic stability research

    NASA Technical Reports Server (NTRS)

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

    1988-01-01

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

  11. Stability analysis of large electric power systems

    SciTech Connect

    Elwood, D.M.

    1993-01-01

    Modern electric power systems are large and complicated, and, in many regions of the world, the generation and transmission systems are operating near their limits. Ensuring the reliable operation of the power system requires engineers to study the response of the system to various disturbances. The responses to large disturbances are examined by numerically solving the nonlinear differential-algebraic equations describing the power system. The response to small disturbances is typically studied via eigenanalysis. The Electric Power Research Institute (EPRI) recently developed the Extended Transient/Mid-term Stability Program (ETMSP) to study large disturbance stability and the Small Signal Stability Program Package (SSSP) to study small signal stability. The primary objectives of the work described in this report were to (1) explore ways of speeding up ETMSP, especially on mid-term voltage stability problems, (2) explore ways of speeding up the Multi-Area Small-Signal Stability program (MASS), one of the codes in SSSP, and (3) explore ways of increasing the size of problem that can be solved by the Cray version of MASS.

  12. Stability Analysis for HIFiRE Experiments

    NASA Technical Reports Server (NTRS)

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

    2012-01-01

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

  13. Stability analysis of spacecraft power systems

    NASA Technical Reports Server (NTRS)

    Halpin, S. M.; Grigsby, L. L.; Sheble, G. B.; Nelms, R. M.

    1990-01-01

    The problems in applying standard electric utility models, analyses, and algorithms to the study of the stability of spacecraft power conditioning and distribution systems are discussed. Both single-phase and three-phase systems are considered. Of particular concern are the load and generator models that are used in terrestrial power system studies, as well as the standard assumptions of load and topological balance that lead to the use of the positive sequence network. The standard assumptions regarding relative speeds of subsystem dynamic responses that are made in the classical transient stability algorithm, which forms the backbone of utility-based studies, are examined. The applicability of these assumptions to a spacecraft power system stability study is discussed in detail. In addition to the classical indirect method, the applicability of Liapunov's direct methods to the stability determination of spacecraft power systems is discussed. It is pointed out that while the proposed method uses a solution process similar to the classical algorithm, the models used for the sources, loads, and networks are, in general, more accurate. Some preliminary results are given for a linear-graph, state-variable-based modeling approach to the study of the stability of space-based power distribution networks.

  14. Stability analysis of automobile driver steering control

    NASA Technical Reports Server (NTRS)

    Allen, R. W.

    1981-01-01

    In steering an automobile, the driver must basically control the direction of the car's trajectory (heading angle) and the lateral deviation of the car relative to a delineated pathway. A previously published linear control model of driver steering behavior which is analyzed from a stability point of view is considered. A simple approximate expression for a stability parameter, phase margin, is derived in terms of various driver and vehicle control parameters, and boundaries for stability are discussed. A field test study is reviewed that includes the measurement of driver steering control parameters. Phase margins derived for a range of vehicle characteristics are found to be generally consistent with known adaptive properties of the human operator. The implications of these results are discussed in terms of driver adaptive behavior.

  15. Analysis of Stabilization Mechanisms in Lifted Flames

    NASA Astrophysics Data System (ADS)

    Navarro-Martinez, S.; Kronenburg, A.

    2009-12-01

    Flame stabilization and the mechanisms that govern the dynamics at the flame base have been subject to numerous studies in recent years. Recent results using a combined Large Eddy Simulation-Conditional Moment Closure (LES-CMC) approach to model the turbulent flow field and the turbulence-chemistry interactions has been successful in predicting flame ignition and stabilization by auto-ignition, but LES-CMCs capability of the accurate modelling of the competition between turbulent quenching and laminar and turbulent flame propagation at the anchor point has not been resolved. This paper will consolidate LES-CMC results by analysing a wide range of lifted flame geometries with different prevailing stabilization mechanisms. The simulations allow a clear distinction of the prevailing stabilization mechanisms for the different flames, LES-CMC accurately predicts the competition between turbulence and chemistry during the auto-ignition process, however, the dynamics of the extinction process and turbulent flame propagation are not well captured. The averaging process inherent in the CMC methods does not allow for an instant response of the transported conditionally averaged reactive species to the changes in the flow conditions and any response of the scalars will therefore be delayed. Stationary or quasi-stationary conditions, however, can be well predicted for all flame configurations.

  16. White Oak Dam stability analysis. Volume I

    SciTech Connect

    Ahmed, S.B.

    1994-01-01

    A parametric study was conducted to evaluate the stability of the White Oak Dam (WOD) embankment and foundation. Slope stability analyses were performed for the upper and lower bound soil properties at three sections of the dam using the PCSTABL4 computer program. Minimum safety factors were calculated for the applicable seismic and static loading conditions. Liquefaction potential of the dam embankment and foundation solid during the seismic event was assessed by using simplified procedures. The WOD is classified as a low hazard facility and the Evaluation Basis Earthquake (EBE) is defined as an earthquake with a magnitude of m{sub b} = 5.6 and a Peak Ground Accelerator (PGA) of 0.13 g. This event is approximately equivalent to a Modified Mercalli Intensity of VI-VIII. The EBE is used to perform the seismic evaluation for slope stability and liquefaction potential. Results of the stability analyses and the liquefaction assessment lead to the conclusion that the White Oak Dam is safe and stable for the static and the seismic events defined in this study. Ogden Environmental, at the request of MMES, has checked and verified the calculations for the critical loading conditions and performed a peer review of this report. Ogden has determined that the WOD is stable under the defined static and seismic loading conditions and the embankment materials are in general not susceptible to liquefaction.

  17. Methods of stability analysis in nonlinear mechanics

    SciTech Connect

    Warnock, R.L.; Ruth, R.D.; Gabella, W.; Ecklund, K.

    1989-01-01

    We review our recent work on methods to study stability in nonlinear mechanics, especially for the problems of particle accelerators, and compare our ideals to those of other authors. We emphasize methods that (1) show promise as practical design tools, (2) are effective when the nonlinearity is large, and (3) have a strong theoretical basis. 24 refs., 2 figs., 2 tabs.

  18. Mathematical modelling and linear stability analysis of laser fusion cutting

    NASA Astrophysics Data System (ADS)

    Hermanns, Torsten; Schulz, Wolfgang; Vossen, Georg; Thombansen, Ulrich

    2016-06-01

    A model for laser fusion cutting is presented and investigated by linear stability analysis in order to study the tendency for dynamic behavior and subsequent ripple formation. The result is a so called stability function that describes the correlation of the setting values of the process and the process' amount of dynamic behavior.

  19. Performance and stability analysis of a photovoltaic power system

    NASA Technical Reports Server (NTRS)

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

    1978-01-01

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

  20. Stability analysis in tachyonic potential chameleon cosmology

    SciTech Connect

    Farajollahi, H.; Salehi, A.; Tayebi, F.; Ravanpak, A. E-mail: a.salehi@guilan.ac.ir E-mail: aravanpak@guilan.ac.ir

    2011-05-01

    We study general properties of attractors for tachyonic potential chameleon scalar-field model which possess cosmological scaling solutions. An analytic formulation is given to obtain fixed points with a discussion on their stability. The model predicts a dynamical equation of state parameter with phantom crossing behavior for an accelerating universe. We constrain the parameters of the model by best fitting with the recent data-sets from supernovae and simulated data points for redshift drift experiment generated by Monte Carlo simulations.

  1. Stability analysis through bifurcation theory, 2

    NASA Astrophysics Data System (ADS)

    Guicheteau, P.

    1993-06-01

    This communication follows a previous communication which was presented in the same Agard Lecture Series (LS 191). In the previous communication, some theoretical foundations of Bifurcation Theory were recalled and a methodology aiming at a systematic prediction of the behavior of non-linear differential equations was presented. This communication mentions some problems which are connected with the introduction of control laws in order to stabilize an unstable dynamic system and presents a brief state of the art related to the determination of the attracting region of a stable equilibrium point.

  2. Sensitivity analysis of hydrodynamic stability operators

    NASA Technical Reports Server (NTRS)

    Schmid, Peter J.; Henningson, Dan S.; Khorrami, Mehdi R.; Malik, Mujeeb R.

    1992-01-01

    The eigenvalue sensitivity for hydrodynamic stability operators is investigated. Classical matrix perturbation techniques as well as the concept of epsilon-pseudoeigenvalues are applied to show that parts of the spectrum are highly sensitive to small perturbations. Applications are drawn from incompressible plane Couette, trailing line vortex flow and compressible Blasius boundary layer flow. Parametric studies indicate a monotonically increasing effect of the Reynolds number on the sensitivity. The phenomenon of eigenvalue sensitivity is due to the non-normality of the operators and their discrete matrix analogs and may be associated with large transient growth of the corresponding initial value problem.

  3. 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.

  4. 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.

  5. Nodal analysis for reactor kinetics and stability. [PWR; BWR

    SciTech Connect

    Park, J.K.; Becker, M.; Park, G.C.

    1983-07-01

    General space kinetics models have been developed for more accurate stability analysis utilizing nodal analysis, a commonly used technique for analyzing power distributions in large power reactors. Kinetics parameters for use in these kinetics models have been properly derived by utilizing self-consistent nodal data and power distributions. The procedure employed in the nodal code SIMULATE has been utilized for power distribution, since that methodology is general and includes various commonly used nodal methods as special cases. Cross sections are correlated as functions of void fraction and exposure. A computer program investigating thermo-hydrodynamic stability, NUFREQ has been modified to accommodate general spatial kinetics models with an improved thermal-hydraulics model. Stability analyses have been performed for density wave oscillations for a representative operating BWR system. Spatial coupling effects on the stability margins were found to be significant.

  6. Equilibrium and Stability Analysis of PEGASUS Plasmas

    NASA Astrophysics Data System (ADS)

    Sontag, Aaron

    2001-10-01

    Magnetic equilibrium analyses of low-A discharges in the PEGASUS Toroidal Experiment have been performed using EFIT and a locally developed code which incorporates a nonlinear least-squares fitting routine coupled to a Grad-Shafranov solver. Induced currents in the continuous, resistive vessel wall are estimated using a time-evolving current filament model and are constrained during the reconstruction by wall-mounted flux loops and B-dot coils. With I_wall/Ip up to 2, the poloidal field due to the walls often dominates early in the discharge. A recent upgrade of the internal magnetics set to include 20 poloidal flux loops, a poloidal array of 20 B-dot coils, and a diamagnetic loop has increased the accuracy of equilibrium reconstructions. Plasmas with A < 1.3, Ip on the order of 0.15 MA, 0.2 < li < 0.8, and betat < 25% have been analyzed. The presence of a broad q ~ 2 region inside the plasma corresponds to the growth of a large 2/1 internal mode. Ideal stability analyses have been performed using DCON.

  7. Analysis of emulsion stability in acrylic dispersions

    NASA Astrophysics Data System (ADS)

    Ahuja, Suresh

    2012-02-01

    Emulsions either micro or nano permit transport or solubilization of hydrophobic substances within a water-based phase. Different methods have been introduced at laboratory and industrial scales: mechanical stirring, high-pressure homogenization, or ultrasonics. In digital imaging, toners may be formed by aggregating a colorant with a latex polymer formed by batch or semi-continuous emulsion polymerization. Latex emulsions are prepared by making a monomer emulsion with monomer like Beta-carboxy ethyl acrylate (β-CEA) and stirring at high speed with an anionic surfactant like branched sodium dodecyl benzene sulfonates , aqueous solution until an emulsion is formed. Initiator for emulsion polymerization is 2-2'- azobis isobutyramide dehydrate with chain transfer agent are used to make the latex. If the latex emulsion is unstable, the resulting latexes produce a toner with larger particle size, broader particle size distribution with relatively higher latex sedimentation, and broader molecular weight distribution. Oswald ripening and coalescence cause droplet size to increase and can result in destabilization of emulsions. Shear thinning and elasticity of emulsions are applied to determine emulsion stability.

  8. Fully Parallel MHD Stability Analysis Tool

    NASA Astrophysics Data System (ADS)

    Svidzinski, Vladimir; Galkin, Sergei; Kim, Jin-Soo; Liu, Yueqiang

    2014-10-01

    Progress on full parallelization of the plasma stability code MARS will be reported. MARS calculates eigenmodes in 2D axisymmetric toroidal equilibria in MHD-kinetic plasma models. It is a powerful tool for studying MHD and MHD-kinetic instabilities and it is widely used by fusion community. Parallel version of MARS is intended for simulations on local parallel clusters. It will be an efficient tool for simulation of MHD instabilities with low, intermediate and high toroidal mode numbers within both fluid and kinetic plasma models, already implemented in MARS. Parallelization of the code includes parallelization of the construction of the matrix for the eigenvalue problem and parallelization of the inverse iterations algorithm, implemented in MARS for the solution of the formulated eigenvalue problem. Construction of the matrix is parallelized by distributing the load among processors assigned to different magnetic surfaces. Parallelization of the solution of the eigenvalue problem is made by repeating steps of the present MARS algorithm using parallel libraries and procedures. Initial results of the code parallelization will be reported. Work is supported by the U.S. DOE SBIR program.

  9. Fully Parallel MHD Stability Analysis Tool

    NASA Astrophysics Data System (ADS)

    Svidzinski, Vladimir; Galkin, Sergei; Kim, Jin-Soo; Liu, Yueqiang

    2013-10-01

    Progress on full parallelization of the plasma stability code MARS will be reported. MARS calculates eigenmodes in 2D axisymmetric toroidal equilibria in MHD-kinetic plasma models. It is a powerful tool for studying MHD and MHD-kinetic instabilities and it is widely used by fusion community. Parallel version of MARS is intended for simulations on local parallel clusters. It will be an efficient tool for simulation of MHD instabilities with low, intermediate and high toroidal mode numbers within both fluid and kinetic plasma models, already implemented in MARS. Parallelization of the code includes parallelization of the construction of the matrix for the eigenvalue problem and parallelization of the inverse iterations algorithm, implemented in MARS for the solution of the formulated eigenvalue problem. Construction of the matrix is parallelized by distributing the load among processors assigned to different magnetic surfaces. Parallelization of the solution of the eigenvalue problem is made by repeating steps of the present MARS algorithm using parallel libraries and procedures. Preliminary results of the code parallelization will be reported. Work is supported by the U.S. DOE SBIR program.

  10. Fully Parallel MHD Stability Analysis Tool

    NASA Astrophysics Data System (ADS)

    Svidzinski, Vladimir; Galkin, Sergei; Kim, Jin-Soo; Liu, Yueqiang

    2015-11-01

    Progress on full parallelization of the plasma stability code MARS will be reported. MARS calculates eigenmodes in 2D axisymmetric toroidal equilibria in MHD-kinetic plasma models. It is a powerful tool for studying MHD and MHD-kinetic instabilities and it is widely used by fusion community. Parallel version of MARS is intended for simulations on local parallel clusters. It will be an efficient tool for simulation of MHD instabilities with low, intermediate and high toroidal mode numbers within both fluid and kinetic plasma models, already implemented in MARS. Parallelization of the code includes parallelization of the construction of the matrix for the eigenvalue problem and parallelization of the inverse iterations algorithm, implemented in MARS for the solution of the formulated eigenvalue problem. Construction of the matrix is parallelized by distributing the load among processors assigned to different magnetic surfaces. Parallelization of the solution of the eigenvalue problem is made by repeating steps of the present MARS algorithm using parallel libraries and procedures. Results of MARS parallelization and of the development of a new fix boundary equilibrium code adapted for MARS input will be reported. Work is supported by the U.S. DOE SBIR program.

  11. Kinematic analysis of rope skipper's stability

    NASA Astrophysics Data System (ADS)

    Ab Ghani, Nor Atikah; Rambely, Azmin Sham

    2014-06-01

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

  12. 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.

  13. Stability over time: Is behavior analysis a trait psychology?

    PubMed Central

    Vyse, Stuart

    2004-01-01

    Historically, behavior analysis and trait psychology have had little in common; however, recent developments in behavior analysis bring it closer to one of the core assumptions of the trait approach: the stability of behavior over time and, to a lesser extent, environments. The introduction of the concept of behavioral momentum and, in particular, the development of molar theories have produced some common features and concerns. Behavior-analytic theories of stability provide improved explanations of many everyday phenomena and make possible the expansion of behavior analysis into areas that have been inadequately addressed. ImagesFigure 1 PMID:22478416

  14. Simple Analysis of Prolate-Spin Attitude Stability

    NASA Astrophysics Data System (ADS)

    Kawase, Sei-Ichiro

    How can a prolate satellite spinning about its axis of minimum moment of inertia be attitude-stabilized using dual spin? To this question, we find a simple, clear answer. We replace the satellite with an equivalent frame model and describe its attitude motion as small deviations from its nominal attitude. We show that a friction-like torque applied to the spin axis reduces its nutation motion, and that a similar torque is generated by a nutation damper on a de-spun platform. Thus, we derive a simple attitude-stability theory using minimal mathematical analysis. This theory is applicable to the spin stabilization of geosynchronous communication satellite.

  15. A comparison of theory and experiment for coupled rotor-body stability of a hingeless rotor model in hover

    NASA Technical Reports Server (NTRS)

    Bousman, William G.

    1988-01-01

    Three cases were selected for correlation from an experiment that examined the aeromechanical stability of a small-scale model of a hingeless rotor and fuselage in hover. The first case examined the stability of a configuration with 0 degree blade pitch so that coupling between dynamic modes was minimized. The second case was identical to the first except the blade pitch was set to 9 degrees which provides flap-lag coupling of the rotor modes. The third case had 9 degrees of blade pitch and also included negative pitch-lag coupling, and therefore was the most highly coupled configuration. Analytical calculations were made by Bell Helicopter Textron, Boeing Vertol, Hughes Helicopters, Sikorsky Aircraft, the U.S. Army Aeromechanics Laboratory, and NASA Ames Research Center and compared to some or all of the experimental cases. Overall, the correlation ranged from very poor-to-poor to good.

  16. 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.

  17. Stability Analysis for a Multi-Camera Photogrammetric System

    PubMed Central

    Habib, Ayman; Detchev, Ivan; Kwak, Eunju

    2014-01-01

    Consumer-grade digital cameras suffer from geometrical instability that may cause problems when used in photogrammetric applications. This paper provides a comprehensive review of this issue of interior orientation parameter variation over time, it explains the common ways used for coping with the issue, and describes the existing methods for performing stability analysis for a single camera. The paper then points out the lack of coverage of stability analysis for multi-camera systems, suggests a modification of the collinearity model to be used for the calibration of an entire photogrammetric system, and proposes three methods for system stability analysis. The proposed methods explore the impact of the changes in interior orientation and relative orientation/mounting parameters on the reconstruction process. Rather than relying on ground truth in real datasets to check the system calibration stability, the proposed methods are simulation-based. Experiment results are shown, where a multi-camera photogrammetric system was calibrated three times, and stability analysis was performed on the system calibration parameters from the three sessions. The proposed simulation-based methods provided results that were compatible with a real-data based approach for evaluating the impact of changes in the system calibration parameters on the three-dimensional reconstruction. PMID:25196012

  18. Pyrosequencing Based Microbial Community Analysis of Stabilized Mine Soils

    NASA Astrophysics Data System (ADS)

    Park, J. E.; Lee, B. T.; Son, A.

    2015-12-01

    Heavy metals leached from exhausted mines have been causing severe environmental problems in nearby soils and groundwater. Environmental mitigation was performed based on the heavy metal stabilization using Calcite and steel slag in Korea. Since the soil stabilization only temporarily immobilizes the contaminants to soil matrix, the potential risk of re-leaching heavy metal still exists. Therefore the follow-up management of stabilized soils and the corresponding evaluation methods are required to avoid the consequent contamination from the stabilized soils. In this study, microbial community analysis using pyrosequencing was performed for assessing the potential leaching of the stabilized soils. As a result of rarefaction curve and Chao1 and Shannon indices, the stabilized soil has shown lower richness and diversity as compared to non-contaminated negative control. At the phyla level, as the degree of contamination increases, most of phyla decreased with only exception of increased proteobacteria. Among proteobacteria, gamma-proteobacteria increased against the heavy metal contamination. At the species level, Methylobacter tundripaludum of gamma-proteobacteria showed the highest relative portion of microbial community, indicating that methanotrophs may play an important role in either solubilization or immobilization of heavy metals in stabilized soils.

  19. Advances in Computational Stability Analysis of Composite Aerospace Structures

    SciTech Connect

    Degenhardt, R.; Araujo, F. C. de

    2010-09-30

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

  20. Analysis of Human Body Bipedal Stability for Neuromotor Disabilities

    NASA Astrophysics Data System (ADS)

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

    2009-04-01

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

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

    SciTech Connect

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

    1992-09-01

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

  2. Stability analysis of the pulmonary liquid bilayer.

    NASA Astrophysics Data System (ADS)

    Halpern, David; Grotberg, James

    2010-11-01

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

  3. Black tea: chemical analysis and stability.

    PubMed

    Li, Shiming; Lo, Chih-Yu; Pan, Min-Hsiung; Lai, Ching-Shu; Ho, Chi-Tang

    2013-01-01

    Tea is the most popular flavored and functional drink worldwide. The nutritional value of tea is mostly from the tea polyphenols that are reported to possess a broad spectrum of biological activities, including anti-oxidant properties, reduction of various cancers, inhibition of inflammation, and protective effects against diabetes, hyperlipidemia and obesity. Tea polyphenols include catechins and gallic acid in green and white teas, and theaflavins and thearubigins as well as other catechin polymers in black and oolong teas. Accurate analysis of black tea polyphenols plays a significant role in the identification of black tea contents, quality control of commercial tea beverages and extracts, differentiation of various contents of theaflavins and catechins and correlations of black tea identity and quality with biological activity, and most importantly, the establishment of the relationship between quantitative tea polyphenol content and its efficacy in animal or human studies. Global research in tea polyphenols has generated much in vitro and in vivo data rationally correlating tea polyphenols with their preventive and therapeutic properties in human diseases such as cancer, and metabolic and cardiovascular diseases etc. Based on these scientific findings, numerous tea products have been developed including flavored tea drinks, tea-based functional drinks, tea extracts and concentrates, and dietary supplements and food ingredients, demonstrating the broad applications of tea and its extracts, particularly in the field of functional food. PMID:23037977

  4. An Efficient and Configurable Preprocessing Algorithm to Improve Stability Analysis.

    PubMed

    Sesia, Ilaria; Cantoni, Elena; Cernigliaro, Alice; Signorile, Giovanna; Fantino, Gianluca; Tavella, Patrizia

    2016-04-01

    The Allan variance (AVAR) is widely used to measure the stability of experimental time series. Specifically, AVAR is commonly used in space applications such as monitoring the clocks of the global navigation satellite systems (GNSSs). In these applications, the experimental data present some peculiar aspects which are not generally encountered when the measurements are carried out in a laboratory. Space clocks' data can in fact present outliers, jumps, and missing values, which corrupt the clock characterization. Therefore, an efficient preprocessing is fundamental to ensure a proper data analysis and improve the stability estimation performed with the AVAR or other similar variances. In this work, we propose a preprocessing algorithm and its implementation in a robust software code (in MATLAB language) able to deal with time series of experimental data affected by nonstationarities and missing data; our method is properly detecting and removing anomalous behaviors, hence making the subsequent stability analysis more reliable. PMID:26540679

  5. Stability Analysis of a Uniformly Heated Channel with Supercritical Water

    SciTech Connect

    Ortega Gomez, T.; Class, A.; Schulenberg, T.; Lahey, R.T. Jr.

    2006-07-01

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

  6. Stability investigations of airfoil flow by global analysis

    NASA Technical Reports Server (NTRS)

    Morzynski, Marek; Thiele, Frank

    1992-01-01

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

  7. Bank stability analysis for fluvial erosion and mass failure

    Technology Transfer Automated Retrieval System (TEKTRAN)

    The central objective of this study was to highlight the differences in magnitude between mechanical and fluvial streambank erosional strength with the purpose of developing a more comprehensive bank stability analysis. Mechanical erosion and ultimately failure signifies the general movement or coll...

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

    EPA Science Inventory

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

  9. Prediction of the biochar carbon stability by thermal analysis

    NASA Astrophysics Data System (ADS)

    Méndez, Ana; Cely, Paola; Plaza, César; Paz-Ferreiro, Jorge; Gascó, Gabriel

    2015-04-01

    Thermal analysis (DTA, DSC, TG and dTG) has been used for decades to characterize carbonaceous materials used as fuels (oil, coal). Our research group has used these techniques for the characterisation of different biochars in order to assess proportions of labile and recalcitrant organic matter and to study the evolution of soil organic matter in soils amended with biochar. Thermal analysis could be used to determine the proximate analysis, i.e., the percentage of humidity, volatile matter and fixed carbon or to calculate the thermostability index, previously identified as a reliable parameter for evaluating the level of stability of organic matter in organic wastes and biochar. Relationship between the stability of biochar, the raw material and the pyrolysis conditions could be established by thermal analysis techniques.

  10. Aeroelastic stability analysis of a Darrieus wind turbine

    SciTech Connect

    Popelka, D.

    1982-02-01

    An aeroelastic stability analysis has been developed for predicting flutter instabilities on vertical axis wind turbines. The analytical model and mathematical formulation of the problem are described as well as the physical mechanism that creates flutter in Darrieus turbines. Theoretical results are compared with measured experimental data from flutter tests of the Sandia 2 Meter turbine. Based on this comparison, the analysis appears to be an adequate design evaluation tool.

  11. Fluid Dynamic and Stability Analysis of a Thin Liquid Sheet

    NASA Technical Reports Server (NTRS)

    McMaster, Matthew S.

    1992-01-01

    Interest in thin sheet flows has recently been renewed due to their potential application in space radiators. Theoretical and experimental studies of the fluid dynamics and stability of thin liquid sheet flows have been carried out in this thesis. A computer program was developed to determine the cross-sectional shape of the edge cylinder given the cross-sectional area of the edge cylinder. A stability analysis was performed on a non-planer liquid sheet. A study was conducted to determine the effects of air resistance on the sheet.

  12. High beta and second stability region transport and stability analysis. Technical progress report

    SciTech Connect

    Hughes, M.H.; Phillps, M.W.; Tood, A.M.M.

    1993-12-01

    This report describes both ideal and resistive MHD stability studies of supershot plasmas in TFTR. The MHD equilibrium and stability modeling of TFTR plasmas has concentrated on those experiments where the safety factor, q, profile was inferred from motional Stark effect measurements (MSE). These are conveniently divided into two groups, first where q is less than unity over some fraction of the plasma radius and, secondly, where q everywhere exceed unity. In the first case, the experimental result that qanalysis pose a major challenge to the validity of ideal MHD theory since these plasmas are usually observed to be free of any coherent 1/1 instability. In the second case where q>l we revisit the resistive stability properties of low {beta}, high q{sub edge} supershots again using MSE q-profiles as a starting point. We find that 2/1 and 3/2 tearing modes can be excited in some circumstances and that the MSE profiles are typically near marginal stability to each of these modes.

  13. Bi-global Stability Analysis of Compressible Open Cavity Flows

    NASA Astrophysics Data System (ADS)

    Sun, Yiyang; Taira, Kunihiko; Cattafesta, Louis; Ukeiley, Lawrence

    2015-11-01

    The effect of compressibility on stability characteristics of rectangular open cavity flows is numerically examined. In our earlier work with two-dimensional direct numerical simulation of open cavity flows, we found that increasing Mach number destabilizes the flow in the subsonic regime but stabilizes the flow in the transonic regime. To further examine the compressibility effect, linear bi-global stability analysis is performed over the same range of Mach numbers to investigate the influence of three-dimensional instabilities in flows over open cavities with length-to-depth ratios of 2 and 6. We identify dominant eigenmodes for varied Mach numbers and spanwise wavelengths with respect to two-dimensional stable and unstable steady states. Over a range of spanwise wavelengths, we reveal the growth/damp rates and frequencies of the dominant global modes. Based on the insights from the present analysis, we compare our findings from global stability analysis with our companion three-dimensional flow control experiments aimed at reducing pressure fluctuation caused by cavity flow unsteadiness. This work was supported by the US Air Force Office of Scientific Research (Grant FA9550-13-1-0091).

  14. Influence of pipeline modeling in stability analysis for severe slugging

    NASA Astrophysics Data System (ADS)

    Azevedo, G. R.; Baliño, J. L.; Burr, K. P.

    2016-06-01

    In this paper a numerical linear stability analysis is performed to a mathematical model for the two-phase flow in a pipeline-riser system. Most of stability criteria and most of the models are based on a simplified pipeline, where it is assumed that the void fraction fluctuation can be neglected. It is evident that a pipeline with a constant void fraction would not be able to capture the flow pattern transition or void fraction propagation waves. Three different models for the pipeline are considered: a lumped parameter model with constant void fraction; a lumped parameter model with time dependent void fraction; a distributed parameter model, with void fraction dependent on time and position. The results showed that a simplified model would lose some stable region for operational conditions, but the complete models would not. As result, a more general modeling is necessary to capture all the influence of the stratified flow over stability and over the pipeline dynamics.

  15. Simple Analysis of Prolate-Spin Attitude Stability

    NASA Astrophysics Data System (ADS)

    Kawase, Sei-Ichiro

    How can a prolate spacecraft spinning about its axis of minimum moment of inertia be attitude-stabilized by using dual spin? To this question, we find a simple, clear answer. We replace the spacecraft with an equivalent point-mass model and describe its attitude motion as small deviations from its nominal attitude. We show that a friction-like torque applied to the spin axis would reduce wobble motions, and that a similar torque is generated by a wobble damper on a de-spun platform. Thus, we derive a simple attitude-stability theory using minimal mathematical analysis, and this theory is applicable to the spin stabilization of geosynchronous communication spacecraft.

  16. Linear stability analysis of three-dimensional compressible boundary layers

    NASA Technical Reports Server (NTRS)

    Malik, Mujeeb R.; Orszag, Steven A.

    1987-01-01

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

  17. Linear stability analysis of inclined two-layer stratified flows

    NASA Astrophysics Data System (ADS)

    Negretti, M. Eletta; Socolofsky, Scott A.; Jirka, Gerhard H.

    2008-09-01

    Two-layer stratified flows are commonly observed in geophysical and environmental contexts. At the interface between the two layers, both velocity shear and buoyancy interplay, resulting in various modes of instability. Results from a temporal linear stability analysis of a two-layer stratified exchange flow under the action of a mean advection are presented, investigating the effect of a mild bottom slope on the stability of the interface. The spatial acceleration is directly included in the governing stability equations. The results demonstrate that increasing the bottom slope has a similar effect on the stability of the flow as does increasing the ratio R of the thickness of the velocity mixing layer δν to that of the density layer δρ as it causes the flow to be more unstable to the Kelvin-Helmholtz instabilities. The transition from Kelvin-Helmholtz modes to stable flow occurs at lower Richardson numbers and wavenumbers compared to the horizontal two-layer flow. Kelvin-Helmholtz modes are decreasingly amplified for 1stability tendency of the interface.

  18. Aero-Mechanical Design Methodology for Subsonic Civil Transport High-Lift Systems

    NASA Technical Reports Server (NTRS)

    vanDam, C. P.; Shaw, S. G.; VanderKam, J. C.; Brodeur, R. R.; Rudolph, P. K. C.; Kinney, D.

    2000-01-01

    In today's highly competitive and economically driven commercial aviation market, the trend is to make aircraft systems simpler and to shorten their design cycle which reduces recurring, non-recurring and operating costs. One such system is the high-lift system. A methodology has been developed which merges aerodynamic data with kinematic analysis of the trailing-edge flap mechanism with minimum mechanism definition required. This methodology provides quick and accurate aerodynamic performance prediction for a given flap deployment mechanism early on in the high-lift system preliminary design stage. Sample analysis results for four different deployment mechanisms are presented as well as descriptions of the aerodynamic and mechanism data required for evaluation. Extensions to interactive design capabilities are also discussed.

  19. Decentralized, cooperative control of multivehicle systems: Design and stability analysis

    NASA Astrophysics Data System (ADS)

    Weitz, Lesley Anne

    2009-12-01

    This dissertation addresses the design and stability analysis of decentralized, cooperative control laws for multivehicle systems. Advances in communication, navigation, and surveillance systems have enabled greater autonomy in multivehicle systems, and there is a shift toward decentralized, cooperative systems for computational efficiency and robustness. In a decentralized control scheme, control inputs are determined onboard each vehicle; therefore, decentralized controllers are more efficient for large numbers of vehicles, and the system is more robust to communication failures and reconfiguration. The design of decentralized, cooperative control laws is explored for a nonlinear vehicle model that can be represented in a double-integrator form. Cooperative controllers are functions of spacing errors with respect to other vehicles in the system, where the communication structure defines the information that is available to each vehicle. Control inputs are selected to achieve internal stability, or zero steady-state spacing errors, between vehicles in the system. Closed-loop equations of motion for the cooperative system can be written in a structural form, where damping and stiffness matrices contain control gains acting on the velocity and positions of the vehicles, respectively. The form of the stiffness matrix is determined by the communication structure, where different communication structures yield different control forms. Communication structures are compared using two structural analysis tools: modal cost and frequency-response functions, which evaluate the response of the multivehicle systems to disturbances. The frequency-response information is shown to reveal the string stability of different cooperative control forms. The effects of time delays in the feedback states of the cooperative control laws on system stability are also investigated. Closed-loop equations of motion are modeled as delay differential equations, and two stability notions are

  20. Progress Toward the Analysis of the Kinetic Stabilizer Concept

    SciTech Connect

    Post, R F; Byers, J A; Cohen, R H; Fowler, T K; Ryutov, D D; Tung, L S

    2005-02-08

    The Kinetic Stabilizer (K-S) concept [1] represents a means for stabilizing axisymmetric mirror and tandem-mirror (T-M) magnetic fusion systems against MHD interchange instability modes. Magnetic fusion research has given us examples of axisymmetric mirror confinement devices in which radial transport rates approach the classical ''Spitzer'' level, i.e. situations in which turbulence if present at all, is at too low a level to adversely affect the radial transport [2,3,4]. If such a low-turbulence condition could be achieved in a T-M system it could lead to a fusion power system that would be simpler, smaller, and easier to develop than one based on closed-field confinement, e.g., the tokamak, where the transport is known to be dominated by turbulence. However, since conventional axisymmetric mirror systems suffer from the MHD interchange instability, the key to exploiting this new opportunity is to find a practical way to stabilize this mode. The K-S represents one avenue to achieving this goal. The starting point for the K-S concept is a theoretical analysis by Ryutov [5]. He showed that a MHD-unstable plasma contained in an axisymmetric mirror cell can be MHD-stabilized by the presence of a low-density plasma on the expanding field lines outside the mirrors. If this plasma communicates well electrically with the plasma in the then this exterior plasma can stabilize the interior, confined, plasma. This stabilization technique was conclusively demonstrated in the Gas Dynamic Trap (GDT) experiment [6] at Novosibirsk, Russia, at mirror-cell plasma beta values of 40 percent. The GDT operates in a high collisionality regime. Thus the effluent plasma leaking through the mirrors, though much lower in density than that of the confined plasma, is still high enough to satisfy the stabilization criterion. This would not, however, be the case in a fusion T-M with axisymmetric plug and central cell fields. In such a case the effluent plasma would be far too low in density to

  1. Linear stability analysis for hydrothermal alteration of kimberlitic rocks

    NASA Astrophysics Data System (ADS)

    Afanasyev, Andrey; Belyaeva, Ekaterina

    2016-06-01

    The influx of groundwater into hot kimberlite deposits results in the reaction of water with olivine-rich rocks. The products of the reaction are serpentine and release of latent heat. The rise of temperature due to the heat release increases the rate of the reaction. Under certain conditions, this self-speeding up of the reaction can result in instabilities associated with a significantly higher final serpentinization in slightly warmer regions of the kimberlite deposit. We conduct linear stability analysis of serpentinization in an isolated volume of porous kimberlitic rocks saturated with water and an inert gas. There is a counteracting interplay between the heat release tending to destabilize the uniform distribution of parameters and the heat conduction tending to stabilize it by smoothing out temperature perturbations. We determine the critical spatial scale separating the parameters where one phenomenon dominates over another. The perturbations of longer-than-critical length grow, whereas the perturbations of shorter-than-critical length fade. The analytical results of the linear stability analysis are supported by direct numerical simulations using a full nonlinear model.

  2. Stability and modal analysis of shock/boundary layer interactions

    NASA Astrophysics Data System (ADS)

    Nichols, Joseph W.; Larsson, Johan; Bernardini, Matteo; Pirozzoli, Sergio

    2016-06-01

    The dynamics of oblique shock wave/turbulent boundary layer interactions is analyzed by mining a large-eddy simulation (LES) database for various strengths of the incoming shock. The flow dynamics is first analyzed by means of dynamic mode decomposition (DMD), which highlights the simultaneous occurrence of two types of flow modes, namely a low-frequency type associated with breathing motion of the separation bubble, accompanied by flapping motion of the reflected shock, and a high-frequency type associated with the propagation of instability waves past the interaction zone. Global linear stability analysis performed on the mean LES flow fields yields a single unstable zero-frequency mode, plus a variety of marginally stable low-frequency modes whose stability margin decreases with the strength of the interaction. The least stable linear modes are grouped into two classes, one of which bears striking resemblance to the breathing mode recovered from DMD and another class associated with revolving motion within the separation bubble. The results of the modal and linear stability analysis support the notion that low-frequency dynamics is intrinsic to the interaction zone, but some continuous forcing from the upstream boundary layer may be required to keep the system near a limit cycle. This can be modeled as a weakly damped oscillator with forcing, as in the early empirical model by Plotkin (AIAA J 13:1036-1040, 1975).

  3. A consistent orbital stability analysis for the GJ 581 system

    SciTech Connect

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

    2014-06-20

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

  4. Real-time Stability Analysis for Disruption Avoidance in ITER

    NASA Astrophysics Data System (ADS)

    Glasser, Alexander; Kolemen, Egemen; Glasser, Alan

    2015-11-01

    ITER is intended to operate at plasma parameters approaching the frontier of achievable stability limits. And yet, plasma disruptions at ITER must be kept to a bare minimum to avoid damage to its plasma-facing structures. These competing goals necessitate real-time plasma stability analysis and feedback control at ITER. This work aims to develop a mechanism for real-time analysis of a large and virulent class of disruptions driven by the rapid growth of ideal MHD unstable modes in tokamak equilibria. Such modes will be identified by a parallelized, low-latency implementation of A.H. Glasser's well-tested DCON (Direct Criterion of Newcomb) code, which measures the energetics of modes in the bulk plasma fluid, as well as M.S. Chance's VACUUM code, which measures the same in the vacuum between the plasma and tokamak chamber wall. Parallelization of these codes is intended to achieve a time-savings of 40x, thereby reducing latency to a timescale of order 100ms and making the codes viable for ideal MHD stability control at ITER. The hardware used to achieve this parallelization will be an Intel Xeon Phi server with 77 cores (308 threads). Supported by the US DOE under DE-AC02-09CH11466.

  5. Flight stability analysis under changes in insect morphology

    NASA Astrophysics Data System (ADS)

    Noest, Robert; Wang, Z. Jane

    2015-11-01

    Insect have an amazing ability to control their flight, being able to perform both fast aerial maneuvers and stable hovering. The insect's neural system has developed various mechanism by which it can control these flying feats, but we expect that insect morphology is equally important in facilitating the aerial control. We perform a computational study using a quasi-steady instantaneous flapping flight model which allows us to freely adapt the insect's morphological parameters. We picked a fruit fly as the basis for the body shape and wing motion, and study the effect of changes to the morphology for a range of wing stroke amplitudes. In each case we determine the periodic flight mode, with the period equal to a single wing beat, and do a Floquet stability analysis of the flight. To interpret our results we will compare the changed morphology to related insects. We discuss the implications of the insects location on the stability diagram.

  6. [Research on the spectral analysis and stability of copper green].

    PubMed

    Li, Man; Wang, Li-Qin; Xia, Yin; Yang, Qiu-Ying

    2013-12-01

    In the history of Chinese pigment, copper green, a pigment, was used in vast territory and for a long time. In the present paper, the nature, spectral characteristics, thermodynamic stability of the four isomers of the basic copper chlorides and also their application in the polychrome relics were discussed. The four isomers can be identified quickly by Raman spectral analysis which is a micro-damage or even a nondestructive technique. The order of their thermodynamic stability is as follows: clinoatacamite>paratacamite>atacamite>botallackite. It was showed that in the relics samples copper green was mostly botallackite and atacamite which were less stable isomers. According to the Ostwald step rule, the environmental monitoring should be strengthened to prevent the change in their physical and chemical structures. PMID:24611389

  7. Analysis of Brace Stiffness Influence on Stability of the Truss

    NASA Astrophysics Data System (ADS)

    Krajewski, M.; Iwicki, P.

    2015-02-01

    The paper is devoted to the numerical and experimental research of stability of a truss with side elastic supports at the top chord. The structure is a model of a real roof truss scaled by factor 1/4. The linear buckling analysis and non-linear static analysis were carried out. The buckling length factor for the compressed top chord was calculated and the limit load for the imperfect truss shell model with respect to brace stiffness was obtained. The relation between brace normal force and loading of the truss is presented. The threshold stiffness of braces necessary to obtain the maximum buckling load was found. The truss load bearing capacity obtained from numerical analysis was compared with Eurocode 3 requirements.

  8. Visual optimality and stability analysis of 3DCT scan positions.

    PubMed

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

    2010-01-01

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

  9. Linear stability analysis for hydrothermal alteration of kimberlitic rocks

    NASA Astrophysics Data System (ADS)

    Afanasyev, Andrey; Belyaeva, Ekaterina

    2016-04-01

    The influx of groundwater into hot kimberlite deposits results in the reaction of water with olivine-rich rocks. The products of the reaction are serpentine and release of latent heat. The rise of temperature due to the heat release increases the rate of the reaction. Under certain conditions, this self-speeding up of the reaction can result in instabilities associated with a significantly higher final serpentinisation in slightly warmer regions of the kimberlite deposit. We conduct linear stability analysis of serpentinisation in an isolated volume of porous kimberlitic rocks saturated with water and an inert gas. There is a counteracting interplay between the heat release tending to destabilise the uniform distribution of parameters and the heat conduction tending to stabilise it by smoothing out temperature perturbations. We determine the critical spatial scale separating the parameters where one phenomenon dominates over another. The perturbations of longer-than-critical length grow, whereas the perturbations of shorter-than-critical length fade. The analytical results of the linear stability analysis are supported by direct numerical simulations using a full nonlinear model. Keywords: Hydrothermal systems, volcaniclastic deposits, phase transitions, instability analysis, numerical solutions

  10. Global stability analysis of turbulent 3D wakes

    NASA Astrophysics Data System (ADS)

    Rigas, Georgios; Sipp, Denis; Juniper, Matthew

    2015-11-01

    At low Reynolds numbers, corresponding to laminar and transitional regimes, hydrodynamic stability theory has aided the understanding of the dynamics of bluff body wake-flows and the application of effective control strategies. However, flows of fundamental importance to many industries, in particular the transport industry, involve high Reynolds numbers and turbulent wakes. Despite their turbulence, such wake flows exhibit organisation which is manifested as coherent structures. Recent work has shown that the turbulent coherent structures retain the shape of the symmetry-breaking laminar instabilities and only those manifest as large-scale structures in the near wake (Rigas et al., JFM vol. 750:R5 2014, JFM vol. 778:R2 2015). Based on the findings of the persistence of the laminar instabilities at high Reynolds numbers, we investigate the global stability characteristics of a turbulent wake generated behind a bluff three-dimensional axisymmetric body. We perform a linear global stability analysis on the experimentally obtained mean flow and we recover the dynamic characteristics and spatial structure of the coherent structures, which are linked to the transitional instabilities. A detailed comparison of the predictions with the experimental measurements will be provided.

  11. Thermal Stability Analysis for Superconducting Coupling Coil in MICE

    SciTech Connect

    Wu, Hong; Wang, Li; Pan, Heng; Guo, XingLong; Green, M.A.

    2010-06-28

    The superconducting coupling coil to be used in the Muon Ionization Cooling Experiment (MICE) with inner radius of 750 mm, length of 285 mm and thickness of 110.4 mm will be cooled by a pair of 1.5 W at 4.2 K cryo-coolers. When the coupling coil is powered to 210 A, it will produce about 7.3 T peak magnetic field at the conductor and it will have a stored energy of 13 MJ. A key issue for safe operation of the coupling coil is the thermal stability of the coil during a charge and discharge. The magnet and its cooling system are designed for a rapid discharge where the magnet is to be discharged in 5400 seconds. The numerical simulation for the thermal stability of the MICE coupling coil has been done using ANSYS. The analysis results show that the superconducting coupling coil has a good stability and can be charged and discharged safely.

  12. Graph theory and stability analysis of protein complex interaction networks.

    PubMed

    Huang, Chien-Hung; Chen, Teng-Hung; Ng, Ka-Lok

    2016-04-01

    Protein complexes play an essential role in many biological processes. Complexes can interact with other complexes to form protein complex interaction network (PCIN) that involves in important cellular processes. There are relatively few studies on examining the interaction topology among protein complexes; and little is known about the stability of PCIN under perturbations. We employed graph theoretical approach to reveal hidden properties and features of four species PCINs. Two main issues are addressed, (i) the global and local network topological properties, and (ii) the stability of the networks under 12 types of perturbations. According to the topological parameter classification, we identified some critical protein complexes and validated that the topological analysis approach could provide meaningful biological interpretations of the protein complex systems. Through the Kolmogorov-Smimov test, we showed that local topological parameters are good indicators to characterise the structure of PCINs. We further demonstrated the effectiveness of the current approach by performing the scalability and data normalization tests. To measure the robustness of PCINs, we proposed to consider eight topological-based perturbations, which are specifically applicable in scenarios of targeted, sustained attacks. We found that the degree-based, betweenness-based and brokering-coefficient-based perturbations have the largest effect on network stability. PMID:26997661

  13. Architectural stability analysis of the rotary-laser scanning technique

    NASA Astrophysics Data System (ADS)

    Xue, Bin; Yang, Xiaoxia; Zhu, Jigui

    2016-03-01

    The rotary-laser scanning technique is an important method in scale measurements due to its high accuracy and large measurement range. This paper first introduces a newly designed measurement station which is able to provide two-dimensional measurement information including the azimuth and elevation by using the rotary-laser scanning technique, then presents the architectural stability analysis of this technique by detailed theoretical derivations. Based on the designed station, a validation using both experiment and simulation is presented in order to verify the analytic conclusion. The results show that the architectural stability of the rotary-laser scanning technique is only affected by the two scanning angles' difference. And the difference which brings the best architectural stability can be calculated by using pre-calibrated parameters of the two laser planes. This research gives us an insight into the rotary-laser scanning technique. Moreover, the measurement accuracy of the rotary-laser scanning technique can be further improved based on the results of the study.

  14. 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.

  15. a Numerical Method for Stability Analysis of Pinned Flexible Mechanisms

    NASA Astrophysics Data System (ADS)

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

    1996-05-01

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

  16. Stability analysis of restricted non-static axial symmetry

    SciTech Connect

    Sharif, M.; Bhatti, M. Zaeem Ul Haq E-mail: mzaeem.math@gmail.com

    2013-11-01

    This paper aims to investigate the instability of very restricted class of non-static axially symmetric spacetime with anisotropic matter configuration. The perturbation scheme is established for the Einstein field equations and conservation laws. The instability range in the Newtonian and post-Newtonian regions are explored by constructing the collapse equation in this scenario. It is found that the adiabatic index plays an important role in the stability analysis which depends upon the physical parameters i.e., energy density and anisotropic pressure of the fluid distribution.

  17. Landslide stability analysis on basis of LIDAR data extraction

    NASA Astrophysics Data System (ADS)

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

    2010-05-01

    Currently, existing contradictory between remediation and acquisition from natural resource induces a series of divergences. With regard to open pit mining, legal regulation requires human to fill back the open pit area with water or recreate new landscape by other materials; on the other hand, human can not help excavating the mining area due to the shortage of power resource. However, to engineering geologists, one coincident problem which takes place not only in filling but also in mining operation should be paid more attention to, i.e. the slope stability analysis within these areas. There are a number of construction activities during remediation or mining process which can directly or indirectly cause slope failure. Lives can be endangered since local failure either while or after remediation; for mining process, slope failure in a bench, which carries a main haul road or is adjacent to human activity area, would be significant catastrophe to the whole mining program. The stability of an individual bench or slope is controlled by several factors, which are geological condition, morphology, climate, excavation techniques and transportation approach. The task which takes the longest time is to collect the morphological data. Consequently, it is one of the most dangerous tasks due to the time consuming in mining field. LIDAR scanning for morphological data collecting can help to skip this obstacle since advantages of LIDAR techniques as follows: • Dynamic range available on the market: from 3 m to beyond 1 km, • Ruggedly designed for demanding field applications, • Compact, easily hand-carried and deployed by a single operator. In 2009, scanning campaigns for 2 open pit quarry have been carried out. The aim for these LIDAR detections is to construct a detailed 3D quarry model and analyze the bench stability to support the filling planning. The 3D quarry surface was built up by using PolyWorks 10.1 on basis of LIDAR data. LIDAR data refining takes an

  18. Wellbore stability analysis during the production of a carbonate reservoir

    NASA Astrophysics Data System (ADS)

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

    2009-04-01

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

  19. Stability analysis of thermocapillary convection in rectangular cavities

    SciTech Connect

    Xu, J.; Zebib, A.

    1996-12-31

    This paper presents stability analysis on thermocapillary convection of acetone (Pr = 4.4) in rectangular cavities using direct numerical simulation. Influence of the Reynolds number (Re) and cavity aspect ratio (Ar) on motion is investigated. Results are exhibited for streamline and isotherm patterns at different values of Re and Ar. Neutral stability curves for transition to time-dependent convection are delineated for this Pr = 4.4 fluid in the Re-Ar plane, and compared with the results for fluids with Pr = 10.0, 6.78 and 1.0. Several interesting features of these diagrams are discussed. One important conclusion the authors have from the comparison is that Ar{sub cr} increases as Pr decreases. Thus, it appears that large values of both Ar and Re are necessary to induce thermocapillary oscillations for small Pr fluids such as liquid metals. On the other hand, energy analysis is performed for the oscillatory flow in the neighborhood of critical points in order to gain insight of mechanisms leading to instability. Results are provided for flows near both critical points with Ar = 3.0.

  20. Stability Analysis of Flow Induced by the Traveling Magnetic Field

    NASA Technical Reports Server (NTRS)

    Mazuruk, Konstantin

    2003-01-01

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

  1. Stability Analysis of Flow Induced by the Traveling Magnetic Field

    NASA Technical Reports Server (NTRS)

    Mazuruk, Konstantin

    2003-01-01

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

  2. Stability of mixed time integration schemes for transient thermal analysis

    NASA Technical Reports Server (NTRS)

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

    1982-01-01

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

  3. Physics-based stability analysis of MOS transistors

    NASA Astrophysics Data System (ADS)

    Ferrara, A.; Steeneken, P. G.; Boksteen, B. K.; Heringa, A.; Scholten, A. J.; Schmitz, J.; Hueting, R. J. E.

    2015-11-01

    In this work, a physics-based model is derived based on a linearization procedure for investigating the electrical, thermal and electro-thermal instability of power metal-oxide-semiconductor (MOS) transistors. The proposed model can be easily interfaced with a circuit or device simulator to perform a failure analysis, making it particularly useful for power transistors. Furthermore, it allows mapping the failure points on a three-dimensional (3D) space defined by the gate-width normalized drain current, drain voltage and junction temperature. This leads to the definition of the Safe Operating Volume (SOV), a powerful frame work for making failure predictions and determining the main root of instability (electrical, thermal or electro-thermal) in different bias and operating conditions. A comparison between the modeled and the measured SOV of silicon-on-insulator (SOI) LDMOS transistors is reported to support the validity of the proposed stability analysis.

  4. Stability analysis of offshore wind farm and marine current farm

    NASA Astrophysics Data System (ADS)

    Shawon, Mohammad Hasanuzzaman

    -trend for large electric energy production using offshore wind generators and marine current generators, respectively. Thus DFIG based offshore wind farm can be an economic solution to stabilize squirrel cage induction generator based marine current farm without installing any addition FACTS devices. This thesis first focuses on the stabilization of fixed speed IG based marine current farm using SDBR. Also stabilization of DFIG based variable speed wind farm utilizing SDBR is studied in this work. Finally a co-operative control strategy is proposed where DFIG is controlled in such a way that it can even provide necessary reactive power demand of induction generator, so that additional cost of FACTS devices can be avoided. In that way, the DFIGs of the offshore wind farm (OWF) will actively compensate the reactive power demand of adjacent IGs of the marine current farm (MCF) during grid fault. Detailed modeling and control scheme for the proposed system are demonstrated considering some realistic scenarios. The power system small signal stability analysis is also carried out by eigenvalue analysis for marine current generator topology, wind turbine generator topology and integrated topology. The relation between the modes and state variables are discussed in light of modal and sensitivity analyses. The results of theoretical analyses are verified by MATLAB/SIMULINK and laboratory standard power system simulator PSCAD/EMTDC.

  5. Adjoint sensitivity analysis of hydrodynamic stability in cyclonic flows

    NASA Astrophysics Data System (ADS)

    Guzman Inigo, Juan; Juniper, Matthew

    2015-11-01

    Cyclonic separators are used in a variety of industries to efficiently separate mixtures of fluid and solid phases by means of centrifugal forces and gravity. In certain circumstances, the vortex core of cyclonic flows is known to precess due to the instability of the flow, which leads to performance reductions. We aim to characterize the unsteadiness using linear stability analysis of the Reynolds Averaged Navier-Stokes (RANS) equations in a global framework. The system of equations, including the turbulence model, is linearised to obtain an eigenvalue problem. Unstable modes corresponding to the dynamics of the large structures of the turbulent flow are extracted. The analysis shows that the most unstable mode is a helical motion which develops around the axis of the flow. This result is in good agreement with LES and experimental analysis, suggesting the validity of the approach. Finally, an adjoint-based sensitivity analysis is performed to determine the regions of the flow that, when altered, have most influence on the frequency and growth-rate of the unstable eigenvalues.

  6. Wellbore stability analysis in carbonate reservoir considering anisotropic behaviour

    NASA Astrophysics Data System (ADS)

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

    2010-05-01

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

  7. Soap Bubble Elasticity: Analysis and Correlation with Foam Stability

    NASA Astrophysics Data System (ADS)

    Karakashev, S. I.; Tsekov, R.; Manev, E. D.; Nguyen, A. V.

    2010-05-01

    A correlation between the elastic modulus of soap bubble and the foam stability was found. A model system was chosen: a soap bubble stabilized by simple nonionic surfactant tetraethylene glycol octyl ether (C8E4) and 10^-5 M NaCl. The Elastic moduli were determined by periodical expansion and shrinking of foam bubbles with frequency of 0.1 Hz and volumetric amplitude of 2 mm 3. The film tension was monitored via commercial profile analysis tensiometer (Sinterface Technologies, GmbH). The elastic moduli of foam bubbles versus surfactant concentration in the range of 2x10^-3 - 10^-2 M were obtained. In addition, the theory of Lucassen and van den Tempel for the elastic modulus of single liquid/air interface at given frequency was exploited as well. The bulk diffusion coefficient of the surfactant molecules is unknown parameter through the adsorption frequency in this theory. Hence, a fitting procedure (with one free parameter) was conducted matching experimental and theoretical data. The value of the bulk diffusion coefficient of C8E4 obtained was 5.1x10^-11 m^2/s, which is an order of magnitude lower value than what is expected for. The foam was generated by shaking method and left to decay. A correlation between the elastic modulus and foam life time upon surfactant concentration was found.

  8. Nonlinear stability analysis, energy exchange and solitons on vortex cores

    NASA Astrophysics Data System (ADS)

    Eftekhari, Kamran

    1999-10-01

    The subject of this dissertation is to develop reliable analytical and numerical methods for the study of the nonlinear stability of a class of slender, incompressible axisymmetric swirling flows. We desire to understanding early nonlinear evolution and possibly gain insight into phenomena such as solitary waves observed on vortex filaments and strongly nonlinear phenomena like vortex breakdown. We use an extension of the method used by Leibovich & Ma [1982] for the development of the equations, which differs in some significant aspects from the formulation of the aforementioned authors. We find, in agreement with Leibovich & Ma [1982], that the complex envelope amplitude of weakly nonlinear asymmetric waves is governed by the cubically nonlinear Schrodinger equation (NLS), however our form for coefficients differs from those of Leibovich & Ma [1982]. Most significantly, our formulation includes an axisymmetric disturbance component at second order (a full order lower than Leibovich & Ma) and thus permits energy exchange between asymmetric and axisymmetric disturbance components. The resulting equations also explicitly demonstrate the possibility of singular points where the group (not phase) velocity of linear disturbance equals the local axial flow velocity (group-velocity critical layer in our terminology) and where the NLS coefficients blow up, thus providing a wavenumber selection mechanism for the weakly nonlinear evolution. After implementation of numerical algorithm, our goal is to investigate the effects of weak nonlinearities on the stability of axisymmetric columnar flows. The analysis is applied to several model vortical flows, namely the Q-vortex and the Batchelor [1964] trailing line vortex.

  9. 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

  10. Bifurcation analysis of aircraft pitching motions near the stability boundary

    NASA Technical Reports Server (NTRS)

    Hui, W. H.; Tobak, M.

    1984-01-01

    Bifuraction theory is used to analyze the nonlinear dynamic stability characteristics of an aircraft subject to single degree of freedom pitching-motion perturbations about a large mean angle of attack. The requisite aerodynamic information in the equations of motion is represented in a form equivalent to the response to finite-amplitude pitching oscillations about the mean angle of attack. This information is deduced from the case of infinitesimal-amplitude oscillations. The bifurcation theory analysis reveals that when the mean angle of attack is increased beyond a critical value at which the aerodynamic damping vanishes, new solutions representing finite-amplitude periodic motions bifurcate from the previously stable steady motion. The sign of a simple criterion, cast in terms of aerodynamic properties, determines whether the bifurcating solutions are stable (supercritical) or unstable (subcritical). For flat-plate airfoils flying at supersonic/hypersonic speed, the bifurcation is subcritical, implying either that exchanges of stability between steady and periodic motion are accompanied by hysteresis phenomena, or that potentially large aperiodic departures from steady motion may develop.

  11. Absolute Stability Analysis of a Phase Plane Controlled Spacecraft

    NASA Technical Reports Server (NTRS)

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

    2010-01-01

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

  12. Models and Stability Analysis of Boiling Water Reactors

    SciTech Connect

    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

  13. Galvanic vestibular stimulation for analysis of postural adaptation and stability.

    PubMed

    Johansson, R; Magnusson, M; Fransson, P A

    1995-03-01

    Human postural dynamics was investigated in 12 normal subjects by means of a force platform recording body sway, induced by bipolar transmastoid galvanic stimulation of the vestibular nerve and labyrinth. The model adopted was that of an inverted segmented pendulum, the dynamics of postural control being assumed to be reflected in the stabilizing forces actuated by the feet as a result of complex muscular activity subject to state feedback of body sway and position. Time-series analysis demonstrates that a transfer function from stimulus to sway-force response with specific parameters can be identified. In addition, adaptation to the vestibular stimulus is demonstrated to exist, and we describe this phenomenon using quantification in terms of a postural adaptation time constant in the range of 40-50 s. The results suggest means to evaluate adaptive behavior and postural control in the erect human being which may be useful in the rehabilitation of individuals striving to regain upright stance. PMID:7698784

  14. Research on Stability Analysis of International Prototype Kilogram

    NASA Astrophysics Data System (ADS)

    Ren, Xiaoping; Zhang, Yue; Wang, Jian; Ren, Qingxiong; Ren, Qingmao

    Today, the kilogram is the last of the seven base units of the International System of Units (SI) which is based on a physical artifact. The demands of modern mass metrology have led to an increasing focus on the surface stability and analysis of mass standard. Methods for evaluating the correlation between the measured mass values of the prototypes of the kilogram includes: collection of historical calibration data for kilogram prototypes, setting up a model for deterministic and random changes in the mass of a kilogram prototype (relative to the IPK), adjustment of parameters in a model using historical calibration data, and prediction of future mass values of a kilogram prototype using model and adjusted parameters.

  15. Symplectic maps for the n-body problem - Stability analysis

    NASA Technical Reports Server (NTRS)

    Wisdom, Jack; Holman, Matthew

    1992-01-01

    The stability of new symplectic n-body maps is examined from the point of view of nonlinear dynamics. The resonances responsible for the principal artifacts are identified. These are resonances between the stepsize and the difference of mean motions between pairs of planets. For larger stepsizes resonant perturbations are evident in the variation of the energy of the system corresponding to these stepsize resonances. It is shown that the principal instability of the method can be predicted and corresponds to the overlap of the stepsize resonances. It is noted that the analysis suggests that other artifacts will occur. For example, the overlap of a stepsize resonance with a resonance of the actual system may also give a region of chaotic behavior that is an artifact. It is pointed out that the fact that the principal artifacts corresponds to a particular set of stepsize resonances suggests that it may be possible to perturbatively remove the effect when the stepsize resonances are nonoverlapping.

  16. Stability analysis and numerical simulation of simplified solid rocket motors

    NASA Astrophysics Data System (ADS)

    Boyer, G.; Casalis, G.; Estivalèzes, J.-L.

    2013-08-01

    This paper investigates the Parietal Vortex Shedding (PVS) instability that significantly influences the Pressure Oscillations of the long and segmented solid rocket motors. The eigenmodes resulting from the stability analysis of a simplified configuration, namely, a cylindrical duct with sidewall injection, are presented. They are computed taking into account the presence of a wall injection defect, which is shown to induce hydrodynamic instabilities at discrete frequencies. These instabilities exhibit eigenfunctions in good agreement with the measured PVS vortical structures. They are successfully compared in terms of temporal evolution and frequencies to the unsteady hydrodynamic fluctuations computed by numerical simulations. In addition, this study has shown that the hydrodynamic instabilities associated with the PVS are the driving force of the flow dynamics, since they are responsible for the emergence of pressure waves propagating at the same frequency.

  17. CFD Based Computations of Flexible Helicopter Blades for Stability Analysis

    NASA Technical Reports Server (NTRS)

    Guruswamy, Guru P.

    2011-01-01

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

  18. Shear-ballooning stability analysis of low-. beta. plasmas

    SciTech Connect

    Yoshikawa, S.

    1981-11-01

    A model of magnetic configurations that has both shear and variation of the field curvature along the magnetic field is constructed. The stability analysis of this system is performed by expanding the perturbation functions to phi/sub 0/ which is constant along the field and phi/sub 1/ which is sinusoidally varied along the field line. The shear term is retained in the form of differntial operations in zeta, the coordinate parallel to the pressure gradient. After several simplifications, the equation reduces itself to the fourth order differential equation. The eigenvalue of this equation is numerically obtained. The calculated critical ..beta.. plotted versus the well depth parameter, h, makes a smooth transition between h < 0 (maximum average B) and h > 0 (minimum average B). Using the same technique, the nondivergent solution to the localized shear mode (Suydam mode) is also obtained by retaining the inertia term.

  19. Stability analysis of three species food chain with competition

    NASA Astrophysics Data System (ADS)

    Abadi, Savitri, D.

    2015-03-01

    We study a food chain system that consists of 1 prey and 2 predators populations. The prey population grows logistically while the predators apply different Holling functional responses. The first predator preys on the prey following Holling type II functional response and the second predator preys on both the prey and the first predator following Holling type II and III functional responses, respectively. The study starts with the stability analysis of critical points of the systems. Then, by using normal form and centre manifold method the information about other nontrivial solutions due to bifurcation including possible limit cycles appearance is obtained. The results are confirmed by numerical simulation using MatCont and biological interpretation of the results are also presented.

  20. GE simplified boiling water reactor stability analysis in time domain

    NASA Astrophysics Data System (ADS)

    Lu, Shanlai

    1997-12-01

    General Electric Simplified Boiling Water Reactor (SBWR) was designed as a next generation light water reactor. It uses natural circulation to remove the heat from the reactor core. Because of this unique in-vessel circulation feature, SBWR is expected to exhibit different stability behaviors. The main emphasis of this thesis is to study the SBWR stability behavior in the time domain. The best-estimate BWR accident/transient analysis computer code, TRAC-BF1, is employed to analyze the SBWR stability behavior. A detailed TRAC-BF1 SBWR model has been developed, which has the capability to model the in-vessel natural circulation and the reactor core kinetics. The model is used to simulate three slow depressurization processes. The simulation results show that the reactor is stable under low pressure and nominal downcomer water level conditions. However, when the downcomer water level is raised to about 19.2 m above the bottom of the reactor vessel, an unstable power oscillation is observed. The identified power oscillation is further analyzed using TRAC-BF1 1-D kinetics and the new TRAC-BF1 3-D kinetics code developed in this thesis. The effects of different time step sizes and vessel model nodalizations are examined. It is found that the power oscillation is in-phase and has a frequency of 0.3 HZ. In order to further explore the physical instabilty initiation mechanisms, a simplified dynamic model consisting of six simple differential equations is developed. The simplified model is able to predict the dominant physical phenomenon identified by the TRAC-BF1 analysis. The results indicate that the system instability is possibly caused by the steam separator hydro-static head oscillation under the high water level condition. In order to explore the higher order spacial effect of power oscillation, a 3-D reactor core kinetics code is coupled with the TRAC-BF1 computer code in the PVM parallel processing environment. A new coupling scheme and a multiple time step marching

  1. Space Shuttle Main Engine real time stability analysis

    NASA Astrophysics Data System (ADS)

    Kuo, F. Y.

    1993-06-01

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

  2. Stability and failure analysis of steering tie-rod

    NASA Astrophysics Data System (ADS)

    Jiang, GongFeng; Zhang, YiLiang; Xu, XueDong; Ding, DaWei

    2008-11-01

    A new car in operation of only 8,000 km, because of malfunction, resulting in lost control and rammed into the edge of the road, and then the basic vehicle scrapped. According to the investigation of the site, it was found that the tie-rod of the car had been broken. For the subjective analysis of the accident and identifying the true causes of rupture of the tierod, a series of studies, from the angle of theory to experiment on the bended broken tie-rod, were conducted. The mechanical model was established; the stability of the defective tie-rod was simulated based on ANSYS software. Meanwhile, the process of the accident was simulated considering the effect of destabilization of different vehicle speed and direction of the impact. Simultaneously, macro graphic test, chemical composition analysis, microstructure analysis and SEM analysis of the fracture were implemented. The results showed that: 1) the toughness of the tie-rod is at a normal level, but there is some previous flaws. One quarter of the fracture surface has been cracked before the accident. However, there is no relationship between the flaw and this incident. The direct cause is the dynamic instability leading to the large deformation of impact loading. 2) The declining safety factor of the tie-rod greatly due to the previous flaws; the result of numerical simulation shows that previous flaw is the vital factor of structure instability, on the basis of the comparison of critical loads of the accident tie-rod and normal. The critical load can decrease by 51.3% when the initial defect increases 19.54% on the cross-sectional area, which meets the Theory of Koiter.

  3. Stability analysis of a bilayer contained within a cylindrical tube

    NASA Astrophysics Data System (ADS)

    Song, Yuanyuan

    Airways in the lung are coated with a liquid bilayer consisting of a serous layer adjacent to a more viscous mucus layer which is contiguous with the air core. An instability due to surface tension at the interfaces may lead to the formation of a liquid plug that blocks the passage of air. This is known as airway closure. A stability analysis is carried out for the case when a Newtonian and immiscible liquid bilayer coats a compliant tube in the presence of an insoluble surfactant monolayer at the mucus-gas interface. A surface active material such as surfactant lowers the surface tension and also generates a surface stress at the interface, both of which are stabilizing, while the wall compliance may accelerate the formation of the liquid bridge. A system of nonlinear coupled equations for the deflections of the interfaces and the surfactant concentration is derived by using an extended lubrication theory analysis. A linear stability study using normal modes is conducted by linearizing the nonlinear evolution equations. A linear eigenvalue problem for the perturbation amplitudes is obtained. Non-trivial solutions are obtained provided the determinant of a linear system is singular. A fourth order polynomial for the growth rate of the disturbances is derived, whose coefficients depend on the wavenumber of the perturbation, the wall characteristics, the Marangoni number, the thickness of the bilayer, the aspect thickness ratio, the viscosity ratio of two liquid layers, and the surface tension ratio. Both stabilizing and destabilizing effects of various system parameters are investigated. A classical lubrication theory model is also derived for cases where a bilayer coats a rigid tube with insoluble surfactant along the liquid-gas interface, and a bilayer coating in a compliant tube with a clean liquid-gas interface. Results serve as a validation of the extended lubrication theory model. The accuracy of the extended lubrication theory model as the bilayer thickness

  4. Linear Stability Analysis of an Acoustically Vaporized Droplet

    NASA Astrophysics Data System (ADS)

    Siddiqui, Junaid; Qamar, Adnan; Samtaney, Ravi

    2015-11-01

    Acoustic droplet vaporization (ADV) is a phase transition phenomena of a superheat liquid (Dodecafluoropentane, C5F12) droplet to a gaseous bubble, instigated by a high-intensity acoustic pulse. This approach was first studied in imaging applications, and applicable in several therapeutic areas such as gas embolotherapy, thrombus dissolution, and drug delivery. High-speed imaging and theoretical modeling of ADV has elucidated several physical aspects, ranging from bubble nucleation to its subsequent growth. Surface instabilities are known to exist and considered responsible for evolving bubble shapes (non-spherical growth, bubble splitting and bubble droplet encapsulation). We present a linear stability analysis of the dynamically evolving interfaces of an acoustically vaporized micro-droplet (liquid A) in an infinite pool of a second liquid (liquid B). We propose a thermal ADV model for the base state. The linear analysis utilizes spherical harmonics (Ynm, of degree m and order n) and under various physical assumptions results in a time-dependent ODE of the perturbed interface amplitudes (one at the vapor/liquid A interface and the other at the liquid A/liquid B interface). The perturbation amplitudes are found to grow exponentially and do not depend on m. Supported by KAUST Baseline Research Funds.

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

    PubMed

    Palma, Palma; Sapragoniene, Marija; Stankevicius, Antanas

    2003-01-01

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

  6. A stability indicating capillary electrophoresis method for analysis of buserelin.

    PubMed

    Tamizi, Elnaz; Kenndler, Ernst; Jouyban, Abolghasem

    2014-01-01

    A simple and rapid stability indicating method based on capillary zone electrophoresis has been developed and validated for the analysis of buserelin (BUS). The best separations were achieved by using a bare fused silica capillary (75 μm i.d.; 65.5 cm total, 57.0 cm effective length), phosphate buffer (pH = 3.00; 26.4 mM), at 35 °C. The sample was hydrodynamically injected at 50 mbar for 5 seconds; the applied voltage was 30 kV and detection was carried out by UV-absorbance at 200 nm. Method validation resulted in the following figures of merit : the method was linear in the concentration range between 0.781 and 500 μg/mL (linear regression coefficient 0.9996), accuracy was between 99.3% and 100.9%, intra assay precision was between 0.3% and 1.0% and intermediate precision was between 1.0% and 2.1%. Evaluation of the specificity of the method showed no interference between excipients or products of force degradation and BUS. Under the selected conditions, separation of BUS and its degradation products was completed in less than 10 min, and BUS could be quantified after different stress conditions without any interference. The results enabled the conclusion that under thermal stress upon exposure to 90 °C BUS is degraded by first order kinetics. It was demonstrated that the method can be applied as a rapid and easy to use method for quantification and stability testing of BUS in biopharmaceutical formulations in quality control laboratories. PMID:25276180

  7. A comparison of theory and experiment for aeroelastic stability of a hingeless rotor model in hover

    NASA Technical Reports Server (NTRS)

    Sharpe, David L.

    1988-01-01

    Theoretical predictions of aeroelastic stability are compared with experimental, isolated, hingeless-rotor data. The six cases selected represent a torsionally soft rotor having either a stiff or soft pitch-control system in combination with zero precone and droop, 5 degree precone, or -5 degree droop. Analyses from Bell Helicopter Textron, Boeing Vertol, Hughes Helicopters, Sikorsky Aircraft, the National Aeronautics and Space Administration, and the U.S. Army Aeromechanics Laboratory were compared with the experimental data. The correlation ranged from poor to fair.

  8. Aeromechanics of the Spider Cricket Jump: How to Jump 60+ Times Your Body Length and Still Land on Your Feet

    NASA Astrophysics Data System (ADS)

    Palmer, Emily; Deshler, Nicolas; Gorman, David; Neves, Catarina; Mittal, Rajat

    2015-11-01

    Flapping, gliding, running, crawling and swimming have all been studied extensively in the past and have served as a source of inspiration for engineering designs. In the current project, we explore a mode of locomotion that straddles ground and air: jumping. The subject of our study is among the most proficient of long-jumpers in Nature: the spider cricket of the family Rhaphidophoridae, which can jump more than 60 times its body length. Despite jumping this immense distance, these crickets usually land on their feet, indicating an ability to control their posture during ``flight.'' We employ high-speed videogrammetry, to examine the jumps and to track the crickets' posture and appendage orientation throughout their jumps. Simple aerodynamic models are developed to predict the aerodynamic forces and moment on the crickets during `flight`. The analysis shows that these wingless insects employ carefully controlled and coordinated positioning of the limbs during flight so as to increase jump distance and to stabilize body posture during flight. The principles distilled from this study could serve as an inspiration for small jumping robots that can traverse complex terrains.

  9. A Closed-Loop Optimal Neural-Network Controller to Optimize Rotorcraft Aeromechanical Behaviour. Volume 2; Output from Two Sample Cases

    NASA Technical Reports Server (NTRS)

    Leyland, Jane Anne

    2001-01-01

    A closed-loop optimal neural-network controller technique was developed to optimize rotorcraft aeromechanical behaviour. This technique utilities a neural-network scheme to provide a general non-linear model of the rotorcraft. A modem constrained optimisation method is used to determine and update the constants in the neural-network plant model as well as to determine the optimal control vector. Current data is read, weighted, and added to a sliding data window. When the specified maximum number of data sets allowed in the data window is exceeded, the oldest data set is and the remaining data sets are re-weighted. This procedure provides at least four additional degrees-of-freedom in addition to the size and geometry of the neural-network itself with which to optimize the overall operation of the controller. These additional degrees-of-freedom are: 1. the maximum length of the sliding data window, 2. the frequency of neural-network updates, 3. the weighting of the individual data sets within the sliding window, and 4. the maximum number of optimisation iterations used for the neural-network updates.

  10. Precessing rotating flows with additional shear: Stability analysis

    NASA Astrophysics Data System (ADS)

    Salhi, A.; Cambon, C.

    2009-03-01

    We consider unbounded precessing rotating flows in which vertical or horizontal shear is induced by the interaction between the solid-body rotation (with angular velocity Ω0 ) and the additional “precessing” Coriolis force (with angular velocity -ɛΩ0 ), normal to it. A “weak” shear flow, with rate 2ɛ of the same order of the Poincaré “small” ratio ɛ , is needed for balancing the gyroscopic torque, so that the whole flow satisfies Euler’s equations in the precessing frame (the so-called admissibility conditions). The base flow case with vertical shear (its cross-gradient direction is aligned with the main angular velocity) corresponds to Mahalov’s [Phys. Fluids A 5, 891 (1993)] precessing infinite cylinder base flow (ignoring boundary conditions), while the base flow case with horizontal shear (its cross-gradient direction is normal to both main and precessing angular velocities) corresponds to the unbounded precessing rotating shear flow considered by Kerswell [Geophys. Astrophys. Fluid Dyn. 72, 107 (1993)]. We show that both these base flows satisfy the admissibility conditions and can support disturbances in terms of advected Fourier modes. Because the admissibility conditions cannot select one case with respect to the other, a more physical derivation is sought: Both flows are deduced from Poincaré’s [Bull. Astron. 27, 321 (1910)] basic state of a precessing spheroidal container, in the limit of small ɛ . A Rapid distortion theory (RDT) type of stability analysis is then performed for the previously mentioned disturbances, for both base flows. The stability analysis of the Kerswell base flow, using Floquet’s theory, is recovered, and its counterpart for the Mahalov base flow is presented. Typical growth rates are found to be the same for both flows at very small ɛ , but significant differences are obtained regarding growth rates and widths of instability bands, if larger ɛ values, up to 0.2, are considered. Finally, both flow cases

  11. Order-2 Stability Analysis of Particle Swarm Optimization.

    PubMed

    Liu, Qunfeng

    2015-01-01

    Several stability analyses and stable regions of particle swarm optimization (PSO) have been proposed before. The assumption of stagnation and different definitions of stability are adopted in these analyses. In this paper, the order-2 stability of PSO is analyzed based on a weak stagnation assumption. A new definition of stability is proposed and an order-2 stable region is obtained. Several existing stable analyses for canonical PSO are compared, especially their definitions of stability and the corresponding stable regions. It is shown that the classical stagnation assumption is too strict and not necessary. Moreover, among all these definitions of stability, it is shown that our definition requires the weakest conditions, and additional conditions bring no benefit. Finally, numerical experiments are reported to show that the obtained stable region is meaningful. A new parameter combination of PSO is also shown to be good, even better than some known best parameter combinations. PMID:24738856

  12. Large-signal stability analysis of PWM converters

    SciTech Connect

    Huynh, P.T.; Cho, B.H.

    1995-12-31

    Investigation of the effects of existing nonlinearities on the stability of PWM converters is performed. The bilinear structure, the duty cycle saturation, and the opamp saturation are the principal nonlinearities in PWM converters. These nonlinearities are incorporated in the large-signal analytical models of PWM converters, and the basic input-output stability theory is applied to analyze their stability. Design and optimization of the small-signal loop gains to counteract the undesirable nonlinear effects are also discussed.

  13. On the boundary conditions in slope stability analysis

    NASA Astrophysics Data System (ADS)

    Chugh, Ashok K.

    2003-09-01

    Boundary conditions can affect computed factor of safety results in two- and three-dimensional stability analyses of slopes. Commonly used boundary conditions in two- and three-dimensional slope stability analyses via limit-equilibrium and continuum-mechanics based solution procedures are described. A sample problem is included to illustrate the importance of boundary conditions in slope stability analyses. The sample problem is solved using two- and three-dimensional numerical models commonly used in engineering practice.

  14. Stability analysis of multigrid acceleration methods for the solution of partial differential equations

    NASA Technical Reports Server (NTRS)

    Fay, John F.

    1990-01-01

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

  15. Crack stability analysis of low alloy steel primary coolant pipe

    SciTech Connect

    Tanaka, T.; Kameyama, M.; Urabe, Y.

    1997-04-01

    At present, cast duplex stainless steel has been used for the primary coolant piping of PWRs in Japan and joints of dissimilar material have been applied for welding to reactor vessels and steam generators. For the primary coolant piping of the next APWR plants, application of low alloy steel that results in designing main loops with the same material is being studied. It means that there is no need to weld low alloy steel with stainless steel and that makes it possible to reduce the welding length. Attenuation of Ultra Sonic Wave Intensity is lower for low alloy steel than for stainless steel and they have advantageous inspection characteristics. In addition to that, the thermal expansion rate is smaller for low alloy steel than for stainless steel. In consideration of the above features of low alloy steel, the overall reliability of primary coolant piping is expected to be improved. Therefore, for the evaluation of crack stability of low alloy steel piping to be applied for primary loops, elastic-plastic future mechanics analysis was performed by means of a three-dimensioned FEM. The evaluation results for the low alloy steel pipings show that cracks will not grow into unstable fractures under maximum design load conditions, even when such a circumferential crack is assumed to be 6 times the size of the wall thickness.

  16. Aeroelastic Stability of Rotor Blades Using Finite Element Analysis

    NASA Technical Reports Server (NTRS)

    Chopra, I.; Sivaneri, N.

    1982-01-01

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

  17. BLSTA: A boundary layer code for stability analysis

    NASA Technical Reports Server (NTRS)

    Wie, Yong-Sun

    1992-01-01

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

  18. Strength analysis of yttria-stabilized tetragonal zirconia polycrystals

    SciTech Connect

    Noguchi, K.; Matsuda, Y.; Oishi, M. ); Masaki, T.; Nakayama, S.; Mizushina, M. )

    1990-09-01

    This paper reports the tensile strength of Y{sub 2}O{sub 3}-stabilized ZrO{sub 2} polycrystals (Y-TZP) measured by a newly developed tensile testing method with a rectangular bar. The tensile strength of Y-TZP was lower than that of the three-point bend strength, and the shape of the tensile strength distribution was quite different from that of the three-point bend strength distribution. It was difficult to predict the distribution curve of the tensile strength using the data of the three-point bend strength by one-modal Weibull distribution. The distribution of the tensile strength was analyzed by two- or three-modal Weibull distribution coupled with an analysis of fracture origins. The distribution curve of the three-point bend strength which was estimated by multimodal Weibull distribution agreed favorably with that of the measured three-point bend strength values. A two-modal Weibull distribution function was formulated approximately from the distributions of the tensile and three-point bend strengths, and the estimated two-modal Weibull distribution function for the four-point bend strength agreed well with the measured four-point bend strength.

  19. Hydrodynamic Stability Analysis of Particle-Laden Solid Rocket Motors

    NASA Astrophysics Data System (ADS)

    Elliott, T. S.; Majdalani, J.

    2014-11-01

    Fluid-wall interactions within solid rocket motors can result in parietal vortex shedding giving rise to hydrodynamic instabilities, or unsteady waves, that translate into pressure oscillations. The oscillations can result in vibrations observed by the rocket, rocket subsystems, or payload, which can lead to changes in flight characteristics, design failure, or other undesirable effects. For many years particles have been embedded in solid rocket propellants with the understanding that their presence increases specific impulse and suppresses fluctuations in the flowfield. This study utilizes a two dimensional framework to understand and quantify the aforementioned two-phase flowfield inside a motor case with a cylindrical grain perforation. This is accomplished through the use of linearized Navier-Stokes equations with the Stokes drag equation and application of the biglobal ansatz. Obtaining the biglobal equations for analysis requires quantification of the mean flowfield within the solid rocket motor. To that end, the extended Taylor-Culick form will be utilized to represent the gaseous phase of the mean flowfield while the self-similar form will be employed for the particle phase. Advancing the mean flowfield by quantifying the particle mass concentration with a semi-analytical solution the finalized mean flowfield is combined with the biglobal equations resulting in a system of eight partial differential equations. This system is solved using an eigensolver within the framework yielding the entire spectrum of eigenvalues, frequency and growth rate components, at once. This work will detail the parametric analysis performed to demonstrate the stabilizing and destabilizing effects of particles within solid rocket combustion.

  20. The Stability of Radiatively Cooling Jets I. Linear Analysis

    NASA Technical Reports Server (NTRS)

    Hardee, Philip E.; Stone, James M.

    1997-01-01

    The results of a spatial stability analysis of a two-dimensional slab jet, in which optically thin radiative cooling is dynamically important, are presented. We study both magnetized and unmagnetized jets at external Mach numbers of 5 and 20. We model the cooling rate by using two different cooling curves: one appropriate to interstellar gas, and the other to photoionized gas of reduced metallicity. Thus, our results will be applicable to both protostellar (Herbig-Haro) jets and optical jets from active galactic nuclei. We present analytical solutions to the dispersion relations in useful limits and solve the dispersion relations numerically over a broad range of perturbation frequencies. We find that the growth rates and wavelengths of the unstable Kelvin-Helmholtz (K-H) modes are significantly different from the adiabatic limit, and that the form of the cooling function strongly affects the results. In particular, if the cooling curve is a steep function of temperature in the neighborhood of the equilibrium state, then the growth of K-H modes is reduced relative to the adiabatic jet. On the other hand, if the cooling curve is a shallow function of temperature, then the growth of K-H modes can be enhanced relative to the adiabatic jet by the increase in cooling relative to heating in overdense regions. Inclusion of a dynamically important magnetic field does not strongly modify the important differences between an adiabatic jet and a cooling jet, provided the jet is highly supermagnetosonic and not magnetic pressure-dominated. In the latter case, the unstable modes behave more like the transmagnetosonic magnetic pressure-dominated adiabatic limit. We also plot fluid displacement surfaces associated with the various waves in a cooling jet in order to predict the structures that might arise in the nonlinear regime. This analysis predicts that low-frequency surface waves and the lowest order body modes will be the most effective at producing observable features in

  1. Rank Stability Analysis of Surface and Profile Soil Moisture

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Although several studies have examined the spatial and rank stability of soil moisture at the surface layer (0-5cm) with the purpose of estimating large scale mean soil moisture, the integration of the rank stability of profile (0-60cm) soil moisture has not been fully considered. This research comb...

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

    NASA Technical Reports Server (NTRS)

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

    1991-01-01

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

  3. Analysis of the linear stability of compressible boundary layers using the PSE. [parabolic stability equations

    NASA Technical Reports Server (NTRS)

    Bertolotti, F. P.; Herbert, TH.

    1991-01-01

    The application of linearized parabolic stability equations (PSE) to compressible flow is considered. The effect of mean-flow nonparallelism is found to be weak on 2D waves and strong on 3D waves. Results for a single choice of free-stream parameters that corresponds to the atmospheric conditions at 15,000 m above sea level are presented.

  4. LONG-TERM STABILITY OF FOOD PATTERNS IDENTIFIED BY USE OF FACTOR ANALYSIS AMONG SWEDISH WOMEN

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Limited data exist on the reproducibility of food patterns measured using factor analysis, as well as the stability of patterns over time. Our primary objective was to explore the long-term stability of food patterns derived using confirmatory factor analysis among 33,840 women participating in the...

  5. Kinematic Analysis of a Posterior-stabilized Knee Prosthesis

    PubMed Central

    Zhao, Zhi-Xin; Wen, Liang; Qu, Tie-Bing; Hou, Li-Li; Xiang, Dong; Bin, Jia

    2015-01-01

    Background: The goal of total knee arthroplasty (TKA) is to restore knee kinematics. Knee prosthesis design plays a very important role in successful restoration. Here, kinematics models of normal and prosthetic knees were created and validated using previously published data. Methods: Computed tomography and magnetic resonance imaging scans of a healthy, anticorrosive female cadaver were used to establish a model of the entire lower limbs, including the femur, tibia, patella, fibula, distal femur cartilage, and medial and lateral menisci, as well as the anterior cruciate, posterior cruciate, medial collateral, and lateral collateral ligaments. The data from the three-dimensional models of the normal knee joint and a posterior-stabilized (PS) knee prosthesis were imported into finite element analysis software to create the final kinematic model of the TKA prosthesis, which was then validated by comparison with a previous study. The displacement of the medial/lateral femur and the internal rotation angle of the tibia were analyzed during 0–135° flexion. Results: Both the output data trends and the measured values derived from the normal knee's kinematics model were very close to the results reported in a previous in vivo study, suggesting that this model can be used for further analyses. The PS knee prosthesis underwent an abnormal forward displacement compared with the normal knee and has insufficient, or insufficiently aggressive, “rollback” compared with the lateral femur of the normal knee. In addition, a certain degree of reverse rotation occurs during flexion of the PS knee prosthesis. Conclusions: There were still several differences between the kinematics of the PS knee prosthesis and a normal knee, suggesting room for improving the design of the PS knee prosthesis. The abnormal kinematics during early flexion shows that the design of the articular surface played a vital role in improving the kinematics of the PS knee prosthesis. PMID:25591565

  6. Stability analysis of genetic regulatory networks with multiple time delays.

    PubMed

    Wu, Fang-Xiang

    2007-01-01

    A genetic regulatory network is a dynamic system to describe interactions among genes (mRNA) and its products (proteins). From the statistic thermodynamics and biochemical reaction principle, a genetic regulatory network can be described by a group of nonlinear differential equations with time delays. Stability is one of interesting properties for genetic regulatory network. Previous studies have investigated stability of genetic regulatory networks with a single time delay. In this paper, we investigate properties of genetic regulatory networks with multiple time delays in the notion of delay-independent stability. We present necessary and sufficient condition for the local delay-independent stability of genetic regulatory network with multiple time delays which are independent or commensurate. PMID:18002223

  7. Vaccine stability study design and analysis to support product licensure.

    PubMed

    Schofield, Timothy L

    2009-11-01

    Stability evaluation supporting vaccine licensure includes studies of bulk intermediates as well as final container product. Long-term and accelerated studies are performed to support shelf life and to determine release limits for the vaccine. Vaccine shelf life is best determined utilizing a formal statistical evaluation outlined in the ICH guidelines, while minimum release is calculated to help assure adequate potency through handling and storage of the vaccine. In addition to supporting release potency determination, accelerated stability studies may be used to support a strategy to recalculate product expiry after an unintended temperature excursion such as a cold storage unit failure or mishandling during transport. Appropriate statistical evaluation of vaccine stability data promotes strategic stability study design, in order to reduce the uncertainty associated with the determination of the degradation rate, and the associated risk to the customer. PMID:19717312

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

    EPA Science Inventory

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

  9. Decomposition-aggregation stability analysis of the spinning Skylab

    NASA Technical Reports Server (NTRS)

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

    1974-01-01

    Stability of an 11-th order linear model of the spinning Skylab is determined by the decomposition-aggregation method based upon the comparison principle and vector Liapunov functions. To reduce the inherent conservativeness of the method an optimization problem is formulated and resolved producing the optimum comparison system. The system provides the best estimate of the stability region of the important structural parameter - asymmetry in the boom settings.

  10. Dynamic remedial action scheme using online transient stability analysis

    NASA Astrophysics Data System (ADS)

    Shrestha, Arun

    Economic pressure and environmental factors have forced the modern power systems to operate closer to their stability limits. However, maintaining transient stability is a fundamental requirement for the operation of interconnected power systems. In North America, power systems are planned and operated to withstand the loss of any single or multiple elements without violating North American Electric Reliability Corporation (NERC) system performance criteria. For a contingency resulting in the loss of multiple elements (Category C), emergency transient stability controls may be necessary to stabilize the power system. Emergency control is designed to sense abnormal conditions and subsequently take pre-determined remedial actions to prevent instability. Commonly known as either Remedial Action Schemes (RAS) or as Special/System Protection Schemes (SPS), these emergency control approaches have been extensively adopted by utilities. RAS are designed to address specific problems, e.g. to increase power transfer, to provide reactive support, to address generator instability, to limit thermal overloads, etc. Possible remedial actions include generator tripping, load shedding, capacitor and reactor switching, static VAR control, etc. Among various RAS types, generation shedding is the most effective and widely used emergency control means for maintaining system stability. In this dissertation, an optimal power flow (OPF)-based generation-shedding RAS is proposed. This scheme uses online transient stability calculation and generator cost function to determine appropriate remedial actions. For transient stability calculation, SIngle Machine Equivalent (SIME) technique is used, which reduces the multimachine power system model to a One-Machine Infinite Bus (OMIB) equivalent and identifies critical machines. Unlike conventional RAS, which are designed using offline simulations, online stability calculations make the proposed RAS dynamic and adapting to any power system

  11. Aeroelasticity and mechanical stability report, 0.27 Mach scale model of the YAH-64 advanced attack helicopter

    NASA Technical Reports Server (NTRS)

    Straub, F. K.; Johnston, R. A.

    1987-01-01

    A 27% dynamically scaled model of the YAH-64 Advanced Attack Helicopter main rotor and hub has been designed and fabricated. The model will be tested in the NASA Langley Research Center V/STOL wind tunnel using the General Rotor Model System (GRMS). This report documents the studies performed to ensure dynamic similarity of the model with its full scale parent. It also contains a preliminary aeroelastic and aeromechanical substantiation for the rotor installation in the wind tunnel. From the limited studies performed no aeroelastic stability or load problems are projected. To alleviate a projected ground resonance problem, a modification of the roll characteristics of the GRMS is recommended.

  12. Stability analysis and trend study of a balloon tethered in a wind, with experimental comparisons

    NASA Technical Reports Server (NTRS)

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

    1973-01-01

    A stability analysis and trend study for a balloon tethered in a steady wind are presented. The linearized, stability-derivative type analysis includes balloon aerodynamics, buoyancy, mass (including apparent mass), and static forces resulting from the tether cable. The analysis has been applied to a balloon 7.64 m in length, and the results are compared with those from tow tests of this balloon. This comparison shows that the analysis gives reasonable predictions for the damping, frequencies, modes of motion, and stability boundaries exhibited by the balloon. A trend study for the 7.64-m balloon was made to illustrate how the stability boundaries are affected by changes in individual stability parameters. The trends indicated in this study may also be applicable to many other tethered-balloon systems.

  13. Liner stability analysis of the two-dimensional Taylor-Green vortices in a stratified flow

    NASA Astrophysics Data System (ADS)

    Suzuki, Shota; Hirota, Makoto; Hattori, Yuji

    2015-11-01

    The linear stability of the two-dimensional Taylor-Green vortices in a stratified fluid is studied by modal stability analysis and short-wavelength stability analysis. By modal stability analysis it is found that the growth rate of the most unstable mode depends on the horizontal Froude number Fh and the stratification effects on the growth rate change as Fh becomes small or stratification becomes strong. There are three regions of Fh where the stratification effects are different: the stabilizing region where the elliptic instability is dominant at large Fh, the region where the growth rate has maximum, the slightly destabilizing region where the zigzag instability is dominant at small Fh. In order to reveal the mechanism of the behavior of the growth rate in the second region, we investigate the local stability of the flow near the vortex center and the flow near the boundaries between vortices by short-wavelength analysis. As a result, it is found that the competition between stabilizing elliptic instability near the vortex center and destabilizing hyperbolic instability near the boundaries occurs in the weakly stratified region. The relation between modal stability and the competition of short-wavelength stabilities will be discussed.

  14. Theoretical foundations for finite-time transient stability and sensitivity analysis of power systems

    NASA Astrophysics Data System (ADS)

    Dasgupta, Sambarta

    Transient stability and sensitivity analysis of power systems are problems of enormous academic and practical interest. These classical problems have received renewed interest, because of the advancement in sensor technology in the form of phasor measurement units (PMUs). The advancement in sensor technology has provided unique opportunity for the development of real-time stability monitoring and sensitivity analysis tools. Transient stability problem in power system is inherently a problem of stability analysis of the non-equilibrium dynamics, because for a short time period following a fault or disturbance the system trajectory moves away from the equilibrium point. The real-time stability decision has to be made over this short time period. However, the existing stability definitions and hence analysis tools for transient stability are asymptotic in nature. In this thesis, we discover theoretical foundations for the short-term transient stability analysis of power systems, based on the theory of normally hyperbolic invariant manifolds and finite time Lyapunov exponents, adopted from geometric theory of dynamical systems. The theory of normally hyperbolic surfaces allows us to characterize the rate of expansion and contraction of co-dimension one material surfaces in the phase space. The expansion and contraction rates of these material surfaces can be computed in finite time. We prove that the expansion and contraction rates can be used as finite time transient stability certificates. Furthermore, material surfaces with maximum expansion and contraction rate are identified with the stability boundaries. These stability boundaries are used for computation of stability margin. We have used the theoretical framework for the development of model-based and model-free real-time stability monitoring methods. Both the model-based and model-free approaches rely on the availability of high resolution time series data from the PMUs for stability prediction. The problem of

  15. Stability analysis of the Euler discretization for SIR epidemic model

    SciTech Connect

    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.

  16. Linear Stability Regime Analysis of the Compressible Reacting Mixing Layer

    NASA Technical Reports Server (NTRS)

    Day, M. J.; Reynolds, William C.; Mansour, N. N.; Rai, Man Mohan (Technical Monitor)

    1995-01-01

    Previous investigations have shown that a compressible reacting mixing layer can develop two peaks in the mean density weighted vorticity profile. Linear stability analyses show that at these peaks two distinct 'outer' instability modes appear in addition to the more common central mode, which exists unaccompanied in incompressible nonreacting flows. The present study parametrically analyzes the effects of compressibility, heat release, stoichiometry, and density ratio on the amplification rate and obliquity of each stability mode. The mean profiles used in the spatial stability calculation are generated by self-similar solutions of the compressible boundary layer equations combined with the assumption of infinitely fast chemistry. It is shown that the influence of stoichiometry and density ratio on the peaks of the density weighted vorticity profile determines which modes will dominate. Of particular interest are the conditions where two modes are equally amplified, causing the mixing layer to develop into a 'colayer' structure.

  17. Perturbed Stability Analysis of External Ideal MHD Modes

    NASA Astrophysics Data System (ADS)

    Comer, K. J.; Callen, J. D.; Hegna, C. C.; Garstka, G. D.; Turnbull, A. D.; Garofalo, A. M.; Cowley, S. C.

    2002-11-01

    Traditionally, numerical parameter scans are performed to study the effects of equilibrium shaping and profiles on long wavelength ideal MHD instabilities. Previously, we introduced a new perturbative technique to more efficiently explore these dependencies: changes in delta-W due to small equilibrium variations are found using a perturbation of the energy principle rather than with an eigenvalue-solver instability code. With this approach, the stability properties of similar equilibria can be efficiently explored without generating complete numerical results for every set of parameters (which is time-intensive for accurate representations of several configurations). Here, we apply this approach to toroidal geometry using GATO (an ideal MHD stability code) and experimental equilibria. In particular, we explore ideal MHD stability of external kink modes in the spherical tokamak Pegasus and resistive wall modes in DIII-D.

  18. Stability analysis of pressure correction schemes for the Navier–Stokes equations with traction boundary conditions

    NASA Astrophysics Data System (ADS)

    Lee, Sanghyun; Salgado, Abner J.

    2016-09-01

    We present a stability analysis for two different rotational pressure correction schemes with open and traction boundary conditions. First, we provide a stability analysis for a rotational version of the grad-div stabilized scheme of [A. Bonito, J.-L. Guermond, and S. Lee. Modified pressure-correction projection methods: Open boundary and variable time stepping. In Numerical Mathematics and Advanced Applications - ENUMATH 2013, volume 103 of Lecture Notes in Computational Science and Engineering, pages 623-631. Springer, 2015]. This scheme turns out to be unconditionally stable, provided the stabilization parameter is suitably chosen. We also establish a conditional stability result for the boundary correction scheme presented in [E. Bansch. A finite element pressure correction scheme for the Navier-Stokes equations with traction boundary condition. Comput. Methods Appl. Mech. Engrg., 279:198-211, 2014]. These results are shown by employing the equivalence between stabilized gauge Uzawa methods and rotational pressure correction schemes with traction boundary conditions.

  19. Advanced techniques for the analysis of crisis stability, deterrence, and latency

    SciTech Connect

    Canavan, G.H.

    1997-12-01

    Studies on crisis stability, deterrence, and latency are presented in chronological order, which also reflects their logical order of development, captures the main features of stability analysis; relates first strike, crisis, and arms control stability as seen from US and Russian perspective; and addresses questions such as whether uncertainty in damage preference or defense deployment can be destabilizing. It illustrates the problems with alternative metrics, latency and reconstitution, and deep unilateral and proportional force reductions.

  20. F-111 natural laminar flow glove flight test data analysis and boundary layer stability analysis

    NASA Technical Reports Server (NTRS)

    Runyan, L. J.; Navran, B. H.; Rozendaal, R. A.

    1984-01-01

    An analysis of 34 selected flight test data cases from a NASA flight program incorporating a natural laminar flow airfoil into partial wing gloves on the F-111 TACT airplane is given. This analysis determined the measured location of transition from laminar to turbulent flow. The report also contains the results of a boundary layer stability analysis of 25 of the selected cases in which the crossflow (C-F) and Tollmien-Schlichting (T-S) disturbance amplification factors are correlated with the measured transition location. The chord Reynolds numbers for these cases ranges from about 23 million to 29 million, the Mach numbers ranged from 0.80 to 0.85, and the glove leading-edge sweep angles ranged from 9 deg to 25 deg. Results indicate that the maximum extent of laminar flow varies from 56% chord to 9-deg sweep on the upper surface, and from 51% chord at 16-deg sweep to 6% chord at 25-deg sweep on the lower. The results of the boundary layer stability analysis indicate that when both C-F and T-S disturbances are amplified, an interaction takes place which reduces the maximum amplification factor of either type of disturbance that can be tolerated without causing transition.

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

    NASA Technical Reports Server (NTRS)

    Bartels, Robert E.

    2011-01-01

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

  2. Dynamical behavior and Jacobi stability analysis of wound strings

    NASA Astrophysics Data System (ADS)

    Lake, Matthew J.; Harko, Tiberiu

    2016-06-01

    We numerically solve the equations of motion (EOM) for two models of circular cosmic string loops with windings in a simply connected internal space. Since the windings cannot be topologically stabilized, stability must be achieved (if at all) dynamically. As toy models for realistic compactifications, we consider windings on a small section of {R}^2, which is valid as an approximation to any simply connected internal manifold if the winding radius is sufficiently small, and windings on an S^2 of constant radius {R}. We then use Kosambi-Cartan-Chern (KCC) theory to analyze the Jacobi stability of the string equations and determine bounds on the physical parameters that ensure dynamical stability of the windings. We find that, for the same initial conditions, the curvature and topology of the internal space have nontrivial effects on the microscopic behavior of the string in the higher dimensions, but that the macroscopic behavior is remarkably insensitive to the details of the motion in the compact space. This suggests that higher-dimensional signatures may be extremely difficult to detect in the effective (3+1)-dimensional dynamics of strings compactified on an internal space, even if configurations with nontrivial windings persist over long time periods.

  3. Fuzzy stability analysis of regenerative chatter in milling

    NASA Astrophysics Data System (ADS)

    Sims, Neil D.; Manson, Graeme; Mann, Brian

    2010-04-01

    During machining, unstable self-excited vibrations known as regenerative chatter can occur, causing excessive tool wear or failure, and a poor surface finish on the machined workpiece. Consequently it is desirable to predict, and hence avoid the onset of this instability. Regenerative chatter is a function of empirical cutting coefficients, and the structural dynamics of the machine-tool system. There can be significant uncertainties in the underlying parameters, so the predicted stability limits do not necessarily agree with those found in practice. In the present study, fuzzy arithmetic techniques are applied to the chatter stability problem. It is first shown that techniques based upon interval arithmetic are not suitable for this problem due to the issue of recursiveness. An implementation of fuzzy arithmetic is then developed based upon the work of Hanss and Klimke. The arithmetic is then applied to two techniques for predicting milling chatter stability: the classical approach of Altintas, and the time-finite element method of Mann. It is shown that for some cases careful programming can reduce the computational effort to acceptable levels. The problem of milling chatter uncertainty is then considered within the framework of Ben-Haim's information-gap theory. It is shown that the presented approach can be used to solve process design problems with robustness to the uncertain parameters. The fuzzy stability bounds are then compared to previously published data, to investigate how uncertainty propagation techniques can offer more insight into the accuracy of chatter predictions.

  4. Remarks on the stability analysis of reactive flows

    NASA Technical Reports Server (NTRS)

    Scheurer, B.

    1987-01-01

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

  5. Stability analysis of impulsive functional systems of fractional order

    NASA Astrophysics Data System (ADS)

    Stamova, Ivanka; Stamov, Gani

    2014-03-01

    In this paper, a class of impulsive fractional functional differential systems is investigated. Sufficient conditions for stability of the zero solution are proved, extending the corresponding theory of impulsive functional differential equations. The investigations are carried out by using the comparison principle, coupled with the Lyapunov function method. We apply our results to an impulsive single species model of Lotka-Volterra type.

  6. Dynamical behavior and Jacobi stability analysis of wound strings

    NASA Astrophysics Data System (ADS)

    Lake, Matthew J.; Harko, Tiberiu

    2016-06-01

    We numerically solve the equations of motion (EOM) for two models of circular cosmic string loops with windings in a simply connected internal space. Since the windings cannot be topologically stabilized, stability must be achieved (if at all) dynamically. As toy models for realistic compactifications, we consider windings on a small section of mathbb {R}^2, which is valid as an approximation to any simply connected internal manifold if the winding radius is sufficiently small, and windings on an S^2 of constant radius mathcal {R}. We then use Kosambi-Cartan-Chern (KCC) theory to analyze the Jacobi stability of the string equations and determine bounds on the physical parameters that ensure dynamical stability of the windings. We find that, for the same initial conditions, the curvature and topology of the internal space have nontrivial effects on the microscopic behavior of the string in the higher dimensions, but that the macroscopic behavior is remarkably insensitive to the details of the motion in the compact space. This suggests that higher-dimensional signatures may be extremely difficult to detect in the effective (3+1)-dimensional dynamics of strings compactified on an internal space, even if configurations with nontrivial windings persist over long time periods.

  7. 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.

  8. Quiet Clean Short-haul Experimental Engine (QCSEE). Aerodynamic and aeromechanical performance of a 50.8 cm (20 inch) diameter 1.34 PR variable pitch fan with core flow

    NASA Technical Reports Server (NTRS)

    Giffin, R. G.; Mcfalls, R. A.; Beacher, B. F.

    1977-01-01

    The fan aerodynamic and aeromechanical performance tests of the quiet clean short haul experimental engine under the wing fan and inlet with a simulated core flow are described. Overall forward mode fan performance is presented at each rotor pitch angle setting with conventional flow pressure ratio efficiency fan maps, distinguishing the performance characteristics of the fan bypass and fan core regions. Effects of off design bypass ratio, hybrid inlet geometry, and tip radial inlet distortion on fan performance are determined. The nonaxisymmetric bypass OGV and pylon configuration is assessed relative to both total pressure loss and induced circumferential flow distortion. Reverse mode performance, obtained by resetting the rotor blades through both the stall pitch and flat pitch directions, is discussed in terms of the conventional flow pressure ratio relationship and its implications upon achievable reverse thrust. Core performance in reverse mode operation is presented in terms of overall recovery levels and radial profiles existing at the simulated core inlet plane. Observations of the starting phenomena associated with the initiation of stable rotor flow during acceleration in the reverse mode are briefly discussed. Aeromechanical response characteristics of the fan blades are presented as a separate appendix, along with a description of the vehicle instrumentation and method of data reduction.

  9. Stability and Change in Work Values: A Meta-Analysis of Longitudinal Studies

    ERIC Educational Resources Information Center

    Jin, Jing; Rounds, James

    2012-01-01

    A meta-analysis of longitudinal studies was conducted to investigate stability and change in work values across the life span. Both rank-order stability and mean-level change were investigated using an integrative classification for intrinsic, extrinsic, social and status work values (Ross, Schwartz, & Surkis, 1999). Results of rank-order…

  10. Does Premarital Cohabitation Predict Subsequent Marital Stability and Marital Quality? A Meta-Analysis

    ERIC Educational Resources Information Center

    Jose, Anita; O'Leary, K. Daniel; Moyer, Anne

    2010-01-01

    Cohabitation with a romantic partner has become common in recent decades. This meta-analysis examined the link between premarital cohabitation and marital stability (k = 16) and marital quality (k = 12). Cohabitation had a significant negative association with both marital stability and marital quality. The negative predictive effect on marital…

  11. Linear stability analysis of thermocapillary convection in a liquid bridge with encapsulation in inverse iterative algorithm

    SciTech Connect

    Li, M.; Sun, Z.; Zeng, D.

    1996-12-31

    Linear stability theory was applied in the present paper to analyze the stability of the basic state solution of thermocapillary convection in a liquid bridge with liquid encapsulation. Discretizing the linearized disturbance equations by using finite-difference approximation, stability analysis is evolved to a complex generalized eigenvalue problem with a complicated band structure of matrix. The influence of dimensionless parameters on the stability of the system is revealed through solving the complex generalized eigenvalue problem by inverse iteration. The results provide a theoretical and numerical foundation for crystal growth by float-zone method and for other engineering applications.

  12. Advanced techniques for the analysis of crisis stability, deterrence, and latency

    SciTech Connect

    Canavan, G.H.

    1998-12-31

    This is the final report of a one-year, Laboratory Directed Research and Development (LDRD) project at Los Alamos National Laboratory (LANL). The principal results of studies on crisis stability, deterrence, and latency are presented in their order of development. They capture the main features of stability analysis; relate first strike, crisis, and arms control stability as seen from US and Russian perspective; and address whether different metrics, uncertain damage preferences, or the deployment of defenses can be destabilizing. The report explores differences between unilateral and proportional force reductions in the region of deep reductions where concern shifts from stability to latency.

  13. Linearized stability analysis of gravastars in noncommutative geometry

    NASA Astrophysics Data System (ADS)

    Lobo, Francisco S. N.; Garattini, Remo

    2013-12-01

    In this work, we find exact gravastar solutions in the context of noncommutative geometry, and explore their physical properties and characteristics. The energy density of these geometries is a smeared and particle-like gravitational source, where the mass is diffused throughout a region of linear dimension due to the intrinsic uncertainty encoded in the coordinate commutator. These solutions are then matched to an exterior Schwarzschild spacetime. We further explore the dynamical stability of the transition layer of these gravastars, for the specific case of β = M 2/ α < 1.9, where M is the black hole mass, to linearized spherically symmetric radial perturbations about static equilibrium solutions. It is found that large stability regions exist and, in particular, located sufficiently close to where the event horizon is expected to form.

  14. Stability and bifurcation analysis of rotor-bearing-seal system

    NASA Astrophysics Data System (ADS)

    Ying, G. Y.; Liu, S. L.; Ma, R.; Zheng, S. Y.

    2016-05-01

    Labyrinth seals were extensively used in turbine units, and the seal fluid forces may induce self-excited vibrations of rotor under certain conditions. It has become the main factor to instability of rotor system. In this paper Muszynska seal fluid force model is used to investigate the stability of the rotor system. Nonlinear equations are numerically solved by Newmark integration method. The effect of different seal clearances and differential pressures on system stability is studied. The calculation results show that the dominant vibration component leading to instability changes with different seal clearance. With the differential pressure increased, the unstable speed is reduced. Then the bifurcation behavior of the system with and without seal force is calculated. Results show that the rotor vibration becomes severe and complicated, and the bifurcation behavior of the system has been changed when seal force is considered.

  15. Linear MHD Stability Analysis of the SSPX Spheromak

    NASA Astrophysics Data System (ADS)

    Jayakumar, R.; Cohen, B. I.; Hooper, E. B.; Lodestro, L. L.; McLean, H. S.; Pearlstein, L. D.; Wood, R.; Turnbull, A. D.; Sovinec, C.

    2007-11-01

    Good correlation between the toroidal mode numbers of measured magnetic fluctuations in high temperature SSPX plasmas and presence of low-order rational surfaces in the reconstructed q profiles, suggests that the quality of magnetic surfaces in SSPX is sufficiently good for applying standard linear MHD stability analyses. Previously we have reported on benchmarking the code NIMROD against GATO, with good agreement in growth rates for ideal-MHD internal kinks and an external kinks with no current on open field lines (for equilibria imported from the code Corsica). Recent stability analyses also show that presence of low order rational surfaces causes internal modes to become unstable. We will report on the progress in applying these tools for assessing beta limits in SSPX, using NIMROD analyses including current on open field lines and for comparison with experiments.

  16. Thermal Stability Analysis for a Heliocentric Gravitational Radiation Detection Mission

    NASA Technical Reports Server (NTRS)

    Folkner, W.; McElroy, P.; Miyake, R.; Bender, P.; Stebbins, R.; Supper, W.

    1994-01-01

    The Laser Interferometer Space Antenna (LISA) mission is designed for detailed studies of low-frequency gravitational radiation. The mission is currently a candidate for ESA's post-Horizon 2000 program. Thermal noise affects the measurement in at least two ways. Thermal variation of the length of the optical cavity to which the lasers are stabilized introduces phase variations in the interferometer signal, which have to be corrected for by using data from the two arms separately.

  17. Preliminary Experimental Analysis of Soil Stabilizers for Contamination Control

    SciTech Connect

    Lagos, L.; Varona, J.; Zidan, A.; Gudavalli, R.; Wu, Kuang-His

    2006-07-01

    A major focus of Department of Energy's (DOE's) environmental management mission at the Hanford site involves characterizing and remediating contaminated soil and groundwater; stabilizing contaminated soil; remediating disposal sites; decontaminating and decommissioning structures, and demolishing former plutonium production process buildings, nuclear reactors, and separation plants; maintaining inactive waste sites; transitioning facilities into the surveillance and maintenance program; and mitigating effects to biological and cultural resources from site development and environmental cleanup and restoration activities. For example, a total of 470,914 metric tons of contaminated soil from 100 Areas remediation activities were disposed at the Environmental Restoration Disposal Facility (ERDF) during 2004. The Applied Research Center (ARC) at Florida International University (FIU) is supporting the Hanford's site remediation program by analyzing the effectiveness of several soil stabilizers (fixatives) for contamination control during excavation activities. The study is focusing on determining the effects of varying soil conditions, temperature, humidity and wind velocity on the effectiveness of the candidate stabilizers. The test matrix consists of a soil penetration-depth study, wind tunnel experiments for determination of threshold velocity, and temperature and moisture-controlled drying/curing experiments. These three set of experiments are designed to verify performance metrics, as well as provide insight into what fundamental forces are altered by the use of the stabilizer. This paper only presents the preliminary results obtained during wind tunnel experiments using dry Hanford soil samples (with 2.7% moisture by weight). These dry soil samples were exposed to varying wind speeds from 2.22 m/sec to 8.88 m/sec. Furthermore, airborne particulate data was collected for the dry Hanford soil experiments using an aerosol analyzer instrument. (authors)

  18. Liapunov functions for non-linear difference equation stability analysis.

    NASA Technical Reports Server (NTRS)

    Park, K. E.; Kinnen, E.

    1972-01-01

    Liapunov functions to determine the stability of non-linear autonomous difference equations can be developed through the use of auxiliary exact difference equations. For this purpose definitions are introduced for the gradient of an implicit function of a discrete variable, a principal sum, a definite sum and an exact difference equation, and a theorem for exactness of a difference form is proved. Examples illustrate the procedure.

  19. Stability analysis of synchronization regimes of spinning rockets

    NASA Astrophysics Data System (ADS)

    Dron, N. M.

    1993-10-01

    A method is studied for estimating the formation of synchronization regimes in rocket ballistic flight in which the roll rate approaches the pitch rate. Supporting resonance angular motion regimes due to induced moments are analyzed, and the nonlinear second-order differential equation of the rolling motion is addressed. The results permit synchronization regimes to be prevented, which is important for motion stability and trajectory parameter dispersion in sounding rockets.

  20. Long-Term Stability of Radio Sources in VLBI Analysis

    NASA Technical Reports Server (NTRS)

    Engelhardt, Gerald; Thorandt, Volkmar

    2010-01-01

    Positional stability of radio sources is an important requirement for modeling of only one source position for the complete length of VLBI data of presently more than 20 years. The stability of radio sources can be verified by analyzing time series of radio source coordinates. One approach is a statistical test for normal distribution of residuals to the weighted mean for each radio source component of the time series. Systematic phenomena in the time series can thus be detected. Nevertheless, an inspection of rate estimation and weighted root-mean-square (WRMS) variations about the mean is also necessary. On the basis of the time series computed by the BKG group in the frame of the ICRF2 working group, 226 stable radio sources with an axis stability of 10 as could be identified. They include 100 ICRF2 axes-defining sources which are determined independently of the method applied in the ICRF2 working group. 29 stable radio sources with a source structure index of less than 3.0 can also be used to increase the number of 295 ICRF2 defining sources.

  1. Stability analysis of underground mining openings with complex geometry

    NASA Astrophysics Data System (ADS)

    Cała, Marek; Stopkowicz, Agnieszka; Kowalski, Michał; Blajer, Mateusz; Cyran, Katarzyna; D'obyrn, Kajetan

    2016-03-01

    Stability of mining openings requires consideration of a number of factors, such as: geological structure, the geometry of the underground mining workings, mechanical properties of the rock mass, changes in stress caused by the influence of neighbouring workings. Long-term prediction and estimation of workings state can be analysed with the use of numerical methods. Application of 3D numerical modelling in stability estimation of workings with complex geometry was described with the example of Crystal Caves in Wieliczka Salt Mine. Preservation of the Crystal Caves reserve is particularly important in view of their unique character and the protection of adjacent galleries which are a part of tourist attraction included in UNESCO list. A detailed 3D model of Crystal Caves and neighbouring workings was built. Application of FLAC3D modelling techniques enabled indication of the areas which are in danger of stability loss. Moreover, the area in which protective actions should be taken as well as recommendations concerning the convergence monitoring were proposed.

  2. An analytical study and wind tunnel tests of an aeromechanical gust-alleviation system for a light airplane

    NASA Technical Reports Server (NTRS)

    Stewart, E. C.

    1976-01-01

    The results of an analytical study of a system using stability derivatives determined in static wind tunnel tests of a 1/6 scale model of a popular, high wing, light airplane equipped with the gust alleviation system are reported. The longitudinal short period mode dynamics of the system are analyzed, and include the following: (1) root loci, (2) airplane frequency responses to vertical gusts, (3) power spectra of the airplane responses in a gust spectrum, (4) time history responses to vertical gusts, and (5) handling characteristics. The system reduces the airplane's normal acceleration response to vertical gusts while simultaneously increasing the pitching response and reducing the damping of the longitudinal short period mode. The normal acceleration response can be minimized by using the proper amount of static alleviation and a fast response system with a moderate amount of damping. The addition of a flap elevator interconnect or a pitch damper system further increases the alleviation while moderating the simultaneous increase in pitching response. The system provides direct lift control and may reduce the stick fixed longitudinal static stability.

  3. SILICATE TECHNOLOGY CORPORATION'S SOLIDIFICATION/ STABILIZATION TECHNOLOGY FOR ORGANIC AND INORGANIC CONTAMINANTS IN SOILS - APPLICATIONS ANALYSIS REPORT

    EPA Science Inventory

    This Applications Analysis Report evaluates the solidification/stabilization treatment process of Silicate Technology Corporation (STC) for the on-site treatment of hazardous waste. The STC immobilization technology utilizes a proprietary product (FMS Silicate) to chemically stab...

  4. SAS applications for Tai's stability analysis and AMMI model in genotype x environmental interaction (GEI) effects.

    PubMed

    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

  5. APPLICATIONS ANALYSIS REPORT: SITE PROGRAM DEMONSTRATION TEST SOLIDITECH, INC. SOLIDIFICATION/ STABILIZATION PROCESS

    EPA Science Inventory

    This Applications Analysis Report evaluates the Soliditech, Inc., solidification/ stabilization process for the on-site treatment of waste materials. The Soliditech process mixes and chemically treats waste material with Urrichem (a proprietary reagent), additives, pozzolanic mat...

  6. Comparison of Implant Stability Using Resonance Frequency Analysis: Osteotome Versus Conventional Drilling

    PubMed Central

    Sadeghi, Rokhsareh; Miremadi, Asghar

    2015-01-01

    Objectives: Implant primary stability is one of the important factors in achieving implant success. The osteotome technique may improve primary stability in patients with poor bone quality. The aim of this study was to compare implant stability using two different techniques namely osteotome versus conventional drilling in the posterior maxilla. Materials and Methods: In this controlled randomized clinical trial, 54 dental implants were placed in 32 patients; 29 implants were placed in the osteotome group and 25 in the conventional drilling group. Implant stability was assessed at four time intervals namely at baseline, one, two and three months after implant placement using resonance frequency analysis (RFA). Results: Primary stability based on implant stability quotient (ISQ) units was 71.4±7 for the osteotome group and 67.4±10 for the control group. There was no statistically significant difference between the two groups in implant stability at any of the measurement times. In each group, changes in implant stability from baseline to one month and also from two months to three months post-operatively were not significant but from one month to two months after implant placement, implant stability showed a significant increase in both groups. Conclusion: The results of this study revealed that in both techniques, good implant stability was achieved and osteotome technique did not have any advantage compared to conventional drilling in this regard. PMID:27148375

  7. Analysis of a Major Electric Grid -- Stability and Adaptive Protection

    NASA Astrophysics Data System (ADS)

    Alanzi, Sultan

    system conditions. This dissertation introduces a combination of quadrilateral and mho characteristics to create a distance relay with a mushroom shape in R-X diagrams. This new relay offers larger protective reach with a lower limitation on loadability. When major disturbances occur, the power balance between load and generation might be disturbed causing the generators to lose synchronism (to be out-of-step) with each other. Out-of-step protection against power swings is essential to provide supervising signals for distance relays to mitigate the effects of the disturbance. A new R-X criterion is proposed to identify out-of-step conditions for large and complex power systems, such as KEG. A proposed Adaptive Out-of-Step Relay (AOSR) will monitor power system conditions and adjust the relay reach accordingly for better power swing classification. When unstable swings are detected, controllable tripping signals are initiated and system separation will create small subsystems or islands of the power system. These smaller systems will be created to achieve a balance of load and available generation. The electric power system chosen to study and to illustrate the criteria for the proposed adaptive relays was that of the country of Kuwait. The small oil-rich country of Kuwait has been dealing with an electric energy crisis that started summer 2006. With a dry dessert climate and intensely hot summers, the 3.6 million residents of Kuwait depend on continuously operated A/C units for living. This is the major reason why the peak load in a summer month reaches almost 11,000 MW while the peak load in a winter month does not exceed 5,000 MW. The Kuwait Electric Grid (KEG) is modelled and analyzed using Power Analytics' software known as PaladinRTM DesignBase(TM). Performance studies produce data to examine distance and out-of-step protection. Power Flow (PF), Short Circuit Analysis (SCA), and Transient Stability Analysis (TSA) are used to verify the model of KEG. These studies

  8. Analysis of a Major Electric Grid -- Stability and Adaptive Protection

    NASA Astrophysics Data System (ADS)

    Alanzi, Sultan

    system conditions. This dissertation introduces a combination of quadrilateral and mho characteristics to create a distance relay with a mushroom shape in R-X diagrams. This new relay offers larger protective reach with a lower limitation on loadability. When major disturbances occur, the power balance between load and generation might be disturbed causing the generators to lose synchronism (to be out-of-step) with each other. Out-of-step protection against power swings is essential to provide supervising signals for distance relays to mitigate the effects of the disturbance. A new R-X criterion is proposed to identify out-of-step conditions for large and complex power systems, such as KEG. A proposed Adaptive Out-of-Step Relay (AOSR) will monitor power system conditions and adjust the relay reach accordingly for better power swing classification. When unstable swings are detected, controllable tripping signals are initiated and system separation will create small subsystems or islands of the power system. These smaller systems will be created to achieve a balance of load and available generation. The electric power system chosen to study and to illustrate the criteria for the proposed adaptive relays was that of the country of Kuwait. The small oil-rich country of Kuwait has been dealing with an electric energy crisis that started summer 2006. With a dry dessert climate and intensely hot summers, the 3.6 million residents of Kuwait depend on continuously operated A/C units for living. This is the major reason why the peak load in a summer month reaches almost 11,000 MW while the peak load in a winter month does not exceed 5,000 MW. The Kuwait Electric Grid (KEG) is modelled and analyzed using Power Analytics' software known as PaladinRTM DesignBase(TM). Performance studies produce data to examine distance and out-of-step protection. Power Flow (PF), Short Circuit Analysis (SCA), and Transient Stability Analysis (TSA) are used to verify the model of KEG. These studies

  9. Stability Analysis for Constrained Principal Axis Slew Maneuvers

    NASA Technical Reports Server (NTRS)

    Seywald, Hans; Lim, Kyong B.; Anthony, Tobin C.

    1996-01-01

    This paper addresses the problem of reorienting a rigid spacecraft from arbitrary initial conditions to prescribed final conditions with zero angular velocity. The control law analyzed is based on quaternion feedback and leaves the user to choose two gains as functions of position, angular rate, and time. For arbitrary initial states, conditions on the controller gains are identified that guarantee global asymptotic stability. For the special case of rest-to-rest reorientations, the control law reduces to earlier results involving a principal axis rotation. The paper also addresses slew rate constraints, both, in terms of the two and infinity norms.

  10. Periodic stellar pulsations - Stability analysis and amplitude equations

    NASA Astrophysics Data System (ADS)

    Buchler, J. R.; Moskalik, Pawel; Kovacs, Geza

    1991-10-01

    The stability properties of nonlinear periodic stellar pulsations are studied within the amplitude equation formalism. Both nonresonant and resonant pulsations are considered. A comparison to a sequence of classical Cepheid models shows that the formalism provides a good qualitative and quantitative description of the behavior of the Floquet coefficients and that it also captures the most important features of the Floquet eigenvectors. It thus helps shed new light on the behavior (bifurcations) of pulsating stars. In addition, the predictive powers of the analytical approach allow a systematic search for models with specific pulsational properties.

  11. Analysis of stability of a homogeneous state of anisotropic plasma

    SciTech Connect

    Zakharov, V. Yu. Chernova, T. G. Stepanov, S. E.

    2015-04-15

    Small-amplitude waves in collisionless magnetized plasma are considered in the framework of one-fluid anisotropic magnetohydrodynamics with allowance for the anisotropy of the pressure and thermal flux. Stability of a homogeneous plasma state is analyzed using an eighth-order dispersion relation. Restrictions on the parameters of the homogeneous state at which the dispersion relation has no complex roots at any value of the angle between the wave vector and the unperturbed magnetic field are obtained. The applied method also makes it possible to determine the types of unstable waves.

  12. Fuzzy Current-Mode Control and Stability Analysis

    NASA Technical Reports Server (NTRS)

    Kopasakis, George

    2000-01-01

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

  13. Magnetic Reconstruction and Stability Analysis of PEGASUS Plasmas

    NASA Astrophysics Data System (ADS)

    Diem, S. J.; Fonck, R. J.; Garstka, G. D.; Sontag, A. C.; Tritz, K. L.

    2001-10-01

    Reconstruction of the magnetic equilibrium for recent discharges in Pegasus are obtained with a locally developed code. This code employs a nonlinear least-squares fitting routine combined with a Grad-Shafranov solver, and has been compared to TokaMak and EFIT analyses. A newly installed, comprehensive set of equilibrium magnetics diagnostics, including a poloidal array of 20 magnetic pick-up coils, 20 poloidal flux loops on the outboard, 6 center stack flux loops, a Rogowski coil for the toroidal plasma current, and a diamagnetic loop are used as constraints. Typical plasmas exhibit broad/flat central q(R) profiles with q(0)< = 2 corresponding to the onset of a large 2/1 mode. The ideal stability limits in q(a) and beta to be expected for Pegasus are under study using the DCON code applied to model equilibria. Plasmas with high edge current gradients are unstable to edge kink modes as expected; a constraint on the edge current gradients was implemented to access more realistic plasmas. A systematic mapping of stability space (e.g. li vs q(0), li vs q(98), etc.) is in progress.

  14. A stability analysis of AVE-4 severe weather soundings

    NASA Technical Reports Server (NTRS)

    Johnson, D. L.

    1982-01-01

    The stability and vertical structure of an average severe storm sounding, consisting of both thermodynamic and wind vertical profiles, were investigated to determine if they could be distinguished from an average lag sounding taken 3 to 6 hours prior to severe weather occurrence. The term average is defined here to indicate the arithmetic mean of a parameter, as a function of altitude, determined from a large number of available observations taken either close to severe weather occurrence, or else more than 3 hours before it occurs. The investigative computations were also done to help determine if a severe storm forecast or index could possibly be used or developed. These mean vertical profiles of thermodynamic and wind parameters as a function of severity of the weather, determined from manually digitized radar (MDR) categories are presented. Profile differences and stability index differences are presented along with the development of the Johnson Lag Index (JLI) which is determined entirely upon environmental vertical parameter differences between conditions 3 hours prior to severe weather, and severe weather itself.

  15. Stability analysis of traffic flow with extended CACC control models

    NASA Astrophysics Data System (ADS)

    Ya-Zhou, Zheng; Rong-Jun, Cheng; Siu-Ming, Lo; Hong-Xia, Ge

    2016-06-01

    To further investigate car-following behaviors in the cooperative adaptive cruise control (CACC) strategy, a comprehensive control system which can handle three traffic conditions to guarantee driving efficiency and safety is designed by using three CACC models. In this control system, some vital comprehensive information, such as multiple preceding cars’ speed differences and headway, variable safety distance (VSD) and time-delay effect on the traffic current and the jamming transition have been investigated via analytical or numerical methods. Local and string stability criterion for the velocity control (VC) model and gap control (GC) model are derived via linear stability theory. Numerical simulations are conducted to study the performance of the simulated traffic flow. The simulation results show that the VC model and GC model can improve driving efficiency and suppress traffic congestion. Project supported by the National Natural Science Foundation of China (Grant Nos. 71571107 and 11302110). The Scientific Research Fund of Zhejiang Province, China (Grant Nos. LY15A020007, LY15E080013, and LY16G010003). The Natural Science Foundation of Ningbo City (Grant Nos. 2014A610030 and 2015A610299), the Fund from the Government of the Hong Kong Administrative Region, China (Grant No. CityU11209614), and the K C Wong Magna Fund in Ningbo University, China.

  16. Slope stability analysis for Valles Marineris, Mars: a numerical analysis of controlling conditions and failure types

    NASA Astrophysics Data System (ADS)

    Crosta, G.; Castellanza, R.; De Blasio, F.; Utili, S.

    2012-04-01

    Valles Marineris (VM hereafter) in the equatorial area of Mars exhibits several gravitative failures often involving the whole 6-8 km thickness of the valley walls. The failures have resulted in a series of long-runout landslides up to several hundred cubic kilometres in volume (Quantin et al., 2004), and the formation of sub-circular alcoves perched on the top. Several questions arise as to forces at play in the stability of the walls of VM, the geometrical shape of the alcoves and the shape and long-runout of the landslides (see for example Lucas et al., 2011). In this work, we concentrate on the stability analysis of the walls of VM with two precise questions in mind starting from past studies (Bigot-Cormier and Montgomery, 2006; Neuffer and Schultz, 2006, Schultz, 2002). The first concerns the properties of the materials that give origin to instability. We performed several finite element and discrete element calculations tailored to slope stability analysis based on the genuine shape of the walls of VM taken from the MOLA topographic data. We considered stratified and differently altered/degraded materials to define the range of physical mechanical properties required for failure to occur and to explain the discrete distribution of failures along the VM valley flanks. A second question addressed in this work is the geometrical shape of the sub-circular alcoves. Normally, these shapes are commonplace for slopes made of uniform and isotropic properties, and are also observed in subaqueous environment. We performed calculations taking into consideration the progressive failure in the slope showing the final results in terms of surface failure geometry. Bigot-Cormier, F., Montgomery, D.R. (2007) Valles Marineris landslides: Evidence for a strength limit to Martian relief? Earth and Planetary Science Letters, 260, 1-2, 15, 179-186 Lucas, A., Mangeney, A., Mège, D., and Bouchut, F., 2011. Influence of the scar geometry on landslide dynamics and deposits

  17. Polynomial elimination theory and non-linear stability analysis for the Euler equations

    NASA Technical Reports Server (NTRS)

    Kennon, S. R.; Dulikravich, G. S.; Jespersen, D. C.

    1986-01-01

    Numerical methods are presented that exploit the polynomial properties of discretizations of the Euler equations. It is noted that most finite difference or finite volume discretizations of the steady-state Euler equations produce a polynomial system of equations to be solved. These equations are solved using classical polynomial elimination theory, with some innovative modifications. This paper also presents some preliminary results of a new non-linear stability analysis technique. This technique is applicable to determining the stability of polynomial iterative schemes. Results are presented for applying the elimination technique to a one-dimensional test case. For this test case, the exact solution is computed in three iterations. The non-linear stability analysis is applied to determine the optimal time step for solving Burgers' equation using the MacCormack scheme. The estimated optimal time step is very close to the time step that arises from a linear stability analysis.

  18. Analysis of cavern stability at the Bryan Mound SPR site.

    SciTech Connect

    Ehgartner, Brian L.; Sobolik, Steven Ronald

    2009-04-01

    This report presents computational analyses that simulate the structural response of caverns at the Strategic Petroleum Reserve Bryan Mound site. The cavern field comprises 20 caverns. Five caverns (1, 2, 4, and 5; 3 was later plugged and abandoned) were acquired from industry and have unusual shapes and a history dating back to 1946. The other 16 caverns (101-116) were leached according to SPR standards in the mid-1980s and have tall cylindrical shapes. The history of the caverns and their shapes are simulated in a 3-D geomechanics model of the site that predicts deformations, strains, and stresses. Future leaching scenarios due to oil drawdowns using fresh water are also simulated by increasing the volume of the caverns. Cavern pressures are varied in the model to capture operational practices in the field. The results of the finite element model are interpreted to provide information on the current and future status of subsidence, well integrity, and cavern stability. The most significant result in this report is relevant to caverns 1, 2, and 5. The caverns have non-cylindrical shapes and have potential regions where the surrounding salt may be damaged during workover procedures. During a workover the normal cavern operating pressure is lowered to service a well. At this point the wellhead pressures are atmospheric. When the workover is complete, the cavern is repressurized. The resulting elastic stresses are sufficient to cause tension and large deviatoric stresses at several locations. With time, these stresses relax to a compressive state due to salt creep. However, the potential for salt damage and fracturing exists. The analyses predict tensile stresses at locations with sharp-edges in the wall geometry, or in the case of cavern 5, in the neck region between the upper and lower lobes of the cavern. The effects do not appear to be large-scale, however, so the only major impact is the potential for stress-induced salt falls in cavern 5, potentially leading to

  19. Kinetic Analysis of Haloacetonitrile Stability in Drinking Waters.

    PubMed

    Yu, Yun; Reckhow, David A

    2015-09-15

    Haloacetonitriles (HANs) are an important class of drinking water disinfection byproducts (DBPs) that are reactive and can undergo considerable transformation on time scales relevant to system distribution (i.e., from a few hours to a week or more). The stability of seven mono-, di-, and trihaloacetonitriles was examined under a variety of conditions including different pH levels and disinfectant doses that are typical of drinking water distribution systems. Results indicated that hydroxide, hypochlorite, and their protonated forms could react with HANs via nucleophilic attack on the nitrile carbon, forming the corresponding haloacetamides (HAMs) and haloacetic acids (HAAs) as major reaction intermediates and end products. Other stable intermediate products, such as the N-chloro-haloacetamides (N-chloro-HAMs), may form during the course of HAN chlorination. A scheme of pathways for the HAN reactions was proposed, and the rate constants for individual reactions were estimated. Under slightly basic conditions, hydroxide and hypochlorite are primary reactants and their associated second-order reaction rate constants were estimated to be 6 to 9 orders of magnitude higher than those of their protonated conjugates (i.e., neutral water and hypochlorous acid), which are much weaker but more predominant nucleophiles at neutral and acidic pHs. Developed using the estimated reaction rate constants, the linear free energy relationships (LFERs) summarized the nucleophilic nature of HAN reactions and demonstrated an activating effect of the electron withdrawing halogens on nitrile reactivity, leading to decreasing HAN stability with increasing degree of halogenation of the substituents, while subsequent shift from chlorine to bromine atoms has a contrary stabilizing effect on HANs. The chemical kinetic model together with the reaction rate constants that were determined in this work can be used for quantitative predictions of HAN concentrations depending on pH and free chlorine

  20. Attachment style, gender, and relationship stability: a longitudinal analysis.

    PubMed

    Kirkpatrick, L A; Davis, K E

    1994-03-01

    Adult attachment styles in 354 heterosexual couples in serious dating relationships were examined. Principal findings included the following: (a) male and female attachment styles were nonrandomly paired, for example, no anxious-anxious or avoidant-avoidant pairs were found; (b) male and female styles related to concurrent relationship ratings of both partners in different but theoretically meaningful ways; (c) male and female styles contributed significantly to longitudinal prediction of relationship stability and status, even when prior duration and commitment to the relationship were statistically controlled; (d) specifically, relationships of avoidant men and of anxious women were surprisingly stable over 3 years, particularly in light of the relatively poor ratings of these relationships by both partners at Time 1. Discussion focuses on the need to integrate gender role considerations and relationship dynamics and processes into theorizing on adult attachment. PMID:8169762

  1. Analysis of stability contributions of high dihedral V-tails

    NASA Technical Reports Server (NTRS)

    Freeman, C. E.; Yeager, W. T., Jr.

    1978-01-01

    An investigation was undertaken to determine the effectiveness of four analytical methods (empirical, modified empirical, vortex-lattice, and an inviscid, three dimensional, potential flow, wing body program) to estimate the lateral and longitudinal static stability characteristics of an isolated V-tail wind tunnel model. The experimental tests were conducted in the V/STOL tunnel at a Mach number of 0.18. Angle-of-attack data were obtained from -12 deg to 8 deg at 0 deg sideslip. Sideslip sweeps from -5 deg to 10 deg were made at angles of attack of 4 deg, 0 deg and -4 deg. The V-tail dihedral angles were 45 deg, 50 deg, 55 deg, and 60 deg.

  2. Dynamic pressure approach to analysis of reactor fuel plate stability

    SciTech Connect

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

    1990-01-01

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

  3. Stability analysis of an extended intelligent driver model and its simulations under open boundary condition

    NASA Astrophysics Data System (ADS)

    Li, Zhipeng; Li, Wenzhong; Xu, Shangzhi; Qian, Yeqing

    2015-02-01

    This paper presents an extended intelligent driver traffic flow model, in which the power of the considered vehicle is strengthened in proportion to that of the immediately preceding vehicle. We analyze the stability against a small perturbation by use of the linear stability method for the proposed traffic flow model on a single lane under open boundary condition, with the finding that the traffic flow stability can be improved by increasing the proportion of the direct power cooperation of the preceding vehicle. The participation of forward power cooperation can help to stabilize the traffic flow and suppress the traffic jams. In addition, the simulations under open boundary single lane are conducted to validate the correctness on theoretical deduction, which shows that numerical results in large-wave and short-wave stability are in good agreement with those of theoretical analysis.

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

    PubMed Central

    Wu, Jiang Hao; Sun, Mao

    2012-01-01

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

  5. Nonmodal linear stability analysis of miscible viscous fingering in porous media

    NASA Astrophysics Data System (ADS)

    Hota, Tapan Kumar; Pramanik, Satyajit; Mishra, Manoranjan

    2015-11-01

    The nonmodal linear stability of miscible viscous fingering in a two-dimensional homogeneous porous medium has been investigated. The linearized perturbed equations for Darcy's law coupled with a convection-diffusion equation is discretized using a finite difference method. The resultant initial value problem is solved by a fourth-order Runge-Kutta method, followed by a singular value decomposition of the propagator matrix. Particular attention is given to the transient behavior rather than the long-time behavior of eigenmodes predicted by the traditional modal analysis. The transient behaviors of the response to external excitations and the response to initial conditions are studied by examining the ɛ -pseudospectra structures and the largest energy growth function, respectively. With the help of nonmodal stability analysis we demonstrate that at early times the displacement flow is dominated by diffusion and the perturbations decay. At later times, when convection dominates diffusion, perturbations grow. Furthermore, we show that the dominant perturbation that experiences the maximum amplification within the linear regime lead to the transient growth. These two important features were previously unattainable in the existing linear stability methods for miscible viscous fingering. To explore the relevance of the optimal perturbation obtained from nonmodal analysis, we performed direct numerical simulations using a highly accurate pseudospectral method. Furthermore, a comparison of the present stability analysis with existing modal and initial value approach is also presented. It is shown that the nonmodal stability results are in better agreement than the other existing stability analyses, with those obtained from direct numerical simulations.

  6. Flexible Launch Vehicle Stability Analysis Using Steady and Unsteady Computational Fluid Dynamics

    NASA Technical Reports Server (NTRS)

    Bartels, Robert E.

    2012-01-01

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

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

    SciTech Connect

    Barkana, Itzhak

    2014-12-10

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

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

    NASA Astrophysics Data System (ADS)

    Barkana, Itzhak

    2014-12-01

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

  9. Analysis of cavern stability at the West Hackberry SPR site.

    SciTech Connect

    Ehgartner, Brian L.; Sobolik, Steven Ronald

    2009-05-01

    This report presents computational analyses that simulate the structural response of caverns at the Strategic Petroleum Reserve (SPR) West Hackberry site. The cavern field comprises 22 caverns. Five caverns (6, 7, 8, 9, 11) were acquired from industry and have unusual shapes and a history dating back to 1946. The other 17 caverns (101-117) were leached according to SPR standards in the mid-1980s and have tall cylindrical shapes. The history of the caverns and their shapes are simulated in a three-dimensional geomechanics model of the site that predicts deformations, strains, and stresses. Future leaching scenarios corresponding to oil drawdowns using fresh water are also simulated by increasing the volume of the caverns. Cavern pressures are varied in the model to capture operational practices in the field. The results of the finite element model are interpreted to provide information on the current and future status of subsidence, well integrity, and cavern stability. The most significant results in this report are relevant to Cavern 6. The cavern is shaped like a bowl with a large ceiling span and is in close proximity to Cavern 9. The analyses predict tensile stresses at the edge of the ceiling during repressuization of Cavern 6 following workover conditions. During a workover the cavern is at low pressure to service a well. The wellhead pressures are atmospheric. When the workover is complete, the cavern is repressurized. The resulting elastic stresses are sufficient to cause tension around the edge of the large ceiling span. With time, these stresses relax to a compressive state because of salt creep. However, the potential for salt fracture and propagation exists, particularly towards Cavern 9. With only 200 ft of salt between the caverns, the operational consequences must be examined if the two caverns become connected. A critical time may be during a workover of Cavern 9 in part because of the operational vulnerabilities, but also because dilatant damage is

  10. Diabetes may affect intracranial aneurysm stabilization in older patients: Analysis based on intraoperative findings

    PubMed Central

    Song, Jihye; Shin, Yong Sam

    2016-01-01

    Background: Only a small proportion of aneurysms progress to rupture. Previous studies have focused on predicting the rupture risk of intracranial aneurysms. Atherosclerotic aneurysm wall appears resistant to rupture. The purpose of this study was to evaluate clinical and morphological factors affecting atherosclerosis of an aneurysm and identify the parameters that predict aneurysm stabilization. Methods: We conducted a retrospective analysis of 253 consecutive patients with 291 unruptured aneurysms who underwent clipping surgery in a single institution between January 2012 and October 2013. Aneurysms were categorized based on intraoperative video findings and assessed morphologic and demographic data. Aneurysms which had the atherosclerotic wall without any super thin and transparent portion were defined as stabilized group and the others as a not-stabilized group. Results: Of the 207 aneurysms, 176 (85.0%) were assigned to the not-stabilized group and 31 (15.0%) to the stabilized group. The relative proportion of stabilized aneurysms increased significantly as the age increased (P < 0.001). Univariate logistic analysis showed that age ≥65 years (P < 0.001), hypertension (P = 0.012), diabetes (P = 0.007), and height ≥3 mm (P = 0.007) were correlated with stabilized aneurysms. Multivariate logistic analysis showed that age ≥65 years (P = 0.009) and hypertension (P = 0.041) were strongly correlated with stable aneurysms. In older patients (≥65 years of age), multivariate logistic regression revealed that only diabetes was associated with stabilized aneurysms (P = 0.027). Conclusions: In patients ≥65 years of age, diabetes mellitus may highly predict the stabilized aneurysms. These results provide useful information in determining treatment and follow-up strategies, especially in older patients. PMID:27313965

  11. Flame stability monitoring and characterization through digital imaging and spectral analysis

    NASA Astrophysics Data System (ADS)

    Sun, Duo; Lu, Gang; Zhou, Hao; Yan, Yong

    2011-11-01

    This paper presents the design, implementation and evaluation of an instrumentation system for the stability monitoring and characterization of combustion flames. The system, incorporating optical sensing, image processing and spectral analysis techniques, is designed to monitor a range of flame characteristic parameters. The stability of the flame is assessed through statistical analysis of the flame parameters obtained. Embedded computer techniques are employed to ensure the compactness and robustness of the system. Experiments were conducted on a gas-fired combustion test rig to evaluate the system. The impact of equivalence ratio on the stability of the gaseous flame is investigated. Further trials were carried out on a 9 MWth heavy-oil-fired combustion test facility. The impact of the swirl vane angle of tertiary air on the oil-fired flames is studied. The results demonstrate the effectiveness of the system for the monitoring and characterization of the flame stability.

  12. Langley Stability and Transition Analysis Code (LASTRAC) Version 1.2 User Manual

    NASA Technical Reports Server (NTRS)

    Chang, Chau-Lyan

    2004-01-01

    LASTRAC is a general-purposed, physics-based transition prediction code released by NASA for Laminar Flow Control studies and transition research. The design and development of the LASTRAC code is aimed at providing an engineering tool that is easy to use and yet capable of dealing with a broad range of transition related issues. It was written from scratch based on the state-of-the-art numerical methods for stability analysis and modern software technologies. At low fidelity, it allows users to perform linear stability analysis and N-factor transition correlation for a broad range of flow regimes and configurations by using either the linear stability theory or linear parabolized stability equations method. At high fidelity, users may use nonlinear PSE to track finite-amplitude disturbances until the skin friction rise. This document describes the governing equations, numerical methods, code development, detailed description of input/output parameters, and case studies for the current release of LASTRAC.

  13. Primary posterior stabilized total knee arthroplasty: analysis of different instrumentation

    PubMed Central

    2014-01-01

    Background Intercondylar femoral bone removal during posterior stabilized (PS) total knee arthroplasty (TKA) makes many cruciate substituting implant designs less appealing than cruciate retaining implants. Bone stock conservation is considered fundamental in the prevision of future revision surgeries. The purpose of this study was to compare the quantity of intercondylar bone removable during PS housing preparation using three contemporary PS TKA instrumentations. Method We compared different box cutting jigs which were utilized for the PS housing of three popular PS knee prostheses. The bone removal area from every PS box cutting jig was three-dimensionally measured. Results Independently from the implant size, the cutting jig for a specific PS TKA always resected significantly less bone than the others: this difference was statistically significant, especially for small- to medium-sized total knee femoral components. Conclusion This study does not establish a clinical relevance of removing more or less bone at primary TKA, but suggests that if a PS design is indicated, it is preferable to select a model which possibly resects less distal femoral bone. PMID:25037275

  14. Stability Analysis of Superhydrophobic Friction Reduction Polymeric Microchannels

    NASA Astrophysics Data System (ADS)

    Kim, Tae Jin; Hidrovo, Carlos

    2010-11-01

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

  15. STC/DBS Power subsystem control loop stability analysis

    SciTech Connect

    Peck, S.R.; Devaux, R.N.

    1984-08-01

    Many types of solar array regulation schemes are utilized throughout the spacecraft design community. Ensuring adequate control loop stability margins while achieving acceptable transient response performance is a complex and difficult task due to the extremely large number of variables and nonlinearities inherent in these systems. In recent years significant improvements in computer software have made this task more manageable and enabled a better understanding of the effects of system parameters. This paper describes the analytical approach utilized to evaluate and optimize the control loops for two partial shunt systems used on Satellite Television Corporation's Direct Broadcast Satellite presently in development at RCA Astro-Electronics. The 100V payload bus regulator is a linear sequential partial shunt system, and the 35.3V housekeeping bus utilizes a linear parallel partial shunt approach. For each case, detailed models of the solar arrays, control electronics, and spacecraft loads were developed and then combined to simulate the complete system. The analytical results have been and/or are being verified by test. The results will be verified with illuminated solar arrays during full-up spacecraft systems testing.

  16. Stability analysis of multiple-robot control systems

    NASA Technical Reports Server (NTRS)

    Wen, John T.; Kreutz, Kenneth

    1989-01-01

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

  17. Contrast analysis and stability on the ExAO testbed

    SciTech Connect

    Evans, J; Thomas, S; Gavel, D; Dillon, D; Macintosh, B

    2008-06-10

    High-contrast adaptive optics systems, such as those needed to image extrasolar planets, are known to require excellent wavefront control and diffraction suppression. The Laboratory for Adaptive Optics at UC Santa Cruz is investigating limits to high-contrast imaging in support of the Gemini Planet Imager. Previous contrast measurements were made with a simple single-opening prolate spheroid shaped pupil that produced a limited region of high-contrast, particularly when wavefront errors were corrected with the 1024-actuator Boston Micromachines MEMS deformable mirror currently in use on the testbed. A more sophisticated shaped pupil is now being used that has a much larger region of interest facilitating a better understanding of high-contrast measurements. In particular we examine the effect of heat sources in the testbed on PSF stability. We find that rms image motion scales as 0.02 {lambda}/D per watt when the heat source is near the pupil plane. As a result heat sources of greater than 5 watts should be avoided near pupil planes for GPI. The safest place to introduce heat is near a focal plane. Heat also can effect the standard deviation of the high-contrast region but in the final instrument other sources of error should be more significant.

  18. Synchronous machine steady-state stability analysis using an artificial neural network

    SciTech Connect

    Chen, C.R.; Hsu, Y.Y. . Dept. of Electrical Engineering)

    1991-03-01

    A new type of artificial neural network is proposed for the steady-state stability analysis of a synchronous generator. In the developed artificial neutral network, those system variables which play an important role in steady-state stability such as generator outputs and power system stabilizer parameters are employed as the inputs. The output of the neural net provides the information on steady-state stability. Once the connection weights of the neural network have been learned using a set of training data derived off-line, the neural net can be applied to analyze the steady-state stability of the system time. To demonstrate the effectiveness of the proposed neural net, steady-state stability analysis is performed on a synchronous generator connected to a large power system. It is found that the proposed neural net requires much less training time than the multilayer feedforward network with backpropagation-momentum learning algorithm. It is also concluded from the test results that correct stability assessment can be achieved by the neural network.

  19. [Trait stability and test site representativeness of sugarcane varieties based on GGE-biplot analysis].

    PubMed

    Luo, Jun; Zhang, Hua; Deng, Zu-Hu; Que, You-Xiong

    2012-05-01

    Arithmetic mean method is commonly used to evaluate the yield stability and adaptability of sugarcane varieties, and variance analysis is applied to estimate the errors in regional trials. However, it is difficult to accurately evaluate the differences of the varieties due to the discrepancies across test sites and years. In this paper, GGE-biplot method was adopted to analyze the data from the regional trials with seven sugarcane varieties at five sites from 2008 to 2009, aimed to objectively evaluate the yield stability and adaptability of sugarcane varieties in China. Among the test sugarcane varieties, Funong No. 30 had higher cane yield and better yield stability, Yuegan No. 18 had higher sugar content and better trait stability, Funong No. 28 and Yunzhe 99-91 had high sucrose content and trait stability, while Yuegan No. 16 had the highest cane yield and sugar content but ordinary stability. In the test sites, Zhangzhou City in Fujian Province and Suixi City in Guangdong Province had the best representativeness and discrimination. This study showed that GGE-biplot analysis provided a simple and effective method to analyze the high yield and stability of sugarcane varieties in regional trials, and supplied the basis for the approval and extension of new sugarcane varieties. PMID:22919843

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

    PubMed

    Bhalekar, Sachin

    2016-08-01

    This paper deals with the stability and bifurcation analysis of a general form of equation D(α)x(t)=g(x(t),x(t-τ)) involving the derivative of order α ∈ (0, 1] and a constant delay τ ≥ 0. The stability of equilibrium points is presented in terms of the stability regions and critical surfaces. We provide a necessary condition to exist chaos in the system also. A wide range of delay differential equations involving a constant delay can be analyzed using the results proposed in this paper. The illustrative examples are provided to explain the theory. PMID:27586623

  1. Comparative structure analysis of non-polar organic ferrofluids stabilized by saturated mono-carboxylic acids.

    PubMed

    Avdeev, M V; Bica, D; Vékás, L; Aksenov, V L; Feoktystov, A V; Marinica, O; Rosta, L; Garamus, V M; Willumeit, R

    2009-06-01

    The structure of ferrofluids (magnetite in decahydronaphtalene) stabilized with saturated mono-carboxylic acids of different chain lengths (lauric, myristic, palmitic and stearic acids) is studied by means of magnetization analysis and small-angle neutron scattering. It is shown that in case of saturated acid surfactants, magnetite nanoparticles are dispersed in the carrier approximately with the same size distribution whose mean value and width are significantly less as compared to the classical stabilization with non-saturated oleic acid. The found thickness of the surfactant shell around magnetite is analyzed with respect to stabilizing properties of mono-carboxylic acids. PMID:19376524

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

    NASA Astrophysics Data System (ADS)

    Bhalekar, Sachin

    2016-08-01

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

  3. Stability analysis of an interactive system of wave equation and heat equation with memory

    NASA Astrophysics Data System (ADS)

    Zhang, Qiong

    2014-10-01

    This paper is devoted to the stability analysis of an interaction system comprised of a wave equation and a heat equation with memory, where the hereditary heat conduction is due to Gurtin-Pipkin law or Coleman-Gurtin law. First, we show the strong asymptotic stability of solutions to this system. Then, the exponential stability of the interaction system is obtained when the hereditary heat conduction is of Gurtin-Pipkin type. Further, we show the lack of uniform decay of the interaction system when the heat conduction law is of Coleman-Gurtin type.

  4. Stability analysis of the motion along re-entry optimal trajectories

    NASA Astrophysics Data System (ADS)

    Popescu, M.

    1983-10-01

    A stability analysis of the equations of motion governing the ricochet re-entry trajectory of a rocket-powered vehicle is presented. The plane case of a vehicle propelled by the time-dependent expulsion of gases is considered, taking the change in mass into account. The zone of stability is defined using a frequency criterion, while the stability domains of the parameters of motion are derived by constructing a Liapunov function. The perturbations of the state variables and their damping-out velocities are estimated.

  5. Thermal gravity analysis for the study of stability of graphene oxide-glycine nanocomposites

    NASA Astrophysics Data System (ADS)

    Najafi, F.; Rajabi, M.

    2015-05-01

    In this work, we synthesized graphene oxide-glycine (GO-G) nanocomposite. To produce this nanocomposite with GO surface, glycine with known concentration was added to GO suspension in ethanol solvent. Nanocomposites provided were characterized by scanning electron microscope (SEM) and Fourier transform infrared (FT-IR) spectroscopy, respectively. Thermogravimetric analysis (TGA) was employed to investigate the thermal stability of these nanocomposites. Results of characterization by SEM and FT-IR showed that nanocomposite was created by the reaction between GO and G. Study of thermal stability by TGA showed that thermal stability of GO was more than that of the GO-G nanocomposite.

  6. Global asymptotic stability analysis for neutral stochastic neural networks with time-varying delays

    NASA Astrophysics Data System (ADS)

    Su, Weiwei; Chen, Yiming

    2009-04-01

    In this paper, the global asymptotic stability is investigated for a class of neutral stochastic neural networks with time-varying delays and norm-bounded uncertainties. Based on Lyapunov stability theory and stochastic analysis approaches, delay-dependent criteria are derived to ensure the global, robust, asymptotic stability of the addressed system in the mean square for all admissible parameter uncertainties. The criteria can be checked easily by the LMI Control Toolbox in Matlab. A numerical example is given to illustrate the feasibility and effectiveness of the results.

  7. Design Analysis Report for 244-AR Interim Stabilization Exhaust Ventilation Ducting

    SciTech Connect

    RUTHERFORD, J.

    2002-11-21

    This report documents the design analysis performed for the exhaust ducting associated with the 244-AR Interim Stabilization Project. The exhaust ducting connects portable exhausters PORO5 and PORO6 to the existing east dog house of the 291-AR filter vault and the vessel ventilation system. This analysis examines loads on the ductwork and ductwork supports.

  8. The Stability of IQ in People with Low Intellectual Ability: An Analysis of the Literature

    ERIC Educational Resources Information Center

    Whitaker, Simon

    2008-01-01

    A meta-analysis of the stability of low IQ (IQ less than 80) was performed on IQ tests that have been commonly used--tests that were derived by D. Wechsler (1949, 1955, 1974, 1981, 1991, 1997) and those based on the Binet scales (L. M. Terman, 1960; L. M. Terman & Merrill, 1972). Weighted-mean stability coefficients of 0.77 and 0.78 were found for…

  9. Fundamental Aeronautics Program. Subsonic Rotary Wing Project: SRW Aeromechanics Overview/UH-60 Airloads Wind Tunnel Test Summary

    NASA Technical Reports Server (NTRS)

    Norman, Thomas R.

    2011-01-01

    Objectives: a) Advance the understanding of phenomena in aerodynamics, dynamics, and active control of rotorcraft. b) Develop and validate first-principles tools. c) Acquire data for tool validation from small and large-scale testing of existing and novel rotorcraft configurations. Recent Accomplishments include: (CFD) - Made significant improvements in structured and unstructured rotorcraft CFD methods (OVERFLOW and FUN3D). (Icing) - a) Continued development of high-fidelity icing analysis tools. b) Completed test of oscillating airfoil in Icing Research Tunnel (IRT). c) Developed plans and began detailed preparations for subscale rotor test in IRT.

  10. Analysis of bifurcation and stability for a tractor semi-trailer in planar motion

    NASA Astrophysics Data System (ADS)

    Ding, Nenggen; Shi, Xiaobo; Zhang, Yipeng; Chen, Wen

    2014-12-01

    This paper is intended for bifurcation analysis of a nonlinear tractor semi-trailer vehicle model in planar motion and for investigating its stability under constant running conditions. Bifurcation analysis shows that bifurcation diagrams of a tractor semi-trailer are quite different from those of a single-unit vehicle. Some instability phenomena of the vehicle system such as jackknifing, sideslip, and spinning are explained by correlating them with the behaviour in the neighbourhood of unstable fixed points based on analysis of eigenvectors, phase trajectories, and status of lateral tyre force saturation. It is also found that yaw planar instability of a tractor semi-trailer is caused by lateral tyre force saturation of the tractor's rear axles and/or the trailer's axles. Moreover, the stability region in the state space is demarcated, and a stability index for evaluating size of the stability region in a feasible domain is proposed. Yaw stability under constant driving conditions is analysed by using the proposed stability index.

  11. The application of cause-and-effect analysis to mathematical models of geophysical phenomena. II - Stability analysis

    NASA Astrophysics Data System (ADS)

    Andronova, Nataliia G.; Schlesinger, Michael E.

    1992-04-01

    The 'cause-and-effect analysis' (CEA) technique is applied to investigate the stability of mathematical models of geophysical phenomena. It is shown that the ith coefficient of p(lambda) is equal to -PL sup (i), the ith order loop effect of the graph analog of matrix B - I, where I is the identity matrix. The classical conditions for stability for both discrete process (DP) and continuous process (CP) systems are then reformulated in terms of the PL sup (i) determined from the graph analog of the system. The use of the result graph analog stability conditions is illustrated by application to two CP systems, the Chapman photochemical cycle and an energy balance climate model, and to a DP system, a finite-differenced differential equation. CEA stability analysis elucidates the interactions among a system's internal variables and thus determines the cause of an instability and facilitates modification of the system to make it stable.

  12. Design and Analysis of the ITER Vertical Stability Coils

    SciTech Connect

    Peter H. Titus, et. al.

    2012-09-06

    The ITER vertical stability (VS) coils have been developed through the preliminary design phase by Princeton Plasma Physics Laboratory (PPPL). Final design, prototyping and construction will be carried out by the Chinese Participant Team contributing lab, Institute of Plasma Physics, Chinese Academy of Sciences (ASIPP). The VS coils are a part of the in-vessel coil systems which include edge localized mode (ELM) coils as well as the VS coils. An overview of the ELM coils is provided in another paper at this conference. 15 The VS design employs four turns of stainless steel jacketed mineral insulated copper (SSMIC) conductors The mineral insulation is Magnesium Oxide (MgO). Joule and nuclear heat is removed by water flowing at 3 m/s through the hollow copper conductor. A key element in the design is that slightly elevated temperatures in the conductor and its support spine during operation impose compressive stresses that mitigate fatigue damage. Away from joints, and break-outs, conductor thermal stresses are low because of the axisymmetry of the winding (there are no corner bends as in the ELM coils).The 120 degree segment joint, and break-out or terminal regions are designed with similar but imperfect constraint compared with the ring coil portion of the VS. The support for the break-out region is made from a high strength copper alloy, CuCrZr. This is needed to conduct nuclear heat to the actively cooled conductor and to the vessel wall. The support "spine" for the ring coil portion of the VS is 316 stainless steel, held to the vessel with preloaded 718 bolts. Lorentz loads resulting from normal operating loads, disruption loads and loads from disruption currents in the support spine shared with vessel, are applied to the VS coil. The transmission of the Lorentz and thermal expansion loads from the "spine" to the vessel rails is via friction augmented with a restraining "lip" to ensure the coil frictional slip is minimal and acceptable. Stresses in the coil

  13. Spreadsheet analysis of stability and meta-stability of low-dimensional magnetic particles using the Ising approach

    NASA Astrophysics Data System (ADS)

    Ehrmann, Andrea; Blachowicz, Tomasz; Zghidi, Hafed

    2015-05-01

    Modelling hysteresis behaviour, as it can be found in a broad variety of dynamical systems, can be performed in different ways. An elementary approach, applied for a set of elementary cells, which uses only two possible states per cell, is the Ising model. While such Ising models allow for a simulation of many systems with sufficient accuracy, they nevertheless depict some typical features which must be taken into account with proper care, such as meta-stability or the externally applied field sweeping speed. This paper gives a general overview of recent results from Ising models from the perspective of a didactic model, based on a 2D spreadsheet analysis, which can be used also for solving general scientific problems where direct next-neighbour interactions take place.

  14. Frequency domain stability analysis of nonlinear active disturbance rejection control system.

    PubMed

    Li, Jie; Qi, Xiaohui; Xia, Yuanqing; Pu, Fan; Chang, Kai

    2015-05-01

    This paper applies three methods (i.e., root locus analysis, describing function method and extended circle criterion) to approach the frequency domain stability analysis of the fast tool servo system using nonlinear active disturbance rejection control (ADRC) algorithm. Root locus qualitative analysis shows that limit cycle is generated because the gain of the nonlinear function used in ADRC varies with its input. The parameters in the nonlinear function are adjustable to suppress limit cycle. In the process of root locus analysis, the nonlinear function is transformed based on the concept of equivalent gain. Then, frequency domain description of the nonlinear function via describing function is presented and limit cycle quantitative analysis including estimating prediction error is presented, which virtually and theoretically demonstrates that the describing function method cannot guarantee enough precision in this case. Furthermore, absolute stability analysis based on extended circle criterion is investigated as a complement. PMID:25532936

  15. Thermodynamic stability analysis of the carbon biogeochemical cycle in aquatic shallow environments

    NASA Astrophysics Data System (ADS)

    Lvov, S. N.; Pastres, R.; Marcomini, A.

    1996-10-01

    We carry out the thermodynamic stability analysis of the carbon cycle in a lagoon. Our approach differs from linear stability analysis, and is based on the excess entropy production. The coupled biogeochemical processes in the lagoon include gas transfer, photosynthesis, respiration, decomposition, sedimentation, and oxidation of algae. The thermodynamic stability criterion derived from this analysis indicates that, in addition to known limiting factors of biomass production such as temperature, light, and nitrogen and phosphorous concentrations, the rate of carbon dioxide delivery from the air reservoir to the water can be also a limiting factor. For the Venice lagoon, the criterion obtained predicts that a doubling of the CO 2 partial pressure in the atmosphere can render the system unstable, driving it to dramatic biomass production and degradation.

  16. Stability analysis of the homogeneous hydrodynamics of a model for a confined granular gas.

    PubMed

    Brey, J Javier; Buzón, V; García de Soria, M I; Maynar, P

    2016-06-01

    The linear hydrodynamic stability of a model for confined quasi-two-dimensional granular gases is analyzed. The system exhibits homogeneous hydrodynamics, i.e., there are macroscopic evolution equations for homogeneous states. The stability analysis is carried out around all these states and not only the homogeneous steady state reached eventually by the system. It is shown that in some cases the linear analysis is not enough to reach a definite conclusion on the stability, and molecular dynamics simulation results are presented to elucidate these cases. The analysis shows the relevance of nonlinear hydrodynamic contributions to describe the behavior of spontaneous fluctuations occurring in the system, that lead even to the transitory formation of clusters of particles. The conclusion is that the system is always stable. The relevance of the results for describing the instabilities of confined granular gases observed experimentally is discussed. PMID:27415347

  17. Analysis of solar radiation pressure induced coupled librations of a gravity stabilized axisymmetric satellite

    NASA Technical Reports Server (NTRS)

    Shrivastava, S. K.; Hablani, H. B.

    1979-01-01

    This paper presents an analysis of solar radiation pressure induced coupled librations of gravity stabilized cylindrical spacecraft with a special reference to geostationary communication satellites. The Lagrangian approach is used to obtain the corresponding equations of motion. The solar induced torques are assumed to be free of librational angles and are represented by their Fourier expansion. The response and periodic solutions are obtained through linear and nonlinear analyses, using the method of harmonic balance in the latter case. The stability conditions are obtained using Routh-Hurwitz criteria. To establish the ranges of validity the analytic response is compared with the numerical solution. Finally, values of the system parameters are suggested to make the satellite behave as desired. Among these is a possible approach to subdue the solar induced roll resonance. It is felt that the approximate analysis presented here should significantly reduce the computational efforts involved in the design and stability analysis of the systems.

  18. 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.

  19. The contribution of particle swarm optimization to three-dimensional slope stability analysis.

    PubMed

    Kalatehjari, Roohollah; Rashid, Ahmad Safuan A; Ali, Nazri; Hajihassani, Mohsen

    2014-01-01

    Over the last few years, particle swarm optimization (PSO) has been extensively applied in various geotechnical engineering including slope stability analysis. However, this contribution was limited to two-dimensional (2D) slope stability analysis. This paper applied PSO in three-dimensional (3D) slope stability problem to determine the critical slip surface (CSS) of soil slopes. A detailed description of adopted PSO was presented to provide a good basis for more contribution of this technique to the field of 3D slope stability problems. A general rotating ellipsoid shape was introduced as the specific particle for 3D slope stability analysis. A detailed sensitivity analysis was designed and performed to find the optimum values of parameters of PSO. Example problems were used to evaluate the applicability of PSO in determining the CSS of 3D slopes. The first example presented a comparison between the results of PSO and PLAXI-3D finite element software and the second example compared the ability of PSO to determine the CSS of 3D slopes with other optimization methods from the literature. The results demonstrated the efficiency and effectiveness of PSO in determining the CSS of 3D soil slopes. PMID:24991652

  20. The Contribution of Particle Swarm Optimization to Three-Dimensional Slope Stability Analysis

    PubMed Central

    A Rashid, Ahmad Safuan; Ali, Nazri

    2014-01-01

    Over the last few years, particle swarm optimization (PSO) has been extensively applied in various geotechnical engineering including slope stability analysis. However, this contribution was limited to two-dimensional (2D) slope stability analysis. This paper applied PSO in three-dimensional (3D) slope stability problem to determine the critical slip surface (CSS) of soil slopes. A detailed description of adopted PSO was presented to provide a good basis for more contribution of this technique to the field of 3D slope stability problems. A general rotating ellipsoid shape was introduced as the specific particle for 3D slope stability analysis. A detailed sensitivity analysis was designed and performed to find the optimum values of parameters of PSO. Example problems were used to evaluate the applicability of PSO in determining the CSS of 3D slopes. The first example presented a comparison between the results of PSO and PLAXI-3D finite element software and the second example compared the ability of PSO to determine the CSS of 3D slopes with other optimization methods from the literature. The results demonstrated the efficiency and effectiveness of PSO in determining the CSS of 3D soil slopes. PMID:24991652

  1. The onset of absolute instability of rotating Hagen-Poiseuille flow: A spatial stability analysis

    NASA Astrophysics Data System (ADS)

    Fernandez-Feria, R.; del Pino, C.

    2002-09-01

    A spatial, viscous stability analysis of Poiseuille pipe flow with superimposed solid body rotation is considered. For each value of the swirl parameter (inverse Rossby number) L>0, there exists a critical Reynolds number Rec)(L above which the flow first becomes convectively unstable to nonaxisymmetric disturbances with azimuthal wave number n=-1. This neutral stability curve confirms previous temporal stability analyses. From this spatial stability analysis, we propose here a relatively simple procedure to look for the onset of absolute instability that satisfies the so-called Briggs-Bers criterion. We find that, for perturbations with n=-1, the flow first becomes absolutely unstable above another critical Reynolds number Ret)(L>Rec)(L, provided that L>0.38, with Ret[right arrow]Rec as L[right arrow]infinity. Other values of the azimuthal wave number n are also considered. For Re>Ret)(L, the disturbances grow both upstream and downstream of the source, and the spatial stability analysis becomes inappropriate. However, for Ret, the spatial analysis provides a useful description on how convectively unstable perturbations become absolutely unstable in this kind of flow.

  2. Slope Stability Analysis In Seismic Areas Of The Northern Apennines (Italy)

    SciTech Connect

    Lo Presti, D.; Fontana, T.; Marchetti, D.

    2008-07-08

    Several research works have been published on the slope stability in the northern Tuscany (central Italy) and particularly in the seismic areas of Garfagnana and Lunigiana (Lucca and Massa-Carrara districts), aimed at analysing the slope stability under static and dynamic conditions and mapping the landslide hazard. In addition, in situ and laboratory investigations are available for the study area, thanks to the activities undertaken by the Tuscany Seismic Survey. Based on such a huge information the co-seismic stability of few ideal slope profiles have been analysed by means of Limit equilibrium method LEM - (pseudo-static) and Newmark sliding block analysis (pseudo-dynamic). The analysis--results gave indications about the most appropriate seismic coefficient to be used in pseudo-static analysis after establishing allowable permanent displacement. Such indications are commented in the light of the Italian and European prescriptions for seismic stability analysis with pseudo-static approach. The stability conditions, obtained from the previous analyses, could be used to define microzonation criteria for the study area.

  3. Stability Analysis of Absorption Chiller-Heaters by Applying Transfer Function

    NASA Astrophysics Data System (ADS)

    Fujii, Tatsuo; Miyake, Satoshi; Oka, Masahiro; Mori, Kiyoyuki

    A transfer function approach is found to be a practical method for ensuring stable operation of absorption chiller-heaters. The transfer function model is based on a solution-circuit of the machine, which dominates the stability of the operation. This model includes a solution pump, a generator with an overflow weir, and a float valve. We found that the solution-circuit system is designed with the cascade control, which makes the system stable. In this construction, the float valve actuates a primary control loop, and the overflow weir actuates a secondary loop. The effects of the characteristic of the solution pump and the overflow weir are estimated by the degree of the stabilities, which are the gain margin and the phase margin. We found that the characteristic of the solution pump strongly effects the stability by enhancing the effect of the cascade control and improving the stability. So it is essential for a better stability analysis model. According to these results, the established model is useful for quantitatively predicting the stabilities of a chiller-heater in operation, and simultaneously reducing its size and improving the stability of operation. We conclude that the methodology based on transfer function can provide compact and reliable absorption chiller-heaters.

  4. Stability analysis and controller synthesis for hybrid dynamical systems.

    PubMed

    Heemels, W P M H; De Schutter, B; Lunze, J; Lazar, M

    2010-11-13

    Wherever continuous and discrete dynamics interact, hybrid systems arise. This is especially the case in many technological systems in which logic decision-making and embedded control actions are combined with continuous physical processes. Also for many mechanical, biological, electrical and economical systems the use of hybrid models is essential to adequately describe their behaviour. To capture the evolution of these systems, mathematical models are needed that combine in one way or another the dynamics of the continuous parts of the system with the dynamics of the logic and discrete parts. These mathematical models come in all kinds of variations, but basically consist of some form of differential or difference equations on the one hand and automata or other discrete-event models on the other hand. The collection of analysis and synthesis techniques based on these models forms the research area of hybrid systems theory, which plays an important role in the multi-disciplinary design of many technological systems that surround us. This paper presents an overview from the perspective of the control community on modelling, analysis and control design for hybrid dynamical systems and surveys the major research lines in this appealing and lively research area. PMID:20921005

  5. Analysis of stability boundaries of satellite's equilibrium attitude in a circular orbit

    NASA Astrophysics Data System (ADS)

    Novikov, M. A.

    2016-03-01

    An asymmetric satellite equipped with control momentum gyroscopes (CMGs) with the center of mass of the system moving uniformly in a circular orbit was considered. The stability of a relative equilibrium attitude of the satellite was analyzed using Lyapunov's direct method. The Lyapunov function V is a positive definite integral of the total energy of the perturbed motion of the system. The asymptotic stability analysis of the stationary motion of the conservative system was based on the Barbashin-Krasovskii theorem on the nonexistence of integer trajectories of the set dot V, which was obtained using the differential equations of motion of the satellite with CMGs. By analyzing the sign definiteness of the quadratic part of V, it was found earlier by V.V. Sazonov that the stability region is described by four strict inequalities. The asymptotic stability at the stability boundary was analyzed by sequentially turning these inequalities into equalities with terms of orders higher than the second taken into account in V. The sign definiteness analysis of the inhomogeneous function V at the stability boundary involved a huge amount of computations related to the multiplication, expansion, substitution, and factorization of symbolic expressions. The computations were performed by applying a computer algebra system on a personal computer.

  6. Classical linear-control analysis applied to business-cycle dynamics and stability

    NASA Technical Reports Server (NTRS)

    Wingrove, R. C.

    1983-01-01

    Linear control analysis is applied as an aid in understanding the fluctuations of business cycles in the past, and to examine monetary policies that might improve stabilization. The analysis shows how different policies change the frequency and damping of the economic system dynamics, and how they modify the amplitude of the fluctuations that are caused by random disturbances. Examples are used to show how policy feedbacks and policy lags can be incorporated, and how different monetary strategies for stabilization can be analytically compared. Representative numerical results are used to illustrate the main points.

  7. Stagnation-point flow and heat transfer over an exponentially shrinking sheet: A stability analysis

    NASA Astrophysics Data System (ADS)

    Ismail, Nurul Syuhada; Arifin, Norihan Md.; Bachok, Norfifah; Mahiddin, Norhasimah

    2016-06-01

    Numerical solutions for the stagnation-point flow and heat transfer over an exponentially shrinking sheet have been investigated. The governing boundary layer equations are transformed into an ordinary differential equation using a non-similar transformation. By using the bvp4c solver in MATLAB, the results of the equations can be solved numerically. Numerical results indicate that in certain parameter, the non-unique solutions for the velocity and the temperature do exist. A linear stability analysis shows that only one solution is linearly stable otherwise is unstable. Then, the stability analysis is performed to identify which solution is stable between the two non-unique solutions.

  8. Submarine pipeline on-bottom stability: Volume 1, Analysis and design guidelines: Final report

    SciTech Connect

    Not Available

    1988-11-01

    This report has been developed as a reference handbook for use in on-bottom pipeline stability analysis and design. It consists of two volumes. Volume one is devoted to descriptions of the various aspects of the problem: the pipeline design process; ocean physics, wave mechanics, hydrodynamic forces, and meteorogical data determination; geotechnical data collection and soil mechanics; and stability design procedures. Volume two describes, lists, and illustrates the analysis software. Diskettes containing the software and examples of the software are also included in Volume two. (115 refs., 127 figs., 7 tabs.)

  9. Formation stability analysis of unmanned multi-vehicles under interconnection topologies

    NASA Astrophysics Data System (ADS)

    Yang, Aolei; Naeem, Wasif; Fei, Minrui

    2015-04-01

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

  10. Beta-turn propensities as paradigms for the analysis of structural motifs to engineer protein stability.

    PubMed Central

    Ohage, E. C.; Graml, W.; Walter, M. M.; Steinbacher, S.; Steipe, B.

    1997-01-01

    The thermodynamic stability of a protein provides an experimental metric for the relationship of protein sequence and native structure. We have investigated an approach based on an analysis of the structural database for stability engineering of an immunoglobulin variable domain. The most frequently occurring residues in specific positions of beta-turn motifs were predicted to increase the folding stability of mutants that were constructed by site-directed mutagenesis. Even in positions in which different residues are conserved in immunoglobulin sequences, the predictions were confirmed. Frequently, mutants with increased beta-turn propensities display increased folding cooperativities, suggesting pronounced effects on the unfolded state independent of the expected effect on conformational entropy. We conclude that structural motifs with predominantly local interactions can serve as templates with which patterns of sequence preferences can be extracted from the database of protein structures. Such preferences can predict the stability effects of mutations for protein engineering and design. PMID:9007995

  11. [Stability Analysis of Susceptible-Infected-Recovered Epidemic Model].

    PubMed

    Pan, Duotao; Shi, Hongyan; Huang, Mingzhong; Yuan, Decheng

    2015-10-01

    With the range of application of computational biology and systems biology gradually expanding, the complexity of the bioprocess models is also increased. To address this difficult problem, it is required to introduce positive alternative analysis method to cope with it. Taking the dynamic model of the epidemic control process as research object, we established an evaluation model in our laboratory. Firstly, the model was solved with nonlinear programming method. The results were shown to be good. Based on biochemical systems theory, the ODE dynamic model was transformed into S-system. The eigen values of the model showed that the system was stable and contained oscillation phenomenon. Next the sensitivities of rate constant and logarithmic gains of the three key parameters were analyzed, as well as the robust of the system. The result indicated that the biochemical systems theory could be applied in different fields more widely. PMID:26964304

  12. Stability analysis of bridged cracks in brittle matrix composites

    NASA Technical Reports Server (NTRS)

    Ballarini, Roberto; Muju, Sandeep

    1991-01-01

    The bridging of matrix cracks by fibers is an important toughening mechanism in fiber reinforced brittle matrix composites. This paper presents the results of a nonlinear finite element analysis of the Mode-I propagation of a bridged matrix crack in a finite size specimen. The composite is modeled as an orthotropic continuum and the bridging due to the fibers is modeled as a distribution of tractions which resist crack opening. A critical stress intensity factor criterion is employed for matrix crack propagation while a critical crack opening condition is used for fiber failure. The structural response of the specimen (load-deflection curves) as well as the stress intensity factor of the propagating crack are calculated for various constituent properties and specimen configurations for both tensile and bending loading. By controlling the length of the bridged crack results are obtained which highlight the transition from stable to unstable behavior of the propagating crack.

  13. Analysis of data reliability and stability in HR-SDN communication module

    NASA Astrophysics Data System (ADS)

    Choi, Dong-Hee; Shin, Jin-Chul; Park, Hong-Seong

    2007-12-01

    Profibus is open industrial communication system for wide range of applications in manufacturing and process automation. In Profibus, FDL service use to need hard real-time system. In these systems required data reliability and stability and real-time feature. Profibus fieldbus networks used in many industrial fields because of it supports real-time industrial communication. So we analyze of data reliability and stabilization in profibus network. In this paper, there was to a station for communication which uses FDL from in the communication module which is used a data transfer possibility at once, and from communication period (ex. 10ms) it analyzed the system effect which it follows in transmission lag occurrence element and a data transfer error ratio it analyzed. Like this analytical result it led and there were from transmission for reliability and data stability they confirmed to HR-SDN communication modules and a guarantee yes or no. In this paper, we try to analysis of transmission delay ability for satisfaction data reliability and stability in specific system, which requested real-time feature. And, we analysis system reconstruction time and data delay time according to data/token packet loss. Packet-error occur physical layer in Profibus. As a result of above analysis, we propose method of enhancement of reliability in system which requested system reliability and stability. And, we confirm proposed method.

  14. GraTeLPy: graph-theoretic linear stability analysis

    PubMed Central

    2014-01-01

    Background A biochemical mechanism with mass action kinetics can be represented as a directed bipartite graph (bipartite digraph), and modeled by a system of differential equations. If the differential equations (DE) model can give rise to some instability such as multistability or Turing instability, then the bipartite digraph contains a structure referred to as a critical fragment. In some cases the existence of a critical fragment indicates that the DE model can display oscillations for some parameter values. We have implemented a graph-theoretic method that identifies the critical fragments of the bipartite digraph of a biochemical mechanism. Results GraTeLPy lists all critical fragments of the bipartite digraph of a given biochemical mechanism, thus enabling a preliminary analysis on the potential of a biochemical mechanism for some instability based on its topological structure. The correctness of the implementation is supported by multiple examples. The code is implemented in Python, relies on open software, and is available under the GNU General Public License. Conclusions GraTeLPy can be used by researchers to test large biochemical mechanisms with mass action kinetics for their capacity for multistability, oscillations and Turing instability. PMID:24572152

  15. Shell stability analysis in a computer aided engineering (CAE) environment

    NASA Technical Reports Server (NTRS)

    Arbocz, J.; Hol, J. M. A. M.

    1993-01-01

    The development of 'DISDECO', the Delft Interactive Shell DEsign COde is described. The purpose of this project is to make the accumulated theoretical, numerical and practical knowledge of the last 25 years or so readily accessible to users interested in the analysis of buckling sensitive structures. With this open ended, hierarchical, interactive computer code the user can access from his workstation successively programs of increasing complexity. The computational modules currently operational in DISDECO provide the prospective user with facilities to calculate the critical buckling loads of stiffened anisotropic shells under combined loading, to investigate the effects the various types of boundary conditions will have on the critical load, and to get a complete picture of the degrading effects the different shapes of possible initial imperfections might cause, all in one interactive session. Once a design is finalized, its collapse load can be verified by running a large refined model remotely from behind the workstation with one of the current generation 2-dimensional codes, with advanced capabilities to handle both geometric and material nonlinearities.

  16. Nonlinear global stability analysis of compressor stall phenomena

    NASA Technical Reports Server (NTRS)

    Razavi, H.

    1985-01-01

    Compressor stall phenomena are analyzed from the point of view of nonlinear control theory, based on bifurcation-catastrophe techniques. This new approach appears promising and offers insight into such well-known compressor instability problems as surge and rotating stall and suggests strategies for recovery. Three interlocking dynamic nonlinear state space models are developed. It is shown that the problem of rotating stall can be viewed as an induced bifurcation of solution of the unstalled model. Hysteresis effects are shown to exist in the stall/recovery process. Surge cycles are observed for some critical parameter values. The oscillatory behavior is seen to be due to development of limit cycles, generated by Hopf bifurcation of solutions. More specifically, it is observed that at certain critical values of parameters, a family of stable limit cycles with growning and then diminishing amplitudes is generated, then giving rise to an unstable family of limit cycles. This unstable family in turn bifurcates into other unstable families. To further illustrate the utility of the methodology, some partial computation of domains is carried out, and parameter sensitivity analysis is performed.

  17. Theoretical study of vapor-liquid homogeneous nucleation using stability analysis of a macroscopic phase.

    PubMed

    Carreón-Calderón, Bernardo

    2012-10-14

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

  18. Slope stability and stabilization methods

    SciTech Connect

    Abramson, L.W.; Lee, T.S.; Boyce, G.M.; Sharma, S.S.

    1995-12-01

    Slope stability can be a major problem during the construction of surface facilities. Cutting into existing ground disturbs the mechanics of the surrounding area, which can result in landslides and rock falls. This practical reference gives you the comprehensive information you need for slope stability analysis, suitable methods of analysis with and without the use of computers, and examples of common stability problems and stabilization methods for cuts and fills. It includes detailed discussions of methods used in slope stability analysis, including the Ordinary Method of Slices, Simplified Janbu Method, Simplified Bishop Method, Spencer`s Method, other limit equilibrium methods, numerical methods, total stress analysis, effective stress analysis, and the use of computer programs to solve problems. Chapters include: General Slope Stability Concepts; Engineering Geology Principles; Groundwater Conditions; Geologic Site Exploration; Laboratory Testing Interpretation; Slope Stability Concepts; Slope Stabilization Methods; and Design, Construction and Maintenance.

  19. Stability analysis of memristor-based fractional-order neural networks with different memductance functions.

    PubMed

    Rakkiyappan, R; Velmurugan, G; Cao, Jinde

    2015-04-01

    In this paper, the problem of the existence, uniqueness and uniform stability of memristor-based fractional-order neural networks (MFNNs) with two different types of memductance functions is extensively investigated. Moreover, we formulate the complex-valued memristor-based fractional-order neural networks (CVMFNNs) with two different types of memductance functions and analyze the existence, uniqueness and uniform stability of such networks. By using Banach contraction principle and analysis technique, some sufficient conditions are obtained to ensure the existence, uniqueness and uniform stability of the considered MFNNs and CVMFNNs with two different types of memductance functions. The analysis results establish from the theory of fractional-order differential equations with discontinuous right-hand sides. Finally, four numerical examples are presented to show the effectiveness of our theoretical results. PMID:25861402

  20. Measurement and analysis of the frequency stability of GPS Navstar clocks

    SciTech Connect

    McCaskill, T.B.; Largay, M.M.; Oaks, O.J.

    1994-12-31

    Analysis of the frequency stability of Global Positioning System (GPS) on-orbit Navstar clocks Z`s performed by the Naval Research Laboratory (NRL). Clock offsets for each Navstar clock are derived from smoothed pseudorange measurements collected as the Navstar space vehicle passes over the tracking station. The clock offsets are further smoothed and estimated at the time of closest approach (TCA) of the space vehicle over the tracking station. Analysis of more than 50 Navstar clocks by NRL shows that the majority of these clocks provide performance that exceeds the GPS frequency stability specification. This precision measurement technique is capable of determining one-day frequency stabilities of the Navstar GPS clocks to an accuracy of better than 1 x 10-13.

  1. Posterior cruciate-retaining versus posterior-stabilized total knee arthroplasty: a meta-analysis.

    PubMed

    Bercik, Michael J; Joshi, Ashish; Parvizi, Javad

    2013-03-01

    The objective of this meta-analysis was to compare outcomes of posterior cruciate-retaining and posterior stabilized prostheses. A computerized literature search was conducted to identify randomized controlled trials comparing the clinical outcomes of cruciate-retaining and posterior-stabilized designs. The table of contents of four major Orthopaedic journals and the references section of two arthroplasty text books were reviewed to identify other relevant studies. Ultimately, 1114 patients (1265 knees) were compared. Statistical analysis revealed a significant difference in flexion and range of motion in favor of posterior-stabilized knees, but no difference in complication rates. The clinical importance of this remains unknown. The decision to use one design versus the other should rest with the surgeon's preference and comfort with a particular design. PMID:23433255

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

    NASA Technical Reports Server (NTRS)

    Regan, Christopher D.

    2008-01-01

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

  3. Nonmodal linear stability analysis of miscible viscous fingering in porous media.

    PubMed

    Hota, Tapan Kumar; Pramanik, Satyajit; Mishra, Manoranjan

    2015-11-01

    The nonmodal linear stability of miscible viscous fingering in a two-dimensional homogeneous porous medium has been investigated. The linearized perturbed equations for Darcy's law coupled with a convection-diffusion equation is discretized using a finite difference method. The resultant initial value problem is solved by a fourth-order Runge-Kutta method, followed by a singular value decomposition of the propagator matrix. Particular attention is given to the transient behavior rather than the long-time behavior of eigenmodes predicted by the traditional modal analysis. The transient behaviors of the response to external excitations and the response to initial conditions are studied by examining the ε-pseudospectra structures and the largest energy growth function, respectively. With the help of nonmodal stability analysis we demonstrate that at early times the displacement flow is dominated by diffusion and the perturbations decay. At later times, when convection dominates diffusion, perturbations grow. Furthermore, we show that the dominant perturbation that experiences the maximum amplification within the linear regime lead to the transient growth. These two important features were previously unattainable in the existing linear stability methods for miscible viscous fingering. To explore the relevance of the optimal perturbation obtained from nonmodal analysis, we performed direct numerical simulations using a highly accurate pseudospectral method. Furthermore, a comparison of the present stability analysis with existing modal and initial value approach is also presented. It is shown that the nonmodal stability results are in better agreement than the other existing stability analyses, with those obtained from direct numerical simulations. PMID:26651779

  4. Computational analysis of noise reduction devices in axial fans with stabilized finite element formulations

    NASA Astrophysics Data System (ADS)

    Corsini, A.; Rispoli, F.; Sheard, A. G.; Tezduyar, T. E.

    2012-12-01

    The paper illustrates how a computational fluid mechanic technique, based on stabilized finite element formulations, can be used in analysis of noise reduction devices in axial fans. Among the noise control alternatives, the study focuses on the use of end-plates fitted at the blade tips to control the leakage flow and the related aeroacoustic sources. The end-plate shape is configured to govern the momentum transfer to the swirling flow at the blade tip. This flow control mechanism has been found to have a positive link to the fan aeroacoustics. The complex physics of the swirling flow at the tip, developing under the influence of the end-plate, is governed by the rolling up of the jet-like leakage flow. The RANS modelling used in the computations is based on the streamline-upwind/Petrov-Galerkin and pressure-stabilizing/Petrov-Galerkin methods, supplemented with the DRDJ stabilization. Judicious determination of the stabilization parameters involved is also a part of our computational technique and is described for each component of the stabilized formulation. We describe the flow physics underlying the design of the noise control device and illustrate the aerodynamic performance. Then we investigate the numerical performance of the formulation by analysing the inner workings of the stabilization operators and of their interaction with the turbulence model.

  5. Stability analysis of a mobile robot base carrying a robotic manipulator

    SciTech Connect

    Bouchard, J.F.; Sias, F.R. Jr.

    1994-12-31

    A robotic manipulator mounted on a mobile robot base is useful for performing tasks in an environment not suitable for humans. However, the capabilities of such a robot may be limited by its physical stability. A mobile robot by itself is designed to have a high degree of stability, with a center of gravity located low to the ground and well within the area enclosed by its wheels. When a manipulator is mounted on a mobile robot, the overall center of gravity is raised and may also be shifted outside of the area of stability, which would cause the robot to tip. Three factors that may influence the physical stability of such a configuration are the position of the manipulator links, the load at the tool position, and the inclide on which the robot is supported. A stability analysis provides numerical information concerning the effect that each of these three factors has on the stability of the robot`s vehicle-manipulator system.

  6. The stability analysis of magnetohydrodynamic equilibria - Comparing the thermodynamic approach with the energy principle

    NASA Technical Reports Server (NTRS)

    Brinkmann, R. P.

    1989-01-01

    This paper is a contribution to the stability analysis of current-carrying plasmas, i.e., plasma systems that are forced by external mchanisms to carry a nonrelaxing electrical current. Under restriction to translationally invariant configurations, the thermodynamic stability criterion for a multicomponent plasma is rederived within the framework of nonideal MHD. The chosen dynamics neglects scalar resistivity, but allows for other types of dissipation effects both in Ohm's law and in the equation of motion. In the second section of the paper, the thermodynamic stability criterion is compared with the ideal MHD based energy principle of Bernstein et al. With the help of Schwarz's inequality, it is shown that the former criterion is always more 'pessimistic' than the latter, i.e., that thermodynamic stability implies stability according to the MHD principle, but not vice versa. This reuslt confirms the physical plausible idea that dissipational effects tend to weaken the stability properties of current-carrying plasma equilibria by breaking the constraints of ideal MHD and allowing for possibly destabilizing effects such as magnetic field line reconfiguration.

  7. Determination of Myoglobin Stability by Circular Dichroism Spectroscopy: Classic and Modern Data Analysis

    ERIC Educational Resources Information Center

    Mehl, Andrew F.; Crawford, Mary A.; Zhang, Lei

    2009-01-01

    Few laboratory procedures describe the use of circular dichroism (CD) at the undergraduate level. To increase the number of laboratory exercises using CD, a thermal denaturation study of myoglobin using CD is described to assess protein stability. Values obtained from a more classic linear data analysis approach are consistent with data analyzed…

  8. Stability of Periodic Solutionsof Conservation Laws with Viscosity:Analysis of the Evans Function

    NASA Astrophysics Data System (ADS)

    Oh, M.; Zumbrun, K.

    We establish instability of periodic traveling waves arising in conservation laws featuring phase transition. The analysis uses the Evans function framework introduced by R.A. Gardner in the periodic case. The main new tool is a periodic generalization of the stability index introduced by Gardner and Zumbrun in the traveling front or pulse case.

  9. Stability of Nonlinear Principal Components Analysis: An Empirical Study Using the Balanced Bootstrap

    ERIC Educational Resources Information Center

    Linting, Marielle; Meulman, Jacqueline J.; Groenen, Patrick J. F.; van der Kooij, Anita J.

    2007-01-01

    Principal components analysis (PCA) is used to explore the structure of data sets containing linearly related numeric variables. Alternatively, nonlinear PCA can handle possibly nonlinearly related numeric as well as nonnumeric variables. For linear PCA, the stability of its solution can be established under the assumption of multivariate…

  10. FLUT - A program for aeroelastic stability analysis. [of aircraft structures in subsonic flow

    NASA Technical Reports Server (NTRS)

    Johnson, E. H.

    1977-01-01

    A computer program (FLUT) that can be used to evaluate the aeroelastic stability of aircraft structures in subsonic flow is described. The algorithm synthesizes data from a structural vibration analysis with an unsteady aerodynamics analysis and then performs a complex eigenvalue analysis to assess the system stability. The theoretical basis of the program is discussed with special emphasis placed on some innovative techniques which improve the efficiency of the analysis. User information needed to efficiently and successfully utilize the program is provided. In addition to identifying the required input, the flow of the program execution and some possible sources of difficulty are included. The use of the program is demonstrated with a listing of the input and output for a simple example.

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

    NASA Technical Reports Server (NTRS)

    Pei, Jing; Newsome, Jerry R.

    2015-01-01

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

  12. Stability analysis for periodic solutions of the Van der Pol-Duffing forced oscillator

    NASA Astrophysics Data System (ADS)

    Cui, Jifeng; Liang, Jiaming; Lin, Zhiliang

    2016-01-01

    Based on the homotopy analysis method (HAM), the high accuracy frequency response curve and the stable/unstable periodic solutions of the Van der Pol-Duffing forced oscillator with the variation of the forced frequency are obtained and studied. The stability of the periodic solutions obtained is analyzed by use of Floquet theory. Furthermore, the results are validated in the light of spectral analysis and bifurcation theory.

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

    NASA Technical Reports Server (NTRS)

    Brown, R. L.

    1979-01-01

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

  14. On the thermal stability of a radiating plasma subject to nonlocal thermal conduction. I - Linear analysis

    NASA Technical Reports Server (NTRS)

    Chun, E.; Rosner, R.

    1993-01-01

    We study the linear stability of an optically thin uniform radiating plasma subject to nonlocal heat transport. We derive the dispersion relation appropriate to this problem, and the marginal wavenumbers for instability. Our analysis indicates that nonlocal heat transport acts to reduce the stabilizing influence of thermal conduction, and that there are critical values for the electron mean free path such that the plasma is always unstable. Our results may be applied to a number of astrophysical plasmas, one such example being the halos of clusters of galaxies.

  15. Stability analysis of the laser system for the TTF photoinjector at Fermilab

    SciTech Connect

    Xi Yang

    2004-05-12

    A solid-state laser system that produces a 1MHz pulse train of 800 pulses with 18 {micro}J per pulse at {lambda} = 263.5 nm has been developed to meet the requirements of the TESLA Test Facility (TTF) at Fermilab and in operation since 1998.[1,2] Besides the production of high charges, high brightness electron beams, the need for high bunch charge stability requires that each laser pulse in the pulse train must have the same energy, and the energy per laser pulse should not vary significantly from shot to shot. This motivates the stability analysis of the laser system for the TTF photoinjector.

  16. Stability analysis of numerical solutions of wave propagation when pseudoviscosity is replaced by real viscosity

    NASA Astrophysics Data System (ADS)

    Fanget, A.

    1996-05-01

    The artificial viscocity method was originally introduced by Von Neuman and Richtmeyer [R.D. Richtmeyer and K. W. Morton, in Difference methods for Initial Value Problem (Interscience, New York, 1967)] to spread the shock over several cells of the mesh. This method is useful if the physical phenomena present in the shock front are not of interest. In some cases, such as for polymers, the amount of viscosity is large enough to spread the front shock naturally. In our problem, pseudoviscosity is ignored. A stability analysis shows that time step restrictions for stability can be less stringent than with pseudoviscosity.

  17. Stability and bifurcation analysis of oscillators with piecewise-linear characteristics - A general approach

    NASA Technical Reports Server (NTRS)

    Noah, S. T.; Kim, Y. B.

    1991-01-01

    A general approach is developed for determining the periodic solutions and their stability of nonlinear oscillators with piecewise-smooth characteristics. A modified harmonic balance/Fourier transform procedure is devised for the analysis. The procedure avoids certain numerical differentiation employed previously in determining the periodic solutions, therefore enhancing the reliability and efficiency of the method. Stability of the solutions is determined via perturbations of their state variables. The method is applied to a forced oscillator interacting with a stop of finite stiffness. Flip and fold bifurcations are found to occur. This led to the identification of parameter ranges in which chaotic response occurred.

  18. Stability and performance analysis of a full-train system with inerters

    NASA Astrophysics Data System (ADS)

    Wang, Fu-Cheng; Hsieh, Min-Ruei; Chen, Hsueh-Ju

    2012-04-01

    This paper discusses the use of inerters to improve the stability and performance of a full-train system. First, we construct a 28 degree-of-freedom train model in AutoSim, and obtain a linearised model for analysis in Matlab. Then, the benefits of inerters are investigated by the critical speed, settling time and passenger comfort. In addition, we apply a new mechatronic network for further performance improvement, and synthesise the optimal electrical circuit for experimental verification. From the results, inerters are shown to be effective in improving the stability and performance of train systems.

  19. Experimental transition and boundary-layer stability analysis for a slotted swept laminar flow control airfoil

    NASA Technical Reports Server (NTRS)

    Harvey, William D.; Harris, Charles D.; Brooks, Cuyler W., Jr.

    1989-01-01

    A swept, supercritical laminar flow control (LFC) airfoil designated NASA SCLFC(1)-0513F was tested at subsonic and transonic speeds in the NASA Langley eight-foot Transonic Pressure Tunnel. This paper examines Tollmien-Schlichting and crossflow disturbance amplification for this airfoil using the linear stability method. The design methodology using linear stability analysis is evaluated and the results of the incompressible and compressible methods are compared. Experimental data on the swept, supercritical LFC airfoil and reference wind tunnel and flight results are used to correlate and evaluate the N-factor method for transition prediction over a speed range M(infinity) from zero to one.

  20. Analysis of a stability valve system for extending the dynamic range of a supersonic inlet

    NASA Technical Reports Server (NTRS)

    Webb, J. A., Jr.; Dustin, M. O.

    1975-01-01

    A stability valve system designed for a full-scale, flight, supersonic, mixed-compression inlet was modeled dynamically by using analog computer techniques. The system uses poppet valves mounted in the inlet cowl to bypass airflow and augments the inlet shock position control system by preventing unstarts caused by high-frequency perturbations. The model was used as a design aid to investigate the effects of varying both the physical configurations of the valve and the flight and wind tunnel conditions. Results of the analysis indicate that the stability valve will provide a bandpass operation of 1 hertz to 17 hertz.

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

    NASA Technical Reports Server (NTRS)

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

    2009-01-01

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

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

    NASA Technical Reports Server (NTRS)

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

    1975-01-01

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

  3. [Analysis and stability of suxamethonium chloride. 2: Study of various factors in the stability of suxamethonium chloride injection solutions].

    PubMed

    Kottke, D; Döge, G; Pohloudek-Fabini, R

    1983-06-01

    The packing material (glass ampoules and plastic disposable syringes) and the degree of purity of the active agent do not affect the stability of injectable suxamethonium chloride solutions. In contrast to this, the stability was markedly improved by lowering the temperature of storage. Injectable suxamethonium chloride solutions may be stored in plastic disposable syringes. PMID:6611640

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

    NASA Astrophysics Data System (ADS)

    Zaki, Afifa Adel

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

  5. Design of Launch Vehicle Flight Control Systems Using Ascent Vehicle Stability Analysis Tool

    NASA Technical Reports Server (NTRS)

    Jang, Jiann-Woei; Alaniz, Abran; Hall, Robert; Bedossian, Nazareth; Hall, Charles; Jackson, Mark

    2011-01-01

    A launch vehicle represents a complicated flex-body structural environment for flight control system design. The Ascent-vehicle Stability Analysis Tool (ASAT) is developed to address the complicity in design and analysis of a launch vehicle. The design objective for the flight control system of a launch vehicle is to best follow guidance commands while robustly maintaining system stability. A constrained optimization approach takes the advantage of modern computational control techniques to simultaneously design multiple control systems in compliance with required design specs. "Tower Clearance" and "Load Relief" designs have been achieved for liftoff and max dynamic pressure flight regions, respectively, in the presence of large wind disturbances. The robustness of the flight control system designs has been verified in the frequency domain Monte Carlo analysis using ASAT.

  6. Stability analysis and compensation of a boost regulator with two-loop control

    NASA Technical Reports Server (NTRS)

    Wester, G. W.

    1974-01-01

    A useful stability measure has been demonstrated by Wester (1973) for switching regulators with a single feedback loop by applying the Nyquist criterion to the approximate loop gain determined by a time-averaging technique. This approach is extended and applied to the characterization, stability analysis, and compensation design of a switching regulator with two-loop control. The role and relative significance of each control loop is clarified on the basis of a description of circuit operation, and the major and minor loops are identified. In view of the inapplicability of linear feedback theory, describing functions of the feedback loops and power stage are derived, using small-signal analysis. Several phenomena revealed from an analysis of the major loop gain are discussed.

  7. Stability analysis of a square rod bundle sub-channel in supercritical water reactor

    NASA Astrophysics Data System (ADS)

    Hai-jun, Wang; Ting, You; Lei, Zhang; Hong-fang, Gu; Yu-shan, Luo; Ji-lian, Bian

    2013-07-01

    Extensive investigations on the flow and heat transfer behavior in SCWR fuel assembly have been undertaken worldwide. However, stability analysis of supercritical water in the sub-channels of tight lattices is still lacking. In this paper, the flow stability of a fuel bundle channel with square pitches has been analyzed using commercial CFD code-ANSYS Fluent. Typical dynamic instability of Density Wave Oscillation (DWO) has occurred in heated channel containing fluids at supercritical pressure. A further discussion about the impacts of various operational parameters (e.g. power input, system pressure, mass velocity, inlet temperature, etc) shows that the system becomes more stable as system pressure and/or mass flow rate increases. An increase in inlet temperature also has a stabilizing effect on the system.

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

    NASA Technical Reports Server (NTRS)

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

    2009-01-01

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

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

    NASA Astrophysics Data System (ADS)

    Chung, J.; Jang, I.

    2003-01-01

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

  10. Boundary-Layer Stability Analysis of the Mean Flows Obtained Using Unstructured Grids

    NASA Technical Reports Server (NTRS)

    Liao, Wei; Malik, Mujeeb R.; Lee-Rausch, Elizabeth M.; Li, Fei; Nielsen, Eric J.; Buning, Pieter G.; Chang, Chau-Lyan; Choudhari, Meelan M.

    2012-01-01

    Boundary-layer stability analyses of mean flows extracted from unstructured-grid Navier- Stokes solutions have been performed. A procedure has been developed to extract mean flow profiles from the FUN3D unstructured-grid solutions. Extensive code-to-code validations have been performed by comparing the extracted mean ows as well as the corresponding stability characteristics to the predictions based on structured-grid solutions. Comparisons are made on a range of problems from a simple at plate to a full aircraft configuration-a modified Gulfstream-III with a natural laminar flow glove. The future aim of the project is to extend the adjoint-based design capability in FUN3D to include natural laminar flow and laminar flow control by integrating it with boundary-layer stability analysis codes, such as LASTRAC.

  11. Stability analysis of nonlinear systems by multiple time scaling. [using perturbation methods

    NASA Technical Reports Server (NTRS)

    Morino, L.

    1974-01-01

    The asymptotic solution for the transient analysis of a general nonlinear system in the neighborhood of the stability boundary was obtained by using the multiple-time-scaling asymptotic-expansion method. The nonlinearities are assumed to be of algebraic nature. Terms of order epsilon to the 3rd power (where epsilon is the order of amplitude of the unknown) are included in the solution. The solution indicates that there is always a limit cycle which is stable (unstable) and exists above (below) the stability boundary if the nonlinear terms are stabilizing (destabilizing). Extension of the solution to include fifth order nonlinear terms is also presented. Comparisons with harmonic balance and with multiple-time-scaling solution of panel flutter equations are also included.

  12. Inelastic Stability Analysis Of Uniaxially Compressed Flat Rectangular Isotropic CCSS Plate

    NASA Astrophysics Data System (ADS)

    Ibearugbulem, O. M.; Eziefula, U. G.; Onwuka, D. O.

    2015-08-01

    This study investigates the inelastic stability of a thin flat rectangular isotropic plate subjected to uniform uniaxial compressive loads using Taylor-Maclaurin series formulated deflection function. The plate has clamped and simply supported edges in both characteristic directions (CCSS boundary conditions). The governing equation is derived using a deformation plasticity theory and a work principle. Values of the plate buckling coefficient are calculated for aspect ratios from 0.1 to 2.0 at intervals of 0.1. The results compared favourably with the elastic stability values and the percentage differences ranged from -0.353% to -7.427%. Therefore, the theoretical approach proposed in this study is recommended for the inelastic stability analysis of thin flat rectangular isotropic plates under uniform in-plane compression.

  13. Exhaustive stability analysis in a consensus system with time delay and irregular topologies

    NASA Astrophysics Data System (ADS)

    Cepeda-Gomez, Rudy; Olgac, Nejat

    2011-04-01

    A consensus problem and its stability are studied for a group of agents with second-order dynamics and communication delays. The communication topologies are taken as irregular but always connected and undirected. The delays are assumed to be quasi-static and the same for all the interagent channels. A decentralised, PD-like control structure is proposed to create a consensus in the position and velocity of the agents. We present an interesting factorisation feature for the characteristic equation of the system which simplifies the stability analysis considerably from a prohibitively large dimensional problem to a manageable small scale. It facilitates a rare stability picture in the space of the control parameters and the delay, utilising a paradigm named cluster treatment of characteristic roots (CTCR). The influence of the individual factors on the absolute and relative stability of the system is studied. This leads to the introduction of two novel concepts: the most exigent eigenvalue, which refers to the one that defines the delay stability margin of the system, and the most critical eigenvalue, which is the one that dictates the consensus speed of the system. It is observed that the most exigent eigenvalue is not always the most critical, and this feature may be used as a design tool for the control logic. Case studies and simulations results are presented to verify these concepts.

  14. Game Theoretical Analysis on Cooperation Stability and Incentive Effectiveness in Community Networks

    PubMed Central

    Liu, Yi; Qian, Depei; Zhang, Han; Cai, Jihong

    2015-01-01

    Community networks, the distinguishing feature of which is membership admittance, appear on P2P networks, social networks, and conventional Web networks. Joining the network costs money, time or network bandwidth, but the individuals get access to special resources owned by the community in return. The prosperity and stability of the community are determined by both the policy of admittance and the attraction of the privileges gained by joining. However, some misbehaving users can get the dedicated resources with some illicit and low-cost approaches, which introduce instability into the community, a phenomenon that will destroy the membership policy. In this paper, we analyze on the stability using game theory on such a phenomenon. We propose a game-theoretical model of stability analysis in community networks and provide conditions for a stable community. We then extend the model to analyze the effectiveness of different incentive policies, which could be used when the community cannot maintain its members in certain situations. Then we verify those models through a simulation. Finally, we discuss several ways to promote community network’s stability by adjusting the network’s properties and give some proposal on the designs of these types of networks from the points of game theory and stability. PMID:26551649

  15. Game Theoretical Analysis on Cooperation Stability and Incentive Effectiveness in Community Networks.

    PubMed

    Song, Kaida; Wang, Rui; Liu, Yi; Qian, Depei; Zhang, Han; Cai, Jihong

    2015-01-01

    Community networks, the distinguishing feature of which is membership admittance, appear on P2P networks, social networks, and conventional Web networks. Joining the network costs money, time or network bandwidth, but the individuals get access to special resources owned by the community in return. The prosperity and stability of the community are determined by both the policy of admittance and the attraction of the privileges gained by joining. However, some misbehaving users can get the dedicated resources with some illicit and low-cost approaches, which introduce instability into the community, a phenomenon that will destroy the membership policy. In this paper, we analyze on the stability using game theory on such a phenomenon. We propose a game-theoretical model of stability analysis in community networks and provide conditions for a stable community. We then extend the model to analyze the effectiveness of different incentive policies, which could be used when the community cannot maintain its members in certain situations. Then we verify those models through a simulation. Finally, we discuss several ways to promote community network's stability by adjusting the network's properties and give some proposal on the designs of these types of networks from the points of game theory and stability. PMID:26551649

  16. Verification of the stability lobes of Inconel 718 milling by recurrence plot applications and composite multiscale entropy analysis

    NASA Astrophysics Data System (ADS)

    Krzysztof, Kecik; Borowiec, Marek; Rafał, Rusinek

    2016-01-01

    Correctness verification of the stability lobe diagrams of milling process determined by commercial software CutPro 9 is the aim of this work. The analysis is performed for nickel superalloy Inconel 718 which is widely used in aviation industry. A methodology of stability analysis which bases on advanced nonlinear methods such as recurrence plot, recurrence quantifications analysis and composite multiscale entropy analysis are applied to the experimental data. Additionally, a new criterion for the determination of the unstable areas is proposed.

  17. Quantitation of protein-protein interactions by thermal stability shift analysis.

    PubMed

    Layton, Curtis J; Hellinga, Homme W

    2011-08-01

    Thermal stability shift analysis is a powerful method for examining binding interactions in proteins. We demonstrate that under certain circumstances, protein-protein interactions can be quantitated by monitoring shifts in thermal stability using thermodynamic models and data analysis methods presented in this work. This method relies on the determination of protein stabilities from thermal unfolding experiments using fluorescent dyes such as SYPRO Orange that report on protein denaturation. Data collection is rapid and straightforward using readily available real-time polymerase chain reaction instrumentation. We present an approach for the analysis of the unfolding transitions corresponding to each partner to extract the affinity of the interaction between the proteins. This method does not require the construction of a titration series that brackets the dissociation constant. In thermal shift experiments, protein stability data are obtained at different temperatures according to the affinity- and concentration-dependent shifts in unfolding transition midpoints. Treatment of the temperature dependence of affinity is, therefore, intrinsic to this method and is developed in this study. We used the interaction between maltose-binding protein (MBP) and a thermostable synthetic ankyrin repeat protein (Off7) as an experimental test case because their unfolding transitions overlap minimally. We found that MBP is significantly stabilized by Off7. High experimental throughput is enabled by sample parallelization, and the ability to extract quantitative binding information at a single partner concentration. In a single experiment, we were able to quantify the affinities of a series of alanine mutants, covering a wide range of affinities (∼ 100 nM to ∼ 100 μM). PMID:21674662

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

    SciTech Connect

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

    2009-09-01

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

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

    SciTech Connect

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

    2008-01-01

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

  20. von Neumann Stability Analysis of Numerical Solution Schemes for 1D and 2D Euler Equations

    NASA Astrophysics Data System (ADS)

    Konangi, Santosh; Palakurthi, Nikhil Kumar; Ghia, Urmila

    2014-11-01

    A von Neumann stability analysis is conducted for numerical schemes for the full system of coupled, density-based 1D and 2D Euler equations, closed by an isentropic equation of state. The governing equations are discretized on a staggered grid, which permits equivalence to finite-volume discretization. Presently, first-order accurate spatial and temporal finite-difference techniques are analyzed. The momentum convection term is treated as explicit, semi-implicit or implicit. Density upwind bias is included in the spatial operator of the continuity equation. By combining the discretization techniques, ten solution schemes are formulated. For each scheme, unstable and stable regimes are identified through the stability analysis, and the maximum allowable CFL number is predicted. The predictions are verified for selected schemes, using the Riemann problem at incompressible and compressible Mach numbers. Very good agreement is obtained between the analytically predicted and ``experimentally'' observed CFL values for all cases, thereby validating the analysis. The demonstrated analysis provides an accurate indication of stability conditions for the Euler equations, in contrast to the simplistic conditions arising from model equations, such as the wave equation.

  1. The Least Squares Stochastic Finite Element Method in Structural Stability Analysis of Steel Skeletal Structures

    NASA Astrophysics Data System (ADS)

    Kamiński, M.; Szafran, J.

    2015-05-01

    The main purpose of this work is to verify the influence of the weighting procedure in the Least Squares Method on the probabilistic moments resulting from the stability analysis of steel skeletal structures. We discuss this issue also in the context of the geometrical nonlinearity appearing in the Stochastic Finite Element Method equations for the stability analysis and preservation of the Gaussian probability density function employed to model the Young modulus of a structural steel in this problem. The weighting procedure itself (with both triangular and Dirac-type) shows rather marginal influence on all probabilistic coefficients under consideration. This hybrid stochastic computational technique consisting of the FEM and computer algebra systems (ROBOT and MAPLE packages) may be used for analogous nonlinear analyses in structural reliability assessment.

  2. Boundary layer stability analysis of a natural laminar flow glove on the F-111 TACT airplane

    NASA Technical Reports Server (NTRS)

    Runyan, L. J.; Steers, L. L.

    1980-01-01

    A natural laminar flow airfoil has been developed as a part of the aircraft energy efficiency program. A NASA flight program incorporating this airfoil into partial wing gloves on the F-111 TACT airplane was scheduled to start in May, 1980. In support of this research effort, an extensive boundary layer stability analysis of the partial glove has been conducted. The results of that analysis show the expected effects of wing leading-edge sweep angle, Reynolds number, and compressibility on boundary layer stability and transition. These results indicate that it should be possible to attain on the order of 60% laminar flow on the upper surface and 50% laminar flow on the lower surface for sweep angles of at least 20 deg, chord Reynolds numbers of 25 x 10 to the 6th and Mach numbers from 0.81 to 0.85.

  3. Electrostatic wave structures and their stability analysis in nonextensive magnetised electron-positron-ion plasma

    NASA Astrophysics Data System (ADS)

    Gill, T. S.; Bala, Parveen; Bains, A. S.

    2015-05-01

    A rigorous theoretical study based on Zakharov Kuznetsov (ZK) equation of ion-acoustic solitary waves (IASWs), their stability analysis in a magnetized e- p- i plasma is presented. The plasma model consists of inertial ions, magnetic field, electrons and positrons obeying q-nonextensive velocity distribution. Reductive perturbation method is used to derive ZK equation. The solitary wave structures are dependent on chosen plasma model, whose parameters influence the solitary characteristics. Particularly, nonextensivity, proportion of positron concentration, magnetic field and difference between electron and positron temperatures play crucial role in the solitary structures. The present work is also extended to give stability analysis and parametric ranges for the existence of stable and unstable solitons. This research work may be useful to understand the physics of nonlinear electrostatic excitations in different astrophysical and cosmic scenarios like stellar polytropes, hadron matter and quark-gluon plasma.

  4. Laser safety and hazard analysis for the temperature stabilized BSLT ARES laser system.

    SciTech Connect

    Augustoni, Arnold L.

    2003-08-01

    A laser safety and hazard analysis was performed for the temperature stabilized Big Sky Laser Technology (BSLT) laser central to the ARES system based on the 2000 version of the American National Standards Institute's (ANSI) Standard Z136.1, for Safe Use of Lasers and the 2000 version of the ANSI Standard Z136.6, for Safe Use of Lasers Outdoors. As a result of temperature stabilization of the BSLT laser the operating parameters of the laser had changed requiring a hazard analysis based on the new operating conditions. The ARES laser system is a Van/Truck based mobile platform, which is used to perform laser interaction experiments and tests at various national test sites.

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

    NASA Astrophysics Data System (ADS)

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

    2011-10-01

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

  6. Further studies on stability analysis of nonlinear Roesser-type two-dimensional systems

    NASA Astrophysics Data System (ADS)

    Dai, Xiao-Lin

    2014-04-01

    This paper is concerned with further relaxations of the stability analysis of nonlinear Roesser-type two-dimensional (2D) systems in the Takagi-Sugeno fuzzy form. To achieve the goal, a novel slack matrix variable technique, which is homogenous polynomially parameter-dependent on the normalized fuzzy weighting functions with arbitrary degree, is developed and the algebraic properties of the normalized fuzzy weighting functions are collected into a set of augmented matrices. Consequently, more information about the normalized fuzzy weighting functions is involved and the relaxation quality of the stability analysis is significantly improved. Moreover, the obtained result is formulated in the form of linear matrix inequalities, which can be easily solved via standard numerical software. Finally, a numerical example is provided to demonstrate the effectiveness of the proposed result.

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

    NASA Technical Reports Server (NTRS)

    Burken, John J.

    1992-01-01

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

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

    NASA Technical Reports Server (NTRS)

    Wolf, R. S.

    1982-01-01

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

  9. A Signal Transmission Technique for Stability Analysis of Multivariable Non-Linear Control Systems

    NASA Technical Reports Server (NTRS)

    Jackson, Mark; Zimpfer, Doug; Adams, Neil; Lindsey, K. L. (Technical Monitor)

    2000-01-01

    Among the difficulties associated with multivariable, non-linear control systems is the problem of assessing closed-loop stability. Of particular interest is the class of non-linear systems controlled with on/off actuators, such as spacecraft thrusters or electrical relays. With such systems, standard describing function techniques are typically too conservative, and time-domain simulation analysis is prohibitively extensive, This paper presents an open-loop analysis technique for this class of non-linear systems. The technique is centered around an innovative use of multivariable signal transmission theory to quantify the plant response to worst case control commands. The technique has been applied to assess stability of thruster controlled flexible space structures. Examples are provided for Space Shuttle attitude control with attached flexible payloads.

  10. The development of a handbook for astrobee F performance and stability analysis

    NASA Technical Reports Server (NTRS)

    Wolf, R. S.

    1982-01-01

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

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

    PubMed

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

    2011-10-01

    The use of acoustic levitation in the fields of analytical chemistry and in the containerless processing of materials requires a good stability of the levitated particle. However, spontaneous oscillations and rotation of the levitated particle have been reported in literature, which can reduce the applicability of the acoustic levitation technique. Aiming to reduce the particle oscillations, this paper presents the analysis of the particle stability in a new acoustic levitator device. The new acoustic levitator consists of a piezoelectric transducer with a concave radiating surface and a concave reflector. The analysis is conducted by determining numerically the axial and lateral forces that act on the levitated object and by measuring the oscillations of a sphere particle by a laser Doppler vibrometer. It is shown that the new levitator design allows to increase the lateral forces and reduce significantly the lateral oscillations of the levitated object. PMID:22047333

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

    NASA Astrophysics Data System (ADS)

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

    2004-05-01

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

    R. Trivedi and W. Kurz, Acta Metall. 34, 1663 (1986)
    ], which is advancing the original treatment of morphological stability by Mullins and Sekerka [
    W. W. Mullins and R. F. Sekerka, J. Appl. Phys. 35, 444 (1964)
    ] to the case of rapid solidification, we extend the model by introducing the local nonequilibrium in the solute diffusion field around the interface. A solution to the heat- and mass-transport problem around the perturbed interface is given in the presence of the local nonequilibrium solute diffusion. Using the developing local nonequilibrium model of solidification, the self-consistent analysis of linear morphological stability is presented with the attribution to the marginal (neutral) and absolute morphological stability of a rapidly moving interface. Special consideration of the interface stability for the cases of solidification in negative and positive thermal gradients is given. A quantitative comparison of the model predictions for the absolute morphological stability is presented with regard to experimental results of Hoglund and Aziz [ D. E. Hoglund and M. J. Aziz, in Kinetics of Phase Transformations, edited by M.O. Thompson, M. J. Aziz, and G. B. Stephenson, MRS Symposia Proceedings No. 205 (Materials Research Society, Pittsburgh, 1991), p. 325 ] on critical solute concentration for the interface breakdown during rapid solidification of Si-Sn alloys.

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

    NASA Technical Reports Server (NTRS)

    Wester, G. W.

    1973-01-01

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

  14. Stability analysis of stagnation-point flow over a stretching/shrinking sheet

    NASA Astrophysics Data System (ADS)

    Awaludin, I. S.; Weidman, P. D.; Ishak, Anuar

    2016-04-01

    The stagnation point flow over a linearly stretching or shrinking sheet is considered in the present study. The transformed ordinary differential equations are solved numerically. Dual solutions are possible for the shrinking case, while the solution is unique for the stretching case. For the shrinking case, a linear temporal stability analysis is performed to determine which one of the solution is stable and thus physically reliable.

  15. Towards understanding the stabilization process in vermicomposting using PARAFAC analysis of fluorescence spectra.

    PubMed

    Lv, Baoyi; Xing, Meiyan; Zhao, Chunhui; Yang, Jian; Xiang, Liang

    2014-12-01

    In this study, fluorescence excitation-emission matrix (EEM) combined with parallel factor analysis (PARAFAC) was employed to trace the behavior of water extractable organic matter and assess the stabilization process during vermicomposting of sewage sludge and cattle dung. Experiments using different mixing ratios of sewage sludge and cattle dung were conducted using Eisenia fetida. The results showed that vermicomposting reduced the DOC, DOC/DON ratio and ammonia, while increased the nitrate content. A three-component model containing two humic-like materials (components 1 and 2) and a protein-like material (component 3) was successfully developed using PARAFAC analysis. Moreover, the initial waste composition had a significant effect on the distribution of each component and the addition of cattle dung improved the stability of sewage sludge in vermicomposting. The PARAFAC results also indicated that protein-like materials were degraded and humic acid-like compounds were evolved during vermicomposting. Pearson correlation analysis showed that components 2 and 3 are more suitable to assess vermicompost maturity than component 1. In all, EEM-PARAFAC can be used to track organic transformation and assess biological stability during the vermicomposting process. PMID:25068534

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

    NASA Astrophysics Data System (ADS)

    Wu, Guohong; Minakawa, Tamotsu; Hayashi, Toshiyuki

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

  17. Low frequency azimuthal stability of the ionization region of the Hall thruster discharge. II. Global analysis

    SciTech Connect

    Escobar, D.; Ahedo, E.

    2015-10-15

    The linear stability of the Hall thruster discharge is analysed against axial-azimuthal perturbations in the low frequency range using a time-dependent 2D code of the discharge. This azimuthal stability analysis is spatially global, as opposed to the more common local stability analyses, already afforded previously (D. Escobar and E. Ahedo, Phys. Plasmas 21(4), 043505 (2014)). The study covers both axial and axial-azimuthal oscillations, known as breathing mode and spoke, respectively. The influence on the spoke instability of different operation parameters such as discharge voltage, mass flow, and thruster size is assessed by means of different parametric variations and compared against experimental results. Additionally, simplified models are used to unveil and characterize the mechanisms driving the spoke. The results indicate that the spoke is linked to azimuthal oscillations of the ionization process and to the Bohm condition in the transition to the anode sheath. Finally, results obtained from local and global stability analyses are compared in order to explain the discrepancies between both methods.

  18. Low frequency azimuthal stability of the ionization region of the Hall thruster discharge. II. Global analysis

    NASA Astrophysics Data System (ADS)

    Escobar, D.; Ahedo, E.

    2015-10-01

    The linear stability of the Hall thruster discharge is analysed against axial-azimuthal perturbations in the low frequency range using a time-dependent 2D code of the discharge. This azimuthal stability analysis is spatially global, as opposed to the more common local stability analyses, already afforded previously (D. Escobar and E. Ahedo, Phys. Plasmas 21(4), 043505 (2014)). The study covers both axial and axial-azimuthal oscillations, known as breathing mode and spoke, respectively. The influence on the spoke instability of different operation parameters such as discharge voltage, mass flow, and thruster size is assessed by means of different parametric variations and compared against experimental results. Additionally, simplified models are used to unveil and characterize the mechanisms driving the spoke. The results indicate that the spoke is linked to azimuthal oscillations of the ionization process and to the Bohm condition in the transition to the anode sheath. Finally, results obtained from local and global stability analyses are compared in order to explain the discrepancies between both methods.

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

    NASA Astrophysics Data System (ADS)

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

    2015-11-01

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

  20. Analytical model and stability analysis of the leading edge spar of a passively morphing ornithopter wing.

    PubMed

    Wissa, Aimy; Calogero, Joseph; Wereley, Norman; Hubbard, James E; Frecker, Mary

    2015-12-01

    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

  1. Stability analysis of simple models for immune cells interacting with normal pathogens and immune system retroviruses.

    PubMed Central

    Reibnegger, G; Fuchs, D; Hausen, A; Werner, E R; Werner-Felmayer, G; Dierich, M P; Wachter, H

    1989-01-01

    A mathematical analysis is presented for several simple dynamical systems that might be considered as crude descriptions for the situation when an immune system retrovirus, immune cells, and normal autonomously replicating pathogens interact. By stability analysis of the steady-state solutions, the destabilizing effect of the immune system retrovirus is described. The qualitative behavior of the solutions depending on the system parameters is analyzed in terms of trajectories moving in a phase space in which the axes are defined by the population numbers of the interacting biological entities. PMID:2522657

  2. Stability analysis and area spectrum of three-dimensional Lifshitz black holes

    NASA Astrophysics Data System (ADS)

    Cuadros-Melgar, Bertha; de Oliveira, Jeferson; Pellicer, C. E.

    2012-01-01

    In this work, we probe the stability of a z=3 three-dimensional Lifshitz black hole by using scalar and spinorial perturbations. We found an analytical expression for the quasinormal frequencies of the scalar probe field, which perfectly agree with the behavior of the quasinormal modes obtained numerically. The results for the numerical analysis of the spinorial perturbations reinforce the conclusion of the scalar analysis, i.e., the model is stable under scalar and spinor perturbations. As an application we found the area spectrum of the Lifshitz black hole, which turns out to be equally spaced.

  3. An experimental investigation of hingeless helicopter rotor-body stability in hover

    NASA Technical Reports Server (NTRS)

    Bousman, W. G.

    1978-01-01

    Model tests of a 1.62 m diameter rotor were performed to investigate the aeromechanical stability of coupled rotor-body systems in hover. Experimental measurements were made of modal frequencies and damping over a wide range of rotor speeds. Good data were obtained for the frequencies of the rotor lead-lag regressing mode. The quality of the damping measurements of the body modes was poor due to nonlinear damping in the gimbal ball bearings. Simulated vacuum testing was performed using substitute blades of tantalum that reduced the effective lock number to 0.2% of the model scale value while keeping the blade inertia constant. The experimental data were compared with theoretical predictions, and the correlation was in general very good.

  4. Adaptability and stability analysis of the juice yield of yellow passion fruit varieties.

    PubMed

    Oliveira, E J; Freitas, J P X; Jesus, O N

    2014-01-01

    This study analyzed the genotype x environment interaction (GE) for the juice productivity (JuProd) of 12 yellow passion fruit varieties (Passiflora edulis Sims. f. flavicarpa Deg.) using additive main effects and multiplicative interaction (AMMI) model and auxiliary parameters. The experiments were conducted in eight environments of Bahia State, Brazil, using a randomized block design with three replications. Analysis of variance showed significant effects (P ≤ 0.01) for environments, genotypes, and GE interaction. The first two interaction principal component axes (IPCAs) explained 81.00% of the sum of squares of the GE interaction. The AMMI1 and AMMI2 models showed that varieties 09 and 11 were the most stable. Other parameters, namely, the AMMI stability value (ASV), yield stability (YSI), sustainability, and stability index (StI), indicated that other varieties were more stable. These varying results were certainly a consequence of methodological differences. In contrast, the ranking of varieties for each of the stability parameters showed significant positive correlations (P ≤ 0.05) between IPCA1 x (ASV, YSI), JuProd x (StI, YSI), YSI x ASV, and StI x YSI. Cluster analysis based on the genotypic profile of the effects of the GE interaction identified three groups that correlated with the distribution of varieties in the AMMI1 biplot. However, the classification of stable genotypes was limited because the association with the productivity was not included in the analysis. Variety 08 showed the most stable and productive behavior, ranking above average in half of the environments, and it should be recommended for use. PMID:25177932

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

    PubMed Central

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

    2014-01-01

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

  6. Analysis of Face Stability during Excavation of Double-O-Tube Shield Tunnel

    PubMed Central

    Yang, Yuyou; Zhou, Qinghong; Li, Hongan; Huang, Xuegang; Tu, Xiaoming

    2013-01-01

    This paper focuses on the face stability analysis of Double-O-Tube shield tunnel. This kind of analysis is significant to ensure the safety of workers and reduce the influence on the surrounding environment. The key point of the stability analysis is to determine the supporting pressure applied to the face by the shield. A collapse failure will occur when the supporting pressure is not sufficient to prevent the movement of the soil mass towards the tunnel. A three-dimensional collapse failure mechanism was presented in this paper. Based on the mechanism of a single circular shield tunnel, the mechanism of Double-O-Tube shield tunnel was established by using the fact that both of the mechanisms are symmetrical. Then by means of the kinematic theorem of limit analysis, the numerical results were obtained, and a design chart was provided. The finite difference software FLAC3D was applied to investigate the face failure mechanism of DOT shield tunnel established in this paper; the critical supporting pressures of the collapse failure mechanism in different strata (sand and silt) were calculated. Through comparative analysis, the theoretical values were very close to the numerical values. This shows that the face failure mechanism of DOT shield tunnel is reasonable, and it can be applied to the sand and silt strata. PMID:24174917

  7. Ant colony optimization analysis on overall stability of high arch dam basis of field monitoring.

    PubMed

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

    2014-01-01

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

  8. Inertial instability of oceanic submesoscale vortices: linear analysis, marginal stability criterion and laboratory experiments

    NASA Astrophysics Data System (ADS)

    Lazar, Ayah; Stegner, Alexandre; Heifetz, Eyal

    2012-11-01

    Inertial instability is a possible mechanism for vertical mixing in the submesoscale ocean. The stability of axisymmetric oceanic-like vortices to inertial perturbations is investigated by linear stability analysis, taking into account the thickness and the stratification of the thermocline, as well as the vertical eddy viscosity. Numerical analysis reveals that the instability is insensitive to the vorticity profile if the intensity of the vortex is characterized by the vortex Rossby number (instead of the local normalized vorticity). This allows extending our analytical solutions for the Rankine vortex to a wide variety of oceanic cases, including results such as the analytic dispersion relation, and the marginal stability criterion. This suits oceanic conditions better than the widely used generalized Rayleigh criterion. Comparison with oceanographic data shows that our criterion permits cases that contradict the common oceanographic hypothesis for inertial instability. For instance, intense submesoscale anticyclones may be stable even with a core region of negative absolute vorticity. We corroborate our findings with large-scale laboratory experiments and find a signature of the instability on the mean-flow, which could be used in future oceanographic measurements.

  9. A linear stability analysis for nonlinear, grey, thermal radiative transfer problems

    SciTech Connect

    Wollaber, Allan B.; Larsen, Edward W.

    2011-02-20

    We present a new linear stability analysis of three time discretizations and Monte Carlo interpretations of the nonlinear, grey thermal radiative transfer (TRT) equations: the widely used 'Implicit Monte Carlo' (IMC) equations, the Carter Forest (CF) equations, and the Ahrens-Larsen or 'Semi-Analog Monte Carlo' (SMC) equations. Using a spatial Fourier analysis of the 1-D Implicit Monte Carlo (IMC) equations that are linearized about an equilibrium solution, we show that the IMC equations are unconditionally stable (undamped perturbations do not exist) if {alpha}, the IMC time-discretization parameter, satisfies 0.5 < {alpha} {<=} 1. This is consistent with conventional wisdom. However, we also show that for sufficiently large time steps, unphysical damped oscillations can exist that correspond to the lowest-frequency Fourier modes. After numerically confirming this result, we develop a method to assess the stability of any time discretization of the 0-D, nonlinear, grey, thermal radiative transfer problem. Subsequent analyses of the CF and SMC methods then demonstrate that the CF method is unconditionally stable and monotonic, but the SMC method is conditionally stable and permits unphysical oscillatory solutions that can prevent it from reaching equilibrium. This stability theory provides new conditions on the time step to guarantee monotonicity of the IMC solution, although they are likely too conservative to be used in practice. Theoretical predictions are tested and confirmed with numerical experiments.

  10. Dynamical investigation and parameter stability region analysis of a flywheel energy storage system in charging mode

    NASA Astrophysics Data System (ADS)

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

    2013-09-01

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

  11. Asymmetrical booster ascent guidance and control system design study. Volume 4: Sampled data stability analysis program (SADSAP) user's guide. [space shuttle development

    NASA Technical Reports Server (NTRS)

    Wilson, J. L.

    1974-01-01

    A users guide to the Sampled Data Stability Analysis Program (SADSAP) is provided. This program is a general purpose sampled data Stability Analysis Program capable of providing frequency response on root locus data.

  12. 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.

  13. Stability analysis of a state dependent delayed, coupled two DOF model of drill-stringvibration

    NASA Astrophysics Data System (ADS)

    Nandakumar, K.; Wiercigroch, Marian

    2013-05-01

    Stick-slip and bit-bounce are dangerous dynamic phenomena encountered during rotary drilling of oil-wells, but their exact origins and interplay are far from obvious. In this paper, we consider a fully coupled two degrees-of-freedom model, which assumes a state-dependent time delay and a viscous damping for both the axial and torsional motions. Without making any asymptotic assumptions, we have conducted a detailed linear stability analysis of the resultant mathematical model, which is composed of two coupled delay differential equations. The main significance of our work lies in providing practically useful results, which are in the form of stability charts in the plane of drilling rates and rotary speeds.

  14. Stability analysis of self-similar behaviors in perfect fluid gravitational collapse

    SciTech Connect

    Mitsuda, Eiji; Tomimatsu, Akira

    2006-06-15

    Stability of self-similar solutions for gravitational collapse is an important problem to be investigated from the perspectives of their nature as an attractor, critical phenomena, and instability of a naked singularity. In this paper we study spherically symmetric non-self-similar perturbations of matter and metrics in spherically symmetric self-similar backgrounds. The collapsing matter is assumed to be a perfect fluid with the equation of state P={alpha}{rho}. We construct a single wave equation governing the perturbations, which makes their time evolution in arbitrary self-similar backgrounds analytically tractable. Further we propose an analytical application of this master wave equation to the stability problem by means of the normal mode analysis for the perturbations having the time dependence given by exp(i{omega}log vertical t vertical bar), and present some sufficient conditions for the absence of nonoscillatory unstable normal modes with purely imaginary {omega}.

  15. Nanometric resolution in the hydrodynamic size analysis of ligand-stabilized gold nanorods.

    PubMed

    Mehtala, Jonathan G; Wei, Alexander

    2014-11-25

    The stability and hydrodynamic size of ligand-coated gold nanorods (GNRs; aspect ratio 3.6) have been characterized by nanoparticle tracking analysis (NTA)-a single-particle counting method that can measure size distributions with low nanometer resolution. Stable aqueous suspensions of citrate-stabilized GNRs (cit-GNRs) are amenable to surface functionalization without loss of dispersion control. Cit-GNRs can be treated with chemisorptive ligands (thiols and dithiocarbamates), nonionic surfactants (Tween 20), and proteins (human serum albumin), all of which produce stable suspensions at low surfactant concentrations. The precision of NTA (relative standard deviation 10-12%, standard error <2%) is sufficient to allow differences in the hydrodynamic size of coated GNRs to be interpreted in terms of surfactant structure and conformation. PMID:25349895

  16. Nanometric Resolution in the Hydrodynamic Size Analysis of Ligand-Stabilized Gold Nanorods

    PubMed Central

    2015-01-01

    The stability and hydrodynamic size of ligand-coated gold nanorods (GNRs; aspect ratio 3.6) have been characterized by nanoparticle tracking analysis (NTA)—a single-particle counting method that can measure size distributions with low nanometer resolution. Stable aqueous suspensions of citrate-stabilized GNRs (cit-GNRs) are amenable to surface functionalization without loss of dispersion control. Cit-GNRs can be treated with chemisorptive ligands (thiols and dithiocarbamates), nonionic surfactants (Tween 20), and proteins (human serum albumin), all of which produce stable suspensions at low surfactant concentrations. The precision of NTA (relative standard deviation 10–12%, standard error <2%) is sufficient to allow differences in the hydrodynamic size of coated GNRs to be interpreted in terms of surfactant structure and conformation. PMID:25349895

  17. Stability analysis of numerical boundary conditions and implicit difference approximations for hyperbolic equations

    NASA Technical Reports Server (NTRS)

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

    1981-01-01

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

  18. Stochastic stability analysis of a reduced galactic dynamo model with perturbed α-effect

    NASA Astrophysics Data System (ADS)

    Kelly, Cónall

    2016-09-01

    We investigate the asymptotic behaviour of a reduced αΩ-dynamo model of magnetic field generation in spiral galaxies where fluctuation in the α-effect results in a system with state-dependent stochastic perturbations. By computing the upper Lyapunov exponent of the linearised model, we can identify regions of instability and stability in probability for the equilibrium of the nonlinear model; in this case the equilibrium solution corresponds to a magnetic field that has undergone catastrophic quenching. These regions are compared to regions of exponential mean-square stability and regions of sub- and super-criticality in the unperturbed linearised model. Prior analysis in the literature which focuses on these latter regions does not adequately address the corresponding transition in the nonlinear stochastic model. Finally we provide a visual representation of the influence of drift non-normality and perturbation intensity on these regions.

  19. Analysis of genetic stability of in vitro propagated potato microtubers using DNA markers.

    PubMed

    Tiwari, Jagesh K; Chandel, Poonam; Gupta, Shruti; Gopal, Jai; Singh, B P; Bhardwaj, Vinay

    2013-10-01

    The genetic stability of in vitro propagated potato microtubers was assessed using random amplified polymorphic DNA (RAPD), inter simple sequence repeat (ISSR), simple sequence repeat (SSR) and amplified fragment length polymorphism (AFLP) markers. Microtubers were developed through in vitro from potato microplants using standardized protocols. The microtubers were conserved for 1 year under three different culture media and consequently microplants were regenerated for the DNA analyses. During the study, a total of 38 (10 RAPD, 11 ISSR, 12 SSR and 5 AFLP) primers produced a total of 407 (58 RAPD, 56 ISSR, 96 SSR and 197 AFLP) clear, distinct and reproducible amplicons. Cluster analysis revealed 100 % genetic similarity among the mother plant and its derivatives within the clusters by SSR, ISSR and RAPD analyses, whereas AFLP analysis revealed from 85 to 100 % genetic similarity. Dendrogram analysis based on the Jaccard's coefficient classified the genotypes into five clusters (I-V), each cluster consisting of mother plant and its derivatives. Principal component analysis (PCA) also plotted mother plant and its genotypes of each cluster together. Based on our results, it is concluded that AFLP is the best method followed by SSR, ISSR and RAPD to detect genetic stability of in vitro conserved potato microtubers. The in vitro conservation medium (T2) is a safe method for conservation of potato microtubers to produce true-to-type plans. PMID:24431528

  20. ASTROP2 Users Manual: A Program for Aeroelastic Stability Analysis of Propfans

    NASA Technical Reports Server (NTRS)

    Reddy, T. S. R.; Lucero, John M.

    1996-01-01

    This manual describes the input data required for using the second version of the ASTROP2 (Aeroelastic STability and Response Of Propulsion systems - 2 dimensional analysis) computer code. In ASTROP2, version 2.0, the program is divided into two modules: 2DSTRIP, which calculates the structural dynamic information; and 2DASTROP, which calculates the unsteady aerodynamic force coefficients from which the aeroelastic stability can be determined. In the original version of ASTROP2, these two aspects were performed in a single program. The improvements to version 2.0 include an option to account for counter rotation, improved numerical integration, accommodation for non-uniform inflow distribution, and an iterative scheme to flutter frequency convergence. ASTROP2 can be used for flutter analysis of multi-bladed structures such as those found in compressors, turbines, counter rotating propellers or propfans. The analysis combines a two-dimensional, unsteady cascade aerodynamics model and a three dimensional, normal mode structural model using strip theory. The flutter analysis is formulated in the frequency domain resulting in an eigenvalue determinant. The flutter frequency and damping can be inferred from the eigenvalues.

  1. Inertial instability of oceanic submesoscale vortices: linear analysis, marginal stability criterion and laboratory experiments

    NASA Astrophysics Data System (ADS)

    Lazar, A.; Stegner, A.; Heifetz, E.

    2012-04-01

    The stability of axisymmetric oceanic-like vortices to inertial perturbations is investigated by means of linear stability analysis, taking into account the thickness and the stratification of the thermocline, as well as the vertical eddy viscosity. The model considers different types of circular barotropic vortices in a linearly stratified shallow layer confined with rigid lids. In this case the aspect ratio (thermocline height to vortex radius ratio) should be added to the parameters that control the stability for columnar vortices, which are the stratification, and the Ekman and Rossby numbers. We show that for strong stratification the Burger number (the radius of the vortex in relation to the Rossby radius of deformation) replaces the aspect ratio and the stratification parameter, and then only three parameters are needed. Numerical analysis reveals that if the intensity of the vortex is characterized by the vortex Rossby number, then for monotonic and non-isolated vortices, the instability is not sensitive to the vorticity profile. This allows extending our analytical solutions for the Rankine vortex to a wide variety of oceanic cases, including results such as the analytic dispersion relation, and the marginal stability criterion. This criterion suits oceanic conditions better than the generalized Rayleigh criterion, which is only valid for non-dissipative and non-stratified eddies. Comparison with literature oceanographic data shows that our criterion allows for cases that seem to contradict the common oceanographic hypothesis for inertial instability: 1. Intense submesoscale anticyclones may be stable even with a core region of negative absolute vorticity; and on the other hand, 2. mesoscale vortices can be unstable. We corroborate our findings with large-scale laboratory experiments, performed at the LEGI-Coriolis platform.

  2. A coupled distributed hydrological-stability analysis on a terraced slope of Valtellina (northern Italy)

    NASA Astrophysics Data System (ADS)

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

    2013-02-01

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

  3. Nonlocal stability analysis of the MHD Kelvin-Helmholtz instability in a compressible plasma

    SciTech Connect

    Miura, A.; Pritchett, P.L.

    1982-09-01

    A general stability analysis is performed for the Kelvin-Helmholtz instability in sheared magnetohydrodynamic flow of finite thickness in a compressible plasma. The analysis allows for arbitrary orientation of the magnetic field B/sub 0/, velocity flow v/sub 0/, and wave vector k in the plane perpendicular to the velocity gradient, and no restrictions are imposed on the sound or Alfven Mach numbers. The stability problem is reduced to the solution of a single-order differential equation, which includes a gravitational term to represent coupling between the Kelvin-Helmholtz mode and the interchange mode. In the incompressible limit it is shown that the Kelvin-Helmholtz mode is completely stabilized for any velocity profile as long as the condition V/sub 0/<2v/sub A/ (kxB/sub 0/)/(kxv/sub 0/) is satisfied, where V/sub 0/ is the total velocity jump across the shear layer. Numerical results are obtained for a hyperbolic tangent velocity profile for the transverse (B/sub 0/perpendicularv/sub 0/) and parallel (B/sub 0/parallelv/sub 0/) flow configurations. Only modes with k..delta..<2 are unstable, where ..delta.. is the scale length of the shear layer. The fastest growing modes occur for k..delta..approx.0.5--1.0. Compressibility and a magnetic field component parallel to the flow are found to be stabilizing effects. For the transverse case, only the fast magnetosonic mode is destabilized, but if the kxB/sub 0/not =0, the instability contains Alfven-mode and slow-mode components as well. The Alfven component gives rise to a field-aligned current inside the shear layer. In the parallel case, both Alfven and slow magnetosonic components are present, with the Alfven mode confined inside the shear layer. The results of the analysis are used to discuss the stability of sheared plasma flow at the magnetopause boundary and in the solar wind. At the magnetopause boundary, the fastest growing Kelvin-Helmholtz mode has a frequency of 0 (V/sub 0//2..delta..), which overlaps with

  4. Linear stability analysis and the speed of gravitational waves in dynamical Chern-Simons modified gravity

    SciTech Connect

    Garfinkle, David; Pretorius, Frans; Yunes, Nicolas

    2010-08-15

    We perform a linear stability analysis of dynamical Chern-Simons modified gravity in the geometric optics approximation and find that it is linearly stable on the backgrounds considered. Our analysis also reveals that gravitational waves in the modified theory travel at the speed of light in Minkowski spacetime. However, on a Schwarzschild background the characteristic speed of propagation along a given direction splits into two modes, one subluminal and one superluminal. The width of the splitting depends on the azimuthal components of the propagation vector, is linearly proportional to the mass of the black hole, and decreases with the third inverse power of the distance from the black hole. Radial propagation is unaffected, implying that as probed by gravitational waves the location of the event horizon of the spacetime is unaltered. The analysis further reveals that when a high frequency, pure gravitational wave is scattered from a black hole, a scalar wave of comparable amplitude is excited, and vice versa.

  5. Solidification/stabilization of electric arc furnace dust using coal fly ash. Analysis of the stabilization process.

    PubMed

    Pereira, C F; Rodríguez-Piñero, M; Vale, J

    2001-03-30

    In this paper, the stabilization of electric arc furnace (EAF) dust containing hazardous metals such as Pb, Cd, Cr or Zn is described. The treatment involves a waste solidification/stabilization (S/S) process, using coal fly ash as the fundamental raw material and main binder. The article also contains a brief review of the most important recent publications related to the use of fly ash as S/S agents. The efficacy of the process has been evaluated mainly through leaching tests on the solidified products and compliance with some imposed leachate limits. The concentration of metals leaching from the S/S products was strongly leachate pH dependent; thus, the final pH of the leachate is the most important variable in reaching the limits and, therefore, in meeting the stabilization goals. In this study, the dependence relationship between the leachate pH and the concentrations of metals in the leachate are analyzed; in some cases, this allows us to estimate the speciation of contaminants in the S/S solids and to understand the mechanism responsible for reduced leachability of heavy metals from solidified wastes. PMID:11230914

  6. The role of Soil Water Retention Curve in slope stability analysis in unsaturated and heterogeneous soils.

    NASA Astrophysics Data System (ADS)

    Antinoro, Chiara; Arnone, Elisa; Noto, Leonardo V.

    2015-04-01

    The mechanisms of rainwater infiltration causing slope instability had been analyzed and reviewed in many scientific works. Rainwater infiltration into unsaturated soil increases the degree of saturation, hence affecting the shear strength properties and thus the probability of slope failure. It has been widely proved that the shear strength properties change with the soil water suction in unsaturated soils; therefore, the accuracy to predict the relationship between soil water content and soil water suction, parameterized by the soil-water characteristic curve, has significant effects on the slope stability analysis. The aim of this study is to investigate how the characterization of SWRC of differently structured unsaturated soils affects the slope stability on a simple infinite slope. In particular, the unimodal and bimodal distributions of the soil pore size were compared. Samples of 40 soils, highly different in terms of structure and texture, were collected and used to calibrate two bimodal SWRCs, i.e. Ross and Smettem (1993) and Dexter et al., (2008). The traditional unimodal van Genuchten (1980) model was also applied for comparison. Slope stability analysis was conducted in terms of Factor of Safety (FS) by applying the infinite slope model for unsaturated soils. In the used formulation, the contribution of the suction effect is tuned by a parameter 'chi' in a rate proportional to the saturation conditions. Different parameterizations of this term were also compared and analyzed. Results indicated that all three SWRC models showed good overall performance in fitting the sperimental SWRCs. Both the RS and DE models described adequately the water retention data for soils with a bimodal behavior confirmed from the analysis of pore size distribution, but the best performance was obtained by DE model confirmed. In terms of FS, the tree models showed very similar results as soil moisture approached to the saturated condition; however, within the residual zone

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

    NASA Astrophysics Data System (ADS)

    Siewniak, Piotr; Grzesik, Bogusław

    2014-10-01

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

  8. Rapid RNA–ligand interaction analysis through high-information content conformational and stability landscapes

    PubMed Central

    Baird, Nathan J.; Inglese, James; Ferré-D'Amaré, Adrian R.

    2015-01-01

    The structure and biological properties of RNAs are a function of changing cellular conditions, but comprehensive, simultaneous investigation of the effect of multiple interacting environmental variables is not easily achieved. We have developed an efficient, high-throughput method to characterize RNA structure and thermodynamic stability as a function of multiplexed solution conditions using Förster resonance energy transfer (FRET). In a single FRET experiment using conventional quantitative PCR instrumentation, 19,400 conditions of MgCl2, ligand and temperature are analysed to generate detailed empirical conformational and stability landscapes of the cyclic diguanylate (c-di-GMP) riboswitch. The method allows rapid comparison of RNA structure modulation by cognate and non-cognate ligands. Landscape analysis reveals that kanamycin B stabilizes a non-native, idiosyncratic conformation of the riboswitch that inhibits c-di-GMP binding. This demonstrates that allosteric control of folding, rather than direct competition with cognate effectors, is a viable approach for pharmacologically targeting riboswitches and other structured RNA molecules. PMID:26638992

  9. High-finesse fiber Fabry-Perot cavities: stabilization and mode matching analysis

    NASA Astrophysics Data System (ADS)

    Gallego, J.; Ghosh, S.; Alavi, S. K.; Alt, W.; Martinez-Dorantes, M.; Meschede, D.; Ratschbacher, L.

    2016-03-01

    Fiber Fabry-Perot cavities, formed by micro-machined mirrors on the end-facets of optical fibers, are used in an increasing number of technical and scientific applications, where they typically require precise stabilization of their optical resonances. Here, we study two different approaches to construct fiber Fabry-Perot resonators and stabilize their length for experiments in cavity quantum electrodynamics with neutral atoms. A piezo-mechanically actuated cavity with feedback based on the Pound-Drever-Hall locking technique is compared to a novel rigid cavity design that makes use of the high passive stability of a monolithic cavity spacer and employs thermal self-locking and external temperature tuning. Furthermore, we present a general analysis of the mode matching problem in fiber Fabry-Perot cavities, which explains the asymmetry in their reflective line shapes and has important implications for the optimal alignment of the fiber resonators. Finally, we discuss the issue of fiber-generated background photons. We expect that our results contribute toward the integration of high-finesse fiber Fabry-Perot cavities into compact and robust quantum-enabled devices in the future.

  10. Analysis of the aerodynamic force in an eye-stabilized flapping flyer.

    PubMed

    Su, Jian-Yuan; Yang, Jing-Tang

    2013-12-01

    Experimental methods and related theories to evaluate the lift force for a flyer are established, but one can traditionally acquire only the magnitude of that lift. We here proffer an analysis based on kinematic theory and experimental visualization of the flow to complete a treatment of the aerodynamic force affecting a hovering flyer that generates a lift force approximately equal to its weight, and remains nearly stationary in midair; the center and direction of the aerodynamic force are accordingly determined with some assumptions made. The principal condition to resolve the problem is the stabilization of the vision of a flyer, which is inspired by a hovering passerine that experiences a substantial upward swing during downstroke periods while its eye remains stabilized. Viewing the aerodynamic force with a bird's eye, we find that the center and direction of this aerodynamic force vary continuously with respect to the lift force. Our results provide practical guidance for engineers to enhance the visual stability of surveillance cameras incorporated in micro aerial vehicles. PMID:24200672

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

    NASA Astrophysics Data System (ADS)

    Chen, Gengsheng; Chen, Shi-Jie

    2011-12-01

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

  12. Stability analysis of Rayleigh-Bénard convection in a cylinder with internal heat generation.

    PubMed

    Wang, Bo-Fu; Zhou, Lin; Wan, Zhen-Hua; Ma, Dong-Jun; Sun, De-Jun

    2016-07-01

    The flow instabilities of Rayleigh-Bénard convection in a cylinder with effect of uniform internal heat source are investigated numerically. The instabilities of the static state and of axisymmetric flows are investigated by linear stability analysis. The convection threshold depends on the strength of internal heat source q and the aspect ratio of the cylinder Γ. The stability of axisymmetric flows is strongly affected by these two parameters, as well as the Prandtl number Pr. Depending on the value of q, three regimes are identified: weak internal heating, moderate internal heating, and strong internal heating regime. In a weak internal heating regime, the instability characteristics are similar to Rayleigh-Bénard convection. In a moderate internal heating regime, intense interaction of buoyancy instability and hydrodynamic instability result in complex instability curves. When q is large enough, the internal heating effect overwhelms the boundary heating effect. Specifically, the influence of Pr on instability is studied at a moderate internal heat strength q=6.4. An extremely multivalued stability curve is observed. At most five critical Rayleigh numbers can be determined for the axisymmetry-breaking instability at a certain Prandtl number. An axisymmetric unsteady instability mode is observed as well. By nonlinear simulation, the oscillatory flow patterns are obtained, and the axisymmetry-breaking bifurcation of the unsteady toroidal flow is studied. PMID:27575218

  13. Rapid RNA-ligand interaction analysis through high-information content conformational and stability landscapes.

    PubMed

    Baird, Nathan J; Inglese, James; Ferré-D'Amaré, Adrian R

    2015-01-01

    The structure and biological properties of RNAs are a function of changing cellular conditions, but comprehensive, simultaneous investigation of the effect of multiple interacting environmental variables is not easily achieved. We have developed an efficient, high-throughput method to characterize RNA structure and thermodynamic stability as a function of multiplexed solution conditions using Förster resonance energy transfer (FRET). In a single FRET experiment using conventional quantitative PCR instrumentation, 19,400 conditions of MgCl2, ligand and temperature are analysed to generate detailed empirical conformational and stability landscapes of the cyclic diguanylate (c-di-GMP) riboswitch. The method allows rapid comparison of RNA structure modulation by cognate and non-cognate ligands. Landscape analysis reveals that kanamycin B stabilizes a non-native, idiosyncratic conformation of the riboswitch that inhibits c-di-GMP binding. This demonstrates that allosteric control of folding, rather than direct competition with cognate effectors, is a viable approach for pharmacologically targeting riboswitches and other structured RNA molecules. PMID:26638992

  14. Rapid RNA-ligand interaction analysis through high-information content conformational and stability landscapes

    SciTech Connect

    Baird, Nathan J.; Inglese, James; Ferré-D’Amaré, Adrian R.

    2015-12-07

    The structure and biological properties of RNAs are a function of changing cellular conditions, but comprehensive, simultaneous investigation of the effect of multiple interacting environmental variables is not easily achieved. We have developed an efficient, high-throughput method to characterize RNA structure and thermodynamic stability as a function of multiplexed solution conditions using Förster resonance energy transfer (FRET). In a single FRET experiment using conventional quantitative PCR instrumentation, 19,400 conditions of MgCl2, ligand and temperature are analysed to generate detailed empirical conformational and stability landscapes of the cyclic diguanylate (c-di-GMP) riboswitch. This method allows rapid comparison of RNA structure modulation by cognate and non-cognate ligands. Landscape analysis reveals that kanamycin B stabilizes a non-native, idiosyncratic conformation of the riboswitch that inhibits c-di-GMP binding. Our research demonstrates that allosteric control of folding, rather than direct competition with cognate effectors, is a viable approach for pharmacologically targeting riboswitches and other structured RNA molecules.

  15. Stability analysis of Rayleigh-Bénard convection in a cylinder with internal heat generation

    NASA Astrophysics Data System (ADS)

    Wang, Bo-Fu; Zhou, Lin; Wan, Zhen-Hua; Ma, Dong-Jun; Sun, De-Jun

    2016-07-01

    The flow instabilities of Rayleigh-Bénard convection in a cylinder with effect of uniform internal heat source are investigated numerically. The instabilities of the static state and of axisymmetric flows are investigated by linear stability analysis. The convection threshold depends on the strength of internal heat source q and the aspect ratio of the cylinder Γ . The stability of axisymmetric flows is strongly affected by these two parameters, as well as the Prandtl number Pr. Depending on the value of q , three regimes are identified: weak internal heating, moderate internal heating, and strong internal heating regime. In a weak internal heating regime, the instability characteristics are similar to Rayleigh-Bénard convection. In a moderate internal heating regime, intense interaction of buoyancy instability and hydrodynamic instability result in complex instability curves. When q is large enough, the internal heating effect overwhelms the boundary heating effect. Specifically, the influence of Pr on instability is studied at a moderate internal heat strength q =6.4 . An extremely multivalued stability curve is observed. At most five critical Rayleigh numbers can be determined for the axisymmetry-breaking instability at a certain Prandtl number. An axisymmetric unsteady instability mode is observed as well. By nonlinear simulation, the oscillatory flow patterns are obtained, and the axisymmetry-breaking bifurcation of the unsteady toroidal flow is studied.

  16. Stability analysis of a thermocapillary spreading film with slip-model.

    PubMed

    Tiwari, Naveen

    2014-11-01

    Thin liquid films spreading on a solid substrate due to thermocapillary stresses are susceptible to rivulet instability at the advancing solid-liquid-vapor contact line. The unstable front is related to the presence of a capillary ridge at the contact line. In this work, the dynamics and stability of thermocapillary-driven films are analyzed using a detailed slip-model to alleviate the stress singularity at the moving contact line. The slip-model is well suited to model partially wetting fluids due to the possibility of defining the contact angle explicitly. The effect of motion of the contact line on the dynamic contact angle and subsequently on the dynamics and stability of the film is explored. The apparent contact angle is a result of the static contact angle and motion of the contact line. It is shown that one can obtain exactly the same base profile with and without taking into account the effect of motion on the contact angle with suitable change of parameters but the linear stability of the two profiles is different. Further the transient growth is found to be somewhat different but small for both configurations. Analysis of the ε -pseudospectra indicates a highly non-normal system for the case of dynamic contact angle. PMID:25428784

  17. Stability analysis of two phase stratified flow in a rectangular channel

    NASA Astrophysics Data System (ADS)

    Bhagavatula, Dinesh; S, Pushpavanam

    2015-11-01

    Two phase stratified flows arise in extraction operations in microfluidic systems. It is well established that stratified flows in between two infinite plates is always unstable. However such flows are experimentally observed in micro channels. To understand this paradox we perform a linear stability analysis of stratified two phase Poiseuille flow in a rectangular duct. A two-dimensional fully developed flow through the rectangular channel is considered. The linearized equations along with the boundary conditions in primitive variable formulation are numerically solved using Chebyshev collocation method. All the primitive variables, which are the velocity and pressure fields, are retained in the linearised governing equations. Since boundary conditions for disturbance pressure do not exist, the corresponding compatibility conditions derived from the Navier-Stokes equations are collocated both at the walls and the interface. The resulting eigen-value problem is solved using a shift and invert Arnoldi algorithm. The role of different parameters such as Aspect ratio, density ratio, viscosity ratio on the stability characteristics is analyzed. The stability results are validated in the limit of large Aspect Ratios. The flow fields are sought as a combination of Chebyshev polynomials in both y and z directions. Ministry of Human Resource and Development (MHDR).

  18. Rapid RNA-ligand interaction analysis through high-information content conformational and stability landscapes

    NASA Astrophysics Data System (ADS)

    Baird, Nathan J.; Inglese, James; Ferré-D'Amaré, Adrian R.

    2015-12-01

    The structure and biological properties of RNAs are a function of changing cellular conditions, but comprehensive, simultaneous investigation of the effect of multiple interacting environmental variables is not easily achieved. We have developed an efficient, high-throughput method to characterize RNA structure and thermodynamic stability as a function of multiplexed solution conditions using Förster resonance energy transfer (FRET). In a single FRET experiment using conventional quantitative PCR instrumentation, 19,400 conditions of MgCl2, ligand and temperature are analysed to generate detailed empirical conformational and stability landscapes of the cyclic diguanylate (c-di-GMP) riboswitch. The method allows rapid comparison of RNA structure modulation by cognate and non-cognate ligands. Landscape analysis reveals that kanamycin B stabilizes a non-native, idiosyncratic conformation of the riboswitch that inhibits c-di-GMP binding. This demonstrates that allosteric control of folding, rather than direct competition with cognate effectors, is a viable approach for pharmacologically targeting riboswitches and other structured RNA molecules.

  19. Application of perturbation theory to the stability analysis of realistic atmospheric flows

    NASA Astrophysics Data System (ADS)

    Borges, Mark D.; Sardeshmukh, Prashant D.

    1997-05-01

    The 1st-order perturbation technique is investigated as a tool for measuring the dynamical significance of a change in a background flow. The focus is on estimating the change in the behavior of the linear disturbance operator as manifest in both the most rapidly growing normal modes as well as initial disturbances that amplify the most over finite time intervals (also known as singular vectors). The notion of a "small change" to a flow can be made more precise by requiring, for instance, that the changes in the flow's stability properties be accurately estimated using first-order perturbation theory. The perturbation theory updates of the eigen- and singular values are economical to compute, thus making this determination feasible even in a practical setting. Furthermore, a simple refinement of the basic algorithm enables an efficient updating of the singular vectors as well. The technique is illustrated and tested for a flow having a substantial number of degrees of freedom, the global 250-mb flow during northern hemisphere winter represented in a T31 spectral space. A complete generalized barotropic stability analysis of the observed long-term mean 250-mb flow is performed first. Various alterations to the flow are then considered, and the perturbation technique is applied to estimate both the asymptotic and finite-time stability of the altered flows. Finally, the accuracy of these estimates is checked against the complete stability analyses of the altered flows, and an assessment is made of what a "small change" is for these cases. It is shown that in many cases the perturbation theory estimates of the stability changes are accurate enough over a sufficiently large parameter range to be of practical use. Applications to the problems of: (1) anticipating variations in forecast skill associated with day-to-day variations in flow stability; and (2) anticipating the relevance and robustness of individual normal modes are discussed. The latter problem is closely

  20. CFD analysis of sludge accumulation and hydraulic performance of a waste stabilization pond.

    PubMed

    Alvarado, Andres; Sanchez, Esteban; Durazno, Galo; Vesvikar, Mehul; Nopens, Ingmar

    2012-01-01

    Sludge management in waste stabilization ponds (WSPs) is essential for safeguarding the system performance. Sludge accumulation patterns in WSPs are strongly influenced by the pond hydrodynamics. CFD modeling was applied to study the relation between velocity profiles and sludge deposition during 10 years of operation of the Ucubamba WSP in Cuenca (Ecuador). One tracer experiment was performed and three sludge accumulation scenarios based on bathymetric surveys were simulated. A residence time distribution (RTD) analysis illustrated the decrease of residence times due to sludge deposition. Sludge accumulation rates were calculated. The influence of flow pattern on the sludge deposition was studied, enabling better planning of future pond operation and desludging. PMID:23032767

  1. Optimal Stabilization of Social Welfare under Small Variation of Operating Condition with Bifurcation Analysis

    NASA Astrophysics Data System (ADS)

    Chanda, Sandip; De, Abhinandan

    2015-07-01

    A social welfare optimization technique has been proposed in this paper with a developed state space based model and bifurcation analysis to offer substantial stability margin even in most inadvertent states of power system networks. The restoration of the power market dynamic price equilibrium has been negotiated in this paper, by forming Jacobian of the sensitivity matrix to regulate the state variables for the standardization of the quality of solution in worst possible contingencies of the network and even with co-option of intermittent renewable energy sources. The model has been tested in IEEE 30 bus system and illustrious particle swarm optimization has assisted the fusion of the proposed model and methodology.

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

    NASA Technical Reports Server (NTRS)

    Gunter, Edgar J.; Branagan, Lyle

    1991-01-01

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

  3. X-ray source assembly having enhanced output stability, and fluid stream analysis applications thereof

    DOEpatents

    Radley, Ian; Bievenue, Thomas J.; Burdett Jr., John H.; Gallagher, Brian W.; Shakshober, Stuart M.; Chen, Zewu; Moore, Michael D.

    2007-04-24

    An x-ray source assembly (2700) and method of operation are provided having enhanced output stability. The assembly includes an anode (2125) having a source spot upon which electrons (2120) impinge and a control system (2715/2720) for controlling position of the anode source spot relative to an output structure. The control system can maintain the anode source spot location relative to the output structure (2710) notwithstanding a change in one or more operating conditions of the x-ray source assembly. One aspect of the disclosed invention is most amenable to the analysis of sulfur in petroleum-based fuels.

  4. X-ray source assembly having enhanced output stability, and fluid stream analysis applications thereof

    DOEpatents

    Radley, Ian; Bievenue, Thomas J.; Burdett, John H.; Gallagher, Brian W.; Shakshober, Stuart M.; Chen, Zewu; Moore, Michael D.

    2008-06-08

    An x-ray source assembly and method of operation are provided having enhanced output stability. The assembly includes an anode having a source spot upon which electrons impinge and a control system for controlling position of the anode source spot relative to an output structure. The control system can maintain the anode source spot location relative to the output structure notwithstanding a change in one or more operating conditions of the x-ray source assembly. One aspect of the disclosed invention is most amenable to the analysis of sulfur in petroleum-based fuels.

  5. Stability analysis and testing of a train of centrifugal compressors for high pressure gas injection

    SciTech Connect

    Memmott, E.A.

    1999-07-01

    This paper describes the rotor dynamic stability analysis and the PTC-10 Class 1 test of a three body centrifugal compressor train for high pressure natural gas injection services. This train had a full load full pressure string test on hydrocarbon gases to a final discharge pressure of 500 BAR (7250 PSIA). Each compressor is of the back to back configuration, and is equipped with tilting pad seals, damper bearings, and a honeycomb labyrinth at the division wall with shunt holes. The driver is a gas turbine.

  6. Stability analysis and numerical simulation of 1 prey - 2 predator system

    NASA Astrophysics Data System (ADS)

    Savitri, D.; Abadi

    2015-03-01

    In this paper, we study an ecological system that consists of 1 prey and 2 predators populations. The prey population grows logistically while Holling type II functional response is applied for both predators . The first predator preys on the prey and the second predator preys on the first one. The study starts with the stability analysis of critical points of the systems. Then, by using normal form and centre manifold method the information about other nontrivial solutions due to bifurcation including possible limit cycles appearance is obtained. The results are confirmed by numerical simulation using MatCont and biological interpretation of the results is also presented.

  7. Three-dimensional stability analysis of the periodic flow around a circular cylinder

    NASA Astrophysics Data System (ADS)

    Noack, Bernd R.; König, Michael; Eckelmann, Helmut

    1993-06-01

    The onset of three-dimensionality in the von Kármán vortex street behind a circular cylinder is investigated by carrying out the first global, nonparallel, three-dimensional stability analysis of the periodic flow. This flow is found to become unstable at a Reynolds number of 170 by a critical, three-dimensional Floquet mode with a spanwise wavelength of 1.8 diam. The spatial structure of this mode indicates that the onset of three-dimensionality is due to a near-wake instability and not caused by a stagnation-line or a boundary-layer instability.

  8. Stability and time-domain analysis of the dispersive tristability in microresonators under modal coupling

    SciTech Connect

    Dumeige, Yannick; Feron, Patrice

    2011-10-15

    Coupled nonlinear resonators have potential applications for the integration of multistable photonic devices. The dynamic properties of two coupled-mode nonlinear microcavities made of Kerr material are studied by linear stability analysis. Using a suitable combination of the modal coupling rate and the frequency detuning, it is possible to obtain configurations where a hysteresis loop is included inside other bistable cycles. We show that a single resonator with two modes both linearly and nonlinearly coupled via the cross-Kerr effect can have a multistable behavior. This could be implemented in semiconductor nonlinear whispering-gallery-mode microresonators under modal coupling for all optical signal processing or ternary optical logic applications.

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

    NASA Technical Reports Server (NTRS)

    Colin, A. D.

    1973-01-01

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

  10. Virial theorem analysis of the structure and stability of magnetized clouds

    NASA Technical Reports Server (NTRS)

    Zweibel, Ellen G.

    1990-01-01

    The tensor virial theorem is used to analyze the structure and stability of self-gravitating, magnetized spheroids surrounded by a low-density medium with pressure and magnetic field. Analytical expressions are developed for the effect of a weak field and calculate critical states when the effect of the field is arbitrarily strong, comparing the results with full magnetohydrostatic calculations. This analysis suggests that a magnetic field may prevent gravitational collapse but may also be destabilizing, depending on its degree of concentration within the cloud.

  11. Analysis of a passive heat sink for temperature stabilization of high-power LED bulbs

    NASA Astrophysics Data System (ADS)

    Balvís, Eduardo; Bendaña, Ricardo; Michinel, Humberto; Fernández de Córdoba, Pedro; Paredes, Angel

    2015-04-01

    In this paper we present a numerical analysis and experimental measurements of the temperature stabilization of high-power LED chips that we have obtained by employing an aluminum passive heat sink, designed to be used in a compact light bulb configuration. We demonstrate that our system keeps the temperature of the LED chip well-below 70° C yielding long-term operation of the device. Our simulations have been performed for a low-cost device ready to install in public streetlights. The experimental measurements performed in different configurations show a nice agreement with the numerical calculations.

  12. Methods for contingency screening and ranking for voltage stability analysis of power systems

    SciTech Connect

    Ejebe, G.C.; Irisarri, G.D.; Mokhtari, S.; Obadina, O.; Ristanovic, P.; Tong, J.

    1996-02-01

    The comparison of performance of four methods for contingency screening and ranking for voltage stability analysis is presented. Three of the methods are existing methods, while a new method is proposed. The performance of all the methods is carried out by comparing with full solutions using a continuation power flow. It is shown that the newly proposed method has the best performance in terms of accuracy and computation time. All the methods are evaluated using a 234-bus system. Additional results using the best performing method are included for a 901-bus power system.

  13. Methods for contingency screening and ranking for voltage stability analysis of power systems

    SciTech Connect

    Ejebe, G.C.; Irisarri, G.D.; Mokhtari, S.; Obadina, O.; Ristanovic, P.; Tong, J.

    1995-12-31

    The comparison of performance of four methods for contingency screening and ranking for voltage stability analysis is presented. Three of the methods are existing methods, while a new method is proposed. The performance of all the methods is carried out by comparing with full solutions using a continuation power flow. It is shown that the newly proposed method has the best performance in terms of accuracy and computation time. All the methods are evaluated using a 234-bus system. Additional results using the best performing method are included for a 901-bus power system.

  14. Synchronization of delay-coupled nonlinear oscillators: An approach based on the stability analysis of synchronized equilibria

    NASA Astrophysics Data System (ADS)

    Michiels, Wim; Nijmeijer, Henk

    2009-09-01

    We consider the synchronization problem of an arbitrary number of coupled nonlinear oscillators with delays in the interconnections. The network topology is described by a directed graph. Unlike the conventional approach of deriving directly sufficient synchronization conditions, the approach of the paper starts from an exact stability analysis in a (gain, delay) parameter space of a synchronized equilibrium and extracts insights from an analysis of its bifurcations and from the corresponding emerging behavior. Instrumental to this analysis a factorization of the characteristic equation is employed that not only facilitates the analysis and reduces computational cost but also allows to determine the precise role of the individual agents and the topology of the network in the (in)stability mechanisms. The study provides an algorithm to perform a stability and bifurcation analysis of synchronized equilibria. Furthermore, it reveals fundamental limitations to synchronization and it explains under which conditions on the topology of the network and on the characteristics of the coupling the systems are expected to synchronize. In the second part of the paper the results are applied to coupled Lorenz systems. The main results show that for sufficiently large coupling gains, delay-coupled Lorenz systems exhibit a generic behavior that does not depend on the number of systems and the topology of the network, as long as some basic assumptions are satisfied, including the strong connectivity of the graph. Here the linearized stability analysis is strengthened by a nonlinear stability analysis which confirms the predictions based on the linearized stability and bifurcation analysis. This illustrates the usefulness of the exact linearized analysis in a situation where a direct nonlinear stability analysis is not possible or where it yields conservative conditions from which it is hard to get qualitative insights in the synchronization mechanisms and their scaling properties

  15. Stability analysis for acoustic wave propagation in tilted TI media by finite differences

    NASA Astrophysics Data System (ADS)

    Bakker, Peter M.; Duveneck, Eric

    2011-05-01

    Several papers in recent years have reported instabilities in P-wave modelling, based on an acoustic approximation, for inhomogeneous transversely isotropic media with tilted symmetry axis (TTI media). In particular, instabilities tend to occur if the axis of symmetry varies rapidly in combination with strong contrasts of medium parameters, which is typically the case at the foot of a steeply dipping salt flank. In a recent paper, we have proposed and demonstrated a P-wave modelling approach for TTI media, based on rotated stress and strain tensors, in which the wave equations reduce to a coupled set of two second-order partial differential equations for two scalar stress components: a normal component along the variable axis of symmetry and a lateral component of stress in the plane perpendicular to that axis. Spatially constant density is assumed in this approach. A numerical discretization scheme was proposed which uses discrete second-derivative operators for the non-mixed second-order derivatives in the wave equations, and combined first-derivative operators for the mixed second-order derivatives. This paper provides a complete and rigorous stability analysis, assuming a uniformly sampled grid. Although the spatial discretization operator for the TTI acoustic wave equation is not self-adjoint, this operator still defines a complete basis of eigenfunctions of the solution space, provided that the solution space is somewhat restricted at locations where the medium is elliptically anisotropic. First, a stability analysis is given for a discretization scheme, which is purely based on first-derivative operators. It is shown that the coefficients of the central difference operators should satisfy certain conditions. In view of numerical artefacts, such a discretization scheme is not attractive, and the non-mixed second-order derivatives of the wave equation are discretized directly by second-derivative operators. It is shown that this modification preserves

  16. Spatio-temporal linear stability analysis of stratified planar wakes: Velocity and density asymmetry effects

    NASA Astrophysics Data System (ADS)

    Emerson, Benjamin; Jagtap, Swapnil; Quinlan, J. Mathew; Renfro, Michael W.; Cetegen, Baki M.; Lieuwen, Tim

    2016-04-01

    This paper explores the hydrodynamic stability of bluff body wakes with non-uniform mean density, asymmetric mean density, and velocity profiles. This work is motivated by experiments [S. Tuttle et al., "Lean blow off behavior of asymmetrically-fueled bluff body-stabilized flames," Combust. Flame 160, 1677 (2013)], which investigated reacting wakes with equivalence ratio stratification and, hence, asymmetry in the base flow density profiles. They showed that highly stratified cases exhibited strong, narrowband oscillations, suggestive of global hydrodynamic instability. In this paper, we present a local hydrodynamic stability analysis for non-uniform density wakes that includes base flow asymmetry. The results show that increasing the degree of base density asymmetry generally has a destabilizing effect and that increasing base velocity asymmetry tends to be stabilizing. Furthermore, we show that increasing base density asymmetry slightly decreases the absolute frequency and that increasing the base velocity asymmetry slightly increases the absolute frequency. In addition, we show that increasing the degree of base density asymmetry distorts the most absolutely unstable hydrodynamic mode from its nominally sinuous structure. This distorted mode exhibits higher amplitude pressure and velocity oscillations near the interface with the smaller density jump than near the one with the bigger density jump. This would then be anticipated to lead to strongly non-symmetric amplitudes of flame flapping, with much stronger flame flapping on the side with lower density ratio. These predictions are shown to be consistent with experimental data. These comparisons support the analytical predictions that increased base density asymmetry are destabilizing and that hydrodynamic velocity fluctuation amplitudes should be greatest at the flame with the lowest density jump.

  17. A comparative analysis of terrain stability models for predicting shallow landslides in colluvial soils

    NASA Astrophysics Data System (ADS)

    Meisina, C.; Scarabelli, S.

    2007-06-01

    Most of the slopes of the hilly areas of the Apennines are composed of colluvial soils originating from the weathering of the bedrock and down slope transportation. Shallow slides affect this superficial cover, depend largely on the surface topography and are a recurrent problem. SINMAP and SHALSTAB are terrain stability models that combine steady state hydrology assumptions with the infinite slope stability model to quantify shallow slope stability. They have a similar physical basis but they use different indices to quantify instability. The purposes of this study are to test and compare the approaches of SINMAP and SHALSTAB models for slope stability analysis and to compare the results of these analyses with the locations of the shallow landslides that occurred on November 2002 in an area of the Oltrepo Pavese (Northern Apennines). The territory of S. Giuletta, characterized by clayey-silty colluvial soils, represents the test site. The Digital Elevation Model was constructed from a 1:5000 scale contour map and was used to estimate the slope of the terrain as well as the potential soil moisture conditions. In situ and laboratory tests provided the basis for measuring values for soil hydraulic and geotechnical parameters (moisture content, soil suction, Atterberg limits, methylene blue dye adsorption, hydraulic conductivity). Soil thickness was extracted from a soil database. An inventory of landslide from interpretation of aerial photographs and field surveys was used to document sites of instability (mostly soil slips) and to provide a test of model performance by comparing observed landslide locations with model predictions. The study discusses the practical advantages and limitations of the two models in connection with the geological characteristics of the studied area, which could be representative of similar geological contexts in the Apennines.

  18. Linear stability analysis for travelling waves of second order in time PDE's

    NASA Astrophysics Data System (ADS)

    Stanislavova, Milena; Stefanov, Atanas

    2012-09-01

    We study travelling waves φc of second order in time PDE's u_{tt}+{ L} u+N(u)=0 . The linear stability analysis for these models is reduced to the question of the stability of quadratic pencils in the form \\lambda^2Id+2c\\lambda \\partial_x+{ H}_c , where { H}_c=c^2 \\partial_{xx}+{ L}+N'(\\varphi_c) . If { H}_c is a self-adjoint operator, with a simple negative eigenvalue and a simple eigenvalue at zero, then we completely characterize the linear stability of φc. More precisely, we introduce an explicitly computable index \\omega^*({ H}_c)\\in (0, \\infty] , so that the wave φc is stable if and only if |c|\\geq \\omega^*({ H}_c) . The results are applicable both in the periodic case and in the whole line case. The method of proof involves a delicate analysis of a function { G} , associated with { H} , whose positive zeros are exactly the positive (unstable) eigenvalues of the pencil \\lambda^2Id+2c\\lambda \\partial_x+{ H} . We would like to emphasize that the function { G} is not the Evans function for the problem, but rather a new object that we define herein, which fits the situation rather well. As an application, we consider three classical models—the ‘good’ Boussinesq equation, the Klein-Gordon-Zakharov (KGZ) system and the fourth order beam equation. In the whole line case, for the Boussinesq case and the KGZ system (and as a direct application of the main results), we compute explicitly the set of speeds which give rise to linearly stable travelling waves (and for all powers of p in the case of Boussinesq). This result is new for the KGZ system, while it generalizes the results of Alexander et al (2012, personal communication) and Alexander and Sachs (1995 Nonlinear World 2 471-507), which apply to the case p = 2. For the beam equation, we provide an implicit formula (depending only on the function \\|\\varphi_c'\\|_{L^2}) , which works for all p and for both the periodic and the whole line cases. Our results complement (and exactly match

  19. Stability analysis of non-inertial thin film flow over a heterogeneously heated porous substrate

    NASA Astrophysics Data System (ADS)

    Kumawat, Tara Chand; Tiwari, Naveen

    2016-02-01

    The dynamics and linear stability of a gravity drive thin film flowing over non-uniformly heated porous substrate are studied. A governing equation for the evolution of film-thickness is derived within the lubrication approximation. Darcy-Brinkman equation is used to model flow in the porous medium along with a tangential stress-jump condition at the interface of the porous layer and the fluid film. A temperature profile is imposed at the solid wall to model an embedded heater beneath the porous layer. At the upstream edge of the heater, an opposing thermocapillary stress at the liquid-air interface leads to the formation of a thermocapillary ridge. The ridge becomes unstable beyond a critical Marangoni number leading to the formation of rivulets that are periodic in the spanwise direction. Increase in the values of parameters such as Darcy number, stress jump coefficient, and porosity is shown to have stabilizing effect on the film dynamics. The critical Marangoni number is shown to increase monotonically with Darcy number for various values of porosity. At large values of stress-jump coefficient, a non-monotonic variation in critical Marangoni number versus Darcy number is shown. A correlation is developed numerically for the ratio of critical Marangoni number at large Darcy number to that for a non-porous substrate as a function of porosity and thickness of the porous substrate. A transient growth analysis is carried out followed by non-linear stability analysis. The non-modal growth is found to be negligible thus indicating that the eigenvalues are physically determinant.

  20. Weakly nonlinear stability analysis of non-isothermal Poiseuille flow in a vertical channel

    NASA Astrophysics Data System (ADS)

    Khandelwal, Manish K.; Bera, P.

    2015-06-01

    A weakly nonlinear stability theory in terms of Landau equation is developed to analyze the nonlinear saturation of stably stratified non-isothermal Poiseuille flow in a vertical channel. The results are presented with respect to fluids: mercury, gases, liquids, and heavy oils. The weakly nonlinear stability results predict only the supercritical instability, in agreement with the published result [Y. C. Chen and J. N. Chung, "A direct numerical simulation of K and H-type flow transition in heated vertical channel," Comput. Fluids 32, 795-822 (2003)] based on direct numerical simulation. Apart from this, the influence of nonlinear interaction among different superimposed waves on the heat transfer rate, real part of wavespeed, and friction coefficient on the wall is also investigated. A substantial enhancement (reduction) in heat transfer rate (friction coefficient) is found for liquids and heavy oils from the basic state beyond the critical Rayleigh number. The amplitude analysis indicates that the equilibrium amplitude decreases on increasing the value of Reynolds number. However, in the case of mercury, influence of nonlinear interaction on the variation of equilibrium amplitude, heat transfer rate, wavespeed, as well as friction coefficient is complex and subtle. The analysis of the nonlinear energy spectra for the disturbance also supports the supercritical instability at and beyond the critical point. Finally, the effect of superimposed waves on the pattern of secondary flow, based on linear stability theory, is also studied. It has been found that the impact of nonlinear interaction of waves on the pattern of secondary flow for mercury is weak compared to gases, which is the consequence of negligible modification in the buoyant production of disturbance kinetic energy of the mercury.

  1. A statistical analysis to assess the maturity and stability of six composts.

    PubMed

    Komilis, Dimitrios P; Tziouvaras, Ioannis S

    2009-05-01

    Despite the long-time application of organic waste derived composts to crops, there is still no universally accepted index to assess compost maturity and stability. The research presented in this article investigated the suitability of seven types of seeds for use in germination bioassays to assess the maturity and phytotoxicity of six composts. The composts used in the study were derived from cow manure, sea weeds, olive pulp, poultry manure and municipal solid waste. The seeds used in the germination bioassays were radish, pepper, spinach, tomato, cress, cucumber and lettuce. Data were analyzed with an analysis of variance at two levels and with pair-wise comparisons. The analysis revealed that composts rendered as phytotoxic to one type of seed could enhance the growth of another type of seed. Therefore, germination indices, which ranged from 0% to 262%, were highly dependent on the type of seed used in the germination bioassay. The poultry manure compost was highly phytotoxic to all seeds. At the 99% confidence level, the type of seed and the interaction between the seeds and the composts were found to significantly affect germination. In addition, the stability of composts was assessed by their microbial respiration, which ranged from approximately 4 to 16g O(2)/kg organic matter and from 2.6 to approximately 11g CO(2)-C/kg C, after seven days. Initial average oxygen uptake rates were all less than approximately 0.35g O(2)/kg organic matter/h for all six composts. A high statistically significant correlation coefficient was calculated between the cumulative carbon dioxide production, over a 7-day period, and the radish seed germination index. It appears that a germination bioassay with radish can be a valid test to assess both compost stability and compost phytotoxicity. PMID:19117746

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

    NASA Astrophysics Data System (ADS)

    Hildebrand, Nathaniel; Nichols, Joseph W.

    2014-11-01

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

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

    NASA Technical Reports Server (NTRS)

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

    1985-01-01

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

  4. Low frequency azimuthal stability of the ionization region of the Hall thruster discharge. I. Local analysis

    SciTech Connect

    Escobar, D.; Ahedo, E.

    2014-04-15

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

  5. Convective flows generated by evaporation: experiments, linear stability analysis and numerical simulations

    NASA Astrophysics Data System (ADS)

    Dunstan, Jocelyn; Lee, Kyoung Jin; Park, Simon; Goldstein, Raymond E.

    A novel form of convection was observed in a suspension of non-motile Photobacterium phosphoreum bacteria. The pattern resembles classical bioconvection, however this strain has limited if any motility, which excludes this possible explanation. After performing a series of control experiments we found that the convection was actually driven by the evaporation of the salty bacterial medium, and the same kind of plumes were observed using polystyrene beads suspended in water with salt added. A mathematical model was formulated for the process and studied using a linear stability analysis and finite element method simulations, reproducing most of the observed experimental features. From the linear stability analysis, a threshold in salt concentration to observe convective motion was obtained, as well as the wavelength of the pattern at the onset of the instability. This was complemented by finite element simulations, which produced plume dynamics remarkably similar to the experimental observations. Evaporation-driven convection on the millimeter scale has not been studied extensively, and its effect may have been underestimated in other experiments.

  6. Stabilized tetrahedral elements for crystal plasticity finite element analysis overcoming volumetric locking

    NASA Astrophysics Data System (ADS)

    Cheng, Jiahao; Shahba, Ahmad; Ghosh, Somnath

    2016-05-01

    Image-based CPFE modeling involves computer generation of virtual polycrystalline microstructures from experimental data, followed by discretization into finite element meshes. Discretization is commonly accomplished using three-dimensional four-node tetrahedral or TET4 elements, which conform to the complex geometries. It has been commonly observed that TET4 elements suffer from severe volumetric locking when simulating deformation of incompressible or nearly incompressible materials. This paper develops and examines three locking-free stabilized finite element formulations in the context of crystal plasticity finite element analysis. They include a node-based uniform strain (NUS) element, a locally integrated B-bar (LIB) based element and a F-bar patch (FP) based element. All three formulations are based on the partitioning of TET4 element meshes and integrating over patches to obtain favorable incompressibility constraint ratios without adding large degrees of freedom. The results show that NUS formulation introduces unstable spurious energy modes, while the LIB and FP elements stabilize the solutions and are preferred for reliable CPFE analysis. The FP element is found to be computationally efficient over the LIB element.

  7. A stabilized complementarity formulation for nonlinear analysis of 3D bimodular materials

    NASA Astrophysics Data System (ADS)

    Zhang, L.; Zhang, H. W.; Wu, J.; Yan, B.

    2016-06-01

    Bi-modulus materials with different mechanical responses in tension and compression are often found in civil, composite, and biological engineering. Numerical analysis of bimodular materials is strongly nonlinear and convergence is usually a problem for traditional iterative schemes. This paper aims to develop a stabilized computational method for nonlinear analysis of 3D bimodular materials. Based on the parametric variational principle, a unified constitutive equation of 3D bimodular materials is proposed, which allows the eight principal stress states to be indicated by three parametric variables introduced in the principal stress directions. The original problem is transformed into a standard linear complementarity problem (LCP) by the parametric virtual work principle and a quadratic programming algorithm is developed by solving the LCP with the classic Lemke's algorithm. Update of elasticity and stiffness matrices is avoided and, thus, the proposed algorithm shows an excellent convergence behavior compared with traditional iterative schemes. Numerical examples show that the proposed method is valid and can accurately analyze mechanical responses of 3D bimodular materials. Also, stability of the algorithm is greatly improved.

  8. Stability analysis of closed-loop super-critical pressure systems

    NASA Astrophysics Data System (ADS)

    Smith, Walter Castro

    The current study investigates the mechanisms governing flow induced stability of super-critical pressure fluid systems. Super-critical pressure fluid systems have been investigated as a mechanism for heat extraction from power systems for over a century. There are numerous benefits to these systems, but also potential pitfalls which must be examined. While super-critical pressure systems do not undergo phase change, they may be subject to the same flow induced instabilities which affect and limit two-phase systems. The objective of the current study is to develop a modeling and analysis framework to evaluate and understand flow-induced instabilities in super-critical pressure systems. The developed framework is used to evaluate experimental systems which have been constructed and tested by other investigators. The developed model shows good comparison with both the steady state and transient results published by other researchers. The model has been used to predict instabilities in experimental systems, as well as to show how some systems are more susceptible to instability than others. Stability maps have been constructed in a similar manner to those published for single heated flow path analysis.

  9. Short-wavelength stability analysis of Hill's vortex with/without swirl

    NASA Astrophysics Data System (ADS)

    Hattori, Y.; Hijiya, K.

    2010-07-01

    The stability of Hill's vortex with/without swirl is studied by the short-wavelength stability analysis or WKB analysis. It is shown that the classical Hill's spherical vortex is subjected not only to the Widnall instability but also to the curvature instability found for thin vortex rings and helical vortex tubes. A new "combined" mode of instability caused by the two instabilities is discovered. The magnitude of the exponential growth rate of the combined mode is similar with the curvature instability around the stagnation point; it exceeds the Widnall instability near the boundary. The effects of swirl on the instabilities are investigated using a family of solutions obtained by Moffatt ["The degree of knottedness of tangled vortex lines," J. Fluid Mech. 35, 117 (1969)]. As the swirl parameter α increases, a stable region appears around the stagnation point; the maxima of the growth rates decrease; the combined mode region disappears for α ≥3. As α increases further, however, the region of the generalized centrifugal instability emerges from the stagnation point.

  10. A stabilized complementarity formulation for nonlinear analysis of 3D bimodular materials

    NASA Astrophysics Data System (ADS)

    Zhang, L.; Zhang, H. W.; Wu, J.; Yan, B.

    2015-10-01

    Bi-modulus materials with different mechanical responses in tension and compression are often found in civil, composite, and biological engineering. Numerical analysis of bimodular materials is strongly nonlinear and convergence is usually a problem for traditional iterative schemes. This paper aims to develop a stabilized computational method for nonlinear analysis of 3D bimodular materials. Based on the parametric variational principle, a unified constitutive equation of 3D bimodular materials is proposed, which allows the eight principal stress states to be indicated by three parametric variables introduced in the principal stress directions. The original problem is transformed into a standard linear complementarity problem (LCP) by the parametric virtual work principle and a quadratic programming algorithm is developed by solving the LCP with the classic Lemke's algorithm. Update of elasticity and stiffness matrices is avoided and, thus, the proposed algorithm shows an excellent convergence behavior compared with traditional iterative schemes. Numerical examples show that the proposed method is valid and can accurately analyze mechanical responses of 3D bimodular materials. Also, stability of the algorithm is greatly improved.

  11. Thin Newtonian film flow down a porous inclined plane: Stability analysis

    NASA Astrophysics Data System (ADS)

    Sadiq, I. Mohammed Rizwan; Usha, R.

    2008-02-01

    The flow of a thin Newtonian fluid layer on a porous inclined plane is considered. Applying the long-wave theory, a nonlinear evolution equation for the thickness of the film is obtained. It is assumed that the flow through the porous medium is governed by Darcy's law. The critical conditions for the onset of instability of a fluid layer flowing down an inclined porous wall, when the characteristic length scale of the pore space is much smaller than the depth of the fluid layer above, are obtained. The results of the linear stability analysis reveal that the film flow system on a porous inclined plane is more unstable than that on a rigid inclined plane and that increasing the permeability of the porous medium enhances the destabilizing effect. A weakly nonlinear stability analysis by the method of multiple scales shows that there is a range of wave numbers with a supercritical bifurcation, and a range of larger wave numbers with a subcritical bifurcation. Numerical solution of the evolution equation in a periodic domain indicates the existence of permanent finite-amplitude waves of different kinds in the supercritical stable region. The long-time waveforms are either time-independent waves of permanent form that propagate or time-dependent modes that oscillate slightly in the amplitude. The presence of the porous substrate promotes this oscillatory behavior. The results show that the shape and amplitude of the waves are influenced by the permeability of the porous medium.

  12. DIAGNOSIS, ANALYSIS, AND RESOLUTION OF THERMAL STABILITY ISSUES WITH HOM COUPLERS ON PROTOTYPE CEBAF SRF CAVITIES

    SciTech Connect

    Charles Reece; Edward Daly; G. Davis; William Hicks; Timothy Rothgeb; H. Phillips; Joseph Preble; Haipeng Wang; Genfa Wu

    2008-02-12

    During initial testing of the prototype cavities incorporated into the developmental cryomodule Renascence severe thermal stability issues were encountered during CW operation. Additional diagnostic instrumentation was added. This enabled identification of an unanticipated thermal impedance between the HOM coupler probe feedthrough assembly and the cavity beamtube. Subsequent detailed FE analysis successfully modeled the situation and indicated the need for alternate cooling path for the couplers on those cavities. HOM damping was measured to be adequate employing only two of the four HOM couplers. The two pickup probes on the couplers at the input power coupler side of each cavity were removed, the remaining HOM probe feedthroughs were heat stationed to two-phase helium supply piping, and a novel heat sink was added to station both the inner and outer conductors of the remaining HOM rf cables. The characterization measurements, analysis, modifications, and resulting performance are presented.

  13. Stabilization of prompt gamma-ray neutron activation analysis (PGNAA) spectra from NaI detectors

    NASA Astrophysics Data System (ADS)

    Metwally, W. A.; Gardner, R. P.

    2004-06-01

    NaI detectors are still used frequently in industrial Prompt Gamma-Ray Neutron Activation Analysis applications such as in bulk material analysis. They have the advantages of being efficient for high-energy gamma rays, being relatively rugged, and being able to be used without cooling. When using NaI detectors, and consequently photomultiplier tubes, the quality of the data can drastically deteriorate through gain and zero shifts that result in spectral smearing due to temperature and/or counting rate changes. A new offline approach is presented to stabilize the NaI spectral drift. The approach is not sensitive to the cause of the drift and takes into account the NaI and ADC non-linearities. Peak resolution is improved substantially when this approach is used in the presence of spectral drift.

  14. A method for analysis of stability of flows in ribbed annuli

    NASA Astrophysics Data System (ADS)

    Moradi, H. V.; Floryan, J. M.

    2016-06-01

    A spectrally-accurate algorithm for the linear stability analysis of pressure-gradient-driven flows in corrugated annuli is presented. The algorithm is suitable to analyze three-dimensional disturbances in the form of spiral traveling waves as well as in the form of streamwise vortices. A separate algorithm for the analysis of axisymmetric disturbances is presented. The discretization method relies on Fourier expansions in the streamwise and circumferential directions and on Chebyshev expansions in the radial direction. The Immersed Boundary Conditions (IBC) method is used to enforce the physical boundary conditions at the corrugated walls. Numerous tests confirm the spectral accuracy of the results. The performance of the algorithm is consistent with the theoretical predictions.

  15. ESF SOUTH PORTAL BOX-CUT/HIGHWALL STABILITY ANALYSIS (SCPB:N/A)

    SciTech Connect

    Saeed Bonabian

    1996-03-28

    The main purpose and objective of this analysis is to design a Box-Cut at the ESF South Portal to accommodate the Tunnel Boring Machine's (TBM) exit at the conclusion of the ESF Main Loop construction. The stability of the Highwall and the sidewalls at the Box-Cut are assessed using analytical methods by numerical modeling techniques. A ground reinforcement system for the South Ramp Box-Cut slopes will be recommended. This report summarizes the results of the analyses and provides the details of the recommended ground reinforcement system for the Box-Cut slopes at the South Portal. The reinforcement design details are then incorporated into design output documents for implementation in the field. Method of excavation for the Box-Cut is also discussed and a recommendation is provided in this analysis.

  16. Three-dimensional linear stability analysis of incompressible viscous flows using the finite element method

    NASA Astrophysics Data System (ADS)

    Ding, Yan; Kawahara, Mutsuto

    1999-09-01

    The linear stability of incompressible flows is investigated on the basis of the finite element method. The two-dimensional base flows computed numerically over a range of Reynolds numbers are perturbed with three-dimensional disturbances. The three-dimensionality in the flow associated with the secondary instability is identified precisely. First, by using linear stability theory and normal mode analysis, the partial differential equations governing the evolution of perturbation are derived from the linearized Navier-Stokes equation with slight compressibility. In terms of the mixed finite element discretization, in which six-node quadratic Lagrange triangular elements with quadratic interpolation for velocities (P2) and three-node linear Lagrange triangular elements for pressure (P1) are employed, a non-singular generalized eigenproblem is formulated from these equations, whose solution gives the dispersion relation between complex growth rate and wave number. Then, the stabilities of two cases, i.e. the lid-driven cavity flow and flow past a circular cylinder, are examined. These studies determine accurately stability curves to identify the critical Reynolds number and the critical wavelength of the neutral mode by means of the Krylov subspace method and discuss the mechanism of instability. For the cavity flow, the estimated critical results are Rec=920.277+/-0.010 for the Reynolds number and kc=7.40+/-0.02 for the wave number. These results are in good agreement with the observation of Aidun et al. and are more accurate than those by the finite difference method. This instability in the cavity is associated with absolute instability [Huerre and Monkewitz, Annu. Rev. Fluid Mech., 22, 473-537 (1990)]. The Taylor-Göertler-like vortices in the cavity are verified by means of the reconstruction of three-dimensional flows. As for the flow past a circular cylinder, the primary instability result shows that the flow has only two-dimensional characteristics at the

  17. Performance & stability analysis of a three lobe journal bearing with varying parameters: Experiments and analysis

    NASA Astrophysics Data System (ADS)

    Biswas, Nabarun; Chakraborti, Prasun; Saha, Ankuran; Biswas, Srijit

    2016-07-01

    3-lobe Hydrodynamic oil journal bearings are widely used in heavy industries as a part of different rotating machinery due to their high level of performances. 3-lobe hydrodynamic oil journal bearing allows the transmission of large amounts of loads at a mean speed of rotation. In this present work, an attempt has been made to investigate the pressure domain and subsequent effects in a 3 lobe journal bearing under different static loads in a stable operating speed. Analytical calculations were carried out with codes generated using Matlab software. Experiments were performed in Journal Bearing test rig incorporating 3-lobe under different loads with stable operating speed of 1000 RPM. It has been observed that an increase in load resulted rise in pressure profile, maximum pressure angle and temperature. A further attempt has been made to see the effect of eccentricity ratio and dynamic viscosity considering no change in the RPM. It has also been observed that dynamic viscosity has a significant effect on the stable operating speed. With the reduction in static load, the stability of operating speed attained at higher values.

  18. Analysis of the factors that significantly influence the stability of fluoroquinolone-metal complexes.

    PubMed

    Urbaniak, Bartosz; Kokot, Zenon J

    2009-08-01

    The aim of the present study was to evaluate factors contributing to the differences between the overall stability constants (logbeta(pqr)) of the fluoroquinolone-metal ion complexes. The experiments were performed using potentiometric titration method in wide pH range. The overall stability constants (logbeta(pqr)) were determined using the Hyperquad program. Complexation equilibria of eight different fluoroquinolones with six divalent and trivalent metal ions were investigated in this study. The authors employed a multifactorial ANOVA analysis, fixed effect model to describe the influence of particular variables affecting the stability of the analyzed complex species. Four different variables were set at different levels labeled. The ligand number (LF) was the first factor. LF determined the number of fluorochinolone molecules in the complex structure, and could take the values 1, 2 or 3. The second factor (Me) was connected with the type of the metal ion bonded in the complex. Since six different metal cations were studied, the Me factor was described with six levels. The number of hydrogen or hydroxide groups substituted into the complex molecule was the third variable (HR) with many levels labeled: q, a, s, d, f and g. The last factor FQ described the type of the fluorochinolone used for complex formations. All variables analyzed here were statistically significant (p value lower than 0.01), which indicates that all of them strongly affect the logbeta(pqr) value. Binary interactions (LF-Me, LF-FQ, Me-HR and Me-FQ) between variables were also stated, which suggests that the effects of these variables were higher than we could calculate based on the effect of each variable alone. The ANOVA analysis has shown that the following factors Me, LF and HR were the most important for the stability of the fluoroquinolone-metal ion complexes. It was also found that according to the FQ factor (type of ligand molecule) all analyzed fluoroquinolones formed stable complexes

  19. A comparison of theory and experiment for the aeroelastic stability of a bearingless model rotor in hover

    NASA Technical Reports Server (NTRS)

    Dawson, Seth

    1988-01-01

    Three cases were selected for correlation from an experiment that examined the aeroelastic stability of a small-scale bearingless motor rotor in hover. The 1.8 m diameter model rotor included flap, lead-lag, and torsional degrees of freedom, but no body degrees of freedom. The first case looked at a configuration with a single pitch link on the leading edge, the second case examined a configuration with a single pitch link on the trailing edge, and the third case examined a configuration with pitch links on the leading and trailing edges to simulate a pitch link with shear restraint. Analyses from Bell Helicopter Textron, Boeing Vertol, Hughes Helicopters, Sikorsky Aircraft, and the U.S. Army Aeromechanics Laboratory were compared with the data, and the correlation ranged from poor to fair.

  20. Stability analysis of a natural circulation lead-cooled fast reactor

    NASA Astrophysics Data System (ADS)

    Lu, Qiyue

    This dissertation is aimed at nuclear-coupled thermal hydraulics stability analysis of a natural circulation lead cooled fast reactor design. The stability concerns arise from the fact that natural circulation operation makes the system susceptible to flow instabilities similar to those observed in boiling water reactors. In order to capture the regional effects, modal expansion method which incorporates higher azimuthal modes is used to model the neutronics part of the system. A reduced order model is used in this work for the thermal-hydraulics. Consistent with the number of heat exchangers (HXs), the reactor core is divided into four equal quadrants. Each quadrant has its corresponding external segments such as riser, plenum, pipes and HX forming an equivalent 1-D closed loop. The local pressure loss along the loop is represented by a lumped friction factor. The heat transfer process in the HX is represented by a model for the coolant temperature at the core inlet that depends on the coolant temperature at the core outlet and the coolant velocity. Additionally, time lag effects are incorporated into this HX model due to the finite coolant speed. A conventional model is used for the fuel pin heat conduction to couple the neutronics and thermal-hydraulics. The feedback mechanisms include Doppler, axial/radial thermal expansion and coolant density effects. These effects are represented by a linear variation of the macroscopic cross sections with the fuel temperature. The weighted residual method is used to convert the governing PDEs to ODEs. Retaining the first and second modes, leads to six ODEs for neutronics, and five ODEs for the thermal-hydraulics in each quadrant. Three models are developed. These are: 1) natural circulation model with a closed coolant flow path but without coupled neutronics, 2) forced circulation model with constant external pressure drop across the heated channels but without coupled neutronics, 3) coupled system including neutronics with

  1. Multiplexed analysis of genes using nucleic acid-stabilized silver-nanocluster quantum dots.

    PubMed

    Enkin, Natalie; Wang, Fuan; Sharon, Etery; Albada, H Bauke; Willner, Itamar

    2014-11-25

    Luminescent nucleic acid-stabilized Ag nanoclusters (Ag NCs) are applied for the optical detection of DNA and for the multiplexed analysis of genes. Two different sensing modules including Ag NCs as luminescence labels are described. One sensing module involves the assembly of a three-component sensing module composed of a nucleic acid-stabilized Ag NC and a quencher-modified nucleic acid hybridized with a nucleic acid scaffold that is complementary to the target DNA. The luminescence of the Ag NCs is quenched in the sensing module nanostructure. The strand displacement of the scaffold by the target DNA separates the nucleic acid-functionalized Ag NCs, leading to the turned-on luminescence of the NCs and to the optical readout of the sensing process. By implementing two different-sized Ag NC-modified sensing modules, the parallel multiplexed analysis of two genes (the Werner Syndrome gene and the HIV, human immunodeficiency, gene), using 615 and 560 nm luminescent Ag NCs, is demonstrated. The second sensing module includes the nucleic acid functionalized Ag NCs and the quencher-modified nucleic acid hybridized with a hairpin DNA scaffold. The luminescence of the Ag NCs is quenched in the sensing module. Opening of the hairpin by the target DNA triggers the luminescence of the Ag NCs, due to the spatial separation of the Ag NCs/quencher units. The system is applied for the optical detection of the BRAC1 gene. In addition, by implementing two-sized Ag NCs, the multiplexed analysis of two genes by the hairpin sensing module approach is demonstrated. PMID:25327411

  2. Dynamic Slope Stability Analysis of Mine Tailing Deposits: the Case of Raibl Mine

    SciTech Connect

    Roberto, Meriggi; Marco, Del Fabbro; Erica, Blasone; Erica, Zilli

    2008-07-08

    Over the last few years, many embankments and levees have collapsed during strong earthquakes or floods. In the Friuli Venezia Giulia Region (North-Eastern Italy), the main source of this type of risk is a slag deposit of about 2x10{sup 6} m{sup 3} deriving from galena and lead mining activity until 1991 in the village of Raibl. For the final remedial action plan, several in situ tests were performed: five boreholes equipped with piezometers, four CPTE and some geophysical tests with different approaches (refraction, ReMi and HVSR). Laboratory tests were conducted on the collected samples: geotechnical classification, triaxial compression tests and constant head permeability tests in triaxial cell. Pressure plate tests were also done on unsaturated slag to evaluate the characteristic soil-water curve useful for transient seepage analysis. A seepage analysis was performed in order to obtain the maximum pore water pressures during the intense rainfall event which hit the area on 29th August 2003. The results highlight that the slag low permeability prevents the infiltration of rainwater, which instead seeps easily through the boundary levees built with coarse materials. For this reason pore water pressures inside the deposits are not particularly influenced by rainfall intensity and frequency. Seismic stability analysis was performed with both the pseudo-static method, coupled with Newmark's method, and dynamic methods, using as design earthquake the one registered in Tolmezzo (Udine) on 6{sup th} May 1976. The low reduction of safety factors and the development of very small cumulative displacements show that the stability of embankments is assured even if an earthquake of magnitude 6.4 and a daily rainfall of 141.6 mm occur at the same time.

  3. Monitoring the Stability of Perfluorocarbon Nanoemulsions by Cryo-TEM Image Analysis and Dynamic Light Scattering

    PubMed Central

    Grapentin, Christoph; Barnert, Sabine; Schubert, Rolf

    2015-01-01

    Perfluorocarbon nanoemulsions (PFC-NE) are disperse systems consisting of nanoscale liquid perfluorocarbon droplets stabilized by an emulsifier, usually phospholipids. Perfluorocarbons are chemically inert and non-toxic substances that are exhaled after in vivo administration. The manufacture of PFC-NE can be done in large scales by means of high pressure homogenization or microfluidization. Originally investigated as oxygen carriers for cases of severe blood loss, their application nowadays is more focused on using them as marker agents in 19F Magnetic Resonance Imaging (19F MRI). 19F is scarce in organisms and thus PFC-NE are a promising tool for highly specific and non-invasive imaging of inflammation via 19F MRI. Neutrophils, monocytes and macrophages phagocytize PFC-NE and subsequently migrate to inflamed tissues. This technique has proven feasibility in numerous disease models in mice, rabbits and mini pigs. The translation to clinical trials in human needs the development of a stable nanoemulsion whose droplet size is well characterized over a long storage time. Usually dynamic light scattering (DLS) is applied as the standard method for determining particle sizes in the nanometer range. Our study uses a second method, analysis of transmission electron microscopy images of cryo-fixed samples (Cryo-TEM), to evaluate stability of PFC-NE in comparison to DLS. Four nanoemulsions of different composition are observed for one year. The results indicate that DLS alone cannot reveal the changes in particle size, but can even mislead to a positive estimation of stability. The combination with Cryo-TEM images gives more insight in the particulate evolution, both techniques supporting one another. The study is one further step in the development of analytical tools for the evaluation of a clinically applicable perfluorooctylbromide nanoemulsion. PMID:26098661

  4. Study of biological stabilization processes of cattle and poultry manure by thermogravimetric analysis and (13)C NMR.

    PubMed

    Gómez, X; Diaz, Miguel C; Cooper, Mick; Blanco, D; Morán, A; Snape, Colin E

    2007-08-01

    The biological stabilization process of cattle and poultry manure was studied using thermogravimetric analysis and (13)C nuclear magnetic resonance. The stabilization processes carried out were composting, anaerobic digestion and a mixed process (partly aerobic, partly anaerobic). It was observed from the analyzed samples that the biological stabilization processes reduce the volatile content of the bio-wastes and increase the degree of aromaticity. The stabilization of cattle manure by means of aerobic processes was able to further oxidize and enriched in aromatic compounds the bio-waste when compared with the digestion process. On the other hand, the stabilization of poultry manure resulted in a greater aromatization under the digestion process. Stabilized samples with a high degree of aromaticity presented a lower volatile content accompanied by a reduction in the intensity of the differential thermogravimetry peak registered under an inert atmosphere, indicative of the thermal decomposition of the organic matter. The thermal decomposition of all the analyzed materials (fresh and stabilized samples) commenced at around 200 degrees C but for the digested poultry manure, which decomposition initiated close to 250 degrees C. All stabilized samples yielded a lower degree of volatilization to that one observed in fresh samples. PMID:17433408

  5. 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

  6. Morphological stability analysis of directional solidification into an oscillatory fluid layer

    NASA Astrophysics Data System (ADS)

    Volfson, Dmitri; Viñals, Jorge

    2001-12-01

    We study the stability of a planar solid-melt boundary during directional solidification of a binary alloy when the solid is being periodically vibrated in the direction parallel to the boundary (or equivalently, under a far field uniform and oscillatory flow parallel to the planar boundary). The analysis is motivated by directional solidification experiments under the low level residual acceleration field characteristic of a microgravity environment, and possible effects on crystal growth in space. It is known that periodic modulation of the solid-melt interface under the conditions stated induces second order stationary streaming flows within a boundary layer adjacent to the interface, the thickness of which is the same as the wavelength of the modulation. We derive an effective solute transport equation by averaging over the fast time scale of the oscillatory flow, and obtain the resulting dispersion relation for a small disturbance of a planar interface. We find both regions of stationary and oscillatory instability. For small ratios of the viscous to solutal layer thicknesses, s, the flow generally destabilizes the planar interface. For s≃1, the flow stabilizes the stationary branch, but it can also excite an oscillatory instability. For large s, the effect of the flow is small.

  7. Title: Chimeras in small, globally coupled networks: Experiments and stability analysis

    NASA Astrophysics Data System (ADS)

    Hart, Joseph D.; Bansal, Kanika; Murphy, Thomas E.; Roy, Rajarshi

    Since the initial observation of chimera states, there has been much discussion of the conditions under which these states emerge. The emphasis thus far has mainly been to analyze large networks of coupled oscillators; however, recent studies have begun to focus on the opposite limit: what is the smallest system of coupled oscillators in which chimeras can exist? We experimentally observe chimeras and other partially synchronous patterns in a network of four globally-coupled chaotic opto-electronic oscillators. By examining the equations of motion, we demonstrate that symmetries in the network topology allow a variety of synchronous states to exist, including cluster synchronous states and a chimera state. Using the group theoretical approach recently developed for analyzing cluster synchronization, we show how to derive the variational equations for these synchronous patterns and calculate their linear stability. The stability analysis gives good agreement with our experimental results. Both experiments and simulations suggest that these chimera states often appear in regions of multistability between global, cluster, and desynchronized states.

  8. Gas uptake and thermal stability analysis of boron nitride and carbon nanotubes

    NASA Astrophysics Data System (ADS)

    Guan, Mengyu

    Carbon nanotubes (CNTs) exist in many forms and can have critical pore diameters on the angstrom length scale, making them suitable for molecular capture. By combining the porous structure of CNTs with the chemical stability of carbide and/or nitride materials, one can create a more robust, nanoporous material for gas capture in high temperature conditions. Boron nitride nanotubes (BNNTs) are more chemically and thermally robust than pure CNTs, and were synthesized using CNTs as a structural precursor. However, this reaction mechanism was found to be unfavorable to produce high-yield and purity BNNTs. Adsorption tests using gases of interest (N2, He) were performed on commercial CNTs and BNNTs to determine their porosity and gas uptake abilities. Their thermal stability and oxidation resistance when heated up to 1773 K in air was also studied using differential scanning calorimetry and thermogravimetric analysis. While the CNTs began to oxidize between 450 °C and 750 °C, depending on the nanotube diameter, the BNNTs remained stable up until 1000 °C.

  9. Longitudinal stability analysis of a suborbital re-entry demonstrator for a deployable capsule

    NASA Astrophysics Data System (ADS)

    Iacovazzo, Michele; Carandente, Valerio; Savino, Raffaele; Zuppardi, Gennaro

    2015-01-01

    In the field of atmospheric re-entry technology several research and industrial projects are based on the design of deployable, umbrella-like Thermal Protection Systems (TPSs) and aero-brakes. These systems are made of flexible, high temperature resistant fabrics, folded at launch and deployed in space for de-orbit and re-entry operations. This technology is very promising for low cost research and industrial applications, but requires to be validated by experimental flight tests. The University of Naples "Federico II" is currently working on the development of different down-scaled technological demonstrators for this kind of capsule to be launched by different classes of sounding rockets. In the present work an aerodynamic longitudinal stability analysis for a possible, suborbital re-entry demonstrator, has been performed in continuum and rarefied regimes. The longitudinal stability behavior of the capsule, along the entire re-entry path, has been investigated in the whole range of angle of attack and, in particular, around the nominal and the reverse equilibrium re-entry attitudes (i.e. around 0° and 180°, respectively) to implement a proper re-entry strategy able not to compromise the effectiveness of the flying system.

  10. A Stability Analysis for a Hydrodynamic Three-Wave Journal Bearing

    NASA Technical Reports Server (NTRS)

    Ene, Nicoleta M.; Dimofte, Florin; Keith, Theo G., Jr.

    2007-01-01

    The influence of the wave amplitude and oil supply pressure on the dynamic behavior of a hydrodynamic three-wave journal bearing is presented. Both, a transient and a small perturbation technique, were used to predict the threshold to fractional frequency whirl (FFW). In addition, the behavior of the rotor after FFW appeared was determined from the transient analysis. The turbulent effects were also included in the computations. Bearings having a diameter of 30 mm, a length of 27.5 mm, and a clearance of 35 microns were analyzed. Numerical results were compared to experimental results obtained at the NASA GRC. Numerical and experimental results showed that the above-mentioned wave bearing with a wave amplitude ratio of 0.305 operates stably at rotational speeds up to 60,000 rpm, regardless of the oil supply pressure. For smaller wave amplitude ratios, a threshold of stability was found. It was observed that the threshold of stability for lower wave amplitude strongly depends on the oil supply pressure and on the wave amplitude. When the FFW occurs, the journal center maintains its trajectory inside the bearing clearance and therefore the rotor can be run safely without damaging the bearing surfaces.

  11. Stability of gene contributions and identification of outliers in multivariate analysis of microarray data

    PubMed Central

    Baty, Florent; Jaeger, Daniel; Preiswerk, Frank; Schumacher, Martin M; Brutsche, Martin H

    2008-01-01

    Background Multivariate ordination methods are powerful tools for the exploration of complex data structures present in microarray data. These methods have several advantages compared to common gene-by-gene approaches. However, due to their exploratory nature, multivariate ordination methods do not allow direct statistical testing of the stability of genes. Results In this study, we developed a computationally efficient algorithm for: i) the assessment of the significance of gene contributions and ii) the identification of sample outliers in multivariate analysis of microarray data. The approach is based on the use of resampling methods including bootstrapping and jackknifing. A statistical package of R functions was developed. This package includes tools for both inferring the statistical significance of gene contributions and identifying outliers among samples. Conclusion The methodology was successfully applied to three published data sets with varying levels of signal intensities. Its relevance was compared with alternative methods. Overall, it proved to be particularly effective for the evaluation of the stability of microarray data. PMID:18570644

  12. A qualitative content analysis of global health engagements in Peacekeeping and Stability Operations Institute's stability operations lessons learned and information management system.

    PubMed

    Nang, Roberto N; Monahan, Felicia; Diehl, Glendon B; French, Daniel

    2015-04-01

    Many institutions collect reports in databases to make important lessons-learned available to their members. The Uniformed Services University of the Health Sciences collaborated with the Peacekeeping and Stability Operations Institute to conduct a descriptive and qualitative analysis of global health engagements (GHEs) contained in the Stability Operations Lessons Learned and Information Management System (SOLLIMS). This study used a summative qualitative content analysis approach involving six steps: (1) a comprehensive search; (2) two-stage reading and screening process to identify first-hand, health-related records; (3) qualitative and quantitative data analysis using MAXQDA, a software program; (4) a word cloud to illustrate word frequencies and interrelationships; (5) coding of individual themes and validation of the coding scheme; and (6) identification of relationships in the data and overarching lessons-learned. The individual codes with the most number of text segments coded included: planning, personnel, interorganizational coordination, communication/information sharing, and resources/supplies. When compared to the Department of Defense's (DoD's) evolving GHE principles and capabilities, the SOLLIMS coding scheme appeared to align well with the list of GHE capabilities developed by the Department of Defense Global Health Working Group. The results of this study will inform practitioners of global health and encourage additional qualitative analysis of other lessons-learned databases. PMID:25826346

  13. Linear stability analysis of Korteweg stresses effect on miscible viscous fingering in porous media

    NASA Astrophysics Data System (ADS)

    Pramanik, Satyajit; Mishra, Manoranjan

    2013-07-01

    Viscous fingering (VF) is an interfacial hydrodynamic instability phenomenon observed when a fluid of lower viscosity displaces a higher viscous one in a porous media. In miscible viscous fingering, the concentration gradient of the undergoing fluids is an important factor, as the viscosity of the fluids are driven by concentration. Diffusion takes place when two miscible fluids are brought in contact with each other. However, if the diffusion rate is slow enough, the concentration gradient of the two fluids remains very large during some time. Such steep concentration gradient, which mimics a surface tension type force, called the effective interfacial tension, appears in various cases such as aqua-organic, polymer-monomer miscible systems, etc. Such interfacial tension effects on miscible VF is modeled using a stress term called Korteweg stress in the Darcy's equation by coupling with the convection-diffusion equation of the concentration. The effect of the Korteweg stresses at the onset of the instability has been analyzed through a linear stability analysis using a self-similar Quasi-steady-state-approximation (SS-QSSA) in which a self-similar diffusive base state profile is considered. The quasi-steady-state analyses available in literature are compared with the present SS-QSSA method and found that the latter captures appropriately the unconditional stability criterion at an earlier diffusive time as well as in long wave approximation. The effects of various governing parameters such as log-mobility ratio, Korteweg parameters, disturbances' wave number, etc., on the onset of the instability are discussed for, (i) the two semi-infinite miscible fluid zones and (ii) VF of the miscible slice cases. The stabilizing property of the Korteweg stresses effect is observed for both of the above mentioned cases. Critical miscible slice lengths are computed to have the onset of the instability for different governing parameters with or without Korteweg stresses. These

  14. Stability Analysis of Attractor Neural Network Model of Inferior Temporal Cortex —Relationship between Attractor Stability and Learning Order—

    NASA Astrophysics Data System (ADS)

    Tomoyuki Kimoto,; Tatsuya Uezu,; Masato Okada,

    2010-06-01

    Miyashita found that the long-term memory of visual stimuli is stored in the monkey’s inferior temporal cortex and that the temporal correlation in terms of the learning order of visual stimuli is converted into spatial correlation in terms of the firing rate patterns of the neuron group. To explain Miyashita’s findings, Griniasty et al. [Neural Comput. 5 (1993) 1] and Amit et al. [J. Neurosci. 14 (1994) 6435] proposed the attractor neural network model, and the Amit model has been examined only for the stable state acquired by storing memory patterns in a fixed sequence. In the real world, however, the learning order has statistical continuity but it also has randomness, and the stability of the state changes depending on the statistical properties of learning order when memory patterns are stored randomly. In addition, it is preferable for the stable state to become an appropriate attractor that reflects the relationship between memory patterns by the statistical properties of the learning order. In this study, we examined the dependence of the stable state on the statistical properties of the learning order without modifying the Amit model. The stable state was found to change from the correlated attractor to the Hopfield or Mp attractor, which is the mixed state with all memory patterns when the rate of random learning increases. Furthermore, we found that if the statistical properties of the learning order change, the stable state can change to an appropriate attractor reflecting the relationship between memory patterns.

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

    NASA Technical Reports Server (NTRS)

    Berry, S. A.

    1986-01-01

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

  16. Nuclear-coupled thermal-hydraulic stability analysis of boiling water reactors

    NASA Astrophysics Data System (ADS)

    Karve, Atul A.

    We have studied the nuclear-coupled thermal-hydraulic stability of boiling water reactors (BWRs) using a model we developed from: the space-time modal neutron kinetics equations based on spatial omega-modes, the equations for two-phase flow in parallel boiling channels, the fuel rod heat conduction equations, and a simple model for the recirculation loop. The model is represented as a dynamical system comprised of time-dependent nonlinear ordinary differential equations, and it is studied using stability analysis, modern bifurcation theory, and numerical simulations. We first determine the stability boundary (SB) in the most relevant parameter plane, the inlet-subcooling-number/external-pressure-drop plane, for a fixed control rod induced external reactivity equal to the 100% rod line value and then transform the SB to the practical power-flow map. Using this SB, we show that the normal operating point at 100% power is very stable, stability of points on the 100% rod line decreases as the flow rate is reduced, and that points are least stable in the low-flow/high-power region. We also determine the SB when the modal kinetics is replaced by simple point reactor kinetics and show that the first harmonic mode has no significant effect on the SB. Later we carry out the relevant numerical simulations where we first show that the Hopf bifurcation, that occurs as a parameter is varied across the SB is subcritical, and that, in the important low-flow/high-power region, growing oscillations can result following small finite perturbations of stable steady-states on the 100% rod line. Hence, a point on the 100% rod line in the low-flow/high-power region, although stable, may nevertheless be a point at which a BWR should not be operated. Numerical simulations are then done to calculate the decay ratios (DRs) and frequencies of oscillations for various points on the 100% rod line. It is determined that the NRC requirement of DR < 0.75-0.8 is not rigorously satisfied in the low

  17. Evaluating network analysis and agent based modeling for investigating the stability of commercial air carrier schedules

    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

  18. Unsteady aerodynamic flow field analysis of the space shuttle configuration. Part 4: 747/orbiter aeroelastic stability

    NASA Technical Reports Server (NTRS)

    Reding, J. P.; Ericsson, L. E.

    1976-01-01

    A quasi-steady analysis of the aeroelastic stability of the lateral (antisymmetric) modes of the 747/orbiter vehicle was accomplished. The interference effect of the orbiter wake on the 747 tail furnishes an aerodynamic undamping contribution to the elastic modes. Likewise, the upstream influence of the 747 tail and aft fuselage on the orbiter beaver-tail rail fairing also is undamping. Fortunately these undamping effects cannot overpower the large damping contribution of the 747 tail and the modes are damped for the configurations analyzed. However, significant interference effects of the orbiter on the 747 tail have been observed in the pitch plane. The high response of the 747 vertical tail in the orbiter wave was also considered. Wind tunnel data points to flapping of the OMS pod wakes as the source of the wake resonance phenomenon.

  19. 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.

  20. 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.

  1. Stability analysis and time-step limits for a Monte Carlo Compton-scattering method

    SciTech Connect

    Densmore, Jeffery D. Warsa, James S. Lowrie, Robert B.

    2010-05-20

    A Monte Carlo method for simulating Compton scattering in high energy density applications has been presented that models the photon-electron collision kinematics exactly [E. Canfield, W.M. Howard, E.P. Liang, Inverse Comptonization by one-dimensional relativistic electrons, Astrophys. J. 323 (1987) 565]. However, implementing this technique typically requires an explicit evaluation of the material temperature, which can lead to unstable and oscillatory solutions. In this paper, we perform a stability analysis of this Monte Carlo method and develop two time-step limits that avoid undesirable behavior. The first time-step limit prevents instabilities, while the second, more restrictive time-step limit avoids both instabilities and nonphysical oscillations. With a set of numerical examples, we demonstrate the efficacy of these time-step limits.

  2. Floquet stability analysis of the wake of an inclined flat plate

    NASA Astrophysics Data System (ADS)

    Yang, Dan; Pettersen, Bjørnar; Andersson, Helge I.; Narasimhamurthy, Vagesh D.

    2013-09-01

    The route from a time-periodic two-dimensional wake flow to a three-dimensional flow has been investigated by means of linear Floquet stability analysis. The critical Reynolds number for the onset of three-dimensional instabilities in the wake behind a flat plate with an angle of attack α in the range from 20° to 30° with respect to the free stream was determined. For all three angles considered, in the lower wavelength range, the two-dimensional base flow first became unstable with respect to the sub-harmonic mode C. Although the critical Reynolds number decreased with increasing angle of attack, the spanwise wavelength remained close to two times the projected plate width. Qualitatively different transition scenarios were obtained for the three angles of attack with a particularly simple scenario for α = 30°.

  3. A new computational technique for the stability analysis of slender rods

    NASA Astrophysics Data System (ADS)

    Sinha, S. C.; Liu, Tai-Sheng; Senthilnathan, N. R.

    1992-07-01

    A new computational technique for the stability analysis of slender rods with variable cross-sections under general loading conditions is presented. In this approach, the dependent variable and the variable coefficients appearing in the governing equations are expanded in a finite series of Chebyshev polynomials. The main feature of this technique is that the original boundary value problem associated with the differential equation is reduced to an algebraic eigenvalue problem. The proposed technique is applied to study the static buckling of Euler column and the flutter behavior of a cantilevel column subjected to uniformly distributed tangential loading. The numerical results from the suggested technique are found to be extremely accurate when compared to other techniques available in literature. It is shown that this approach can also be employed in a symbolic form. The merits of the present method in comparison to the standard solution procedures like finite difference and Galerkin methods are discussed.

  4. Modeling and stability analysis for the upper atmosphere research satellite auxiliary array switch component

    NASA Technical Reports Server (NTRS)

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

    1987-01-01

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

  5. Solubility and Thermal Stability Investigation of Titan Tholins: New Insight from NMR Analysis

    NASA Astrophysics Data System (ADS)

    He, Chao; Smith, M. A.

    2012-10-01

    We investigated the solubility and thermal stability of Titan’s aerosol analogs (tholins) to understand the basic property of organics on Titan and the potential for chemical modification upon in situ sampling. The tholin generated by AC discharge in CH4/N2 (5/95) mixture preferentially dissolves in polar solvent to non-polar solvent, totally soluble in DMSO (>21.5 mg/mL), 60% in mass soluble in methanol, 25% in acetone, 27% in acetonitrile and 30% in water while only 1% in benzene and chloroform. The 1H solution-state NMR spectra of respective deuterated solutions exhibit the structural information of the soluble fraction in each solvent, confirming the large percentage of polar species in tholins. The solubility study not only helps us understand the solubility of Titan’s aerosols in possible liquid phase in Titan’s surface/atmosphere, but also provides the basis for the solvent selection and methods development of liquid separation and/or solution based analysis in future Titan missions. These include methods such as NMR and LC/MS, which can be non-destructive providing objective information regarding nascent chemical identification. Thermal stability studies demonstrate the thermal lability of tholins and indicate significant structural changes of when heated beyond 150 oC for even short time periods in inert atmospheres. Dynamic studies at 200 oC demonstrate that several predominant chemical reactions fit first-order reaction kinetics with half-lives between 5 to 141 minutes. This study is critical to ongoing discussion regarding the development of in situ analysis methods and instruments for Titan mission and other outer planet exploration.

  6. Longitudinal data analysis in support of functional stability concepts for leachate management at closed municipal landfills

    SciTech Connect

    Gibbons, Robert D.; Morris, Jeremy W.F.; Prucha, Christopher P.; Caldwell, Michael D.; Staley, Bryan F.

    2014-09-15

    Highlights: • Longitudinal data analysis using a mixed-effects regression model. • Dataset consisted of a total of 1402 samples from 101 closed municipal landfills. • Target analytes and classes generally showed predictable degradation trends. • Validates historical studies focused on macro organic indicators such as BOD. • BOD can serve as “gateway” indicator for planning leachate management. - Abstract: Landfill functional stability provides a target that supports no environmental threat at the relevant point of exposure in the absence of active control systems. With respect to leachate management, this study investigates “gateway” indicators for functional stability in terms of the predictability of leachate characteristics, and thus potential threat to water quality posed by leachate emissions. Historical studies conducted on changes in municipal solid waste (MSW) leachate concentrations over time (longitudinal analysis) have concentrated on indicator compounds, primarily chemical oxygen demand (COD) and biochemical oxygen demand (BOD). However, validation of these studies using an expanded database and larger constituent sets has not been performed. This study evaluated leachate data using a mixed-effects regression model to determine the extent to which leachate constituent degradation can be predicted based on waste age or operational practices. The final dataset analyzed consisted of a total of 1402 samples from 101 MSW landfills. Results from the study indicated that all leachate constituents exhibit a decreasing trend with time in the post-closure period, with 16 of the 25 target analytes and aggregate classes exhibiting a statistically significant trend consistent with well-studied indicators such as BOD. Decreasing trends in BOD concentration after landfill closure can thus be considered representative of trends for many leachate constituents of concern.

  7. Stability of hypersonic reacting stagnation flow of a detonatable gas mixture by dynamical systems analysis

    SciTech Connect

    Tivanov, G.; Rom, J.

    1995-12-01

    The stability characteristics of the reacting hypersonic flow of the fuel/oxidizer mixture in the stagnation region of a blunt body are studied. The conditions for oscillations of the combustion front are assumed to be determined mainly by the flow conditions at the stagnation region. The density at the stagnation region is assumed to be constant at hypersonic flow conditions. By assuming a simplified flow model, the time dependent flow equations, including the heat addition due to the chemical reactions, are reduced to a second-order nonlinear differential equation for the instantaneous temperature. The solutions are analyzed assuming a one-step chemical reaction with zero-order and first-order processes using dynamical systems methods. These methods are used to determine the stability boundaries in terms of the flow and chemical reaction parameters. It is shown that the zero-order reaction has nonperiodic solutions that may lead to explosion whereas the first-order and higher-order reactions may have periodic solutions indicating oscillations. The zero-order analysis also reaffirms the requirements for a minimum size blunt body for the establishment of a detonation (in agreement with classical detonation theory) and the first-order analysis indicates a minimum body size for establishment of oscillations. The oscillation frequencies are calculated using the small perturbation approximation for the temperature oscillations. These frequencies are compared with results from published data on spheres and hemisphere cylindrical bodies fired into hydrogen-oxygen and acetylene oxygen mixtures. Very good agreement is found between the measured and calculated results.

  8. Solid-state stability study of meropenem – solutions based on spectrophotometric analysis

    PubMed Central

    2013-01-01

    Background B-Lactam antibiotics are still the most common group of chemotherapeutic drugs that are used in the treatment of bacterial infections. However, due to their chemical instability the potential to apply them as oral pharmacotherapeutics is often limited and so it is vital to employ suitable non-destructive analytical methods. Hence, in order to analyze such labile drugs as β-lactam analogs, the application of rapid and reliable analytical techniques which do not require transferring to solutions or using organic solvents, following the current green approach to pharmaceutical analysis, is necessary. The main objective of the present research was to develop analytical methods for the evaluation of changes in meropenem in the solid state during a stability study. Results The UV, FT-IR and Raman spectra of meropenem were recorded during a solid-state stability study. The optimum molecular geometry, harmonic vibrational frequencies, infrared intensities and Raman scattering activities were calculated according to the density-functional theory (DFT/B3LYP method) with a 6-31G(d,p) basis set. As the differences between the observed and scaled wavenumber values were small, a detailed interpretation of the FT-IR and Raman spectra was possible for non-degraded and degraded samples of meropenem. The problem of the overlapping spectra of meropenem and ring-containing degradation products was solved by measuring changes in the values of the first-derivative amplitudes of the zero-order spectra of aqueous solutions of meropenem. Also, molecular electrostatic potential (MEP), front molecular orbitals (FMOs) and the gap potential between highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) were determined. Conclusions Based on the findings of this work, it appears possible to use time-saving and reliable spectrophotometric analytical methods, supported by quantum-chemical calculations, for solid-state stability investigations of

  9. Linear Stability Analysis of Magnetohydrodynamic Richtmyer-Meshkov Instability in Cyindrical Geometry

    NASA Astrophysics Data System (ADS)

    Bakhsh, Abeer; Samtaney, Ravi

    2015-11-01

    Numerical simulations and analysis in Cartesian slab geometry for nonlinear ideal magnetohydrodynamics (MHD) indicate that the Richtmyer-Meshkov instability (RMI) is suppressed in the presence of a magnetic field. An analytical solution of incompressible 2-D MHD RMI of an impulsively accelerated interface was investigated by Wheatley et al. (Phys. Rev. Lett. 2005; J. Fluid Mech. 2005) who found that, for a finite magnetic field, although the initial growth rate of the interface is unaffected by the presence of magnetic field, the late-time amplitude of the interface asymptotes to a constant value. In the framework of incompressible MHD, we examine analytically the behavior of an impulsively accelerated interface separating conducting fluids of different densities in cylindrical geometry. We investigate the stability properties of such a system and study the influence of the magnetic field on the growth rate of the interface. In converging cylindrical geometry, the RMI is followed by a Rayleigh-Taylor (RT) phase. Our analysis does not account for the RT phase of the instability but is valid for the duration of the RMI phase. We compare results of the incompressible analysis with linear compressible MHD simulations. Supported by the KAUST Office of Competitive Research Funds under Award No. URF/1/2162-01.

  10. Stability and performance analysis of a jump linear control system subject to digital upsets

    NASA Astrophysics Data System (ADS)

    Wang, Rui; Sun, Hui; Ma, Zhen-Yang

    2015-04-01

    This paper focuses on the methodology analysis for the stability and the corresponding tracking performance of a closed-loop digital jump linear control system with a stochastic switching signal. The method is applied to a flight control system. A distributed recoverable platform is implemented on the flight control system and subject to independent digital upsets. The upset processes are used to stimulate electromagnetic environments. Specifically, the paper presents the scenarios that the upset process is directly injected into the distributed flight control system, which is modeled by independent Markov upset processes and independent and identically distributed (IID) processes. A theoretical performance analysis and simulation modelling are both presented in detail for a more complete independent digital upset injection. The specific examples are proposed to verify the methodology of tracking performance analysis. The general analyses for different configurations are also proposed. Comparisons among different configurations are conducted to demonstrate the availability and the characteristics of the design. Project supported by the Young Scientists Fund of the National Natural Science Foundation of China (Grant No. 61403395), the Natural Science Foundation of Tianjin, China (Grant No. 13JCYBJC39000), the Scientific Research Foundation for the Returned Overseas Chinese Scholars, State Education Ministry, China, the Tianjin Key Laboratory of Civil Aircraft Airworthiness and Maintenance in Civil Aviation of China (Grant No. 104003020106), and the Fund for Scholars of Civil Aviation University of China (Grant No. 2012QD21x).

  11. Geotechnical stability analysis, fragility of structures and velocity of movement to assess landslides vulnerability

    NASA Astrophysics Data System (ADS)

    Cuanalo, O.; Bernal, E.; Polanco, G.

    2014-09-01

    Landslides are geohazards that can be potential risks to life and property; these phenomena usually cause disasters when they occur in densely populated communities as those that inhabit mountainous and steep regions. Hazard and vulnerability are parameters determined by probability mathematical analysis with values between 0 and 1. When there are no records or enough information regards historical events on the phenomenon in study, that have occurred in a specific area (as in several mountainous regions of Mexico inhabited by ethnic groups), it has the disadvantage of not being able to perform a statistical analysis to properly evaluate the hazard nor the vulnerability. To solve the problem, this paper presents a proposal for evaluating the physical and functional vulnerability of the elements at risk, from two fundamental aspects: (a) the exposure level (EL), and (b) the expected damage degree (EDD). First of these factors is determined by the severity index (SI) and the safety factor from geotechnical stability analysis (SFgeo); the second one from the construction type (degree of fragility of structures) and the velocity that may have the landslide. For evaluating the parameters aforementioned, included tables, graphs and equations proposed by the authors.

  12. Kinetic analysis of the hydrolysis of methyl parathion using citrate-stabilized 10 nm gold nanoparticles.

    PubMed

    Nita, Rafaela; Trammell, Scott A; Ellis, Gregory A; Moore, Martin H; Soto, Carissa M; Leary, Dagmar H; Fontana, Jake; Talebzadeh, Somayeh F; Knight, D Andrew

    2016-02-01

    "Ligand-free" citrate-stabilized 10 nm gold nanoparticles (AuNPs) promote the hydrolysis of the thiophosphate ester methyl parathion (MeP) on the surface of gold as a function of pH and two temperature values. At 50 °C, the active surface gold atoms show catalytic turnover ∼4 times after 8 h and little turnover of gold surface atoms at 25 °C with only 40% of the total atoms being active. From Michaelis-Menten analysis, k(cat) increases between pH 8 and 9 and decreases above pH 9. A global analysis of the spectral changes confirmed the stoichiometric reaction at 25 °C and the catalytic reaction at 50 °C and mass spectrometry confirmed the identity of p-nitrophenolate (PNP) product. Additional decomposition pathways involving oxidation and hydrolysis independent of the formation of PNP were also seen at 50 °C for both catalyzed and un-catalyzed reactions. This work represents the first kinetic analysis of ligand-free AuNP catalyzed hydrolysis of a thiophosphate ester. PMID:26547026

  13. Theoretical analysis of solid oxide fuel cells with two-layer, composite electrolytes - Electrolyte stability

    NASA Astrophysics Data System (ADS)

    Virkar, Anil V.

    1991-05-01

    Theoretical analysis of solid oxide fuel cells (SOFCs) using two-layer, composite electrolytes consisting of a solid electrolyte of a significantly higher conductivity compared to zirconia (such as ceria or bismuth oxide) with a thin layer of zirconia or thoria on the fuel side is presented. Electrochemical transport in the two-layer composite electrolytes is examined by taking both ionic and electronic fluxes into account. Similar to most electrochemical transport phenomena, it is assumed that local equilibrium prevails. An equivalent circuit approach is used to estimate the partial pressure of oxygen at the interface. It is shown that thermodynamic stability of the electrolyte (ceria or bismuth oxide) depends upon the transport characteristics of the composite electrolyte, in particular the electronic conductivity of the air-side part of the electrolyte. The analysis shows that it would be advantageous to use composite electrolytes instead of all-zirconia electrolytes, thus making low-temperature (about 600-800 C) SOFCs feasible. Implications of the analysis from the standpoint of the desired characteristics of SOFC components are discussed.

  14. A multiloop generalization of the circle criterion for stability margin analysis

    NASA Technical Reports Server (NTRS)

    Safonov, M. G.; Athans, M.

    1979-01-01

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

  15. Analysis on Global Stability of Stochastic Neural Networks of Neutral Type

    NASA Astrophysics Data System (ADS)

    Park, Ju H.; Kwon, O. M.

    In this paper, the problem of global asymptotic stability of stochastic neural networks of neutral type is considered. Based on the Lyapunov stability theory, a new delay-dependent stability criterion for the network is derived in terms of LMI (linear matrix inequality). A numerical example is given to show the effectiveness of the proposed method.

  16. Biomechanical evaluation of oversized drilling technique on primary implant stability measured by insertion torque and resonance frequency analysis

    PubMed Central

    Santamaría-Arrieta, Gorka; Brizuela-Velasco, Aritza; Fernández-González, Felipe J.; Chávarri-Prado, David; Chento-Valiente, Yelko; Solaberrieta, Eneko; Diéguez-Pereira, Markel; Yurrebaso-Asúa, Jaime

    2016-01-01

    Background This study evaluated the influence of implant site preparation depth on primary stability measured by insertion torque and resonance frequency analysis (RFA). Material and Methods Thirty-two implant sites were prepared in eight veal rib blocks. Sixteen sites were prepared using the conventional drilling sequence recommended by the manufacturer to a working depth of 10mm. The remaining 16 sites were prepared using an oversize drilling technique (overpreparation) to a working depth of 12mm. Bone density was determined using cone beam computerized tomography (CBCT). The implants were placed and primary stability was measured by two methods: insertion torque (Ncm), and RFA (implant stability quotient [ISQ]). Results The highest torque values were achieved by the conventional drilling technique (10mm). The ANOVA test confirmed that there was a significant correlation between torque and drilling depth (p<0.05). However, no statistically significant differences were obtained between ISQ values at 10 or 12 mm drilling depths (p>0.05) at either measurement direction (cortical and medullar). No statistical relation between torque and ISQ values was identified, or between bone density and primary stability (p >0.05). Conclusions Vertical overpreparation of the implant bed will obtain lower insertion torque values, but does not produce statistically significant differences in ISQ values. Key words:Implant stability quotient, overdrilling, primary stability, resonance frequency analysis, torque. PMID:27398182

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

    NASA Technical Reports Server (NTRS)

    Zimmerman, Charles H

    1937-01-01

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

  18. Orbital stability analysis and chaotic dynamics of exoplanets in multi-stellar systems

    NASA Astrophysics Data System (ADS)

    Satyal, Suman

    -aperiodic orbits. The stability of the system is defined in terms of its lifetime and maximum eccentricity during the integration period then a regime is established for the known and injected planet's orbital parameters. The de-stabilizing resonances due to the outer planet extend by 1.36 AU towards the star, nonetheless, existence of two Earth-mass planets seems plausible. The radial velocity (RV) curves generated for the test planets reveals a weak RV signal that cannot be measured by currently available instruments. A theory has been developed by extrapolating the radio emission processes in the Jupiter-Io system, which could reveal the presence of exomoons around the giant exoplanets. Based on this theory, maximum distance, radius and masses of exoplanets and exomoons are calculated that could be detected by the available radio telescopes. Observation time at the Low Frequency Array (LOFAR) radio telescope has been proposed to detect exomoon in five different stellar systems. Subjects of my future studies include analysis of the data from LOFAR, search for the additional transiting planets in Kepler 47 circumbinary system and observation at the Subaru telescope to verify the predicted planets in GJ 832 system by the method of direct imaging.

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

    NASA Technical Reports Server (NTRS)

    Kayten, Gerald G

    1945-01-01

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

  20. Rock Cavern Stability Analysis Under Different Hydro-Geological Conditions Using the Coupled Hydro-Mechanical Model

    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.

  1. A hybrid method for quasi-three-dimensional slope stability analysis in a municipal solid waste landfill

    SciTech Connect

    Yu, L.; Batlle, F.

    2011-12-15

    Highlights: > A quasi-three-dimensional slope stability analysis method was proposed. > The proposed method is a good engineering tool for 3D slope stability analysis. > Factor of safety from 3D analysis is higher than from 2D analysis. > 3D analysis results are more sensitive to cohesion than 2D analysis. - Abstract: Limited space for accommodating the ever increasing mounds of municipal solid waste (MSW) demands the capacity of MSW landfill be maximized by building landfills to greater heights with steeper slopes. This situation has raised concerns regarding the stability of high MSW landfills. A hybrid method for quasi-three-dimensional slope stability analysis based on the finite element stress analysis was applied in a case study at a MSW landfill in north-east Spain. Potential slides can be assumed to be located within the waste mass due to the lack of weak foundation soils and geosynthetic membranes at the landfill base. The only triggering factor of deep-seated slope failure is the higher leachate level and the relatively high and steep slope in the front. The valley-shaped geometry and layered construction procedure at the site make three-dimensional slope stability analyses necessary for this landfill. In the finite element stress analysis, variations of leachate level during construction and continuous settlement of the landfill were taken into account. The 'equivalent' three-dimensional factor of safety (FoS) was computed from the individual result of the two-dimensional analysis for a series of evenly spaced cross sections within the potential sliding body. Results indicate that the hybrid method for quasi-three-dimensional slope stability analysis adopted in this paper is capable of locating roughly the spatial position of the potential sliding mass. This easy to manipulate method can serve as an engineering tool in the preliminary estimate of the FoS as well as the approximate position and extent of the potential sliding mass. The result that Fo

  2. A New Method for System Reliability Analysis of Tailings Dam Stability

    NASA Astrophysics Data System (ADS)

    Liu, X.; Tang, H.; Xiong, C.; Ni, W.

    2012-12-01

    For the purpose of stability evaluation, a tailings dam can be considered as an artificial slope made of special soil materials which mainly come from mine tailings. As a particular engineering project, a tailings dam generally has experienced multi-loop hydraulic sediments as well as a long-term consolidation in the process of construction. The characteristics of sediment and consolidation result in a unique distribution of the soil layers with significant uncertainties, which come from both nature development and various human activities, and thus cause the discrete and the variability of the physical-mechanical properties dramatically greater than the natural geo-materials. Therefore, the location of critical slip surface (CSS) of the dam usually presents a notable drift. So, it means that the reliability evaluation task for a tailings dam is a system reliability problem indeed. Unfortunately, the previous research of reliability of tailings dam was mainly confined to the limit equilibrium method (LEM), which has three obvious drawbacks. First, it just focused on the variability along the slip surface rather than the whole space of the dam. Second, a fixed CSS, instead of variable one, was concerned in most cases. Third, the shape of the CSS was usually simplified to a circular. The present paper tried to construct a new reliability analysis model combined with several advanced techniques involving finite difference method (FDM), Monte Carlo simulation (MCS), support vector machine (SVM) and particle swarm optimization (PSO). The new framework was consisted of four modules. The first one is the limit equilibrium finite difference mode, which employed the FLAC3D code to generate stress fields and then used PSO algorithm to search the location of CSS and corresponding minimum factor of safety (FOS). The most value of this module was that each realization of stress field would lead to a particular CSS and its FOS. In other words, the consideration of the drift of

  3. Glass Stability and Kinetic Analysis of Iron-Metalloid Bulk Metallic Glass

    NASA Astrophysics Data System (ADS)

    Santhaweesuk, Charuayporn

    Multicomponent Fe-based bulk metallic glasses (BMGs) with a combination of excellent properties such as good soft magnetic properties, high strength, high hardness, and high corrosion resistance have attracted increasing attention both from a basic science research standpoint and due to their industrial application potential. However, many of the elemental additions which lead to the easiest glass formation are expensive. The identification of alloys composed of abundant and inexpensive elements that still retain excellent properties would promote applications for engineering and industry. In short, the development of the Fe-based BMG without any glass-forming metal elements and with high glass forming ability is desired. This study shows that the thermal stability of the Fe-based alloys can be improved beyond a simple rule of mixtures prediction by utilizing a well-balance multi-metalloid approach. The kinetics aspect of glass-forming ability is studied experimentally for Fe-B-Si-P alloys. The systematic variation in alloy composition gives access to differences in phase selection and the final dimensions of glass formation. Two alloys, representing the best glass-forming composition and the poorest glass-forming composition, were studied in terms of their stability to crystallization, solidification microstructure evolution and thermal history. The utility of the wedge-casting technique is developed to examine bulk glass-forming alloys by combining multiple temperature profiles of the quenching melt with a measurement-based kinetic analysis of the phase selection competition and critical cooling rate conditions. Based upon direct thermal measurement, microstructural analysis and kinetic modeling, it was found that both representative alloys show a board spectrum of solidification microstructures which include a critical cooling rate range. The kinetic competition in the formation of certain phases can enhance or detract from the final dimension of bulk glass

  4. Global mode analysis of axisymmetric bluff-body wakes: Stabilization by base bleed

    NASA Astrophysics Data System (ADS)

    Sanmiguel-Rojas, E.; Sevilla, A.; Martínez-Bazán, C.; Chomaz, J.-M.

    2009-11-01

    The flow around a slender body with a blunt trailing edge is unstable in most situations of interest. Usually the flow instabilities are generated within the wake behind the bluff body, inducing fluctuating forces and introducing the possibility of resonance mechanisms with modes of the structure. Base bleed is a simple and well-known means of stabilizing the wake. In the present research, we investigate the global instability properties of the laminar-incompressible flow that develops behind a cylinder with sharp edges and axis aligned with the free stream using a spectral domain decomposition method. In particular, we describe the flow instability characteristics as a function of the Reynolds number, Re=ρW∞D/μ, and the bleed coefficient, defined as the bleed-to-free-stream velocity ratio, Cb=Wb/W∞, where D is the diameter of the body and ρ and μ the density and viscosity of the free stream, respectively. For a truncated cylinder of aspect ratio L /D=5, where L is the length of the body, our calculations reveal the presence of a first steady bifurcation in the wake at Re≃391, as well as a second oscillatory one at Re≃715 with an associated Strouhal number St≃0.0905 for the most unstable azimuthal mode |m|=1. In addition, we report the existence of two critical values of the bleed coefficient Cb1∗(Re,|m |) and Cb2∗(Re,|m |)stabilize both the first and second bifurcations in the range of Reynolds numbers under study, 0≤Re≤2200. Finally, the numerical results for the oscillatory mode obtained for a bulletlike body of aspect ratio L /D=2 without base bleed are compared with experiments performed in a wind tunnel using hot-wire anemometry, showing the limitations of using an axisymmetric basic flow at Reynolds numbers higher than the critical one corresponding to the first steady bifurcation in the global stability analysis.

  5. Rapid Analysis of Glibenclamide Using an Environmentally Benign Stability-Indicating RP-HPLC Method

    PubMed Central

    Haq, Nazrul; Alanazi, Fars Kaed; Alsarra, Ibrahim Abdullah; Shakeel, Faiyaz

    2014-01-01

    An environmentally benign RP-HPLC approach for rapid analysis of glibenclamide in pure form, developed nanoemulsion and commercial tablets was developed and validated in present investigation. The green chromatographic identification was performed on Lichrosphere 250 X 4.0 mm RP C8 column having a 5 μm packing as a stationary phase using a combination of ethanol: methanol (50:50 % v/v) as a mobile phase, at a flow rate of 1.0 mL/min with UV detection at 245 nm. The proposed method was validated for linearity, selectivity, accuracy, precision, robustness, sensitivity and specificity as per international conference on harmonization (ICH) guidelines. The utility of proposed method was verified by assay of glibenclamide in developed nanoemulsion and commercial tablets. The proposed method was found to be satisfactory in terms of selectivity, precision, accuracy, robustness, sensitivity and specificity. The content of glibenclamide in developed nanoemulsion and commercial tablets was found to be 100.50 % and 99.15 % respectively. The proposed method successfully resoled glibenclamide peak in the presence of its all type of degradation products which indicated stability-indicating property of the proposed method. These results indicated that the green chromatographic method could be successfully employed for routine analysis of glibenclamide in pure drug and various commercial formulations. PMID:25276186

  6. Implementation of Bounding Surface Model into ABAQUS and Its Application to Wellbore Stability Analysis

    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.

  7. Gap symmetry and stability analysis in the multi-orbital Fe-based superconductors

    NASA Astrophysics Data System (ADS)

    Fischer, Mark H.

    2013-07-01

    The iron-based superconductors allow for a zoo of possible order parameters due to their orbital degrees of freedom. These order parameters are often written in an orbital basis for a microscopic analysis and a comprehensive symmetry classification. Unlike in standard single-band superconductors, where electrons of the same band—and hence, energy—are paired, a general order parameter in such a multi-orbital system also contains pairing of electrons belonging to different bands. As this corresponds to pairing of electrons of different energy, such order parameters are energetically less stable. Here, we present a simple criterion for a stability analysis of the orbital part of the gap function based on the basic principle that electrons of equal energy are paired in the superconducting state. This not only allows us to find the most stable states, but also to identify the terms in a (tight-binding) Hamiltonian suppressing any given superconducting state. Our approach thus allows us to identify the minimal Hamiltonian necessary to compare competing instabilities.

  8. Potentiometric analysis of UDP-galactopyranose mutase: stabilization of the flavosemiquinone by substrate.

    PubMed

    Fullerton, Stephen W B; Daff, Simon; Sanders, David A R; Ingledew, W John; Whitfield, Chris; Chapman, Stephen K; Naismith, James H

    2003-02-25

    UDP-galactopyranose mutase is a flavoprotein which catalyses the interconversion of UDP-galactopyranose and UDP-galactofuranose. The enzyme is of interest because it provides the activated biosynthetic precursor of galactofuranose, a key cell wall component of many bacterial pathogens. The reaction mechanism of this mutase is intriguing because the anomeric oxygen forms a glycosidic bond, which means that the reaction must proceed by a novel mechanism involving ring breakage and closure. The structure of the enzyme is known, but the mechanism, although speculated on, is not resolved. The overall reaction is electrically neutral but a crypto-redox reaction is suggested by the requirement that the flavin must adopt the reduced form for activity. Herein we report a thermodynamic analysis of the enzyme's flavin cofactor with the objective of defining the system and setting parameters for possible reaction schemes. The analysis shows that the neutral semiquinone (FADH(*)) is stabilized in the presence of substrate and the fully reduced flavin is the anionic FADH(-) rather than the neutral FADH(2). The anionic FADH(-) has the potential to act as a rapid 1-electron donor/acceptor without being slowed by a coupled proton transfer and is therefore an ideal crypto-redox cofactor. PMID:12590598

  9. Estimation of upper limit of pore pressure by fault stability analysis

    NASA Astrophysics Data System (ADS)

    Chen, Zijian; Deng, Jingen; Yu, Baohua; Zhang, Yanan; Chen, Zhuo

    2016-06-01

    Generally, the pore pressure for a pre-drill well is predicted using empirical parameters, which are regressed from the drilled well's data. However, for areas with large geological differences, empirical parameters which are obtained using traditional methods may fail because intense tectonic movement would result in huge differences between the pre-drill well and drilled well. Firstly, in order to overcome this problem, the method of fault stability analysis is introduced. Analysis indicates that when abnormal overpressure exceeds a certain value, the fault ruptures and the overpressured fluid escapes, so that there is an upper limit of pore pressure (ULPP) for the stable fault. Secondly, the influences of fault angle, formation Poisson ratio and modulus of elasticity on the ULPP are discussed further. The results show that the ULPP of a fault with angle of 65.2° is the minimum, and the critical angle increases with the increase of internal friction coefficient. For reverse faults and strike faults, the influences of Poisson ratio and modulus of elasticity are small, but for normal faults these are significant. Finally, three kinds of ULPP for these different faults are proposed, respectively. The application of this method in the Xihu Sag in the East China Sea has proved that reference to ULPP can verify and correct regressed empirical parameters, so as to improve pore pressure prediction accuracy.

  10. Chemical pathway analysis of the lower Martian atmosphere: The CO2 stability problem

    NASA Astrophysics Data System (ADS)

    Stock, J. W.; Grenfell, J. L.; Lehmann, R.; Patzer, A. B. C.; Rauer, H.

    2012-08-01

    The chemical composition and hence the structure of terrestrial planetary atmospheres can be critically controlled by trace species which can act in catalytic cycles. Identifying such chemical pathways is in general challenging. Due to the complexity of chemical reaction networks, like those used in Martian atmospheric chemistry, automated methods become more and more useful to cope with this task. Here, we investigate the applicability of a unique analysis tool PAP (Pathway Analysis Program) to the chemistry at Mars' atmospheric surface conditions, for which we have developed a photochemical box-model. PAP is applied for the first time to the output of this model to investigate the well-known CO2 stability problem of the Martian atmosphere. We identify and rank the most dominant pathways responsible for CO2 formation and prove thereby the applicability of PAP for Mars atmospheric conditions by comparison with known chemical cycles. Furthermore, we propose here an additional new catalytic CO2 formation cycle which is also involved in the production of ozone.

  11. Analysis of microseismic signals and temperature recordings for rock slope stability investigations in high mountain areas

    NASA Astrophysics Data System (ADS)

    Occhiena, C.; Coviello, V.; Arattano, M.; Chiarle, M.; Morra di Cella, U.; Pirulli, M.; Pogliotti, P.; Scavia, C.

    2012-07-01

    The permafrost degradation is a probable cause for the increase of rock instabilities and rock falls observed in recent years in high mountain areas, particularly in the Alpine region. The phenomenon causes the thaw of the ice filling rock discontinuities; the water deriving from it subsequently freezes again inducing stresses in the rock mass that may lead, in the long term, to rock falls. To investigate these processes, a monitoring system composed by geophones and thermometers was installed in 2007 at the Carrel hut (3829 m a.s.l., Matterhorn, NW Alps). In 2010, in the framework of the Interreg 2007-2013 Alcotra project no. 56 MASSA, the monitoring system has been empowered and renovated in order to meet project needs. In this paper, the data recorded by this renewed system between 6 October 2010 and 5 October 2011 are presented and 329 selected microseismic events are analysed. The data processing has concerned the classification of the recorded signals, the analysis of their distribution in time and the identification of the most important trace characteristics in time and frequency domain. The interpretation of the results has evidenced a possible correlation between the temperature trend and the event occurrence. The research is still in progress and the data recording and interpretation are planned for a longer period to better investigate the spatial-temporal distribution of microseismic activity in the rock mass, with specific attention to the relation of microseismic activity with temperatures. The overall goal is to verify the possibility to set up an effective monitoring system for investigating the stability of a rock mass under permafrost conditions, in order to supply the researchers with useful data to better understand the relationship between temperature and rock mass stability and, possibly, the technicians with a valid tool for decision-making.

  12. Evaluation of liver tissue damage and grasp stability using finite element analysis.

    PubMed

    Cheng, Lei; Hannaford, Blake

    2016-01-01

    Minimizing tissue damage and maintaining grasp stability are essential considerations in surgical grasper design. Most past and current research analyzing graspers used for tissue manipulation in minimally invasive surgery is based on in vitro experiments. Most previous work assessed tissue injury and grasp security by visual inspection; only a few studies have quantified it. The goal of the present work is to develop a methodology with which to compute tissue damage magnitude and grasp quality that is appropriate for a wide range of grasper-tissue interaction. Using finite element analysis (FEA), four graspers with varying radii of curvature and four graspers with different tooth sizes were analyzed while squeezing and pulling liver tissue. All graspers were treated as surgical steel with linear elastic material properties. Nonlinear material properties of tissue used in the FEA as well as damage evaluation were derived from previously reported in vivo experiments. Computed peak stress, integrated stress, and tissue damage were compared. Applied displacement is vertical and then horizontal to the tissue surface to represent grasp and retraction. A close examination of the contact status of each node within the grasper-tissue interaction surface was carried out to investigate grasp stability. The results indicate less tissue damage with increasing radius of curvature. A smooth wave pattern reduced tissue damage at the cost of inducing higher percentage of slipping area. This methodology may be useful for researchers to develop and test various designs of graspers. Also it could improve surgical simulator performance by reflecting more realistic tissue material properties and predicting tissue damage for the student. PMID:25408249

  13. Test-retest Stability Analysis of Resting Brain Activity Revealed by BOLD fMRI

    PubMed Central

    Li, Zhengjun; Kadivar, Aniseh; Pluta, John; Dunlop, John; Wang, Ze

    2012-01-01

    Purpose To assess test-retest stability of four fMRI-derived resting brain activity metrics: the seed-region-based functional connectivity (SRFC), independent component analysis (ICA)-derived network-based FC (NTFC), regional homogeneity (ReHo), and the amplitude of low frequency fluctuation (ALFF). Methods Simulations were used to assess the sensitivity of SRFC, ReHo, and ALFF to noise interference. Repeat resting blood-oxygen-level-dependent (BOLD) fMRI were acquired from 32 healthy subjects. The intra-class correlation coefficient (ICC) was used to assess the stability of the 4 metrics. Results Random noise yielded small random SRFC, small but consistent ReHo and ALFF. A neighborhood size greater than 20 voxels should be used for calculating ReHo in order to reduce the noise interference. Both the anterior cingulate cortex (ACC) and posterior cingulate cortex (PCC)-based SRFC were reproducible in more spatially extended regions than ICA NTFC. The two regional spontaneous brain activity (SBA) measures, ReHo and ALFF, showed test-retest reproducibility in almost the whole grey matter. Conclusion SRFC, ReHo, and ALFF are robust to random noise interference. The neighborhood size for calculating ReHo should be larger than 20 voxels. ICC>0.5 and cluster size>11 should be used to assess the ICC maps for ACC/PCC SRFC, ReHo and ALFF. BOLD fMRI-based SBA can be reliably measured using ACC/PCC SRFC, ReHo and ALFF after two months. PMID:22535702

  14. Linearized blade row compression component model. Stability and frequency response analysis of a J85-3 compressor

    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.

  15. Attitude stability of spinning satellites

    NASA Technical Reports Server (NTRS)

    Caughey, T. K.

    1980-01-01

    Some problems of attitude stability of spinning satellites are treated in a rigorous manner. With certain restrictions, linearized stability analysis correctly predicts the attitude stability of spinning satellites, even in the critical cases of the Liapunov-Poincare stability theory.

  16. Stability of Molasse: TLS for structural analysis in the valley of Gotteron-Fribourg, Switzerland

    NASA Astrophysics Data System (ADS)

    Ben Hammouda, Mariam; Jaboyedoff, Michel; Derron, Marc Henri; Bouaziz, Samir; Mazotti, Benoit

    2016-04-01

    The marine molasses of Fribourg (Switzerland) is an area where the cliff collapses and rockfalls are quite frequent and difficult to predict due to this particular lithology, a poorly consolidated greywacke. Because of some recent rockfall events, the situation became critical especially in the valley of Gotteron where a big block has slightly moved down and might destroy a house in case of rupture. The cliff made of jointed sandstone and thin layers of clay and siltstone presents many fractures, joints and massive cross bedding surfaces which increases the possibility of slab failure. This paper presents a detailed structural analysis of the cliff and the identification of the potential failure mechanisms. The methodology is about combining field observation and terrestrial LiDAR scanning point cloud in order to assess the stability of potential slope instabilities of molasses. Three LiDAR scans were done i) to extract discontinuity families depending to the dip and the dip direction of joints and ii) to run kinematic tests in order to identify responsible sets for each potential failure mechanisms. Raw point clouds were processed using IMAlign module of Polyworks and CloudCompare software. The structural analysis based on COLTOP 3D (Jaboyedoff et al. 2007) allowed the identification of four discontinuity sets that were not measured in the field. Two different failure mechanisms have been identified as critical: i) planar sliding which is the main responsible mechanism of the present fallen block and ii) wedge sliding. The planar sliding is defined by the discontinuity sets J1 and J5 with a direction parallel to the slope and with a steep dip angle. The wedges, defined by couples of discontinuity sets, contribute to increase cracks' opening and to the detachment of slabs. The use of TLS combined with field survey provides us a first interpretation of instabilities and a very promising structural analysis.

  17. Coupled flexural-longitudinal vibration of delaminated composite beams with local stability analysis

    NASA Astrophysics Data System (ADS)

    Szekrényes, András

    2014-09-01

    A novel analytical model is developed to solve the problem of free vibration of delaminated composite beams. The beam with a single delamination was modelled by six equivalent single layers by establishing the kinematic continuity in the undelaminated portion of the system. In the delaminated region the layers were captured by the traditional theories. First, Timoshenko beam theory is applied to solve the problem, then by reducing the model, the corresponding Euler-Bernoulli solution is presented. Both the free and constrained models were considered. The most important aspect of the present analysis is that the beams of the delaminated region are subjected to normal forces, as well. That is the essential reason for leading to a coupled flexural-longitudinal vibration problem. It is also concluded that delamination buckling can take place if the normal force is compressive in one of the half-periods of the vibration and reaches a critical value. The problem was also investigated experimentally by modal hammer and sweep excitation tests on beams made of E-glass/polyester in order to measure the natural frequencies and mode shapes. The comparison of the analytical and experimental results indicates the importance of the independent rotations provided by Timoshenko beams over the simple beam theory. The delamination buckling of the beams was captured based on the static stability analysis in the first step. Further results show that the problem is more complex than it was thought before, e.g., some nonlinearity, time-dependent stiffness as well as parametric excitation aspects were discovered during the present analysis.

  18. A multiloop generalization of the circle criterion for stability margin analysis

    NASA Technical Reports Server (NTRS)

    Safonov, M. G.; Athans, M.

    1981-01-01

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

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

    NASA Technical Reports Server (NTRS)

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

    2004-01-01

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

  20. Stability analysis of titanium alloy milling by multiscale entropy and Hurst exponent

    NASA Astrophysics Data System (ADS)

    Rusinek, Rafał; Borowiec, Marek

    2015-10-01

    This paper discusses the problem of stability in a milling process for titanium super-alloy Ti6242. The phenomenon of chatter vibration is analysed by the multiscale entropy method and Hurst exponent. Although this problem is often considered based on stability lobe diagrams, theoretical findings do not always agree with experimental results. First, a stability lobe diagram is created based on parameters determined by impact testing. Next, cutting forces are measured in an experiment where the axial cutting depth is gradually increased. Finally, the obtained experimental signals are investigated with respect to stability using the multiscale entropy method and Hurst exponent.