Delay-dependent stability and added damping of SDOF real-time dynamic hybrid testing

NASA Astrophysics Data System (ADS)

Chi, Fudong; Wang, Jinting; Jin, Feng

2010-09-01

It is well-recognized that a transfer system response delay that reduces the test stability inevitably exists in real-time dynamic hybrid testing (RTDHT). This paper focuses on the delay-dependent stability and added damping of SDOF systems in RTDHT. The exponential delay term is transferred into a rational fraction by the Padé approximation, and the delay-dependent stability conditions and instability mechanism of SDOF RTDHT systems are investigated by the root locus technique. First, the stability conditions are discussed separately for the cases of stiffness, mass, and damping experimental substructure. The use of root locus plots shows that the added damping effect and instability mechanism for mass are different from those for stiffness. For the stiffness experimental substructure case, the instability results from the inherent mode because of an obvious negative damping effect of the delay. For the mass case, the delay introduces an equivalent positive damping into the inherent mode, and instability occurs at an added high frequency mode. Then, the compound stability condition is investigated for a general case and the results show that the mass ratio may have both upper and lower limits to remain stable. Finally, a high-emulational virtual shaking table model is built to validate the stability conclusions.

Stability analysis of internally damped rotating composite shafts using a finite element formulation

NASA Astrophysics Data System (ADS)

Ben Arab, Safa; Rodrigues, José Dias; Bouaziz, Slim; Haddar, Mohamed

2018-04-01

This paper deals with the stability analysis of internally damped rotating composite shafts. An Euler-Bernoulli shaft finite element formulation based on Equivalent Single Layer Theory (ESLT), including the hysteretic internal damping of composite material and transverse shear effects, is introduced and then used to evaluate the influence of various parameters: stacking sequences, fiber orientations and bearing properties on natural frequencies, critical speeds, and instability thresholds. The obtained results are compared with those available in the literature using different theories. The agreement in the obtained results show that the developed Euler-Bernoulli finite element based on ESLT including hysteretic internal damping and shear transverse effects can be effectively used for the stability analysis of internally damped rotating composite shafts. Furthermore, the results revealed that rotor stability is sensitive to the laminate parameters and to the properties of the bearings.

Some effects of nonlinear variation in the directional-stability and damping-in-yawing derivatives on the lateral stability of an airplane

NASA Technical Reports Server (NTRS)

Sternfield, Leonard

1951-01-01

A theoretical investigation has been made to determine the effect of nonlinear stability derivatives on the lateral stability of an airplane. Motions were calculated on the assumption that the directional-stability and the damping-in-yawing derivatives are functions of the angle of sideslip. The application of the Laplace transform to the calculation of an airplane motion when certain types of nonlinear derivatives are present is described in detail. The types of nonlinearities assumed correspond to the condition in which the values of the directional-stability and damping-in-yawing derivatives are zero for small angle of sideslip.

Damping in flapping flight and its implications for manoeuvring, scaling and evolution.

PubMed

Hedrick, Tyson L

2011-12-15

Flying animals exhibit remarkable degrees of both stability and manoeuvrability. Our understanding of these capabilities has recently been improved by the identification of a source of passive damping specific to flapping flight. Examining how this damping effect scales among different species and how it affects active manoeuvres as well as recovery from perturbations provides general insights into the flight of insects, birds and bats. These new damping models offer a means to predict manoeuvrability and stability for a wide variety of flying animals using prior reports of the morphology and flapping motions of these species. Furthermore, the presence of passive damping is likely to have facilitated the evolution of powered flight in animals by providing a stability benefit associated with flapping.

Space shuttle orbit maneuvering engine reusable thrust chamber program

NASA Technical Reports Server (NTRS)

Senneff, J. M.

1975-01-01

Reusable thrust chamber and injector concepts were evaluated for the space shuttle orbit maneuvering engine (OME). Parametric engine calculations were carried out by computer program for N2O4/amine, LOX/amine and LOX/hydrocarbon propellant combinations for engines incorporating regenerative cooled and insulated columbium thrust chambers. The calculation methods are described including the fuel vortex film cooling method of combustion gas temperature control, and performance prediction. A method of acceptance of a regeneratively cooled heat rejection reduction using a silicone oil additive was also demonstrated by heated tube heat transfer testing. Regeneratively cooled thrust chamber operation was also demonstrated where the injector was characterized for the OME application with a channel wall regenerative thrust chamber. Bomb stability testing of the demonstration chambers/injectors demonstrated recovery for the nominal design of acoustic cavities. Cavity geometry changes were also evaluated to assess their damping margin. Performance and combustion stability was demonstrated of the originally developed 10 inch diameter combustion pattern operating in an 8 inch diameter thrust chamber.

Some Static Oscillatory and Free Body Tests of Blunt Bodies at Low Subsonic Speeds

NASA Technical Reports Server (NTRS)

Lichtenstein, Jacob H.; Fisher, Lewis R.; Scher, Stanley H.; Lawrence, George F.

1959-01-01

Some blunt-body shapes considered suitable for entry into the earth's atmosphere were tested by both static and oscillatory methods in the Langley stability tunnel. In addition, free-fall tests of some similar models were made in the Langley 20-foot free-spinning tunnel. The results of the tests show that increasing the flare of the body shape increased the dynamic stability and that for flat-faced shapes increasing the corner radius increased the stability. The test data from the Langley stability tunnel were used to compute the damping factor for the models tested in the langley 20-foot free-spinning tunnel. For these cases in which the damping factor was low, -1/2 or less, the stability was critical and sensitive to disturbance. When the damping factor was about -2, damping was generally obtained.

On the experimental prediction of the stability threshold speed caused by rotating damping

NASA Astrophysics Data System (ADS)

Vervisch, B.; Derammelaere, S.; Stockman, K.; De Baets, P.; Loccufier, M.

2016-08-01

An ever increasing demand for lighter rotating machinery and higher operating speeds results in a raised probability of instabilities. Rotating damping is one of the reasons, instability occurs. Rotating damping, or rotor internal damping, is the damping related to all rotating parts while non-rotating damping appearing in the non-rotating parts. The present study describes a rotating setup, designed to investigate rotating damping experimentally. An efficient experimental procedure is presented to predict the stability threshold of a rotating machine. The setup consists of a long thin shaft with a disk in the middle and clamped boundary conditions. The goal is to extract the system poles as a function of the rotating speed. The real parts of these poles are used to construct the decay rate plot, which is an indication for the stability. The efficiency of the experimental procedure relies on the model chosen for the rotating shaft. It is shown that the shaft behavior can be approximated by a single degree of freedom model that incorporates a speed dependent damping. As such low measurement effort and only one randomly chosen measurement location are needed to construct the decay rate plot. As an excitation, an automated impact hammer is used and the response is measured by eddy current probes. The proposed method yields a reliable prediction of the stability threshold speed which is validated through measurements.

Magnetic damping of thermocapillary convection in the floating-zone growth of semiconductor crystals

NASA Astrophysics Data System (ADS)

Morthland, Timothy Edward

The floating zone is one process used to grow high purity semiconductor single crystals. In the floating-zone process, a liquid bridge of molten semiconductor, or melt, is held by surface tension between the upper, melting polycrystalline feed rod and the lower, solidifying single crystal. A perfect crystal would require a quiescent melt with pure diffusion of dopants during the entire period needed to grow the crystal. However, temperature variations along the free surface of the melt lead to gradients of the temperature-dependent surface tension, driving a strong and unsteady flow in the melt, commonly labeled thermocapillary or Marangoni convection. For small temperature differences along the free surface, unsteady thermocapillary convection occurs, disrupting the diffusion controlled solidification and creating undesirable dopant concentration variations in the semiconductor single crystal. Since molten semiconductors are good electrical conductors, an externally applied, steady magnetic field can eliminate the unsteadiness in the melt and can reduce the magnitude of the residual steady motion. Crystal growers hope that a strong enough magnetic field will lead to diffusion controlled solidification, but the magnetic field strengths needed to damp the unsteady thermocapillary convection as a function of floating-zone process parameters is unknown. This research has been conducted in the area of the magnetic damping of thermocapillary convection in floating zones. Both steady and unsteady flows have been investigated. Due to the added complexities in solving Maxwells equations in these magnetohydrodynamic problems and due to the thin boundary layers in these flows, a direct numerical simulation of the fluid and heat transfer in the floating zone is virtually impossible, and it is certainly impossible to run enough simulations to search for neutral stability as a function of magnetic field strength over the entire parameter space. To circumvent these difficulties, we have used matched asymptotic expansions, linear stability theory and numerics to characterize these flows. Some fundamental aspects of the heat transfer and fluid mechanics in these magnetohydrodynamic flows are elucidated in addition to the calculation of the magnetic field strengths required to damp unsteady thermocapillary convection as a function of process parameters.

Damping seals for turbomachinery

NASA Technical Reports Server (NTRS)

Vonpragenau, G. L.

1985-01-01

Rotor whirl stabilization of high performance turbomachinery which operates at supercritical speed is discussed. Basic whirl driving forces are reviewed. Stabilization and criteria are discussed. Damping seals are offered as a solution to whirl and high vibration problems. Concept, advantages, retrofitting, and limits of damping seals are explained. Dynamic and leakage properties are shown to require a rough stator surface for stability and efficiency. Typical seal characteristics are given for the case of the high pressure oxidizer turbopump of the Space Shuttle. Ways of implementation and bearing load effects are discussed.

Enhanced Adhesion of EVA Laminates to Primed Glass Substrates Subjected to Damp-Heat Exposure

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pern, F. J.; Jorgensen, G. J.

2005-02-01

We investigated the effectiveness of glass-surface priming to promote enhanced adhesion of EVA laminates during damp-heat exposure at 85 C and 85% relative humidity. The primary objective was to develop advanced encapsulant formulations by incorporation of various primer formulations that exhibit improved adhesion during damp-heat exposure. Several primer formulations were identified that greatly enhanced the EVA adhesion strength, including to the extent that peeling could not be initiated, even for the laminates of the glass substrate/fast-cure EVA15295P/TPE backsheet (a Tedlar/polyester/EVA tri-laminate) that were exposed in a damp-heat test chamber for more than 750 h. The results show that a synergisticmore » increase in the interfacial hydrophobicity, siloxane density, and cross-linking density are the key attributes to the improvement in the EVA adhesion strength.« less

Solar coronal loop heating by cross-field wave transport

NASA Technical Reports Server (NTRS)

Amendt, Peter; Benford, Gregory

1989-01-01

Solar coronal arches heated by turbulent ion-cyclotron waves may suffer significant cross-field transport by these waves. Nonlinear processes fix the wave-propagation speed at about a tenth of the ion thermal velocity, which seems sufficient to spread heat from a central core into a large cool surrounding cocoon. Waves heat cocoon ions both through classical ion-electron collisions and by turbulent stochastic ion motions. Plausible cocoon sizes set by wave damping are in roughly kilometers, although the wave-emitting core may be only 100 m wide. Detailed study of nonlinear stabilization and energy-deposition rates predicts that nearby regions can heat to values intermediate between the roughly electron volt foot-point temperatures and the about 100 eV core, which is heated by anomalous Ohmic losses. A volume of 100 times the core volume may be affected. This qualitative result may solve a persistent problem with current-driven coronal heating; that it affects only small volumes and provides no way to produce the extended warm structures perceptible to existing instruments.

On the stability of motion of several types of heavy symmetric gyroscopes with damping torques

NASA Astrophysics Data System (ADS)

Ge, Z.-M.; Wu, M.-H.

Sufficient conditions for the stability of motion of several gyroscopes are obtained using Liapunov's direct method. The stability of a 'temporarily' sleeping top with damping torque is considered for the cases of the support being fixed, being in vertical harmonic motion, and being in vertical periodic motion. Sufficient conditions are also obtained for the stability of a heavy symmetric gyroscope with damping torque and motor torque for the cases of regular precession, vertical axis permanent rotation with and without the axis of the outer gimbal being inclined, and the gyroscope being in a Newtonian central gravitational field.

Estimation and Optimization of the Parameters Preserving the Lustre of the Fabrics

NASA Astrophysics Data System (ADS)

Prodanova, Krasimira

2009-11-01

The paper discusses the optimization of the continuance of the Damp-Heating Process of a steaming iron press machine, and the preserving of the lustre of the fabrics. In order to be obtained high qualitative damp-heating processing, it is necessary to monitor parameters such as temperature, damp, and pressure during the process. The purpose of the present paper is a mathematical model to be constructed that adequately describes the technological process using multivariate data analysis. It was established that the full factorial design of type 23 is not adequate. The research has proceeded with central rotatable design of experiment. The obtained model adequately describes the technological process of damp-heating treatment in the defined factor space. The present investigation is helpful to the technological improvement and modernization in sewing companies.

Factors Controlling Superelastic Damping Capacity of SMAs

NASA Astrophysics Data System (ADS)

Heller, L.; Šittner, P.; Pilch, J.; Landa, M.

2009-08-01

In this paper, questions linked to the practical use of superelastic damping exploiting stress-induced martensitic transformation for vibration damping are addressed. Four parameters, particularly vibration amplitude, prestrain, temperature of surroundings, and frequency, are identified as having the most pronounced influence on the superelastic damping. Their influence on superelastic damping of a commercially available superelastic NiTi wire was experimentally investigated using a self-developed dedicated vibrational equipment. Experimental results show how the vibration amplitude, frequency, prestrain, and temperature affect the capacity of a superelastic NiTi wire to dissipate energy of vibrations through the superelastic damping. A special attention is paid to the frequency dependence (i.e., rate dependence) of the superelastic damping. It is shown that this is nearly negligible in case the wire is in the thermal chamber controlling actively the environmental temperature. In case of wire exposed to free environmental temperature in actual damping applications, however, the superelastic damping capacity significantly decreases with increasing frequency. This was explained to be a combined effect of the heat effects affecting the mean wire temperature and material properties with the help of simulations using the heat equation coupled phenomenological SMA model.

Design, analysis, and testing of high frequency passively damped struts

NASA Technical Reports Server (NTRS)

Yiu, Y. C.; Davis, L. Porter; Napolitano, Kevin; Ninneman, R. Rory

1993-01-01

Objectives of the research are: (1) to develop design requirements for damped struts to stabilize control system in the high frequency cross-over and spill-over range; (2) to design, fabricate and test viscously damped strut and viscoelastically damped strut; (3) to verify accuracy of design and analysis methodology of damped struts; and (4) to design and build test apparatus, and develop data reduction algorithm to measure strut complex stiffness. In order to meet the stringent performance requirements of the SPICE experiment, the active control system is used to suppress the dynamic responses of the low order structural modes. However, the control system also inadvertently drives some of the higher order modes unstable in the cross-over and spill-over frequency range. Passive damping is a reliable and effective way to provide damping to stabilize the control system. It also improves the robustness of the control system. Damping is designed into the SPICE testbed as an integral part of the control-structure technology.

Delay of Transition Using Forced Damping

NASA Technical Reports Server (NTRS)

Exton, Reginald J.

2014-01-01

Several experiments which have reported a delay of transition are analyzed in terms of the frequencies of the induced disturbances generated by different flow control elements. Two of the experiments employed passive stabilizers in the boundary layer, one leading-edge bluntness, and one employed an active spark discharge in the boundary layer. It is found that the frequencies generated by the various elements lie in the damping region of the associated stability curve. It is concluded that the creation of strong disturbances in the damping region stabilizes the boundary-layer and delays the transition from laminar to turbulent flow.

Development of Damp-Heat Resistant Self-Primed EVA and Non-EVA Encapsulant Formulations at NREL

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pern, F. J.; Jorgensen, G. J.

2005-11-01

Self-primed ethylene-vinyl acetate (EVA) and non-EVA (PMG) encapsulant formulations were developed that have greater resistance to damp heat exposure at 85 deg C and 85% relative humidity (RH) (in terms of adhesion strength to glass substrates) than a commonly used commercial EVA product. The self-primed EVA formulations were developed on the basis of high-performing glass priming formulations that have previously proven to significantly enhance the adhesion strength of unprimed and primed EVA films on glass substrates during damp heat exposure. The PMG encapsulant formulations were based on an ethylene-methylacrylate copolymer containing glycidyl methacrylate.

Quasi-linear heating and acceleration in bi-Maxwellian plasmas

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hellinger, Petr; Passot, Thierry; Sulem, Pierre-Louis

2013-12-15

Quasi-linear acceleration and heating rates are derived for drifting bi-Maxwellian distribution functions in a general nonrelativistic case for arbitrary wave vectors, propagation angles, and growth/damping rates. The heating rates in a proton-electron plasma due to ion-cyclotron/kinetic Alfvén and mirror waves for a wide range of wavelengths, directions of propagation, and growth or damping rates are explicitly computed.

A Numerical Study of 2-D Surface Roughness Effects on the Growth of Wave Modes in Hypersonic Boundary Layers

NASA Astrophysics Data System (ADS)

Fong, Kahei Danny

The current understanding and research efforts on surface roughness effects in hypersonic boundary-layer flows focus, almost exclusively, on how roughness elements trip a hypersonic boundary layer to turbulence. However, there were a few reports in the literature suggesting that roughness elements in hypersonic boundary-layer flows could sometimes suppress the transition process and delay the formation of turbulent flow. These reports were not common and had not attracted much attention from the research community. Furthermore, the mechanisms of how the delay and stabilization happened were unknown. A recent study by Duan et al. showed that when 2-D roughness elements were placed downstream of the so-called synchronization point, the unstable second-mode wave in a hypersonic boundary layer was damped. Since the second-mode wave is typically the most dangerous and dominant unstable mode in a hypersonic boundary layer for sharp geometries at a zero angle of attack, this result has pointed to an explanation on how roughness elements delay transition in a hypersonic boundary layer. Such an understanding can potentially have significant practical applications for the development of passive flow control techniques to suppress hypersonic boundary-layer transition, for the purpose of aero-heating reduction. Nevertheless, the previous study was preliminary because only one particular flow condition with one fixed roughness parameter was considered. The study also lacked an examination on the mechanism of the damping effect of the second mode by roughness. Hence, the objective of the current research is to conduct an extensive investigation of the effects of 2-D roughness elements on the growth of instability waves in a hypersonic boundary layer. The goal is to provide a full physical picture of how and when 2-D roughness elements stabilize a hypersonic boundary layer. Rigorous parametric studies using numerical simulation, linear stability theory (LST), and parabolized stability equation (PSE) are performed to ensure the fidelity of the data and to study the relevant flow physics. All results unanimously confirm the conclusion that the relative location of the synchronization point with respect to the roughness element determines the roughness effect on the second mode. Namely, a roughness placed upstream of the synchronization point amplifies the unstable waves while placing a roughness downstream of the synchronization point damps the second-mode waves. The parametric study also shows that a tall roughness element within the local boundary-layer thickness results in a stronger damping effect, while the effect of the roughness width is relatively insignificant compared with the other roughness parameters. On the other hand, the fact that both LST and PSE successfully predict the damping effect only by analyzing the meanflow suggests the mechanism of the damping is by the meanflow alteration due to the existence of roughness elements, rather than new mode generation. In addition to studying the unstable waves, the drag force and heating with and without roughness have been investigated by comparing the numerical simulation data with experimental correlations. It is shown that the increase in drag force generated by the Mach wave around a roughness element in a hypersonic boundary layer is insignificant compared to the reduction of drag force by suppressing turbulent flow. The study also shows that, for a cold wall flow which is the case for practical flight applications, the Stanton number decreases as roughness elements smooth out the temperature gradient in the wall-normal direction. Based on the knowledge of roughness elements damping the second mode gained from the current study, a novel passive transition control method using judiciously placed roughness elements has been developed, and patented, during the course of this research. The main idea of the control method is that, with a given geometry and flow condition, it is possible to find the most unstable second-mode frequency that can lead to transition. And by doing a theoretical analysis such as LST, the synchronization location for the most unstable frequency can be found. Roughness elements are then strategically placed downstream of the synchronization point to damp out this dangerous second-mode wave, thus stabilizing the boundary layer and suppressing the transition process. This method is later experimentally validated in Purdue's Mach 6 quiet wind tunnel. Overall, this research has not only provided details of when and how 2-D roughness stabilizes a hypersonic boundary layer, it also has led to a successful application of numerical simulation data to the development of a new roughness-based transition delay method, which could potentially have significant contributions to the design of future generation hypersonic vehicles.

Computational study of elements of stability of a four-helix bundle protein biosurfactant

NASA Astrophysics Data System (ADS)

Schaller, Andrea; Connors, Natalie K.; Dwyer, Mirjana Dimitrijev; Oelmeier, Stefan A.; Hubbuch, Jürgen; Middelberg, Anton P. J.

2015-01-01

Biosurfactants are surface-active molecules produced principally by microorganisms. They are a sustainable alternative to chemically-synthesized surfactants, having the advantages of being non-toxic, highly functional, eco-friendly and biodegradable. However they are currently only used in a few industrial products due to costs associated with production and purification, which exceed those for commodity chemical surfactants. DAMP4, a member of a four-helix bundle biosurfactant protein family, can be produced in soluble form and at high yield in Escherichia coli, and can be recovered using a facile thermal phase-separation approach. As such, it encompasses an interesting synergy of biomolecular and chemical engineering with prospects for low-cost production even for industrial sectors. DAMP4 is highly functional, and due to its extraordinary thermal stability it can be purified in a simple two-step process, in which the combination of high temperature and salt leads to denaturation of all contaminants, whereas DAMP4 stays stable in solution and can be recovered by filtration. This study aimed to characterize and understand the fundamental drivers of DAMP4 stability to guide further process and surfactant design studies. The complementary use of experiments and molecular dynamics simulation revealed a broad pH and temperature tolerance for DAMP4, with a melting point of 122.4 °C, suggesting the hydrophobic core as the major contributor to thermal stability. Simulation of systematically created in silico variants of DAMP4 showed an influence of number and location of hydrophilic mutations in the hydrophobic core on stability, demonstrating a tolerance of up to three mutations before a strong loss in stability occurred. The results suggest a consideration of a balance of stability, functionality and kinetics for new designs according to their application, aiming for maximal functionality but at adequate stability to allow for cost-efficient production using thermal phase separation approaches.

Improved Power System Stability Using Backtracking Search Algorithm for Coordination Design of PSS and TCSC Damping Controller.

PubMed

Niamul Islam, Naz; Hannan, M A; Mohamed, Azah; Shareef, Hussain

2016-01-01

Power system oscillation is a serious threat to the stability of multimachine power systems. The coordinated control of power system stabilizers (PSS) and thyristor-controlled series compensation (TCSC) damping controllers is a commonly used technique to provide the required damping over different modes of growing oscillations. However, their coordinated design is a complex multimodal optimization problem that is very hard to solve using traditional tuning techniques. In addition, several limitations of traditionally used techniques prevent the optimum design of coordinated controllers. In this paper, an alternate technique for robust damping over oscillation is presented using backtracking search algorithm (BSA). A 5-area 16-machine benchmark power system is considered to evaluate the design efficiency. The complete design process is conducted in a linear time-invariant (LTI) model of a power system. It includes the design formulation into a multi-objective function from the system eigenvalues. Later on, nonlinear time-domain simulations are used to compare the damping performances for different local and inter-area modes of power system oscillations. The performance of the BSA technique is compared against that of the popular particle swarm optimization (PSO) for coordinated design efficiency. Damping performances using different design techniques are compared in term of settling time and overshoot of oscillations. The results obtained verify that the BSA-based design improves the system stability significantly. The stability of the multimachine power system is improved by up to 74.47% and 79.93% for an inter-area mode and a local mode of oscillation, respectively. Thus, the proposed technique for coordinated design has great potential to improve power system stability and to maintain its secure operation.

Measurement of the Static Stability and Control and the Damping Derivatives of a 0.13-Scale Model of the Convair XFY-1 Airplane, TED No. NACA DE 368

NASA Technical Reports Server (NTRS)

Johnson, Joseph L.

1954-01-01

An investigation has been conducted to determine the static stability and control and damping in roll and yaw of a 0.13-scale model of the Convair XFY-1 airplane with propellers off from 0 deg to 90 deg angle of attack. The tests showed that a slightly unstable pitch-up tendency occurred simultaneously with a break in the normal-force curve in the angle-of-attack range from about 27 deg to 36 deg. The top vertical tail contributed positive values of static directional stability and effective dihedral up to an angle of attack of about 35 deg. The bottom tail contributed positive values of static directional stability but negative values of effective dihedral throughout the angle-of-attack range. Effectiveness of the control surfaces decreased to very low values at the high angles of attack, The model had positive damping in yaw and damping in roll about the body axes over the angle-of-attack range but the damping in yaw decreased to about zero at 90 deg angle of attack.

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.

Wave propagation in elastic and damped structures with stabilized negative-stiffness components

NASA Astrophysics Data System (ADS)

Drugan, W. J.

2017-09-01

Effects on wave propagation achievable by introduction of a negative-stiffness component are investigated via perhaps the simplest discrete repeating element that can remain stable in the component's presence. When the system is elastic, appropriate tuning of the stabilized component's negative stiffness introduces a no-pass zone theoretically extending from zero to an arbitrarily high frequency, tunable by a mass ratio adjustment. When the negative-stiffness component is tuned to the system's stability limit and a mass ratio is sufficiently small, the system restricts propagation to waves of approximately a single arbitrary frequency, adjustable by tuning the stiffness ratio of the positive-stiffness components. The elastic system's general solutions are closed-form and transparent. When damping is added, the general solutions are still closed-form, but so complex that they do not clearly display how the negative stiffness component affects the system's response and how it should best be tuned to achieve desired effects. Approximate solutions having these features are obtained via four perturbation analyses: one for long wavelengths; one for small damping; and two for small mass ratios. The long-wavelengths solution shows that appropriate tuning of the negative-stiffness component can prevent propagation of long-wavelength waves. The small damping solution shows that the zero-damping low-frequency no-pass zone remains, while waves that do propagate are highly damped when a mass ratio is made small. Finally, very interesting effects are achievable at the full system's stability limit. For small mass ratios, the wavelength range of waves prohibited from propagation can be adjusted, from all to none, by tuning the system's damping: When one mass ratio is small, all waves with wavelengths larger than an arbitrary damping-adjusted value can be prohibited from propagation, while when the inverse of this mass ratio is small, all waves with wavelengths outside an arbitrary single adjustable value or range of values can be prohibited from propagation. All of the approximate solutions' analytically-transparent predictions are confirmed by the exact solution. The conclusions are that a stabilized tuned negative-stiffness component greatly enhances control of wave propagation in a purely elastic system, and when adjustable damping is added, even further control is facilitated.

Resonant Vibrations and Vibrational Heating of Physically Nonlinear Viscoelastic Shells and Their Damping Using Piezoelectric Sensor and Actuator

NASA Astrophysics Data System (ADS)

Kirichok, I. F.

2017-09-01

Forced axisymmetric resonant vibrations and vibrational heating of viscoelastic, physically nonlinear, closed, spherical, and infinitely long cylindrical shells and ring with piezoelectric sensor and actuator are considered. The effect of physical nonlinearity of passive material on the vibration amplitude and vibrational heating temperature is studied. The possibility of active damping of vibrations by piezoelectric sensors and actuators is demonstrated.

Hybrid passive/active damping for robust multivariable acoustic control in composite plates

NASA Astrophysics Data System (ADS)

Veeramani, Sudha; Wereley, Norman M.

1996-05-01

Noise transmission through a flexible kevlar-epoxy composite trim panel into an acoustic cavity or box is studied with the intent of controlling the interior sound fields. A hybrid noise attenuation technique is proposed which uses viscoelastic damping layers in the composite plate for passive attenuation of high frequency noise transmission, and uses piezo-electric patch actuators for active control in the low frequency range. An adaptive feedforward noise control strategy is applied. The passive structural damping augmentation incorporated in the composite plates is also intended to increase stability robustness of the active noise control strategy. A condenser microphone in the interior of the enclosure functions as the error sensor. Three composite plates were experimentally evaluated: one with no damping layer, the second with a 10 mil damping layer, and the third with a 15 mil damping layer. The damping layer was cocured in the kevlar-epoxy trim panels. Damping in the plates was increased from 1.6% for the plate with no damping layer, to 5.9% for the plate with a 15 mil damping layer. In experimental studies, the improved stability robustness of the controller was demonstrated by improved adaptive feedforward control algorithm convergence. A preliminary analytical model is presented that describes the dynamic behavior of a composite panel actuated by piezoelectric actuators bonded to its surface.

Cyclic Strain Amplitude and Heat Treatment Effects on the High Damping Behavior of INCRAMUTE Alloy under Random Vibration Loading in the 50-1000 Hz Frequency Range

DTIC Science & Technology

1986-09-01

for each mode and heat treament condition are plotted versus the average peak strain, £_) ea ^. in Figures 4.10, 4.11, and 4.12. For Mode 1 resonance...specimen reversed its relative position to the other heat treament conditions (i.e., it showed the lowest damping levels in Modes 2 and 3). However, as...LATTICE PARAMETERS FOR EACH HEAT TREATMENT CONDITION OF INCRAMUTE Heat Treament Lattice Parameter (Angstrons) AQ 3.7484 1 Hour Age 3.737864 2 Hour Age

Dynamic Longitudinal and Directional Stability Derivatives for a 45 deg. Sweptback-Wing Airplane Model at Transonic Speeds

NASA Technical Reports Server (NTRS)

Bielat, Ralph P.; Wiley, Harleth G.

1959-01-01

An investigation was made at transonic speeds to determine some of the dynamic stability derivatives of a 45 deg. sweptback-wing airplane model. The model was sting mounted and was rigidly forced to perform a single-degree-of-freedom angular oscillation in pitch or yaw of +/- 2 deg. The investigation was made for angles of attack alpha, from -4 deg. to 14 deg. throughout most of the transonic speed range for values of reduced-frequency parameter from 0.015 to 0.040 based on wing mean aerodynamic chord and from 0.04 to 0.14 based on wing span. The results show that reduced frequency had only a small effect on the damping-in-pitch derivative and the oscillatory longitudinal stability derivative for all Mach numbers M and angles of attack with the exception of the values of damping coefficient near M = 1.03 and alpha = 8 deg. to 14 deg. In this region, the damping coefficient changed rapidly with reduced frequency and negative values of damping coefficient were measured at low values of reduced frequency. This abrupt variation of pitch damping with reduced frequency was a characteristic of the complete model or wing-body-vertical-tail combination. The damping-in-pitch derivative varied considerably with alpha and M for the horizontal-tail-on and horizontal-tail-off configurations, and the damping was relatively high at angles of attack corresponding to the onset of pitch-up for both configurations. The damping-in-yaw derivative was generally independent of reduced frequency and M at alpha = -4 deg. to 4 deg. At alpha = 8 deg. to 14 deg., the damping derivative increased with an increase in reduced frequency and alpha for the configurations having the wing, whereas the damping derivative was either independent of or decreased with increase in reduced frequency for the configuration without the wing. The oscillatory directional stability derivative for all configurations generally decreased with an increase in the reduced-frequency parameter, and, in some instances, unstable values were measured for the model configuration with the horizontal tail removed.

Chatter reduction in boring process by using piezoelectric shunt damping with experimental verification

NASA Astrophysics Data System (ADS)

Yigit, Ufuk; Cigeroglu, Ender; Budak, Erhan

2017-09-01

Chatter is a self-excited type of vibration that develops during machining due to process-structure dynamic interactions resulting in modulated chip thickness. Chatter is an important problem as it results in poor surface quality, reduced productivity and tool life. The stability of a cutting process is strongly influenced by the frequency response function (FRF) at the cutting point. In this study, the effect of piezoelectric shunt damping on chatter vibrations in a boring process is studied. In piezoelectric shunt damping method, an electrical impedance is connected to a piezoelectric transducer which is bonded on cutting tool. Electrical impedance of the circuit consisting of piezoceramic transducer and passive shunt is tuned to the desired natural frequency of the cutting tool in order to maximize damping. The optimum damping is achieved in analytical and finite element models (FEM) by using a genetic algorithm focusing on the real part of the tool point FRF rather than the amplitude. Later, a practical boring bar is considered where the optimum circuit parameters are obtained by the FEM. Afterwards, the effect of the optimized piezoelectric shunt damping on the dynamic rigidity and absolute stability limit of the cutting process are investigated experimentally by modal analysis and cutting tests. It is both theoretically and experimentally shown that application of piezoelectric shunt damping results in a significant increase in the absolute stability limit in boring operations.

Combined effects of trapped energetic ions and resistive layer damping on the stability of the resistive wall mode

DOE Office of Scientific and Technical Information (OSTI.GOV)

He, Yuling; Liu, Yue, E-mail: Yueqiang.Liu@ccfe.ac.uk, E-mail: liuyue@dlut.edu.cn; Liu, Chao

2016-01-15

A dispersion relation is derived for the stability of the resistive wall mode (RWM), which includes both the resistive layer damping physics and the toroidal precession drift resonance damping from energetic ions in tokamak plasmas. The dispersion relation is numerically solved for a model plasma, for the purpose of systematic investigation of the RWM stability in multi-dimensional plasma parameter space including the plasma resistivity, the radial location of the resistive wall, as well as the toroidal flow velocity. It is found that the toroidal favorable average curvature in the resistive layer contributes a significant stabilization of the RWM. This stabilizationmore » is further enhanced by adding the drift kinetic contribution from energetic ions. Furthermore, two traditionally assumed inner layer models are considered and compared in the dispersion relation, resulting in different predictions for the stability of the RWM.« less

Subsonic and transonic dynamic stability characteristics of the space shuttle launch vehicle

NASA Technical Reports Server (NTRS)

Freeman, D. C., Jr.; Boyden, R. P.; Davenport, E. E.

1976-01-01

An investigation has been conducted to determine the subsonic and transonic dynamic stability characteristics of a 0.015 scale model of the space shuttle launch vehicle. These tests were conducted in the Langley 8-foot transonic pressure tunnel over a Mach number range from 0.3 to 1.2. Forced oscillation equipment was used to determine the damping characteristics of several configurations about all three axes. The test results show that the model exhibited positive damping in pitch except at the highest Mach number (1.2) where there was a region of negative damping at 2 deg angle of attack. The yawing oscillation tests show that the model exhibited nonlinearities and negative damping at Mach numbers of 0.3 and 0.6. The model exhibited positive roll damping throughout the test angle of attack and Mach range.

Magnetic Damping For Maglev

DOE PAGES

Zhu, S.; Cai, Y.; Rote, D. M.; ...

1998-01-01

Magnetic damping is one of the important parameters that control the response and stability of maglev systems. An experimental study to measure magnetic damping directly is presented. A plate attached to a permanent magnet levitated on a rotating drum was tested to investigate the effect of various parameters, such as conductivity, gap, excitation frequency, and oscillation amplitude, on magnetic damping. The experimental technique is capable of measuring all of the magnetic damping coefficients, some of which cannot be measured indirectly.

Wave propagation and noncollisional heating in neutral loop and helicon discharges

DOE Office of Scientific and Technical Information (OSTI.GOV)

Celik, Y.; Crintea, D. L.; Luggenhoelscher, D.

2011-02-15

Heating mechanisms in two types of magnetized low pressure rf (13.56 MHz) discharges are investigated: a helicon discharge and a neutral loop discharge. Radial B-dot probe measurements demonstrate that the neutral loop discharge is sustained by helicon waves as well. Axial B-dot probe measurements reveal standing wave and beat patterns depending on the dc magnetic field strength and plasma density. In modes showing a strong wave damping, the plasma refractive index attains values around 100, leading to electron-wave interactions. In strongly damped modes, the radial plasma density profiles are mainly determined by power absorption of the propagating helicon wave, whereasmore » in weakly damped modes, inductive coupling dominates. Furthermore, an azimuthal diamagnetic drift is identified. Measurements of the helicon wave phase demonstrate that initial plane wave fronts are bent during their axial propagation due to the inhomogeneous density profile. A developed analytical standing wave model including Landau damping reproduces very well the damping of the axial helicon wave field. This comparison underlines the theory whereupon Landau damping of electrons traveling along the field lines at speeds close to the helicon phase velocity is the main damping mechanism in both discharges.« less

Practical Methodology for the Inclusion of Nonlinear Slosh Damping in the Stability Analysis of Liquid-Propelled Space Vehicles

NASA Technical Reports Server (NTRS)

Ottander, John A.; Hall, Robert A.; Powers, Joseph F.

2017-01-01

One of the challenges of developing flight control systems for liquid-propelled space vehicles is ensuring stability and performance in the presence of parasitic minimally damped slosh dynamics in the liquid propellants. This can be especially difficult when the fundamental frequencies of the slosh motions are in proximity to the frequency used for vehicle control. The challenge is partially alleviated since the energy dissipation and effective damping in the slosh modes increases with amplitude. However, traditional launch vehicle control design methodology is performed with linearized systems using a fixed slosh damping corresponding to a slosh motion amplitude based on heritage values. This papers presents a method for performing the control design and analysis using damping at slosh amplitudes chosen based on the resulting limit cycle amplitude of the vehicle thrust vector system due to a control-slosh interaction under degraded phase and gain margin conditions.

Practical Methodology for the Inclusion of Nonlinear Slosh Damping in the Stability Analysis of Liquid-propelled Space Vehicles

NASA Technical Reports Server (NTRS)

Ottander, John A.; Hall, Robert A., Jr.; Powers, Joseph F.

2017-01-01

One of the challenges of developing flight control systems for liquid-propelled space vehicles is ensuring stability and performance in the presence of parasitic minimally damped slosh dynamics in the liquid propellants. This can be especially difficult when the fundamental frequencies of the slosh motions are in proximity to the frequency used for vehicle control. The challenge is partially alleviated since the energy dissipation and effective damping in the slosh modes increases with amplitude. However, traditional launch vehicle control design methodology is performed with linearized systems using a fixed slosh damping corresponding to a slosh motion amplitude based on heritage values. This papers presents a method for performing the control design and analysis using damping at slosh amplitudes chosen based on the resulting limit cycle amplitude of the vehicle thrust vector system due to a control-slosh interaction under degraded phase and gain margin conditions.

The stability of a class of synchronous generator damping model

NASA Astrophysics Data System (ADS)

Liu, Jun

2018-03-01

Electricity is indispensable to modern society and the most convenient energy, it can be easily transformed into other forms of energy, has been widely used in engineering, transportation and so on, this paper studied the generator model with damping machine, using the Lyapunov function method, we obtain sufficient conditions for the asymptotic stability of the model.

Experimental Equipment for Damping Capacity Analyze of High or Low Internal Friction Metallic Materials

NASA Astrophysics Data System (ADS)

Gârnet, I. A.; Stanciu, S.; Hopulele, I.; Zaharia, M. G.; Cimpoesu, N.; Chicet, D. L.; Crăciun, R. C.

2017-06-01

An experimental equipment, type torsion pendulum was made in laboratory in order to analyze the damping capacity of metallic materials. The scheme of the equipment is presented, 2D and 3D visions at real scale. The equipment functioning (mechanical and electrical part) and principles are presented. In this article we present some preliminary experimental results obtained on different materials (aluminium, steel etc.) using two different methods for registration the outputs (one based on optoelectronic device with Arduino acquisition board and second on video analyze (cinematic review: video to jpeg) of the damped motion of the lead pendulum). Steel materials were with shoot penning surface modification with and without heat treatment in order to establish the heat treatment influence on the damping capacity property.

Tuned dynamics stabilizes an idealized regenerative axial-torsional model of rotary drilling

NASA Astrophysics Data System (ADS)

Gupta, Sunit K.; Wahi, Pankaj

2018-01-01

We present an exact stability analysis of a dynamical system idealizing rotary drilling. This system comprises lumped parameter axial-torsional modes of the drill-string coupled via the cutting forces and torques. The kinematics of cutting is modeled through a functional description of the cut surface which evolves as per a partial differential equation (PDE). Linearization of this model is straightforward as opposed to the traditional state-dependent delay (SDDE) model and both the approaches result in the same characteristic equation. A systematic study on the key system parameters influencing the stability characteristics reveals that torsional damping is very critical and stable drilling is, in general, not possible in its absence. The stable regime increases as the natural frequency of the axial mode approaches that of the torsional mode and a 1:1 internal resonance leads to a significant improvement in the system stability. Hence, from a practical point of view, a drill-string with 1:1 internal resonance is desirable to avoid vibrations during rotary drilling. For the non-resonant case, axial damping reduces the stable range of operating parameters while for the resonant case, an optimum value of axial damping (equal to the torsional damping) results in the largest stable regime. Interestingly, the resonant (tuned) system has a significant parameter regime corresponding to stable operation even in the absence of damping.

Model based PI power system stabilizer design for damping low frequency oscillations in power systems.

PubMed

Salgotra, Aprajita; Pan, Somnath

2018-05-01

This paper explores a two-level control strategy by blending local controller with centralized controller for the low frequency oscillations in a power system. The proposed control scheme provides stabilization of local modes using a local controller and minimizes the effect of inter-connection of sub-systems performance through a centralized control. For designing the local controllers in the form of proportional-integral power system stabilizer (PI-PSS), a simple and straight forward frequency domain direct synthesis method is considered that works on use of a suitable reference model which is based on the desired requirements. Several examples both on one machine infinite bus and multi-machine systems taken from the literature are illustrated to show the efficacy of the proposed PI-PSS. The effective damping of the systems is found to be increased remarkably which is reflected in the time-responses; even unstable operation has been stabilized with improved damping after applying the proposed controller. The proposed controllers give remarkable improvement in damping the oscillations in all the illustrations considered here and as for example, the value of damping factor has been increased from 0.0217 to 0.666 in Example 1. The simulation results obtained by the proposed control strategy are favourably compared with some controllers prevalent in the literature. Copyright © 2018 ISA. Published by Elsevier Ltd. All rights reserved.

A Study of Alfven Wave Propagation and Heating the Chromosphere

NASA Astrophysics Data System (ADS)

Tu, J.; Song, P.

2013-12-01

Alfven wave propagation, reflection and heating of the solar atmosphere are studied for a one-dimensional solar atmosphere by self-consistently solving plasma and neutral fluid equations and Maxwell's equations with incorporation of the Hall effect, strong electron-neutral, electron-ion, and ion-neutral collisions. The governing equations are very stiff because of the strong coupling between the charged and neutral fluids. We have developed a numerical model based on an implicit backward difference formula (BDF2) of second order accuracy both in time and space to overcome the stiffness. A non-reflecting boundary condition is applied to the top boundary of the simulation domain so that the wave reflection within the domain due to the density gradient can be unambiguously determined. It is shown that the Alfven waves are partially reflected throughout the chromosphere. The reflection is increasingly stronger at higher altitudes and the strongest reflection occurs at the transition region. The waves are damped in the lower chromosphere dominantly through Joule dissipation due to electron collisions with neutrals and ions. The heating resulting from the wave damping is strong enough to balance the radiation energy loss for the quiet chromosphere. The collisional dissipation of the Alfven waves in the weakly collisional corona is negligible. The heating rates are larger for weaker background magnetic fields. In addition, higher frequency waves are subject to heavier damping. There is an upper cutoff frequency, depending on the background magnetic field, above which the waves are completely damped. At the frequencies below which the waves are not strongly damped, the waves may be strongly reflected at the transition region. The reflected waves interacting with the upward propagating waves may produce power at their double frequencies, which leads to more damping. Due to the reflection and damping, the energy flux of the waves transmitted to the corona is one order of magnitude smaller than that of the driving source.

Thermoelastic damping effect of the micro-ring resonator with irregular mass and stiffness

NASA Astrophysics Data System (ADS)

Kim, Jung-Hwan; Kim, Ji-Hwan

2016-05-01

Fundamentally, vibration characteristic is a main factor for the stability of structures. In this regard, the irregularity of mass and stiffness distributions for the structure have been an interesting issue for many years. Recently, the Micro Electro Mechanical Systems (MEMS) are developed for various applications such as gyro sensors. In the present work, in-plane vibration of micro-ring structure with multiple finite-sized imperfections is investigated. Then, the unbalance of the structure is represented using Heaviside Step Function for the inextensional modeling of the ring. Also, thermoelastic damping (TED) due to internal friction is studied based on Fourier's one-dimensional heat conduction equation using Laplace Transform. To obtain the quality-factors (Q-factors) for imperfect micro-ring, analytical solutions are calculated from governing equations of motion with TED. And then, the natural frequencies and the Q-factors are observed to separate into lower and higher modes. Additionally, the vibration mode shapes are presented, and the frequency trimming concept due to attached imperfections is investigated.

Properties of Alfven Eigenmodes in the TAE range on the National Spherical Torus Experiment-Upgrade

DOE Office of Scientific and Technical Information (OSTI.GOV)

None

2013-04-24

A second Neutral Beam (NB) injection line is being installed on the NSTX Upgrade device, resulting in six NB sources with di erent tangency radii that will be available for heating and current drive. This work explores the properties of instabilities in the frequency range of the Toroidal Alfv en Eigenmode (TAE) for NSTX-U scenarios with various NB injection geometries, from more perpendicular to more tangential, and with increased toroidal magnetic eld with respect to previous NSTX scenarios. Predictions are based on analysis through the ideal MHD code NOVA-K. For the scenarios considered in this work, modi cations of themore » Alfv en continuum result in a frequency upshift and a broadening of the radial mode structure. The latter e ect may have consequences for fast ion transport and loss. Preliminary stability considerations indicate that TAEs are potentially unstable, with ion Landau damping representing the dominant damping mechanism« less

Steady-state sinusoidal behavior of elastomeric dampers

NASA Astrophysics Data System (ADS)

Madhavan, Vijay; Wereley, Norman M.; Sieg, Thierry

1999-06-01

This paper presents an experimental and analytical investigation of an elastomeric damping material and assesses its potential application to stability augmentation of hingeless and bearingless helicopter rotors. Double lap shear specimens were tested on a servo-hydraulic testing machine. Single frequency sinusoidal tests were conducted over a strain amplitude range of 0 - 30% at three frequencies (lag/rev, 1/rev and a lower harmonic of the rotor). The frequencies were chosen such that the effect of the damper in mitigating instability phenomena, like ground and air resonance, could be analyzed. The effects of frequency, amplitude, pre-load and material self-heating were studied. A three-element mechanisms-based damper model was developed that accurately captures the energy dissipation and hysteresis behavior of the damper. The model incorporates a linear stiffness, viscous damping and a non-linear slip element that are placed in parallel to each other. The parameters of the model were identified using an LMS technique. The model was validated by reconstructing measured hysteresis cycles using these parameters.

SU-E-T-410: Fringe Stability and Phase Shift Measurements in a Michelson Interferometer for Optical Calorimetry

DOE Office of Scientific and Technical Information (OSTI.GOV)

Flores-Martinez, E; Malin, M; DeWerd, L

2014-06-01

Purpose: To identify the variables limiting the resolution of a Michelson interferometer used to measure phase shifts (PS) in water as part of a radiometric calorimeter. Methods: We investigated the output stability of a He-Ne laser and a laser diode. The short and long term stability of the fringe pattern in a Michelson interferometer was tested with different types of lasers, thermal insulation arrangements, damping systems and optical mounts to optimize system performance. PS were induced by electrically heating water in a 1 cm quartz cuvette located in one of the interferometer arms. The PS was calculated from fringe intensitymore » changes and compared to a calculated PS using thermocouple-measured temperature changes in the water. Results: The intensity of the laser diode is more stable, but the gas laser’s profile is more suitable for fringe analysis and has better temporal coherence. The laser requires a warm-up time of 4 hours before its output is stabilized (SNR>95). The fringe’s stability strongly depends on the thermal insulation. When the interferometer is exposed to ambient temperature swings of 0.7 K, it is not possible to stabilize the fringe pattern. Enclosing the system in a 2.5 cm-thick Styrofoam box improves the SNR, but further insulation will be needed to increase the SNR above 50. High frequency noise is significantly reduced by damping the system.Inducing a temperature rise in water, starting at 299 K, the average temperature increase for a 2π PS is 0.29 ± 0.02 K and the proportionality constant is -21.1 ± 0.8 radians/K. This is 5.8% lower than the calculated value using the thermocouple. Conclusion: Interferometric PS measurements of temperature may provide an alternative to thermistors for water calorimetry. The resolution of the current prototype is limited by ambient temperature stability. Calculated and measured thermally-induced PS in water agreed to within 5.8%.« less

Translational damping on high-frequency flapping wings

NASA Astrophysics Data System (ADS)

Parks, Perry A.

Flapping fliers such as insects and birds depend on passive translational and rotational damping to terminate quick maneuvers and to provide a source of partial stability in an otherwise unstable dynamic system. Additionally, passive translational and rotational damping reduce the amount of active kinematic changes that must be made to terminate maneuvers and maintain stability. The study of flapping-induced damping phenomena also improves the understanding of micro air vehicle (MAV) dynamics needed for the synthesis of effective flight control strategies. Aerodynamic processes which create passive translational and rotational damping as a direct result of symmetric flapping with no active changes in wing kinematics have been previously studied and were termed flapping counter-force (FCF) and flapping counter-torque (FCT), respectively. In this first study of FCF measurement in air, FCF generation is measured using a pendulum system designed to isolate and measure the relationship of translational flapping-induced damping with wingbeat frequency for a 2.86 gram mechanical flapper equipped with real cicada wings. Analysis reveals that FCF generation and wingbeat frequency are directly proportional, as expected from previous work. The quasi-steady FCF model using Blade-Element-Theory is used as an estimate for translational flapping-induced damping. In most cases, the model proves to be accurate in predicting the relationship between flapping-induced damping and wingbeat frequency. "Forward-backward" motion proves to have the strongest flapping-induced damping while "up-down" motion has the weakest.

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.

Two methods for damping torsional vibrations in DFIG-based wind generators using power converters

NASA Astrophysics Data System (ADS)

Zhao, Zuyi; Lu, Yupu; Xie, Da; Yu, Songtao; Wu, Wangping

2017-01-01

This paper proposes novel damping control algorithms by using static synchronous compensator (STATCOM) and energy storage system (ESS) to damp torsional vibrations in doubly fed induction generator (DFIG) based wind turbine systems. It first analyses the operating characteristics of STATCOM and ESS for regulating power variations to increase grid voltage stability. Then, new control strategies for STATCOM and ESS are introduced to damp the vibrations. It is followed by illustration of their effectiveness to damp the drive train torsional vibrations of wind turbines, which can be caused by grid disturbances, such as voltage sags and frequency fluctuations. Results suggest that STATCOM is a promising technology to mitigate the torsional vibrations caused by grid voltage sags. By contrast, the ESS connected to the point of common coupling (PCC) of wind turbine systems shows even obvious advantages because of its capability of absorbing/releasing both active and reactive power. It can thus be concluded that STATCOM is useful for stabilizing power system voltage fluctuations, and ESS is more effective both in regulating PCC voltage fluctuations and damping torsional vibrations caused by grid voltage frequency fluctuations.

Environmental testing of CIS based modules

DOE Office of Scientific and Technical Information (OSTI.GOV)

Willett, D.

1995-11-01

This report describes environmental testing of Siemen`s CIS modules. Charts and diagrams are presented on data concerning: temporary power loss of laminated mini-modules; the 50 thermal cycle test; the 10 humidity freeze cycle test; results after 1000 hours of exposure to damp heat; and interconnect test structures in damp heat testing. It is concluded that moisture ingress causes permanent increases in the series resistance of modules, and that improved packaging is needed for better high humidity reliability. Also, dry dark heat caused temporary power losses which were recovered in sunlight.

Modifications to Marshall's Annular Seal Test (MAST) Rig and Facility for Improved Rotordynamic Coefficient Testing of Annular Seals and Fluid Film Bearings

NASA Technical Reports Server (NTRS)

Darden, J. M.; Earhart, E. M.

2011-01-01

The limits of rotordynamic stability continue to be pushed by the high power densities and rotational speeds of modern rocket engine turbomachinery. Destabilizing forces increase dramatically with rotor speed. Rotordynamic stability is lost when these destabilizing forces overwhelm the stabilizing forces. The vibration from the unstable rotor grows until it is limited by some nonlinearity. For example, a rolling element bearing with a stiffness characteristic that increases with deflection may limit the vibration amplitude. The loads and deflections resulting from this limit cycle vibration (LCV) can lead to bearing and seal damage which promotes ever increasing levels of subsynchronous vibration. Engineers combat LCV by introducing rotordynamic elements that generate increased stabilizing forces and reduced destabilizing forces. For example, replacing a labyrinth seal with a damping seal results in substantial increases in the damping and stiffness rotordynamic coefficients. Adding a swirl brake to the damping seal greatly reduces the destabilizing cross-coupled forces generated by the damping seal for even further increases in the stabilizing capacity. Marshall?s Annular Seal Test (MAST) rig is designed to experimentally measure the stabilizing capacity of new annular seal designs. The rig has been moved to a new facility and outfitted with a new slave bearing to allow increased test durations and to enable the testing of fluid film bearings. The purpose of this paper is to describe the new facility and the new bearing arrangement. Several novel seal and bearing designs will also be discussed.

Energy balance and stability. [in stellar coronae

NASA Technical Reports Server (NTRS)

Hammer, R.

1982-01-01

The energy balance of the outer atmospheres of solarlike stars is discussed. The energy balance of open coronal regions is considered, discussing the construction and characteristics of models of such regions in some detail. In particular, the temperature as a function of height is considered, as are the damping length dependence of the global energy balance in the region between the base of the transition region and the critical point, and the effects of changing the amount of coronal heating, the stellar mass, and the stellar radius. Models of coronal loops are more briefly discussed. The chromosphere is then included in the discussion of the energy balance, and the connection between global energy balance and global thermal stability is addressed. The observed positive correlations between the chromospheric and coronal energy losses and the pressure of the transition region is qualitatively explained.

Parametres pour l'instabilite fluidelastique: Derivees de stabilite et amortissement diphasique

NASA Astrophysics Data System (ADS)

Charreton, Constant

Heat exchangers and steam generators are crucial components in nuclear power plants. Water heated by nuclear fission is flowing through thousands of tubes inside a steam generator. Heat is transmitted to a second water network, external to the tubes. Steam is generated from the water of the secondary to power the turbines that produce electrical power. In this process, two-phase cross flow across the tubes causes several excitation phenomena. Vibration induced on the tubes can compromise the structural integrity of the steam generator, and can lead to power plant shutdowns. Better understanding of parameters at stake would lead to improved power plant safety and reliability. Fluidelastic instability is without doubt one of the most destructive vibration phenomena. It causes the steam generator tubes to collide against one another. This can lead to premature wear on the tubes, cracks due to fatigue and eventually, leaks leading to radioactive water contamination. Therefore, predicting conditions leading to fluidelastic instability would allow to control the damage on the tubes. In this thesis, we aim at identifying the key parameters to predict fluidelastic instability. To do so, a theoretical approach is based on the quasi-steady model. It is shown that the equation used to predict fluidelastic instability comprises two parameters that are hard to characterize. There is, on one hand, the derivative of the lift coefficient on a cylinder, and damping on the other hand. The main objective of this project is to measure these parameters experimentally. Knowing that the sign of the lift coefficient derivative is a sufficient indicator of fluidelastic instability, this derivative was measured. The experiments were carried out on the center tube of an array. The flow is single-phase and values of Reynolds number are low to moderate, thus filling a gap in the literature. Indeed, the lift coefficient derivative is known for high values of the Reynolds number only. Meanwhile, numerical methods are developed. They are based on the direct resolution of Navier-Stokes equations with the finite-element method, and on potential flow theory. Results for the lift coefficient derivative are compared to the measurements. Furthermore, the influence of geometric parameters of the array are investigated. The trend in the results show that the derivative of the lift coefficient becomes Reynolds independent for high values. From the literature and the measurements, a relationship is proposed for the lift coefficient derivative with respect to the Reynolds number. Values are injected in the quasi-steady model to predict the critical velocity for the onset of instability of a single flexible tube. Stability maps for various Reynolds numbers are proposed, using typical values for the tube damping. However, the maps do not compare well with critical velocities found in the literature for high values of the Reynolds number. Stability tests would be necessary to confirm the validity of the maps for low Reynolds, as fluidelastic has never been investigated in this range of Reynolds number. Yet, for high values of the Reynolds number, it seems like the quasi-steady model fails to predict the behavior of the experiments. An accurate value for the total damping of a tube is required to locate instability results on a map. However, in steam generators subjected to two-phase flow, damping on a tube is much more important than for single-phase flow. Yet, its origin is unknown. Therefore, we measured two-phase damping for internal flow using a specific test section. Indeed, a few studies on two-phase flow suggest that the damping mechanism is the same for a tube in cross-flow and for a tube subjected to internal flow. The present study focuses on the physics underlying the two-phase damping mechanism. The test bench consists of a sliding rigid tube subjected to upward internal two-phase flow. It essentially is a mass-spring system subjected to a transverse sinusoidal force. The damping is extracted from the frequency response function of the tube. Meanwhile, gas phase motion is characterized through video processing of the oscillating tube. The relative amplitude of the gas phase is related to two-phase flow damping values via a model of the forces acting on the bubbles. Varying excitation parameters such as frequency and excitation force confirms that two-phase damping is a viscous (velocity dependent) dissipation mechanism. Its direct relation with flow pattern transitions was confirmed. Furthermore, the combination of the videos and the analytical model suggests that the power dissipated by the drag force on the bubbles is significant in the two-phase damping mechanism. However, the model over-predicts the amplitude of the gas phase. This suggests that pseudo-turbulence generated by the motion of the tube is to be considered. The results of this study form an experimental database that can be used as input for fluidelastic instability models. Particularly, two-phase flow experiments will eventually help validating numerical methods, regarding the damping as well as the behavior of the gas phase. This work contributes to modeling and understanding two-phase flow induced vibration.

Non-Linear Slosh Damping Model Development and Validation

NASA Technical Reports Server (NTRS)

Yang, H. Q.; West, Jeff

2015-01-01

Propellant tank slosh dynamics are typically represented by a mechanical model of spring mass damper. This mechanical model is then included in the equation of motion of the entire vehicle for Guidance, Navigation and Control (GN&C) analysis. For a partially-filled smooth wall propellant tank, the critical damping based on classical empirical correlation is as low as 0.05%. Due to this low value of damping, propellant slosh is potential sources of disturbance critical to the stability of launch and space vehicles. It is postulated that the commonly quoted slosh damping is valid only under the linear regime where the slosh amplitude is small. With the increase of slosh amplitude, the critical damping value should also increase. If this nonlinearity can be verified and validated, the slosh stability margin can be significantly improved, and the level of conservatism maintained in the GN&C analysis can be lessened. The purpose of this study is to explore and to quantify the dependence of slosh damping with slosh amplitude. Accurately predicting the extremely low damping value of a smooth wall tank is very challenging for any Computational Fluid Dynamics (CFD) tool. One must resolve thin boundary layers near the wall and limit numerical damping to minimum. This computational study demonstrates that with proper grid resolution, CFD can indeed accurately predict the low damping physics from smooth walls under the linear regime. Comparisons of extracted damping values with experimental data for different tank sizes show very good agreements. Numerical simulations confirm that slosh damping is indeed a function of slosh amplitude. When slosh amplitude is low, the damping ratio is essentially constant, which is consistent with the empirical correlation. Once the amplitude reaches a critical value, the damping ratio becomes a linearly increasing function of the slosh amplitude. A follow-on experiment validated the developed nonlinear damping relationship. This discovery can lead to significant savings by reducing the number and size of slosh baffles in liquid propellant tanks.

Gravity-oriented satellite dynamics subject to gravitational and active damping torques

NASA Astrophysics Data System (ADS)

Sarychev, V. A.; Gutnik, S. A.

2018-01-01

The dynamics of the rotational motion of a satellite moving in the central Newtonian field of force over a circular orbit under the effect of gravitational and active damping torques, which depend on the satellite angular velocity projections, has been investigated. The paper proposes a method of determining all equilibrium positions (equilibrium orientations) of a satellite in the orbital coordinate system for specified values of damping coefficients and principal central moments of inertia. The conditions of their existence have been obtained. For a zero equilibrium position where the axes of the satellite-centered coordinate system coincide with the axes of the orbital coordinate system, the necessary and sufficient conditions for asymptotic stability are obtained using the Routh-Hurwitz criterion. A detailed analysis of the regions where the conditions of the asymptotic stability of a zero equilibrium position are fulfilled have been obtained depending on three dimensionless parameters of the problem, and the numerical study of the process of attenuation of satellite's spatial oscillations for various damping coefficients has been carried out. It has been shown that there is a wide range of damping parameters from which, by choosing the necessary values, one can provide the asymptotic stability of satellite's zero equilibrium position in the orbital coordinate system.

Exponential stabilization of magnetoelastic waves in a Mindlin-Timoshenko plate by localized internal damping

NASA Astrophysics Data System (ADS)

Grobbelaar-Van Dalsen, Marié

2015-08-01

This article is a continuation of our earlier work in Grobbelaar-Van Dalsen (Z Angew Math Phys 63:1047-1065, 2012) on the polynomial stabilization of a linear model for the magnetoelastic interactions in a two-dimensional electrically conducting Mindlin-Timoshenko plate. We introduce nonlinear damping that is effective only in a small portion of the interior of the plate. It turns out that the model is uniformly exponentially stable when the function , that represents the locally distributed damping, behaves linearly near the origin. However, the use of Mindlin-Timoshenko plate theory in the model enforces a restriction on the region occupied by the plate.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Song, P.

A model of the solar chromosphere that consists of two fundamentally different regions, a lower region and an upper region, is proposed. The lower region is covered mostly by weak locally closed magnetic field and small network areas of extremely strong, locally open field. The field in the upper region is relatively uniform and locally open, connecting to the corona. The chromosphere is heated by strong collisional damping of Alfvén waves, which are driven by turbulent motions below the photosphere. The heating rate depends on the field strength, wave power from the photosphere, and altitude in the chromosphere. The wavesmore » in the internetwork area are mostly damped in the lower region, supporting radiation in the lower chromosphere. The waves in the network area, carrying more Poynting flux, are only weakly damped in the lower region. They propagate into the upper region. As the thermal pressure decreases with height, the network field expands to form the magnetic canopy where the damping of the waves from the network area supports radiation in the whole upper region. Because of the vertical stratification and horizontally nonuniform distribution of the magnetic field and heating, one circulation cell is formed in each of the upper and lower regions. The two circulation cells distort the magnetic field and reinforce the funnel-canopy-shaped magnetic geometry. The model is based on classical processes and is semi-quantitative. The estimates are constrained according to observational knowledge. No anomalous process is invoked or needed. Overall, the heating mechanism is able to damp 50% of the total wave energy.« less

Exact solutions for discrete breathers in a forced-damped chain.

PubMed

Gendelman, O V

2013-06-01

Exact solutions for symmetric on-site discrete breathers (DBs) are obtained in a forced-damped linear chain with on-site vibro-impact constraints. The damping in the system is caused by inelastic impacts; the forcing functions should satisfy conditions of periodicity and antisymmetry. Global conditions for existence and stability of the DBs are established by a combination of analytic and numeric methods. The DB can lose its stability through either pitchfork, or Neimark-Sacker bifurcations. The pitchfork bifurcation is related to the internal dynamics of each individual oscillator. It is revealed that the coupling can suppress this type of instability. To the contrary, the Neimark-Sacker bifurcation occurs for relatively large values of the coupling, presumably due to closeness of the excitation frequency to a boundary of the propagation zone of the chain. Both bifurcation mechanisms seem to be generic for the considered type of forced-damped lattices. Some unusual phenomena, like nonmonotonous dependence of the stability boundary on the forcing amplitude, are revealed analytically for the initial system and illustrated numerically for small periodic lattices.

Application of polynomial control to design a robust oscillation-damping controller in a multimachine power system.

PubMed

Hasanvand, Hamed; Mozafari, Babak; Arvan, Mohammad R; Amraee, Turaj

2015-11-01

This paper addresses the application of a static Var compensator (SVC) to improve the damping of interarea oscillations. Optimal location and size of SVC are defined using bifurcation and modal analysis to satisfy its primary application. Furthermore, the best-input signal for damping controller is selected using Hankel singular values and right half plane-zeros. The proposed approach is aimed to design a robust PI controller based on interval plants and Kharitonov's theorem. The objective here is to determine the stability region to attain robust stability, the desired phase margin, gain margin, and bandwidth. The intersection of the resulting stability regions yields the set of kp-ki parameters. In addition, optimal multiobjective design of PI controller using particle swarm optimization (PSO) algorithm is presented. The effectiveness of the suggested controllers in damping of local and interarea oscillation modes of a multimachine power system, over a wide range of loading conditions and system configurations, is confirmed through eigenvalue analysis and nonlinear time domain simulation. Copyright © 2015 ISA. Published by Elsevier Ltd. All rights reserved.

Dynamic stability characteristics in pitch, yaw, and roll of a supercritical-wing research airplane model. [langley 8-foot transonic tunnel tests

NASA Technical Reports Server (NTRS)

Boyden, R. P.

1974-01-01

The aerodynamic damping in pitch, yaw, and roll and the oscillatory stability in pitch and yaw of a supercritical-wing research airplane model were determined for Mach numbers of 0.25 to 1.20 by using the small-amplitude forced-oscillation technique. The angle-of-attack range was from -2 deg to 20 deg. The effects of the underwing leading-edge vortex generators and the contributions of the wing, vertical tail, and horizontal tail to the appropriate damping and stability were measured.

23.6%-efficient monolithic perovskite/silicon tandem solar cells with improved stability

NASA Astrophysics Data System (ADS)

Bush, Kevin A.; Palmstrom, Axel F.; Yu, Zhengshan J.; Boccard, Mathieu; Cheacharoen, Rongrong; Mailoa, Jonathan P.; McMeekin, David P.; Hoye, Robert L. Z.; Bailie, Colin D.; Leijtens, Tomas; Peters, Ian Marius; Minichetti, Maxmillian C.; Rolston, Nicholas; Prasanna, Rohit; Sofia, Sarah; Harwood, Duncan; Ma, Wen; Moghadam, Farhad; Snaith, Henry J.; Buonassisi, Tonio; Holman, Zachary C.; Bent, Stacey F.; McGehee, Michael D.

2017-02-01

As the record single-junction efficiencies of perovskite solar cells now rival those of copper indium gallium selenide, cadmium telluride and multicrystalline silicon, they are becoming increasingly attractive for use in tandem solar cells due to their wide, tunable bandgap and solution processability. Previously, perovskite/silicon tandems were limited by significant parasitic absorption and poor environmental stability. Here, we improve the efficiency of monolithic, two-terminal, 1-cm2 perovskite/silicon tandems to 23.6% by combining an infrared-tuned silicon heterojunction bottom cell with the recently developed caesium formamidinium lead halide perovskite. This more-stable perovskite tolerates deposition of a tin oxide buffer layer via atomic layer deposition that prevents shunts, has negligible parasitic absorption, and allows for the sputter deposition of a transparent top electrode. Furthermore, the window layer doubles as a diffusion barrier, increasing the thermal and environmental stability to enable perovskite devices that withstand a 1,000-hour damp heat test at 85 ∘C and 85% relative humidity.

Mechanics of Boundary Layer Transition. Part 5: Boundary Layer Stability theory in incompressible and compressible flow

NASA Technical Reports Server (NTRS)

Mack, L. M.

1967-01-01

The fundamentals of stability theory, its chief results, and the physical mechanisms at work are presented. The stability theory of the laminar boundary determines whether a small disturbance introduced into the boundary layer will amplify or damp. If the disturbance damps, the boundary layer remains laminar. If the disturbance amplifies, and by a sufficient amount, then transition to turbulence eventually takes place. The stability theory establishes those states of the boundary layer which are most likely to lead to transition, identifys those frequencies which are the most dangerous, and indicates how the external parameters can best be changed to avoid transition.

Explicit approximations to estimate the perturbative diffusivity in the presence of convectivity and damping. III. Cylindrical approximations for heat waves traveling inwards

DOE Office of Scientific and Technical Information (OSTI.GOV)

Berkel, M. van; Fellow of the Japan Society for the Promotion of Science; FOM Institute DIFFER-Dutch Institute for Fundamental Energy Research, Association EURATOM-FOM, Trilateral Euregio Cluster, P.O. Box 1207, 3430 BE Nieuwegein

In this paper, a number of new explicit approximations are introduced to estimate the perturbative diffusivity (χ), convectivity (V), and damping (τ) in cylindrical geometry. For this purpose, the harmonic components of heat waves induced by localized deposition of modulated power are used. The approximations are based on the heat equation in cylindrical geometry using the symmetry (Neumann) boundary condition at the plasma center. This means that the approximations derived here should be used only to estimate transport coefficients between the plasma center and the off-axis perturbative source. If the effect of cylindrical geometry is small, it is also possiblemore » to use semi-infinite domain approximations presented in Part I and Part II of this series. A number of new approximations are derived in this part, Part III, based upon continued fractions of the modified Bessel function of the first kind and the confluent hypergeometric function of the first kind. These approximations together with the approximations based on semi-infinite domains are compared for heat waves traveling towards the center. The relative error for the different derived approximations is presented for different values of the frequency, transport coefficients, and dimensionless radius. Moreover, it is shown how combinations of different explicit formulas can be used to estimate the transport coefficients over a large parameter range for cases without convection and damping, cases with damping only, and cases with convection and damping. The relative error between the approximation and its underlying model is below 2% for the case, where only diffusivity and damping are considered. If also convectivity is considered, the diffusivity can be estimated well in a large region, but there is also a large region in which no suitable approximation is found. This paper is the third part (Part III) of a series of three papers. In Part I, the semi-infinite slab approximations have been treated. In Part II, cylindrical approximations are treated for heat waves traveling towards the plasma edge assuming a semi-infinite domain.« less

Significance of modeling internal damping in the control of structures

NASA Technical Reports Server (NTRS)

Banks, H. T.; Inman, D. J.

1992-01-01

Several simple systems are examined to illustrate the importance of the estimation of damping parameters in closed-loop system performance and stability. The negative effects of unmodeled damping are particularly pronounced in systems that do not use collocated sensors and actuators. An example is considered for which even the actuators (a tip jet nozzle and flexible hose) for a simple beam produce significant damping which, if ignored, results in a model that cannot yield a reasonable time response using physically meaningful parameter values. It is concluded that correct damping modeling is essential in structure control.

Resolving electrical conductivities from collisionally damped plasmons in isochorically heated warm dense aluminum

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sperling, P.; Fletcher, L. B.; Chung, H. -K.

2016-03-29

We measure the highly-resolved inelastic x-ray scattering spectrum of isochorically ultrafast heated aluminum. In the x-ray forward scattering spectra the electron temperature could be measured from the down- and upshifted plasmon, where the electron density of ne = 1:8 1023 cm 3 is known a priori. We have studied the plasmon damping by applying electron-particle collision models beyond the Born approximation determining the electrical conductivity of warm dense aluminum.

Parametric study of the mode coupling instability for a simple system with planar or rectilinear friction

NASA Astrophysics Data System (ADS)

Charroyer, L.; Chiello, O.; Sinou, J.-J.

2016-12-01

In this paper, the study of a damped mass-spring system of three degrees of freedom with friction is proposed in order to highlight the differences in mode coupling instabilities between planar and rectilinear friction assumptions. Well-known results on the effect of structural damping in the field of friction-induced vibration are extended to the specific case of a damped mechanical system with planar friction. It is emphasised that the lowering and smoothing effects are not so intuitive in this latter case. The stability analysis is performed by calculating the complex eigenvalues of the linearised system and by using the Routh-Hurwitz criterion. Parametric studies are carried out in order to evaluate the effects of various system parameters on stability. Special attention is paid to the understanding of the role of damping and the associated destabilisation paradox in mode-coupling instabilities with planar and rectilinear friction assumptions.

Aeroelastic Stability of Modern Bearingless Rotors: A Parametric Investigation

NASA Technical Reports Server (NTRS)

Nguyen, Khanh Q.

1994-01-01

The University of Maryland Advanced Rotorcraft Code (UMARC) is utilized to study the effects of blade design parameters on the aeroelastic stability of an isolated modern bearingless rotor blade in hover. The McDonnell Douglas Advanced Rotor Technology (MDART) Rotor is the baseline rotor investigated. Results indicate that kinematic pitch-lag coupling introduced through the control system geometry and the damping levels of the shear lag dampers strongly affect the hover inplane damping of the baseline rotor blade. Hub precone, pitchcase chordwise stiffness, and blade fundamental torsion frequency have small to moderate influence on the inplane damping, while blade pre-twist and placements of blade fundamental flapwise and chord-wise frequencies have negligible effects. A damperless configuration with a leading edge pitch-link, 15 deg of pitch-link cant angle, and reduced pitch-link stiffness is shown to be stable with an inplane damping level in excess of 2.7 percent critical at the full hover tip speed.

Flight Flutter Testing of Rotary Wing Aircraft Using a Control System Oscillation Technique

NASA Technical Reports Server (NTRS)

Yen, J. G.; Viswanathan, S.; Matthys, C. G.

1976-01-01

A flight flutter testing technique is described in which the rotor controls are oscillated by series actuators to excite the rotor and airframe modes of interest, which are then allowed to decay. The moving block technique is then used to determine the damped frequency and damping variation with rotor speed. The method proved useful for tracking the stability of relatively well damped modes. The results of recently completed flight tests of an experimental soft-in-plane rotor are used to illustrate the technique. Included is a discussion of the application of this technique to investigation of the propeller whirl flutter stability characteristics of the NASA/Army XV-15 VTOL tilt rotor research aircraft.

A Study on Multi-Swing Stability Analysis of Power System using Damping Rate Inversion

NASA Astrophysics Data System (ADS)

Tsuji, Takao; Morii, Yuki; Oyama, Tsutomu; Hashiguchi, Takuhei; Goda, Tadahiro; Nomiyama, Fumitoshi; Kosugi, Narifumi

In recent years, much attention is paid to the nonlinear analysis method in the field of stability analysis of power systems. Especially for the multi-swing stability analysis, the unstable limit cycle has an important meaning as a stability margin. It is required to develop a high speed calculation method of stability boundary regarding multi-swing stability because the real-time calculation of ATC is necessary to realize the flexible wheeling trades. Therefore, the authors have developed a new method which can calculate the unstable limit cycle based on damping rate inversion method. Using the unstable limit cycle, it is possible to predict the multi-swing stability at the time when the fault transmission line is reclosed. The proposed method is tested in Lorenz equation, single-machine infinite-bus system model and IEEJ WEST10 system model.

The use of plastic optical fibres and shape memory alloys for damage assessment and damping control in composite materials

NASA Astrophysics Data System (ADS)

Kuang, K. S. C.; Cantwell, W. J.

2003-08-01

This paper reports the use of a plastic fibre sensor for detecting impact damage in carbon fibre epoxy cantilever beams by monitoring their damping response under free vibration loading conditions. The composite beams were impacted at impact energies up to 8 J. The residual strengths and stiffnesses of the damaged laminates were measured in order to relate reductions in their mechanical properties to changes in their damping characteristics. Here, optical fibre sensors were surface bonded to carbon fibre composite beams which were subjected to free vibration tests to monitor their dynamic response. In the second part of this study, Ni-Ti shape memory alloy (SMA) wires were employed to control and modify the damping response of a composite beam. The SMA wires were initially trained to obtain the desired shape when activated. Here, the trained SMA wires were heated locally using a nickel/chromium wire that was wrapped around the trained region of the SMA. By using this method to activate the SMA wire (as opposed to direct electrical heating), it is possible to obtain localized actuation without heating the entire length of the wire. This procedure minimizes any damage to the host material that may result from local heat transfer between the SMA wire and the composite structure. In addition, the reduction in power requirements to achieve SMA activation permits the use of small-size power packs which can in turn lead to a potential weight reduction in weight-critical applications. The findings of this study demonstrate that a trained SMA offers a superior damping capability to that exhibited by an 'as-supplied' flat-annealed wire.

Spatially Localized Particle Energization by Landau Damping in Current Sheets

NASA Astrophysics Data System (ADS)

Howes, G. G.; Klein, K. G.; McCubbin, A. J.

2017-12-01

Understanding the mechanisms of particle energization through the removal of energy from turbulent fluctuations in heliospheric plasmas is a grand challenge problem in heliophysics. Under the weakly collisional conditions typical of heliospheric plasma, kinetic mechanisms must be responsible for this energization, but the nature of those mechanisms remains elusive. In recent years, the spatial localization of plasma heating near current sheets in the solar wind and numerical simulations has gained much attention. Here we show, using the innovative and new field-particle correlation technique, that the spatially localized particle energization occurring in a nonlinear gyrokinetic simulation has the velocity space signature of Landau damping, suggesting that this well-known collisionless damping mechanism indeed actively leads to spatially localized heating in the vicinity of current sheets.

Fast and slow active control of combustion instabilities in liquid-fueled combustors

NASA Astrophysics Data System (ADS)

Lee, Jae-Yeon

This thesis describes an experimental investigation of two different novel active control approaches that are employed to suppress combustion instabilities in liquid-fueled combustors. A "fast" active controller requires continuous modulation of the fuel injection rate at the frequency of the instability with proper phase and gain. Use of developed optical tools reveals that the "fast" active control system suppresses the instability by changing the nearly flat distribution of the phase between pressure and heat release oscillations to a gradually varying phase distribution, thus dividing the combustion zone into regions that alternately damp and drive combustor oscillations. The effects of these driving/damping regions tend to counter one another, which result in significant damping of the unstable oscillations. In contrast, a "slow" active controller operates at a rate commensurate with that at which operating conditions change during combustor operation. Consequently, "slow" controllers need infrequent activation in response to changes in engine operating conditions to assure stable operation at all times. Using two types of fuel injectors that can produce large controllable variation of fuel spray properties, it is shown that by changing the spray characteristics it is possible to significantly damp combustion instabilities. Similar to the aforementioned result of the "fast" active control study, "slow" change of the fuel spray properties also modifies the nearly flat phase distribution during unstable operation to a gradually varying phase distribution, resulting in combustor "stabilization". Furthermore, deconvolutions of CH*-chemiluminescence images reveal the presence of vortex-flame interaction during unstable operation. Strong driving of instabilities occurs where the mean axial velocity of the flow is approximately zero, a short distance downstream of the flame holder where a significant fraction of the fuel burns in phase with the pressure oscillations. It is shown that the "fast" and "slow" active control approaches suppress combustion instabilities in a different manner. Nevertheless, the both control approaches successfully suppress combustion instabilities by modifying the temporal and spatial behavior of the combustion process heat release that is responsible for driving the instability.

Second Sound in Systems of One-Dimensional Fermions

DOE PAGES

Matveev, K. A.; Andreev, A. V.

2017-12-27

We study sound in Galilean invariant systems of one-dimensional fermions. At low temperatures, we find a broad range of frequencies in which in addition to the waves of density there is a second sound corresponding to ballistic propagation of heat in the system. The damping of the second sound mode is weak, provided the frequency is large compared to a relaxation rate that is exponentially small at low temperatures. At lower frequencies the second sound mode is damped, and the propagation of heat is diffusive.

Second Sound in Systems of One-Dimensional Fermions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Matveev, K. A.; Andreev, A. V.

We study sound in Galilean invariant systems of one-dimensional fermions. At low temperatures, we find a broad range of frequencies in which in addition to the waves of density there is a second sound corresponding to ballistic propagation of heat in the system. The damping of the second sound mode is weak, provided the frequency is large compared to a relaxation rate that is exponentially small at low temperatures. At lower frequencies the second sound mode is damped, and the propagation of heat is diffusive.

Second Sound in Systems of One-Dimensional Fermions

NASA Astrophysics Data System (ADS)

Matveev, K. A.; Andreev, A. V.

2017-12-01

We study sound in Galilean invariant systems of one-dimensional fermions. At low temperatures, we find a broad range of frequencies in which in addition to the waves of density there is a second sound corresponding to the ballistic propagation of heat in the system. The damping of the second sound mode is weak, provided the frequency is large compared to a relaxation rate that is exponentially small at low temperatures. At lower frequencies, the second sound mode is damped, and the propagation of heat is diffusive.

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

NASA Astrophysics Data System (ADS)

Agarwal, Sandeep

2005-11-01

Lead-lag dampers are present in most rotors to provide the required level of damping in all flight conditions. These dampers are a critical component of the rotor system, but they also represent a major source of maintenance cost. In present rotor systems, both hydraulic and elastomeric lead-lag dampers have been used. Hydraulic dampers are complex mechanical components that require hydraulic fluids and have high associated maintenance costs. Elastomeric dampers are conceptually simpler and provide a "dry" rotor, but are rather costly. Furthermore, their damping characteristics can degrade with time without showing external signs of failure. Hence, the dampers must be replaced on a regular basis. A semi-active friction based lead-lag damper is proposed as a replacement for hydraulic and elastomeric dampers. Damping is provided by optimized energy dissipation due to frictional forces in semi-active joints. An actuator in the joint modulates the normal force that controls energy dissipation at the frictional interfaces, resulting in large hysteretic loops. Various selective damping strategies are developed and tested for a simple system containing two different frequency modes in its response, one of which needs to be damped out. The system reflects the situation encountered in rotor response where 1P excitation is present along with the potentially unstable regressive lag motion. Simulation of the system response is obtained to compare their effectiveness. Next, a control law governing the actuation in the lag damper is designed to generate the desired level of damping for performing adaptive selective damping of individual blade lag motion. Further, conceptual design of a piezoelectric friction based lag damper for a full-scale rotor is presented and various factors affecting size, design and maintenance cost, damping capacity, and power requirements of the damper are discussed. The selective semi-active damping strategy is then studied in the context of classical 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.

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.

Airplane stability calculations with a card programmable pocket calculator

NASA Technical Reports Server (NTRS)

Sherman, W. L.

1978-01-01

Programs are presented for calculating airplane stability characteristics with a card programmable pocket calculator. These calculations include eigenvalues of the characteristic equations of lateral and longitudinal motion as well as stability parameters such as the time to damp to one-half amplitude or the damping ratio. The effects of wind shear are included. Background information and the equations programmed are given. The programs are written for the International System of Units, the dimensional form of the stability derivatives, and stability axes. In addition to programs for stability calculations, an unusual and short program is included for the Euler transformation of coordinates used in airplane motions. The programs have been written for a Hewlett Packard HP-67 calculator. However, the use of this calculator does not constitute an endorsement of the product by the National Aeronautics and Space Administration.

Inter-decadal change in El Niño-Southern Oscillation examined with Bjerknes stability index analysis

NASA Astrophysics Data System (ADS)

An, Soon-Il; Bong, Hayoung

2016-08-01

Characteristics of El Niño-Southern Oscillation (ENSO) have changed since the late 1970s as it synchronized with the Pacific Decadal Oscillation (PDO). In order to investigate the primary feedback process responsible for the interdecadal change in ENSO characteristics according to the PDO, using the ocean assimilation data (SODA) and the reanalysis data (NCEP/NCAR), we performed Bjerknes linear stability index (BJ index) analysis of two decadal periods: one before the late 1970s (the nPDO period) and the other after the late 1970s (the pPDO period). The BJ index for the pPDO period (-0.07 year-1 for the growth rate of the eastern Pacific SST anomaly) is significantly larger than that for the nPDO period (-0.25 year-1). The larger BJ index value is primarily due to the enhanced zonal advection feedback (ZA; +0.44 year-1), thermocline feedback (TH; +0.33 year-1), and the reduced damping by the mean meridional current (MD; +0.16 year-1). The increases in ZA and TH are mainly attributed to the shoaling of the mean thermocline depth, which increased the sensitivity of the ocean dynamic fields to the wind forcing; and the reduced MD is related to the reduced mean meridional current associated with the weakened trade wind. The enhanced positive feedback is partly compensated by the enhanced thermodynamic damping including the shortwave, sensible heat flux and latent heat flux (collectively, -0.88 year-1). Interestingly, the change in air-sea coupling strength from the nPDO to the pPDO period was small. Without the two extreme El Niño events (1982-1983 and 1997-1998) in the pPDO period (pPDO_noBIG), the difference in BJ index between nPDO and pPDO_noBIG periods became smaller (~0.07 year-1), indicating that the two extreme El Niño events largely contribute to the larger ENSO variability of the pPDO period, possibly due to nonlinear feedback processes. Nevertheless, qualitative similarity in each of the feedback and damping components of BJ index exists between the pPDO and pPDO_noBIG periods, which suggests that the tropical climate states of the pPDO period provided more favorable conditions for the emergence of extreme El Niño events by intensifying the linear feedback processes.

A Study on Rotordynamic Characteristics of Swirl Brakes for Three Types of Seals

NASA Astrophysics Data System (ADS)

Xu, Wanjun; Yang, Jiangang

2017-03-01

In order to understand swirl brakes mechanisms and their influence on rotordynamic characteristics for different types of seals, a three-dimensional flow numerical simulation was presented. Three typical seals including labyrinth seal, fully partitioned damper seal and hole-pattern seal were compared under three inlet conditions of no preswirl, preswirl and preswirl with swirl brakes. FAN boundary condition was used to provide inlet preswirl. A modified identification method of effective damping was proposed. Feasibility of the swirl brakes on improving performance of damper seals was discussed. The results show that the swirl brakes influence the seal stability characteristics with whirl frequency. For the labyrinth seal the swirl brakes reverse the sign of effective damping at low frequency and improve the seal stability performance in a wide frequency range. The swirl brakes also improve the damper seals’ stability performance by increasing the low frequency effective damping and reducing their crossover frequency. Further results indicate the swirl brakes affect the rotational direction of the maximum (minimum) pressure positions and enhance the stability of the seals by reducing tangential force in each cavity.

Influence of composition and heat treatment on damping and magnetostrictive properties of Fe–18%(Ga + Al) alloys

DOE PAGES

Golovin, I. S.; Palacheva, V. V.; Zadorozhnyy, V. Yu.; ...

2014-07-16

The structure, magnetostriction and damping properties of Fe 82Ga (18–x)Al x (x = 0, 5, 8, 12) alloys were analyzed. The anelastic response of Fe–18(Ga + Al) alloys was studied as a function of temperature (from 0 to 600 °C), frequency (from 0.01 to 200 Hz) and amplitude (from 0.0004% to 0.2%) of forced vibrations. The origin of the relatively high damping capacity of Fe–Ga–Al alloy at room temperature was determined by applying a magnetic field and different heat treatment regimes. The substitution of Ga by Al in Fe–18% Ga alloys was found to decrease magnetostriction and damping. The heatmore » treatment of alloys influences the damping capacity of alloys more than variations of their chemical compositions. Thermally activated frequency and temperature-dependent anelastic effects in Fe–Ga–Al alloys were analyzed and the corresponding activation parameters for relaxation processes were evaluated. Internal friction effects caused by structural transformations were recorded and were found to be consistent with the A2 → D0 3 → L1 2 reaction. Thus, the physical mechanisms for all anelastic effects are discussed.« less

Wide-area Power System Damping Control Coordination Based on Particle Swarm Optimization with Time Delay Considered

NASA Astrophysics Data System (ADS)

Zhang, J. Y.; Jiang, Y.

2017-10-01

To ensure satisfactory dynamic performance of controllers in time-delayed power systems, a WAMS-based control strategy is investigated in the presence of output feedback delay. An integrated approach based on Pade approximation and particle swarm optimization (PSO) is employed for parameter configuration of PSS. The coordination configuration scheme of power system controllers is achieved by a series of stability constraints at the aim of maximizing the minimum damping ratio of inter-area mode of power system. The validity of this derived PSS is verified on a prototype power system. The findings demonstrate that the proposed approach for control design could damp the inter-area oscillation and enhance the small-signal stability.

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.

The research for the clinical curative effect through combing traditional Chinese medicine with insulin to cure diabetes.

PubMed

Wu, Qianfeng; Fan, Hongxia

2014-07-01

The clinical curative effect is observed through curing type 2 diabetes mellitus with the therapy of combing Traditional Chinese Medicine (TCM) with insulin. Both the insulin prescription and the treatment of traditional Chinese medicine prescription are applied as mutual comparison. And the dosage, time, blood sugar level and curative effect etc are recorded. Healthy human body is taken as comparison for monitoring physical indicators. Through comparing insulin prescription and the combing therapy of insulin and traditional Chinese medicine, the insulin treatment group is better than contrast group (P<0.05). For the blending use group, the ISI in each group is significantly lower than that of health control group (P<0.01), where accumulation of damp heat in spleen type is the lowest; the BM I, H bA1C of type 2 diabetic patient is higher than health control group, its accumulation of damp heat in spleen type is the highest, TC, TG typical accumulation of damp heat in spleen are higher than other pattern of syndrome. the treatment method of combing TCM with insulin in curing type 2 diabetes mellitus has better effect than using insulin treatment alone; the resistance degree of insulin demonstrates the changing trend of first increase and later decrease with the development of disease course. Accumulation of damp heat in spleen type accounts for the highest proportion in type 2 diabetic patients, and there exists serious insulin resistance.

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.

Non-inductive current driven by Alfvén waves in solar coronal loops

NASA Astrophysics Data System (ADS)

Elfimov, A. G.; de Azevedo, C. A.; de Assis, A. S.

1996-08-01

It has been shown that Alfvén waves can drive non-inductive current in solar coronal loops via collisional or collisionless damping. Assuming that all the coronal-loop density of dissipated wave power (W= 10-3 erg cm-3 s-1), which is necessary to keep the plasma hot, is due to Alfvén wave electron heating, we have estimated the axial current density driven by Alfvén waves to be ≈ 103 105 statA cm-2. This current can indeed support the quasi-stationary equilibrium and stability of coronal loops and create the poloidal magnetic field up to B θ≈1-5 G.

Bifurcation physics of magnetic islands and stochasticity explored by heat pulse propagation studies in toroidal plasmas

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ida, K.; Kobayashi, T.; Yoshinuma, M.

Bifurcation physics of the magnetic island was investigated using the heat pulse propagation technique produced by the modulation of electron cyclotron heating. There are two types of bifurcation phenomena observed in LHD and DIII-D. One is a bifurcation of the magnetic topology between nested and stochastic fields. The nested state is characterized by the bi-directional (inward and outward) propagation of the heat pulse with slow propagation speed. The stochastic state is characterized by the fast propagation of the heat pulse with electron temperature flattening. The other bifurcation is between magnetic island with larger thermal diffusivity and that with smaller thermalmore » diffusivity. The damping of toroidal flow is observed at the O-point of the magnetic island both in helical plasmas and in tokamak plasmas during a mode locking phase with strong flow shears at the boundary of the magnetic island. Associated with the stochastization of the magnetic field, the abrupt damping of toroidal flow is observed in LHD. The toroidal flow shear shows a linear decay, while the ion temperature gradient shows an exponential decay. Lastly, this observation suggests that this flow damping is due to the change in the non-diffusive term of momentum transport.« less

Bifurcation physics of magnetic islands and stochasticity explored by heat pulse propagation studies in toroidal plasmas

DOE PAGES

Ida, K.; Kobayashi, T.; Yoshinuma, M.; ...

2016-07-29

Bifurcation physics of the magnetic island was investigated using the heat pulse propagation technique produced by the modulation of electron cyclotron heating. There are two types of bifurcation phenomena observed in LHD and DIII-D. One is a bifurcation of the magnetic topology between nested and stochastic fields. The nested state is characterized by the bi-directional (inward and outward) propagation of the heat pulse with slow propagation speed. The stochastic state is characterized by the fast propagation of the heat pulse with electron temperature flattening. The other bifurcation is between magnetic island with larger thermal diffusivity and that with smaller thermalmore » diffusivity. The damping of toroidal flow is observed at the O-point of the magnetic island both in helical plasmas and in tokamak plasmas during a mode locking phase with strong flow shears at the boundary of the magnetic island. Associated with the stochastization of the magnetic field, the abrupt damping of toroidal flow is observed in LHD. The toroidal flow shear shows a linear decay, while the ion temperature gradient shows an exponential decay. Lastly, this observation suggests that this flow damping is due to the change in the non-diffusive term of momentum transport.« less

Investigation of the Low-Subsonic Stability and Control Characteristics of a Free-Flying Model of a Thick 70 deg Delta Reentry Configuration

NASA Technical Reports Server (NTRS)

Paulson, John W.; Shanks, Robert E.

1961-01-01

An investigation of the low-subsonic flight characteristics of a thick 70 deg delta reentry configuration having a diamond cross section has been made in the Langley full-scale tunnel over an angle-of-attack range from 20 to 45 deg. Flight tests were also made at angles of attack near maximum lift (alpha = 40 deg) with a radio-controlled model dropped from a helicopter. Static and dynamic force tests were made over an angle-of-attack range from 0 to 90 deg. The longitudinal stability and control characteristics were considered satisfactory when the model had positive static longitudinal stability. It was possible to fly the model with a small amount of static instability, but the longitudinal characteristics were considered unsatisfactory in this condition. At angles of attack above the stall the model developed a large, constant-amplitude pitching oscillation. The lateral stability characteristics were considered to be only fair at angles of attack from about 20 to 35 deg because of a lightly damped Dutch roll oscillation. At higher angles of attack the oscillation was well damped and the lateral stability was generally satisfactory. The Dutch roll damping at the lower angles of attack was increased to satisfactory values by means of a simple rate-type roll damper. The lateral control characteristics were generally satisfactory throughout the angle- of-attack range, but there was some deterioration in aileron effectiveness in the high angle-of-attack range due mainly to a large increase in damping in roll.

Effectiveness of large booms as nutation dampers for spin stabilized spacecraft

NASA Technical Reports Server (NTRS)

Eke, F. O.

1991-01-01

The issue of using long slender booms as pendulous nutation damping devices on spinning aircraft is discussed. Motivation comes from experience with the Galileo Spacecraft, whose magnetometer boom also serves as a passive nutation damper for the spacecraft. Performance analysis of a spacecraft system equipped with such systems are relatively insensitive to changes in the damping constant of the device. However, the size and arrangement of such a damper raises important questions concerning spacecraft stability in general.

The Satellite Test Unit (STU), part of the Passive Aerodynamically Stabilized Magnetically Damped

NASA Technical Reports Server (NTRS)

1996-01-01

STS-77 ESC VIEW --- The Satellite Test Unit (STU), part of the Passive Aerodynamically Stabilized Magnetically Damped Satellite (PAMS) is seen moments after its ejection from the cargo bay of the Space Shuttle Endeavour. The scene was photographed with an Electronic Still Camera (ESC) onboard Endeavour's crew cabin during the deployment. The six-member crew will continue operations (tracking, rendezvousing and station-keeping) with PAMS-STU periodically throughout the remainder of the mission. GMT: 03:29:31.

The Satellite Test Unit (STU), part of the Passive Aerodynamically Stabilized Magnetically Damped

NASA Technical Reports Server (NTRS)

1996-01-01

STS-77 ESC VIEW --- The Satellite Test Unit (STU), part of the Passive Aerodynamically Stabilized Magnetically Damped Satellite (PAMS) is seen moments after its ejection from the cargo bay of the Space Shuttle Endeavour. The scene was photographed with an Electronic Still Camera (ESC) onboard Endeavour's crew cabin during the deployment. The six-member crew will continue operations (tracking, rendezvousing and station-keeping) with PAMS-STU periodically throughout the remainder of the mission. GMT: 03:29:43.

The Satellite Test Unit (STU), part of the Passive Aerodynamically Stabilized Magnetically Damped

NASA Technical Reports Server (NTRS)

1996-01-01

STS-77 ESC VIEW --- The Satellite Test Unit (STU), part of the Passive Aerodynamically Stabilized Magnetically Damped Satellite (PAMS) is seen moments after its ejection from the cargo bay of the Space Shuttle Endeavour. The scene was photographed with an Electronic Still Camera (ESC) onboard Endeavour's crew cabin during the deployment. The six-member crew will continue operations (tracking, rendezvousing and station-keeping) with PAMS-STU periodically throughout the remainder of the mission. GMT: 03:29:29.

Damping Analysis of Cylindrical Composite Structures with Enhanced Viscoelastic Properties

NASA Astrophysics Data System (ADS)

Kliem, Mathias; Høgsberg, Jan; Vanwalleghem, Joachim; Filippatos, Angelos; Hoschützky, Stefan; Fotsing, Edith-Roland; Berggreen, Christian

2018-04-01

Constrained layer damping treatments are widely used in mechanical structures to damp acoustic noise and mechanical vibrations. A viscoelastic layer is thereby applied to a structure and covered by a stiff constraining layer. When the structure vibrates in a bending mode, the viscoelastic layer is forced to deform in shear mode. Thus, the vibration energy is dissipated as low grade frictional heat. This paper documents the efficiency of passive constrained layer damping treatments for low frequency vibrations of cylindrical composite specimens made of glass fibre-reinforced plastics. Different cross section geometries with shear webs have been investigated in order to study a beneficial effect on the damping characteristics of the cylinder. The viscoelastic damping layers are placed at different locations within the composite cylinder e.g. circumferential and along the neutral plane to evaluate the location-dependent efficiency of constrained layer damping treatments. The results of the study provide a thorough understanding of constrained layer damping treatments and an improved damping design of the cylindrical composite structure. The highest damping is achieved when placing the damping layer in the neutral plane perpendicular to the bending load. The results are based on free decay tests of the composite structure.

Transmission problems for Mindlin–Timoshenko plates: frictional versus viscous damping mechanisms

NASA Astrophysics Data System (ADS)

Ferreira, Marcio V.; Muñoz Rivera, Jaime E.; Suárez, Fredy M. S.

2018-06-01

In this article, we make a comparative analysis of the stabilizing effect of the frictional dissipation with the dissipation produced by viscous materials of Kelvin-Voigt type both located in a part of a Mindlin-Timoshenko plate. We model these dissipative mechanisms through transmission problems and show that localized frictional damping, when effective over a strategic component of the plate, produces exponential stability of the corresponding semigroup. On the other hand, although the dissipation of Kelvin-Voigt is considered a strong dissipation, we prove that it loses its uniform stabilizing properties when localized over a component of the material and provides only a slower polynomial decay.

Transonic static and dynamic stability characteristics of a finned projectile configuration

NASA Technical Reports Server (NTRS)

Boyden, R. P.; Brooks, C. W., Jr.; Davenport, E. E.

1978-01-01

Static and dynamic stability tests were made of a finned projectile configuration with the aft-mounted fins arranged in a cruciform pattern. The tests were made at free stream Mach numbers of 0.7, 0.9, 1.1, and 1.2 in the Langley 8-foot transonic pressure tunnel. Some of the parameters measured during the tests were lift, drag, pitching moment, pitch damping, and roll damping. Configurations tested included the body with undeflected fins, the body with various fin deflections for control, and the body with fins removed. Theoretical estimates of the stability derivatives were made for the fins on configuration.

Mapping of elasticity and damping in an α + β titanium alloy through atomic force acoustic microscopy

PubMed Central

Phani, M Kalyan; Kumar, Anish; Jayakumar, T; Samwer, Konrad

2015-01-01

Summary The distribution of elastic stiffness and damping of individual phases in an α + β titanium alloy (Ti-6Al-4V) measured by using atomic force acoustic microscopy (AFAM) is reported in the present study. The real and imaginary parts of the contact stiffness k * are obtained from the contact-resonance spectra and by using these two quantities, the maps of local elastic stiffness and the damping factor are derived. The evaluation of the data is based on the mass distribution of the cantilever with damped flexural modes. The cantilever dynamics model considering damping, which was proposed recently, has been used for mapping of indentation modulus and damping of different phases in a metallic structural material. The study indicated that in a Ti-6Al-4V alloy the metastable β phase has the minimum modulus and the maximum damping followed by α′- and α-phases. Volume fractions of the individual phases were determined by using a commercial material property evaluation software and were validated by using X-ray diffraction (XRD) and electron back-scatter diffraction (EBSD) studies on one of the heat-treated samples. The volume fractions of the phases and the modulus measured through AFAM are used to derive average modulus of the bulk sample which is correlated with the bulk elastic properties obtained by ultrasonic velocity measurements. The average modulus of the specimens estimated by AFAM technique is found to be within 5% of that obtained by ultrasonic velocity measurements. The effect of heat treatments on the ultrasonic attenuation in the bulk sample could also be understood based on the damping measurements on individual phases using AFAM. PMID:25977847

Mapping of elasticity and damping in an α + β titanium alloy through atomic force acoustic microscopy.

PubMed

Phani, M Kalyan; Kumar, Anish; Jayakumar, T; Arnold, Walter; Samwer, Konrad

2015-01-01

The distribution of elastic stiffness and damping of individual phases in an α + β titanium alloy (Ti-6Al-4V) measured by using atomic force acoustic microscopy (AFAM) is reported in the present study. The real and imaginary parts of the contact stiffness k (*) are obtained from the contact-resonance spectra and by using these two quantities, the maps of local elastic stiffness and the damping factor are derived. The evaluation of the data is based on the mass distribution of the cantilever with damped flexural modes. The cantilever dynamics model considering damping, which was proposed recently, has been used for mapping of indentation modulus and damping of different phases in a metallic structural material. The study indicated that in a Ti-6Al-4V alloy the metastable β phase has the minimum modulus and the maximum damping followed by α'- and α-phases. Volume fractions of the individual phases were determined by using a commercial material property evaluation software and were validated by using X-ray diffraction (XRD) and electron back-scatter diffraction (EBSD) studies on one of the heat-treated samples. The volume fractions of the phases and the modulus measured through AFAM are used to derive average modulus of the bulk sample which is correlated with the bulk elastic properties obtained by ultrasonic velocity measurements. The average modulus of the specimens estimated by AFAM technique is found to be within 5% of that obtained by ultrasonic velocity measurements. The effect of heat treatments on the ultrasonic attenuation in the bulk sample could also be understood based on the damping measurements on individual phases using AFAM.

Dynamic profile of a prototype pivoted proof-mass actuator. [damping the vibration of large space structures

NASA Technical Reports Server (NTRS)

Miller, D. W.

1981-01-01

A prototype of a linear inertial reaction actuation (damper) device employing a flexure-pivoted reaction (proof) mass is discussed. The mass is driven by an electromechanic motor using a dc electromagnetic field and an ac electromagnetic drive. During the damping process, the actuator dissipates structural kinetic energy as heat through electromagnetic damping. A model of the inertial, stiffness and damping properties is presented along with the characteristic differential equations describing the coupled response of the actuator and structure. The equations, employing the dynamic coefficients, are oriented in the form of a feedback control network in which distributed sensors are used to dictate actuator response leading to a specified amount of structural excitation or damping.

Exploiting heat treatment effects on SMAs macro and microscopic properties in developing fire protection devices

NASA Astrophysics Data System (ADS)

Burlacu, L.; Cimpoeşu, N.; Bujoreanu, L. G.; Lohan, N. M.

2017-08-01

Ni-Ti shape memory alloys (SMAs) are intelligent alloys which demonstrate unique properties, such as shape memory effect, two-way shape memory effect, super-elasticity and vibration damping which, accompanied by good processability, excellent corrosion resistance and biocompatibility as well as fair wear resistance and cyclic stability, enabled the development of important industrial applications (such as sensors, actuators, fasteners, couplings and valves), medical applications (such as stents, bone implants, orthodontic archwires, minimal invasive surgical equipment) as well as environmental health and safety devices (anti-seismic dampers, fire safety devices). The phase transitions in Ni-Ti SMAs are strongly influenced by processing methods, chemical compositions and thermomechanical history. This paper presents a study of the effects of heat treatment on the mechanical and thermal properties of commercial Ni-Ti shape memory alloy (SMA). The experimental work involved subjecting a SMA rod to heat-treatment consisting in heating up to 500°C, 10 minutes-maintaining and water quenching. Mechanical properties were highlighted by microhardness tests while thermal characteristics were emphasized by differential scanning calorimetry (DSC). The presence of chemical composition fluctuations was checked by X-ray energy dispersive spectroscopy performed with an EDAX Bruker analyzer.

Stiffness and Damping in Postural Control Increase with Age

PubMed Central

Cenciarini, Massimo; Loughlin, Patrick J.; Sparto, Patrick J.; Redfern, Mark S.

2011-01-01

Upright balance is believed to be maintained through active and passive mechanisms, both of which have been shown to be impacted by aging. A compensatory balance response often observed in older adults is increased co-contraction, which is generally assumed to enhance stability by increasing joint stiffness. We investigated the effect of aging on standing balance by fitting body sway data to a previously-developed postural control model that includes active and passive stiffness and damping parameters. Ten young (24 ± 3 y) and seven older (75 ± 5 y) adults were exposed during eyes-closed stance to perturbations consisting of lateral pseudorandom floor tilts. A least-squares fit of the measured body sway data to the postural control model found significantly larger active stiffness and damping model parameters in the older adults. These differences remained significant even after normalizing to account for different body sizes between the young and older adult groups. An age effect was also found for the normalized passive stiffness, but not for the normalized passive damping parameter. This concurrent increase in active stiffness and damping was shown to be more stabilizing than an increase in stiffness alone, as assessed by oscillations in the postural control model impulse response. PMID:19770083

Non-synchronous rotating damping effects in gyroscopic rotating systems

NASA Astrophysics Data System (ADS)

Brusa, Eugenio; Zolfini, Giacomo

2005-03-01

The effects of non-synchronous rotating damping, i.e., of energy dissipation in elements rotating at a speed different from that of the main rotor, on the dynamic behaviour of the latter have been already studied in a previous paper (J. Rotating Machinery 6 (6) (2000)) for the case of non-gyroscopic rotating systems. A planar model, namely the Jeffcott's rotor, was used. The present study is aimed at investigating, through analytical and numerical models, the behaviour of rotors having a non-negligible gyroscopic effect. The parameters of the system affecting the dynamic stability are identified and the threshold of instability is then computed. A sort of map of stability is provided to allow mechanical engineers predicting possibile range of instability for forward and backward whirling motions. An experimental validation on a simple test rig is presented in order to show the effectiveness of the proposed stability analysis. Non-synchronous rotating damping is implemented by using a non-synchronous electromagnetic damper based on eddy currents.

Comparative study of popular objective functions for damping power system oscillations in multimachine system.

PubMed

Islam, Naz Niamul; Hannan, M A; Shareef, Hussain; Mohamed, Azah; Salam, M A

2014-01-01

Power oscillation damping controller is designed in linearized model with heuristic optimization techniques. Selection of the objective function is very crucial for damping controller design by optimization algorithms. In this research, comparative analysis has been carried out to evaluate the effectiveness of popular objective functions used in power system oscillation damping. Two-stage lead-lag damping controller by means of power system stabilizers is optimized using differential search algorithm for different objective functions. Linearized model simulations are performed to compare the dominant mode's performance and then the nonlinear model is continued to evaluate the damping performance over power system oscillations. All the simulations are conducted in two-area four-machine power system to bring a detailed analysis. Investigated results proved that multiobjective D-shaped function is an effective objective function in terms of moving unstable and lightly damped electromechanical modes into stable region. Thus, D-shape function ultimately improves overall system damping and concurrently enhances power system reliability.

A Study of Longitudinal Control Problems at Low and Negative Damping and Stability with Emphasis on Effects of Motion Cues

NASA Technical Reports Server (NTRS)

Sadoff, Melvin; McFadden, Norman M.; Heinle, Donovan R.

1961-01-01

As part of a general investigation to determine the effects of simulator motions on pilot opinion and task performance over a wide range of vehicle longitudinal dynamics, a cooperative NASA-AMAL program was conducted on the centrifuge at Johnsville, Pennsylvania. The test parameters and measurements for this program duplicated those of earlier studies made at Ames Research Center with a variable-stability airplane and with a pitch-roll chair flight simulator. Particular emphasis was placed on the minimum basic damping and stability the pilots would accept and on the minimum dynamics they considered controllable in the event of stability-augmentation system failure. Results of the centrifuge-simulator program indicated that small positive damping was required by the pilots over most of the frequency range covered for configurations rated acceptable for emergency conditions only (e.g., failure of a pitch damper). It was shown that the pilot's tolerance for unstable dynamics was dependent primarily on the value of damping. For configurations rated acceptable for emergency operation only, the allowable instability and damping corresponded to a divergence time to double amplitude of about 1 second. Comparisons were made of centrifuge, pitch-chair and fixed-cockpit simulator tests with flight tests. Pilot ratings indicated that the effects of incomplete or spurious motion cues provided by these three modes of simulation were important only for high-frequency, lightly damped dynamics or unstable, moderately damped dynamics. The pitch- chair simulation, which provided accurate angular-acceleration cues to the pilot, compared most favorably with flight. For the centrifuge simulation, which furnished accurate normal accelerations but spurious pitching and longitudinal accelerations, there was a deterioration of pilots' opinion relative to flight results. Results of simulator studies with an analog pilot replacing the human pilot illustrated the adaptive capability of human pilots in coping with the wide range of vehicle dynamics and the control problems covered in this study. It was shown that pilot-response characteristics, deduced by the analog-pilot method, could be related to pilot opinion. Possible application of these results for predicting flight-control problems was illustrated by means of an example control-problem analysis. The results of a brief evaluation of a pencil-type side-arm controller in the centrifuge showed a considerable improvement in the pilots' ability to cope with high-frequency, low-damping dynamics, compared to results obtained with the center stick. This improvement with the pencil controller was attributed primarily to a marked reduction in the adverse effects of large and exaggerated pitching and longitudinal accelerations on pilot control precision.

[Textural research on the origin and evolution of the"theory of drying dampness"and its initiator].

PubMed

Zhou, X M; Hu, J P

2016-07-28

There are two different records, namely,"vulnerability to dampness in autumn"and"dryness prevailing"in autumn, in the Neijing ( Inner Canon ). In the Jin and Yuan Dynasties, Liu Wansu supplemented the pathogenesis of dryness pathogen, whereas Wang Andao explained the contradictory records in the Neijing . In the Qing Dynasty, Yu Chang definitely challenged the theory"vulnerability to dampness in autumn"of the Neijing ,triggering a debate on the recognition of"drying dampness". In fact, Yu Guopei was the initiator of"theory of drying dampness", who discussed the nature of Yin and Yang of"drying dampness"based on the laws of correspondence between human body and natural environment, elucidating that drying dampness should be the root of both exogenous disease and internal damage, and elaborating the etiology and pathogenesis of"drying dampness", the diagnosis and the nature of the drugs for drying dampness. Shi Shoutang inherited Yu's theory and made a further development. In modern times, some scholars advocated that"drying dampness"should be consideredalong with Yin and Yang, superficies and interior, excess and deficiency, cold and heat, as the guiding principle for syndrome differentiation.

Computation of Stability Derivatives of an oscillating cone for specific heat ratio = 1.66

NASA Astrophysics Data System (ADS)

Shabana, Aysha; Monis, Renita Sharon; Crasta, Asha; Khan, S. A.

2018-05-01

In this paper the expressions for stiffness and Damping derivatives are obtained in a closed form for perfect gas where the flow is quasi-steady and axi-axisymmetric, and the nose semi angle of the cone is such that the Mach number M 2 behind the shock M 2 ≥ 2.5. Results are presented for an oscillating cone for gas with = 1.666, at different Mach numbers and semi cone angles. The Stiffness derivative decreases with pivot position and also with semi vertex angle, there is substantial change in the stiffness derivative when semi-vertex has been increased from 5 degrees to ten degrees, further increase in the semi-vertex angle results in marginal change in the stiffness derivative. Due the marginal change in the Mach number level there is marginal increase in the magnitude of the stability and with further increase in the inertia level the stability derivative conform to the Mach number independence principle. The present theory for Oscillating cone is restricted to quasi-steady case. Viscous effects have been neglected. The expressions so obtained for stability derivative in pitch are valid for a slender ogive which often approximates to the whole fuselage of an aircraft.

Environmental stability of high-mobility indium-oxide based transparent electrodes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tohsophon, Thanaporn; Dabirian, Ali; De Wolf, Stefaan

2015-11-01

Large-scale deployment of a wide range of optoelectronic devices, including solar cells, critically depends on the long-term stability of their front electrodes. Here, we investigate the performance of Sn-doped In{sub 2}O{sub 3} (ITO), H-doped In{sub 2}O{sub 3} (IO:H), and Zn-doped In{sub 2}O{sub 3} (IZO) electrodes under damp heat (DH) conditions (85 °C, 85% relative humidity). ITO, IO:H capped with ITO, and IZO show high stability with only 3%, 9%, and 13% sheet resistance (R{sub s}) degradation after 1000 h of DH, respectively. For uncapped IO:H, we find a 75% R{sub s} degradation, due to losses in electron Hall mobility (μ{sub Hall}).more » We propose that this degradation results from chemisorbed OH- or H{sub 2}O-related species in the film, which is confirmed by thermal desorption spectroscopy and x-ray photoelectron spectroscopy. While μ{sub Hall} strongly degrades during DH, the optical mobility (μ{sub optical}) remains unchanged, indicating that the degradation mainly occurs at grain boundaries.« less

Passive damping in EDS maglev systems.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rote, D. M.

2002-05-03

There continues to be strong interest in the subjects of damping and drag forces associated with electrodynamic suspension (EDS) systems. While electromagnetic drag forces resist the forward motion of a vehicle and therefore consume energy, damping forces control, at least in part, the response of the vehicle to disturbances. Ideally, one would like to reduce the drag forces as much as possible while retaining adequate damping forces to insure dynamic stability and satisfactory ride quality. These two goals turn out to be difficult to achieve in practice. It is well known that maglev systems tend to be intrinsically under damped.more » Consequently it is often necessary in a practical system design to enhance the damping passively or actively. For reasons of cost and simplicity, it is desirable to rely as much as possible on passive damping mechanisms. In this paper, rough estimates are made of the passive damping and drag forces caused by various mechanisms in EDS systems. No attention will be given to active control systems or secondary suspension systems which are obvious ways to augment passive damping mechanisms if the latter prove to be inadequate.« less

On the stability analysis of a pair of van der Pol oscillators with delayed self-connection, position and velocity couplings

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hu, Kun; Department of Mathematics, City University of Hong Kong, 83 Tat Chee Avenue, Kowloon; Chung, Kwok-wai, E-mail: makchung@cityu.edu.hk

2013-11-15

In this paper, we perform a stability analysis of a pair of van der Pol oscillators with delayed self-connection, position and velocity couplings. Bifurcation diagram of the damping, position and velocity coupling strengths is constructed, which gives insight into how stability boundary curves come into existence and how these curves evolve from small closed loops into open-ended curves. The van der Pol oscillator has been considered by many researchers as the nodes for various networks. It is inherently unstable at the zero equilibrium. Stability control of a network is always an important problem. Currently, the stabilization of the zero equilibriummore » of a pair of van der Pol oscillators can be achieved only for small damping strength by using delayed velocity coupling. An interesting question arises naturally: can the zero equilibrium be stabilized for an arbitrarily large value of the damping strength? We prove that it can be. In addition, a simple condition is given on how to choose the feedback parameters to achieve such goal. We further investigate how the in-phase mode or the out-of-phase mode of a periodic solution is related to the stability boundary curve that it emerges from a Hopf bifurcation. Analytical expression of a periodic solution is derived using an integration method. Some illustrative examples show that the theoretical prediction and numerical simulation are in good agreement.« less

Vibration exciting mechanisms induced by flow in turbomachine stages

NASA Technical Reports Server (NTRS)

Thompson, W. E.

1980-01-01

The quasisteady computer analysis of the perturbated centrifugal impeller passage flow was reviewed. A total of 115 stage calculations were used to define the fluid damping coefficient, delta sub fluid. Results indicate that the average total damping coefficient per stage needed for stability is delta sub total 1.85.

Turbine Engine Stability/Instability With Rub Forces Axisymmetric Rotor-Support Stiffness

NASA Technical Reports Server (NTRS)

Gallardo, Vicente; Lawrence, Charles

2004-01-01

The stability/instability condition of a turbine rotor with axisymmetric supports is determined in the presence of gyroscopic loads and rub-induced destabilizing forces. A modal representation of the turbine engine is used, with one mode in each of the vertical and horizontal planes. The use of non-spinning rotor modes permits an explicit treatment of gyroscopic effects. The two linearized modal equations of motion of a rotor with axisymmetric supports are reduced to a single equation in a complex variable. The resulting eigenvalues yield explicit expressions at the stability boundary, for the whirl frequency as well as the required damping for stability in the presence of the available rub-induced destabilization. Conversely, the allowable destabilization in the presence of the available damping is also given.

Mode transition of a Hall thruster discharge plasma

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hara, Kentaro, E-mail: kenhara@umich.edu; Sekerak, Michael J., E-mail: msekerak@umich.edu; Boyd, Iain D.

2014-05-28

A Hall thruster is a cross-field plasma device used for spacecraft propulsion. An important unresolved issue in the development of Hall thrusters concerns the effect of discharge oscillations in the range of 10–30 kHz on their performance. The use of a high speed Langmuir probe system and ultra-fast imaging of the discharge plasma of a Hall thruster suggests that the discharge oscillation mode, often called the breathing mode, is strongly correlated to an axial global ionization mode. Stabilization of the global oscillation mode is achieved as the magnetic field is increased and azimuthally rotating spokes are observed. A hybrid-direct kinetic simulationmore » that takes into account the transport of electronically excited atoms is used to model the discharge plasma of a Hall thruster. The predicted mode transition agrees with experiments in terms of the mean discharge current, the amplitude of discharge current oscillation, and the breathing mode frequency. It is observed that the stabilization of the global oscillation mode is associated with reduced electron transport that suppresses the ionization process inside the channel. As the Joule heating balances the other loss terms including the effects of wall loss and inelastic collisions, the ionization oscillation is damped, and the discharge oscillation stabilizes. A wide range of the stable operation is supported by the formation of a space charge saturated sheath that stabilizes the electron axial drift and balances the Joule heating as the magnetic field increases. Finally, it is indicated from the numerical results that there is a strong correlation between the emitted light intensity and the discharge current.« less

Linear stability analysis of the three-dimensional thermally-driven ocean circulation: application to interdecadal oscillations

NASA Astrophysics Data System (ADS)

Huck, Thierry; Vallis, Geoffrey K.

2001-08-01

What can we learn from performing a linear stability analysis of the large-scale ocean circulation? Can we predict from the basic state the occurrence of interdecadal oscillations, such as might be found in a forward integration of the full equations of motion? If so, do the structure and period of the linearly unstable modes resemble those found in a forward integration? We pursue here a preliminary study of these questions for a case in idealized geometry, in which the full nonlinear behavior can also be explored through forward integrations. Specifically, we perform a three-dimensional linear stability analysis of the thermally-driven circulation of the planetary geostrophic equations. We examine the resulting eigenvalues and eigenfunctions, comparing them with the structure of the interdecadal oscillations found in the fully nonlinear model in various parameter regimes. We obtain a steady state by running the time-dependent, nonlinear model to equilibrium using restoring boundary conditions on surface temperature. If the surface heat fluxes are then diagnosed, and these values applied as constant flux boundary conditions, the nonlinear model switches into a state of perpetual, finite amplitude, interdecadal oscillations. We construct a linearized version of the model by empirically evaluating the tangent linear matrix at the steady state, under both restoring and constant-flux boundary conditions. An eigen-analysis shows there are no unstable eigenmodes of the linearized model with restoring conditions. In contrast, under constant flux conditions, we find a single unstable eigenmode that shows a striking resemblance to the fully-developed oscillations in terms of three-dimensional structure, period and growth rate. The mode may be damped through either surface restoring boundary conditions or sufficiently large horizontal tracer diffusion. The success of this simple numerical method in idealized geometry suggests applications in the study of the stability of the ocean circulation in more realistic configurations, and the possibility of predicting potential oceanic modes, even weakly damped, that might be excited by stochastic atmospheric forcing or mesoscale ocean eddies.

Parametric survey of longitudinal prominence oscillation simulations

NASA Astrophysics Data System (ADS)

Zhang, Q. M.; Chen, P. F.; Xia, C.; Keppens, R.; Ji, H. S.

2013-06-01

Context. Longitudinal filament oscillations recently attracted increasing attention, while the restoring force and the damping mechanisms are still elusive. Aims: We intend to investigate the underlying physics for coherent longitudinal oscillations of the entire filament body, including their triggering mechanism, dominant restoring force, and damping mechanisms. Methods: With the MPI-AMRVAC code, we carried out radiative hydrodynamic numerical simulations of the longitudinal prominence oscillations. We modeled two types of perturbations of the prominence, impulsive heating at one leg of the loop and an impulsive momentum deposition, which cause the prominence to oscillate. We studied the resulting oscillations for a large parameter scan, including the chromospheric heating duration, initial velocity of the prominence, and field line geometry. Results: We found that both microflare-sized impulsive heating at one leg of the loop and a suddenly imposed velocity perturbation can propel the prominence to oscillate along the magnetic dip. Our extensive parameter survey resulted in a scaling law that shows that the period of the oscillation, which weakly depends on the length and height of the prominence and on the amplitude of the perturbations, scales with √R/g⊙, where R represents the curvature radius of the dip, and g⊙ is the gravitational acceleration of the Sun. This is consistent with the linear theory of a pendulum, which implies that the field-aligned component of gravity is the main restoring force for the prominence longitudinal oscillations, as confirmed by the force analysis. However, the gas pressure gradient becomes significant for short prominences. The oscillation damps with time in the presence of non-adiabatic processes. Radiative cooling is the dominant factor leading to damping. A scaling law for the damping timescale is derived, i.e., τ~ l1.63 D0.66w-1.21v0-0.30, showing strong dependence on the prominence length l, the geometry of the magnetic dip (characterized by the depth D and the width w), and the velocity perturbation amplitude v0. The larger the amplitude, the faster the oscillation damps. We also found that mass drainage significantly reduces the damping timescale when the perturbation is too strong.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Huang, Zhenyu; Zhou, Ning; Tuffner, Francis K.

Small signal stability problems are one of the major threats to grid stability and reliability in the U.S. power grid. An undamped mode can cause large-amplitude oscillations and may result in system breakups and large-scale blackouts. There have been several incidents of system-wide oscillations. Of those incidents, the most notable is the August 10, 1996 western system breakup, a result of undamped system-wide oscillations. Significant efforts have been devoted to monitoring system oscillatory behaviors from measurements in the past 20 years. The deployment of phasor measurement units (PMU) provides high-precision, time-synchronized data needed for detecting oscillation modes. Measurement-based modal analysis,more » also known as ModeMeter, uses real-time phasor measurements to identify system oscillation modes and their damping. Low damping indicates potential system stability issues. Modal analysis has been demonstrated with phasor measurements to have the capability of estimating system modes from both oscillation signals and ambient data. With more and more phasor measurements available and ModeMeter techniques maturing, there is yet a need for methods to bring modal analysis from monitoring to actions. The methods should be able to associate low damping with grid operating conditions, so operators or automated operation schemes can respond when low damping is observed. The work presented in this report aims to develop such a method and establish a Modal Analysis for Grid Operation (MANGO) procedure to aid grid operation decision making to increase inter-area modal damping. The procedure can provide operation suggestions (such as increasing generation or decreasing load) for mitigating inter-area oscillations.« less

Effect of hot working on the damping capacity and mechanical properties of AZ31 magnesium alloy

NASA Astrophysics Data System (ADS)

Lee, K.; Kang, C.; Kim, K.

2015-04-01

Magnesium alloys have received much attention for their lightweight and other excellent properties, such as low density, high specific strength, and good castability, for use in several industrial and commercial applications. However, both magnesium and its alloys show limited room-temperature formability owing to the limited number of slip systems associated with their hexagonal close-packed crystal structure. It is well known that crystallographic texture plays an important role in both plastic deformation and macroscopic anisotropy of magnesium alloys. Many authors have concentrated on improving the room- temperature formability of Mg alloys. However, despite having a lot of excellent properties in magnesium alloy, the study for various properties of magnesium alloy have not been clarified enough yet. Mg alloys are known to have a good damping capacity compared to other known metals and their alloys. Also, the damping properties of metals are generally recognized to be dependent on microstructural factors such as grain size and texture. However, there are very few studies on the relationship between the damping capacity and texture of Magnesium alloys. Therefore, in this study, specimens of the AZ31 magnesium alloy, were processed by hot working, and their texture and damping property investigated. A 60 mm × 60 mm × 40 mm rectangular plate was cut out by machining an ingot of AZ31 magnesium alloy (Mg-3Al-1Zn in mass%), and rolling was carried out at 673 K to a rolling reduction of 30%. Then, heat treatment was carried out at temperatures in the range of 573-723 K for durations in the range of 30-180 min. The samples were immediately quenched in oil after heat treatment to prevent any change in the microstructure. Texture was evaluated on the compression planes by the Schulz reflection method using nickel-filtered Cu Kα radiation. Electron backscatter diffraction measurements were conducted to observe the spatial distribution of various orientations. Specimens for damping capacity measurements were machined from the rolled specimen, to have a length of 120 mm, width of 20 mm, and thickness of 1 mm. The damping capacity was measured with a flexural internal friction measurement machine at room temperature. It was found that the damping capacity increases with both increasing heat-treatment temperature and time, due to grain growth and the increased pole densities of textures.

Physical explanations of the destabilizing effect of damping in rotating parts

NASA Technical Reports Server (NTRS)

Crandall, S. H.

1980-01-01

The destabilizing effect of rotating damping was investigated. When the rotation was faster than the whirl, rotating damping drags the orbiting particle forward. When stationary damping was also present, the stability borderline was readily determined by balancing the backward and forward drags. A key notion was that a forward whirl at rate omega a sub n with respect to stationary axes appears to be a backward whirl at rate Omega - omega sub n with respect to a system rotating supercritically at rate Omega. The growth rate of unstable whirls (or the decay rate of stable whirls was readily estimated by a simple energy balance.

Suppression of Instabilities Generated by an Anti-Damper with a Nonlinear Magnetic Element in IOTA

DOE Office of Scientific and Technical Information (OSTI.GOV)

Stern, E.

The Integrable Optics Test Accelerator (IOTA) storage ring is being constructed at Fermilab as a testbed for new accelerator concepts. One important series of experiments tests the use of a novel nonlinear magnetic insert to damp coherent instabilities. To test the damping power of the element, an instability of desired strength may be intentionally excited with an anti-damper. We report on simulations of beam stabilization using the Synergia modeling framework over ranges of driving and damping strengths.

A full-scale wind tunnel investigation of a helicopter bearingless main rotor. [Ames 40 by 80 Wind Tunnel

NASA Technical Reports Server (NTRS)

Warmbrodt, W.; Mccloud, J. L., II

1981-01-01

A helicopter bearingless main rotor was tested. Areas of investigation included aeroelastic stability, aerodynamic performance, and rotor loads as a function of collective pitch setting, RPM, airspeed and shaft angle. The rotor/support system was tested with the wind tunnel balance dampers installed and, subsequently, removed. Modifications to the rotor hub were tested. These included a reduction in the rotor control system stiffness and increased flexbeam structural damping. The primary objective of the test was to determine aeroelastic stability of the fundamental flexbeam/blade chordwise bending mode. The rotor was stable for all conditions. Damping of the rotor chordwise bending mode increases with increased collective pitch angle at constant operating conditions. No significant decrease in rotor damping occured due to frequency coalescence between the blade chordwise fundamental bending mode and the support system.

A modified precise integration method for transient dynamic analysis in structural systems with multiple damping models

NASA Astrophysics Data System (ADS)

Ding, Zhe; Li, Li; Hu, Yujin

2018-01-01

Sophisticated engineering systems are usually assembled by subcomponents with significantly different levels of energy dissipation. Therefore, these damping systems often contain multiple damping models and lead to great difficulties in analyzing. This paper aims at developing a time integration method for structural systems with multiple damping models. The dynamical system is first represented by a generally damped model. Based on this, a new extended state-space method for the damped system is derived. A modified precise integration method with Gauss-Legendre quadrature is then proposed. The numerical stability and accuracy of the proposed integration method are discussed in detail. It is verified that the method is conditionally stable and has inherent algorithmic damping, period error and amplitude decay. Numerical examples are provided to assess the performance of the proposed method compared with other methods. It is demonstrated that the method is more accurate than other methods with rather good efficiency and the stable condition is easy to be satisfied in practice.

Reliable Channel-Adapted Error Correction: Bacon-Shor Code Recovery from Amplitude Damping

NASA Astrophysics Data System (ADS)

Piedrafita, Álvaro; Renes, Joseph M.

2017-12-01

We construct two simple error correction schemes adapted to amplitude damping noise for Bacon-Shor codes and investigate their prospects for fault-tolerant implementation. Both consist solely of Clifford gates and require far fewer qubits, relative to the standard method, to achieve exact correction to a desired order in the damping rate. The first, employing one-bit teleportation and single-qubit measurements, needs only one-fourth as many physical qubits, while the second, using just stabilizer measurements and Pauli corrections, needs only half. The improvements stem from the fact that damping events need only be detected, not corrected, and that effective phase errors arising due to undamped qubits occur at a lower rate than damping errors. For error correction that is itself subject to damping noise, we show that existing fault-tolerance methods can be employed for the latter scheme, while the former can be made to avoid potential catastrophic errors and can easily cope with damping faults in ancilla qubits.

Optimization of a Nutation Damper Attached to a Spin-Stabilized Satellite.

DTIC Science & Technology

1994-12-01

characteristic roots describe the damping of the simple system. The damping time index, as proposed by Borelli and Leliakov (5:345), is defined as the...Viscous Ring Damper for a Freely Precessing Satellite." International Journal of Mechanical Sciences. Vol. 8. 1966. pp. 383- 395. 5. Borelli , R. L

Stabilizing the long-time behavior of the forced Navier-Stokes and damped Euler systems by large mean flow

NASA Astrophysics Data System (ADS)

Cyranka, Jacek; Mucha, Piotr B.; Titi, Edriss S.; Zgliczyński, Piotr

2018-04-01

The paper studies the issue of stability of solutions to the forced Navier-Stokes and damped Euler systems in periodic boxes. It is shown that for large, but fixed, Grashoff (Reynolds) number the turbulent behavior of all Leray-Hopf weak solutions of the three-dimensional Navier-Stokes equations, in periodic box, is suppressed, when viewed in the right frame of reference, by large enough average flow of the initial data; a phenomenon that is similar in spirit to the Landau damping. Specifically, we consider an initial data which have large enough spatial average, then by means of the Galilean transformation, and thanks to the periodic boundary conditions, the large time independent forcing term changes into a highly oscillatory force; which then allows us to employ some averaging principles to establish our result. Moreover, we also show that under the action of fast oscillatory-in-time external forces all two-dimensional regular solutions of the Navier-Stokes and the damped Euler equations converge to a unique time-periodic solution.

Research of vibration control based on current mode piezoelectric shunt damping circuit

NASA Astrophysics Data System (ADS)

Liu, Weiwei; Mao, Qibo

2017-12-01

The piezoelectric shunt damping circuit using current mode approach is imposed to control the vibration of a cantilever beam. Firstly, the simulated inductance with large values are designed for the corresponding RL series shunt circuits. Moreover, with an example of cantilever beam, the second natural frequency of the beam is targeted to control for experiment. By adjusting the values of the equivalent inductance and equivalent resistance of the shunt circuit, the optimal damping of the shunt circuit is obtained. Meanwhile, the designed piezoelectric shunt damping circuit stability is experimental verified. Experimental results show that the proposed piezoelectric shunt damping circuit based on current mode circuit has good vibration control performance. However, the control performance will be reduced if equivalent inductance and equivalent resistance values deviate from optimal values.

Symbolic-Numerical Modeling of the Influence of Damping Moments on Satellite Dynamics

NASA Astrophysics Data System (ADS)

Gutnik, Sergey A.; Sarychev, Vasily A.

2018-02-01

The dynamics of a satellite on a circular orbit under the influence of gravitational and active damping torques, which are proportional to the projections of the angular velocity of the satellite, is investigated. Computer algebra Gröbner basis methods for the determination of all equilibrium orientations of the satellite in the orbital coordinate system with given damping torque and given principal central moments of inertia were used. The conditions of the equilibria existence depending on three damping parameters were obtained from the analysis of the real roots of the algebraic equations spanned by the constructed Gröbner basis. Conditions of asymptotic stability of the satellite equilibria and the transition decay processes of the spatial oscillations of the satellite at different damping parameters have also been obtained.

Efficiency of perfectly matched layers for seismic wave modeling in second-order viscoelastic equations

NASA Astrophysics Data System (ADS)

Ping, Ping; Zhang, Yu; Xu, Yixian; Chu, Risheng

2016-12-01

In order to improve the perfectly matched layer (PML) efficiency in viscoelastic media, we first propose a split multi-axial PML (M-PML) and an unsplit convolutional PML (C-PML) in the second-order viscoelastic wave equations with the displacement as the only unknown. The advantage of these formulations is that it is easy and efficient to revise the existing codes of the second-order spectral element method (SEM) or finite-element method (FEM) with absorbing boundaries in a uniform equation, as well as more economical than the auxiliary differential equations PML. Three models which are easily suffered from late time instabilities are considered to validate our approaches. Through comparison the M-PML with C-PML efficiency of absorption and stability for long time simulation, it can be concluded that: (1) for an isotropic viscoelastic medium with high Poisson's ratio, the C-PML will be a sufficient choice for long time simulation because of its weak reflections and superior stability; (2) unlike the M-PML with high-order damping profile, the M-PML with second-order damping profile loses its stability in long time simulation for an isotropic viscoelastic medium; (3) in an anisotropic viscoelastic medium, the C-PML suffers from instabilities, while the M-PML with second-order damping profile can be a better choice for its superior stability and more acceptable weak reflections than the M-PML with high-order damping profile. The comparative analysis of the developed methods offers meaningful significance for long time seismic wave modeling in second-order viscoelastic wave equations.

An experimental investigation of the flap-lag-torsion aeroelastic stability of a small-scale hingeless helicopter rotor in hover

NASA Technical Reports Server (NTRS)

Sharpe, David L.

1986-01-01

A small scale, 1.92 m diam, torsionally soft, hingeless helicopter rotor was investigated in hover to determine isolated rotor stability characteristics. The two-bladed, untwisted rotor was tested on a rigid test stand at tip speeds up to 101 m/sec. The rotor mode of interest is the lightly damped lead-lag mode. The dimensionless lead-lag frequency of the mode is approximately 1.5 at the highest tip speed. The hub was designed to allow variation in precone, blade droop, pitch control stiffness, and blade pitch angle. Measurements of modal frequency and damping were obtained for several combinations of these hub parameters at several values of rotor speed. Steady blade bending moments were also measured. The lead-lag damping measurements were found to agree well with theoretical predictions for low values of blade pitch angle. The test data confirmed the predicted effects of precone, droop, and pitch control stiffness parameters on lead-lag damping. The correlation between theory and experiment was found to be poor for the mid-to-high range of pitch angles where the theory substantially overpredicted the experimental lead-lag damping. The poor correlation in the mid-to-high blade pitch angle range is attributed to low Reynolds number nonlinear aerodynamics effects not included in the theory. The experimental results also revealed an asymmetry in lead-lag damping between positive and negative thrust conditions.

Flight Dynamics of an Aeroshell Using an Attached Inflatable Aerodynamic Decelerator

NASA Technical Reports Server (NTRS)

Cruz, Juan R.; Schoenenberger, Mark; Axdahl, Erik; Wilhite, Alan

2009-01-01

An aeroelastic analysis of the behavior of an entry vehicle utilizing an attached inflatable aerodynamic decelerator during supersonic flight is presented. The analysis consists of a planar, four degree of freedom simulation. The aeroshell and the IAD are assumed to be separate, rigid bodies connected with a spring-damper at an interface point constraining the relative motion of the two bodies. Aerodynamic forces and moments are modeled using modified Newtonian aerodynamics. The analysis includes the contribution of static aerodynamic forces and moments as well as pitch damping. Two cases are considered in the analysis: constant velocity flight and planar free flight. For the constant velocity and free flight cases with neutral pitch damping, configurations with highly-stiff interfaces exhibit statically stable but dynamically unstable aeroshell angle of attack. Moderately stiff interfaces exhibit static and dynamic stability of aeroshell angle of attack due to damping induced by the pitch angle rate lag between the aeroshell and IAD. For the free-flight case, low values of both the interface stiffness and damping cause divergence of the aeroshell angle of attack due to the offset of the IAD drag force with respect to the aeroshell center of mass. The presence of dynamic aerodynamic moments was found to influence the stability characteristics of the vehicle. The effect of gravity on the aeroshell angle of attack stability characteristics was determined to be negligible for the cases investigated.

Turbulent dissipation challenge: a community-driven effort

NASA Astrophysics Data System (ADS)

Parashar, Tulasi N.; Salem, Chadi; Wicks, Robert T.; Karimabadi, H.; Gary, S. Peter; Matthaeus, William H.

2015-10-01

> Many naturally occurring and man-made plasmas are collisionless and turbulent. It is not yet well understood how the energy in fields and fluid motions is transferred into the thermal degrees of freedom of constituent particles in such systems. The debate at present primarily concerns proton heating. Multiple possible heating mechanisms have been proposed over the past few decades, including cyclotron damping, Landau damping, heating at intermittent structures and stochastic heating. Recently, a community-driven effort was proposed (Parashar & Salem, 2013, arXiv:1303.0204) to bring the community together and understand the relative contributions of these processes under given conditions. In this paper, we propose the first step of this challenge: a set of problems and diagnostics for benchmarking and comparing different types of 2.5D simulations. These comparisons will provide insights into the strengths and limitations of different types of numerical simulations and will help guide subsequent stages of the challenge.

The Walker circulation, diabatic heating, and outgoing longwave radiation

NASA Astrophysics Data System (ADS)

Stechmann, S. N.; Ogrosky, H. R.

2014-12-01

For the tropical atmosphere on planetary scales, it is common to model the circulation using strong damping. Here, with new data analysis techniques, evidence suggests that damping can actually be neglected. Specifically, near the equator, the east--west overturning circulation is in agreement with the undamped wave response to atmospheric heating. To estimate the heating, satellite observations of outgoing longwave radiation (OLR) are used. Frequently OLR is used as a heuristic indicator of cloudiness. Here, the results further suggest that OLR variations are actually proportional to total diabatic heating variations, with a proportionality constant of 18 W m-2 (K/day)-1. While the agreement holds best over long time averages of years or decades, it also holds over shorter periods of one season or one month. Consequently, it is suggested that the strength of the Walker circulation -- and its evolution in time -- could be estimated using satellite data.

GOES-R active vibration damping controller design, implementation, and on-orbit performance

NASA Astrophysics Data System (ADS)

Clapp, Brian R.; Weigl, Harald J.; Goodzeit, Neil E.; Carter, Delano R.; Rood, Timothy J.

2018-01-01

GOES-R series spacecraft feature a number of flexible appendages with modal frequencies below 3.0 Hz which, if excited by spacecraft disturbances, can be sources of undesirable jitter perturbing spacecraft pointing. To meet GOES-R pointing stability requirements, the spacecraft flight software implements an Active Vibration Damping (AVD) rate control law which acts in parallel with the nadir point attitude control law. The AVD controller commands spacecraft reaction wheel actuators based upon Inertial Measurement Unit (IMU) inputs to provide additional damping for spacecraft structural modes below 3.0 Hz which vary with solar wing angle. A GOES-R spacecraft dynamics and attitude control system identified model is constructed from pseudo-random reaction wheel torque commands and IMU angular rate response measurements occurring over a single orbit during spacecraft post-deployment activities. The identified Fourier model is computed on the ground, uplinked to the spacecraft flight computer, and the AVD controller filter coefficients are periodically computed on-board from the Fourier model. Consequently, the AVD controller formulation is based not upon pre-launch simulation model estimates but upon on-orbit nadir point attitude control and time-varying spacecraft dynamics. GOES-R high-fidelity time domain simulation results herein demonstrate the accuracy of the AVD identified Fourier model relative to the pre-launch spacecraft dynamics and control truth model. The AVD controller on-board the GOES-16 spacecraft achieves more than a ten-fold increase in structural mode damping for the fundamental solar wing mode while maintaining controller stability margins and ensuring that the nadir point attitude control bandwidth does not fall below 0.02 Hz. On-orbit GOES-16 spacecraft appendage modal frequencies and damping ratios are quantified based upon the AVD system identification, and the increase in modal damping provided by the AVD controller for each structural mode is presented. The GOES-16 spacecraft AVD controller frequency domain stability margins and nadir point attitude control bandwidth are presented along with on-orbit time domain disturbance response performance.

GOES-R Active Vibration Damping Controller Design, Implementation, and On-Orbit Performance

NASA Technical Reports Server (NTRS)

Clapp, Brian R.; Weigl, Harald J.; Goodzeit, Neil E.; Carter, Delano R.; Rood, Timothy J.

2017-01-01

GOES-R series spacecraft feature a number of flexible appendages with modal frequencies below 3.0 Hz which, if excited by spacecraft disturbances, can be sources of undesirable jitter perturbing spacecraft pointing. In order to meet GOES-R pointing stability requirements, the spacecraft flight software implements an Active Vibration Damping (AVD) rate control law which acts in parallel with the nadir point attitude control law. The AVD controller commands spacecraft reaction wheel actuators based upon Inertial Measurement Unit (IMU) inputs to provide additional damping for spacecraft structural modes below 3.0 Hz which vary with solar wing angle. A GOES-R spacecraft dynamics and attitude control system identified model is constructed from pseudo-random reaction wheel torque commands and IMU angular rate response measurements occurring over a single orbit during spacecraft post-deployment activities. The identified Fourier model is computed on the ground, uplinked to the spacecraft flight computer, and the AVD controller filter coefficients are periodically computed on-board from the Fourier model. Consequently, the AVD controller formulation is based not upon pre-launch simulation model estimates but upon on-orbit nadir point attitude control and time-varying spacecraft dynamics. GOES-R high-fidelity time domain simulation results herein demonstrate the accuracy of the AVD identified Fourier model relative to the pre-launch spacecraft dynamics and control truth model. The AVD controller on-board the GOES-16 spacecraft achieves more than a ten-fold increase in structural mode damping of the fundamental solar wing mode while maintaining controller stability margins and ensuring that the nadir point attitude control bandwidth does not fall below 0.02 Hz. On-orbit GOES-16 spacecraft appendage modal frequencies and damping ratios are quantified based upon the AVD system identification, and the increase in modal damping provided by the AVD controller for each structural mode is presented. The GOES-16 spacecraft AVD controller frequency domain stability margins and nadir point attitude control bandwidth are presented along with on-orbit time domain disturbance response performance.

Stability Limits of a PD Controller for a Flywheel Supported on Rigid Rotor and Magnetic Bearings

NASA Technical Reports Server (NTRS)

Kascak, Albert F.; Brown, Gerald V.; Jansen, Ralph H.; Dever, TImothy P.

2006-01-01

Active magnetic bearings are used to provide a long-life, low-loss suspension of a high-speed flywheel rotor. This paper describes a modeling effort used to understand the stability boundaries of the PD controller used to control the active magnetic bearings on a high speed test rig. Limits of stability are described in terms of allowable stiffness and damping values which result in stable levitation of the nonrotating rig. Small signal stability limits for the system is defined as a nongrowth in vibration amplitude of a small disturbance. A simple mass-force model was analyzed. The force resulting from the magnetic bearing was linearized to include negative displacement stiffness and a current stiffness. The current stiffness was then used in a PD controller. The phase lag of the control loop was modeled by a simple time delay. The stability limits and the associated vibration frequencies were measured and compared to the theoretical values. The results show a region on stiffness versus damping plot that have the same qualitative tendencies as experimental measurements. The resulting stability model was then extended to a flywheel system. The rotor dynamics of the flywheel was modeled using a rigid rotor supported on magnetic bearings. The equations of motion were written for the center of mass and a small angle linearization of the rotations about the center of mass. The stability limits and the associated vibration frequencies were found as a function of nondimensional magnetic bearing stiffness and damping and nondimensional parameters of flywheel speed and time delay.

Theoretical and experimental research in aeroelastic stability of an advanced bearingless rotor for future helicopters

NASA Technical Reports Server (NTRS)

Wang, James M.

1991-01-01

The aeroelastic stability of a shaft-fixed bearingless rotor is analyzed in wind-tunnel tests for a wide range of operating conditions in order to determine whether such a system could be made aeroelastically stable without incorporating auxiliary dampers. The model rotor and blade properties are determined and used as an input to a bearingless-rotor analysis. Theoretical predictions are compared with experimental results in hover and forward flights. The analysis predicts the lag mode damping satisfactorily for collective pitch between 5 deg and 10 deg; however, the quasi-steady linear aerodynamic modeling overpredicts the damping values for higher collective pitch settings. It is noted that soft blade pitch links improve aeroelastic stability in hover and at low advance ratio.

Sub-millikelvin stabilization of a closed cycle cryocooler

DOE PAGES

Dubuis, Guy; He, Xi; Božović, Ivan

2014-10-03

In this study, intrinsic temperature oscillations (with the amplitude up to 1 K) of a closed cycle cryocooler are stabilized by a simple thermal damping system. It employs three different materials with different thermal conductivity and capacity at various temperatures. The amplitude of oscillations of the sample temperature is reduced to less than 1 mK, in the temperature range from 4 K to 300 K, while the cooling power is virtually undiminished. The damping system is small, inexpensive, can be retrofitted to most existing closed cycle cryocoolers, and may improve measurements of any temperature-sensitive physics properties.

Damping torque analysis of VSC-based system utilizing power synchronization control

NASA Astrophysics Data System (ADS)

Fu, Q.; Du, W. J.; Zheng, K. Y.; Wang, H. F.

2017-05-01

Power synchronization control is a new control strategy of VSC-HVDC for connecting a weak power system. Different from the vector control method, this control method utilizes the internal synchronization mechanism in ac systems, in principle, similar to the operation of a synchronous machine. So that the parameters of controllers in power synchronization control will change the electromechanical oscillation modes and make an impact on the transient stability of power system. This paper present a mathematical model for small-signal stability analysis of VSC station used power synchronization control and analyse the impact of the dynamic interactions by calculating the contribution of the damping torque from the power synchronization control, besides, the parameters of controllers which correspond to damping torque and synchronous torque in the power synchronization control is defined respectively. At the end of the paper, an example power system is presented to demonstrate and validate the theoretical analysis and associated conclusions are made.

Estimation of Rotary Stability Derivatives at Subsonic and Transonic Speeds

NASA Technical Reports Server (NTRS)

Tobak, Murray; Lessing, Henry C.

1961-01-01

The first part of this paper pertains to the estimation of subsonic rotary stability derivatives of wings. The unsteady potential flow problem is solved by a superposition of steady flow solutions. Numerical results for the damping coefficients of triangular wings are presented as functions of aspect ratio and Mach number, and are compared with experimental results over the Mach number range 0 to 1. In the second part, experimental results are used. to point out a close correlation between the nonlinear variations with angle of attack of the static pitching-moment curve slope and the damping-in-pitch coefficient. The underlying basis for the correlation is found as a result of an analysis in which the indicial function concept and. the principle of super-position are adapted to apply to the nonlinear problem. The form of the result suggests a method of estimating nonlinear damping coefficients from results of static wind-tunnel measurements.

Damping of High-temperature Shape Memory Alloys

NASA Technical Reports Server (NTRS)

Duffy, Kirsten P.; Padula, Santo A., II; Scheiman, Daniel A.

2008-01-01

Researchers at NASA Glenn Research Center have been investigating high temperature shape memory alloys as potential damping materials for turbomachinery rotor blades. Analysis shows that a thin layer of SMA with a loss factor of 0.04 or more would be effective at reducing the resonant response of a titanium alloy beam. Two NiTiHf shape memory alloy compositions were tested to determine their loss factors at frequencies from 0.1 to 100 Hz, at temperatures from room temperature to 300 C, and at alternating strain levels of 34-35x10(exp -6). Elevated damping was demonstrated between the M(sub s) and M(sub f) phase transformation temperatures and between the A(sub s) and A(sub f) temperatures. The highest damping occurred at the lowest frequencies, with a loss factor of 0.2-0.26 at 0.1 Hz. However, the peak damping decreased with increasing frequency, and showed significant temperature hysteresis in heating and cooling. Keywords: High-temperature, shape memory alloy, damping, aircraft engine blades, NiTiHf

Avoid the Wet Basement Blues: Construction Methods Guarantee Success

ERIC Educational Resources Information Center

Domermuth, David

2006-01-01

A damp basement can be a nightmare, especially after mildew creates its eye-watering, nose-offending stench. There are two enemies to overcome: damp air condensing on interior walls and ground water penetrating the exterior. One can address condensation by drying or heating the air in a basement to raise it above the dew point. The simple way to…

Simulations of High Harmonic Fast Wave Heating on the C-2U Advanced Beam-Driven Field-Reversed Configuration Device

NASA Astrophysics Data System (ADS)

Yang, Xiaokang; Petrov, Yuri; Ceccherini, Francesco; Koehn, Alf; Galeotti, Laura; Dettrick, Sean; Binderbauer, Michl

2017-10-01

Numerous efforts have been made at Tri-Alpha Energy (TAE) to theoretically explore the physics of microwave electron heating in field-reversed configuration (FRC) plasmas. For the fixed 2D profiles of plasma density and temperature for both electrons and thermal ions and equilibrium field of the C-2U machine, simulations with GENRAY-C ray-tracing code have been conducted for the ratios of ω/ωci[D] in the range of 6 - 20. Launch angles and antenna radial and axial positions have been optimized in order to simultaneously achieve good wave penetration into the core of FRC plasmas and efficient power damping on electrons. It is found that in an optimal regime, single pass absorption efficiency is 100% and most of the power is deposited inside the separatrix of FRC plasmas, with power damping efficiency of about 72% on electrons and less than 19% on ions. Calculations have clearly demonstrated that substantial power absorption on electrons is mainly attributed to high beta enhancement of magnetic pumping; complete power damping occurs before Landau damping has a significant effect on power absorption.

Thermoelastic damping in thin microrings with two-dimensional heat conduction

NASA Astrophysics Data System (ADS)

Fang, Yuming; Li, Pu

2015-05-01

Accurate determination of thermoelastic damping (TED) is very challenging in the design of micro-resonators. Microrings are widely used in many micro-resonators. In the past, to model the TED effect on the microrings, some analytical models have been developed. However, in the previous works, the heat conduction within the microring is modeled by using the one-dimensional approach. The governing equation for heat conduction is solved only for the one-dimensional heat conduction along the radial thickness of the microring. This paper presents a simple analytical model for TED in microrings. The two-dimensional heat conduction over the thermoelastic temperature gradients along the radial thickness and the circumferential direction are considered in the present model. A two-dimensional heat conduction equation is developed. The solution of the equation is represented by the product of an assumed sine series along the radial thickness and an assumed trigonometric series along the circumferential direction. The analytical results obtained by the present 2-D model show a good agreement with the numerical (FEM) results. The limitations of the previous 1-D model are assessed.

Stabilizing and destabilizing protein surfactant-based foams in the presence of a chemical surfactant: Effect of adsorption kinetics.

PubMed

Li, Huazhen; Le Brun, Anton P; Agyei, Dominic; Shen, Wei; Middelberg, Anton P J; He, Lizhong

2016-01-15

Stimuli-responsive protein surfactants promise alternative foaming materials that can be made from renewable sources. However, the cost of protein surfactants is still higher than their chemical counterparts. In order to reduce the required amount of protein surfactant for foaming, we investigated the foaming and adsorption properties of the protein surfactant, DAMP4, with addition of low concentrations of the chemical surfactant sodium dodecylsulfate (SDS). The results show that the small addition of SDS can enhance foaming functions of DAMP4 at a lowered protein concentration. Dynamic surface tension measurements suggest that there is a synergy between DAMP4 and SDS which enhances adsorption kinetics of DAMP4 at the initial stage of adsorption (first 60s), which in turn stabilizes protein foams. Further interfacial properties were revealed by X-ray reflectometry measurements, showing that there is a re-arrangement of adsorbed protein-surfactant layer over a long period of 1h. Importantly, the foaming switchability of DAMP4 by metal ions is not affected by the presence of SDS, and foams can be switched off by the addition of zinc ions at permissive pH. This work provides fundamental knowledge to guide formulation using a mixture of protein and chemical surfactants towards a high performance of foaming at a low cost. Copyright © 2015 Elsevier Inc. All rights reserved.

Absorption of whistler mode waves in the ionosphere of venus.

PubMed

Taylor, W W; Scarf, F L; Russell, C T; Brace, L H

1979-07-06

It is shown that whistler mode waves from the ionosheath of Venus are absorbed by Landau damping at the dayside ionosphere boundary. This process heats the ionospheric electrons and it may provide an important energy input into the dayside ionosphere. Cyclotron damping of the waves does not occur in the same region. However, Landau damping of ionosheath waves is apparently not an important energy source in the nightside ionosphere. Impulsive events in the nightside ionosphere seem to fall into two classes: (i) lightning signals (near periapsis) and (ii) noise, which may be caused by gradient or current instabilities.

Damping in Space Constructions

NASA Astrophysics Data System (ADS)

de Vreugd, Jan; de Lange, Dorus; Winters, Jasper; Human, Jet; Kamphues, Fred; Tabak, Erik

2014-06-01

Monolithic structures are often used in optomechanical designs for space applications to achieve high dimensional stability and to prevent possible backlash and friction phenomena. The capacity of monolithic structures to dissipate mechanical energy is however limited due to the high Q-factor, which might result in high stresses during dynamic launch loads like random vibration, sine sweeps and shock. To reduce the Q-factor in space applications, the effect of constrained layer damping (CLD) is investigated in this work. To predict the damping increase, the CLD effect is implemented locally at the supporting struts in an existing FE model of an optical instrument. Numerical simulations show that the effect of local damping treatment in this instrument could reduce the vibrational stresses with 30-50%. Validation experiments on a simple structure showed good agreement between measured and predicted damping properties. This paper presents material characterization, material modeling, numerical implementation of damping models in finite element code, numerical results on space hardware and the results of validation experiments.

Orthogonal optimization of a water hydraulic pilot-operated pressure-reducing valve

NASA Astrophysics Data System (ADS)

Mao, Xuyao; Wu, Chao; Li, Bin; Wu, Di

2017-12-01

In order to optimize the comprehensive characteristics of a water hydraulic pilot-operated pressure-reducing valve, numerical orthogonal experimental design was adopted. Six parameters of the valve, containing diameters of damping plugs, volume of spring chamber, half cone angle of main spool, half cone angle of pilot spool, mass of main spool and diameter of main spool, were selected as the orthogonal factors, and each factor has five different levels. An index of flowrate stability, pressure stability and pressure overstrike stability (iFPOS) was used to judge the merit of each orthogonal attempt. Embedded orthogonal process turned up and a final optimal combination of these parameters was obtained after totally 50 numerical orthogonal experiments. iFPOS could be low to a fairly low value which meant that the valve could have much better stabilities. During the optimization, it was also found the diameters of damping plugs and main spool played important roles in stability characteristics of the valve.

Damping of Bernstein-Greene-Kruskal modes in collisional plasmas

DOE Office of Scientific and Technical Information (OSTI.GOV)

Valentini, Francesco

2008-02-15

In this paper, the effect of Coulomb collisions on the stability of Bernstein-Greene-Kruskal (BGK) modes [I. B. Bernstein, J. M. Greene, and M. D. Krukal, Phys. Rev. 108, 546 (1957)] is analyzed by comparing the numerical results of collisional particle-in-cell (PIC) simulations with the theoretical predictions by Zakharov and Karpman [V. E. Zakharov and V. I. Karpman, Sov. Phys. JETP 16, 351 (1963)], for the collisional damping of nonlinear plasma waves. In the absence of collisions, BGK modes are undamped nonlinear electrostatic oscillations, solutions of the Vlasov-Poisson equations; in these structures nonlinearity manifests as the formation of a plateau inmore » the resonant region of the particle distribution function, due to trapping of resonant particles, thus preventing linear Landau damping. When particle-particle Coulomb collisions are effective, this plateau is smoothed out since collisions drive the velocity distribution towards the Maxwellian shape, thus destroying the BGK structure. As shown by Zakharov and Karpman in 1963, under certain assumptions, an exponential time decay with constant damping rate is predicted for the electric field amplitude and a linear dependence of the damping rate on the collision frequency is found. In this paper, the theory by Zakharov and Karpman is revisited and the effects of collisions on the stability of BGK modes and on the long time evolution of nonlinear Landau damping are numerically investigated. The numerical results are obtained through a collisional PIC code that reproduces a physical phenomenology also observed in recent experiments with trapped pure electron plasmas.« less

Correlation and evaluation of inplane stability characteristics for an advanced bearingless main rotor

NASA Technical Reports Server (NTRS)

Weller, W. H.

1983-01-01

A program of experimental and analytical research was performed to demonstrate the degree of correlation achieved between measured and computed rotor inplane stability characteristics. The experimental data were obtained from hover and wind tunnel tests of a scaled bearingless main rotor model. Both isolated rotor and free-hub conditions were tested. Test parameters included blade built-in cone and sweep angles; rotor inplane structural stiffness and damping; pitch link stiffness and location; and fuselage damping, inertia, and natural frequency. Analytical results for many test conditions were obtained. In addition, the analytical and experimental results were examined to ascertain the effects of the test parameters on rotor ground and air resonance stability. The results from this program are presented herein in tabular and graphical form.

Flutter Analysis of a Transonic Fan

NASA Technical Reports Server (NTRS)

Srivastava, R.; Bakhle, M. A.; Keith, T. G., Jr.; Stefko, G. L.

2002-01-01

This paper describes the calculation of flutter stability characteristics for a transonic forward swept fan configuration using a viscous aeroelastic analysis program. Unsteady Navier-Stokes equations are solved on a dynamically deforming, body fitted, grid to obtain the aeroelastic characteristics using the energy exchange method. The non-zero inter-blade phase angle is modeled using phase-lagged boundary conditions. Results obtained show good correlation with measurements. It is found that the location of shock and variation of shock strength strongly influenced stability. Also, outboard stations primarily contributed to stability characteristics. Results demonstrate that changes in blade shape impact the calculated aerodynamic damping, indicating importance of using accurate blade operating shape under centrifugal and steady aerodynamic loading for flutter prediction. It was found that the calculated aerodynamic damping was relatively insensitive to variation in natural frequency.

Design and application of squeeze film dampers for turbomachinery stabilization

NASA Technical Reports Server (NTRS)

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

1975-01-01

The steady-state transient response of the squeeze film damper bearing was investigated. Both the steady-state and transient equations for the hydrodynamic bearing forces are derived; the steady-state equations were used to determine the damper equivalent stiffness and damping coefficients. These coefficients are used to find the damper configuration which will provide the optimum support characteristics based on a stability analysis of the rotor-bearing system. The effects of end seals and cavitated fluid film are included. The transient analysis of rotor-bearing systems was conducted by coupling the damping and rotor equations and integrating forward in time. The effects of unbalance, cavitation, and retainer springs are included. Methods of determining the stability of a rotor-bearing system under the influence of aerodynamic forces and internal shaft friction are discussed.

Optimal line drop compensation parameters under multi-operating conditions

NASA Astrophysics Data System (ADS)

Wan, Yuan; Li, Hang; Wang, Kai; He, Zhe

2017-01-01

Line Drop Compensation (LDC) is a main function of Reactive Current Compensation (RCC) which is developed to improve voltage stability. While LDC has benefit to voltage, it may deteriorate the small-disturbance rotor angle stability of power system. In present paper, an intelligent algorithm which is combined by Genetic Algorithm (GA) and Backpropagation Neural Network (BPNN) is proposed to optimize parameters of LDC. The objective function proposed in present paper takes consideration of voltage deviation and power system oscillation minimal damping ratio under multi-operating conditions. A simulation based on middle area of Jiangxi province power system is used to demonstrate the intelligent algorithm. The optimization result shows that coordinate optimized parameters can meet the multioperating conditions requirement and improve voltage stability as much as possible while guaranteeing enough damping ratio.

Experimental Research and Analysis of Rotordynamic Characteristics for a New Kind of Tilting-pad Gas Seal

NASA Astrophysics Data System (ADS)

Cao, Hao; Cao, Xiaoyu; Chen, Fei; Li, Ming; Zhang, Bolin; Wei, Jilong

2017-12-01

This paper presents a new kind of tilting-pad gas seal. This design is introduced to reduce the tangential seal force and to improve the stability of rotor system finally. A seal test rig is set up. The paper compares the leakage between tilting-pad seal and fixed pad seal. The result shows that the leakage ratio of the tilting-pad seal is close to the leakage ratio of the fixed pad seal. The work done by seal force on the cylinder system is calculated as an index of comparison between these two seals. Result shows that the work done by the fixed pad seal is greater than the work done by the tilting-pad seal. Moreover, system damping factor is used to compare the stabilities of these two seals. The impact tests on the cylinder system are done under different conditions. The system damping factors are calculated from the damped waves of system vibration. Test results show that the damping factor of the tilting pad seal is higher than that of the fixed pad seal in both the vertical and the horizontal directions.

Cloud-Radiative Driving of the Madden-Julian Oscillation as Seen by the A-Train

NASA Technical Reports Server (NTRS)

Del Genio, Anthony; Chen, Yonghua

2015-01-01

Cloud and water vapor radiative heating anomalies associated with convection may be an effective source of moist static energy driving the Madden-Julian Oscillation (MJO). In this paper five years of radiative heating profiles derived from CloudSat radar and Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation data are analyzed to document radiative heating anomalies during the MJO. Atmospheric shortwave absorption and surface longwave radiation anomalies are of opposite sign and 10-20% as large as top-of-atmosphere outgoing longwave radiation (OLR) anomalies, confirming that OLR provides a useful estimate of the total column radiative heating anomaly. Positive anomalies generally peak about one week before the MJO peak and are smallest over the Indian Ocean. Anomalies over the Maritime Continent are strongest, and coincident with the MJO peak. Shortwave heating profile anomalies are about half as large as longwave anomalies in the active region of the MJO but generally of opposite sign; thus shortwave heating damps the longwave destabilization of the lower troposphere. The exception is the onset phase of the MJO, where shortwave and longwave heating anomalies due to thin cirrus are both positive in the upper troposphere and exert a stabilizing influence. Specific humidity anomalies in the middle troposphere reach 0.5 g kg(exp. -1), but the associated clear sky heating anomaly is very small. Radiative enhancement of column moist static energy becomes significant about 10 days before the MJO peak, when precipitation anomalies are still increasing, and then remains high after the MJO peak after precipitation has begun to decline.

Design of static synchronous series compensator based damping controller employing invasive weed optimization algorithm.

PubMed

Ahmed, Ashik; Al-Amin, Rasheduzzaman; Amin, Ruhul

2014-01-01

This paper proposes designing of Static Synchronous Series Compensator (SSSC) based damping controller to enhance the stability of a Single Machine Infinite Bus (SMIB) system by means of Invasive Weed Optimization (IWO) technique. Conventional PI controller is used as the SSSC damping controller which takes rotor speed deviation as the input. The damping controller parameters are tuned based on time integral of absolute error based cost function using IWO. Performance of IWO based controller is compared to that of Particle Swarm Optimization (PSO) based controller. Time domain based simulation results are presented and performance of the controllers under different loading conditions and fault scenarios is studied in order to illustrate the effectiveness of the IWO based design approach.

Effects of Temperature on the Performance of a Small Internal Combustion Engine at Altitude

DTIC Science & Technology

2013-03-21

flexible diaphragm was attached to damp out pulses in the air flow pulsations . Their method of temperature control was electric heating of the intake air...42  Figure 14. Heat exchanger ................................................................................................ 45  Figure...15. Both liquid nitrogen lines from Dewar ............................................................ 45  Figure 16. Engine inlet flow path heat

Relaxation model of the heat production

NASA Astrophysics Data System (ADS)

Zimin, B. A.; Zorin, I. S.; Sventitskaya, V. E.

2018-05-01

The work is devoted to the study of the heat generation process in the problem of the dynamics of oscillations of a one-dimensional chain simulating heat formation in an elastic continuous medium under mechanical influences. Formulas for estimating the effect of thermoelasticity are obtained and an analogy is made with the energy of damped oscillations of an anharmonic oscillator.

Feedback-assisted extension of the tokamak operating space to low safety factor

DOE PAGES

Hanson, Jeremy M.; Bialek, James M.; Baruzzo, M.; ...

2014-07-07

Recent DIII-D and RFX-mod experiments have demonstrated stable tokamak operation at very low values of the edge safety factor q( a) near and below 2. The onset of n = 1 resistive wall mode (RWM) kink instabilities leads to a disruptive stability limit, encountered at q( a) = 2 (limiter plasmas) and q 95 = 2 (divertor plasmas). However, passively stable operation can be attained for q( a) and q 95 values as low as 2.2. RWM damping in the q( a) = 2 regime was measured using active MHD spectroscopy. Although consistent with theoretical predictions, the amplitude of themore » damped response does not increase significantly as the q( a) = 2 limit is approached, in contrast with damping measurements made approaching the pressure-driven RWM limit. Applying proportional gain magnetic feedback control of the n = 1 modes has resulted in stabilized operation with q 95 values reaching as low as 1.9 in DIII-D and q( a) reaching 1.55 in RFX-mod. In addition to being consistent with the q( a) = 2 external kink mode stability limit, the unstable modes have growth rates on the order of the characteristic wall eddy-current decay timescale in both devices, and a dominant m = 2 poloidal structure that is consistent with ideal MHD predictions. As a result, the experiments contribute to validating MHD stability theory and demonstrate that a key tokamak stability limit can be overcome with feedback.« less

Decentralized Control of Sound Radiation using a High-Authority/Low-Authority Control Strategy with Anisotropic Actuators

NASA Technical Reports Server (NTRS)

Schiller, Noah H.; Cabell, Randolph H.; Fuller, Chris R.

2008-01-01

This paper describes a combined control strategy designed to reduce sound radiation from stiffened aircraft-style panels. The control architecture uses robust active damping in addition to high-authority linear quadratic Gaussian (LQG) control. Active damping is achieved using direct velocity feedback with triangularly shaped anisotropic actuators and point velocity sensors. While active damping is simple and robust, stability is guaranteed at the expense of performance. Therefore the approach is often referred to as low-authority control. In contrast, LQG control strategies can achieve substantial reductions in sound radiation. Unfortunately, the unmodeled interaction between neighboring control units can destabilize decentralized control systems. Numerical simulations show that combining active damping and decentralized LQG control can be beneficial. In particular, augmenting the in-bandwidth damping supplements the performance of the LQG control strategy and reduces the destabilizing interaction between neighboring control units.

Vibrational Properties of High- Superconductors Levitated Above a Bipolar Permanent Magnetic Guideway

NASA Astrophysics Data System (ADS)

Liu, Lu; Wang, Jiasu

2014-05-01

A bipolar permanent magnetic guideway (PMG) has a unique magnetic field distribution profile which may introduce a better levitation performance and stability to the high- superconducting (HTS) maglev system. The dynamic vibration properties of multiple YBCO bulks arranged into different arrays positioned above a bipolar PMG and free to levitate were investigated. The acceleration and resonance frequencies were experimentally measured, and the stiffness and damping coefficients were evaluated for dynamic stability. Results indicate that the levitation stiffness is closely related to the field-cooling-height and sample positioning. The damping ratio was found to be low and nonlinear for the Halbach bipolar HTS-PMG system.

Bifurcations and chaos in a parametrically damped two-well Duffing oscillator subjected to symmetric periodic pulses.

PubMed

Chacón, R; Martínez García-Hoz, A

1999-06-01

We study a parametrically damped two-well Duffing oscillator, subjected to a periodic string of symmetric pulses. The order-chaos threshold when altering solely the width of the pulses is investigated theoretically through Melnikov analysis. We show analytically and numerically that most of the results appear independent of the particular wave form of the pulses provided that the transmitted impulse is the same. By using this property, the stability boundaries of the stationary solutions are determined to first approximation by means of an elliptic harmonic balance method. Finally, the bifurcation behavior at the stability boundaries is determined numerically.

Full scale wind tunnel investigation of a bearingless main helicopter rotor. [Ames 40 by 80 foot wind tunnel test using the BO-105 helicopter

NASA Technical Reports Server (NTRS)

1980-01-01

A stability test program was conducted to determine the effects of airspeed, collective pitch, rotor speed and shaft angle on stability and loads at speeds beyond that attained in the BMR/BO-105 flight test program. Loads and performance data were gathered at forward speeds up to 165 knots. The effect of cyclic pitch perturbations on rotor response was investigated at simulated level flight conditions. Two configuration variations were tested for their effect on stability. One variable was the control system stiffness. An axially softer pitch link was installed in place of the standard BO-105 pitch link. The second variation was the addition of elastomeric damper strips to increase the structural damping. The BMR was stable at all conditions tested. At fixed collective pitch, shaft angle and rotor speed, damping generally increased between hover and 60 knots, remained relatively constant from 60 to 90 knots, then decreased above 90 knots. Analytical predictions are in good agreement with test data up to 90 knots, but the trend of decreasing damping above 90 knots is contrary to the theory.

Dynamic stability test results on an 0.024 scale B-1 air vehicle

NASA Technical Reports Server (NTRS)

Beeman, R. R.

1972-01-01

Dynamic longitudinal and lateral-directional stability characteristics of the B-1 air vehicle were investigated in three wind tunnels at the Langley Research Center. The main rotary derivatives were obtained for an angle of attack range of -3 degrees to +16 degrees for a Mach number range of 0.2 to 2.16. Damping in roll data could not be obtained at the supersonic Mach numbers. The Langley 7 x 10 foot high speed tunnel, the 8 foot transonic pressure tunnel, and the 4 foot Unitary Plan wind tunnel were the test sites. An 0.024 scale light-weight model was used on a forced oscillation type balance. Test Reynolds number varied from 474,000/ft to 1,550,000/ft. through the Mach number range tested. The results showed that the dynamic stability characteristics of the model in pitch and roll were generally satisfactory up to an angle attack of about +6 degrees. In the wing sweep range from 15 to 25 degrees the positive damping levels in roll deteriorated rapidly above +2 degrees angle of attack. This reduction in roll damping is believed to be due to the onset of separation over the wing as stall is approached.

Diagnosing collisionless energy transfer using field-particle correlations: Vlasov-Poisson plasmas

NASA Astrophysics Data System (ADS)

Howes, Gregory G.; Klein, Kristopher G.; Li, Tak Chu

2017-02-01

Turbulence plays a key role in the conversion of the energy of large-scale fields and flows to plasma heat, impacting the macroscopic evolution of the heliosphere and other astrophysical plasma systems. Although we have long been able to make direct spacecraft measurements of all aspects of the electromagnetic field and plasma fluctuations in near-Earth space, our understanding of the physical mechanisms responsible for the damping of the turbulent fluctuations in heliospheric plasmas remains incomplete. Here we propose an innovative field-particle correlation technique that can be used to measure directly the secular energy transfer from fields to particles associated with collisionless damping of the turbulent fluctuations. Furthermore, this novel procedure yields information about the collisionless energy transfer as a function of particle velocity, providing vital new information that can help to identify the dominant collisionless mechanism governing the damping of the turbulent fluctuations. Kinetic plasma theory is used to devise the appropriate correlation to diagnose Landau damping, and the field-particle correlation technique is thoroughly illustrated using the simplified case of the Landau damping of Langmuir waves in a 1D-1V (one dimension in physical space and one dimension in velocity space) Vlasov-Poisson plasma. Generalizations necessary to apply the field-particle correlation technique to diagnose the collisionless damping of turbulent fluctuations in the solar wind are discussed, highlighting several caveats. This novel field-particle correlation technique is intended to be used as a primary analysis tool for measurements from current, upcoming and proposed spacecraft missions that are focused on the kinetic microphysics of weakly collisional heliospheric plasmas, including the Magnetospheric Multiscale (MMS), Solar Probe Plus, Solar Orbiter and Turbulence Heating ObserveR (THOR) missions.

Damping behavior of polymer composites with high volume fraction of NiMnGa powders

NASA Astrophysics Data System (ADS)

Sun, Xiaogang; Song, Jie; Jiang, Hong; Zhang, Xiaoning; Xie, Chaoying

2011-03-01

Polymer composites inserted with high volume fraction (up to 70 Vol%) of NiMnGa powders were fabricated and their damping behavior was investigated by dynamic mechanical analysis. It is found that the polymer matrix has little influence on the transformation temperatures of NiMnGa powders. A damping peak appears for NiMnGa/epoxy resin (EP) composites accompanying with the martensitic transformation or reverse martensitic transformation of NiMnGa powders during cooling or heating. The damping capacity for NiMnGa/EP composites increases linearly with the increase of volume fraction of NiMnGa powders and, decreases dramatically as the test frequency increases. The fracture strain of NiMnGa/EP composites decrease with the increase of NiMnGa powders.

Exact intrinsic localized excitation of an anisotropic ferromagnetic spin chain in external magnetic field with Gilbert damping, spin current and PT -symmetry

DOE PAGES

Lakshmanan, Muthusamy; Saxena, Avadh

2018-04-27

Inmore » this work, we obtain the exact one-spin intrinsic localized excitation in an anisotropic Heisenberg ferromagnetic spin chain in a constant/variable external magnetic field with Gilbert damping included. We also point out how an appropriate magnitude spin current term in a spin transfer nano-oscillator (STNO) can stabilize the tendency towards damping. Further, we show how this excitation can be sustained in a recently suggested PT -symmetric magnetic nanostructure. We also briefly consider more general spin excitations.« less

Exact intrinsic localized excitation of an anisotropic ferromagnetic spin chain in external magnetic field with Gilbert damping, spin current and PT -symmetry

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lakshmanan, Muthusamy; Saxena, Avadh

Inmore » this work, we obtain the exact one-spin intrinsic localized excitation in an anisotropic Heisenberg ferromagnetic spin chain in a constant/variable external magnetic field with Gilbert damping included. We also point out how an appropriate magnitude spin current term in a spin transfer nano-oscillator (STNO) can stabilize the tendency towards damping. Further, we show how this excitation can be sustained in a recently suggested PT -symmetric magnetic nanostructure. We also briefly consider more general spin excitations.« less

Damping Goes the Distance in Golf

NASA Technical Reports Server (NTRS)

2004-01-01

In the late 1980s, Dr. Benjamin Dolgin of NASA s Jet Propulsion Laboratory developed a concept for a high-damping graphite/viscoelastic material for the Strategic Defense Initiative (popularly referred to as "Star Wars"), as part of a space-based laser anti-missile program called "Asterix." Dolgin drummed up this concept with the intention of stabilizing weapons launch platforms in space, where there is no solid ground to firmly support these structures. Without the inclusion of high-damping material, the orbital platforms were said to vibrate for 20 minutes after force was applied - a rate deemed "unacceptable" by leaders of the Strategic Defense Initiative.

Optimal integral force feedback for active vibration control

NASA Astrophysics Data System (ADS)

Teo, Yik R.; Fleming, Andrew J.

2015-11-01

This paper proposes an improvement to Integral Force Feedback (IFF), which is a popular method for active vibration control of structures and mechanical systems. Benefits of IFF include robustness, guaranteed stability and simplicity. However, the maximum damping performance is dependent on the stiffness of the system; hence, some systems cannot be adequately controlled. In this paper, an improvement to the classical force feedback control scheme is proposed. The improved method achieves arbitrary damping for any mechanical system by introducing a feed-through term. The proposed improvement is experimentally demonstrated by actively damping an objective lens assembly for a high-speed confocal microscope.

Improved gyro-flotation /damping/ fluids

NASA Technical Reports Server (NTRS)

Jacobs, S. S.

1969-01-01

Synthesis of a metal-stabilized halophosphazene compound with a density of 3 gm/cc at 137 degrees F serves as an improved stabilizer fluid for floated gyros. Gyro sensitivity can be increased with a fluid of higher density which could support a heavier float.

Heat-driven spin torques in antiferromagnets

NASA Astrophysics Data System (ADS)

Białek, Marcin; Bréchet, Sylvain; Ansermet, Jean-Philippe

2018-04-01

Heat-driven magnetization damping, which is a linear function of a temperature gradient, is predicted in antiferromagnets by considering the sublattice dynamics subjected to a heat-driven spin torque. This points to the possibility of achieving spin torque oscillator behavior. The model is based on the magnetic Seebeck effect acting on sublattices which are exchange coupled. The heat-driven spin torque is estimated and the feasibility of detecting this effect is discussed.

Isentropic phase changes in dissociating gases and the method of sound dispersion for the investigation of homogeneous gas reactions with very high speed : Conclusion

NASA Technical Reports Server (NTRS)

Damkohler, Gerhard

1950-01-01

The analytical results of Part I are also applied to sound dispersion by friction and heat conduction, An irreversible change of momentum, energy, and type of particle corresponding to friction, heat conduction, and diffusion effects can appear both in the direction of the sound field and traverse to it. Longitudinal damping, the coupling of longitudinal damping and that due to chemical and physical changes, and coupling of diffusion and compositional changes are treated for a plane sound wave of infinite extent. The same principles are also applied to sound effects in cylindrical tubes. The limitations of the method are discussed in some detail.

Liquid rocket engine combustion stabilization devices

NASA Technical Reports Server (NTRS)

1974-01-01

Combustion instability, which results from a coupling of the combustion process and the fluid dynamics of the engine system, was investigated. The design of devices which reduce coupling (combustion chamber baffles) and devices which increase damping (acoustic absorbers) are described. Included in the discussion are design criteria and recommended practices, structural and mechanical design, thermal control, baffle geometry, baffle/engine interactions, acoustic damping analysis, and absorber configurations.

Hover test of a full-scale hingeless helicopter rotor: Aeroelastic stability, performance and loads data. [wind tunnel tests

NASA Technical Reports Server (NTRS)

Peterson, R. L.; Warmbrodt, W.

1984-01-01

A hover test of a full-scale, hingeless rotor system was conducted in the NASA Ames 40- by 80-foot wind tunnel. The rotor was tested on the Ames rotor test apparatus. Rotor aeroelastic stability, performance, and loads at various rotational speeds and thrust coefficients were investigated. The primary objective was to determine the inplane stability characteristics of the rotor system. Rotor inplane damping data were obtained for operation between 350 and 425 rpm (design speed), and for thurst coefficients between 0.0 and 0.12. The rotor was stable for all conditions tested. At constant rotor rotational speed, a minimum inplane dampling level was obtained at a thrust coefficient approximately = 0.02. At constant rotor lift, a minimum in rotor inplane damping was measured at 400 rpm.

An identification method for damping ratio in rotor systems

NASA Astrophysics Data System (ADS)

Wang, Weimin; Li, Qihang; Gao, Jinji; Yao, Jianfei; Allaire, Paul

2016-02-01

Centrifugal compressor testing with magnetic bearing excitations is the last step to assure the compressor rotordynamic stability in the designed operating conditions. To meet the challenges of stability evaluation, a new method combining the rational polynomials method (RPM) with the weighted instrumental variables (WIV) estimator to fit the directional frequency response function (dFRF) is presented. Numerical simulation results show that the method suggested in this paper can identify the damping ratio of the first forward and backward modes with high accuracy, even in a severe noise environment. Experimental tests were conducted to study the effect of different bearing configurations on the stability of rotor. Furthermore, two example centrifugal compressors (a nine-stage straight-through and a six-stage back-to-back) were employed to verify the feasibility of identification method in industrial configurations as well.

Calibrating damping rates with LEGACY linewidths

NASA Astrophysics Data System (ADS)

Houdek, Günter

2017-10-01

Linear damping rates of radial oscillation modes in selected Kepler stars are estimated with the help of a nonadiabatic stability analysis. The convective fluxes are obtained from a nonlocal, time-dependent convection model. The mixing-length parameter is calibrated to the surface-convection-zone depth of a stellar model obtained from fitting adiabatic frequencies to the LEGACY* observations, and two of the three nonlocal convection parameters are calibrated to the corresponding LEGACY* linewidth measurements. The atmospheric structure in the 1D stability analysis adopts a temperature-optical-depth relation derived from 3D hydrodynamical simulations. Results from 3D simulations are also used to calibrate the turbulent pressure and to guide the functional form of the depth-dependence of the anisotropy of the turbulent velocity field in the 1D stability computations.

The Effect of Global and Local Damping on the Perception of Hardness.

PubMed

van Beek, Femke Elise; Heck, Dennis J F; Nijmeijer, Henk; Bergmann Tiest, Wouter M; Kappers, Astrid M L

2016-01-01

In tele-operation systems, damping is often injected to guarantee system stability during contact with hard objects. In this study, we used psychophysical experiments to assess the effect of adding damping on the user's perception of object hardness. In Experiments 1 and 2, combinations of stiffness and damping were tested to assess their effect on perceived hardness. In both experiments, two tasks were used: an in-contact task, starting at the object's surface, and a contact-transition task, including a free-air movement. In Experiment 3, the difference between inserting damping globally (equally throughout the workspace) and locally (inside the object only) was tested. In all experiments, the correlation between the participant's perceptual decision and force and position data was also investigated. Experiments 1 and 2 show that when injecting damping globally, perceived hardness slightly increased for an in-contact task, while it decreased considerably for a contact-transition task. Experiment 3 shows that this effect was mainly due to inserting damping globally, since there was a large perceptual difference between inserting damping globally and locally. The force and position parameters suggest that participants used the same force profile during the two movements of one trial and assessed the system's reaction to this force to perceive hardness.

High-harmonic fast magnetosonic wave coupling, propagation, and heating in a spherical torus plasma

NASA Astrophysics Data System (ADS)

Menard, J.; Majeski, R.; Kaita, R.; Ono, M.; Munsat, T.; Stutman, D.; Finkenthal, M.

1999-05-01

A novel rotatable two-strap antenna has been installed in the current drive experiment upgrade (CDX-U) [T. Jones, Ph.D. thesis, Princeton University (1995)] in order to investigate high-harmonic fast wave coupling, propagation, and electron heating as a function of strap angle and strap phasing in a spherical torus plasma. Radio-frequency-driven sheath effects are found to fit antenna loading trends at very low power and become negligible above a few kilowatts. At sufficiently high power, the measured coupling efficiency as a function of strap angle is found to agree favorably with cold plasma wave theory. Far-forward microwave scattering from wave-induced density fluctuations in the plasma core tracks the predicted fast wave loading as the antenna is rotated. Signs of electron heating during rf power injection have been observed in CDX-U with central Thomson scattering, impurity ion spectroscopy, and Langmuir probes. While these initial results appear promising, damping of the fast wave on thermal ions at high ion-cyclotron-harmonic number may compete with electron damping at sufficiently high ion β—possibly resulting in a significantly reduced current drive efficiency and production of a fast ion population. Preliminary results from ray-tracing calculations which include these ion damping effects are presented.

The effect of inertia, viscous damping, temperature and normal stress on chaotic behaviour of the rate and state friction model

NASA Astrophysics Data System (ADS)

Sinha, Nitish; Singh, Arun K.; Singh, Trilok N.

2018-04-01

A fundamental understanding of frictional sliding at rock surfaces is of practical importance for nucleation and propagation of earthquakes and rock slope stability. We investigate numerically the effect of different physical parameters such as inertia, viscous damping, temperature and normal stress on the chaotic behaviour of the two state variables rate and state friction (2sRSF) model. In general, a slight variation in any of inertia, viscous damping, temperature and effective normal stress reduces the chaotic behaviour of the sliding system. However, the present study has shown the appearance of chaos for the specific values of normal stress before it disappears again as the normal stress varies further. It is also observed that magnitude of system stiffness at which chaotic motion occurs, is less than the corresponding value of critical stiffness determined by using the linear stability analysis. These results explain the practical observation why chaotic nucleation of an earthquake is a rare phenomenon as reported in literature.

Noisy oscillator: Random mass and random damping.

PubMed

Burov, Stanislav; Gitterman, Moshe

2016-11-01

The problem of a linear damped noisy oscillator is treated in the presence of two multiplicative sources of noise which imply a random mass and random damping. The additive noise and the noise in the damping are responsible for an influx of energy to the oscillator and its dissipation to the surrounding environment. A random mass implies that the surrounding molecules not only collide with the oscillator but may also adhere to it, thereby changing its mass. We present general formulas for the first two moments and address the question of mean and energetic stabilities. The phenomenon of stochastic resonance, i.e., the expansion due to the noise of a system response to an external periodic signal, is considered for separate and joint action of two sources of noise and their characteristics.

Comment on “In-depth Plasma-Wave Heating of Dense Plasma Irradiated by Short Laser Pulses”

DOE PAGES

Kemp, A. J.; Sentoku, Y.

2016-04-14

Sherlock et al. have reported on the heating of solid density targets by collisional damping of wakefields that are driven by relativistic electron bunches generated in relativistic laser matter interaction. Analyzing collisional particle-in-cell simulations they calculate the fast electron current jf inside the plasma by adding contributions from electrons with energies greater than E cut = 50 keV; time-integrating the specific resistive energy deposition η j2f they arrive at a temperature profile and compare the result to the one 'measured' in their simulation, defined as the energy of particles with E < 30 keV; the discrepancy is due to collisionalmore » damping of wake fields (CDW). Here, we disagree with their metric of fast current, which leads to false conclusions about CDW heating being a volumetric, rather than surface effect.« less

An implicit finite-difference solution to the viscous shock layer, including the effects of radiation and strong blowing

NASA Technical Reports Server (NTRS)

Garrett, L. B.; Smith, G. L.; Perkins, J. N.

1972-01-01

An implicit finite-difference scheme is developed for the fully coupled solution of the viscous, radiating stagnation-streamline equations, including strong blowing. Solutions are presented for both air injection and injection of carbon-phenolic ablation products into air at conditions near the peak radiative heating point in an earth entry trajectory from interplanetary return missions. A detailed radiative-transport code that accounts for the important radiative exchange processes for gaseous mixtures in local thermodynamic and chemical equilibrium is utilized in the study. With minimum number of assumptions for the initially unknown parameters and profile distributions, convergent solutions to the full stagnation-line equations are rapidly obtained by a method of successive approximations. Damping of selected profiles is required to aid convergence of the solutions for massive blowing. It is shown that certain finite-difference approximations to the governing differential equations stabilize and improve the solutions. Detailed comparisons are made with the numerical results of previous investigations. Results of the present study indicate lower radiative heat fluxes at the wall for carbonphenolic ablation than previously predicted.

Supersonic Pitch Damping Predictions of Blunt Entry Vehicles from Static CFD Solutions

NASA Technical Reports Server (NTRS)

Schoenenberger, Mark

2013-01-01

A technique for predicting supersonic pitch damping of blunt axisymmetric bodies from static CFD data is presented. The contributions to static pitching moment due to forebody and aftbody pressure distributions are broken out and considered separately. The one-dimension moment equation is cast to model the separate contributions from forebody and aftbody pressures with no traditional damping term included. The aftbody contribution to pitching moment is lagged by a phase angle of the natural oscillation period. This lag represents the time for aftbody wake structures to equilibrate while the body is oscillation. The characteristic equation of this formulation indicates that the lagged backshell moment adds a damping moment equivalent in form to a constant pitch damping term. CFD calculations of the backshell's contribution to the static pitching moment for a range of angles-of-attack is used to predict pitch damping coefficients. These predictions are compared with ballistic range data taken of the Mars Exploration Rover (MER) capsule and forced oscillation data of the Mars Viking capsule. The lag model appears to capture dynamic stability variation due to backshell geometry as well as Mach number.

The temporal behaviour of MHD waves in a partially ionized prominence-like plasma: Effect of heating and cooling

NASA Astrophysics Data System (ADS)

Ballester, J. L.; Carbonell, M.; Soler, R.; Terradas, J.

2018-01-01

Context. During heating or cooling processes in prominences, the plasma microscopic parameters are modified due to the change of temperature and ionization degree. Furthermore, if waves are excited on this non-stationary plasma, the changing physical conditions of the plasma also affect wave dynamics. Aims: Our aim is to study how temporal variation of temperature and microscopic plasma parameters modify the behaviour of magnetohydrodynamic (MHD) waves excited in a prominence-like hydrogen plasma. Methods: Assuming optically thin radiation, a constant external heating, the full expression of specific internal energy, and a suitable energy equation, we have derived the profiles for the temporal variation of the background temperature. We have computed the variation of the ionization degree using a Saha equation, and have linearized the single-fluid MHD equations to study the temporal behaviour of MHD waves. Results: For all the MHD waves considered, the period and damping time become time dependent. In the case of Alfvén waves, the cut-off wavenumbers also become time dependent and the attenuation rate is completely different in a cooling or heating process. In the case of slow waves, while it is difficult to distinguish the slow wave properties in a cooling partially ionized plasma from those in an almost fully ionized plasma, the period and damping time of these waves in both plasmas are completely different when the plasma is heated. The temporal behaviour of the Alfvén and fast wave is very similar in the cooling case, but in the heating case, an important difference appears that is related with the time damping. Conclusions: Our results point out important differences in the behaviour of MHD waves when the plasma is heated or cooled, and show that a correct interpretation of the observed prominence oscillations is very important in order to put accurate constraints on the physical situation of the prominence plasma under study, that is, to perform prominence seismology.

Flexibility damps macromolecular crowding effects on protein folding dynamics: Application to the murine prion protein (121-231)

NASA Astrophysics Data System (ADS)

Bergasa-Caceres, Fernando; Rabitz, Herschel A.

2014-01-01

A model of protein folding kinetics is applied to study the combined effects of protein flexibility and macromolecular crowding on protein folding rate and stability. It is found that the increase in stability and folding rate promoted by macromolecular crowding is damped for proteins with highly flexible native structures. The model is applied to the folding dynamics of the murine prion protein (121-231). It is found that the high flexibility of the native isoform of the murine prion protein (121-231) reduces the effects of macromolecular crowding on its folding dynamics. The relevance of these findings for the pathogenic mechanism are discussed.

Film stability in a vertical rotating tube with a core-gas flow.

NASA Technical Reports Server (NTRS)

Sarma, G. S. R.; Lu, P. C.; Ostrach, S.

1971-01-01

The linear hydrodynamic stability of a thin-liquid layer flowing along the inside wall of a vertical tube rotating about its axis in the presence of a core-gas flow is examined. The stability problem is formulated under the conditions that the liquid film is thin, the density and viscosity ratios of gas to liquid are small and the relative (axial) pressure gradient in the gas is of the same order as gravity. The resulting eigenvalue problem is first solved by a perturbation method appropriate to axisymmetric long-wave disturbances. The damped nature (to within the thin-film and other approximations made) of the nonaxisymmetric and short-wave disturbances is noted. In view of the limitations on a truncated perturbation solution when the disturbance wavenumber is not small, an initial value method using digital computer is presented. Stability characteristics of neutral, growing, and damped modes are presented showing the influences of rotation, surface tension, and the core-gas flow. Energy balance in a neutral mode is also illustrated.

Aspects of Coulomb damping in rotors supported on hydrodynamic bearings

NASA Technical Reports Server (NTRS)

Morton, P. G.

1982-01-01

The paper is concerned with the effect of friction in drive couplings on the non-sychronous whirling of a shaft. A simplified model is used to demonstrate the effect of large coupling misalignments on the stability of the system. It is concluded that provided these misalignments are large enough, the system becomes totally stable provided the shaft is supported on bearings exhibiting a viscous damping capacity.

Application of the Moment Method in the Slip and Transition Regime for Microfluidic Flows

DTIC Science & Technology

2011-01-01

systems ( MEMS ), fluid flow at the micro- and nano-scale has received considerable attention [1]. A basic understanding of the nature of flow and heat ...Couette Flow Many MEMS devices contain oscillating parts where air (viscous) damping plays an important role. To understand the damping mechanisms...transfer in these devices is considered essential for efficient design and control of MEMS . Engineering applications for gas microflows include

Aeroelastic Stability of a Four-Bladed Semi-Articulated Soft-Inplane Tiltrotor Model

NASA Technical Reports Server (NTRS)

Nixon, Mark W.; Langston, Chester W.; Singleton, Jeffrey D.; Piatak, David J.; Kvaternik, Raymond G.; Corso, Lawrence M.; Brown, Ross K.

2003-01-01

A new four-bladed, semi-articulated, soft-inplane rotor system, designed as a candidate for future heavy-lift rotorcraft, was tested at model scale on the Wing and Rotor Aeroelastic Testing System (WRATS), a 1/5-size aeroelastic wind-tunnel model based on the V-22. The experimental investigation included a hover test with the model in helicopter mode subject to ground resonance conditions, and a forward flight test with the model in airplane mode subject to whirl-flutter conditions. An active control system designed to augment system damping was also tested as part of this investigation. Results of this study indicate that the new four-bladed, soft-inplane rotor system in hover has adequate damping characteristics and is stable throughout its rotor-speed envelope. However, in airplane mode it produces very low damping in the key wing beam-bending mode, and has a low whirl-flutter stability boundary with respect to airspeed. The active control system was successful in augmenting the damping of the fundamental system modes, and was found to be robust with respect to changes in rotor speed and airspeed. Finally, conversion-mode dynamic loads were measured on the rotor and these were found to be signi.cantly lower for the new soft-inplane hub than for the previous baseline stiff - inplane hub.

Aeroelastic Stability of a Four-Bladed Semi-Articulated Soft-Inplane Tiltrotor Model

NASA Technical Reports Server (NTRS)

Nixon, Mark W.; Langston, Chester W.; Singleton, Jeffrey D.; Piatak, David J.; Kvaternik, Raymond G.; Corso, Lawrence M.; Brown, Ross

2003-01-01

A new four-bladed, semi-articulated, soft-inplane rotor system, designed as a candidate for future heavy-lift rotorcraft, was tested at model scale on the Wing and Rotor Aeroelastic Testing System (WRATS), a 1/5-size aeroelastic wind-tunnel model based on the V-22. The experimental investigation included a hover test with the model in helicopter mode subject to ground resonance conditions, and a forward flight test with the model in airplane mode subject to whirl-flutter conditions. An active control system designed to augment system damping was also tested as part of this investigation. Results of this study indicate that the new four-bladed, soft-inplane rotor system in hover has adequate damping characteristics and is stable throughout its rotor-speed envelope. However, in airplane mode it produces very low damping in the key wing beam-bending mode, and has a low whirl-flutter stability boundary with respect to airspeed. The active control system was successful in augmenting the damping of the fundamental system modes, and was found to be robust with respect to changes in rotor-speed and airspeed. Finally, conversion-mode dynamic loads were measured on the rotor and these were found to be significantly lower for the new soft-inplane hub than for the previous baseline stiff-inplane hub.

An introduction to the physical aspects of helicopter stability

NASA Technical Reports Server (NTRS)

Gessow, Alfred; Amer, Kenneth B

1950-01-01

In order to provide engineers interested in rotating-wing aircraft, but with no specialized training in stability theory, some understanding of the factors that influence the flying qualities of the helicopter, an explanation is made of both the static stability and the stick-fixed oscillation in hovering and forward flight in terms of fundamental physical quantities. Three significant stability factors -- static stability with angle of attack, static stability with speed, and damping due to a pitching or rolling velocity -- are explained in detail.

Gyrofluid theory and simulation of electromagnetic turbulence and transport in tokamak plasmas

NASA Astrophysics Data System (ADS)

Snyder, Philip Benjamin

1999-11-01

Turbulence and transport in toroidal plasmas is studied via the development of an electromagnetic gyrofluid model, and its implementation in realistic nonlinear simulations. This work extends earlier electrostatic gyrofluid models to include magnetic fluctuations and non-adiabatic passing electron dynamics. A new set of electron fluid equations is derived from the drift kinetic equation, via an expansion in the electron-ion mass ratio. These electron equations include descriptions of linear and nonlinear drift motion, Landau damping, and electron-ion collisions. Ion moment equations are derived from the electromagnetic gyrokinetic equation, and the gyrokinetic Poisson's Equation and Ampere's Law close the system. The model is benchmarked with linear gyrokinetic calculations, and good agreement is found for both the finite-β ion temperature gradient (ITG) and kinetic Alfvén ballooning (KBM) instabilities. Nonlinear simulations of ITG and KBM-driven turbulence are performed in toroidal flux tube geometry at a range of values of plasma β, and electromagnetic effects are found to significantly impact turbulent heat and particle transport. At low values of β, transport is reduced, as expected due to the finite-β stabilization of the ITG mode. However, as β approaches the Ideal-MHD stability threshold, transport can increase. In the presence of dissipation provided by a model of electron Landau damping and electron-ion collisions, this transport increase can be quite dramatic. Finally, the results of the simulations are compared to tokamak experiments, and encouraging agreement is found with measured density and temperature fluctuation spectra. Direct comparisons of transport fluxes reveal that electromagnetic effects are important at characteristic edge parameters, bringing predicted fluxes more closely in line with observations.

Effect of damping on excitability of high-order normal modes. [for a large space telescope spacecraft

NASA Technical Reports Server (NTRS)

Merchant, D. H.; Gates, R. M.; Straayer, J. W.

1975-01-01

The effect of localized structural damping on the excitability of higher-order large space telescope spacecraft modes is investigated. A preprocessor computer program is developed to incorporate Voigt structural joint damping models in a finite-element dynamic model. A postprocessor computer program is developed to select critical modes for low-frequency attitude control problems and for higher-frequency fine-stabilization problems. The selection is accomplished by ranking the flexible modes based on coefficients for rate gyro, position gyro, and optical sensor, and on image-plane motions due to sinusoidal or random PSD force and torque inputs.

Low-G fluid behavior technology summaries

NASA Technical Reports Server (NTRS)

Stark, J. A.; Bradshaw, R. D.; Blatt, M. H.

1974-01-01

This report presents a summarization and categorization of the pertinent literature associated with low-g fluid behavior technology. Initially a literature search was conducted to obtain pertinent documents for review. Reports determined to be of primary significance are summarized in detail. Each summary, where applicable, consists of; (1) report identification, (2) objective(s) of the work, (3) description of pertinent work performed, (4) major results, and (5) comments of the reviewer (GD/C). Pertinent figures are presented on a single facing page separate from the text. Specific areas covered are; interface configuration, interface stability, natural frequency and damping, liquid reorientation, bubbles and droplets, fluid inflow, fluid outflow, convection, boiling and condensation heat transfer, venting effects, and fluid properties. Reports which were reviewed and not summarized, along with reasons for not summarizing, are also listed. Cryogenic thermal control and fluid management systems technology are presented.

Durable crystalline Si photovoltaic modules based on silicone-sheet encapsulants

NASA Astrophysics Data System (ADS)

Hara, Kohjiro; Ohwada, Hiroto; Furihata, Tomoyoshi; Masuda, Atsushi

2018-02-01

Crystalline Si photovoltaic (PV) modules were fabricated with sheets of poly(dimethylsiloxane) (silicone) as an encapsulant. The long-term durability of the silicone-encapsulated PV modules was experimentally investigated. The silicone-based modules enhanced the long-term durability against potential-induced degradation (PID) and a damp-heat (DH) condition at 85 °C with 85% relative humidity (RH). In addition, we designed and fabricated substrate-type Si PV modules based on the silicone encapsulant and an Al-alloy plate as the substratum, which demonstrated high impact resistance and high incombustible performance. The high chemical stability, high volume resistivity, rubber-like elasticity, and incombustibility of the silicone encapsulant resulted in the high durability of the modules. Our results indicate that silicone is an attractive encapsulation material, as it improves the long-term durability of crystalline Si PV modules.

Damping SOFIA: passive and active damping for the Stratospheric Observatory for Infrared Astronomy

NASA Astrophysics Data System (ADS)

Maly, Joseph R.; Keas, Paul J.; Glaese, Roger M.

2001-07-01

The Stratospheric Observatory For Infrared Astronomy, SOFIA is being developed by NASA and the German space agency, Deutschen Zentrum fur Luft- und Raumfahrt (DLR), with an international contractor team. The 2.5-meter reflecting telescope of SOFIA will be the world's largest airborne telescope. Flying in an open cavity on a modified 747 aircraft, SOFIA will perform infrared astronomy while cruising at 41,000 feet and while being buffeted by a 550- mile-per-hour slipstream. A primary system requirement of SOFIA is tracking stability of 0.2 arc-seconds, and a 3-axis pointing control model has been used to evaluate the feasibility of achieving this kind of stability. The pointing control model shows that increased levels of damping in certain elastic modes of the telescope assembly will help achieve the tracking stability goal and also expand the bandwidth of the attitude controller. This paper describes the preliminary work that has been done to approximate the reduction in image motion yielded by various structure configurations that use reaction masses to attenuate the flexible motions of the telescope structure. Three approaches are considered: passive tuned-mass dampers, active-mass dampers, and attitude control with reaction-mass actuators. Expected performance improvements for each approach, and practical advantages and disadvantages associated with each are presented.

Divergence instability of pipes conveying fluid with uncertain flow velocity

NASA Astrophysics Data System (ADS)

Rahmati, Mehdi; Mirdamadi, Hamid Reza; Goli, Sareh

2018-02-01

This article deals with investigation of probabilistic stability of pipes conveying fluid with stochastic flow velocity in time domain. As a matter of fact, this study has focused on the randomness effects of flow velocity on stability of pipes conveying fluid while most of research efforts have only focused on the influences of deterministic parameters on the system stability. The Euler-Bernoulli beam and plug flow theory are employed to model pipe structure and internal flow, respectively. In addition, flow velocity is considered as a stationary random process with Gaussian distribution. Afterwards, the stochastic averaging method and Routh's stability criterion are used so as to investigate the stability conditions of system. Consequently, the effects of boundary conditions, viscoelastic damping, mass ratio, and elastic foundation on the stability regions are discussed. Results delineate that the critical mean flow velocity decreases by increasing power spectral density (PSD) of the random velocity. Moreover, by increasing PSD from zero, the type effects of boundary condition and presence of elastic foundation are diminished, while the influences of viscoelastic damping and mass ratio could increase. Finally, to have a more applicable study, regression analysis is utilized to develop design equations and facilitate further analyses for design purposes.

Piloted simulator investigation of helicopter control systems effects on handling qualities during instrument flight

NASA Technical Reports Server (NTRS)

Forrest, R. D.; Chen, R. T. N.; Gerdes, R. M.; Alderete, T. S.; Gee, D. R.

1979-01-01

An exploratory piloted simulation was conducted to investigate the effects of the characteristics of helicopter flight control systems on instrument flight handling qualities. This joint FAA/NASA study was motivated by the need to improve instrument flight capability. A near-term objective is to assist in updating the airworthiness criteria for helicopter instrument flight. The experiment consisted of variations of single-rotor helicopter types and levels of stability and control augmentation systems (SCAS). These configurations were evaluated during an omnirange approach task under visual and instrument flight conditions. The levels of SCAS design included a simple rate damping system, collective decoupling plus rate damping, and an attitude command system with collective decoupling. A limited evaluation of stick force versus airspeed stability was accomplished. Some problems were experienced with control system mechanization which had a detrimental effect on longitudinal stability. Pilot ratings, pilot commentary, and performance data related to the task are presented.

Ensemble Simulations of Proton Heating in the Solar Wind via Turbulence and Ion Cyclotron Resonance

NASA Astrophysics Data System (ADS)

Cranmer, Steven R.

2014-07-01

Protons in the solar corona and heliosphere exhibit anisotropic velocity distributions, violation of magnetic moment conservation, and a general lack of thermal equilibrium with the other particle species. There is no agreement about the identity of the physical processes that energize non-Maxwellian protons in the solar wind, but a traditional favorite has been the dissipation of ion cyclotron resonant Alfvén waves. This paper presents kinetic models of how ion cyclotron waves heat protons on their journey from the corona to interplanetary space. It also derives a wide range of new solutions for the relevant dispersion relations, marginal stability boundaries, and nonresonant velocity-space diffusion rates. A phenomenological model containing both cyclotron damping and turbulent cascade is constructed to explain the suppression of proton heating at low alpha-proton differential flow speeds. These effects are implemented in a large-scale model of proton thermal evolution from the corona to 1 AU. A Monte Carlo ensemble of realistic wind speeds, densities, magnetic field strengths, and heating rates produces a filled region of parameter space (in a plane described by the parallel plasma beta and the proton temperature anisotropy ratio) similar to what is measured. The high-beta edges of this filled region are governed by plasma instabilities and strong heating rates. The low-beta edges correspond to weaker proton heating and a range of relative contributions from cyclotron resonance. On balance, the models are consistent with other studies that find only a small fraction of the turbulent power spectrum needs to consist of ion cyclotron waves.

Flutter prediction for a wing with active aileron control

NASA Technical Reports Server (NTRS)

Penning, K.; Sandlin, D. R.

1983-01-01

A method for predicting the vibrational stability of an aircraft with an analog active aileron flutter suppression system (FSS) is expained. Active aileron refers to the use of an active control system connected to the aileron to damp vibrations. Wing vibrations are sensed by accelerometers and the information is used to deflect the aileron. Aerodynamic force caused by the aileron deflection oppose wing vibrations and effectively add additional damping to the system.

W-transform for exponential stability of second order delay differential equations without damping terms.

PubMed

Domoshnitsky, Alexander; Maghakyan, Abraham; Berezansky, Leonid

2017-01-01

In this paper a method for studying stability of the equation [Formula: see text] not including explicitly the first derivative is proposed. We demonstrate that although the corresponding ordinary differential equation [Formula: see text] is not exponentially stable, the delay equation can be exponentially stable.

Laboratory test methods for combustion stability properties of solid propellants

NASA Technical Reports Server (NTRS)

Strand, L. D.; Brown, R. S.

1992-01-01

An overview is presented of experimental methods for determining the combustion-stability properties of solid propellants. The methods are generally based on either the temporal response to an initial disturbance or on external methods for generating the required oscillations. The size distribution of condensed-phase combustion products are characterized by means of the experimental approaches. The 'T-burner' approach is shown to assist in the derivation of pressure-coupled driving contributions and particle damping in solid-propellant rocket motors. Other techniques examined include the rotating-valve apparatus, the impedance tube, the modulated throat-acoustic damping burner, and the magnetic flowmeter. The paper shows that experimental methods do not exist for measuring the interactions between acoustic velocity oscillations and burning propellant.

Vibration control in smart coupled beams subjected to pulse excitations

NASA Astrophysics Data System (ADS)

Pisarski, Dominik; Bajer, Czesław I.; Dyniewicz, Bartłomiej; Bajkowski, Jacek M.

2016-10-01

In this paper, a control method to stabilize the vibration of adjacent structures is presented. The control is realized by changes of the stiffness parameters of the structure's couplers. A pulse excitation applied to the coupled adjacent beams is imposed as the kinematic excitation. For such a representation, the designed control law provides the best rate of energy dissipation. By means of a stability analysis, the performance in different structural settings is studied. The efficiency of the proposed strategy is examined via numerical simulations. In terms of the assumed energy metric, the controlled structure outperforms its passively damped equivalent by over 50 percent. The functionality of the proposed control strategy should attract the attention of practising engineers who seek solutions to upgrade existing damping systems.

Numerical Study of Magnetic Damping During Unidirectional Solidification

NASA Technical Reports Server (NTRS)

Li, Ben Q.

1997-01-01

A fully 3-D numerical model is developed to represent magnetic damping of complex fluid flow, heat transfer and electromagnetic field distributions in a melt cavity. The model is developed based on our in-house finite element code for the fluid flow, heat transfer and electromagnetic field calculations. The computer code has been tested against benchmark test problems that are solved by other commercial codes as well as analytical solutions whenever available. The numerical model is tested against numerical and experimental results for water reported in literature. With the model so tested, various numerical simulations are carried out for the Sn-35.5% Pb melt convection and temperature distribution in a cylindrical cavity with and without the presence of a transverse magnetic field. Numerical results show that magnetic damping can be effectively applied to reduce turbulence and flow levels in the melt undergoing solidification and over a certain threshold value a higher magnetic field resulted in a higher velocity reduction. It is found also that for a fully 3-D representation of the magnetic damping effects, the electric field induced in the melt by the applied DC magnetic field does not vanish, as some researchers suggested, and must be included even for molten metal and semiconductors. Also, for the study of the melt flow instability, a long enough time has to be applied to ensure the final fluid flow recirculation pattern. Moreover, our numerical results suggested that there seems to exist a threshold value of applied magnetic field, above which magnetic damping becomes possible and below which the convection in the melt is actually enhanced. Because of the limited financial resource allocated for the project, we are unable to carry out extensive study on this effect, which should warrant further theoretical and experimental study. In that endeavor, the developed numerical model should be very useful; and the model should serve as a useful tool for exploring necessary design parameters for planning magnetic damping experiments and interpreting the experimental results.

Combustion stability with baffles, absorbers and velocity sensitive combustion. [liquid propellant rocket combustors

NASA Technical Reports Server (NTRS)

Mitchell, C. E.

1980-01-01

Analytical and computational techniques were developed to predict the stability behavior of liquid propellant rocket combustors using damping devices such as acoustic liners, slot absorbers, and injector face baffles. Models were developed to determine the frequency and decay rate of combustor oscillations, the spatial and temporal pressure waveforms, and the stability limits in terms of combustion response model parameters.

Motion of a pendulum with damping and vibrating axis of suspension at unconventional values of parameters

NASA Astrophysics Data System (ADS)

Demidov, Ivan; Sorokin, Vladislav

2018-05-01

Motion of a pendulum with damping and vibrating axis of suspension is considered at unconventional values of parameters. Case when the frequency of external loading and the natural frequency of the pendulum in the absence of this loading are of the same order is studied. Vibration intensity is assumed to be relatively low. In this case, the corresponding equation of the pendulum's motions doesn't involve an explicit small parameter. To solve the equation a new modification of the method of direct separation of motions is used. As the result, stability conditions of the pendulum inverted position are determined. Effects of damping on these conditions are discussed.

Synthesis of the adaptive continuous system for the multi-axle wheeled vehicle body oscillation damping

NASA Astrophysics Data System (ADS)

Zhileykin, M. M.; Kotiev, G. O.; Nagatsev, M. V.

2018-02-01

In order to meet the growing mobility requirements for the wheeled vehicles on all types of terrain the engineers have to develop a large number of specialized control algorithms for the multi-axle wheeled vehicle (MWV) suspension improving such qualities as ride comfort, handling and stability. The authors have developed an adaptive algorithm of the dynamic damping of the MVW body oscillations. The algorithm provides high ride comfort and high mobility of the vehicle. The article discloses a method for synthesis of an adaptive dynamic continuous algorithm of the MVW body oscillation damping and provides simulation results proving high efficiency of the developed control algorithm.

Highly Maneuverable Aircraft Technology (HiMAT) flight-flutter test program

NASA Technical Reports Server (NTRS)

Kehoe, M. W.

1984-01-01

The highly maneuverable aircraft technology (HiMAT) vehicle was evaluated in a joint NASA and Air Force flight test program. The HiMAT vehicle is a remotely piloted research vehicle. Its design incorporates the use of advanced composite materials in the wings, and canards for aeroelastic tailoring. A flight-flutter test program was conducted to clear a sufficient flight envelope to allow for performance, stability and control, and loads testing. Testing was accomplished with and without flight control-surface dampers. Flutter clearance of the vehicle indicated satisfactory damping and damping trends for the structural modes of the HiMAT vehicle. The data presented include frequency and damping plotted as a function of Mach number.

Damping-tunable energy-harvesting vehicle damper with multiple controlled generators: Design, modeling and experiments

NASA Astrophysics Data System (ADS)

Xie, Longhan; Li, Jiehong; Li, Xiaodong; Huang, Ledeng; Cai, Siqi

2018-01-01

Hydraulic dampers are used to decrease the vibration of a vehicle, where vibration energy is dissipated as heat. In addition to resulting in energy waste, the damping coefficient in hydraulic dampers cannot be changed during operation. In this paper, an energy-harvesting vehicle damper was proposed to replace traditional hydraulic dampers. The goal is not only to recover kinetic energy from suspension vibration but also to change the damping coefficient during operation according to road conditions. The energy-harvesting damper consists of multiple generators that are independently controlled by switches. One of these generators connects to a tunable resistor for fine tuning the damping coefficient, while the other generators are connected to a control and rectifying circuit, each of which both regenerates electricity and provides a constant damping coefficient. A mathematical model was built to investigate the performance of the energy-harvesting damper. By controlling the number of switched-on generators and adjusting the value of the external tunable resistor, the damping can be fine tuned according to the requirement. In addition to the capability of damping tuning, the multiple controlled generators can output a significant amount of electricity. A prototype was built to test the energy-harvesting damper design. Experiments on an MTS testing system were conducted, with results that validated the theoretical analysis. Experiments show that changing the number of switched-on generators can obviously tune the damping coefficient of the damper and simultaneously produce considerable electricity.

High Harmonic Fast Wave Damping on an Ion Beam: NSTX and DIII-D Regimes Compared

NASA Astrophysics Data System (ADS)

Pinsker, R. I.; Choi, C. C.; Petty, C. C.; Porkolab, M.; Wilson, J. R.; Murakami, M.; Harvey, R. W.

2004-11-01

Both NSTX and DIII-D use the combination of fast Alfven waves (FW) and neutral beam injection (NBI) for central electron heating and current drive. Damping of the fast wave on the beam ions at moderate to high harmonics (4th--20th) of the beam ion cyclotron frequency represents a loss process. In DIII-D current drive experiments at low density in which 4th and 8th harmonics were compared, damping at the 8th harmonic damping was much weaker than at the 4th [1]. However, recent simulations have predicted that in higher density and higher beam power regimes (of interest to the Advanced Tokamak program) the beam ion absorption will transition to the unmagnetized ion regime, where the damping is significant and essentially independent of harmonic number. In the present work, the transition from magnetized to unmagnetized ion regimes for the NSTX and DIII-D HHFW experiments is studied theoretically, with a combination of simple semi-analytic models and numerical models. \\vspace0.25 em [1] C.C. Petty, et al., Plasma Phys. and Contr. Fusion 43, 1747 (2001).

DOE Office of Scientific and Technical Information (OSTI.GOV)

Haker, C.D.; Rix, G.J.; Lai, C.G.

The seismic stability of municipal solid waste (MSW) landfills is often a significant consideration in landfill design. However, until recently, the dynamic properties of the waste material itself, which govern the seismic response of MSW landfills, have often been approximated or assumed. Tests to determine the dynamic properties of the material directly have been limited. Measurements of seismic surface waves were used to determine the dynamic properties of MSW, which are the initial tangent shear modulus and low-strain hysteretic damping ratio. Surface wave tests were performed at three MSW landfills to determine their shear modulus and damping ratio profiles. Surfacemore » wave tests are ideal for measuring the near-surface shear modulus and damping profiles of MSW landfills because the tests are non-invasive, an advantage for testing environmentally sensitive waste material. Factors which influence the dynamic properties of waste including density, confinement, age, and placement techniques are used to interpret the measured shear modulus and damping ratio profiles.« less

Direct measurement of Kramers turnover with a levitated nanoparticle

NASA Astrophysics Data System (ADS)

Rondin, Loïc; Gieseler, Jan; Ricci, Francesco; Quidant, Romain; Dellago, Christoph; Novotny, Lukas

2017-12-01

Understanding the thermally activated escape from a metastable state is at the heart of important phenomena such as the folding dynamics of proteins, the kinetics of chemical reactions or the stability of mechanical systems. In 1940, Kramers calculated escape rates both in the high damping and low damping regimes, and suggested that the rate must have a maximum for intermediate damping. This phenomenon, today known as the Kramers turnover, has triggered important theoretical and numerical studies. However, as yet, there is no direct and quantitative experimental verification of this turnover. Using a nanoparticle trapped in a bistable optical potential, we experimentally measure the nanoparticle's transition rates for variable damping and directly resolve the Kramers turnover. Our measurements are in agreement with an analytical model that is free of adjustable parameters. The levitated nanoparticle presented here is a versatile experimental platform for studying and simulating a wide range of stochastic processes and testing theoretical models and predictions.

Acoustical power amplification and damping by temperature gradients.

PubMed

Biwa, Tetsushi; Komatsu, Ryo; Yazaki, Taichi

2011-01-01

Ceperley proposed a concept of a traveling wave heat engine ["A pistonless Stirling engine-The traveling wave heat engine," J. Acoust. Soc. Am. 66, 1508-1513 (1979).] that provided a starting point of thermoacoustics today. This paper verifies experimentally his idea through observation of amplification and strong damping of a plane acoustic traveling wave as it passes through axial temperature gradients. The acoustic power gain is shown to obey a universal curve specified by a dimensionless parameter ωτα; ω is the angular frequency and τα is the relaxation time for the gas to thermally equilibrate with channel walls. As an application of his idea, a three-stage acoustic power amplifier is developed, which attains the gain up to 10 with a moderate temperature ratio of 2.3.

Liquid Droplet Dynamics in Gravity Compensating High Magnetic Field

NASA Technical Reports Server (NTRS)

Bojarevics, V.; Easter, S.; Pericleous, K.

2012-01-01

Numerical models are used to investigate behavior of liquid droplets suspended in high DC magnetic fields of various configurations providing microgravity-like conditions. Using a DC field it is possible to create conditions with laminar viscosity and heat transfer to measure viscosity, surface tension, electrical and thermal conductivities, and heat capacity of a liquid sample. The oscillations in a high DC magnetic field are quite different for an electrically conducting droplet, like liquid silicon or metal. The droplet behavior in a high magnetic field is the subject of investigation in this paper. At the high values of magnetic field some oscillation modes are damped quickly, while others are modified with a considerable shift of the oscillating droplet frequencies and the damping constants from the non-magnetic case.

The design of delay-dependent wide-area DOFC with prescribed degree of stability α for damping inter-area low-frequency oscillations in power system.

PubMed

Sun, Miaoping; Nian, Xiaohong; Dai, Liqiong; Guo, Hua

2017-05-01

In this paper, the delay-dependent wide-area dynamic output feedback controller (DOFC) with prescribed degree of stability is proposed for interconnected power system to damp inter-area low-frequency oscillations. Here, the prescribed degree of stability α is used to maintain all the poles on the left of s=-α in the s-plane. Firstly, residue approach is adopted to select input-output control signals and the schur balanced truncation model reduction method is utilized to obtain the reduced power system model. Secondly, based on Lyapunov stability theory and transformation operation in complex plane, the sufficient condition of asymptotic stability for closed-loop power system with prescribed degree of stability α is derived. Then, a novel method based on linear matrix inequalities (LMIs) is presented to obtain the parameters of DOFC and calculate delay margin of the closed-loop system considering the prescribed degree of stability α. Finally, case studies are carried out on the two-area four-machine system, which is controlled by classical wide-area power system stabilizer (WAPSS) in reported reference and our proposed DOFC respectively. The effectiveness and advantages of the proposed method are verified by the simulation results under different operating conditions. Copyright © 2017 ISA. Published by Elsevier Ltd. All rights reserved.

[DAMPs (damage-associated molecular patterns) and inflammation].

PubMed

Ooboshi, Hiroaki; Shichita, Takashi

2016-04-01

Post-ischemic inflammation is re-appraised as an important player in the progression of ischemic stroke. Activation of inflammatory cells via Toll-like receptor 2 (TLR2) and TLR4 is caused by several damage-associated molecular patterns (DAMPs), including high mobility group box-1 (HMGB-1) and heat shock proteins. We have recently found that peroxiredoxin (Prx) is one of the strong DAMPs and activates infiltrating macrophages in brain ischemia. We have also found that interleukin-23 (IL-23) from the activated macrophages stimulates γδT cells which release IL-17, thereby causing the delayed expansion of infarct lesions. Further investigation of the innate immune response would lead to development of novel stroke treatment with a broad therapeutic time window.

14 CFR Appendix B to Part 29 - Airworthiness Criteria for Helicopter Instrument Flight

Code of Federal Regulations, 2010 CFR

2010-01-01

.... Dynamic stability. (a) Any oscillation having a period of less than 5 seconds must damp to 1/2 amplitude... achieve double amplitude in less than 9 seconds. VII. Stability Augmentation System (SAS) (a) If a SAS is... control system must be considered. In addition— (i) The controllability and maneuverability requirements...

Low-Temperature Fabrication of Robust, Transparent, and Flexible Thin-Film Transistors with a Nanolaminated Insulator.

PubMed

Kwon, Jeong Hyun; Park, Junhong; Lee, Myung Keun; Park, Jeong Woo; Jeon, Yongmin; Shin, Jeong Bin; Nam, Minwoo; Kim, Choong-Ki; Choi, Yang-Kyu; Choi, Kyung Cheol

2018-05-09

The lack of reliable, transparent, and flexible electrodes and insulators for applications in thin-film transistors (TFTs) makes it difficult to commercialize transparent, flexible TFTs (TF-TFTs). More specifically, conventional high process temperatures and the brittleness of these elements have been hurdles in developing flexible substrates vulnerable to heat. Here, we propose electrode and insulator fabrication techniques considering process temperature, transmittance, flexibility, and environmental stability. A transparent and flexible indium tin oxide (ITO)/Ag/ITO (IAI) electrode and an Al 2 O 3 /MgO (AM)-laminated insulator were optimized at the low temperature of 70 °C for the fabrication of TF-TFTs on a polyethylene terephthalate (PET) substrate. The optimized IAI electrode with a sheet resistance of 7 Ω/sq exhibited the luminous transmittance of 85.17% and maintained its electrical conductivity after exposure to damp heat conditions because of an environmentally stable ITO capping layer. In addition, the electrical conductivity of IAI was maintained after 10 000 bending cycles with a tensile strain of 3% because of the ductile Ag film. In the metal/insulator/metal structure, the insulating and mechanical properties of the optimized AM-laminated film deposited at 70 °C were significantly improved because of the highly dense nanolaminate system, compared to those of the Al 2 O 3 film deposited at 70 °C. In addition, the amorphous indium-gallium-zinc oxide (a-IGZO) was used as the active channel for TF-TFTs because of its excellent chemical stability. In the environmental stability test, the ITO, a-IGZO, and AM-laminated films showed the excellent environmental stability. Therefore, our IGZO-based TFT with IAI electrodes and the 70 °C AM-laminated insulator was fabricated to evaluate robustness, transparency, flexibility, and process temperature, resulting in transfer characteristics comparable to those of an IGZO-based TFT with a 150 °C Al 2 O 3 insulator.

A model of the planetary boundary layer over a snow surface

NASA Technical Reports Server (NTRS)

Halberstam, I.; Melendez, R.

1979-01-01

A model of the planetary boundary layer over a snow surface has been developed. It contains the vertical heat exchange processes due to radiation, conduction, and atmospheric turbulence. Parametrization of the boundary layer is based on similarity functions developed by Hoffert and Sud (1976), which involve a dimensionless variable, dependent on boundary-layer height and a localized Monin-Obukhov length. The model also contains the atmospheric surface layer and the snowpack itself, where snowmelt and snow evaporation are calculated. The results indicate a strong dependence of surface temperatures, especially at night, on the bursts of turbulence which result from the frictional damping of surface-layer winds during periods of high stability, as described by Businger (1973). The model also shows the cooling and drying effect of the snow on the atmosphere, which may be the mechanism for air mass transformation in sub-Arctic regions.

Load and stability measurements on a soft-inplane rotor system incorporating elastomeric lead-lag dampers

NASA Technical Reports Server (NTRS)

Weller, W. H.

1977-01-01

An experimental investigation was conducted of the dynamic response and inplane stability associated with a new soft-inplane helicopter rotor. The unique feature of this rotor was the use of an internal elastomeric damper to restrain the blade inplane motion about the lead-lag hinge. The properties of the elastomer were selected to provide both a nominal first inplane frequency ratio of 0.65 and sufficient damping to eliminate the need for additional external damping sources to prevent ground resonance on a typical fuselage structure. For this investigation a 1/5-scale aeroelastic model was used to represent the rotor. The four-blade model had a diameter of 3.05 m (10 ft) and a solidity of 0.103. The first out-of-plane frequency ratio was 1.06. The model was tested in hover and in forward flight up to an advance ratio of 0.45. At each forward speed the rotor lift was varied up to simulated maneuver conditions. The measured rotor loads and response were within acceptable limits, and no adverse response qualities were observed. Moderate out-of-plane hub moments were measured, even for zero lift, to indicate the beneficial control power available for this design. Blade inplane stability testing indicated that the rotor system damping remained at moderate levels throughout the operating envelope.

Heating of the Interstellar Diffuse Ionized Gas via the Dissipation of Turbulence

NASA Astrophysics Data System (ADS)

Minter, Anthony H.; Spangler, Steven R.

1997-08-01

We have recently published observations that specify most of the turbulent and mean plasma characteristics for a region of the sky containing the interstellar diffuse ionized gas (DIG). These observations have provided virtually all of the information necessary to calculate the heating rate from dissipation of turbulence. We have calculated the turbulent dissipation heating rate employing two models for the interstellar turbulence. The first is a customary modeling as a superposition of magnetohydrodynamic waves. The second is a fluid-turbulence-like model based on the ideas of Higdon. This represents the first time that such calculations have been carried out with full and specific interstellar turbulence parameters. The wave model of interstellar turbulence encounters the severe difficulty that plausible estimates of heating by Landau damping exceed the radiative cooling capacity of the interstellar DIG by 3-4 orders of magnitude. Clearly interstellar turbulence does not behave like an ensemble of obliquely propagating fast magnetosonic waves. The heating rate due to two other wave dissipation mechanisms, ion-neutral collisional damping and the parametric decay instability, are comparable to the cooling capacity of the diffuse ionized medium. We find that the fluid-like turbulence model is an acceptable and realistic model of the turbulence in the interstellar medium once the effects of ion-neutral collisions are included in the model. This statement is contingent on an assumption that the dissipation of such turbulence because of Landau damping is several orders of magnitude less than that from an ensemble of obliquely propagating magnetosonic waves with the same energy density. Arguments as to why this may be the case are made in the paper. Rough parity between the turbulent heating rate and the radiative cooling rate in the DIG also depends on the hydrogen ionization fraction being in excess of 90% or on a model-dependent lower limit to the heating rate being approximately valid. We conclude that the dissipation of turbulence is capable of providing a substantial and perhaps major contribution to the energy budget of the diffuse ionized medium.

The role of DAMPS in ALA-PDT for skin squamous cell carcinoma (Conference Presentation)

NASA Astrophysics Data System (ADS)

Wang, Xiuli; Wang, Xiaojie; Ji, Jie; Zhang, Haiyan; Shi, Lei

2016-03-01

5-Aminolevulinic acid mediated photodynamic therapy (ALA-PDT) is an established local approach for skin squamous cell carcinoma. It is believed that dangerous signals damage-associated molecular patterns (DAMPs) play an important role in ALA-PDT. In this study, we evaluated in vitro and in vivo expressions of major DAMPs, calreticulin (CRT), heat shock proteins 70 (HSP70), and high mobility group box 1 (HMGB1), induced by ALA-PDT using immunohistochemistry, western blot, and ELISA in a squamous cell carcinoma (SCC) mouse model. The role of DAMPs in the maturation of DCs potentiated by ALA-PDT-treated tumor cells was detected by FACS and ELISA. Our results showed that ALA-PDT enhanced the expression of CRT, HSP70, and HMGB1. These induced DAMPs played an important role in activating DCs by PDT-treated tumor cells, including phenotypic maturation (upregulation of surface expression of MHC-II, CD80, and CD86) and functional maturation (enhanced capability to secrete IFN-γ and IL-12). Furthermore, injecting ALA-PDT-treated tumor cells into naïve mice resulted in complete protection against cancer cells of the same origin. Our findings indicate that ALA-PDT can upregulate DAMPs and enhance tumor immunogenicity, providing a promising strategy for inducing a systemic anticancer immune response.

High temperature dynamic modulus and damping of aluminum and titanium matrix composites

NASA Technical Reports Server (NTRS)

Dicarlo, J. A.; Maisel, J. E.

1979-01-01

Dynamic modulus and damping capacity property data were measured from 20 to over 500 C for unidirectional B/Al (1100), B/Al (6061), B/SiC/Al (6061), Al2O3/Al, SiC/Ti-6Al-4V, and SiC/Ti composites. The measurements were made under vacuum by the forced vibration of composite bars at free-free flexural resonance near 2000 Hz and at amplitudes below 0.000001. Whereas little variation was observed in the dynamic moduli of specimens with approximately the same fiber content (50 percent), the damping of B/Al composites was found at all temperatures to be significantly greater than the damping of the Al2O3/Al and SiC/Ti composites. For those few situations where slight deviations from theory were observed, the dynamic data were examined for information concerning microstructural changes induced by composite fabrication and thermal treatment. The 270 C damping peak observed in B/Al (6061) composites after heat treatment above 460 C appears to be the result of a change in the 6061 aluminum alloy microstructure induced by interaction with the boron fibers. The growth characteristics of the damping peak suggest its possible value for monitoring fiber strength degration caused by excess thermal treatment during B/Al (6061) fabrication and use.

A Weakly Nonlinear Model for the Damping of Resonantly Forced Density Waves in Dense Planetary Rings

NASA Astrophysics Data System (ADS)

Lehmann, Marius; Schmidt, Jürgen; Salo, Heikki

2016-10-01

In this paper, we address the stability of resonantly forced density waves in dense planetary rings. Goldreich & Tremaine have already argued that density waves might be unstable, depending on the relationship between the ring’s viscosity and the surface mass density. In the recent paper Schmidt et al., we have pointed out that when—within a fluid description of the ring dynamics—the criterion for viscous overstability is satisfied, forced spiral density waves become unstable as well. In this case, linear theory fails to describe the damping, but nonlinearity of the underlying equations guarantees a finite amplitude and eventually a damping of the wave. We apply the multiple scale formalism to derive a weakly nonlinear damping relation from a hydrodynamical model. This relation describes the resonant excitation and nonlinear viscous damping of spiral density waves in a vertically integrated fluid disk with density dependent transport coefficients. The model consistently predicts density waves to be (linearly) unstable in a ring region where the conditions for viscous overstability are met. Sufficiently far away from the Lindblad resonance, the surface mass density perturbation is predicted to saturate to a constant value due to nonlinear viscous damping. The wave’s damping lengths of the model depend on certain input parameters, such as the distance to the threshold for viscous overstability in parameter space and the ground state surface mass density.

Dynamics stability derivatives of space shuttle orbiter obtained from wind-tunnel and approach and landing flight tests

NASA Technical Reports Server (NTRS)

Freeman, D. C., Jr.

1980-01-01

A comparison was made between ground facility measurements, the aerodynamic design data book values, and the dynamic damping derivatives extracted from the space shuttle orbiter approach and landing flight tests. The comparison covers an angle of attack range from 2 deg to 10 deg at subsonic Mach numbers. The parameters of pitch, yaw, and roll damping, as well as the yawing moment due to rolling velocity and rolling moment due to yawing velocity are compared.

Acoustic cavity technology for high performance injectors

NASA Technical Reports Server (NTRS)

1976-01-01

The feasibility of damping more than one mode of rocket engine combustion instability by means of differently tuned acoustic cavities sharing a common entrance was shown. Analytical procedures and acoustic modeling techniques for predicting the stability behavior of acoustic cavity designs in hot firings were developed. Full scale testing of various common entrance, dual cavity configurations, and subscale testing for the purpose of obtaining motion pictures of the cavity entrance region, to aid in determining the mechanism of cavity damping were the two major aspects of the program.

Prediction of Ship Roll Damping. A State of the Art

DTIC Science & Technology

1981-09-01

Armin W. Troesch and Mr. John P. Hackett for their valuable advice, discussions and encouragement. The author also feels grateful to Professor Norio...Hadd- . (60], and Lewison [61] have proposed expressing the roll damping in a cubi orm without quadratic term, B 1 +B 3 0 , for con- venience in the...34 Internat. Shipbuildin; Progress, Vo.l. 20 (1973). 61. Lewison , G.R.G.: "Optimum Design of Passive Roll Stabilizer Tanks," The Naval Architect (1976). Ij t

Coronal loop seismology using damping of standing kink oscillations by mode coupling. II. additional physical effects and Bayesian analysis

NASA Astrophysics Data System (ADS)

Pascoe, D. J.; Anfinogentov, S.; Nisticò, G.; Goddard, C. R.; Nakariakov, V. M.

2017-04-01

Context. The strong damping of kink oscillations of coronal loops can be explained by mode coupling. The damping envelope depends on the transverse density profile of the loop. Observational measurements of the damping envelope have been used to determine the transverse loop structure which is important for understanding other physical processes such as heating. Aims: The general damping envelope describing the mode coupling of kink waves consists of a Gaussian damping regime followed by an exponential damping regime. Recent observational detection of these damping regimes has been employed as a seismological tool. We extend the description of the damping behaviour to account for additional physical effects, namely a time-dependent period of oscillation, the presence of additional longitudinal harmonics, and the decayless regime of standing kink oscillations. Methods: We examine four examples of standing kink oscillations observed by the Atmospheric Imaging Assembly (AIA) onboard the Solar Dynamics Observatory (SDO). We use forward modelling of the loop position and investigate the dependence on the model parameters using Bayesian inference and Markov chain Monte Carlo (MCMC) sampling. Results: Our improvements to the physical model combined with the use of Bayesian inference and MCMC produce improved estimates of model parameters and their uncertainties. Calculation of the Bayes factor also allows us to compare the suitability of different physical models. We also use a new method based on spline interpolation of the zeroes of the oscillation to accurately describe the background trend of the oscillating loop. Conclusions: This powerful and robust method allows for accurate seismology of coronal loops, in particular the transverse density profile, and potentially reveals additional physical effects.

Turbomachinery Application of Lagrangian Dynamics to the Motion of Continuous Discrete Rotors

NASA Technical Reports Server (NTRS)

2005-01-01

The stability/instability condition of a turbine rotor with axisymmetric supports is determined in the presence of gyroscopic loads and rub-induced destabilizing forces. A modal representation of the turbine engine is used, with one mode in each of the vertical and horizontal planes. The use of non-spinning rotor modes permits an explicit treatment of gyroscopic effects. The two linearized modal equations of motion of a rotor with axisymmetric supports are reduced to a single equation in a complex variable. The resulting eigenvalues yield explicit expressions at the stability boundary, for the whirl frequency as well as the required damping in the presence of the available rub-induced destabilization. Conversely, the allowable destabilization in the presence of the available damping is also given.

FOKKER-PLANCK ANALYSIS OF TRANSVERSE COLLECTIVE INSTABILITIES IN ELECTRON STORAGE RINGS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lindberg, R. R.

We analyze single bunch transverse instabilities due to wakefields using a Fokker-Planck model. We expand on the work of Suzuki [1], writing out the linear matrix equation including chromaticity, both dipolar and quadrupolar transverse wakefields, and the effects of damping and diffusion due to the synchrotron radiation. The eigenvalues and eigenvectors determine the collective stability of the beam, and we show that the predicted threshold current for transverse instability and the profile of the unstable agree well with tracking simulations. In particular, we find that predicting collective stability for high energy electron beams at moderate to large values of chromaticitymore » requires the full Fokker-Planck analysis to properly account for the effects of damping and diffusion due to synchrotron radiation.« less

Bubble dynamics in viscoelastic soft tissue in high-intensity focal ultrasound thermal therapy.

PubMed

Zilonova, E; Solovchuk, M; Sheu, T W H

2018-01-01

The present study is aimed to investigate bubble dynamics in a soft tissue, to which HIFU's continuous harmonic pulse is applied by introducing a viscoelastic cavitation model. After a comparison of some existing cavitation models, we decided to employ Gilmore-Akulichev model. This chosen cavitation model should be coupled with the Zener viscoelastic model in order to be able to simulate soft tissue features such as elasticity and relaxation time. The proposed Gilmore-Akulichev-Zener model was investigated for exploring cavitation dynamics. The parametric study led us to the conclusion that the elasticity and viscosity both damp bubble oscillations, whereas the relaxation effect depends mainly on the period of the ultrasound wave. The similar influence of elasticity, viscosity and relaxation time on the temperature inside the bubble can be observed. Cavitation heat source terms (corresponding to viscous damping and pressure wave radiated by bubble collapse) were obtained based on the proposed model to examine the cavitation significance during the treatment process. Their maximum values both overdominate the acoustic ultrasound term in HIFU applications. Elasticity was revealed to damp a certain amount of deposited heat for both cavitation terms. Copyright © 2017 Elsevier B.V. All rights reserved.

Effect of Local Thermal Equilibrium Misbalance on Long-wavelength Slow Magnetoacoustic Waves

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nakariakov, V. M.; Afanasyev, A. N.; Kumar, S.

Evolution of slow magnetoacoustic waves guided by a cylindrical magnetic flux tube that represents a coronal loop or plume, is modeled accounting for the effects of finite gas pressure, weak nonlinearity, dissipation by thermal conduction and viscosity, and the misbalance between the cooling by optically thin radiation and unspecified heating of the plasma. An evolutionary equation of the Burgers–Malthus type is derived. It is shown that the cooling/heating misbalance, determined by the derivatives of the combined radiative cooling and heating function, with respect to the density, temperature, and magnetic field at the thermal equilibrium affect the wave rather strongly. Thismore » effect may either cause additional damping, or counteract it, or lead to the gradual amplification of the wave. In the latter case, the coronal plasma acts as an active medium for the slow magnetoacoustic waves. The effect of the cooling/heating misbalance could be important for coronal slow waves, and could be responsible for certain discrepancies between theoretical results and observations, in particular, the increased or decreased damping lengths and times, detection of the waves at certain heights only, and excitation of compressive oscillations. The results obtained open up a possibility for the diagnostics of the coronal heating function by slow magnetoacoustic waves.« less

Nonlinear oscillatory rarefied gas flow inside a rectangular cavity

NASA Astrophysics Data System (ADS)

Wang, Peng; Zhu, Lianhua; Su, Wei; Wu, Lei; Zhang, Yonghao

2018-04-01

The nonlinear oscillation of rarefied gas flow inside a two-dimensional rectangular cavity is investigated on the basis of the Shakhov kinetic equation. The gas dynamics, heat transfer, and damping force are studied numerically via the discrete unified gas-kinetic scheme for a wide range of parameters, including gas rarefaction, cavity aspect ratio, and oscillation frequency. Contrary to the linear oscillation where the velocity, temperature, and heat flux are symmetrical and oscillate with the same frequency as the oscillating lid, flow properties in nonlinear oscillatory cases turn out to be asymmetrical, and second-harmonic oscillation of the temperature field is observed. As a consequence, the amplitude of the shear stress near the top-right corner of the cavity could be several times larger than that at the top-left corner, while the temperature at the top-right corner could be significantly higher than the wall temperature in nearly the whole oscillation period. For the linear oscillation with the frequency over a critical value, and for the nonlinear oscillation, the heat transfer from the hot to cold region dominates inside the cavity, which is contrary to the anti-Fourier heat transfer in a low-speed rarefied lid-driven cavity flow. The damping force exerted on the oscillating lid is studied in detail, and the scaling laws are developed to describe the dependency of the resonance and antiresonance frequencies (corresponding to the damping force at a local maximum and minimum, respectively) on the reciprocal aspect ratio from the near hydrodynamic to highly rarefied regimes. These findings could be useful in the design of the micro-electro-mechanical devices operating in the nonlinear-flow regime.

Effect of length of Handley Page tip slots on the lateral-stability factor, damping in roll

NASA Technical Reports Server (NTRS)

Weick, Fred E; Wenzinger, Carl J

1932-01-01

Tests have been made in the NACA 7 by 10 foot wind tunnel on a Clark Y wing model equipped with various lengths of Handley Page slots extending inward from the wing tips. The slot lengths tested ranged from 20 to 100 per cent of the semi span. The effect of slot lengths on damping in roll was determined by means of both free-autorotation and forced-rotation test. In addition, the maximum lift coefficient was found with each slot length. The optimum length of slot for satisfactory damping in roll over a large range of angles of attack was found to be slightly over 50 per cent of the semispan for the form of slot tested.

High stability design for new centrifugal compressor

NASA Technical Reports Server (NTRS)

Kanki, H.; Katayama, K.; Morii, S.; Mouri, Y.; Umemura, S.; Ozawa, U.; Oda, T.

1989-01-01

It is essential that high-performance centrifugal compressors be free of subsynchronous vibrations. A new high-performance centrifugal compressor has been developed by applying the latest rotordynamics knowledge and design techniques: (1) To improve the system damping, a specially designed oil film seal was developed. This seal attained a damping ratio three times that of the conventional design. The oil film seal contains a special damper ring in the seal cartridge. (2) To reduce the destabilizing effect of the labyrinth seal, a special swirl canceler (anti-swirl nozzle) was applied to the balance piston seal. (3) To confirm the system damping margin, the dynamic simulation rotor model test and the full load test applied the vibration exciting test in actual load conditions.

Comparing the floquet stability of open and breathing fatigue cracks in an overhung rotordynamic system

NASA Astrophysics Data System (ADS)

Varney, Philip; Green, Itzhak

2017-11-01

Rotor cracks represent an uncommon but serious threat to rotating machines and must be detected early to avoid catastrophic machine failure. An important aspect of analyzing rotor cracks is understanding their influence on the rotor stability. It is well-known that the extent of rotor instability versus shaft speed is exacerbated by deeper cracks. Consequently, crack propagation can eventually result in an unstable response even if the shaft speed remains constant. Most previous investigations of crack-induced rotor instability concern simple Jeffcott rotors. This work advances the state-of-the-art by (a) providing a novel inertial-frame model of an overhung rotor, and (b) assessing the stability of the cracked overhung rotor using Floquet stability analysis. The rotor Floquet stability analysis is performed for both an open crack and a breathing crack, and conclusions are drawn regarding the importance of appropriately selecting the crack model. The rotor stability is analyzed versus crack depth, external viscous damping ratio, and rotor inertia. In general, this work concludes that the onset of instability occurs at lower shaft speeds for thick rotors, lower viscous damping ratios, and deeper cracks. In addition, when comparing commensurate cracks, the breathing crack is shown to induce more regions of instability than the open crack, though the open crack generally predicts an unstable response for shallower cracks than the breathing crack. Keywords: rotordynamics, stability, rotor cracks.

Aeroelastic Stability of Idling Wind Turbines

NASA Astrophysics Data System (ADS)

Wang, Kai; Riziotis, Vasilis A.; Voutsinas, Spyros G.

2016-09-01

Wind turbine rotors in idling operation mode can experience high angles of attack, within the post stall region that are capable of triggering stall-induced vibrations. In the present paper rotor stability in slow idling operation is assessed on the basis of non-linear time domain and linear eigenvalue analysis. Analysis is performed for a 10 MW conceptual wind turbine designed by DTU. First the flow conditions that are likely to favour stall induced instabilities are identified through non-linear time domain aeroelastic analysis. Next, for the above specified conditions, eigenvalue stability simulations are performed aiming at identifying the low damped modes of the turbine. Finally the results of the eigenvalue analysis are evaluated through computations of the work of the aerodynamic forces by imposing harmonic vibrations following the shape and frequency of the various modes. Eigenvalue analysis indicates that the asymmetric and symmetric out-of-plane modes have the lowest damping. The results of the eigenvalue analysis agree well with those of the time domain analysis.

Improving Small Signal Stability through Operating Point Adjustment

DOE Office of Scientific and Technical Information (OSTI.GOV)

Huang, Zhenyu; Zhou, Ning; Tuffner, Francis K.

2010-09-30

ModeMeter techniques for real-time small signal stability monitoring continue to mature, and more and more phasor measurements are available in power systems. It has come to the stage to bring modal information into real-time power system operation. This paper proposes to establish a procedure for Modal Analysis for Grid Operations (MANGO). Complementary to PSS’s and other traditional modulation-based control, MANGO aims to provide suggestions such as increasing generation or decreasing load for operators to mitigate low-frequency oscillations. Different from modulation-based control, the MANGO procedure proactively maintains adequate damping for all time, instead of reacting to disturbances when they occur. Effectmore » of operating points on small signal stability is presented in this paper. Implementation with existing operating procedures is discussed. Several approaches for modal sensitivity estimation are investigated to associate modal damping and operating parameters. The effectiveness of the MANGO procedure is confirmed through simulation studies of several test systems.« less

Wind-tunnel investigation of the flight characteristics of a canard general-aviation airplane configuration

NASA Technical Reports Server (NTRS)

Satran, D. R.

1986-01-01

A 0.36-scale model of a canard general-aviation airplane with a single pusher propeller and winglets was tested in the Langley 30- by 60-Foot Wind Tunnel to determine the static and dynamic stability and control and free-flight behavior of the configuration. Model variables made testing of the model possible with the canard in high and low positions, with increased winglet area, with outboard wing leading-edge droop, with fuselage-mounted vertical fin and rudder, with enlarged rudders, with dual deflecting rudders, and with ailerons mounted closer to the wing tips. The basic model exhibited generally good longitudinal and lateral stability and control characteristics. The removal of an outboard leading-edge droop degraded roll damping and produced lightly damped roll (wing rock) oscillations. In general, the model exhibited very stable dihedral effect but weak directional stability. Rudder and aileron control power were sufficiently adequate for control of most flight conditions, but appeared to be relatively weak for maneuvering compared with those of more conventionally configured models.

Thermoelastic vibration test techniques

NASA Technical Reports Server (NTRS)

Kehoe, Michael W.; Snyder, H. Todd

1991-01-01

The structural integrity of proposed high speed aircraft can be seriously affected by the extremely high surface temperatures and large temperature gradients throughout the vehicle's structure. Variations in the structure's elastic characteristics as a result of thermal effects can be observed by changes in vibration frequency, damping, and mode shape. Analysis codes that predict these changes must be correlated and verified with experimental data. The experimental modal test techniques and procedures used to conduct uniform, nonuniform, and transient thermoelastic vibration tests are presented. Experimental setup and elevated temperature instrumentation considerations are also discussed. Modal data for a 12 by 50 inch aluminum plate heated to a temperature of 475 F are presented. These data show the effect of heat on the plate's modal characteristics. The results indicated that frequency decreased, damping increased, and mode shape remained unchanged as the temperature of the plate was increased.

Investigation of flame driving and flow turning in axial solid rocket instabilities

NASA Astrophysics Data System (ADS)

Zinn, Ben T.; Daniel, Brady R.; Matta, Lawrence M.

1993-08-01

An understanding of the processes responsible for driving and damping acoustic oscillations in solid rocket motors is necessary for developing practical design methods that eliminate or reduce the occurrence combustion instabilities. While state of the art solid rocket stability prediction methods generally account for the flow turning loss, the magnitude and characteristics of this loss have never been fully investigated. Results of an investigation of the role of the flow turning loss in the stability of solid rockets and its dependence upon motor design and operating parameters are described. A one dimensional acoustic stability equation that verifies that the flow turning loss term is appropriately included in the one dimensional stability formulation was derived for a chamber with a constant mean temperature and pressure by an approach independent from that of Culick. This study was extended providing the background and expressions needed to guide an experimental study of the flow turning loss in the presence of mean temperature and density gradients. This allows the study of combustion systems in which mean temperature gradients and heat losses are significant. The relevant conservation equations were solved numerically for the experimental configuration in order to predict the behavior of the flow turning loss and to assist in the analysis of experimental results. Experiments performed, with and without combustion, showed that the flow turning loss strongly depends upon the propellant burning rate and the location of the flow turning region relative to the standing pressure wave.

Wave energy in white dwarf atmospheres. I - Magnetohydrodynamic energy spectra for homogeneous DB and layered DA stars

NASA Technical Reports Server (NTRS)

Musielak, Zdzislaw E.

1987-01-01

The radiative damping of acoustic and MHD waves that propagate through white dwarf photospheric layers is studied, and other damping processes that may be important for the propagation of the MHD waves are calculated. The amount of energy remaining after the damping processes have occurred in different types of waves is estimated. The results show that lower acoustic fluxes should be expected in layered DA and homogeneous DB white dwarfs than had previously been estimated. Acoustic emission manifests itself in an enhancement of the quadrupole term, but this term may become comparable to or even lower than the dipole term for cool white dwarfs. Energy carried by the acoustic waves is significantly dissipated in deep photospheric layers, mainly because of radiative damping. Acoustically heated corona cannot exist around DA and DB white dwarfs in a range T(eff) = 10,000-30,000 K and for log g = 7 and 8. However, relatively hot and massive white dwarfs could be exceptions.

Chief Characteristics and Advantages of Tailless Airplanes

NASA Technical Reports Server (NTRS)

Dufaure De Lajarte, A

1936-01-01

This study will be concerned with the critical examination of two main questions, mainly, susceptibility of centering and more generally, the conditions of static stability, longitudinal equilibrium, and the question of dynamic stability, or at least the damping of longitudinal vibrations about a position of equilibrium that may result from a small variation in the angle of attack.

First Test of Long-Range Collisional Drag via Plasma Wave Damping

NASA Astrophysics Data System (ADS)

Affolter, Matthew

2017-10-01

In magnetized plasmas, the rate of particle collisions is enhanced over classical predictions when the cyclotron radius rc is less than the Debye length λD. Classical theories describe local velocity scattering collisions with impact parameters ρ

Effect of chemical exchange on radiation damping in aqueous solutions of the osmolyte glycine.

PubMed

Rodríguez, Juan Carlos; Jennings, Patricia A; Melacini, Giuseppe

2002-06-05

Radiation damping is of central relevance in NMR spectroscopy especially with the advent of ultrahigh-field magnets and of supersensitive probes. Furthermore, the recent realization that the combined effect of the distant dipole field and of radiation damping causes the resurrection of undesired crushed water magnetization emphasizes the need for a thorough understanding of all the factors affecting radiation damping. While the effects of pulsed-field gradients and of active feedback have been extensively investigated, the consequences on radiation damping of chemical exchange between water and co-solutes is not as well understood. Here it is demonstrated that the rate of water radiation damping is significantly affected by free glycine (Gly), a representative of an important class of biocompatible osmolytes often used at molar concentrations as protein stabilizers. The pH and temperature dependencies of this effect were investigated and rationalized in terms of radiation damping attenuation caused by incoherent dephasing occurring in the intermediate exchange regime. For instance, at pH 6.0 and at a temperature of 313 K the Gly NH3+/water exchange has the same dramatic effect on radiation damping as a series of repeated weak PFGs, increasing the water inversion-recovery zero-crossing delay from approximately 30 ms to approximately 2.3 s. In addition, under these conditions, the Gly NH3+/water exchange suppresses the resurrection of unwanted crushed water magnetization. When used in combination with PFGs and water flip-back schemes, glycine is therefore expected to tame chaotic dynamics and improve the reproducibility of the NMR experiments affected by it.

Damping of transient energy growth of three-dimensional perturbations in hydromagnetic pipe flow

NASA Astrophysics Data System (ADS)

Åkerstedt, Hans O.

1995-05-01

The stability of infinitesimal three-dimensional perturbations in hydromagnetic pipe flow where the applied magnetic field is in the streamwise direction is considered. The study is limited to the case of small magnetic Reynolds numbers and the main objective of the paper is to study the transient evolution of the kinetic energy. A general effect of the magnetic field is to increase the damping of the eigenvalues of the individual perturbation modes. For the case of infinitely long perturbations, which in the non-magnetic case has been found to have the largest transient growth, the magnetic field perturbations are decoupled from the flow and there is no effect on the stability properties of the flow. For shorter waves, and for moderate values of the interaction parameter ( I = RmA2 ≈ 1-3) the hydromagnetic damping effect on the transient energy growth is, however, substantial, especially for small azimuthal mode numbers n. (Here Rm is the magnetic Reynolds number and A is the Alfvén number.) This parameter range has been found in experiments to give significantly higher transitional Reynolds numbers (Fraim and Heiser, 1968). Since the hydromagnetic damping effect is weak for long waves and large for shorter waves, the implications of the results to ordinary pipe flow is that the energy growth found for short waves may be more crucial as a mechanism for transition than the corresponding growth for longer waves.

Comprehensive evaluation of the linear stability of Alfvén eigenmodes driven by alpha particles in an ITER baseline scenario

NASA Astrophysics Data System (ADS)

Figueiredo, A. C. A.; Rodrigues, P.; Borba, D.; Coelho, R.; Fazendeiro, L.; Ferreira, J.; Loureiro, N. F.; Nabais, F.; Pinches, S. D.; Polevoi, A. R.; Sharapov, S. E.

2016-07-01

The linear stability of Alfvén eigenmodes in the presence of fusion-born alpha particles is thoroughly assessed for two variants of an ITER baseline scenario, which differ significantly in their core and pedestal temperatures. A systematic approach based on CASTOR-K (Borba and Kerner 1999 J. Comput. Phys. 153 101; Nabais et al 2015 Plasma Sci. Technol. 17 89) is used that considers all possible eigenmodes for a given magnetic equilibrium and determines their growth rates due to alpha-particle drive and Landau damping on fuel ions, helium ashes and electrons. It is found that the fastest growing instabilities in the aforementioned ITER scenario are core-localized, low-shear toroidal Alfvén eigenmodes. The largest growth-rates occur in the scenario variant with higher core temperatures, which has the highest alpha-particle density and density gradient, for eigenmodes with toroidal mode numbers n≈ 30 . Although these eigenmodes suffer significant radiative damping, which is also evaluated, their growth rates remain larger than those of the most unstable eigenmodes found in the variant of the ITER baseline scenario with lower core temperatures, which have n≈ 15 and are not affected by radiative damping.

Spreadsheets in Science Teaching.

ERIC Educational Resources Information Center

Elliot, Chris

1988-01-01

Described is the use of a spreadsheet to model dynamic phenomena using numerical iterative methods. Uses the discharge of a capacitor, simple and damped harmonic motion, and the flow of heat along a bar as examples. (Author/CW)

14 CFR 29.181 - Dynamic stability: Category A rotorcraft.

Code of Federal Regulations, 2011 CFR

2011-01-01

... VY to VNE must be positively damped with the primary flight controls free and in a fixed position... TRANSPORTATION AIRCRAFT AIRWORTHINESS STANDARDS: TRANSPORT CATEGORY ROTORCRAFT Flight Flight Characteristics § 29...

14 CFR 29.181 - Dynamic stability: Category A rotorcraft.

Code of Federal Regulations, 2012 CFR

2012-01-01

... VY to VNE must be positively damped with the primary flight controls free and in a fixed position... TRANSPORTATION AIRCRAFT AIRWORTHINESS STANDARDS: TRANSPORT CATEGORY ROTORCRAFT Flight Flight Characteristics § 29...

14 CFR 29.181 - Dynamic stability: Category A rotorcraft.

Code of Federal Regulations, 2013 CFR

2013-01-01

... VY to VNE must be positively damped with the primary flight controls free and in a fixed position... TRANSPORTATION AIRCRAFT AIRWORTHINESS STANDARDS: TRANSPORT CATEGORY ROTORCRAFT Flight Flight Characteristics § 29...

14 CFR 29.181 - Dynamic stability: Category A rotorcraft.

Code of Federal Regulations, 2010 CFR

2010-01-01

... VY to VNE must be positively damped with the primary flight controls free and in a fixed position... TRANSPORTATION AIRCRAFT AIRWORTHINESS STANDARDS: TRANSPORT CATEGORY ROTORCRAFT Flight Flight Characteristics § 29...

14 CFR 29.181 - Dynamic stability: Category A rotorcraft.

Code of Federal Regulations, 2014 CFR

2014-01-01

... VY to VNE must be positively damped with the primary flight controls free and in a fixed position... TRANSPORTATION AIRCRAFT AIRWORTHINESS STANDARDS: TRANSPORT CATEGORY ROTORCRAFT Flight Flight Characteristics § 29...

Proceedings of the International Symposium on Detonation (9th) Held in Portland, Oregon on 28 August - 1 September 1989. Volume 1

DTIC Science & Technology

1989-09-01

damp TATB, and water is sprayed onto the mixture while it is heated to drive off the EXPLOSIVE MANUFACTURE solvent. Charge fabrication is then carried...Foil Gauge S Y Song and J . W . L ee ..... .... ..... ............ ..................... ........ 47 1 ix VOLUME I CONTENTS (Cont.) Page Heat of...deformed. During shear, materials may be ignition thresholds, and to characterize the heated by viscoplastic work. Shear plays a role relative shear

Decoupled Modulation Control

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Shaobu; Huang, Renke; Huang, Zhenyu

The objective of this research work is to develop decoupled modulation control methods for damping inter-area oscillations with low frequencies, so the damping control can be more effective and easier to design with less interference among different oscillation modes in the power system. A signal-decoupling algorithm was developed that can enable separation of multiple oscillation frequency contents and extraction of a “pure” oscillation frequency mode that are fed into Power System Stabilizers (PSSs) as the modulation input signals. As a result, instead of introducing interferences between different oscillation modes from the traditional approaches, the output of the new PSS modulationmore » control signal mainly affects only one oscillation mode of interest. The new decoupled modulation damping control algorithm has been successfully developed and tested on the standard IEEE 4-machine 2-area test system and a minniWECC system. The results are compared against traditional modulation controls, which demonstrates the validity and effectiveness of the newly-developed decoupled modulation damping control algorithm.« less

Validation of High-Resolution CFD Method for Slosh Damping Extraction of Baffled Cryogenic Propellant Tanks

NASA Technical Reports Server (NTRS)

Yang, H. Q.; West, Jeff

2016-01-01

Propellant slosh is a potential source of disturbance critical to the stability of space vehicles. The slosh dynamics are typically represented by a mechanical model of a spring-mass-damper. This mechanical model is then included in the equation of motion of the entire vehicle for Guidance, Navigation and Control analysis. A Volume-Of-Fluid (VOF) based Computational Fluid Dynamics (CFD) program developed at MSFC was applied to extract slosh damping in the baffled tank from the first principle. First the experimental data using water with sub-scale smooth wall tank were used as the baseline validation. It is demonstrated that CFD can indeed accurately predict low damping values from the smooth wall at different fill levels. The damping due to a ring baffles at different depths from the free surface was then simulated, and fairly good agreement with experimental measurement was observed. Comparison with an empirical correlation of Miles equation is also made.

Simulation of a slope adapting ankle prosthesis provided by semi-active damping.

PubMed

LaPrè, Andrew K; Sup, Frank

2011-01-01

Modern passive prosthetic foot/ankles cannot adapt to variations in ground slope. The lack of active adaptation significantly compromises an amputee's balance and stability on uneven terrains. To address this deficit, this paper proposes an ankle prosthesis that uses semi-active damping as a mechanism to provide active slope adaptation. The conceptual ankle prosthesis consists of a modulated damper in series with a spring foot that allows the foot to conform to the angle of the surface in the sagittal plane. In support of this approach, biomechanics data is presented showing unilateral transtibial amputees stepping on a wedge with their daily-use passive prosthesis. Based on this data, a simulation of the ankle prosthesis with semi-active damping is developed. The model shows the kinematic adaptation of the prosthesis to sudden changes in ground slope. The results show the potential of an ankle prosthesis with semi-active damping to actively adapt to the ground slope at each step.

Modified computation of the nozzle damping coefficient in solid rocket motors

NASA Astrophysics Data System (ADS)

Liu, Peijin; Wang, Muxin; Yang, Wenjing; Gupta, Vikrant; Guan, Yu; Li, Larry K. B.

2018-02-01

In solid rocket motors, the bulk advection of acoustic energy out of the nozzle constitutes a significant source of damping and can thus influence the thermoacoustic stability of the system. In this paper, we propose and test a modified version of a historically accepted method of calculating the nozzle damping coefficient. Building on previous work, we separate the nozzle from the combustor, but compute the acoustic admittance at the nozzle entry using the linearized Euler equations (LEEs) rather than with short nozzle theory. We compute the combustor's acoustic modes also with the LEEs, taking the nozzle admittance as the boundary condition at the combustor exit while accounting for the mean flow field in the combustor using an analytical solution to Taylor-Culick flow. We then compute the nozzle damping coefficient via a balance of the unsteady energy flux through the nozzle. Compared with established methods, the proposed method offers competitive accuracy at reduced computational costs, helping to improve predictions of thermoacoustic instability in solid rocket motors.

First Demonstration of Electrostatic Damping of Parametric Instability at Advanced LIGO

NASA Astrophysics Data System (ADS)

Blair, Carl; Gras, Slawek; Abbott, Richard; Aston, Stuart; Betzwieser, Joseph; Blair, David; DeRosa, Ryan; Evans, Matthew; Frolov, Valera; Fritschel, Peter; Grote, Hartmut; Hardwick, Terra; Liu, Jian; Lormand, Marc; Miller, John; Mullavey, Adam; O'Reilly, Brian; Zhao, Chunnong; Abbott, B. P.; Abbott, T. D.; Adams, C.; Adhikari, R. X.; Anderson, S. B.; Ananyeva, A.; Appert, S.; Arai, K.; Ballmer, S. W.; Barker, D.; Barr, B.; Barsotti, L.; Bartlett, J.; Bartos, I.; Batch, J. C.; Bell, A. S.; Billingsley, G.; Birch, J.; Biscans, S.; Biwer, C.; Bork, R.; Brooks, A. F.; Ciani, G.; Clara, F.; Countryman, S. T.; Cowart, M. J.; Coyne, D. C.; Cumming, A.; Cunningham, L.; Danzmann, K.; Da Silva Costa, C. F.; Daw, E. J.; DeBra, D.; DeSalvo, R.; Dooley, K. L.; Doravari, S.; Driggers, J. C.; Dwyer, S. E.; Effler, A.; Etzel, T.; Evans, T. M.; Factourovich, M.; Fair, H.; Fernández Galiana, A.; Fisher, R. P.; Fulda, P.; Fyffe, M.; Giaime, J. A.; Giardina, K. D.; Goetz, E.; Goetz, R.; Gray, C.; Gushwa, K. E.; Gustafson, E. K.; Gustafson, R.; Hall, E. D.; Hammond, G.; Hanks, J.; Hanson, J.; Harry, G. M.; Heintze, M. C.; Heptonstall, A. W.; Hough, J.; Izumi, K.; Jones, R.; Kandhasamy, S.; Karki, S.; Kasprzack, M.; Kaufer, S.; Kawabe, K.; Kijbunchoo, N.; King, E. J.; King, P. J.; Kissel, J. S.; Korth, W. Z.; Kuehn, G.; Landry, M.; Lantz, B.; Lockerbie, N. A.; Lundgren, A. P.; MacInnis, M.; Macleod, D. M.; Márka, S.; Márka, Z.; Markosyan, A. S.; Maros, E.; Martin, I. W.; Martynov, D. V.; Mason, K.; Massinger, T. J.; Matichard, F.; Mavalvala, N.; McCarthy, R.; McClelland, D. E.; McCormick, S.; McIntyre, G.; McIver, J.; Mendell, G.; Merilh, E. L.; Meyers, P. M.; Mittleman, R.; Moreno, G.; Mueller, G.; Munch, J.; Nuttall, L. K.; Oberling, J.; Oppermann, P.; Oram, Richard J.; Ottaway, D. J.; Overmier, H.; Palamos, J. R.; Paris, H. R.; Parker, W.; Pele, A.; Penn, S.; Phelps, M.; Pierro, V.; Pinto, I.; Principe, M.; Prokhorov, L. G.; Puncken, O.; Quetschke, V.; Quintero, E. A.; Raab, F. J.; Radkins, H.; Raffai, P.; Reid, S.; Reitze, D. H.; Robertson, N. A.; Rollins, J. G.; Roma, V. J.; Romie, J. H.; Rowan, S.; Ryan, K.; Sadecki, T.; Sanchez, E. J.; Sandberg, V.; Savage, R. L.; Schofield, R. M. S.; Sellers, D.; Shaddock, D. A.; Shaffer, T. J.; Shapiro, B.; Shawhan, P.; Shoemaker, D. H.; Sigg, D.; Slagmolen, B. J. J.; Smith, B.; Smith, J. R.; Sorazu, B.; Staley, A.; Strain, K. A.; Tanner, D. B.; Taylor, R.; Thomas, M.; Thomas, P.; Thorne, K. A.; Thrane, E.; Torrie, C. I.; Traylor, G.; Vajente, G.; Valdes, G.; van Veggel, A. A.; Vecchio, A.; Veitch, P. J.; Venkateswara, K.; Vo, T.; Vorvick, C.; Walker, M.; Ward, R. L.; Warner, J.; Weaver, B.; Weiss, R.; Weßels, P.; Willke, B.; Wipf, C. C.; Worden, J.; Wu, G.; Yamamoto, H.; Yancey, C. C.; Yu, Hang; Yu, Haocun; Zhang, L.; Zucker, M. E.; Zweizig, J.; LSC Instrument Authors

2017-04-01

Interferometric gravitational wave detectors operate with high optical power in their arms in order to achieve high shot-noise limited strain sensitivity. A significant limitation to increasing the optical power is the phenomenon of three-mode parametric instabilities, in which the laser field in the arm cavities is scattered into higher-order optical modes by acoustic modes of the cavity mirrors. The optical modes can further drive the acoustic modes via radiation pressure, potentially producing an exponential buildup. One proposed technique to stabilize parametric instability is active damping of acoustic modes. We report here the first demonstration of damping a parametrically unstable mode using active feedback forces on the cavity mirror. A 15 538 Hz mode that grew exponentially with a time constant of 182 sec was damped using electrostatic actuation, with a resulting decay time constant of 23 sec. An average control force of 0.03 nN was required to maintain the acoustic mode at its minimum amplitude.

Migration of planets into and out of mean motion resonances in protoplanetary discs: analytical theory of second-order resonances

NASA Astrophysics Data System (ADS)

Xu, Wenrui; Lai, Dong

2017-07-01

Recent observations of Kepler multiplanet systems have revealed a number of systems with planets very close to second-order mean motion resonances (MMRs, with period ratio 1 : 3, 3 : 5, etc.). We present an analytic study of resonance capture and its stability for planets migrating in gaseous discs. Resonance capture requires slow convergent migration of the planets, with sufficiently large eccentricity damping time-scale Te and small pre-resonance eccentricities. We quantify these requirements and find that they can be satisfied for super-Earths under protoplanetary disc conditions. For planets captured into resonance, an equilibrium state can be reached, in which eccentricity excitation due to resonant planet-planet interaction balances eccentricity damping due to planet-disc interaction. This 'captured' equilibrium can be overstable, leading to partial or permanent escape of the planets from the resonance. In general, the stability of the captured state depends on the inner to outer planet mass ratio q = m1/m2 and the ratio of the eccentricity damping times. The overstability growth time is of the order of Te, but can be much larger for systems close to the stability threshold. For low-mass planets undergoing type I (non-gap opening) migration, convergent migration requires q ≲ 1, while the stability of the capture requires q ≳ 1. These results suggest that planet pairs stably captured into second-order MMRs have comparable masses. This is in contrast to first-order MMRs, where a larger parameter space exists for stable resonance capture. We confirm and extend our analytical results with N-body simulations, and show that for overstable capture, the escape time from the MMR can be comparable to the time the planets spend migrating between resonances.

HTS flywheel energy storage system with rotor shaft stabilized by feed-back control of armature currents of motor-generator

NASA Astrophysics Data System (ADS)

Tsukamoto, O.; Utsunomiya, A.

2007-10-01

We propose an HTS bulk bearing flywheel energy system (FWES) with rotor shaft stabilization system using feed-back control of the armature currents of the motor-generator. In the proposed system the rotor shift has a pivot bearing at one end of the shaft and an HTS bulk bearing (SMB) at the other end. The fluctuation of the rotor shaft with SMB is damped by feed-back control of the armature currents of the motor-generator sensing the position of the rotor shaft. The method has merits that the fluctuations are damped without active control magnet bearings and extra devices which may deteriorate the energy storage efficiency and need additional costs. The principle of the method was demonstrated by an experiment using a model permanent magnet motor.

Thermoelastic damping in microrings with circular cross-section

NASA Astrophysics Data System (ADS)

Li, Pu; Fang, Yuming; Zhang, Jianrun

2016-01-01

Predicting thermoelastic damping (TED) is crucial in the design of high Q micro-resonators. Microrings are often critical components in many micro-resonators. Some analytical models for TED in microrings have already been developed in the past. However, the previous works are limited to the microrings with rectangular cross-section. The temperature field in the rectangular cross-section is one-dimensional. This paper deals with TED in the microrings with circular cross-section. The temperature field in the circular cross-section is two-dimensional. This paper first presents a 2-D analytical model for TED in the microrings with circular cross-section. Only the two-dimensional heat conduction in the circular cross-section is considered. The heat conduction along the circumferential direction of the microring is neglected in the 2-D model. Then the 2-D model has been extended to cover the circumferential heat conduction, and a 3-D analytical model for TED has been developed. The analytical results from the present 2-D and 3-D models show good agreement with the numerical results of FEM model. The limitations of the present 2-D analytical model are assessed.

Device physics of Cu(In,Ga)Se2 solar cells for long-term operation

NASA Astrophysics Data System (ADS)

Nishinaga, J.; Shibata, H.

2017-02-01

The degradation mechanism of Cu(In,Ga)Se2 (CIGS) solar cells on exposure to air has been investigated. Exposure to air at room temperature slightly reduces the conversion efficiency of CIGS solar cells, and the conversion efficiency decreases significantly under damp heat testing at 85 °C and 85% relative humidity due to low shunt resistance. On the other hand, shunt resistance increases after dry nitrogen heating. Therefore, oxygen and humidity should degenerate the solar cell performance. The low shunt resistance and conversion efficiency are completely recovered after removing the side edges of the CIGS solar cells by mechanical scribing. These results suggest that low-resistive layers are formed on the sidewalls of the solar cells during damp heat testing. The low-resistive layers on the sidewalls are identified to be molybdenum oxides and sodium molybdate by Auger electron spectroscopy. After etching the oxides on the sidewalls by alkaline solution, the saturation current density and ideality factor are confirmed to be improved. These results suggest that metal oxides on the sidewalls of CIGS solar cells may act as recombination centers.

Damping of acoustic waves in a 1 kHz repetition rate XeCl laser

NASA Astrophysics Data System (ADS)

Sentis, M. L.; Canarelli, P.; Delaporte, Ph.; Forestier, B. M.; Fontaine, B. L.

To increase the pulse repetition frequency, the average power, and the beam quality of excimer laser systems, the problem of damping of the strong acoustic waves induced by the active medium excitation must be solved. In order to achieve this goal, different electrodes and acoustic damping configuration have been studied. Excitation of the active medium at high repetition rate (up to 1000 Hz) in a subsonic loop was achieved by means of a classical discharge, through transfer capacitors. The discharge is preionized by X-rays generated by a wire ion plasma gun. The effects of different kinds of electrodes (solid, screen, nickel felt) and transversal acoustic dampers on the stability of the discharge and on the pulse to pulse output energy are discussed.

Flutter Sensitivity to Boundary Layer Thickness, Structural Damping, and Static Pressure Differential for a Shuttle Tile Overlay Repair Concept

NASA Technical Reports Server (NTRS)

Scott, Robert C.; Bartels, Robert E.

2009-01-01

This paper examines the aeroelastic stability of an on-orbit installable Space Shuttle patch panel. CFD flutter solutions were obtained for thick and thin boundary layers at a free stream Mach number of 2.0 and several Mach numbers near sonic speed. The effect of structural damping on these flutter solutions was also examined, and the effect of structural nonlinearities associated with in-plane forces in the panel was considered on the worst case linear flutter solution. The results of the study indicated that adequate flutter margins exist for the panel at the Mach numbers examined. The addition of structural damping improved flutter margins as did the inclusion of nonlinear effects associated with a static pressure difference across the panel.

Dynamics and stability of wind turbine generators

NASA Technical Reports Server (NTRS)

Hinrichsen, E. N.; Nolan, P. J.

1981-01-01

Synchronous and induction generators are considered. A comparison is made between wind turbines, steam, and hydro units. The unusual phenomena associated with wind turbines are emphasized. The general control requirements are discussed, as well as various schemes for torsional damping such as speed sensitive stabilizer and blade pitch control. Integration between adjacent wind turbines in a wind farm is also considered.

Development of Magnetorheological Fluid Elastomeric Dampers for Helicopter Stability Augmentation

DTIC Science & Technology

2005-01-01

ABSTRACT Title of Dissertation: DEVELOPMENT OF MAGNETORHEOLOGICAL FLUID ELASTOMERIC DAMPERS FOR HELICOPTER STABILITY AUGMENTATION Wei Hu, Doctor of...motion increases. Magnetorheological (MR) fluids based dampers have controllable damping with little or no stiffness. In order to combine the...advantages of both elastomeric materials and MR flu- ids, semi-active magnetorheological fluid elastomeric (MRFE) lag dampers are developed in this thesis. In

Strategies for the stabilization of longitudinal forward flapping flight revealed using a dynamically-scaled robotic fly.

PubMed

Elzinga, Michael J; van Breugel, Floris; Dickinson, Michael H

2014-06-01

The ability to regulate forward speed is an essential requirement for flying animals. Here, we use a dynamically-scaled robot to study how flapping insects adjust their wing kinematics to regulate and stabilize forward flight. The results suggest that the steady-state lift and thrust requirements at different speeds may be accomplished with quite subtle changes in hovering kinematics, and that these adjustments act primarily by altering the pitch moment. This finding is consistent with prior hypotheses regarding the relationship between body pitch and flight speed in fruit flies. Adjusting the mean stroke position of the wings is a likely mechanism for trimming the pitch moment at all speeds, whereas changes in the mean angle of attack may be required at higher speeds. To ensure stability, the flapping system requires additional pitch damping that increases in magnitude with flight speed. A compensatory reflex driven by fast feedback of pitch rate from the halteres could provide such damping, and would automatically exhibit gain scheduling with flight speed if pitch torque was regulated via changes in stroke deviation. Such a control scheme would provide an elegant solution for stabilization across a wide range of forward flight speeds.

Control of large space structures

NASA Technical Reports Server (NTRS)

Gran, R.; Rossi, M.; Moyer, H. G.; Austin, F.

1979-01-01

The control of large space structures was studied to determine what, if any, limitations are imposed on the size of spacecraft which may be controlled using current control system design technology. Using a typical structure in the 35 to 70 meter size category, a control system design that used actuators that are currently available was designed. The amount of control power required to maintain the vehicle in a stabilized gravity gradient pointing orientation that also damped various structural motions was determined. The moment of inertia and mass properties of this structure were varied to verify that stability and performance were maintained. The study concludes that the structure's size is required to change by at least a factor of two before any stability problems arise. The stability margin that is lost is due to the scaling of the gravity gradient torques (the rigid body control) and as such can easily be corrected by changing the control gains associated with the rigid body control. A secondary conclusion from the study is that the control design that accommodates the structural motions (to damp them) is a little more sensitive than the design that works on attitude control of the rigid body only.

Guiding principle for crystalline Si photovoltaic modules with high tolerance to acetic acid

NASA Astrophysics Data System (ADS)

Masuda, Atsushi; Hara, Yukiko

2018-04-01

A guiding principle for highly reliable crystalline Si photovoltaic modules, especially those with high tolerance to acetic acid generated by hydrolysis reaction between water vapor and an ethylene-vinyl acetate (EVA) encapsulant, is proposed. Degradation behavior evaluated by the damp heat test strongly depends on Ag finger electrodes and also EVA encapsulants. The acetic acid concentration in EVA on the glass side directly determines the degradation behavior. The most important factor for high tolerance is the type of Ag finger electrode materials when using an EVA encapsulant. Photovoltaic modules using newly developed crystalline Si cells with improved Ag finger electrode materials keep their maximum power of 80% of the initial value even after the damp heat test at 85 °C and 85% relative humidity for 10000 h. The pattern of dark regions in electroluminescence images is also discussed on the basis of the dynamics of acetic acid in the modules.

Potential-Induced Degradation-Delamination Mode in Crystalline Silicon Modules: Preprint

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hacke, Peter L; Kempe, Michael D; Wohlgemuth, John

A test sequence producing potential-induced degradation-delamination (PID-d) in crystalline silicon modules has been tested and found comparable under visual inspection to cell/encapsulant delamination seen in some fielded modules. Four commercial modules were put through this sequence, 85 degrees C, 85%, 1000 h damp heat, followed by an intensive PID stress sequence of 72 degrees C, 95% RH, and -1000 V, with the module face grounded using a metal foil. The 60 cell c-Si modules exhibiting the highest current transfer (4.4 center dot 10-4 A) exhibited PID-d at the first inspection after 156 h of PID stress. Effects promoting PID-d aremore » reduced adhesion caused by damp heat, sodium migration further reducing adhesion to the cells, and gaseous products of electrochemical reactions driven by the applied system voltage. A new work item proposal for an IEC test standard to evaluate for PID-d is anticipated.« less

Microcantilever-based gas sensor employing two simultaneous physical sensing modes

DOEpatents

Loui, Albert; Sirbuly, Donald J; Elhadj, Selim; McCall, Scott K; Hart, Bradley R; Ratto, Timothy V

2014-06-24

According to one embodiment, a system for detecting and identifying gases includes a piezoresistive microcantilever transducer, wherein dissipation of heat from the piezoresistive microcantilever into one or more gases is measured by changes in an electrical resistance of the piezoresistor, a vibrating microcantilever transducer, wherein shifts are measured in resonant frequency of the vibrating microcantilever due to viscous damping thereof by the one or more gases, and a subsystem for correlating the measured resistance changes and the resonant frequency shifts to the one or more gases. In another embodiment, a method for detecting and identifying one or more gases includes determining dissipation of heat from a microcantilever into one or more gases, and determining shifts in resonant frequency of the microcantilever due to viscous damping thereof by the one or more gases. Other systems, methods, and computer program products are also described according to more embodiments.

Supersonic dynamic stability characteristics of a space shuttle orbiter. [wind tunnel tests of scale models

NASA Technical Reports Server (NTRS)

Freeman, D. C., Jr.; Boyden, R. P.; Davenport, E. E.

1976-01-01

Supersonic forced-oscillation tests of a 0.0165-scale model of a modified 089B Rockwell International shuttle orbiter were conducted in a wind tunnel for several configurations over a Mach range from 1.6 to 4.63. The tests covered angles of attack up to 30 deg. The period and damping of the basic unaugmented vehicle were calculated along the entry trajectory using the measured damping results. Some parameter analysis was made with the measured dynamic derivatives. Photographs of the test configurations and test equipment are shown.

Prediction and experimental observation of damage dependent damping in laminated composite beams

NASA Technical Reports Server (NTRS)

Allen, D. H.; Harris, C. E.; Highsmith, A. L.

1987-01-01

The equations of motion are developed for laminated composite beams with load-induced matrix cracking. The damage is accounted for by utilizing internal state variables. The net result of these variables on the field equations is the introduction of both enhanced damping, and degraded stiffness. Both quantities are history dependent and spatially variable, thus resulting in nonlinear equations of motion. It is explained briefly how these equations may be quasi-linearized for laminated polymeric composites under certain types of structural loading. The coupled heat conduction equation is developed, and it is shown that an enhanced Zener damping effect is produced by the introduction of microstructural damage. The resulting equations are utilized to demonstrate how damage dependent material properties may be obtained from dynamic experiments. Finaly, experimental results are compared to model predictions for several composite layups.

Transient enhancement of magnetization damping in CoFeB film via pulsed laser excitation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu, Bo; Ruan, Xuezhong, E-mail: xzruan@nju.edu.cn, E-mail: ybxu@nju.edu.cn; Wu, Zhenyao

2016-07-25

Laser-induced spin dynamics of in-plane magnetized CoFeB films has been studied by using time-resolved magneto-optical Kerr effect measurements. While the effective demagnetization field shows little dependence on the pump laser fluence, the intrinsic damping constant has been found to be increased from 0.008 to 0.076 with the increase in the pump fluence from 2 mJ/cm{sup 2} to 20 mJ/cm{sup 2}. This sharp enhancement has been shown to be transient and ascribed to the heating effect induced by the pump laser excitation, as the damping constant is almost unchanged when the pump-probe measurements are performed at a fixed pump fluence ofmore » 5 mJ/cm{sup 2} after irradiation by high power pump pulses.« less

RESONANT ABSORPTION OF AXISYMMETRIC MODES IN TWISTED MAGNETIC FLUX TUBES

DOE Office of Scientific and Technical Information (OSTI.GOV)

Giagkiozis, I.; Verth, G.; Goossens, M.

2016-06-01

It has been shown recently that magnetic twist and axisymmetric MHD modes are ubiquitous in the solar atmosphere, and therefore the study of resonant absorption for these modes has become a pressing issue because it can have important consequences for heating magnetic flux tubes in the solar atmosphere and the observed damping. In this investigation, for the first time, we calculate the damping rate for axisymmetric MHD waves in weakly twisted magnetic flux tubes. Our aim is to investigate the impact of resonant damping of these modes for solar atmospheric conditions. This analytical study is based on an idealized configurationmore » of a straight magnetic flux tube with a weak magnetic twist inside as well as outside the tube. By implementing the conservation laws derived by Sakurai et al. and the analytic solutions for weakly twisted flux tubes obtained recently by Giagkiozis et al. we derive a dispersion relation for resonantly damped axisymmetric modes in the spectrum of the Alfvén continuum. We also obtain an insightful analytical expression for the damping rate in the long wavelength limit. Furthermore, it is shown that both the longitudinal magnetic field and the density, which are allowed to vary continuously in the inhomogeneous layer, have a significant impact on the damping time. Given the conditions in the solar atmosphere, resonantly damped axisymmetric modes are highly likely to be ubiquitous and play an important role in energy dissipation. We also suggest that, given the character of these waves, it is likely that they have already been observed in the guise of Alfvén waves.« less

Asymmetric Response of the Equatorial Pacific SST to Climate Warming and Cooling

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu, Fukai; Luo, Yiyong; Lu, Jian

The response of the equatorial Pacific Ocean to heat fluxes of equal amplitude but opposite sign is investigated using the Community Earth System Model (CESM). Results show a strong asymmetry in SST changes. In the eastern equatorial Pacific (EEP), the warming responding to the positive forcing exceeds the cooling to the negative forcing; while in the western equatorial Pacific (WEP), it is the other way around and the cooling surpasses the warming. This leads to a zonal dipole asymmetric structure, with positive values in the east and negative values in the west. A surface heat budget analysis suggests that themore » SST asymmetry is mainly resulted from the oceanic horizontal advection and vertical entrainment, with both of their linear and nonlinear components playing a role. For the linear component, its change appears to be more significant over the EEP (WEP) in the positive (negative) forcing scenario, favoring the seesaw pattern of the SST asymmetry. For the nonlinear component, its change acts to warm (cool) the EEP (WEP) in both scenarios, also favorable for the development of the SST asymmetry. Additional experiments with a slab ocean confirm the dominant role of ocean dynamical processes for this SST asymmetry. The net surface heat flux, in contrast, works to reduce the SST asymmetry through its shortwave radiation and latent heat flux components, with the former being related to the nonlinear relationship between SST and convection, and the latter being attributable to Newtonian damping and air-sea stability effects. The suppressing effect of shortwave radiation on SST asymmetry is further verified by partially coupled overriding experiments.« less

Asymmetric response of the equatorial Pacific SST to climate warming and cooling

NASA Astrophysics Data System (ADS)

Luo, Y.; Liu, F.; Lu, J.

2017-12-01

The response of the equatorial Pacific Ocean to heat fluxes of equal amplitude but opposite sign is investigated using the Community Earth System Model (CESM). Results show a strong asymmetry in SST changes. In the eastern equatorial Pacific (EEP), the warming responding to the positive forcing exceeds the cooling to the negative forcing; while in the western equatorial Pacific (WEP), it is the other way around and the cooling surpasses the warming. This leads to a zonal dipole asymmetric structure, with positive values in the east and negative values in the west. A surface heat budget analysis suggests that the SST asymmetry is mainly resulted from the oceanic horizontal advection and vertical entrainment, with both of their linear and nonlinear components playing a role. For the linear component, its change appears to be more significant over the EEP (WEP) in the positive (negative) forcing scenario, favoring the seesaw pattern of the SST asymmetry. For the nonlinear component, its change acts to warm (cool) the EEP (WEP) in both scenarios, also favorable for the development of the SST asymmetry. Additional experiments with a slab ocean confirm the dominant role of ocean dynamical processes for this SST asymmetry. The net surface heat flux, in contrast, works to reduce the SST asymmetry through its shortwave radiation and latent heat flux components, with the former being related to the nonlinear relationship between SST and convection, and the latter being attributable to Newtonian damping and air-sea stability effects. The suppressing effect of shortwave radiation on SST asymmetry is further verified by partially coupled overriding experiments.

RF absorption and ion heating in helicon sources.

PubMed

Kline, J L; Scime, E E; Boivin, R F; Keesee, A M; Sun, X; Mikhailenko, V S

2002-05-13

Experimental data are presented that are consistent with the hypothesis that anomalous rf absorption in helicon sources is due to electron scattering arising from parametrically driven ion-acoustic waves downstream from the antenna. Also presented are ion temperature measurements demonstrating anisotropic heating (T( perpendicular)>T(parallel)) at the edge of the discharge. The most likely explanation is ion-Landau damping of electrostatic slow waves at a local lower-hybrid-frequency resonance.

55 Nitinol Alloys

DTIC Science & Technology

1967-01-01

Urn 1~I.tion of-heat (courtesy of Goodyear C.2 Aerospace Corporation) Name derived from N i-Ti.NOL. Prefix numerical value (e.g., 55. Nitinol ... Nitinol plastically deformed below its critical, temperature (A5) will recover its original’ shape-when heated above its critical temperature, THIS...of Nitinol and other high damping materials is given in Reference 11. f WORKING CHARACTERISTICS: May be hot worked directly from the arc-melted ingot

Study of Plastic Deformation in Binary Aluminum Alloys by Internal-Friction Methods

NASA Technical Reports Server (NTRS)

Olson, E. C.; Maringer, R. E.; Marsh, L. L.; Manning, G. K.

1959-01-01

The damping capacity of several aluminum-copper alloys has been investigated during tensile elongation. This damping is shown to depend on strain rate, strain, temperature, alloy content, and heat treatment. A tentative hypothesis, based on the acceleration of solute atom diffusion by deformation-produced vacancies, is proposed to account for the observed behavior. Internal-friction maxima are observed in deformed aluminum and aluminum-copper alloys at -70 deg and -50 deg C. The peaks appear to be relatively insensitive to frequency and alloy content, but they disappear after annealing at temperatures nearing the recrystallization temperature.

Discovery and Utilization of Nanoscale and Mesoscale Enabling Materials and Processes for Optoelectronics and Electronic Interconnects

DTIC Science & Technology

2003-12-01

Heating and Cooling Device 42 5.2.3 Multiple Tip STM ~ 43 5.2.3.1 Novel Nanomanipulator MM3 43 5.2.3.2 Four Tip STM Assembly 44 5.2.3.3 Vibration ...Analysis of Eddy Current Damping System of Multiple TIP STM " 44 5.2.3.4 Active Vibration Damping System 46 5.3 First Results 47 5.3.1 UHV-SEM...side: Actual device side and top view. 44 46. Setup for the vibration analysis experiment. 45 47. Relaxation of the STM unit, (a) without the eddy

Rotor dynamic behaviour of a high-speed oil-free motor compressor with a rigid coupling supported on four radial magnetic bearings

NASA Technical Reports Server (NTRS)

Schmied, J.; Pradetto, J. C.

1994-01-01

The combination of a high-speed motor, dry gas seals, and magnetic bearings realized in this unit facilitates the elimination of oil. The motor is coupled with a quill shaft to the compressor. This yields higher natural frequencies of the rotor than with the use of a diaphragm coupling and helps to maintain a sufficient margin of the maximum speed to the frequency of the second compressor bending mode. However, the controller of each bearing then has to take the combined modes of both machines into account. The requirements for the controller to ensure stability and sufficient damping of all critical speeds are designed and compared with the implemented controller. The calculated closed loop behavior was confirmed experimentally, except the stability of some higher modes due to slight frequency deviations of the rotor model to the actual rotor. The influence of a mechanical damper as a device to provide additional damping to high models is demonstrated theoretically. After all, it was not necessary to install the damper, since all modes cold be stabilized by the controller.

Aeroelastic Stability of A Soft-Inplane Gimballed Tiltrotor Model In Hover

NASA Technical Reports Server (NTRS)

Nixon, Mark W.; Langston, Chester W.; Singleton, Jeffrey D.; Piatak, David J.; Kvaternik, Raymond G.; Corso, Lawrence M.; Brown, Ross

2001-01-01

Soft-inplane rotor systems can significantly reduce the inplane rotor loads generated during the maneuvers of large tiltrotors, thereby reducing the strength requirements and the associated structural weight of the hub. Soft-inplane rotor systems. however, are subject to instabilities associated with ground resonance, and for tiltrotors this instability has increased complexity as compared to a conventional helicopter. Researchers at Langley Research Center and Bell Helicopter-Textron, Inc. have completed ail initial study of a soft-inplane gimballed tiltrotor model subject to ground resonance conditions in hover. Parametric variations of the rotor collective pitch and blade root damping, and their associated effects oil the model stability were examined. Also considered in the study was the effectiveness of ail active swash-plate and a generalized predictive control (GPC) algorithm for stability augmentation of the ground resonance conditions. Results of this study show that the ground resonance behavior of a gimballed soft-inplane tiltrotor can be significantly different from that of a classical soft-inplane helicopter rotor. The GPC-based active swash-plate was successfully implemented, and served to significantly augment damping of the critical modes to an acceptable value.

Self-stabilized Fractality of Sea-coasts Through Damped Erosion

NASA Astrophysics Data System (ADS)

Sapoval, B.; Baldassari, A.; Gabrielli, A.

2004-05-01

Coastline morphology is of current interest in geophysical research and coastline erosion has important economic consequences. At the same time, although the geometry of seacoasts is often used as an introductory archetype of fractal morphology in nature there has been no explanation about which physical mechanism could justify that empirical observation. The present work propose a minimal, but robust, model of evolution of rocky coasts towards fractality. The model describes how a stationary fractal geometry arises spontaneously from the mutual self-stabilization of a rocky coast morphology and sea eroding power. If, on one hand, erosion generally increases the geometrical irregularity of the coast, on the other hand this increase creates a stronger damping of the sea and a consequent diminution of its eroding power. The increased damping argument relies on the studies of fractal acoustical cavities, which have shown that viscous damping is augmented on a longer, irregular, surface. A minimal two-dimensional model of erosion is introduced which leads to the through a complex dynamics of the earth-sea interface, to the appearance of a stationary fractal seacoast with dimension close to 4/3. Fractal geometry plays here the role of a morphological attractor directly related to percolation geometry. The model reproduces at least qualitatively some of the features of real coasts using only simple ingredients: the randomness of the lithology and the decrease of the erosion power of the sea. B. Sapoval, Fractals (Aditech, Paris, 1989). B. Sapoval, O. Haeberlé, and S.Russ, J. Acoust. Soc. Am., 2014 (1997). B. Hébert B., B. Sapoval, and S.Russ, J. Acoust. Soc. Am., 1567 (1999).

Using Field-Particle Correlations to Diagnose the Collisionless Damping of Plasma Turbulence

NASA Astrophysics Data System (ADS)

Howes, Gregory; Klein, Kristropher

2016-10-01

Plasma turbulence occurs ubiquitously throughout the heliosphere, yet our understanding of how turbulence governs energy transport and plasma heating remains incomplete, constituting a grand challenge problem in heliophysics. In weakly collisional heliospheric plasmas, such as the solar corona and solar wind, damping of the turbulent fluctuations occurs due to collisionless interactions between the electromagnetic fields and the individual plasma particles. A particular challenge in diagnosing this energy transfer is that spacecraft measurements are typically limited to a single point in space. Here we present an innovative field-particle correlation technique that can be used with single-point measurements to estimate the energization of the plasma particles due to the damping of the electromagnetic fields, providing vital new information about this how energy transfer is distributed as a function of particle velocity. This technique has the promise to transform our ability to diagnose the kinetic plasma physical mechanisms responsible for not only the damping of turbulence, but also the energy conversion in both collisionless magnetic reconnection and particle acceleration. The work has been supported by NSF CAREER Award AGS-1054061, NSF AGS-1331355, and DOE DE-SC0014599.

DAMPs, ageing, and cancer: The 'DAMP Hypothesis'.

PubMed

Huang, Jin; Xie, Yangchun; Sun, Xiaofang; Zeh, Herbert J; Kang, Rui; Lotze, Michael T; Tang, Daolin

2015-11-01

Ageing is a complex and multifactorial process characterized by the accumulation of many forms of damage at the molecular, cellular, and tissue level with advancing age. Ageing increases the risk of the onset of chronic inflammation-associated diseases such as cancer, diabetes, stroke, and neurodegenerative disease. In particular, ageing and cancer share some common origins and hallmarks such as genomic instability, epigenetic alteration, aberrant telomeres, inflammation and immune injury, reprogrammed metabolism, and degradation system impairment (including within the ubiquitin-proteasome system and the autophagic machinery). Recent advances indicate that damage-associated molecular pattern molecules (DAMPs) such as high mobility group box 1, histones, S100, and heat shock proteins play location-dependent roles inside and outside the cell. These provide interaction platforms at molecular levels linked to common hallmarks of ageing and cancer. They can act as inducers, sensors, and mediators of stress through individual plasma membrane receptors, intracellular recognition receptors (e.g., advanced glycosylation end product-specific receptors, AIM2-like receptors, RIG-I-like receptors, and NOD1-like receptors, and toll-like receptors), or following endocytic uptake. Thus, the DAMP Hypothesis is novel and complements other theories that explain the features of ageing. DAMPs represent ideal biomarkers of ageing and provide an attractive target for interventions in ageing and age-associated diseases. Copyright © 2014 Elsevier B.V. All rights reserved.

Landau Damping of Beam Instabilities by Electron Lenses

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shiltsev, V.; Alexahin, Yuri; Burov, A.

2017-06-26

Modern and future particle accelerators employ increasingly higher intensity and brighter beams of charged particles and become operationally limited by coherent beam instabilities. Usual methods to control the instabilities, such as octupole magnets, beam feedback dampers and use of chromatic effects, become less effective and insufficient. We show that, in contrast, Lorentz forces of a low-energy, a magnetically stabilized electron beam, or "electron lens", easily introduces transverse nonlinear focusing sufficient for Landau damping of transverse beam instabilities in accelerators. It is also important that, unlike other nonlinear elements, the electron lens provides the frequency spread mainly at the beam core,more » thus allowing much higher frequency spread without lifetime degradation. For the parameters of the Future Circular Collider, a single conventional electron lens a few meters long would provide stabilization superior to tens of thousands of superconducting octupole magnets.« less

Landau Damping of Beam Instabilities by Electron Lenses

DOE PAGES

Shiltsev, V.; Alexahin, Yuri; Burov, A.; ...

2017-09-27

Modern and future particle accelerators employ increasingly higher intensity and brighter beams of charged particles and become operationally limited by coherent beam instabilities. Usual methods to control the instabilities, such as octupole magnets, beam feedback dampers, and use of chromatic effects, become less effective and insufficient. Here, we show that, in contrast, Lorentz forces of a low-energy, magnetically stabilized electron beam, or “electron lens,” easily introduce transverse nonlinear focusing sufficient for Landau damping of transverse beam instabilities in accelerators. It is also important to note that, unlike other nonlinear elements, the electron lens provides the frequency spread mainly at themore » beam core, thus allowing much higher frequency spread without lifetime degradation. For the parameters of the Future Circular Collider, a single conventional electron lens a few meters long would provide stabilization superior to tens of thousands of superconducting octupole magnets.« less

Fokker-Planck analysis of transverse collective instabilities in electron storage rings

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lindberg, Ryan R.

We analyze single bunch transverse instabilities due to wakefields using a Fokker-Planck model. We first expand on the work of T. Suzuki, Part. Accel. 12, 237 (1982) to derive the theoretical model including chromaticity, both dipolar and quadrupolar transverse wakefields, and the effects of damping and diffusion due to the synchrotron radiation. We reduce the problem to a linear matrix equation, whose eigenvalues and eigenvectors determine the collective stability of the beam. We then show that various predictions of the theory agree quite well with results from particle tracking simulations, including the threshold current for transverse instability and the profilemore » of the unstable mode. In particular, we find that predicting collective stability for high energy electron beams at moderate to large values of chromaticity requires the full Fokker-Planck analysis to properly account for the effects of damping and diffusion due to synchrotron radiation.« less

Flight test results for a separate surface stability augmented Beech model 99

NASA Technical Reports Server (NTRS)

Jenks, G. E.; Henry, H. F.; Roskam, J.

1977-01-01

A flight evaluation of a Beech model 99 equipped with an attitude command control system incorporating separate surface stability augmentation (SSSA) was conducted to determine whether an attitude command control system could be implemented using separate surface controls, and to determine whether the handling and ride qualities of the aircraft were improved by the SSSA attitude command system. The results of the program revealed that SSSA is a viable approach to implementing attitude command and also that SSSA has the capability of performing less demanding augmentation tasks such as yaw damping, wing leveling, and pitch damping. The program also revealed that attitude command did improve the pilot rating and ride qualities of the airplane while flying an IFR mission in turbulence. Some disadvantages of the system included the necessity of holding aileron force in a banked turn and excessive stiffness in the pitch axis.

Development of Semi-Empirical Damping Equation for Baffled Tank with Oblate Spheroidal Dome

NASA Technical Reports Server (NTRS)

Yang, H. Q.; West, Jeff; Brodnick, Jacob; Eberhart, Chad

2016-01-01

Propellant slosh is a potential source of disturbance that can significantly impact the stability of space vehicles. The slosh dynamics are typically represented by a mechanical model of a spring-mass-damper. This mechanical model is then included in the equation of motion of the entire vehicle for Guidance, Navigation and Control analysis. The typical parameters required by the mechanical model include natural frequency of the slosh, slosh mass, slosh mass center location, and the critical damping ratio. A fundamental study has been undertaken at NASA MSFC to understand the fluid damping physics from a ring baffle in the barrel section of a propellant tank. An asymptotic damping equation and CFD blended equation have been derived by NASA MSFC team to complement the popularly used Miles equation at different flow regimes. The new development has found success in providing a nonlinear damping model for the Space Launch System. The purpose of this study is to further extend the semi-empirical damping equations into the oblate spheroidal dome section of the propellant tanks. First, previous experimental data from the spherical baffled tank are collected and analyzed. Several methods of taking the dome curvature effect, including a generalized Miles equation, area projection method, and equalized fill height method, are assessed. CFD simulation is used to shed light on the interaction of vorticity around the baffle with the locally curved wall and liquid-gas interface. The final damping equation will be validated by a recent subscale test with an oblate spheroidal dome conducted at NASA MSFC.

Analysis of the passive stabilization of the long duration exposure facility

NASA Technical Reports Server (NTRS)

Siegel, S. H.; Vishwanath, N. S.

1977-01-01

The nominal Long Duration Exposure Facility (LDEF) configurations and the anticipated orbit parameters are presented. A linear steady state analysis was performed using these parameters. The effects of orbit eccentricity, solar pressure, aerodynamic pressure, magnetic dipole, and the magnetically anchored rate damper were evaluated to determine the configuration sensitivity to variations in these parameters. The worst case conditions for steady state errors were identified, and the performance capability calculated. Garber instability bounds were evaluated for the range of configuration and damping coefficients under consideration. The transient damping capabilities of the damper were examined, and the time constant as a function of damping coefficient and spacecraft moment of inertia determined. The capture capabilities of the damper were calculated, and the results combined with steady state, transient, and Garber instability analyses to select damper design parameters.

Experimental determination of dynamic characteristics of the VentrAssist implantable rotary blood pump.

PubMed

Chung, Michael K H; Zhang, Nong; Tansley, Geoff D; Qian, Yi

2004-12-01

The VentrAssist implantable rotary blood pump, intended for long-term ventricular assist, is under development and is currently being tested for its rotor-dynamic stability. The pump consists of a shaftless impeller, which also acts as the rotor of the brushless DC motor. The impeller remains passively suspended in the pump cavity by hydrodynamic forces, which result from the small clearances between the outside surfaces of the impeller and the pump cavity. These small clearances range from approximately 50 microm to 230 microm in size in the version of pump reported here. This article presents experimental investigation into the dynamic characteristics of the impeller-bearing-pump housing system of the rotary blood pump for increasing pump speeds at different flow rates. The pump was mounted on a suspension system consisting of a platform and springs, where the natural frequency and damping ratio for the suspension system were determined. Real-time measurements of the impeller's displacement were performed using Hall effect sensors. A vertical disturbance force was exerted onto the pump housing, causing the impeller to be displaced in vertical direction from its dynamic equilibrium position within the pump cavity. The impeller displacement was represented by a decaying sine wave, which indicated the impeller restoring to its equilibrium position. From the decaying sine wave the natural frequency and stiffness coefficient of the system were determined. Furthermore, the logarithmic decrement method was used to determine the damping ratio and eventually the damping coefficient of the system. Results indicate that stiffness and damping coefficients increased as flow rate and pump speed increased, representing an increase in stability with these changing conditions. However, pump speed had a greater influence on the stiffness and damping coefficients than flow rate did, which was evident through dynamic analysis. Overall the experimental method presented in this article was successful in determining the dynamic characteristics of the system.

Modeling, Analysis and Mitigation of Sub-Synchronous Interactions between Full- and Partial-Scale Voltage-Source Converters and Power Networks

NASA Astrophysics Data System (ADS)

Alawasa, Khaled Mohammad

Voltage-source converters (VSCs) have gained widespread acceptance in modern power systems. The stability and dynamics of power systems involving these devices have recently become salient issues. In the small-signal sense, the dynamics of VSC-based systems is dictated by its incremental output impedance, which is formed by a combination of 'passive' circuit components and 'active' control elements. Control elements such as control parameters, control loops, and control topologies play a significant role in shaping the impedance profile. Depending on the control schemes and strategies used, VSC-based systems can exhibit different incremental impedance dynamics. As the control elements and dynamics are involved in the impedance structure, the frequency-dependent output impedance might have a negative real-part (i.e., a negative resistance). In the grid-connected mode, the negative resistance degrades the system damping and negatively impacts the stability. In high-voltage networks where high-power VSC-based systems are usually employed and where sub-synchronous dynamics usually exist, integrating large VSC-based systems might reduce the overall damping and results in unstable dynamics. The objectives of this thesis are to (1) investigate and analyze the output impedance properties under different control strategies and control functions, (2) identify and characterize the key contributors to the impedance and sub-synchronous damping profiles, and (3) propose mitigation techniques to minimize and eliminate the negative impact associated with integrating VSC-based systems into power systems. Different VSC configurations are considered in this thesis; in particular, the full-scale and partial-scale topologies (doubly fed-induction generators) are addressed. Additionally, the impedance and system damping profiles are studied under two different control strategies: the standard vector control strategy and the recently-developed power synchronization control strategy. Furthermore, this thesis proposes a simple and robust technique for damping the sub-synchronous resonance in a power system.

Organic Heat Stabilizers for Polyvinyl Chloride (PVC): A Synergistic Behavior of Eugenol and Uracil Derivative

NASA Astrophysics Data System (ADS)

Asawakosinchai, Aran; Jubsilp, Chanchira; Mora, Phattarin; Rimdusit, Sarawut

2017-10-01

Recycling ability, mechanical, and thermal properties of PVC stabilized with organic heat stabilizers, i.e., uracil (DAU) and eugenol were investigated to substitute PVCs stabilized with commercial lead, Ca/Zn, and organic-based stabilizer for PVC pipe production. PVC stabilized with the DAU and the eugenol can be processable at 30 °C lower than that of the PVC stabilized with commercial heat stabilizers. The most remarkable short-term thermal stability belonged to the PVC stabilized with the DAU, and its original color can be maintained at least up to 3 processing cycles. Synergistic behavior in thermal stability of the PVC mixed with DAU and eugenol at mass ratios of 1.5:1.5 was observed. Mechanical properties of DAU- and eugenol-stabilized PVC were higher than the samples with other heat stabilizers. Glass transition temperature of the PVC stabilized with all heat stabilizers was determined to be 99 °C with the exception of the value of 89 °C for eugenol-stabilized PVC. Therefore, the DAU and the eugenol showed high potential to be used as an organic heat stabilizer for PVC because of their non-toxic and good heat resistance properties.

Rotation in vibration, optimization, and aeroelastic stability problems. Ph.D. Thesis

NASA Technical Reports Server (NTRS)

Kaza, K. R. V.

1974-01-01

The effects of rotation in the areas of vibrations, dynamic stability, optimization, and aeroelasticity were studied. The governing equations of motion for the study of vibration and dynamic stability of a rapidly rotating deformable body were developed starting from the nonlinear theory of elasticity. Some common features such as the limitations of the classical theory of elasticity, the choice of axis system, the property of self-adjointness, the phenomenon of frequency splitting, shortcomings of stability methods as applied to gyroscopic systems, and the effect of internal and external damping on stability in gyroscopic systems are identified and discussed, and are then applied to three specific problems.

Free-Flight Investigation of the Static and Dynamic Longitudinal Stability Characteristics of 1/3.7-Scale Rocket-Powered Models of the Bell MX-776A

NASA Technical Reports Server (NTRS)

Michal, David H.

1950-01-01

An investigation of the static and dynamic longitudinal stability characteristics of 1/3.7 scale rocket-powered model of the Bell MX-776A has been made for a Mach number range from 0.8 to 1.6. Two models were tested with all control surfaces at 0 degree deflection and centers of gravity located 1/4 and 1/2 body diameters, respectively, ahead of the equivalent design location. Both models were stable about the trim conditions but did not trim at 0 degree angle of attack because of slight constructional asymmetries. The results indicated that the variation of lift and pitching moment was not linear with angle of attack. Both lift-curve slope and pitching-moment-curve slope were of the smallest magnitude near 0 degree angle of attack. In general, an increase in angle of attack was accompanied by a rearward movement of the aerodynamic center as the rear wing moved out of the downwash from the forward surfaces. This characteristic was more pronounced in the transonic region. The dynamic stability in the form of total damping factor varied with normal-force coefficient but was greatest for both models at a Mach number of approximately 1.25. The damping factor was greater at the lower trim normal-force coefficients except at a Mach number of 1.0. At that speed the damping factor was of about the same magnitude for both models. The drag coefficient increased with trim normal-force coefficient and was largest in the transonic region.

Stability of a rigid rotor supported on flexible oil journal bearings

NASA Technical Reports Server (NTRS)

Majumdar, B. C.; Brewe, D. E.; Khonsari, M. M.

1988-01-01

This investigation deals with the stability characteristics of oil journal bearings, including the effect of elastic distortions in the bearing liner. Graphical results are presented for (1) steady-state load, (2) stiffness and damping coefficients, and (3) the stability. These results are given for various slenderness ratios, eccentricity ratios, and elasticity parameters. The lubricant is first assumed to be isoviscous. The analysis is then extended to the case of a pressure-dependent viscosity. It has been found that stability decreases with increase of the elasticity parameter of the bearing liner for heavily loaded bearings.

Stability of a rigid rotor supported on flexible oil journal bearings

NASA Technical Reports Server (NTRS)

Majumdar, Bankim C.; Brewe, David E.; Khonsari, Michael M.

1987-01-01

This investigation deals with the stability characteristics of oil journal bearings, including the effect of elastic distortions in the bearing liner. Graphical results are presented for (1) steady-state load, (2) stiffness and damping coefficients, and (3) the stability. These results are given for various slenderness ratios, eccentricity ratios, and elasticity parameters. The lubricant is first assumed to be isoviscous. The analysis is then extended to the case of a pressure-dependent viscosity. It has been found that stability decreases with increase of the elasticity parameter of the bearing liner for heavily loaded bearings.

Preliminary Results Obtained from Flight Test of a Rocket Model Having the Tail Only of the Grumman XF10F Airplane Configuration, TED No. NACA DE 354

NASA Technical Reports Server (NTRS)

Gardner, William N.; Edmondson, James L.

1950-01-01

A flight test was made to determine the servoplane effectiveness and stability characteristics of the free-floating horizontal stabilizer to be used on the XF10F airplane. The results of this test indicate that servoplane effectiveness is practically constant through the speed range up to a Mach number of 1.15, and the stabilizer static stability is satisfactory. A loss of damping occurs over a narrow Mach number range near M = 1.0, resulting in dynamic instability of the stabilizer in this narrow range. Above M = 1.0 there is a gradual positive trim change of the stabilizer.

Summary of methods for calculating dynamic lateral stability and response and for estimating aerodynamic stability derivatives

NASA Technical Reports Server (NTRS)

Campbell, John P; Mckinney, Marion O

1952-01-01

A summary of methods for making dynamic lateral stability and response calculations and for estimating the aerodynamic stability derivatives required for use in these calculations is presented. The processes of performing calculations of the time histories of lateral motions, of the period and damping of these motions, and of the lateral stability boundaries are presented as a series of simple straightforward steps. Existing methods for estimating the stability derivatives are summarized and, in some cases, simple new empirical formulas are presented. Detailed estimation methods are presented for low-subsonic-speed conditions but only a brief discussion and a list of references are given for transonic and supersonic speed conditions.

7 CFR 58.926 - Heat stability.

Code of Federal Regulations, 2010 CFR

2010-01-01

... 7 Agriculture 3 2010-01-01 2010-01-01 false Heat stability. 58.926 Section 58.926 Agriculture... Procedures § 58.926 Heat stability. Prior to thermal processing of concentrated products and where stabilizers are allowed, tests should be made on the heat stability of the product to determine necessity for...

7 CFR 58.926 - Heat stability.

Code of Federal Regulations, 2011 CFR

2011-01-01

... 7 Agriculture 3 2011-01-01 2011-01-01 false Heat stability. 58.926 Section 58.926 Agriculture... Procedures § 58.926 Heat stability. Prior to thermal processing of concentrated products and where stabilizers are allowed, tests should be made on the heat stability of the product to determine necessity for...

7 CFR 58.926 - Heat stability.

Code of Federal Regulations, 2014 CFR

2014-01-01

... 7 Agriculture 3 2014-01-01 2014-01-01 false Heat stability. 58.926 Section 58.926 Agriculture... Procedures § 58.926 Heat stability. Prior to thermal processing of concentrated products and where stabilizers are allowed, tests should be made on the heat stability of the product to determine necessity for...

7 CFR 58.926 - Heat stability.

Code of Federal Regulations, 2013 CFR

2013-01-01

... 7 Agriculture 3 2013-01-01 2013-01-01 false Heat stability. 58.926 Section 58.926 Agriculture... Procedures § 58.926 Heat stability. Prior to thermal processing of concentrated products and where stabilizers are allowed, tests should be made on the heat stability of the product to determine necessity for...

7 CFR 58.926 - Heat stability.

Code of Federal Regulations, 2012 CFR

2012-01-01

... 7 Agriculture 3 2012-01-01 2012-01-01 false Heat stability. 58.926 Section 58.926 Agriculture... Procedures § 58.926 Heat stability. Prior to thermal processing of concentrated products and where stabilizers are allowed, tests should be made on the heat stability of the product to determine necessity for...

Integration of Thermal Energy Harvesting in Semi-Active Piezoelectric Shunt-Damping Systems

NASA Astrophysics Data System (ADS)

Lubieniecki, Michał; Uhl, Tadeusz

2015-01-01

The opportunities to energize a broad range of devices by use of energy available almost anywhere and in many forms are almost unlimited. A major advantage of energy harvesting is the manufacture of small autonomous electronic devices with no need for power supply and maintenance. Shunt damping circuits, although unfavorably affected by the size and mass of bulky coil inductors, started to base on synthetic inductors losing their passivity. In this paper we report a study of the feasibility of powering shunt damping circuits by use of thermal energy otherwise irrevocably lost from a bearing. The heat generated in the bearing is converted thermoelectrically into electric energy which is then used to power synthetic inductance circuitry. We show that the power demand of such circuit can be satisfied by use of a thermoelectric generator paired with a moderately loaded bearing.

Ion heating and short wavelength fluctuations in a helicon plasma source

DOE Office of Scientific and Technical Information (OSTI.GOV)

Scime, E. E.; Carr, J. Jr.; Galante, M.

2013-03-15

For typical helicon source parameters, the driving antenna can couple to two plasma modes; the weakly damped 'helicon' wave, and the strongly damped, short wavelength, slow wave. Here, we present direct measurements, obtained with two different techniques, of few hundred kHz, short wavelength fluctuations that are parametrically driven by the primary antenna and localized to the edge of the plasma. The short wavelength fluctuations appear for plasma source parameters such that the driving frequency is approximately equal to the lower hybrid frequency. Measurements of the steady-state ion temperature and fluctuation amplitude radial profiles suggest that the anomalously high ion temperaturesmore » observed at the edge of helicon sources result from damping of the short wavelength fluctuations. Additional measurements of the time evolution of the ion temperature and fluctuation profiles in pulsed helicon source plasmas support the same conclusion.« less

Role of low-energy phonons with mean-free-paths >0.8 μm in heat conduction in silicon

DOE PAGES

Jiang, Puqing; Lindsay, Lucas R.; Koh, Yee Kan

2016-06-30

Despite recent progress in the first-principles calculations and measurements of phonon mean-free-paths (ℓ), contribution of low-energy phonons to heat conduction in silicon is still inconclusive, as exemplified by the discrepancies as large as 30% between different first-principles calculations. In this study, we investigate the contribution of low-energy phonons with ℓ>0.8 μm by accurately measuring the cross-plane thermal conductivity (Λ cross) of crystalline silicon films by time-domain thermoreflectance (TDTR), over a wide range of film thicknesses 1≤ h f ≤ 10 μm and temperatures 100 ≤ T ≤ 300 K. We employ a dual-frequency TDTR approach to improve the accuracy ofmore » our Λ cross measurements. We find from our Λ cross measurements that phonons with ℓ>0.8 μm contribute 53 W m -1 K -1 (37%) to heat conduction in natural Si at 300 K while phonons with ℓ>3 μm contribute 523 W m -1 K -1 (61%) at 100 K, >20% lower than first-principles predictions of 68 W m -1 K -1 (47%) and 717 W m -1 K -1 (76%), respectively. Using a relaxation time approximation (RTA) model, we demonstrate that macroscopic damping (e.g., Akhieser s damping) eliminates the contribution of phonons with mean-free-paths >20 μm at 300 K, which contributes 15 W m -1 K -1 (10%) to calculated heat conduction in Si. Thus, we propose that omission of the macroscopic damping for low-energy phonons in the first-principles calculations could be one of the possible explanations for the observed differences between our measurements and calculations. Finally, our work provides an important benchmark for future measurements and calculations of the distribution of phonon mean-free-paths in crystalline silicon.« less

Time-domain simulation of damped impacted plates. II. Numerical model and results.

PubMed

Lambourg, C; Chaigne, A; Matignon, D

2001-04-01

A time-domain model for the flexural vibrations of damped plates was presented in a companion paper [Part I, J. Acoust. Soc. Am. 109, 1422-1432 (2001)]. In this paper (Part II), the damped-plate model is extended to impact excitation, using Hertz's law of contact, and is solved numerically in order to synthesize sounds. The numerical method is based on the use of a finite-difference scheme of second order in time and fourth order in space. As a consequence of the damping terms, the stability and dispersion properties of this scheme are modified, compared to the undamped case. The numerical model is used for the time-domain simulation of vibrations and sounds produced by impact on isotropic and orthotropic plates made of various materials (aluminum, glass, carbon fiber and wood). The efficiency of the method is validated by comparisons with analytical and experimental data. The sounds produced show a high degree of similarity with real sounds and allow a clear recognition of each constitutive material of the plate without ambiguity.

Foucault pendulum with eddy-current damping of the elliptical motion

NASA Astrophysics Data System (ADS)

Mastner, G.; Vokurka, V.; Maschek, M.; Vogt, E.; Kaufmann, H. P.

1984-10-01

A newly designed Foucault pendulum is described in which the mechanical Charron ring, used throughout in previous designs for damping of the elliptical motion of the pendulum, is replaced by an electromagnetic eddy-current brake, consisting of a permanent magnet attached to the bottom of the bob and a metallic ring. This damping device is very efficient, as it is self-aligning, symmetrical in the damping effect, and never wears out. The permanent magnet is also used, together with a coil assembly and an electronic circuitry, for the dipole-torque drive of the pendulum as well as for accurate stabilization of the amplitude of the swing. A latched time display, controlled by Hall probes activated by the magnet, is used to visualize the Foucault rotation. The pendulum system and its associated electronic circuitry are described in detail. The optimizing of the drive mode is discussed. Measurements of deviations from theoretical value of the Foucault rotation velocity made automatically in a continuous run show a reproducible accuracy of ±1% or better in individual 360° rotations during the summer months. The quality factor of the pendulum as mechanical resonator was measured as a function of the amplitude in the presence of the eddy-current damping ring.

Proceedings of the 3rd Annual SCOLE Workshop

NASA Technical Reports Server (NTRS)

Taylor, Lawrence W., Jr. (Compiler)

1987-01-01

Topics addressed include: modeling and controlling the Spacecraft Control Laboratory Experiment (SCOLE) configurations; slewing maneuvers; mathematical models; vibration damping; gravitational effects; structural dynamics; finite element method; distributed parameter system; on-line pulse control; stability augmentation; and stochastic processes.

Dynamic Confinement of ITER Plasma by O-Mode Driver at Electron Cyclotron Frequency Range

NASA Astrophysics Data System (ADS)

Stefan, V. Alexander

2009-05-01

A low B-field side launched electron cyclotron O-Mode driver leads to the dynamic rf confinement, in addition to rf turbulent heating, of ITER plasma. The scaling law for the local energy confinement time τE is evaluated (τE ˜ 3neTe/2Q, where (3/2) neTe is the local plasma thermal energy density and Q is the local rf turbulent heating rate). The dynamics of unstable dissipative trapped particle modes (DTPM) strongly coupled to Trivelpiece-Gould (T-G) modes is studied for gyrotron frequency 170GHz; power˜24 MW CW; and on-axis B-field ˜ 10T. In the case of dynamic stabilization of DTPM turbulence and for the heavily damped T-G modes, the energy confinement time scales as τE˜(I0)-2, whereby I0(W/m^2) is the O-Mode driver irradiance. R. Prater et. al., Nucl. Fusion 48, No 3 (March 2008). E. P. Velikhov, History of the Russian Tokamak and the Tokamak Thermonuclear Fusion Research Worldwide That Led to ITER (Documentary movie; Stefan Studios Int'l, La Jolla, CA, 2008; E. P. Velikhov, V. Stefan.) M N Rosenbluth, Phys. Scr. T2A 104-109 1982 B. B. Kadomtsev and O. P. Pogutse, Nucl. Fusion 11, 67 (1971).

Pulse Repetition Frequency Effects In A High Average Power X-Ray Preionised Excimer Laser

NASA Astrophysics Data System (ADS)

Fontaine, Bernard L.; Forestier, Bernard M.; Delaporte, Philippe C.; Canarelli, Patrick

1989-10-01

Experimental study of waves damping in a high repetition rate excimer laser is undertaken. Excitation of laser active medium in a subsonic loop is achieved by means of a classical discharge, through transfer capacitors. The discharge stability is controlled by a wire ion plasma (w.i.p.) X-rays gun. The strong acoustic waves induced by the active medium excitation may lead to a decrease, at high PRF, of the energy per pulse. First results of the influence of a damping of induced density perturbations between two successive pulses are presented.

First Experiments with e-e-H- H- Plasmas: Enhanced Mode Damping and Transport

NASA Astrophysics Data System (ADS)

Kabantsev, A. A.; Thompson, K. A.; Driscoll, C. F.

2017-10-01

Negative Hydrogen ions are produced and confined in a room-temperature electron plasma, causing enhanced mode damping and particle transport effects. We accumulate an H- charge fraction nH-nH-ne 20 % ne 20 % in about 200 seconds, as externally excited H2 molecules undergo dissociative electron attachment in the plasma. The accumulated H- fraction causes a novel algebraic damping of diocotron mode amplitude A(t) , and the damping is coincident with an enhanced outward drift υr of the H- ions. That is, dA dA dt = - α dt = - α , with α nH- *υr . We observe that heating the e-e-H- H- plasma terminates the enhanced damping and enhanced centrifugal separation, both of which resume when plasma re-cools by cyclotron radiation at B = 1.2T. Other interesting observations include: (1) enhanced e- cooling from collisions with H- cooled by neutrals; (2) enhanced damping of plasma waves due to e-e-H- H- collisional drag; (3) strong exponential damping of diocotron modes in a ``floppy'' nearly-pure H- plasma, created by rapid axial ejection of the electrons. Additional novel drift modes and instabilities are predicted theoretically in such a plasma. Supported by NSF/DoE Partnership Grants PHY-1414570 and DE-SC0008693.

Stability of exact solutions describing two-layer flows with evaporation at the interface

NASA Astrophysics Data System (ADS)

Bekezhanova, V. B.; Goncharova, O. N.

2016-12-01

A new exact solution of the equations of free convection has been constructed in the framework of the Oberbeck-Boussinesq approximation of the Navier-Stokes equations. The solution describes the joint flow of an evaporating viscous heat-conducting liquid and gas-vapor mixture in a horizontal channel. In the gas phase the Dufour and Soret effects are taken into account. The consideration of the exact solution allows one to describe different classes of flows depending on the values of the problem parameters and boundary conditions for the vapor concentration. A classification of solutions and results of the solution analysis are presented. The effects of the external disturbing influences (of the liquid flow rates and longitudinal gradients of temperature on the channel walls) on the stability characteristics have been numerically studied for the system HFE7100-nitrogen in the common case, when the longitudinal temperature gradients on the boundaries of the channel are not equal. In the system both monotonic and oscillatory modes can be formed, which damp or grow depending on the values of the initial perturbations, flow rates and temperature gradients. Hydrodynamic perturbations are most dangerous under large gas flow rates. The increasing oscillatory perturbations are developed due to the thermocapillary effect under large longitudinal gradients of temperature. The typical forms of the disturbances are shown.

Enceladus: three-act play and current state

NASA Astrophysics Data System (ADS)

Luan, J.; Goldreich, P.

2017-12-01

Eccentricity (e) growth as Enceladus migrates deeper into mean motion resonance with Dione results in increased tidal heating. As the bottom of the ice shell melts, the rate of tidal heating jumps and runaway melting ensues. At the end of run-away melting, the shell's thickness has fallen below the value at which the frequency of free libration equals the orbital mean motion and e has damped to well below its current value. Subsequently, both the shell thickness and e partake in a limit cycle. As e damps toward its minimum value, the shell's thickness asymptotically approaches its resonant value from below. After minimum e, the shell thickens quickly and e grows even faster. This cycle is likely to have been repeated multiple times in the past. Currently, e is much smaller than its equilibrium value corresponding to the shell thickness. Physical libration resonance resolves this mystery, it ensures that the low-e and medium-thickness state is present for most of the time between consecutive limit cycles. It is a robust scenario that avoids fine tuning or extreme parameter choice, and naturally produces episodic stages of high heating, consistent with softening of topographical features on Enceladus.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jiang, Puqing; Lindsay, Lucas R.; Koh, Yee Kan

Despite recent progress in the first-principles calculations and measurements of phonon mean-free-paths (ℓ), contribution of low-energy phonons to heat conduction in silicon is still inconclusive, as exemplified by the discrepancies as large as 30% between different first-principles calculations. In this study, we investigate the contribution of low-energy phonons with ℓ>0.8 μm by accurately measuring the cross-plane thermal conductivity (Λ cross) of crystalline silicon films by time-domain thermoreflectance (TDTR), over a wide range of film thicknesses 1≤ h f ≤ 10 μm and temperatures 100 ≤ T ≤ 300 K. We employ a dual-frequency TDTR approach to improve the accuracy ofmore » our Λ cross measurements. We find from our Λ cross measurements that phonons with ℓ>0.8 μm contribute 53 W m -1 K -1 (37%) to heat conduction in natural Si at 300 K while phonons with ℓ>3 μm contribute 523 W m -1 K -1 (61%) at 100 K, >20% lower than first-principles predictions of 68 W m -1 K -1 (47%) and 717 W m -1 K -1 (76%), respectively. Using a relaxation time approximation (RTA) model, we demonstrate that macroscopic damping (e.g., Akhieser s damping) eliminates the contribution of phonons with mean-free-paths >20 μm at 300 K, which contributes 15 W m -1 K -1 (10%) to calculated heat conduction in Si. Thus, we propose that omission of the macroscopic damping for low-energy phonons in the first-principles calculations could be one of the possible explanations for the observed differences between our measurements and calculations. Finally, our work provides an important benchmark for future measurements and calculations of the distribution of phonon mean-free-paths in crystalline silicon.« less

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

NASA Astrophysics Data System (ADS)

Casiano, Matthew J.

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

Investigation of Stability and Control Characteristics of a 1/10-scale Model of a Canadian Tailless Glider in the Langley Free-flight Tunnel

NASA Technical Reports Server (NTRS)

Johnson, Joseph L.

1949-01-01

An investigation of the stability and control characteristics of a 1/10-scale model of a Canadian tailless glider has been conducted in the 10 Langley free-flight tunnel. The glider designated the N.R.L. tailless glider has a straight center section and outboard panels sweptback 43 deg. along the leading edge of the wing. The aspect ratio is 5.83 and the taper ratio is 0.323. From the results of the investigation and on the basis of comparison with higher-scale static tests of the National Research Council of Canada, it is expected that the longitudinal stability of the airplane will be satisfactory with flap up but unsatisfactory near the stall with flap down. The airplane is expected to have unsatisfactory lateral stability and control characteristics in the design configuration with either flap up or flap down. The model flights showed very low damping of the lateral oscillation. Increasing the vertical-tail area improved the lateral stability, and it appeared that a value of the directional-stability parameter C(sub n beta) of at least 0.002 per degree would probably be necessary for satisfactory lateral flying characteristics. A comparison of the calculated dynamic lateral stability characteristics of the N.R.L. tailless glider with those of a conventional-type sweptback airplane having a similar wing plan form and about the same inclination of the principal longitudinal axis of inertia showed that the tailless glider had poorer lateral stability because of the relatively larger radius of gyration in roll and the smaller damping-in-yaw factor C(sub nr).

On-orbit Status and Light Attenuation Behavior of the DAMPE-PSD

NASA Astrophysics Data System (ADS)

Li, Y.; Zhang, Y. P.; Zhang, Y. J.; Sun, Z. Y.; Yu, Y. H.; Dong, T. K.; Ma, P. X.; Wang, Y. P.; Yuan, Q.

2017-11-01

The DArk Matter Particle Explorer (DAMPE) is a high-resolution multi-purpose space-borne device for detecting the high-energy cosmic-rays like e±, γ-rays, protons, and heavy-ions, which was launched on 2015 December 17th. The Plastic Scintillator Detector (PSD) is the top-most sub-detector of DAMPE. The PSD is designed to measure the charge of incident high-energy particles, and to serve as a veto detector for discriminating γ-rays from the charged particles. In this paper, the on-orbit status of the PSD after launching in terms of high voltage (HV) and temperature stabilities is presented. The temperature and the HV variations of the PSD are less than 1°C and 0.5%, respectively. By using the on-orbit data, the attenuation lengths of PSD bars are obtained according to an empirical formula. A preliminary charge spectrum reconstructed from the X-layer of the PSD is obtained.

An experimental study of the effect of tail configuration on the spinning characteristics of general aviation aircraft. M.S. Thesis; [static wind tunnel force measurements

NASA Technical Reports Server (NTRS)

Ballin, M. G.

1982-01-01

The feasibility of using static wind tunnel tests to obtain information about spin damping characteristics of an isolated general aviation aircraft tail was investigated. A representative tail section was oriented to the tunnel free streamline at angles simulating an equilibrium spin. A full range of normally encountered spin conditions was employed. Results of parametric studies performed to determine the effect of spin damping on several tail design parameters show satisfactory agreement with NASA rotary balance tests. Wing and body interference effects are present in the NASA studies at steep spin attitudes, but agreement improves with increasing pitch angle and spin rate, suggesting that rotational flow effects are minimal. Vertical position of the horizontal stabilizer is found to be a primary parameter affecting yaw damping, and horizontal tail chordwise position induces a substantial effect on pitching moment.

Pole-placement Predictive Functional Control for under-damped systems with real numbers algebra.

PubMed

Zabet, K; Rossiter, J A; Haber, R; Abdullah, M

2017-11-01

This paper presents the new algorithm of PP-PFC (Pole-placement Predictive Functional Control) for stable, linear under-damped higher-order processes. It is shown that while conventional PFC aims to get first-order exponential behavior, this is not always straightforward with significant under-damped modes and hence a pole-placement PFC algorithm is proposed which can be tuned more precisely to achieve the desired dynamics, but exploits complex number algebra and linear combinations in order to deliver guarantees of stability and performance. Nevertheless, practical implementation is easier by avoiding complex number algebra and hence a modified formulation of the PP-PFC algorithm is also presented which utilises just real numbers while retaining the key attributes of simple algebra, coding and tuning. The potential advantages are demonstrated with numerical examples and real-time control of a laboratory plant. Copyright © 2017 ISA. All rights reserved.

Direct heuristic dynamic programming for damping oscillations in a large power system.

PubMed

Lu, Chao; Si, Jennie; Xie, Xiaorong

2008-08-01

This paper applies a neural-network-based approximate dynamic programming method, namely, the direct heuristic dynamic programming (direct HDP), to a large power system stability control problem. The direct HDP is a learning- and approximation-based approach to addressing nonlinear coordinated control under uncertainty. One of the major design parameters, the controller learning objective function, is formulated to directly account for network-wide low-frequency oscillation with the presence of nonlinearity, uncertainty, and coupling effect among system components. Results include a novel learning control structure based on the direct HDP with applications to two power system problems. The first case involves static var compensator supplementary damping control, which is used to provide a comprehensive evaluation of the learning control performance. The second case aims at addressing a difficult complex system challenge by providing a new solution to a large interconnected power network oscillation damping control problem that frequently occurs in the China Southern Power Grid.

Stability of the cometary ionopause

NASA Astrophysics Data System (ADS)

Ershkovich, A. I.; Axford, W. I.; Ip, W.-H.; Flammer, K. R.

MHD stability of the cometary ionopause is discussed in the context of the Giotto mission to comet Halley. A mechanism associated with the plasma compressibility is suggested here as being responsible for the apparent stability of the Halley ionopause: when the phase velocity of surface waves at the ionopause approaches the fast magnetoacoustic speed the unstable surface waves are transformed into stable body waves in the whole fluid resulting in an effective damping of the instability. The effects of both mass loading (due to photoionization) and dissociative recombination are also studied.

A Linear Stochastic Dynamical Model of ENSO. Part II: Analysis.

NASA Astrophysics Data System (ADS)

Thompson, C. J.; Battisti, D. S.

2001-02-01

In this study the behavior of a linear, intermediate model of ENSO is examined under stochastic forcing. The model was developed in a companion paper (Part I) and is derived from the Zebiak-Cane ENSO model. Four variants of the model are used whose stabilities range from slightly damped to moderately damped. Each model is run as a simulation while being perturbed by noise that is uncorrelated (white) in space and time. The statistics of the model output show the moderately damped models to be more realistic than the slightly damped models. The moderately damped models have power spectra that are quantitatively quite similar to observations, and a seasonal pattern of variance that is qualitatively similar to observations. All models produce ENSOs that are phase locked to the annual cycle, and all display the `spring barrier' characteristic in their autocorrelation patterns, though in the models this `barrier' occurs during the summer and is less intense than in the observations (inclusion of nonlinear effects is shown to partially remedy this deficiency). The more realistic models also show a decadal variability in the lagged autocorrelation pattern that is qualitatively similar to observations.Analysis of the models shows that the greatest part of the variability comes from perturbations that project onto the first singular vector, which then grow rapidly into the ENSO mode. Essentially, the model output represents many instances of the ENSO mode, with random phase and amplitude, stimulated by the noise through the optimal transient growth of the singular vectors.The limit of predictability for each model is calculated and it is shown that the more realistic (moderately damped) models have worse potential predictability (9-15 months) than the deterministic chaotic models that have been studied widely in the literature. The predictability limits are strongly correlated with the stability of the models' ENSO mode-the more highly damped models having much shorter limits of predictability. A comparison of the two most realistic models shows that even though these models have similar statistics, they have very different predictability limits. The models have a strong seasonal dependence to their predictability limits.The results of this study (with the companion paper) suggest that the linear, stable dynamical model of ENSO is indeed a plausible hypothesis for the observed ENSO. With very reasonable levels of stochastic forcing, the model produces realistic levels of variance, has a realistic spectrum, and qualitatively reproduces the observed seasonal pattern of variance, the autocorrelation pattern, and the ENSO-like decadal variability.

Prediction of Liquid Slosh Damping Using a High Resolution CFD Tool

NASA Technical Reports Server (NTRS)

Yang, H. Q.; Purandare, Ravi; Peugeot, John; West, Jeff

2012-01-01

Propellant slosh is a potential source of disturbance critical to the stability of space vehicles. The slosh dynamics are typically represented by a mechanical model of a spring mass damper. This mechanical model is then included in the equation of motion of the entire vehicle for Guidance, Navigation and Control analysis. Our previous effort has demonstrated the soundness of a CFD approach in modeling the detailed fluid dynamics of tank slosh and the excellent accuracy in extracting mechanical properties (slosh natural frequency, slosh mass, and slosh mass center coordinates). For a practical partially-filled smooth wall propellant tank with a diameter of 1 meter, the damping ratio is as low as 0.0005 (or 0.05%). To accurately predict this very low damping value is a challenge for any CFD tool, as one must resolve a thin boundary layer near the wall and must minimize numerical damping. This work extends our previous effort to extract this challenging parameter from first principles: slosh damping for smooth wall and for ring baffle. First the experimental data correlated into the industry standard for smooth wall were used as the baseline validation. It is demonstrated that with proper grid resolution, CFD can indeed accurately predict low damping values from smooth walls for different tank sizes. The damping due to ring baffles at different depths from the free surface and for different sizes of tank was then simulated, and fairly good agreement with experimental correlation was observed. The study demonstrates that CFD technology can be applied to the design of future propellant tanks with complex configurations and with smooth walls or multiple baffles, where previous experimental data is not available.

The Modeling of Vibration Damping in SMA Wires

DOE Office of Scientific and Technical Information (OSTI.GOV)

Reynolds, D R; Kloucek, P; Seidman, T I

Through a mathematical and computational model of the physical behavior of shape memory alloy wires, this study shows that localized heating and cooling of such materials provides an effective means of damping vibrational energy. The thermally induced pseudo-elastic behavior of a shape memory wire is modeled using a continuum thermodynamic model and solved computationally as described by the authors in [23]. Computational experiments confirm that up to 80% of an initial shock of vibrational energy can be eliminated at the onset of a thermally-induced phase transformation through the use of spatially-distributed transformation regions along the length of a shape memorymore » alloy wire.« less

30 CFR 56.6132 - Magazine requirements.

Code of Federal Regulations, 2010 CFR

2010-07-01

... 30 Mineral Resources 1 2010-07-01 2010-07-01 false Magazine requirements. 56.6132 Section 56.6132....6132 Magazine requirements. (a) Magazines shall be— (1) Structurally sound; (2) Noncombustible or the... the inside; (5) Ventilated to control dampness and excessive heating within the magazine; (6) Posted...

Quasilinear diffusion coefficients in a finite Larmor radius expansion for ion cyclotron heated plasmas

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lee, Jungpyo; Wright, John; Bertelli, Nicola

In this study, a reduced model of quasilinear velocity diffusion by a small Larmor radius approximation is derived to couple the Maxwell’s equations and the Fokker Planck equation self-consistently for the ion cyclotron range of frequency waves in a tokamak. The reduced model ensures the important properties of the full model by Kennel-Engelmann diffusion, such as diffusion directions, wave polarizations, and H-theorem. The kinetic energy change (Wdot ) is used to derive the reduced model diffusion coefficients for the fundamental damping (n = 1) and the second harmonic damping (n = 2) to the lowest order of the finite Larmormore » radius expansion. The quasilinear diffusion coefficients are implemented in a coupled code (TORIC-CQL3D) with the equivalent reduced model of the dielectric tensor. We also present the simulations of the ITER minority heating scenario, in which the reduced model is verified within the allowable errors from the full model results.« less

Vibration damping and heat transfer using material phase changes

NASA Technical Reports Server (NTRS)

Kloucek, Petr (Inventor); Reynolds, Daniel R. (Inventor)

2009-01-01

A method and apparatus wherein phase changes in a material can dampen vibrational energy, dampen noise and facilitate heat transfer. One embodiment includes a method for damping vibrational energy in a body. The method comprises attaching a material to the body, wherein the material comprises a substrate, a shape memory alloy layer, and a plurality of temperature change elements. The method further comprises sensing vibrations in the body. In addition, the method comprises indicating to at least a portion of the temperature change elements to provide a temperature change in the shape memory alloy layer, wherein the temperature change is sufficient to provide a phase change in at least a portion of the shape memory alloy layer, and further wherein the phase change consumes a sufficient amount of kinetic energy to dampen at least a portion of the vibrational energy in the body. In other embodiments, the shape memory alloy layer is a thin film. Additional embodiments include a sensor connected to the material.

Sensing coherent phonons with two-photon interference

NASA Astrophysics Data System (ADS)

Ding, Ding; Yin, Xiaobo; Li, Baowen

2018-02-01

Detecting coherent phonons pose different challenges compared to coherent photons due to the much stronger interaction between phonons and matter. This is especially true for high frequency heat carrying phonons, which are intrinsic lattice vibrations experiencing many decoherence events with the environment, and are thus generally assumed to be incoherent. Two photon interference techniques, especially coherent population trapping (CPT) and electromagnetically induced transparency (EIT), have led to extremely sensitive detection, spectroscopy and metrology. Here, we propose the use of two photon interference in a three-level system to sense coherent phonons. Unlike prior works which have treated phonon coupling as damping, we account for coherent phonon coupling using a full quantum-mechanical treatment. We observe strong asymmetry in absorption spectrum in CPT and negative dispersion in EIT susceptibility in the presence of coherent phonon coupling which cannot be accounted for if only pure phonon damping is considered. Our proposal has application in sensing heat carrying coherent phonons effects and understanding coherent bosonic multi-pathway interference effects in three coupled oscillator systems.

Quasilinear diffusion coefficients in a finite Larmor radius expansion for ion cyclotron heated plasmas

DOE PAGES

Lee, Jungpyo; Wright, John; Bertelli, Nicola; ...

2017-04-24

In this study, a reduced model of quasilinear velocity diffusion by a small Larmor radius approximation is derived to couple the Maxwell’s equations and the Fokker Planck equation self-consistently for the ion cyclotron range of frequency waves in a tokamak. The reduced model ensures the important properties of the full model by Kennel-Engelmann diffusion, such as diffusion directions, wave polarizations, and H-theorem. The kinetic energy change (Wdot ) is used to derive the reduced model diffusion coefficients for the fundamental damping (n = 1) and the second harmonic damping (n = 2) to the lowest order of the finite Larmormore » radius expansion. The quasilinear diffusion coefficients are implemented in a coupled code (TORIC-CQL3D) with the equivalent reduced model of the dielectric tensor. We also present the simulations of the ITER minority heating scenario, in which the reduced model is verified within the allowable errors from the full model results.« less

A novel approach based on OCT for tongue inspection in traditional Chinese medicine

NASA Astrophysics Data System (ADS)

Dong, Haixin; Guo, Zhouyi; Zeng, Changchun; Zhong, Huiqing; Gong, Xin; He, Yonghong; Wang, Ruikang K.; Liu, Songhao

2007-11-01

The aim of this report is to establish a tongue inspection method based on OCT imaging for quantifying the tongue properties in traditional Chinese medical diagnosis. The measurement was performed in the model of rats suffering with Spleen-Stomach Dampness-Heat Syndrome using OCT equipment, OCT image and histology estimates of the glossal layer of microstructure were obtained, and the accurate thickness and moisture degree of the tongue coating were analyzed. These OCT image showed that tongue every layer matched the histology estimates of the glossal microstructure, and compared with normal control group the thickness of tongue coating increased in rats suffering with Spleen-Stomach Dampness-Heat Syndrome than normal control rats (P<0.01), yet the moisture degree of tongue body of model group decreased (P<0.01). Therefore, OCT image technique may be benefit and helpful as a tool to provide an objective diagnostic standard for study on tongue inspection in the clinical practice and research of TCM.

Nonlinear Gyro-Landau-Fluid Equations

NASA Astrophysics Data System (ADS)

Raskolnikov, I.; Mattor, Nathan; Parker, Scott E.

1996-11-01

We present fluid equations which describe the effects of both linear and nonlinear Landau damping (wave-particle-wave effects). These are derived using a recently developed analytical method similar to renormalization group theory. (Scott E. Parker and Daniele Carati, Phys. Rev. Lett. 75), 441 (1995). In this technique, the phase space structure inherent in Landau damping is treated analytically by building a ``renormalized collisionality'' onto a bare collisionality (which may be taken as vanishingly small). Here we apply this technique to the nonlinear ion gyrokinetic equation in slab geometry, obtaining nonlinear fluid equations for density, parallel momentum and heat. Wave-particle resonances are described by two functions appearing in the heat equation: a renormalized ``collisionality'' and a renormalized nonlinear coupling coeffient. It will be shown that these new equations may correct a deficiency in existing gyrofluid equations, (G. W. Hammett and F. W. Perkins, Phys. Rev. Lett. 64,) 3019 (1990). which can severely underestimate the strength of nonlinear interaction in regimes where linear resonance is strong. (N. Mattor, Phys. Fluids B 4,) 3952 (1992).

Vibration damping and heat transfer using material phase changes

DOEpatents

Kloucek, Petr [Houston, TX; Reynolds, Daniel R [Oakland, CA

2009-03-24

A method and apparatus wherein phase changes in a material can dampen vibrational energy, dampen noise and facilitate heat transfer. One embodiment includes a method for damping vibrational energy in a body. The method comprises attaching a material to the body, wherein the material comprises a substrate, a shape memory alloy layer, and a plurality of temperature change elements. The method further comprises sensing vibrations in the body. In addition, the method comprises indicating to at least a portion of the temperature change elements to provide a temperature change in the shape memory alloy layer, wherein the temperature change is sufficient to provide a phase change in at least a portion of the shape memory alloy layer, and further wherein the phase change consumes a sufficient amount of kinetic energy to dampen at least a portion of the vibrational energy in the body. In other embodiments, the shape memory alloy layer is a thin film. Additional embodiments include a sensor connected to the material.

A model of energetic ion effects on pressure driven tearing modes in tokamaks

DOE PAGES

Halfmoon, M. R.; Brennan, D. P.

2017-06-05

Here, the effects that energetic trapped ions have on linear resistive magnetohydrodynamic (MHD) instabilities are studied in a reduced model that captures the essential physics driving or damping the modes through variations in the magnetic shear. The drift-kinetic orbital interaction of a slowing down distribution of trapped energetic ions with a resistive MHD instability is integrated to a scalar contribution to the perturbed pressure, and entered into an asymptotic matching formalism for the resistive MHD dispersion relation. Toroidal magnetic field line curvature is included to model trapping in the particle distribution, in an otherwise cylindrical model. The focus is onmore » a configuration that is driven unstable to the m/n = 2/1 mode by increasing pressure, where m is the poloidal mode number and n is the toroidal. The particles and pressure can affect the mode both in the core region where there can be low and reversed shear and outside the resonant surface in significant positive shear. The results show that the energetic ions damp and stabilize the mode when orbiting in significant positive shear, increasing the marginal stability boundary. However, the inner core region contribution with low and reversed shear can drive the mode unstable. This effect of shear on the energetic ion pressure contribution is found to be consistent with the literature. These results explain the observation that the 2/1 mode was found to be damped and stabilized by energetic ions in delta δf-MHD simulations of tokamak experiments with positive shear throughout, while the 2/1 mode was found to be driven unstable in simulations of experiments with weakly reversed shear in the core. This is also found to be consistent with related experimental observations of the stability of the 2/1 mode changing significantly with core shear.« less

An Investigation of Rotorcraft Stability-Phase Margin Requirements in Hover

NASA Technical Reports Server (NTRS)

Blanken, Chris L.; Lusardi, Jeff A.; Ivler, Christina M.; Tischler, Mark B.; Hoefinger, Marc T.; Decker, William A.; Malpica, Carlos A.; Berger, Tom; Tucker, George E.

2009-01-01

A cooperative study was performed to investigate the handling quality effects from reduced flight control system stability margins, and the trade-offs with higher disturbance rejection bandwidth (DRB). The piloted simulation study, perform on the NASA-Ames Vertical Motion Simulator, included three classes of rotorcraft in four configurations: a utility-class helicopter; a medium-lift helicopter evaluated with and without an external slung load; and a large (heavy-lift) civil tiltrotor aircraft. This large aircraft also allowed an initial assessment of ADS-33 handling quality requirements for an aircraft of this size. Ten experimental test pilots representing the U.S. Army, Marine Corps, NASA, rotorcraft industry, and the German Aerospace Center (DLR), evaluated the four aircraft configurations, for a range of flight control stability-margins and turbulence levels, while primarily performing the ADS-33 Hover and Lateral Reposition MTEs. Pilot comments and aircraft-task performance data were analyzed. The preliminary stability margin results suggest higher DRB and less phase margin cases are preferred as the aircraft increases in size. Extra care will need to be taken to assess the influence of variability when nominal flight control gains start with reduced margins. Phase margins as low as 20-23 degrees resulted in low disturbance-response damping ratios, objectionable oscillations, PIO tendencies, and a perception of an incipient handling qualities cliff. Pilot comments on the disturbance response of the aircraft correlated well to the DRB guidelines provided in the ADS-33 Test Guide. The A D-3S3 mid-term response-to-control damping ratio metrics can be measured and applied to the disturbance-response damping ratio. An initial assessment of LCTR yaw bandwidth shows the current Level 1 boundary needs to be relaxed to help account for a large pilot off-set from the c.g. Future efforts should continue to investigate the applicability/refinement of the current ADS-33 requirements to large vehicles, like an LCTR.

A model of energetic ion effects on pressure driven tearing modes in tokamaks

DOE Office of Scientific and Technical Information (OSTI.GOV)

Halfmoon, M. R.; Brennan, D. P.

Here, the effects that energetic trapped ions have on linear resistive magnetohydrodynamic (MHD) instabilities are studied in a reduced model that captures the essential physics driving or damping the modes through variations in the magnetic shear. The drift-kinetic orbital interaction of a slowing down distribution of trapped energetic ions with a resistive MHD instability is integrated to a scalar contribution to the perturbed pressure, and entered into an asymptotic matching formalism for the resistive MHD dispersion relation. Toroidal magnetic field line curvature is included to model trapping in the particle distribution, in an otherwise cylindrical model. The focus is onmore » a configuration that is driven unstable to the m/n = 2/1 mode by increasing pressure, where m is the poloidal mode number and n is the toroidal. The particles and pressure can affect the mode both in the core region where there can be low and reversed shear and outside the resonant surface in significant positive shear. The results show that the energetic ions damp and stabilize the mode when orbiting in significant positive shear, increasing the marginal stability boundary. However, the inner core region contribution with low and reversed shear can drive the mode unstable. This effect of shear on the energetic ion pressure contribution is found to be consistent with the literature. These results explain the observation that the 2/1 mode was found to be damped and stabilized by energetic ions in delta δf-MHD simulations of tokamak experiments with positive shear throughout, while the 2/1 mode was found to be driven unstable in simulations of experiments with weakly reversed shear in the core. This is also found to be consistent with related experimental observations of the stability of the 2/1 mode changing significantly with core shear.« less

Full wave simulations of fast wave efficiency and power losses in the scrape-off layer of tokamak plasmas in mid/high harmonic and minority heating regimes

DOE PAGES

Bertelli, N.; Jaeger, E. F.; Hosea, J. C.; ...

2015-12-17

Here, several experiments on different machines and in different fast wave (FW) heating regimes, such as hydrogen minority heating and high harmonic fast waves (HHFW), have found strong interaction between radio-frequency (RF) waves and the scrape-off layer (SOL) region. This paper examines the propagation and the power loss in the SOL by using the full wave code AORSA, in which the edge plasma beyond the last closed flux surface (LCFS) is included in the solution domain and a collisional damping parameter is used as a proxy to represent the real, and most likely nonlinear, damping processes. 2D and 3D AORSAmore » results for the National Spherical Torus eXperiment (NSTX) have shown a strong transition to higher SOL power losses (driven by the RF field) when the FW cut-off is removed from in front of the antenna by increasing the edge density. Here, full wave simulations have been extended for 'conventional' tokamaks with higher aspect ratios, such as the DIII-D, Alcator C-Mod, and EAST devices. DIII-D results in HHFW regime show similar behavior found in NSTX and NSTX-U, consistent with previous DIII-D experimental observations. In contrast, a different behavior has been found for C-Mod and EAST, which operate in the minority heating regime.« less

Theoretical Study of Gilbert Damping and Spin Dynamics in Spintronic Devices

NASA Astrophysics Data System (ADS)

Qu, Tao

The determination of damping mechanisms is one of the most fundamental problems of magnetism. It represents the elimination of the magnetic energy and thus has broad impact in both science and technology. The dynamic time scale in spintronic devices is controlled by the damping and the consumed power depends on the damping constant squared. In recent years, the interest in high perpendicular anisotropy materials and thin film structures have increased considerably, owing to their stability over a wide temperature range when scaling devices to nanometer length scales. However, the conventional measurement method-Ferromagnetic resonance (FMR) can not produce accurate damping results in the high magnetic crystalline anisotropy materials/structures, and the intrinsic damping reported experimentally diverges among investigators, probably due to the varying fabrication techniques. This thesis describes the application of the Kambersky torque correlation technique, within the tight binding method, to multiple materials with high perpendicular magnetic anisotropy ( 10 7 erg/cm3), in both bulk and thin film structures. The impact of the inevitable experimental defects on the energy dissipation is identified and the experimental damping divergence among investigators due to the material degree of order is explained. It is demonstrated that this corresponds to an enhanced DOS at the Fermi level, owing to the rounding of the DOS with loss of long-range order. The consistency of the predicted damping constant with experimental measurement is demonstrated and the interface contribution to the energy damping constant in potential superlattices and heterostructures for spintronic devices is explored. An optimized structure will be a tradeoff involving both anisotropy and damping. The damping related spin dynamics in spintronic devices for different applications is investigated. One device is current perpendicular to planes(CPP) spin valve. Incoherent scattering matrices are applied to calculate the angle dependent magnetoresistantce and obtain analytic expressions for the spin valve. The non-linearity of magnetoresistance can be quantitatively explained by reflected electrons using only experimental spin polarization as input. The other device is a spin-transfer-torque nano-oscillator. The Landau-Lifshitz-Gilbert equation is applied and the synchronization requirement for experimentally fabricated non-identical multi spintronic oscillators is explored. Power enhancement and noise decrease for the synchronized state is demonstrated in a temperature range. Through introducing combined electric and magnetic coupling effect, a design for an optimized feasible nanopillar structure suitable for thin-film deposition is developed.

Evaluation of a Heuristic Model for Tropical Cyclone Resilience

DTIC Science & Technology

2015-01-26

in which the effective static stability vanishes in rising and sinking regions, the 13 heuristic model yields a poor approximation to the simulated...tilt configuration. However, in the moist-neutral 12 limit, in which the effective static stability vanishes in rising and sinking regions, the 13...larger, leading to more effective 13 damping of the tilt mode (e.g., Schecter and Montgomery 2007; see their Figs. 10 and 11 14 and accompanying

Bifurcation analysis of parametrically excited bipolar disorder model

NASA Astrophysics Data System (ADS)

Nana, Laurent

2009-02-01

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

Design of an unified chassis controller for rollover prevention, manoeuvrability and lateral stability

NASA Astrophysics Data System (ADS)

Yoon, Jangyeol; Yim, Seongjin; Cho, Wanki; Koo, Bongyeong; Yi, Kyongsu

2010-11-01

This paper describes a unified chassis control (UCC) strategy to prevent vehicle rollover and improve both manoeuvrability and lateral stability. Since previous researches on rollover prevention are only focused on the reduction of lateral acceleration, the manoeuvrability and lateral stability cannot be guaranteed. For this reason, it is necessary to design a UCC controller to prevent rollover and improve lateral stability by integrating electronic stability control, active front steering and continuous damping control. This integration is performed through switching among several control modes and a simulation is performed to validate the proposed method. Simulation results indicate that a significant improvement in rollover prevention, manoeuvrability and lateral stability can be expected from the proposed UCC system.

A numerical retroaction model relates rocky coast erosion to percolation theory

NASA Astrophysics Data System (ADS)

Sapoval, B.; Baldassarri, A.

2011-12-01

Rocky coasts are estimated to represent 75% of the world's shorelines [1]. We discuss various situations where the formation of rocky coast morphology could be attributed to the retroaction of the coast morphology on the erosive power of the see. In the case of rocky coasts, erosion can spontaneously create irregular seashores. But, in turn, the geometrical irregularity participates to the damping of sea-waves, decreasing the average wave amplitude and erosive power. There may then exist a mutual self-stabilization of the waves amplitude together with the irregular morphology of the coast. A simple model of such stabilization is discussed. It leads, through a complex avalanche dynamics of the earth-sea interface, to the spontaneous appearance of an irregular sea-shore. The final coast morphology is found to depend on the morphology/damping coupling of the coast and on the possible existence of built-in correlations within the coast lithologic properties. In the limit case where the morphology/damping coupling is weak and when the earth lithology distribution exhibit only short range correlations, the process spontaneously build fractal morphologies with a dimension close to 4/3 [2]. This dimension refers to the dimension of the accessible perimeter in percolation theory. However, even rugged but non-fractal sea-coasts morphology may emerge for strong damping or during the erosion process. When the distributions of the lithologies exhibit long range correlations, a variety of complex morphologies are obtained which mimics observed coastline complexity, well beyond simple fractality. This approach, which links erosion of rocky coasts to percolation theory, provide a natural frame to explain the frequent field observation that the statistics of erosion events follow power law behavior. In a somewhat different perspective, the design of breakwaters is suggested to be improved by using global irregular geometry with features sizes of the order of the wave-length of the sea oscillations. [1] R. A. Davis, Jr, D. M. Fitzgerald, Beaches and Coasts,(Blackwell, Oxford 2004). [2] B. Sapoval, A. Baldassarri, A. Gabrielli, Self-stabilized Fractality of Sea-coasts through Erosion, Phys. Rev. Lett. 93, 098501 (2004).

Retro-action model for the erosion of rocky coasts

NASA Astrophysics Data System (ADS)

Sapoval, B.; Baldassarri, A.

2009-12-01

Rocky coasts are estimated to represent 75% of the world’s shorelines [1]. We discuss various situations where the formation of rocky coast morphology could be attributed to the retro-action of the coast morphology on the erosive power of the see. In the case of rocky coasts, erosion can spontaneously create irregular seashores. But, in turn, the geometrical irregularity participates to the damping of sea-waves, decreasing the average wave amplitude and erosive power. There may then exist a mutual self-stabilization of the waves amplitude together with the irregular morphology of the coast. A simple model of such stabilization is discussed. It leads, through a complex dynamics of the earth-sea interface, to the spontaneous appearance of an irregular sea-shore. The final coast morphology is found to depend on the morphology/damping coupling of the coast and on the possible existence of built-in correlations within the coast lithologic properties. This is illustrated in the figure. In the limit case where the morphology/damping coupling is weak and when the earth lithology distribution exhibit only short range correlations, the process spontaneously build fractal morphologies with a dimension close to 4/3 [2]. It is shown that this dimension refers to the dimension of the so-called accessible perimeter in gradient percolation. However, even rugged but non-fractal sea-coasts morphology may emerge for strong damping or during the erosion process. When the distributions of the lithologies exhibit long range correlations, a variety of complex morphologies are obtained which mimics observed coastline complexity, well beyond simple fractality. On a somewhat different perspective, the design of breakwaters is suggested to be improved by using global irregular geometry with features sizes of the order of the wave-length of the sea oscillations. [1] R. A. Davis, Jr, D. M. Fitzgerald, Beaches and Coasts,(Blackwell, Oxford 2004). [2] B. Sapoval, A. Baldassarri, A. Gabrielli, Self-stabilized Fractality of Sea-coasts through Erosion, Phys. Rev. Lett. 93, 098501 (2004). Time evolution of the coastline morphology starting with a flat sea-shore. Left and right columns correspond respectively to weak and strong coupling. Top to bottom: suc- cessive morphologies with the final morphologies at the bottom.

Structural Dynamics and Control of Large Space Structures, 1982

NASA Technical Reports Server (NTRS)

Brumfield, M. L. (Compiler)

1983-01-01

Basic research in the control of large space structures is discussed. Active damping and control of flexible beams, active stabilization of flexible antenna feed towers, spacecraft docking, and robust pointing control of large space platform payloads are among the topics discussed.

Coupling between lower-tropospheric convective mixing and low-level clouds: Physical mechanisms and dependence on convection scheme.

PubMed

Vial, Jessica; Bony, Sandrine; Dufresne, Jean-Louis; Roehrig, Romain

2016-12-01

Several studies have pointed out the dependence of low-cloud feedbacks on the strength of the lower-tropospheric convective mixing. By analyzing a series of single-column model experiments run by a climate model using two different convective parametrizations, this study elucidates the physical mechanisms through which marine boundary-layer clouds depend on this mixing in the present-day climate and under surface warming. An increased lower-tropospheric convective mixing leads to a reduction of low-cloud fraction. However, the rate of decrease strongly depends on how the surface latent heat flux couples to the convective mixing and to boundary-layer cloud radiative effects: (i) on the one hand, the latent heat flux is enhanced by the lower-tropospheric drying induced by the convective mixing, which damps the reduction of the low-cloud fraction, (ii) on the other hand, the latent heat flux is reduced as the lower troposphere stabilizes under the effect of reduced low-cloud radiative cooling, which enhances the reduction of the low-cloud fraction. The relative importance of these two different processes depends on the closure of the convective parameterization. The convective scheme that favors the coupling between latent heat flux and low-cloud radiative cooling exhibits a stronger sensitivity of low-clouds to convective mixing in the present-day climate, and a stronger low-cloud feedback in response to surface warming. In this model, the low-cloud feedback is stronger when the present-day convective mixing is weaker and when present-day clouds are shallower and more radiatively active. The implications of these insights for constraining the strength of low-cloud feedbacks observationally is discussed.

Coupling between lower‐tropospheric convective mixing and low‐level clouds: Physical mechanisms and dependence on convection scheme

PubMed Central

Bony, Sandrine; Dufresne, Jean‐Louis; Roehrig, Romain

2016-01-01

Abstract Several studies have pointed out the dependence of low‐cloud feedbacks on the strength of the lower‐tropospheric convective mixing. By analyzing a series of single‐column model experiments run by a climate model using two different convective parametrizations, this study elucidates the physical mechanisms through which marine boundary‐layer clouds depend on this mixing in the present‐day climate and under surface warming. An increased lower‐tropospheric convective mixing leads to a reduction of low‐cloud fraction. However, the rate of decrease strongly depends on how the surface latent heat flux couples to the convective mixing and to boundary‐layer cloud radiative effects: (i) on the one hand, the latent heat flux is enhanced by the lower‐tropospheric drying induced by the convective mixing, which damps the reduction of the low‐cloud fraction, (ii) on the other hand, the latent heat flux is reduced as the lower troposphere stabilizes under the effect of reduced low‐cloud radiative cooling, which enhances the reduction of the low‐cloud fraction. The relative importance of these two different processes depends on the closure of the convective parameterization. The convective scheme that favors the coupling between latent heat flux and low‐cloud radiative cooling exhibits a stronger sensitivity of low‐clouds to convective mixing in the present‐day climate, and a stronger low‐cloud feedback in response to surface warming. In this model, the low‐cloud feedback is stronger when the present‐day convective mixing is weaker and when present‐day clouds are shallower and more radiatively active. The implications of these insights for constraining the strength of low‐cloud feedbacks observationally is discussed. PMID:28239438

Heat stabilization of blood spot samples for determination of metabolically unstable drug compounds

PubMed Central

Blessborn, Daniel; Sköld, Karl; Zeeberg, David; Kaewkhao, Karnrawee; Sköld, Olof; Ahnoff, Martin

2014-01-01

Background Sample stability is critical for accurate analysis of drug compounds in biosamples. The use of additives to eradicate the enzymatic activity causing loss of these analytes has its limitations. Results A novel technique for sample stabilization by rapid, high-temperature heating was used. The stability of six commercial drugs in blood and blood spots was investigated under various conditions with or without heat stabilization at 95°C. Oseltamivir, cefotaxime and ribavirin were successfully stabilized by heating whereas significant losses were seen in unheated samples. Amodiaquine was stable with and without heating. Artemether and dihydroartemisinin were found to be very heat sensitive and began to decompose even at 60°C. Conclusion Heat stabilization is a viable technique to maintain analytes in blood spot samples, without the use of chemical additives, by stopping the enzymatic activity that causes sample degradation. PMID:23256470

Lower solar chromosphere-corona transition region. II - Wave pressure effects for a specific form of the heating function

NASA Technical Reports Server (NTRS)

Woods, D. Tod; Holzer, Thomas E.; Macgregor, Keith B.

1990-01-01

Lower transition region models with a balance between mechanical heating and radiative losses are expanded to include wave pressure effects. The models are used to study the simple damping length form of the heating function. The results are compared to the results obtained by Woods et al. (1990) for solutions in the lower transition region. The results suggest that a mixture of fast-mode and slow-mode waves may provide the appropriate heating mechanism in the lower transition region, with the decline in effective vertical wave speed caused by the refraction and eventual total reflection of the fast-mode wave resulting from the decreasing atmospheric density.

Wangen EVS-solarhouse with a positive balance sheet

NASA Astrophysics Data System (ADS)

1980-05-01

The results achieved with a solar house after one year of operation are reviewed. It is stressed that conventional solar collectors are not sufficient for heating the test house. Further, improvements are also needed for the task of hot water heating. Other disadvantages of solar collectors and of heatpumps working only with ambient air are discussed. It is demonstrated that a heat pump system using solar absorbers and a heat storage tank of damp soil, achieved the best results. In addition, such solar absorbers can be used in a decorative fashion, such as fences, which improves their marketability. Finally, it is noted that the widespread use of such systems will require an adequate supply of electricity.

Empirical Constraints on Proton and Electron Heating in the Fast Solar Wind

NASA Technical Reports Server (NTRS)

Cranmer, Steven R.; Matthaeus, William H.; Breech, Benjamin A.; Kasper, Justin C.

2009-01-01

This paper presents analyses of measured proton and electron temperatures in the high-speed solar wind that are used to calculate the separate rates of heat deposition for protons and electrons. It was found that the protons receive about 60% of the total plasma heating in the inner heliosphere, and that this fraction increases to approximately 80% by the orbit of Jupiter. The empirically derived partitioning of heat between protons and electrons is in rough agreement with theoretical predictions from a model of linear Vlasov wave damping. For a modeled power spectrum consisting only of Alfvenic fluctuations, the best agreement was found for a distribution of wavenumber vectors that evolves toward isotropy as distance increases.

Investigation at low speeds of the effect of aspect ratio and sweep on rolling stability derivatives of untapered wings

NASA Technical Reports Server (NTRS)

Goodman, Alex; Fisher, Lewis R.

1949-01-01

A low scale wind tunnel investigation was conducted in rolling flow to determine the effects of aspect ratio and sweep (when varied independently) on the rolling stability derivatives for a series of untapered wings. Test results indicate that when the aspect ratio was held constant, an increase in the sweepback angle caused a significant reduction in the damping in roll at low lift coefficients for only the higher aspect ratios that were tested. This result was in agreement with available swept wing theory which indicated no effect of sweep for aspect ratios near zero. The result of the linear theory that the damping in roll is independent of lift coefficient and that the yawing moment and lateral force due to rolling are directly proportional to the lift coefficient was found to be valid for only a very limited lift coefficient range when the wings were highly swept. For such wings, the damping was found to increase in magnitude and the yawing moment due to rolling, to change from negative to positive at moderate lift coefficients. The effect of wing tip suction, not acounted for by present theory, was found to be very important with regard to the yawing moment due to rolling, particularly for low aspect ratio swept wings. An empirical means of correcting present theory for the effect of tip suction is suggested.

Effect of Extended State Observer and Automatic Voltage Regulator on Synchronous Machine Connected to Infinite Bus Power System

NASA Astrophysics Data System (ADS)

Angu, Rittu; Mehta, R. K.

2018-04-01

This paper presents a robust controller known as Extended State Observer (ESO) in order to improve the stability and voltage regulation of a synchronous machine connected to an infinite bus power system through a transmission line. The ESO-based control scheme is implemented with an automatic voltage regulator in conjunction with an excitation system to enhance the damping of low frequency power system oscillations, as the Power System Stabilizer (PSS) does. The implementation of PSS excitation control techniques however requires reliable information about the entire states, though they are not always directly measureable. To address this issue, the proposed ESO provides the estimate of system states as well as disturbance state together in order to improve not only the damping but also compensates system efficiently in presence of parameter uncertainties and external disturbances. The Closed-Loop Poles (CLPs) of the system have been assigned by the symmetric root locus technique, with the desired level of system damping provided by the dominant CLPs. The performance of the system is analyzed through simulating at different operating conditions. The control method is not only capable of providing zero estimation error in steady-state, but also shows robustness in tracking the reference command under parametric variations and external disturbances. Illustrative examples have been provided to demonstrate the effectiveness of the developed methodology.

Control of rotordynamic instability in a typical gas turbine's power system

NASA Technical Reports Server (NTRS)

Veikos, N. M.; Page, R. H.; Tornillo, E. J.

1984-01-01

The effect of rotor internal friction on the system's stability was studied when operated above the first critical speed. This internal friction is commonly caused by sliding press fits or sliding splines. Under conditions of high speed and low bearing damping, these systems will occassionally whirl at a frequency less than the shaft's rotational speed. This subsynchronous precession is a self excited phenomenon and stress reversals are created. This phenomenon was observed during engine testing. The reduction of spline friction and/or the inclusion of squeeze film damping have controlled the instability. Case history and the detail design of the squeeze film dampers is discussed.

A structural dynamics study of a wing-pylon-tiltrotor system

NASA Astrophysics Data System (ADS)

Khader, N.; Abu-Mallouh, R.

1992-12-01

A simple structural model for a three-bladed tiltrotor-pylon-wing assembly is presented, which accounts for chordwise, transverse, and torsional wing deformations, rigid pylon pitching motion with respect to the wing tip cross-section in its deformed position, lead-lag, flap, and torsional deformations of rotor blades. The model considers equivalent viscous damping associated with blade and wing elastic deformations and with rigid pylon pitching motion. It is established that blade-to wing bending rigidity ratio, pylon pitching frequency, equivalent viscous damping associated with blade elastic deformations, and rotational speed, are the most important design parameters, whose effect on system frequencies and stability boundaries is evaluated.

ExoMars Entry Demonstrator Module Dynamic Stability

NASA Astrophysics Data System (ADS)

Dormieux, Marc; Gulhan, Ali; Berner, Claude

2011-05-01

In the frame of ExoMars DM aerodynamics characterization, pitch damping derivatives determination is required as it drives the parachute deployment conditions. Series of free-flight and free- oscillation tests (captive model) have been conducted with particular attention for data reduction. 6 Degrees- of-Freedom (DoF) analysis tools require the knowledge of local damping derivatives. In general ground tests do not provide them directly but only effective damping derivatives. Free-flight (ballistic range) tests with full oscillations around trim angle have been performed at ISL for 0.5

Combustion Dynamics and Stability Modeling of a Liquid Oxygen/RP-2 Oxygen-Rich Staged Combustion Preburner and Thrust Chamber Assembly with Gas-Centered Swirl Coaxial Injector Elements

NASA Technical Reports Server (NTRS)

Casiano, M. J.; Kenny, R. J.; Protz, C. S.; Garcia, C. P.; Simpson, S. P.; Elmore, J. L.; Fischbach, S. R.; Giacomoni, C. B.; Hulka, J. R.

2016-01-01

The Combustion Stability Tool Development (CSTD) project, funded by the Air Force Space and Missile Systems Center, began in March 2015 supporting a renewed interest in the development of a liquid oxygen/hydrocarbon, oxygen-rich combustion engine. The project encompasses the design, assembly, and hot-fire testing of the NASA Marshall Space Flight Center 40-klbf Integrated Test Rig (MITR). The test rig models a staged-combustion configuration by combining an oxygen-rich preburner (ORPB), to generate hot gas, with a thrust chamber assembly (TCA) using gas-centered swirl coaxial injector elements. There are five separately designed interchangeable injectors in the TCA that each contain 19- or 27- injector elements. A companion paper in this JANNAF conference describes the design characteristics, rationale, and fabrication issues for all the injectors. The data acquired from a heavily instrumented rig encompasses several injectors, several operating points, and stability bomb tests. Another companion paper in this JANNAF conference describes this test program in detail. In this paper, dynamic data from the hot-fire testing is characterized and used to identify the responses in the ORPB and TCA. A brief review of damping metrics are discussed and applied as a measure of stability margin for damped acoustic modes. Chug and longitudinal combustion stability models and predictions are described which includes new dynamic models for compressible flow through an orifice and a modification to incorporate a third feed line for inclusion of the fuel-film coolant. Flow-acoustics finite element modeling is used to investigate the anticipated TCA acoustics, the effects of injector element length on stability margin, and the potential use of an ORPB orifice trip ring for improving longitudinal stability margin.

Supersonic dynamic stability characteristics of the test technique demonstrator NASP configuration

NASA Technical Reports Server (NTRS)

Dress, David A.; Boyden, Richmond P.; Cruz, Christopher I.

1992-01-01

Wind tunnel tests of a National Aero-Space Plane (NASP) configuration were conducted in both test sections of the Langley Unitary Plan Wind Tunnel. The model used is a Langley designed blended body NASP configuration. Dynamic stability characteristics were measured on this configuration at Mach numbers of 2.0, 2.5, 3.5, and 4.5. In addition to tests of the baseline configuration, component buildup tests were conducted. The test results show that the baseline configuration generally has positive damping about all three axes with only isolated exceptions. In addition, there was generally good agreement between the in-pulse dynamic parameters and the corresponding static data which were measured during another series of tests in the Unitary Plan Wind Tunnel. Also included are comparisons of the experimental damping parameters with results from the engineering predictive code APAS (Aerodynamic Preliminary Analysis System). These comparisons show good agreement at low angles of attack; however, the comparisons are generally not as good at the higher angles of attack.

Grain size effects on stability of nonlinear vibration with nanocrystalline NiTi shape memory alloy

NASA Astrophysics Data System (ADS)

Xia, Minglu; Sun, Qingping

2017-10-01

Grain size effects on stability of thermomechanical responses for a nonlinear torsional vibration system with nanocrystalline superelastic NiTi bar are investigated in the frequency and amplitude domains. NiTi bars with average grain size from 10 nm to 100 nm are fabricated through cold-rolling and subsequent annealing. Thermomechanical responses of the NiTi bar as a softening nonlinear damping spring in the torsional vibration system are obtained by synchronised acquisition of rotational angle and temperature under external sinusoidal excitation. It is shown that nonlinearity and damping capacity of the NiTi bar decrease as average grain size of the material is reduced below 100 nm. Therefore jump phenomena of thermomechanical responses become less significant or even vanish and the vibration system becomes more stable. The work in this paper provides a solid experimental base for manipulating the undesired jump phenomena of thermomechanical responses and stabilising the mechanical vibration system through grain refinement of NiTi SMA.

Active vibration absorber for CSI evolutionary model: Design and experimental results

NASA Technical Reports Server (NTRS)

Bruner, Anne M.; Belvin, W. Keith; Horta, Lucas G.; Juang, Jer-Nan

1991-01-01

The development of control of large flexible structures technology must include practical demonstration to aid in the understanding and characterization of controlled structures in space. To support this effort, a testbed facility was developed to study practical implementation of new control technologies under realistic conditions. The design is discussed of a second order, acceleration feedback controller which acts as an active vibration absorber. This controller provides guaranteed stability margins for collocated sensor/actuator pairs in the absence of sensor/actuator dynamics and computational time delay. The primary performance objective considered is damping augmentation of the first nine structural modes. Comparison of experimental and predicted closed loop damping is presented, including test and simulation time histories for open and closed loop cases. Although the simulation and test results are not in full agreement, robustness of this design under model uncertainty is demonstrated. The basic advantage of this second order controller design is that the stability of the controller is model independent.

On the Stability of Shocks with Particle Pressure

NASA Astrophysics Data System (ADS)

Finazzi, Stefano; Vietri, Mario

2008-11-01

We perform a linear stability analysis for corrugations of a Newtonian shock, with particle pressure included, for an arbitrary diffusion coefficient. We study first the dispersion relation for homogeneous media, showing that, besides the conventional pressure waves and entropy/vorticity disturbances, two new perturbation modes exist, dominated by the particles' pressure and damped by diffusion. We show that, due to particle diffusion into the upstream region, the fluid will be perturbed also upstream; we treat these perturbation in the short-wavelength (WKBJ) regime. We then show how to construct a corrugational mode for the shock itself, one, that is, where the shock executes free oscillations (possibly damped or growing) and sheds perturbations away from itself; this global mode requires the new modes. Then, using the perturbed Rankine-Hugoniot conditions, we show that this leads to the determination of the corrugational eigenfrequency. We solve numerically the equations for the eigenfrequency in the WKBJ regime for the models of Amato & Blasi, showing that they are stable. We then discuss the differences between our treatment and previous work.

Consequences of eccentricity and inclination damping for the in-situ formation of STIPs

NASA Astrophysics Data System (ADS)

Granados Contreras, Agueda Paula

2018-01-01

In Boley, Granados, and Gladman (2016), we proposed that hot and warm Jupiters could form in-situ from the consolidation of planets in meta-stable, high-multiplicity System with Tightly-packed Inner Planets (STIPs) in the presence of gas. Under this hypothesis, the timing of instability within the STIP relative to the gas depletion timescale can lead to a wide range of planetary diversity, from short-orbital period gas giants to high-density, massive planets. The simulations used Kepler-11 as a base and assumed that a gas giant could form if instability in the gaseous disc led to the consolidation of a 10 Mearth core. The results showed that such consolidation could work, in principle. However, in the simulations we excluded the effects of eccentricity and inclination damping. We present new simulations that explore this effect on the consolidation paradigm. For the parameters so far explored, gas damping significantly increases the stability of the system, although consolidation does occur in some cases. We further find that the eccentricity damping can lead to the formation of stable co-orbiting planets, although this is a rare outcome. Briefly, we explore the implications of the detection of transiting co-orbital planets.

Oscillation Amplitude Growth for a Decelerating Object with Constant Pitch Damping

NASA Technical Reports Server (NTRS)

Schoenenberger, Mark; Queen, Eric M.; Litton, Daniel

2006-01-01

The equations governing the deceleration and oscillation of a blunt body moving along a planar trajectory are re-expressed in the form of the Euler-Cauchy equation. An analytic solution of this equation describes the oscillation amplitude growth and frequency dilation with time for a statically stable decelerating body with constant pitch damping. The oscillation histories for several constant pitch damping values, predicted by the solution of the Euler-Cauchy equation are compared to POST six degree-of-freedom (6-DoF) trajectory simulations. The simulations use simplified aerodynamic coefficients matching the Euler-Cauchy approximations. Agreement between the model predictions and simulation results are excellent. Euler-Cauchy curves are also fit through nonlinear 6-DoF simulations and ballistic range data to identify static stability and pitch damping coefficients. The model os shown to closely fit through the data points and capture the behavior of the blunt body observed in simulation and experiment. The extracted coefficients are in reasonable agreement with higher fidelity, nonlinear parameter identification results. Finally, a nondimensional version of the Euler-Cauchy equation is presented and shown to be a simple and effective tool for designing dynamically scaled experiments for decelerating blunt capsule flight.

Modelisation de l'instabilite fluidelastique d'un faisceau de tubes soumis a un ecoulement diphasique transverse

NASA Astrophysics Data System (ADS)

Sawadogo, Teguewinde

This study focuses on the modeling of fluidelastic instability induced by two-phase cross-flow in tube bundles of steam generators. The steam generators in CANDU type nuclear power plants for e.g., designed in Canada by AECL and exploited worldwide, have thousands of tubes assembled in bundles that ensure the heat exchange between the internal circuit of heated heavy water coming from the reactor core and the external circuit of light water evaporated and directed toward the turbines. The main objective of this research project is to extend the theoretical models for fluidelastic instability to two-phase flow, validate the models and develop a computer program for simulating flow induced vibrations in tube bundles. The quasi-steady model has been investigated in scope of this research project. The time delay between the structure motion and the fluid forces generated thereby has been extensively studied in two-phase flow. The study was conducted for a rotated triangular tube array. Firstly, experimental measurements of unsteady and quasi-static fluid forces (in the lift direction) acting on a tube subject to two-phase flow were conducted. Quasi-static fluid force coefficients were measured at the same Reynolds number, Re = 2.8x104, for void fractions ranging from 0% to 80%. The derivative of the lift coefficient with respect to the quasi-static dimensionless displacement in the lift direction was deduced from the experimental measurements. This derivative is one of the most important parameters of the quasi-steady model because this parameter, in addition to the time delay, generates the fluid negative damping that causes the instability. This derivative was found to be positive in liquid flow and negative in two-phase flow. It seemed to vanish at 5% of void fraction, challenging the ability of the quasi-steady model to predict fluidelastic instability in this case. However, stability tests conducted at 5% void fraction clearly showed fluidelastic instability. Stability tests were conducted in the second stage of the project to validate the theoretical model. The two phase damping, the added mass and the critical velocity for fluidelastic instability were measured in two-phase flow. A viscoelastic damper was designed to vary the damping of the flexible tube and thus measure the critical velocity for a certain range of the mass-damping parameter. A new formulation of the added mass as a function of the void fraction was proposed. This formulation has a better agreement with the experimental results because it takes into account the reduction of the void fraction in the vicinity of the tubes in a rotated triangular tube array. The experimental data were used to validate the theoretical results of the quasi-steady model. The validity of the quasi-steady model for two-phase flow was confirmed by the good agreement between its results and the experimental data. The time delay parameter determined in the first stage of the project has improved significantly the theoretical results, especially for high void fractions (90%). However, the model could not be verified for void fractions lower or equal to 50% because of the limitation of the water pump capability. Further studies are consequently required to clarify this point. However, this model can be used to simulate the flow induced vibrations in steam generators' tube bundles as their most critical parts operate at high void fractions (≥ 60%). Having verified the quasi-steady model for high void fractions in two-phase flow, the third and final stage of the project was devoted to the development of a computer code for simulating flow induced vibrations of a steam generator tube subjected to fluidelastic and turbulence forces. This code was based on the ABAQUS finite elements code for solving the equation of motion of the fluid-structure system, and a development of a subroutine in which the fluid forces are calculated and applied to the tube. (Abstract shortened by UMI.)

7 CFR 29.3002 - Air-cured.

Code of Federal Regulations, 2013 CFR

2013-01-01

... 7 Agriculture 2 2013-01-01 2013-01-01 false Air-cured. 29.3002 Section 29.3002 Agriculture... Air-cured. Tobacco cured under natural atmospheric conditions. Artificial heat is sometimes used to control excess humidity during the curing period to prevent house-burn and barn-burn in damp weather. Air...

7 CFR 29.3002 - Air-cured.

Code of Federal Regulations, 2012 CFR

2012-01-01

... 7 Agriculture 2 2012-01-01 2012-01-01 false Air-cured. 29.3002 Section 29.3002 Agriculture... Air-cured. Tobacco cured under natural atmospheric conditions. Artificial heat is sometimes used to control excess humidity during the curing period to prevent house-burn and barn-burn in damp weather. Air...

7 CFR 29.3002 - Air-cured.

Code of Federal Regulations, 2014 CFR

2014-01-01

... 7 Agriculture 2 2014-01-01 2014-01-01 false Air-cured. 29.3002 Section 29.3002 Agriculture... Air-cured. Tobacco cured under natural atmospheric conditions. Artificial heat is sometimes used to control excess humidity during the curing period to prevent house-burn and barn-burn in damp weather. Air...

7 CFR 29.3002 - Air-cured.

Code of Federal Regulations, 2011 CFR

2011-01-01

... 7 Agriculture 2 2011-01-01 2011-01-01 false Air-cured. 29.3002 Section 29.3002 Agriculture... Air-cured. Tobacco cured under natural atmospheric conditions. Artificial heat is sometimes used to control excess humidity during the curing period to prevent house-burn and barn-burn in damp weather. Air...

7 CFR 29.3002 - Air-cured.

Code of Federal Regulations, 2010 CFR

2010-01-01

... 7 Agriculture 2 2010-01-01 2010-01-01 false Air-cured. 29.3002 Section 29.3002 Agriculture... Air-cured. Tobacco cured under natural atmospheric conditions. Artificial heat is sometimes used to control excess humidity during the curing period to prevent house-burn and barn-burn in damp weather. Air...

Ion and electron heating characteristics of magnetic reconnection in tokamak plasma merging experiments

NASA Astrophysics Data System (ADS)

Ono, Y.; Tanabe, H.; Yamada, T.; Inomoto, M.; T, Ii; Inoue, S.; Gi, K.; Watanabe, T.; Gryaznevich, M.; Scannell, R.; Michael, C.; Cheng, C. Z.

2012-12-01

Recently, the TS-3 and TS-4 tokamak merging experiments revealed significant plasma heating during magnetic reconnection. A key question is how and where ions and electrons are heated during magnetic reconnection. Two-dimensional measurements of ion and electron temperatures and plasma flow made clear that electrons are heated inside the current sheet mainly by the Ohmic heating and ions are heated in the downstream areas mainly by the reconnection outflows. The outflow kinetic energy is thermalized by the fast shock formation and viscous damping. The magnetic reconnection converts the reconnecting magnetic field energy mostly to the ion thermal energy in the outflow region whose size is much larger than the current sheet size for electron heating. The ion heating energy is proportional to the square of the reconnection magnetic field component B_p^2 . This scaling of reconnection heating indicates the significant ion heating effect of magnetic reconnection, which leads to a new high-field reconnection heating experiment for fusion plasmas.

Development of the novel ferrous-based stainless steel for biomedical applications, part I: high-temperature microstructure, mechanical properties and damping behavior.

PubMed

Wu, Ching-Zong; Chen, Shih-Chung; Shih, Yung-Hsun; Hung, Jing-Ming; Lin, Chia-Cheng; Lin, Li-Hsiang; Ou, Keng-Liang

2011-10-01

This research investigated the high-temperature microstructure, mechanical properties, and damping behavior of Fe-9 Al-30 Mn-1C-5 Co (wt.%) alloy by means of electron microscopy, experimental model analysis, and hardness and tensile testing. Subsequent microstructural transformation occurred when the alloy under consideration was subjected to heat treatment in the temperature range of 1000-1150 °C: γ → (γ+κ). The κ-phase carbides had an ordered L'1(2)-type structure with lattice parameter a = 0.385 nm. The maximum yield strength (σ(y)), hardness, elongation, and damping coefficient of this alloy are 645 MPa, Hv 292, ~54%, and 178.5 × 10(-4), respectively. These features could be useful in further understanding the relationship between the biocompatibility and the wear and corrosion resistance of the alloy, so as to allow the development of a promising biomedical material. Copyright © 2011 Elsevier Ltd. All rights reserved.

The influence of dynamic inflow and torsional flexibility on rotor damping in forward flight from symbolically generated equations

NASA Technical Reports Server (NTRS)

Reddy, T. S. R.; Warmbrodt, W.

1985-01-01

The combined effects of blade torsion and dynamic inflow on the aeroelastic stability of an elastic rotor blade in forward flight are studied. The governing sets of equations of motion (fully nonlinear, linearized, and multiblade equations) used in this study are derived symbolically using a program written in FORTRAN. Stability results are presented for different structural models with and without dynamic inflow. A combination of symbolic and numerical programs at the proper stage in the derivation process makes the obtainment of final stability results an efficient and straightforward procedure.

Experimental Investigations of Generalized Predictive Control for Tiltrotor Stability Augmentation

NASA Technical Reports Server (NTRS)

Nixon, Mark W.; Langston, Chester W.; Singleton, Jeffrey D.; Piatak, David J.; Kvaternik, Raymond G.; Bennett, Richard L.; Brown, Ross K.

2001-01-01

A team of researchers from the Army Research Laboratory, NASA Langley Research Center (LaRC), and Bell Helicopter-Textron, Inc. have completed hover-cell and wind-tunnel testing of a 1/5-size aeroelastically-scaled tiltrotor model using a new active control system for stability augmentation. The active system is based on a generalized predictive control (GPC) algorithm originally developed at NASA LaRC in 1997 for un-known disturbance rejection. Results of these investigations show that GPC combined with an active swashplate can significantly augment the damping and stability of tiltrotors in both hover and high-speed flight.

Lateral stability analysis for X-29A drop model using system identification methodology

NASA Technical Reports Server (NTRS)

Raney, David L.; Batterson, James G.

1989-01-01

A 22-percent dynamically scaled replica of the X-29A forward-swept-wing airplane has been flown in radio-controlled drop tests at the NASA Langley Research Center. A system identification study of the recorded data was undertaken to examine the stability and control derivatives that influence the lateral behavior of this vehicle with particular emphasis on an observed wing rock phenomenon. All major lateral stability derivatives and the damping-in-roll derivative were identified for angles of attack from 5 to 80 degrees by using a data-partitioning methodology and a modified stepwise regression algorithm.

Stabilization of computational procedures for constrained dynamical systems

NASA Technical Reports Server (NTRS)

Park, K. C.; Chiou, J. C.

1988-01-01

A new stabilization method of treating constraints in multibody dynamical systems is presented. By tailoring a penalty form of the constraint equations, the method achieves stabilization without artificial damping and yields a companion matrix differential equation for the constraint forces; hence, the constraint forces are obtained by integrating the companion differential equation for the constraint forces in time. A principal feature of the method is that the errors committed in each constraint condition decay with its corresponding characteristic time scale associated with its constraint force. Numerical experiments indicate that the method yields a marked improvement over existing techniques.

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.

Modeling of Synergy Between 4th and 6th Harmonic Absorptions of Fast Waves on Injected Beams in DIII-D Tokamak

DOE Office of Scientific and Technical Information (OSTI.GOV)

Choi, M.; Pinsker, R. I.; Chan, V. S.

2011-12-23

In recent moderate to high harmonic fast wave heating and current drive experiments in DIII-D, a synergy effect was observed when the 6{sup th} harmonic 90 MHz fast wave power is applied to the plasma preheated by neutral beams and the 4{sup th} harmonic 60 MHz fast wave. In this paper, we investigate how the synergy can occur using ORBIT-RF coupled with AORSA. Preliminary simulations suggest that damping of 4{sup th} harmonic FW on beam ions accelerates them above the injection energy, which may allow significant damping of 6{sup th} harmonic FW on beam ion tails to produce synergy.

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.

TEM heat transport and fluctuations in the HSX stellarator: experiments and comparison with gyrokinetic simulation

NASA Astrophysics Data System (ADS)

Smoniewski, J.; Faber, B. J.; Sánchez, E.; Calvo, I.; Pueschel, M. J.; Likin, K. M.; Deng, C. B.; Talmadge, J. N.

2017-10-01

The Helically Symmetric eXperiment (HSX) has demonstrated reduced neoclassical transport in the plasma core with quasi-symmetry [Lore Thesis 2010], while outside this region the electron thermal diffusivity is well above the neoclassical level, likely due to the Trapped Electron Mode (TEM) [Weir PoP 2015, Faber PoP 2015]. We compare gyrokinetic simulations of the TEM to experimental heat flux and density fluctuation measurements for two configurations: Quasi-Helical Symmetry (QHS) and broken symmetry (Mirror). Both experiment and simulation show that the heat flux for Mirror is larger than for QHS by about a factor of two. Initial interferometer measurements provide evidence that density-gradient-driven TEMs are driving turbulence. Calculations of the collisionless damping of zonal flows provide another perspective into the difference between geometries. Similar to other stellarators [Monreal PPCF 2016], the zonal flow residual goes to zero at long wavelengths in both configurations. Additionally, the very short time decay of the zonal flow due to neoclassical polarization is constant between configurations. However, the collisionless damping time is longer and the zonal flow oscillation frequency is smaller in QHS than Mirror, consistent with reduced radial particle drifts. Work supported by the US DOE under Grant DE-FG02-93ER54222.

Electron Heating and Acceleration from High Amplitude Driven Alfvén Waves in the LAPD

NASA Astrophysics Data System (ADS)

Auerbach, David; Carter, Troy; Brugman, Brian

2006-10-01

High amplitude (δB/B ˜1 %) shear Alfvén waves are generated in the Large Plasma Device Upgrade (LAPD) at UCLA, and elevated electron temperatures and high energy electrons are observed using triple probes and Langmuir current traces. The Poynting flux of the observed waves is calculated, and wave power is compared to estimates of power input required to cause the observed heating. Theoretical calculations of power transfer from wave to plasma due to Landau damping and collisional heating are also presented and compared to experimental measurements. Heating by antenna near field effects is also being explored. The density and potential structures of these waves are explored using interferometer and triple probe measurements. Applications to Auroral generation and plasma heating are discussed.

Achievements and challenges in legume breeding for pest and disease resistance

USDA-ARS?s Scientific Manuscript database

Yield stability of legume crops is constrained by a number of pest and diseases. Major diseases are rusts, powdery and downy mildews, ascochyta blight, botrytis gray molds, anthracnoses, damping-off, root rots, collar rot, vascular wilts and white mold. Parasitic weeds, viruses, bacteria, nematodes ...

[Effect of heat transfer in the packages on the stability of thiamine nitrate under uncontrolled temperature conditions].

PubMed

Nakamura, Toru; Yamaji, Takayuki; Takayama, Kozo

2013-01-01

To accurately predict the stability of thiamine nitrate as a model drug in pharmaceutical products under uncontrolled temperature conditions, the average reaction rate constant was determined, taking into account the heat transfer from the atmosphere to the product. The stability tests of thiamine nitrate in the three packages with different heat transfers were performed under non-isothermal conditions. The stability data observed were compared with the predictions based on a newly developed method, showing that the stability was well predicted by the method involving the heat transfer. By contrast, there were some deviations observed from the predicted data, without considering heat transfer in the packages with low heat transfer. The above-mentioned result clearly shows that heat transfer should be considered to ensure accurate prediction of the stability of commercial pharmaceutical products under non-isothermal atmospheres.

Interactions Between the Thermohaline Circulation and Tropical Atlantic SST in a Coupled General Circulation Model

NASA Technical Reports Server (NTRS)

Miller, Ron; Jiang, Xing-Jian; Travis, Larry (Technical Monitor)

2001-01-01

Tropical Atlantic SST shows a (statistically well-defined) decadal time scale in a 104-year simulation of unforced variability by a coupled general circulation model (CGCM). The SST anomalies superficially resemble observed Tropical Atlantic variability (TAV), and are associated with changes in the atmospheric circulation. Brazilian rainfall is modulated with a decadal time scale, along with the strength of the Atlantic trade winds, which are associated with variations in evaporation and the net surface heat flux. However, in contrast to observed tropical Atlantic variability, the trade winds damp the associated anomalies in ocean temperature, indicating a negative feedback. Tropical SST anomalies in the CGCM, though opposed by the surface heat flux, are advected in from the Southern Hemisphere mid-latitudes. These variations modulate the strength of the thermohaline circulation (THC): warm, salty anomalies at the equator sink drawing cold, fresh mid-latitude water. Upon reaching the equator, the latter inhibit vertical overturning and advection from higher latitudes, which allows warm, salty anomalies to reform, returning the cycle to its original state. Thus, the cycle results from advection of density anomalies and the effect of these anomalies upon the rate of vertical overturning and surface advection. This decadal modulation of Tropical Atlantic SST and the thermohaline circulation is correlated with ocean heat transport to the Northern Hemisphere high latitudes and Norwegian Sea SST. Because of the central role of equatorial convection, we question whether this mechanism is present in the current climate, although we speculate that it may have operated in palaeo times, depending upon the stability of the tropical water column.

Numerical and Experimental Characterizations of Damping Properties of SMAs Composite for Vibration Control Systems

NASA Astrophysics Data System (ADS)

Biffi, Carlo Alberto; Bassani, P.; Tuissi, A.; Carnevale, M.; Lecis, N.; LoConte, A.; Previtali, B.

2012-12-01

Shape memory alloys (SMAs) are very interesting smart materials not only for their shape memory and superelastic effects but also because of their significant intrinsic damping capacity. The latter is exhibited upon martensitic transformations and especially in martensitic state. The combination of these SMA properties with the mechanical and the lightweight of fiberglass-reinforced polymer (FGRP) is a promising solution for manufacturing of innovative composites for vibration suppression in structural applications. CuZnAl sheets, after laser patterning, were embedded in a laminated composite between a thick FGRP core and two thin outer layers with the aim of maximizing the damping capacity of the beam for passive vibration suppression. The selected SMA Cu66Zn24Al10 at.% was prepared by vacuum induction melting; the ingot was subsequently hot-and-cold rolled down to 0.2 mm thickness tape. The choice of a copper alloy is related to some advantages in comparison with NiTiCu SMA alloys, which was tested for the similar presented application in a previous study: lower cost, higher storage modulus and consequently higher damping properties in martensitic state. The patterning of the SMA sheets was performed by means of a pulsed fiber laser. After the laser processing, the SMA sheets were heat treated to obtain the desired martensitic state at room temperature. The transformation temperatures were measured by differential scanning calorimetry (DSC). The damping properties were determined, at room temperature, on full-scale sheet, using a universal testing machine (MTS), with cyclic tensile tests at different deformation amplitudes. Damping properties were also determined as a function of the temperature on miniature samples with a dynamical mechanical analyzer (DMA). Numerical modeling of the laminated composite, done with finite element method analysis and modal strain energy approaches, was performed to estimate the corresponding total damping capacity and then compared to experimental results.

Electrostatic stability of electron-positron plasmas in dipole geometry

NASA Astrophysics Data System (ADS)

Mishchenko, Alexey; Plunk, Gabriel G.; Helander, Per

2018-04-01

The electrostatic stability of electron-positron plasmas is investigated in the point-dipole and Z-pinch limits of dipole geometry. The kinetic dispersion relation for sub-bounce-frequency instabilities is derived and solved. For the zero-Debye-length case, the stability diagram is found to exhibit singular behaviour. However, when the Debye length is non-zero, a fluid mode appears, which resolves the observed singularity, and also demonstrates that both the temperature and density gradients can drive instability. It is concluded that a finite Debye length is necessary to determine the stability boundaries in parameter space. Landau damping is investigated at scales sufficiently smaller than the Debye length, where instability is absent.

Modelling, design and stability analysis of an improved SEPIC converter for renewable energy systems

NASA Astrophysics Data System (ADS)

G, Dileep; Singh, S. N.; Singh, G. K.

2017-09-01

In this paper, a detailed modelling and analysis of a switched inductor (SI)-based improved single-ended primary inductor converter (SEPIC) has been presented. To increase the gain of conventional SEPIC converter, input and output side inductors are replaced with SI structures. Design and stability analysis for continuous conduction mode operation of the proposed SI-SEPIC converter has also been presented in this paper. State space averaging technique is used to model the converter and carry out the stability analysis. Performance and stability analysis of closed loop configuration is predicted by observing the open loop behaviour using Nyquist diagram and Nichols chart. System was found to stable and critically damped.

Static Magnetic Fields in Semiconductor Floating-Zone Growth

NASA Technical Reports Server (NTRS)

Croll, Arne; Benz, K. W.

1999-01-01

Heat and mass transfer in semiconductor float-zone processing are strongly influenced by convective flows in the zone, originating from sources such as buoyancy convection, thermocapillary (Marangoni) convection, differential rotation, or radio frequency heating. Because semiconductor melts are conducting, flows can be damped by the use of static magnetic fields to influence the interface shape and the segregation of dopants and impurities. An important objective is often the suppression of time-dependent flows and the ensuing dopant striations. In RF-heated Si-FZ - crystals, fields up to O.STesla show some flattening of the interface curvature and a reduction of striation amplitudes. In radiation-heated (small-scale) SI-FZ crystals, fields of 0.2 - 0.5 Tesla already suppress the majority of the dopant striations. The uniformity of the radial segregation is often compromised by using a magnetic field, due to the directional nature of the damping. Transverse fields lead to an asymmetric interface shape and thus require crystal rotation (resulting in rotational dopant striations) to achieve a radially symmetric interface, whereas axial fields introduce a coring effect. A complete suppression of dopant striations and a reduction of the coring to insignificant values, combined with a shift of the axial segregation profile towards a more diffusion-limited case, are possible with axial static fields in excess of 1 Tesla. Strong static magnetic fields, however, can also lead to the appearance of thermoelectromagnetic convection, caused by the interaction of thermoelectric currents with the magnetic field.

Superconducting Meissner effect bearings for cryogenic turbomachines, phase 2

NASA Astrophysics Data System (ADS)

Valenzuela, Javier A.; Martin, Jerry L.

1994-02-01

This is the final report of a Phase 2 SBIR project to develop Meissner effect bearings for miniature cryogenic turbomachines. The bearing system was designed for use in miniature cryogenic turboexpanders in reverse-Brayton-cycle cryocoolers. The cryocoolers are designed to cool sensors on satellites. Existing gas bearings for this application run in a relatively warm state. The heat loss from the bearings into the shaft and into the cold process gas imposes a penalty on the cycle efficiency. By using cold Meissner effect bearings, this heat loss could be minimized, and the input power per unit of cooling for these cryocoolers could be reduced. Two bearing concepts were explored in this project. The first used an all-magnetic passive radial suspension to position the shaft over a range of temperatures from room temperature to 77 K. This bearing concept was proven to be feasible, but impractical for the miniature high-speed turbine application since it lacked the required shaft positioning accuracy. A second bearing concept was then developed. In this concept, the Meissner effect bearings are combined with self-acting gas bearings. The Meissner effect bearing provides the additional stiffness and damping required to stabilize the shaft at low temperature, while the gas bearing provides the necessary accuracy to allow very small turbine tip clearances (5mm) and high speeds (greater than 500,000 rpm).

Recent Dynamic Measurements and Considerations for Aerodynamic Modeling of Fighter Airplane Configurations

NASA Technical Reports Server (NTRS)

Brandon, Jay M.; Foster, John V.

1998-01-01

As airplane designs have trended toward the expansion of flight envelopes into the high angle of attack and high angular rate regimes, concerns regarding modeling the complex unsteady aerodynamics for simulation have arisen. Most current modeling methods still rely on traditional body axis damping coefficients that are measured using techniques which were intended for relatively benign flight conditions. This paper presents recent wind tunnel results obtained during large-amplitude pitch, roll and yaw testing of several fighter airplane configurations. A review of the similitude requirements for applying sub-scale test results to full-scale conditions is presented. Data is then shown to be a strong function of Strouhal number - both the traditional damping terms, but also the associated static stability terms. Additionally, large effects of sideslip are seen in the damping parameter that should be included in simulation math models. Finally, an example of the inclusion of frequency effects on the data in a simulation is shown.

Time-domain damping models in structural acoustics using digital filtering

NASA Astrophysics Data System (ADS)

Parret-Fréaud, Augustin; Cotté, Benjamin; Chaigne, Antoine

2016-02-01

This paper describes a new approach in order to formulate well-posed time-domain damping models able to represent various frequency domain profiles of damping properties. The novelty of this approach is to represent the behavior law of a given material directly in a discrete-time framework as a digital filter, which is synthesized for each material from a discrete set of frequency-domain data such as complex modulus through an optimization process. A key point is the addition of specific constraints to this process in order to guarantee stability, causality and verification of thermodynamics second law when transposing the resulting discrete-time behavior law into the time domain. Thus, this method offers a framework which is particularly suitable for time-domain simulations in structural dynamics and acoustics for a wide range of materials (polymers, wood, foam, etc.), allowing to control and even reduce the distortion effects induced by time-discretization schemes on the frequency response of continuous-time behavior laws.

Study to eliminate ground resonance using active controls

NASA Technical Reports Server (NTRS)

Straub, F. K.

1984-01-01

The effectiveness of active control blade feathering in increasing rotor body damping and the possibility to eliminate ground resonance instabilities were investigated. An analytical model representing rotor flapping and lead-lag degrees of freedom and body pitch, roll, longitudinal and lateral motion is developed. Active control blade feathering is implemented as state variable feedback through a conventional swashplate. The influence of various feedback states, feedback gain, and weighting between the cyclic controls is studied through stability and response analyses. It is shown that blade cyclic inplane motion, roll rate and roll acceleration feedback can add considerable damping to the system and eliminate ground resonance instabilities, which the feedback phase is also a powerful parameter, if chosen properly, it maximizes augmentation of the inherent regressing lag mode damping. It is shown that rotor configuration parameters, like blade root hinge offset, flapping stiffness, and precone considerably influence the control effectiveness. It is found that active control is particularly powerful for hingeless and bearingless rotor systems.

Internal alignment and position resolution of the silicon tracker of DAMPE determined with orbit data

NASA Astrophysics Data System (ADS)

Tykhonov, A.; Ambrosi, G.; Asfandiyarov, R.; Azzarello, P.; Bernardini, P.; Bertucci, B.; Bolognini, A.; Cadoux, F.; D'Amone, A.; De Benedittis, A.; De Mitri, I.; Di Santo, M.; Dong, Y. F.; Duranti, M.; D'Urso, D.; Fan, R. R.; Fusco, P.; Gallo, V.; Gao, M.; Gargano, F.; Garrappa, S.; Gong, K.; Ionica, M.; La Marra, D.; Lei, S. J.; Li, X.; Loparco, F.; Marsella, G.; Mazziotta, M. N.; Peng, W. X.; Qiao, R.; Salinas, M. M.; Surdo, A.; Vagelli, V.; Vitillo, S.; Wang, H. Y.; Wang, J. Z.; Wang, Z. M.; Wu, D.; Wu, X.; Zhang, F.; Zhang, J. Y.; Zhao, H.; Zimmer, S.

2018-06-01

The DArk Matter Particle Explorer (DAMPE) is a space-borne particle detector designed to probe electrons and gamma-rays in the few GeV to 10 TeV energy range, as well as cosmic-ray proton and nuclei components between 10 GeV and 100 TeV. The silicon-tungsten tracker-converter is a crucial component of DAMPE. It allows the direction of incoming photons converting into electron-positron pairs to be estimated, and the trajectory and charge (Z) of cosmic-ray particles to be identified. It consists of 768 silicon micro-strip sensors assembled in 6 double layers with a total active area of 6.6 m2. Silicon planes are interleaved with three layers of tungsten plates, resulting in about one radiation length of material in the tracker. Internal alignment parameters of the tracker have been determined on orbit, with non-showering protons and helium nuclei. We describe the alignment procedure and present the position resolution and alignment stability measurements.

Next generation HOM-damping

NASA Astrophysics Data System (ADS)

Marhauser, Frank

2017-06-01

Research and development for superconducting radio-frequency cavities has made enormous progress over the last decades from the understanding of theoretical limitations to the industrial mass fabrication of cavities for large-scale particle accelerators. Key technologies remain hot topics due to continuously growing demands on cavity performance, particularly when in pursuit of high quality beams at higher beam currents or higher luminosities than currently achievable. This relates to higher order mode (HOM) damping requirements. Meeting the desired beam properties implies avoiding coupled multi-bunch or beam break-up instabilities depending on the machine and beam parameters that will set the acceptable cavity impedance thresholds. The use of cavity HOM-dampers is crucial to absorb the wakefields, comprised by all beam-induced cavity Eigenmodes, to beam-dynamically safe levels and to reduce the heat load at cryogenic temperature. Cavity damping concepts may vary, but are principally based on coaxial and waveguide couplers as well as beam line absorbers or any combination. Next generation energy recovery linacs and circular colliders call for cavities with strong HOM-damping that can exceed the state-of-the-art, while the operating mode efficiency shall not be significantly compromised concurrently. This imposes major challenges given the rather limited damping concepts. A detailed survey of established cavities is provided scrutinizing the achieved damping performance, shortcomings, and potential improvements. The scaling of the highest passband mode impedances is numerically evaluated in dependence on the number of cells for a single-cell up to a nine-cell cavity, which reveals the increased probability of trapped modes. This is followed by simulations for single-cell and five-cell cavities, which incorporate multiple damping schemes to assess the most efficient concepts. The usage and viability of on-cell dampers is elucidated for the single-cell cavity since it can push the envelope towards quasi HOM-free operation suited for next generation storage and collider rings. Geometrical end-cell shape alterations for the five-cell cavity with already efficient mode damping are discussed as a possibility to further lower specific high impedance modes. The findings are eventually put into relation with demanding impedance instability thresholds in future collider rings.

Next generation HOM-damping

DOE PAGES

Marhauser, Frank

2017-05-15

Research and development for superconducting radio-frequency cavities has made enormous progress over the last decades from the understanding of theoretical limitations to the industrial mass fabrication of cavities for large-scale particle accelerators. Key technologies remain hot topics due to continuously growing demands on cavity performance, particularly when in pursuit of high quality beams at higher beam currents or higher luminosities than currently achievable. This relates to Higher Order Mode (HOM) damping requirements. Meeting the desired beam properties implies avoiding coupled multi-bunch or beam break-up instabilities depending on the machine and beam parameters that will set the acceptable cavity impedance thresholds.more » The use of cavity HOM-dampers is crucial to absorb the wakefields, comprised by all beam-induced cavity Eigenmodes, to beam-dynamically safe levels and to reduce the heat load at cryogenic temperature. Cavity damping concepts may vary, but are principally based on coaxial and waveguide couplers as well as beam line absorbers or any combination. Next generation Energy Recovery Linacs and circular colliders call for cavities with strong HOM-damping that can exceed the state-of-the-art, while the operating mode efficiency shall not be significantly compromised concurrently. This imposes major challenges given the rather limited damping concepts. A detailed survey of established cavities is provided scrutinizing the achieved damping performance, shortcomings, and potential improvements. The scaling of the highest passband mode impedances is numerically evaluated in dependence on the number of cells for a single-cell up to a nine-cell cavity, which reveals the increased probability of trapped modes. This is followed by simulations for single-cell and five-cell cavities, which incorporate multiple damping schemes to assess the most efficient concepts. The usage and viability of on-cell dampers is elucidated for the single-cell cavity since it can push the envelope towards quasi HOM-free operation suited for next generation storage and collider rings. Geometrical end-cell shape alterations for the five-cell cavity with already efficient mode damping are discussed as a possibility to further lower specific high impedance modes. Lastly, the findings are eventually put into relation with demanding impedance instability thresholds in future collider rings.« less

Study of stability and control moment gyro wobble damping of flexible, spinning space stations

NASA Technical Reports Server (NTRS)

Berman, H.; Markowitz, J.; Holmer, W.

1972-01-01

An executive summary and an analysis of the results are discussed. A user's guide for the digital computer program that simulates the flexible, spinning space station is presented. Control analysis activities and derivation of dynamic equations of motion and the modal analysis are also cited.

Effects of electrolytes and surfactants on the morphology and stability of advanced silver nano-materials

DOE Office of Scientific and Technical Information (OSTI.GOV)

Obaid, Abdullah Yousif; AL-Thabaiti, Shaeel Ahmed; El-Mossalamy, E.H.

2013-03-15

Highlights: ► Stoichiometric ratio of S{sub 2}O{sub 3}{sup 2−} and Ag{sup +} ions are responsible to the formation of prefect transparent yellow colored silver sol. ► Higher S{sub 2}O{sub 3}{sup 2−} concentrations has damping effect. ► Head group of the surfactants and nature of the electrolytes have significant effect on the stability of silver nanoparticles. - Abstract: The impact of electrolytes, stabilizing and/or capping agents on morphology of colloidal silver nano-materials (AgNPs) has been studied spectroscopically. Sodium thiosulfate acts as reducing-, stabilizing- and damping-agents. Stoichiometric ratios of S{sub 2}O{sub 3}{sup 2−} and Ag{sup +} ions were responsible to the formationmore » stable and prefect transparent dark yellow colored AgNPs. The S{sub 2}O{sub 3}{sup 2−}-stabilized AgNPs were significantly more stable in inorganic electrolytes (NaNO{sub 3}, Na{sub 2}SO{sub 4}, Na{sub 2}CO{sub 3} and KBr). S{sub 2}O{sub 3}{sup 2−} is adsorbed more strongly than the used other anions. The addition of cetyltrimethylammonium bromide (CTAB) and sodium dodecylsulfate (SDS) has significant effects on the absorbance of S{sub 2}O{sub 3}{sup 2−}-stabilized AgNPs which can be rationalized in terms of electrostatic attraction and repulsion between the adsorbed S{sub 2}O{sub 3}{sup 2−} ions on to the surface of AgNPs and cationic and/or anionic head groups of used surfactants, respectively. Transmission electron microscopy images suggest that AgNPs are polydispersed, spherical and exhibiting an interesting irregular morphology.« less

A simple and low-cost platform technology for producing pexiganan antimicrobial peptide in E. coli.

PubMed

Zhao, Chun-Xia; Dwyer, Mirjana Dimitrijev; Yu, Alice Lei; Wu, Yang; Fang, Sheng; Middelberg, Anton P J

2015-05-01

Antimicrobial peptides, as a new class of antibiotics, have generated tremendous interest as potential alternatives to classical antibiotics. However, the large-scale production of antimicrobial peptides remains a significant challenge. This paper reports a simple and low-cost chromatography-free platform technology for producing antimicrobial peptides in Escherichia coli (E. coli). A fusion protein comprising a variant of the helical biosurfactant protein DAMP4 and the known antimicrobial peptide pexiganan is designed by joining the two polypeptides, at the DNA level, via an acid-sensitive cleavage site. The resulting DAMP4(var)-pexiganan fusion protein expresses at high level and solubility in recombinant E. coli, and a simple heat-purification method was applied to disrupt cells and deliver high-purity DAMP4(var)-pexiganan protein. Simple acid cleavage successfully separated the DAMP4 variant protein and the antimicrobial peptide. Antimicrobial activity tests confirmed that the bio-produced antimicrobial peptide has the same antimicrobial activity as the equivalent product made by conventional chemical peptide synthesis. This simple and low-cost platform technology can be easily adapted to produce other valuable peptide products, and opens a new manufacturing approach for producing antimicrobial peptides at large scale using the tools and approaches of biochemical engineering. © 2014 Wiley Periodicals, Inc.

Damping of spin-dipole mode and generation of quadrupole mode excitations in a spin-orbit coupled Bose-Einstein condensate

NASA Astrophysics Data System (ADS)

Li, Chuan-Hsun; Blasing, David; Chen, Yong

2017-04-01

In cold atom systems, spin excitations have been shown to be a sensitive probe of interactions and quantum statistical effects, and can be used to study spin transport in both Fermi and Bose gases. In particular, spin-dipole mode (SDM) is a type of excitation that can generate a spin current without a net mass current. We present recent measurements and analysis of SDM in a disorder-free, interacting three-dimensional (3D) 87Rb Bose-Einstein condensate (BEC) by applying spin-dependent synthetic electric fields to actuate head-on collisions between two BECs of different spin states. We experimentally study and compare the behaviors of the system following SDM excitations in the presence as well as absence of synthetic 1D spin-orbit coupling (SOC). We find that in the absence of SOC, SDM is relatively weakly damped, accompanied with collision-induced thermalization which heats up the atomic cloud. However, in the presence of SOC, we find that SDM is more strongly damped with reduced thermalization, and observe excitation of a quadrupole mode that exhibits BEC shape oscillation even after SDM is damped out. Such a mode conversion bears analogies with the Beliaev coupling process or the parametric frequency down conversion of light in nonlinear optics.

Effects of capacitors, resistors, and residual charges on the static and dynamic performance of electrostatically actuated devices

NASA Astrophysics Data System (ADS)

Chan, Edward K.; Dutton, Robert W.

1999-03-01

The important practical and realistic design issues of an electrostatic actuator/positioner with full-gap travel are discussed. Analytic expressions and numerical simulations show that parasitic capacitances, and non-uniform deformation in two and three dimensions influence the range of travel of an electrostatic positioner stabilized by the addition of a series capacitor. The effects of residual charge on electrostatically-actuated devices are described. The dynamic stepping characteristics of the positioner under compressible squeeze-film damping and resistive damping are compared. The physical descriptions of devices being fabricated in the MUMPs process are presented along with 3D simulation results that demonstrate viability.

Mechanical properties of the human hand digits: Age-related differences

PubMed Central

Park, Jaebum; Pazin, Nemanja; Friedman, Jason; Zatsiorsky, Vladimir M.; Latash, Mark L.

2014-01-01

Background Mechanical properties of human digits may have significant implications for the hand function. We quantified several mechanical characteristics of individual digits in young and older adults. Methods Digit tip friction was measured at several normal force values using a method of induced relative motion between the digit tip and the object surface. A modified quick-release paradigm was used to estimate digit apparent stiffness, damping, and inertial parameters. The subjects grasped a vertical handle instrumented with force/moment sensors using a prismatic grasp with four digits; the handle was fixed to the table. Unexpectedly, one of the sensors yielded leading to a quick displacement of the corresponding digit. A second-order, linear model was used to fit the force/displacement data. Findings Friction of the digit pads was significantly lower in older adults. The apparent stiffness coefficient values were higher while the damping coefficients were lower in older adults leading to lower damping ratio. The damping ratio was above unity for most data in young adults and below unity for older adults. Quick release of a digit led to force changes in other digits of the hand, likely due to inertial hand properties. These phenomena of “mechanical enslaving” were smaller in older adults although no significant difference was found in the inertial parameter in the two groups. Interpretations The decreased friction and damping ratio present challenges for the control of everyday prehensile tasks. They may lead to excessive digit forces and low stability of the grasped object. PMID:24355703

Status of E-ELT M5 scale-one demonstrator

NASA Astrophysics Data System (ADS)

Barriga, Pablo; Sedghi, Babak; Dimmler, Martin; Kornweibel, Nick

2014-07-01

The fifth mirror of the European Extremely Large Telescope optical train is a field stabilization tip/tilt unit responsible for correcting the dynamical tip and tilt caused mainly by wind load on the telescope. A scale-one prototype including the inclined support, the fixed frame and a basic control system was designed and manufactured by NTE-SENER (Spain) and CSEM (Switzerland) as part of the prototyping and design activities. All interfaces to the mirror have been reproduced on a dummy structure reproducing the inertial characteristics of the optical element. The M5 unit is required to have sufficient bandwidth for tip/tilt reference commands coming from the wavefront control system. Such a bandwidth can be achieved using local active damping loop to damp the low frequency mechanical modes before closing a position loop. Prototyping on the M5 unit has been undertaken in order to demonstrate the E-ELT control system architecture, concepts and development standards and to further study active damping strategies. The control system consists of two nested loops: a local damping loop and a position loop. The development of this control system was undertaken following the E-ELT control system development standards in order to determine their applicability and performance and includes hardware selection, communication, synchronization, configuration, and data logging. In this paper we present the current status of the prototype M5 control system and the latest results on the active damping control strategy, in particular the promising results obtained with the method of positive position feedback.

Foil bearings

NASA Astrophysics Data System (ADS)

Elrod, David A.

1993-11-01

The rolling element bearings (REB's) which support many turbomachinery rotors offer high load capacity, low power requirements, and durability. Two disadvantages of REB's are: (1) rolling or sliding contact within the bearing has life-limiting consequences; and (2) REB's provide essentially no damping. The REB's in the Space Shuttle Main Engine (SSME) turbopumps must sustain high static and dynamic loads, at high speeds, with a cryogenic fluid as lubricant and coolant. The pump end ball bearings limit the life of the SSME high pressure oxygen turbopump (HPOTP). Compliant foil bearing (CFB) manufacturers have proposed replacing turbopump REB's with CFB's CFB's work well in aircraft air cycle machines, auxiliary power units, and refrigeration compressors. In a CFB, the rotor only contracts the foil support structure during start up and shut down. CFB damping is higher than REB damping. However, the load capacity of the CFB is low, compared to a REB. Furthermore, little stiffness and damping data exists for the CFB. A rotordynamic analysis for turbomachinery critical speeds and stability requires the input of bearing stiffness and damping coefficients. The two basic types of CFB are the tension-dominated bearing and the bending-dominated bearing. Many investigators have analyzed and measured characteristics of tension-dominated foil bearings, which are applied principally in magnetic tape recording. The bending-dominated CFB is used more in rotating machinery. This report describes the first phase of a structural analysis of a bending-dominated, multileaf CFB. A brief discussion of CFB literature is followed by a description and results of the present analysis.

Analysis of permafrost depths on Mars

NASA Technical Reports Server (NTRS)

Crescenti, G. H.

1984-01-01

The Martian surface thermal characteristics as they effect the thickness and distribution of the permafrost are discussed. Parameters such as temperature mean, maximum, and minimum, heat flow values, and damping depths are derived and applied to a model of the Martian cryosphere. A comparison is made between the permafrost layers of Earth and Mars.

Sequential accelerated tests: Improving the correlation of accelerated tests to module performance in the field

NASA Astrophysics Data System (ADS)

Felder, Thomas; Gambogi, William; Stika, Katherine; Yu, Bao-Ling; Bradley, Alex; Hu, Hongjie; Garreau-Iles, Lucie; Trout, T. John

2016-09-01

DuPont has been working steadily to develop accelerated backsheet tests that correlate with solar panels observations in the field. This report updates efforts in sequential testing. Single exposure tests are more commonly used and can be completed more quickly, and certain tests provide helpful predictions of certain backsheet failure modes. DuPont recommendations for single exposure tests are based on 25-year exposure levels for UV and humidity/temperature, and form a good basis for sequential test development. We recommend a sequential exposure of damp heat followed by UV then repetitions of thermal cycling and UVA. This sequence preserves 25-year exposure levels for humidity/temperature and UV, and correlates well with a large body of field observations. Measurements can be taken at intervals in the test, although the full test runs 10 months. A second, shorter sequential test based on damp heat and thermal cycling tests mechanical durability and correlates with loss of mechanical properties seen in the field. Ongoing work is directed toward shorter sequential tests that preserve good correlation to field data.

Plasma Surface Modification of Polymer Backsheets: Origins of Future Interfacial Barrier/Backsheet Failure (Poster)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pankow, J. W.; Glick, S. H.

2006-05-01

Flexible polymer substrates coated with inorganic oxide moisture barriers are a potential replacement for glass backsheets in thin-film PV (photovoltaic) modules. Silicon oxynitride (SiO{sub x}N{sub y}) deposited by plasma enhanced chemical vapor deposition (PECVD) on polyethylene terephthalate (PET) represents one potential new backsheet candidate. Barrier deposition runs at NREL have included a nitrogen-rich plasma pretreatment prior to barrier deposition with the intention of cleaning the PET surface and enhancing adhesion of the SiO{sub x}N{sub y} barrier film to PET; however, test coupons of PET/barrier/EVA/TPE failed after damp-heat exposure. (EVA is ethylene vinyl acetate and TPE is Tedlar{reg_sign}-PET-EVA). PET substrates exposedmore » to plasma conditions similar to those used in pretreatment were examined by X-ray photoelectron spectroscopy (XPS) to reveal that new low molecular weight PET fragments were created at the PET surface. These fragments are responsible for barrier/PET interfacial failure and barrier transfer to the EVA encapsulant side following damp heat exposure.« less

Damping of Resonantly Forced Density Waves in Dense Planetary Rings

NASA Astrophysics Data System (ADS)

Lehmann, Marius; Schmidt, Jürgen; Salo, Heikki

2016-10-01

We address the stability of resonantly forced density waves in dense planetary rings.Already by Goldreich and Tremaine (1978) it has been argued that density waves might be unstable, depending on the relationship between the ring's viscosity and the surface mass density. In the recent paper (Schmidt et al. 2016) we have pointed out that when - within a fluid description of the ring dynamics - the criterion for viscous overstability is satisfied, forced spiral density waves become unstable as well. In this case, linear theory fails to describe the damping.We apply the multiple scale formalism to derive a weakly nonlinear damping relation from a hydrodynamical model.This relation describes the resonant excitation and nonlinear viscous damping of spiral density waves in a vertically integrated fluid disk with density dependent transport coefficients. The model consistently predicts linear instability of density waves in a ring region where the conditions for viscous overstability are met. In this case, sufficiently far away from the Lindblad resonance, the surface mass density perturbation is predicted to saturate to a constant value due to nonlinear viscous damping. In general the model wave damping lengths depend on a set of input parameters, such as the distance to the threshold for viscous overstability and the ground state surface mass density.Our new model compares reasonably well with the streamline model for nonlinear density waves of Borderies et al. 1986.Deviations become substantial in the highly nonlinear regime, corresponding to strong satellite forcing.Nevertheless, we generally observe good or at least qualitative agreement between the wave amplitude profiles of both models. The streamline approach is superior at matching the total wave profile of waves observed in Saturn's rings, while our new damping relation is a comparably handy tool to gain insight in the evolution of the wave amplitude with distance from resonance, and the different regimes of wave formation and the dependence on the parameters of the model.

Elimination of fuel pressure fluctuation and multi-injection fuel mass deviation of high pressure common-rail fuel injection system

NASA Astrophysics Data System (ADS)

Li, Pimao; Zhang, Youtong; Li, Tieshuan; Xie, Lizhe

2015-03-01

The influence of fuel pressure fluctuation on multi-injection fuel mass deviation has been studied a lot, but the fuel pressure fluctuation at injector inlet is still not eliminated efficiently. In this paper, a new type of hydraulic filter consisting of a damping hole and a chamber is developed for elimination of fuel pressure fluctuation and multi-injection fuel mass deviation. Linear model of the improved high pressure common-rail system(HPCRS) including injector, the pipe connecting common-rail with injector and the hydraulic filter is built. Fuel pressure fluctuation at injector inlet, on which frequency domain analysis is conducted through fast Fourier transformation, is acquired at different target pressure and different damping hole diameter experimentally. The linear model is validated and can predict the natural frequencies of the system. Influence of damping hole diameter on fuel pressure fluctuation is analyzed qualitatively based on the linear model, and it can be inferred that an optimal diameter of the damping hole for elimination of fuel pressure fluctuation exists. Fuel pressure fluctuation and fuel mass deviation under different damping hole diameters are measured experimentally, and it is testified that the amplitude of both fuel pressure fluctuation and fuel mass deviation decreases first and then increases with the increasing of damping hole diameter. The amplitude of main injection fuel mass deviation can be reduced by 73% at most under pilot-main injection mode, and the amplitude of post injection fuel mass deviation can be reduced by 92% at most under main-post injection mode. Fuel mass of a single injection increases with the increasing of the damping hole diameter. The hydraulic filter proposed by this research can be potentially used to eliminate fuel pressure fluctuation at injector inlet and improve the stability of HPCRS fuel injection.

Calcium promotes activity and confers heat stability on plant peroxidases

PubMed Central

Plieth, Christoph; Vollbehr, Sonja

2012-01-01

In this paper we demonstrate how peroxidase (PO) activities and their heat stability correlate with the availability of free Ca2+ ions. Calcium ions work as a molecular switch for PO activity and exert a protective function, rendering POs heat stable. The concentration ranges of these two activities differ markedly. POs are activated by µM Ca2+ concentration ranges, whereas heat stabilization is observed in the nM range. This suggests the existence of different Ca2+ binding sites. The heat stability of POs depends on the source plant species. Terrestrial plants have POs that exhibit higher temperature stability than those POs from limnic and marine plants. Different POs from a single species can differ in terms of heat stability. The abundance of different POs within a plant is dependent on age and developmental stage. The heat stability of a PO does not necessarily correlate with the maximum temperature the source species is usually exposed to in its natural habitat. This raises questions on the role of POs in the heat tolerance of plants. Consequently, detailed investigations are needed to identify and characterize individual POs, with regard to their genetic origin, subcellular expression, tissue abundance, developmental emergence and their functions in innate and acquired heat tolerance. PMID:22580695

Whirl Flutter Stability and Its Influence on the Design of the Distributed Electric Propeller Aircraft X- 57

NASA Technical Reports Server (NTRS)

Hoover, Christian B.; Shen, Jinwei; Kreshock, Andrew R.; Stanford, Bret K.; Piatak, David J.; Heeg, Jennifer

2017-01-01

This paper studies the whirl flutter stability of the NASA experimental electric propulsion aircraft designated the X-57 Maxwell. whirl flutter stability is studied at two flight conditions: sea level at 2700 RPM to represent take-off and landing and 8000 feet at 2250 RPM to represent cruise. Two multibody dynamics analyses are used: CAMRAD II and Dymore. The CAMRAD II model is a semi-span X-57 model with a modal representation for the wing/pylon system. The Dymore model is a semi-span wing with a propeller composed of beam elements for the wing/pylon system that airloads can be applied to. The two multibody dynamics analyses were verified by comparing structural properties between each other and the NASTRAN analysis. For whirl flutter, three design revisions of the wing and pylon mount system are studied. The predicted frequencies and damping ratio of the wing modes show good agreements between the two analyses. Dymore tended to predict a slightly lower damping ratio as velocity increased for all three dynamic modes presented. Whirl flutter for the semi-span model was not present up to 500 knots for the latest design, well above the operating range of the X-57.

Stability of large horizontal-axis axisymmetric wind turbines. Ph.D. Thesis - Delaware Univ.

NASA Technical Reports Server (NTRS)

Hirschbein, M. S.; Young, M. I.

1980-01-01

The stability of large horizontal axis, axi-symmetric, power producing wind turbines was examined. The analytical model used included the dynamic coupling of the rotor, tower and power generating system. The aerodynamic loading was derived from blade element theory. Each rotor blade was permitted tow principal elastic bending degrees of freedom, one degree of freedom in torsion and controlled pitch as a rigid body. The rotor hub was mounted in a rigid nacelle which may yaw freely or in a controlled manner. The tower can bend in two principal directions and may twist. Also, the rotor speed can vary and may induce perturbation reactions within the power generating equipment. Stability was determined by the eigenvalues of a set of linearized constant coefficient differential equations. All results presented are based on a 3 bladed, 300 ft. diameter, 2.5 megawatt wind turbine. Some of the parameters varied were; wind speed, rotor speed structural stiffness and damping, the effective stiffness and damping of the power generating system and the principal bending directions of the rotor blades. Unstable or weakly stable behavior can be caused by aerodynamic forces due to motion of the rotor blades and tower in the plane of rotation or by mechanical coupling between the rotor system and the tower.

9 CFR 318.23 - Heat-processing and stabilization requirements for uncured meat patties.

Code of Federal Regulations, 2011 CFR

2011-01-01

... 9 Animals and Animal Products 2 2011-01-01 2011-01-01 false Heat-processing and stabilization...; REINSPECTION AND PREPARATION OF PRODUCTS General § 318.23 Heat-processing and stabilization requirements for... been heat processed for less time or using lower internal temperatures than are prescribed by paragraph...

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sanz, J.; Betti, R.

A sharp boundary model for the deceleration phase of imploding capsules in inertial confinement fusion, in both direct and indirect drive, has been developed. The model includes heat conduction, local {alpha}-particle energy deposition, and shell compressibility effects. A differential equation for the temporal evolution of the modal amplitude interface is obtained. It is found that the {alpha}-particle energy has a strong influence on the evolution of the low l modes, via the compressibility of the shell. The modes are damped by vorticity convection, fire polishing, and {alpha}-particle energy deposition. The existence of a cutoff l number arises from the highmore » blow of velocity into the hot region (rocket effect) if density gradient scale length effects are taken into account at the interface. The differential equation for the modal amplitude is used as a postprocessor to the results of 1D-SARA code [J. J. Honrubia, J. Quant. Spectrosc. Radiat. Transfer. 49, 491 (1993)] in a typical capsule for indirect-drive ignition designed on the National Ignition Facility. It is found that modes with l>180 are completely stabilized. The results are in agreement with two-dimensional simulations.« less

Stability improvement of wind turbine penetrated using power system stabilizer (PSS) on South Sulawesi transmission system

NASA Astrophysics Data System (ADS)

Siswanto, Agus; Gunadin, Indar Chaerah; Said, Sri Mawar; Suyuti, Ansar

2018-03-01

The purpose of this research is to improve the stability of interconnection of South Sulawesi system caused by penetration new wind turbine in Sidrap area on bus 2 and in Jeniponto area on bus 34. The method used in this research was via software Power System analysis Toolbox (PSAT) under MATLAB. In this research, there are two problems that are evaluated, the stability of the system before and after penetration wind turbine into the system South Sulawesi system. From the simulation result shows that penetration of wind turbine on bus 2 Sidrap, bus 37 Jeniponto give effect oscillation on the system. The oscillation was damped by installation of Power System Stabilizer (PSS) on bus 29 area Sungguminasa, that South Sulawesi system stable according to normal condition.

Spacecraft Stabilization and Control for Capture of Non-Cooperative Space Objects

NASA Technical Reports Server (NTRS)

Joshi, Suresh; Kelkar, Atul G.

2014-01-01

This paper addresses stabilization and control issues in autonomous capture and manipulation of non-cooperative space objects such as asteroids, space debris, and orbital spacecraft in need of servicing. Such objects are characterized by unknown mass-inertia properties, unknown rotational motion, and irregular shapes, which makes it a challenging control problem. The problem is further compounded by the presence of inherent nonlinearities, signi cant elastic modes with low damping, and parameter uncertainties in the spacecraft. Robust dissipativity-based control laws are presented and are shown to provide global asymptotic stability in spite of model uncertainties and nonlinearities. It is shown that robust stabilization can be accomplished via model-independent dissipativity-based controllers using thrusters alone, while stabilization with attitude and position control can be accomplished using thrusters and torque actuators.

First-principles Theory of Inelastic Transport and Local Heating in Atomic Gold Wires

NASA Astrophysics Data System (ADS)

Frederiksen, Thomas; Paulsson, Magnus; Brandbyge, Mads; Jauho, Antti-Pekka

2007-04-01

We present theoretical calculations of the inelastic transport properties in atomic gold wires. Our method is based on a combination of density functional theory and non-equilibrium Green's functions. The vibrational spectra for extensive series of wire geometries have been calculated using SIESTA, and the corresponding effects in the conductance are analyzed. In particular, we focus on the heating of the active vibrational modes. By a detailed comparison with experiments we are able to estimate an order of magnitude for the external damping of the active vibrations.

Damping of Quasi-stationary Waves Between Two Miscible Liquids

NASA Technical Reports Server (NTRS)

Duval, Walter M. B.

2002-01-01

Two viscous miscible liquids with an initially sharp interface oriented vertically inside a cavity become unstable against oscillatory external forcing due to Kelvin-Helmholtz instability. The instability causes growth of quasi-stationary (q-s) waves at the interface between the two liquids. We examine computationally the dynamics of a four-mode q-s wave, for a fixed energy input, when one of the components of the external forcing is suddenly ceased. The external forcing consists of a steady and oscillatory component as realizable in a microgravity environment. Results show that when there is a jump discontinuity in the oscillatory excitation that produced the four-mode q-s wave, the interface does not return to its equilibrium position, the structure of the q-s wave remains imbedded between the two fluids over a long time scale. The damping characteristics of the q-s wave from the time history of the velocity field show overdamped and critically damped response; there is no underdamped oscillation as the flow field approaches steady state. Viscous effects serve as a dissipative mechanism to effectively damp the system. The stability of the four-mode q-s wave is dependent on both a geometric length scale as well as the level of background steady acceleration.

A review of rigid body response on sting supported models at high angles of incidence

NASA Astrophysics Data System (ADS)

Mabey, D. G.; Welsh, B. L.; Pyne, C. R.

The new requirement to test wind tunnel models of combat aircraft at high angles of incidence and high kinetic pressures has led to a review of the factors controlling the model stability. The review suggested that dangerous motions might occur (possibly without prior warning) on models at high angles of incidence unless special preventive measures were taken. An internal tuned damper and balance bump stops were recommended to limit the responses. The bump stops would also prevent the moment limits of the strain gauge balance from being exceeded. The effectiveness of both devices was confirmed by tests on a swept wing model which experienced dangerous bending oscillations in a vertical plane at a Mach number of 0.50 in the incidence range from about 27-29° together with dangerous yawing oscillations in a horizontal plane above an incidence of about 35°. Further research is recommended to ensure the safety of other models. For sting supported models in a conventional wind tunnel, it is shown by analysis that the structural damping in the sting bending mode needs to be about 4 to 6% critical damping. In a cryogenic wind tunnel corresponding levels would need to be 7 to 10% critical damping because of the possibility of increased negative aerodynamic damping relative to ambient conditions.

Mitigation of Subsynchronous Resonance with Fractional-order PI based UPFC controller

NASA Astrophysics Data System (ADS)

Raju, D. Koteswara; Umre, Bhimrao S.; Junghare, Anjali S.; Babu, B. Chitti

2017-02-01

Due to incorporation of series capacitor compensation in transmission line for stability improvement, subsynchronous oscillations are generated at turbine-generator shaft. These oscillations can damage the shaft system if these are not well suppressed. In order to damp out these oscillations, usually power system network should have sufficient damping and the increase of network damping is obtained by the injection of subsynchronous component of voltage and current into the line, which are extracted from the measured signal of the system. However, the effectiveness of damp out of these subsynchronous oscillations is possibly by incorporating UPFC in the transmission line network is of high interest and it should be further investigated. This research article proposes the mitigation of subsynchronous resonance (SSR) using fractional-order PI (FOPI) based unified power flow controller (UPFC). The robustness of the proposed controller is tested for 25%, 55% and 70% series compensation with a symmetrical fault (L-L-L fault). Further, Eigenvalue analysis and Fast Fourier Transform (FFT) analysis against operating point variations and uncertainties in the system are also examined. The IEEE first benchmark model is adopted for this study and the superiority of the FOPI based UPFC controller over PI based UPFC controller is discussed by comparing the results with various performance indices.

Explicit approximations to estimate the perturbative diffusivity in the presence of convectivity and damping. I. Semi-infinite slab approximations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Berkel, M. van; Fellow of the Japan Society for the Promotion of Science; FOM Institute DIFFER-Dutch Institute for Fundamental Energy Research, Association EURATOM- FOM, Trilateral Euregio Cluster, PO Box 1207, 3430 BE Nieuwegein

2014-11-15

In this paper, a number of new approximations are introduced to estimate the perturbative diffusivity (χ), convectivity (V), and damping (τ) in cylindrical geometry. For this purpose, the harmonic components of heat waves induced by localized deposition of modulated power are used. The approximations are based on semi-infinite slab approximations of the heat equation. The main result is the approximation of χ under the influence of V and τ based on the phase of two harmonics making the estimate less sensitive to calibration errors. To understand why the slab approximations can estimate χ well in cylindrical geometry, the relationships betweenmore » heat transport models in slab and cylindrical geometry are studied. In addition, the relationship between amplitude and phase with respect to their derivatives, used to estimate χ, is discussed. The results are presented in terms of the relative error for the different derived approximations for different values of frequency, transport coefficients, and dimensionless radius. The approximations show a significant region in which χ, V, and τ can be estimated well, but also regions in which the error is large. Also, it is shown that some compensation is necessary to estimate V and τ in a cylindrical geometry. On the other hand, errors resulting from the simplified assumptions are also discussed showing that estimating realistic values for V and τ based on infinite domains will be difficult in practice. This paper is the first part (Part I) of a series of three papers. In Part II and Part III, cylindrical approximations based directly on semi-infinite cylindrical domain (outward propagating heat pulses) and inward propagating heat pulses in a cylindrical domain, respectively, will be treated.« less

Linking the micro and macro: L-H transition dynamics and threshold physics

DOE Office of Scientific and Technical Information (OSTI.GOV)

Malkov, M. A., E-mail: mmalkov@ucsd.edu; Diamond, P. H.; Miki, K.

2015-03-15

The links between the microscopic dynamics and macroscopic threshold physics of the L → H transition are elucidated. Emphasis is placed on understanding the physics of power threshold scalings, and especially on understanding the minimum in the power threshold as a function of density P{sub thr} (n). By extending a numerical 1D model to evolve both electron and ion temperatures, including collisional coupling, we find that the decrease in P{sub thr} (n) along the low-density branch is due to the combination of an increase in collisional electron-to-ion energy transfer and an increase in the heating fraction coupled to the ions.more » Both processes strengthen the edge diamagnetic electric field needed to lock in the mean electric field shear for the L→H transition. The increase in P{sub thr} (n) along the high-density branch is due to the increase with ion collisionality of damping of turbulence-driven shear flows. Turbulence driven shear flows are needed to trigger the transition by extracting energy from the turbulence. Thus, we identify the critical transition physics components of the separatrix ion heat flux and the zonal flow excitation. The model reveals a power threshold minimum in density scans as a crossover between the threshold decrease supported by an increase in heat fraction received by ions (directly or indirectly, from electrons) and a threshold increase, supported by the rise in shear flow damping. The electron/ion heating mix emerges as important to the transition, in that it, together with electron-ion coupling, regulates the edge diamagnetic electric field shear. The importance of possible collisionless electron-ion heat transfer processes is explained.« less

Polynomial stability of a magneto-thermoelastic Mindlin-Timoshenko plate model

NASA Astrophysics Data System (ADS)

Ferreira, Marcio V.; Muñoz Rivera, Jaime E.

2018-02-01

In this paper, we consider the magneto-thermoelastic interactions in a two-dimensional Mindlin-Timoshenko plate. Our main result is concerned with the strong asymptotic stabilization of the model. In particular, we determine the rate of polynomial decay of the associated energy. In contrast with what was observed in other related articles, geometrical hypotheses on the plate configuration (such as radial symmetry) are not imposed in this study nor any kind of frictional damping mechanism. A suitable multiplier is instrumental in establishing the polynomial stability with the aid of a recent result due to Borichev and Tomilov (Math Ann 347(2):455-478, 2010).

Stability of wave processes in a rotating electrically conducting fluid

NASA Astrophysics Data System (ADS)

Peregudin, S. I.; Peregudina, E. S.; Kholodova, S. E.

2018-05-01

The paper puts forward a mathematical model of dynamics of spatial large-scale motions in a rotating layer of electrically conducting incompressible perfect fluid of variable depth with due account of dissipative effects. The resulting boundary-value problem is reduced to a vector system of partial differential equations for any values of the Reynolds number. Theoretical analysis of the so-obtained analytical solution reveals the effect of the magnetic field diffusion on the stability of the wave mode — namely, with the removed external magnetic field, the diffusion of the magnetic field promotes its damping. Besides, a criterion of stability of a wave mode is obtained.

Robust controller designs for second-order dynamic system: A virtual passive approach

NASA Technical Reports Server (NTRS)

Juang, Jer-Nan; Phan, Minh

1990-01-01

A robust controller design is presented for second-order dynamic systems. The controller is model-independent and itself is a virtual second-order dynamic system. Conditions on actuator and sensor placements are identified for controller designs that guarantee overall closed-loop stability. The dynamic controller can be viewed as a virtual passive damping system that serves to stabilize the actual dynamic system. The control gains are interpreted as virtual mass, spring, and dashpot elements that play the same roles as actual physical elements in stability analysis. Position, velocity, and acceleration feedback are considered. Simple examples are provided to illustrate the physical meaning of this controller design.

Damping ratio analysis of tooth stability under various simulated degrees of vertical alveolar bone loss and different root types.

PubMed

Ho, Kuo-Ning; Lee, Sheng-Yang; Huang, Haw-Ming

2017-08-03

The purpose of this study was to evaluate the feasibility of using damping ratio (DR) analysis combined with resonance frequency (RF) and periotest (PTV) analyses to provide additional information about natural tooth stability under various simulated degrees of alveolar vertical bone loss and various root types. Three experimental tooth models, including upper central incisor, upper first premolar, and upper first molar were fabricated using Ti6Al4V alloy. In the tooth models, the periodontal ligament and alveolar bone were simulated using a soft lining material and gypsum, respectively. Various degrees of vertical bone loss were simulated by decreasing the surrounding bone level apically from the cementoenamel junction in 2-mm steps incrementally downward for 10 mm. A commercially available RF analyzer was used to measure the RF and DR of impulse-forced vibrations on the tooth models. The results showed that DRs increased as alveolar vertical bone height decreased and had high coefficients of determination in the linear regression analysis. The damping ratio of the central incisor model without a simulated periodontal ligament were 11.95 ± 1.92 and 27.50 ± 0.67% respectively when their bone levels were set at 2 and 10 mm apically from the cementoenamel junction. These values significantly changed to 28.85 ± 2.54% (p = 0.000) and 51.25 ± 4.78% (p = 0.003) when the tooth model was covered with simulated periodontal ligament. Moreover, teeth with different root types showed different DR and RF patterns. Teeth with multiple roots had lower DRs than teeth with single roots. Damping ratio analysis combined with PTV and RF analysis provides more useful information on the assessment of changes in vertical alveolar bone loss than PTV or RF analysis alone.

The effect of radiation processing and filler morphology on the biomechanical stability of a thermoset polyester composite.

PubMed

Jayabalan, M; Shalumon, K T; Mitha, M K; Ganesan, K; Epple, M

2010-04-01

The effect of radiation processing and filler morphology on the biodegradation and biomechanical stability of a poly(propylene fumarate)/hydroxyapatite composite was investigated. Radiation processing influenced both cross-linking and biodegradation of the composites. Irradiation with a dose of 3 Mrad resulted in enhanced cross-linking, mechanical properties and a higher storage modulus which are favourable for dimensional stability of the implant. The particle morphology of the added hydroxyapatite in the highly cross-linked state significantly influenced the biomechanical and interfacial stability of the composites. Reorganization of agglomerated hydroxyapatite occurred in the cross-linked polymeric matrix under dynamic mechanical loading under simulated physiological conditions. Such a reorganization may increase the damping characteristics of the composite.

A generalized plasma dispersion function for electron damping in tokamak plasmas

DOE PAGES

Berry, L. A.; Jaeger, E. F.; Phillips, C. K.; ...

2016-10-14

Radio frequency wave propagation in finite temperature, magnetized plasmas exhibits a wide range of physics phenomena. The plasma response is nonlocal in space and time, and numerous modes are possible with the potential for mode conversions and transformations. Additionally, diffraction effects are important due to finite wavelength and finite-size wave launchers. Multidimensional simulations are required to describe these phenomena, but even with this complexity, the fundamental plasma response is assumed to be the uniform plasma response with the assumption that the local plasma current for a Fourier mode can be described by the Stix conductivity. But, for plasmas with non-uniformmore » magnetic fields, the wave vector itself is nonlocal. When resolved into components perpendicular (k ) and parallel (k ||) to the magnetic field, locality of the parallel component can easily be violated when the wavelength is large. The impact of this inconsistency is that estimates of the wave damping can be incorrect (typically low) due to unresolved resonances. For the case of ion cyclotron damping, this issue has already been addressed by including the effect of parallel magnetic field gradients. In this case, a modified plasma response (Z function) allows resonance broadening even when k || = 0, and this improves the convergence and accuracy of wave simulations. In our paper, we extend this formalism to include electron damping and find improved convergence and accuracy for parameters where electron damping is dominant, such as high harmonic fast wave heating in the NSTX-U tokamak, and helicon wave launch for off-axis current drive in the DIII-D tokamak.« less

Numerical Prediction of Pitch Damping Stability Derivatives for Finned Projectiles

DTIC Science & Technology

2013-11-01

in part by a grant of high-performance computing time from the U.S. DOD High Performance Computing Modernization Program (HPCMP) at the Army...to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data...12 3.3.2 Time -Accurate Simulations

An aeroelastic analysis of the Darrieus wind turbine

NASA Astrophysics Data System (ADS)

Meyer, E. E.; Smith, C. E.

1983-12-01

The stability of a single Darrieus wind turbine blade spinning in still air is investigated using linearized equations of motion. The three most dangerous flutter modes are characterized for a one-parameter family of blades. In addition, the influence of blade density, mass and aerodynamic center offsets, and structural damping is presented.

Instability of a witness bunch in a plasma bubble

DOE Office of Scientific and Technical Information (OSTI.GOV)

Burov, A.; Lebedev, V.; Nagaitsev, S.

2016-02-16

The stability of a trailing witness bunch, accelerated by a plasma wake accelerator (PWA) in a blow-out regime, is discussed. The instability growth rate as well as the energy spread, required for BNS damping, are obtained. A relationship between the PWA power efficiency and the BNS energy spread is derived.

Anomalous temperature-dependent heat transport in one-dimensional momentum-conserving systems with soft-type interparticle interaction

NASA Astrophysics Data System (ADS)

Xiong, Daxing

2017-04-01

We numerically investigate the heat transport problem in a one-dimensional momentum-conserving lattice with a soft-type (ST) anharmonic interparticle interaction. It is found that with the increase of the system's temperature, while the introduction of ST anharmonicity softens phonons and decreases their velocities, this type of nonlinearity like its hard type (HT) counterpart, can still not be able to fully damp the longest wavelength phonons. Therefore, a usual anomalous temperature dependence of heat transport with certain scaling properties similarly to those shown in the Fermi-Pasta-Ulam-β -like systems with HT interactions can be seen. Our detailed examination from simulations verifies this temperature-dependent behavior well.

Experimental and simulation studies of hard contact in force reflecting teleoperation

NASA Technical Reports Server (NTRS)

Hannaford, Blake; Anderson, Robert

1988-01-01

Experiments and simulations of a single-axis force-reflecting teleoperation system have been conducted to investigate the problem of contacting a hard environment and maintaining a controlled force in teleoperation in which position is fed forward from the hand controller (master) to the manipulator (slave), and force is fed back to the human operator through motors in the master. The simulations, using an electrical circuit model, reproduce the behavior of the real system, including effects of human operator biomechanics. It is shown that human operator properties, which vary as a result of different types of grasp of the handle, affect the stability of the system in the hard-contact task. The effect of a heavier grasp on the handle is equivalent to increased hand-controller velocity damping in terms of the systems stability in the contact task, but control system damping sufficient to guarantee stable contact results in perceptible sluggishness of the control handle's response in free motion. These results suggest that human operator biomechanics must be taken into account to guarantee stable and ergonomic performance of advanced teleoperators.

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.

Approximate analytical relationships for linear optimal aeroelastic flight control laws

NASA Astrophysics Data System (ADS)

Kassem, Ayman Hamdy

1998-09-01

This dissertation introduces new methods to uncover functional relationships between design parameters of a contemporary control design technique and the resulting closed-loop properties. Three new methods are developed for generating such relationships through analytical expressions: the Direct Eigen-Based Technique, the Order of Magnitude Technique, and the Cost Function Imbedding Technique. Efforts concentrated on the linear-quadratic state-feedback control-design technique applied to an aeroelastic flight control task. For this specific application, simple and accurate analytical expressions for the closed-loop eigenvalues and zeros in terms of basic parameters such as stability and control derivatives, structural vibration damping and natural frequency, and cost function weights are generated. These expressions explicitly indicate how the weights augment the short period and aeroelastic modes, as well as the closed-loop zeros, and by what physical mechanism. The analytical expressions are used to address topics such as damping, nonminimum phase behavior, stability, and performance with robustness considerations, and design modifications. This type of knowledge is invaluable to the flight control designer and would be more difficult to formulate when obtained from numerical-based sensitivity analysis.

Energy balance of stellar coronae. I - Methods and examples. II - Effect of coronal heating

NASA Technical Reports Server (NTRS)

Hammer, R.

1982-01-01

Simplified models of magnetically open coronal regions are computed, with the aim of fulfilling appropriate boundary conditions at the base of the atmosphere, at the critical point, and at infinity. The models are determined by the stellar mass and radius and by the amount and location of coronal heating, and this dependence is analyzed in terms of pressure, temperature, characteristic heights, energy losses, mass loss, and asymptotic behavior. The results are used to classify the magnetically open coronal regions according to the energy loss mechanism that dominates in the region between the base and the critical point, and it is shown that more complicated heating mechanisms may be replaced by the presented exponential heating law, provided that the damping length is suitably chosen.

A New Global Multi-fluid MHD Model of the Solar Corona

NASA Astrophysics Data System (ADS)

van der Holst, B.; Chandran, B. D. G.; Alterman, B. L.; Kasper, J. C.; Toth, G.

2017-12-01

We present a multi-fluid generalization of the AWSoM model, a global magnetohydrodynamic (MHD) solar corona model with low-frequency Alfven wave turbulence (van der Holst et al., 2014). This new extended model includes electron and multi-ion temperatures and velocities (protons and alpha particles). The coronal heating and acceleration is addressed via outward propagating low-frequency Alfven waves that are partially reflected by Alfven speed gradients. The nonlinear interaction of these counter-propagating waves results in turbulent energy cascade. To apportion the wave dissipation to the electron and ion temperatures, we employ the results of the theories of linear wave damping and nonlinear stochastic heating as described by Chandran et al. (2011, 2013). This heat partitioning results in a more than mass proportional heating among ions.

Microbial and human heat shock proteins as 'danger signals' in sarcoidosis.

PubMed

Dubaniewicz, Anna

2013-12-01

In the light of the Matzinger's model of immune response, human heat shock proteins (HSPs) as main 'danger signals' (tissue damage-associated molecular patterns-DAMPs) or/and microbial HSPs as pathogen-associated molecular patterns (PAMPs) recognized by pattern recognition receptors (PRR), may induce sarcoid granuloma by both infectious and non-infectious factors in genetically different predisposed host. Regarding infectious causes of sarcoid models, low-virulence strains of, e.g. mycobacteria and propionibacteria recognized through changed PRR and persisting in altered host phagocytes, generate increased release of both human and microbial HSPs with their molecular and functional homology. High chronic spread of human and microbial HSPs altering cytokines, co-stimulatory molecules, and Tregs expression, apoptosis, oxidative stress, induces the autoimmunity, considered in sarcoidosis. Regarding non-infectious causes of sarcoidosis, human HSPs may be released at high levels during chronic low-grade exposure to misfolding amyloid precursor protein in stressed cells, phagocyted metal fumes, pigments with/without aluminum in tattoos, and due to heat shock in firefighters. Therefore, human HSPs as DAMPs and/or microbial HSPs as PAMPs produced as a result of non-infectious and infectious factors may induce different models of sarcoidosis, depending on the genetic background of the host. The number/expression of PRRs/ligands may influence the occurrence of sarcoidosis in particular organs. Copyright © 2013 American Society for Histocompatibility and Immunogenetics. Published by Elsevier Inc. All rights reserved.

Shedding light on the eccentricity valley: Gap heating and eccentricity excitation of giant planets in protoplanetary disks

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tsang, David; Cumming, Andrew; Turner, Neal J., E-mail: dtsang@physics.mcgill.ca

2014-02-20

We show that the first order (non-co-orbital) corotation torques are significantly modified by entropy gradients in a non-barotropic protoplanetary disk. Such non-barotropic torques can dramatically alter the balance that, for barotropic cases, results in the net eccentricity damping for giant gap-clearing planets embedded in the disk. We demonstrate that stellar illumination can heat the gap enough for the planet's orbital eccentricity to instead be excited. We also discuss the 'Eccentricity Valley' noted in the known exoplanet population, where low-metallicity stars have a deficit of eccentric planets between ∼0.1 and ∼1 AU compared to metal-rich systems. We show that this featuremore » in the planet distribution may be due to the self-shadowing of the disk by a rim located at the dust sublimation radius ∼0.1 AU, which is known to exist for several T Tauri systems. In the shadowed region between ∼0.1 and ∼1 AU, lack of gap insolation allows disk interactions to damp eccentricity. Outside such shadowed regions stellar illumination can heat the planetary gaps and drive eccentricity growth for giant planets. We suggest that the self-shadowing does not arise at higher metallicity due to the increased optical depth of the gas interior to the dust sublimation radius.« less

Detection of High-Frequency Oscillations and Damping from Multi-slit Spectroscopic Observations of the Corona

NASA Astrophysics Data System (ADS)

Samanta, T.; Singh, J.; Sindhuja, G.; Banerjee, D.

2016-01-01

During the total solar eclipse of 11 July 2010, multi-slit spectroscopic observations of the solar corona were performed from Easter Island, Chile. To search for high-frequency waves, observations were taken at a high cadence in the green line at 5303 Å that is due to [Fe xiv] and the red line at 6374 Å that is due to [Fe x]. The data were analyzed to study the periodic variations in intensity, Doppler velocity, and line width using wavelet analysis. The data with high spectral and temporal resolution enabled us to study the rapid dynamical changes within coronal structures. We find that at certain locations, each parameter shows significant oscillation with periods ranging from 6 - 25 s. For the first time, we were able to detect damping of high-frequency oscillations with periods of about 10 s. If the observed damped oscillations are due to magnetohydrodynamic waves, then they can contribute significantly to the heating of the corona. From a statistical study we try to characterize the nature of the observed oscillations while considering the distribution of power in different line parameters.

ATMOSPHERIC CIRCULATION OF HOT JUPITERS: DAYSIDE–NIGHTSIDE TEMPERATURE DIFFERENCES

DOE Office of Scientific and Technical Information (OSTI.GOV)

Komacek, Thaddeus D.; Showman, Adam P., E-mail: tkomacek@lpl.arizona.edu

The full-phase infrared light curves of low-eccentricity hot Jupiters show a trend of increasing dayside-to-nightside brightness temperature difference with increasing equilibrium temperature. Here, we present a three-dimensional model that explains this relationship, in order to provide insight into the processes that control heat redistribution in tidally locked planetary atmospheres. This three-dimensional model combines predictive analytic theory for the atmospheric circulation and dayside–nightside temperature differences over a range of equilibrium temperatures, atmospheric compositions, and potential frictional drag strengths with numerical solutions of the circulation that verify this analytic theory. The theory shows that the longitudinal propagation of waves mediates dayside–nightside temperaturemore » differences in hot Jupiter atmospheres, analogous to the wave adjustment mechanism that regulates the thermal structure in Earth’s tropics. These waves can be damped in hot Jupiter atmospheres by either radiative cooling or potential frictional drag. This frictional drag would likely be caused by Lorentz forces in a partially ionized atmosphere threaded by a background magnetic field, and would increase in strength with increasing temperature. Additionally, the amplitude of radiative heating and cooling increases with increasing temperature, and hence both radiative heating/cooling and frictional drag damp waves more efficiently with increasing equilibrium temperature. Radiative heating and cooling play the largest role in controlling dayside–nightside temperature differences in both our analytic theory and numerical simulations, with frictional drag only being important if it is stronger than the Coriolis force. As a result, dayside–nightside temperature differences in hot Jupiter atmospheres increase with increasing stellar irradiation and decrease with increasing pressure.« less

Open and Closed Loop Stability of Hingeless Rotor Helicopter Air and Ground Resonance

NASA Technical Reports Server (NTRS)

Young, M. I.; Bailey, D. J.; Hirschbein, M. S.

1974-01-01

The air and ground resonance instabilities of hingeless rotor helicopters are examined on a relatively broad parametric basis including the effects of blade tuning, virtual hinge locations, and blade hysteresis damping, as well as size and scale effects in the gross weight range from 5,000 to 48,000 pounds. A special case of a 72,000 pound helicopter air resonance instability is also included. The study shows that nominal to moderate and readily achieved levels of blade inertial hysteresis damping in conjunction with a variety of tuning and/or feedback conditions are highly effective in dealing with these instabilities. Tip weights and reductions in pre-coning angles are also shown to be effective means for improving the air resonance instability.

Longitudinal Stability and Control Characteristics from a Flight Investigation of a Cruciform Canard Missile Configuration Having an Exposed Wing-canard Area Ratio of 16:1

NASA Technical Reports Server (NTRS)

Moul, Martin T; Wineman, Andrew R

1952-01-01

A flight investigation has been made to determine the longitudinal stability and control characteristics of a 60 0 delta-wing-canard missile configuration with an exposed wing-canard area ratio of 16:1. The results presented include the longitudinal stability derivatives, control effectiveness, and drag characteristics for a Mach number range of 0.75 to 1.80 and are compared with the results of a similar configuration having larger 6ontrols. Stability characteristics are also presented from the flights of an interdigitated canard configuration at a Mach number of 2.08 and a wing-body configuration at Mach numbers of 1.25 to 1.45. The stability derivatives varied gradually with Mach number with the exception of the damping-in-pitch derivative. Aerodynamic damping in pitch decreased to a minimum at a Mach number of 1.0 3, then increased to a peak value at a Mach number of 1.26 followed by a gradual decrease at higher Mach numbers. The aerodynamic-center location of the in-line canard configuration shifted rearward 13 percent of the mean aerodynamic chord at transonic speeds. The pitching-moment curve slope was 25 percent greater for the model having no canards than for the in-line configuration. No large effects of interdigitation were noted in the stability derivatives. Pitching effectiveness of the in-line configuration was maintained throughout the Mach number range. A comparison of the stability and control characteristics of two canard configurations having different area controls showed that decreasing the control area 44 percent decreased the pitching effectiveness proportionally, shifted the aerodynamic-center location rearward 9 to 14 percent of the mean aerodynamic chord, and reduced the total hinge moments required for 10 trimmed flight about 50 percent at transonic speeds.

Fast wave direct electron heating in advanced inductive and ITER baseline scenario discharges in DIII-D

DOE PAGES

Pinsker, R. I.; Austin, M. E.; Diem, S. J.; ...

2014-02-12

Fast Wave (FW) heating and electron cyclotron heating (ECH) are used in the DIII-D tokamak to study plasmas with low applied torque and dominant electron heating characteristic of burning plasmas. FW heating via direct electron damping has reached the 2.5 MW level in high performance ELMy H-mode plasmas. In Advanced Inductive (AI) plasmas, core FW heating was found to be comparable to that of ECH, consistent with the excellent first-pass absorption of FWs predicted by ray-tracing models at high electron beta. FW heating at the ~2 MW level to ELMy H-mode discharges in the ITER Baseline Scenario (IBS) showed unexpectedlymore » strong absorption of FW power by injected neutral beam (NB) ions, indicated by significant enhancement of the D-D neutron rate, while the intended absorption on core electrons appeared rather weak. As a result, the AI and IBS discharges are compared in an effort to identify the causes of the different response to FWs.« less

Fast wave direct electron heating in advanced inductive and ITER baseline scenario discharges in DIII-D

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pinsker, R. I.; Jackson, G. L.; Luce, T. C.

Fast Wave (FW) heating and electron cyclotron heating (ECH) are used in the DIII-D tokamak to study plasmas with low applied torque and dominant electron heating characteristic of burning plasmas. FW heating via direct electron damping has reached the 2.5 MW level in high performance ELMy H-mode plasmas. In Advanced Inductive (AI) plasmas, core FW heating was found to be comparable to that of ECH, consistent with the excellent first-pass absorption of FWs predicted by ray-tracing models at high electron beta. FW heating at the ∼2 MW level to ELMy H-mode discharges in the ITER Baseline Scenario (IBS) showed unexpectedlymore » strong absorption of FW power by injected neutral beam (NB) ions, indicated by significant enhancement of the D-D neutron rate, while the intended absorption on core electrons appeared rather weak. The AI and IBS discharges are compared in an effort to identify the causes of the different response to FWs.« less

Fast wave direct electron heating in advanced inductive and ITER baseline scenario discharges in DIII-D

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pinsker, R. I.; Austin, M. E.; Diem, S. J.

Fast Wave (FW) heating and electron cyclotron heating (ECH) are used in the DIII-D tokamak to study plasmas with low applied torque and dominant electron heating characteristic of burning plasmas. FW heating via direct electron damping has reached the 2.5 MW level in high performance ELMy H-mode plasmas. In Advanced Inductive (AI) plasmas, core FW heating was found to be comparable to that of ECH, consistent with the excellent first-pass absorption of FWs predicted by ray-tracing models at high electron beta. FW heating at the ~2 MW level to ELMy H-mode discharges in the ITER Baseline Scenario (IBS) showed unexpectedlymore » strong absorption of FW power by injected neutral beam (NB) ions, indicated by significant enhancement of the D-D neutron rate, while the intended absorption on core electrons appeared rather weak. As a result, the AI and IBS discharges are compared in an effort to identify the causes of the different response to FWs.« less

B-52 stability augmentation system reliability

NASA Technical Reports Server (NTRS)

Bowling, T. C.; Key, L. W.

1976-01-01

The B-52 SAS (Stability Augmentation System) was developed and retrofitted to nearly 300 aircraft. It actively controls B-52 structural bending, provides improved yaw and pitch damping through sensors and electronic control channels, and puts complete reliance on hydraulic control power for rudder and elevators. The system has experienced over 300,000 flight hours and has exhibited service reliability comparable to the results of the reliability test program. Development experience points out numerous lessons with potential application in the mechanization and development of advanced technology control systems of high reliability.

Static and dynamic stability analysis of the space shuttle vehicle-orbiter

NASA Technical Reports Server (NTRS)

Chyu, W. J.; Cavin, R. K.; Erickson, L. L.

1978-01-01

The longitudinal static and dynamic stability of a Space Shuttle Vehicle-Orbiter (SSV Orbiter) model is analyzed using the FLEXSTAB computer program. Nonlinear effects are accounted for by application of a correction technique in the FLEXSTAB system; the technique incorporates experimental force and pressure data into the linear aerodynamic theory. A flexible Orbiter model is treated in the static stability analysis for the flight conditions of Mach number 0.9 for rectilinear flight (1 g) and for a pull-up maneuver (2.5 g) at an altitude of 15.24 km. Static stability parameters and structural deformations of the Orbiter are calculated at trim conditions for the dynamic stability analysis, and the characteristics of damping in pitch are investigated for a Mach number range of 0.3 to 1.2. The calculated results for both the static and dynamic stabilities are compared with the available experimental data.

Damping of prominence longitudinal oscillations due to mass accretion

NASA Astrophysics Data System (ADS)

Ruderman, Michael S.; Luna, Manuel

2016-06-01

We study the damping of longitudinal oscillations of a prominence thread caused by the mass accretion. We suggested a simple model describing this phenomenon. In this model we considered a thin curved magnetic tube filled with the plasma. The prominence thread is in the central part of the tube and it consists of dense cold plasma. The parts of the tube at the two sides of the thread are filled with hot rarefied plasma. We assume that there are flows of rarefied plasma toward the thread caused by the plasma evaporation at the magnetic tube footpoints. Our main assumption is that the hot plasma is instantaneously accommodated by the thread when it arrives at the thread, and its temperature and density become equal to those of the thread. Then we derive the system of ordinary differential equations describing the thread dynamics. We solve this system of ordinary differential equations in two particular cases. In the first case we assume that the magnetic tube is composed of an arc of a circle with two straight lines attached to its ends such that the whole curve is smooth. A very important property of this model is that the equations describing the thread oscillations are linear for any oscillation amplitude. We obtain the analytical solution of the governing equations. Then we obtain the analytical expressions for the oscillation damping time and periods. We find that the damping time is inversely proportional to the accretion rate. The oscillation periods increase with time. We conclude that the oscillations can damp in a few periods if the inclination angle is sufficiently small, not larger that 10°, and the flow speed is sufficiently large, not less that 30 km s-1. In the second model we consider the tube with the shape of an arc of a circle. The thread oscillates with the pendulum frequency dependent exclusively on the radius of curvature of the arc. The damping depends on the mass accretion rate and the initial mass of the threads, that is the mass of the thread at the moment when it is perturbed. First we consider small amplitude oscillations and use the linear description. Then we consider nonlinear oscillations and assume that the damping is slow, meaning that the damping time is much larger that the characteristic oscillation time. The thread oscillations are described by the solution of the nonlinear pendulum problem with slowly varying amplitude. The nonlinearity reduces the damping time, however this reduction is small. Again the damping time is inversely proportional to the accretion rate. We also obtain that the oscillation periods decrease with time. However even for the largest initial oscillation amplitude considered in our article the period reduction does not exceed 20%. We conclude that the mass accretion can damp the motion of the threads rapidly. Thus, this mechanism can explain the observed strong damping of large-amplitude longitudinal oscillations. In addition, the damping time can be used to determine the mass accretion rate and indirectly the coronal heating.

Analysis of higher harmonics on bidirectional heat pulse propagation experiment in helical and tokamak plasmas

NASA Astrophysics Data System (ADS)

Kobayashi, T.; Ida, K.; Inagaki, S.; Tsuchiya, H.; Tamura, N.; Choe, G. H.; Yun, G. S.; Park, H. K.; Ko, W. H.; Evans, T. E.; Austin, M. E.; Shafer, M. W.; Ono, M.; López-bruna, D.; Ochando, M. A.; Estrada, T.; Hidalgo, C.; Moon, C.; Igami, H.; Yoshimura, Y.; Tsujimura, T. Ii.; Itoh, S.-I.; Itoh, K.

2017-07-01

In this contribution we analyze modulation electron cyclotron resonance heating (MECH) experiment and discuss higher harmonic frequency dependence of transport coefficients. We use the bidirectional heat pulse propagation method, in which both inward propagating heat pulse and outward propagating heat pulse are analyzed at a radial range, in order to distinguish frequency dependence of transport coefficients due to hysteresis from that due to other reasons, such as radially dependent transport coefficients, a finite damping term, or boundary effects. The method is applied to MECH experiments performed in various helical and tokamak devices, i.e. Large Helical Device (LHD), TJ-II, Korea Superconducting Tokamak Advanced Research (KSTAR), and Doublet III-D (DIII-D) with different plasma conditions. The frequency dependence of transport coefficients are clearly observed, showing a possibility of existence of transport hysteresis in flux-gradient relation.

Stabilizing Gyroscopic Modes in Magnetic-Bearing-Supported Flywheels by Using Cross-Axis Proportional Gains

NASA Technical Reports Server (NTRS)

Brown, Gerald V.; Kascak, Albert F.; Jansen, Ralph H.; Dever, Timothy P.; Duffy, Kirsten P.

2006-01-01

For magnetic-bearing-supported high-speed rotating machines with significant gyroscopic effects, it is necessary to stabilize forward and backward tilt whirling modes. Instability or low damping of these modes can prevent the attainment of desired shaft speed. We show analytically that both modes can be stabilized by using cross-axis proportional gains and high- and low-pass filters in the magnetic bearing controller. Furthermore, at high shaft speeds, where system phase lags degrade the stability of the forward-whirl mode, a phasor advance of the control signal can partially counteract the phase lag. In some range of high shaft speed, the derivative gain for the tilt modes (essential for stability for slowly rotating shafts) can be removed entirely. We show analytically how the tilt eigenvalues depend on shaft speed and on various controller feedback parameters.

Effect of boundary (support) conditions on piezoelectric damping in the case of SSDI vibration control technique

NASA Astrophysics Data System (ADS)

Guyomar, D.; Mohammadi, S.; Richard, C.

2009-02-01

Piezoelectric transducers in conjunction with appropriate electric networks can be used as a mechanical energy dissipation device. If a piezoelectric element is attached to a structure, it is strained as the structure deforms and converts a portion of the vibration energy into electrical energy that can be dissipated through a shunt network in the form of heating. These vibration control devices experienced a great development in recent years, due to their performances and advantages compared with active techniques. One of them is the synchronized switch damping (SSD) and derived techniques, which were developed in the field of piezoelectric damping, and which lead to a very good trade-off between the simplicity, the required power supply and their performances. This technique consists in a non-linear processing of the piezoelectric voltage, which induces an increase in electromechanical energy conversion. The control law consists in triggering the inverting switch on each extremum of voltage (or displacement). In this study, the proposed method for the switching sequence is based on the statistical evaluation of structural deflection. The purpose of this paper is to present an experimental study of the synchronized switch damping on inductance (SSDI) control technique sensitivity to the system boundary conditions. It is observed that the fundamental natural frequency greatly depends on these conditions. The effect of these constraints is distributed all over the system and significantly affects the results.

Mean-field and linear regime approach to magnetic hyperthermia of core-shell nanoparticles: can tiny nanostructures fight cancer?

NASA Astrophysics Data System (ADS)

Carrião, Marcus S.; Bakuzis, Andris F.

2016-04-01

The phenomenon of heat dissipation by magnetic materials interacting with an alternating magnetic field, known as magnetic hyperthermia, is an emergent and promising therapy for many diseases, mainly cancer. Here, a magnetic hyperthermia model for core-shell nanoparticles is developed. The theoretical calculation, different from previous models, highlights the importance of heterogeneity by identifying the role of surface and core spins on nanoparticle heat generation. We found that the most efficient nanoparticles should be obtained by selecting materials to reduce the surface to core damping factor ratio, increasing the interface exchange parameter and tuning the surface to core anisotropy ratio for each material combination. From our results we propose a novel heat-based hyperthermia strategy with the focus on improving the heating efficiency of small sized nanoparticles instead of larger ones. This approach might have important implications for cancer treatment and could help improving clinical efficacy.The phenomenon of heat dissipation by magnetic materials interacting with an alternating magnetic field, known as magnetic hyperthermia, is an emergent and promising therapy for many diseases, mainly cancer. Here, a magnetic hyperthermia model for core-shell nanoparticles is developed. The theoretical calculation, different from previous models, highlights the importance of heterogeneity by identifying the role of surface and core spins on nanoparticle heat generation. We found that the most efficient nanoparticles should be obtained by selecting materials to reduce the surface to core damping factor ratio, increasing the interface exchange parameter and tuning the surface to core anisotropy ratio for each material combination. From our results we propose a novel heat-based hyperthermia strategy with the focus on improving the heating efficiency of small sized nanoparticles instead of larger ones. This approach might have important implications for cancer treatment and could help improving clinical efficacy. Electronic supplementary information (ESI) available: Unit cells per region calculation; core-shell Hamiltonian; magnetisation description functions; energy argument of Brillouin function; polydisperse models; details of experimental procedure; LRT versus core-shell model; model calculation software; and shell thickness study. See DOI: 10.1039/C5NR09093H

Electrophilic dark matter with dark photon: From DAMPE to direct detection

NASA Astrophysics Data System (ADS)

Gu, Pei-Hong; He, Xiao-Gang

2018-03-01

The electron-positron excess reported by the DAMPE collaboration recently may be explained by an electrophilic dark matter (DM). A standard model singlet fermion may play the role of such a DM when it is stabilized by some symmetries, such as a dark U(1)X gauge symmetry, and dominantly annihilates into the electron-positron pairs through the exchange of a scalar mediator. The model, with appropriate Yukawa couplings, can well interpret the DAMPE excess. Naively one expects that in this type of models the DM-nucleon cross section should be small since there is no tree-level DM-quark interactions. We however find that at one-loop level, a testable DM-nucleon cross section can be induced for providing ways to test the electrophilic model. We also find that a U (1) kinetic mixing can generate a sizable DM-nucleon cross section although the U(1)X dark photon only has a negligible contribution to the DM annihilation. Depending on the signs of the mixing parameter, the dark photon can enhance/reduce the one-loop induced DM-nucleon cross section.

Simulation of a flexible spinning vehicle

NASA Technical Reports Server (NTRS)

Baudry, W. A.

1972-01-01

Results are presented of experimental investigation of the controlled and uncontrolled dynamical behavior of a rotating or artificial gravity space station including flexible body effects. A dynamically scaled model was supported by a spherical air bearing which provided a nearly moment free environment. Reaction jet system were provided for spin-up and spin-down and for damping of wobble motion. Two single-gimbal gyros were arranged as a control moment gyro wobble damping system. Remotely controllable movable masses were provided to simulate mass shift disturbances such as arise from crew motions. An active mass balance wobble damping system which acted to minimize the wobble motions induced by crew motions was also installed. Flexible body effects were provided by a pair of inertia augmentation booms. Inertia augmentation booms are contemplated for use on rotating space stations to cause the spin axis moment of inertia to be the largest of the three moments of inertia as is necessary to assure gyroscopic stability. Test runs were made with each of the control systems with the booms locked (rigid body) and unlocked (flexible body).

An experimental study on pseudoelasticity of a NiTi-based damper for civil applications

NASA Astrophysics Data System (ADS)

Nespoli, Adelaide; Bassani, Enrico; Della Torre, Davide; Donnini, Riccardo; Villa, Elena; Passaretti, Francesca

2017-10-01

In this work, a pseudoelastic damper composed by NiTi wires is tested at 0.5, 1 and 2 Hz for 1000 mechanical cycles. The damping performances were evaluated by three key parameters: the damping capacity, the dissipated energy per cycle and the maximum force. During testing, the temperature of the pseudoelastic elements was registered as well. Results show that the damper assures a bi-directional motion throughout the 1000 cycles together with the maintenance of the recentering. It was observed a stabilization process in the first 50 mechanical cycles, where the key parameters reach stable values; in particular it was found that the damping capacity and the dissipated energy both decrease with frequency. Besides, the mean temperature of the pseudoleastic elements reaches a stable value during tests and confirms the different response of the pseudoelastic wires accordingly with the specific length and stain. Finally, interesting thermal effects were observed at 1 and 2 Hz: at these frequencies and at high strains, the maximum force increases but the temperature of the NiTi wire decreases being in contraddiction with the Clausius-Clapeyron law.

Dynamic Analysis of a Rotor System Supported on Squeeze Film Damper with Air Entrainment

NASA Astrophysics Data System (ADS)

Zhang, Wei; Han, Bingbing; Zhang, Kunpeng; Ding, Qian

2017-12-01

Squeeze film dampers (SFDs) are widely used in compressors and turbines to suppress the vibration while traversing critical speeds. In practical applications, air ingestion from the outside environment and cavitation may lead to a foamy lubricant that weakens oil film damping and dynamic performance of rotor system. In this paper, a rigid rotor model is established considering both lateral and pitching vibration under different imbalance excitations to evaluate the effect of air entrainment on rotor system. Tests with three different imbalances are carried out on a rotor-SFD apparatus. Volume controlled air in mixture ranging from pure oil to all air are supplied to the SFD. The transient response of rotor is measured in the experiments. The results show that two-phase flow produces significant influence on the system stability and dynamical response. The damping properties are weakened by entrained air, such as the damping on high frequency components of rolling ball bearing. Super-harmonic resonance and bifurcation are observed, as well as the low frequency components due to air entrainment.

Quantum thermodynamics for driven dissipative bosonic systems

NASA Astrophysics Data System (ADS)

Ochoa, Maicol A.; Zimbovskaya, Natalya; Nitzan, Abraham

2018-02-01

We investigate two prototypical dissipative bosonic systems under slow driving and arbitrary system-bath coupling strength, recovering their dynamic evolution as well as the heat and work rates, and we verify that thermodynamic laws are respected. Specifically, we look at the damped harmonic oscillator and the damped two-level system. For the former, we study independently the slow time-dependent perturbation in the oscillator frequency and in the coupling strength. For the latter, we concentrate on the slow modulation of the energy gap between the two levels. Importantly, we are able to find the entropy production rates for each case without explicitly defining nonequilibrium extensions for the entropy functional. This analysis also permits the definition of phenomenological friction coefficients in terms of structural properties of the system-bath composite.

Investigation of excitation control for wind-turbine generator stability

NASA Technical Reports Server (NTRS)

Gebben, V. D.

1977-01-01

High speed horizontal axis wind turbine generators with blades on the downwind side of the support tower require special design considerations to handle disturbances introduced by the flow wake behind the tower. Experiments and analytical analyses were made to determine benefits that might be obtained by using the generator exciter to provide system damping for reducing power fluctuations.

Acoustic waves in the solar atmosphere. VII - Non-grey, non-LTE H(-) models

NASA Technical Reports Server (NTRS)

Schmitz, F.; Ulmschneider, P.; Kalkofen, W.

1985-01-01

The propagation and shock formation of radiatively damped acoustic waves in the solar chromosphere are studied under the assumption that H(-) is the only absorber; the opacity is non-grey. Deviations from local thermodynamic equilibrium (LTE) are permitted. The results of numerical simulations show the depth dependence of the heating by the acoustic waves to be insensitive to the mean state of the atmosphere. After the waves have developed into shocks, their energy flux decays exponentially with a constant damping length of about 1.4 times the pressure scale height, independent of initial flux and wave period. Departures from LTE have a strong influence on the mean temperature structure in dynamical chromosphere models; this is even more pronounced in models with reduced particle density - simulating conditions in magnetic flux tubes - which show significantly increased temperatures in response to mechanical heating. When the energy dissipation of the waves is sufficiently large to dissociate most of the H(-) ions, a strong temperature rise is found that is reminiscent of the temperature structure in the transition zone between chromosphere and corona; the energy flux remaining in the waves then drives mass motions.

On the self-damping nature of densification in photonic sintering of nanoparticles

PubMed Central

MacNeill, William; Choi, Chang-Ho; Chang, Chih-Hung; Malhotra, Rajiv

2015-01-01

Sintering of nanoparticle inks over large area-substrates is a key enabler for scalable fabrication of patterned and continuous films, with multiple emerging applications. The high speed and ambient condition operation of photonic sintering has elicited significant interest for this purpose. In this work, we experimentally characterize the temperature evolution and densification in photonic sintering of silver nanoparticle inks, as a function of nanoparticle size. It is shown that smaller nanoparticles result in faster densification, with lower temperatures during sintering, as compared to larger nanoparticles. Further, high densification can be achieved even without nanoparticle melting. Electromagnetic Finite Element Analysis of photonic heating is coupled to an analytical sintering model, to examine the role of interparticle neck growth in photonic sintering. It is shown that photonic sintering is an inherently self-damping process, i.e., the progress of densification reduces the magnitude of subsequent photonic heating even before full density is reached. By accounting for this phenomenon, the developed coupled model better captures the experimentally observed sintering temperature and densification as compared to conventional photonic sintering models. Further, this model is used to uncover the reason behind the experimentally observed increase in densification with increasing weight ratio of smaller to larger nanoparticles. PMID:26443492

Self-tuning pressure-feedback control by pole placement for vibration reduction of excavator with independent metering fluid power system

NASA Astrophysics Data System (ADS)

Ding, Ruqi; Xu, Bing; Zhang, Junhui; Cheng, Min

2017-08-01

Independent metering control systems are promising fluid power technologies compared with traditional valve controlled systems. By breaking the mechanical coupling between the inlet and outlet, the meter-out valve can open as large as possible to reduce energy consumptions. However, the lack of damping in outlet causes stronger vibrations. To address the problem, the paper designs a hybrid control method combining dynamic pressure-feedback and active damping control. The innovation resides in the optimization of damping by introducing pressure feedback to make trade-offs between high stability and fast response. To achieve this goal, the dynamic response pertaining to the control parameters consisting of feedback gain and cut-off frequency, are analyzed via pole-zero locations. Accordingly, these parameters are tuned online in terms of guaranteed dominant pole placement such that the optimal damping can be accurately captured under a considerable variation of operating conditions. The experiment is deployed in a mini-excavator. The results pertaining to different control parameters confirm the theoretical expectations via pole-zero locations. By using proposed self-tuning controller, the vibrations are almost eliminated after only one overshoot for different operation conditions. The overshoots are also reduced with less decrease of the response time. In addition, the energy-saving capability of independent metering system is still not affected by the improvement of controllability.

Sub-synchronous resonance damping using high penetration PV plant

NASA Astrophysics Data System (ADS)

Khayyatzadeh, M.; Kazemzadeh, R.

2017-02-01

The growing need to the clean and renewable energy has led to the fast development of transmission voltage-level photovoltaic (PV) plants all over the world. These large scale PV plants are going to be connected to power systems and one of the important subjects that should be investigated is the impact of these plants on the power system stability. Can large scale PV plants help to damp sub-synchronous resonance (SSR) and how? In this paper, this capability of a large scale PV plant is investigated. The IEEE Second Benchmark Model aggregated with a PV plant is utilized as the case study. A Wide Area Measurement System (WAMS) based conventional damping controller is designed and added to the main control loop of PV plant in order to damp the SSR and also investigation of the destructive effect of time delay in remote feedback signal. A new optimization algorithm called teaching-learning-based-optimization (TLBO) algorithm has been used for managing the optimization problems. Fast Furrier Transformer (FFT) analysis and also transient simulations of detailed nonlinear system are considered to investigate the performance of the controller. Robustness of the proposed system has been analyzed by facing the system with disturbances leading to significant changes in generator and power system operating point, fault duration time and PV plant generated power. All the simulations are carried out in MATLAB/SIMULINK environment.

Improved modeling of turbulent forced convection heat transfer in straight ducts

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rokni, M.; Sunden, B.

1999-08-01

This investigation concerns numerical calculation of turbulent forced convective heat transfer and fluid flow in their fully developed state at low Reynolds number. The authors have developed a low Reynolds number version of the nonlinear {kappa}-{epsilon} model combined with the heat flux models of simple eddy diffusivity (SED), low Reynolds number version of generalized gradient diffusion hypothesis (GGDH), and wealth {proportional_to} earning {times} time (WET) in general three-dimensional geometries. The numerical approach is based on the finite volume technique with a nonstaggered grid arrangement and the SIMPLEC algorithm. Results have been obtained with the nonlinear {kappa}-{epsilon} model, combined with themore » Lam-Bremhorst and the Abe-Kondoh-Nagano damping functions for low Reynolds numbers.« less

A GDT-based fusion neutron source for academic and industrial applications

NASA Astrophysics Data System (ADS)

Anderson, J. K.; Forest, C. B.; Mirnov, V. V.; Peterson, E. E.; Waleffe, R.; Wallace, J.; Harvey, R. W.

2017-10-01

The design of a fusion neutron source based on the gas dynamic trap (GDT) configuration is underway. The motivation is both the ends and the means. There are immediate applications for neutrons including medical isotope production and actinide burners. Taking the next step in the magnetic mirror path will leverage advances in high-temperature superconducting magnets and additive manufacturing in confining a fusion plasma, and both the technological and physics bases exist. Recent breakthrough results at the GDT facility in Russia demonstrate stable confinement of a beta 60% mirror plasma at high Te ( 1 keV). These scale readily to a fusion neutron source with an increase in magnetic field, mirror ratio, and ion energy. Studies of a next-step compact device focus on calculations of MHD equilibrium and stability, and Fokker-Planck modeling to optimize the heating scenario. The conceptualized device uses off-the-shelf MRI magnets for a 1 T central field, REBCO superconducting mirror coils (which can currently produce fields in excess of 30T), and existing 75 keV NBI and 140 GHz ECRH. High harmonic fast wave injection is damped on beam ions, dramatically increasing the fusion reactivity for an incremental bump in input power. MHD stability is achieved with the vortex confinement scheme, where a biasing profile imposes optimal ExB rotation of the plasma. Liquid metal divertors are being considered in the end cells. Work supported by the Wisconsin Alumni Research Foundation.

Unidirectional spin-wave heat conveyer.

PubMed

An, T; Vasyuchka, V I; Uchida, K; Chumak, A V; Yamaguchi, K; Harii, K; Ohe, J; Jungfleisch, M B; Kajiwara, Y; Adachi, H; Hillebrands, B; Maekawa, S; Saitoh, E

2013-06-01

When energy is introduced into a region of matter, it heats up and the local temperature increases. This energy spontaneously diffuses away from the heated region. In general, heat should flow from warmer to cooler regions and it is not possible to externally change the direction of heat conduction. Here we show a magnetically controllable heat flow caused by a spin-wave current. The direction of the flow can be switched by applying a magnetic field. When microwave energy is applied to a region of ferrimagnetic Y3Fe5O12, an end of the magnet far from this region is found to be heated in a controlled manner and a negative temperature gradient towards it is formed. This is due to unidirectional energy transfer by the excitation of spin-wave modes without time-reversal symmetry and to the conversion of spin waves into heat. When a Y3Fe5O12 film with low damping coefficients is used, spin waves are observed to emit heat at the sample end up to 10 mm away from the excitation source. The magnetically controlled remote heating we observe is directly applicable to the fabrication of a heat-flow controller.

[Observation of curative effect of herpes zoster treated with acupuncture based on syndrome differentiation combined with pricking and cupping].

PubMed

Pan, Hua

2011-10-01

To compare the differences of curative effects of herpes zoster treated with acupuncture based on syndrome differentiation combined with pricking and cupping and simple pricking and cupping. Eighty-six cases were randomly divided into an observation group (43 cases) and a control group (43 cases). In observation group, acupoints selection based on syndrome differentiation i.e. Quchi (LI 11), Zusanli (ST 36), Sanyinjiao (SP 6), etc. were selected and pricking and cupping at affected parts were applied, and the cases were classified into damp heat in liver and gallbladder, damp retention and spleen deficiency, and qi deficiency and blood stasis. In control group, all the cases were simplely treated with pricking and cupping at affected parts. The treatment was given once a day, and seven days were made one session. The curative effect was evaluated after 2 courses, and the follow-up was carried on after 1 month. The cured and markedly effective rate was 93.0% (40/43) in observation group, superior to that of 67.4% (29/43) in control group (P < 0.01). Postherpetic neuralgia: there was 2.3% (1/43) in observation group, inferior to that of 14.0% (6/43) in control group. Comparison in 3 types: the cured and markedly effective rate of damp heat in liver and gallbladder: 94.7% (18/19) in observation group, and 85.7% (18/21) in control group, showing no significant difference between groups (P > 0.05). The cured and markedly effective rate of damp retention and spleen deficiency: 93.8% (15/16) in observation group, superior to that of 60.0% (9/15) in control group (P < 0. 05). The cured and markedly effective rate of qi deficiency and blood stasis: 87.5% (7/8) in observation group, superior to that of 28.6% (2/7) in control group (P < 0.05). For herpes zoster, acupoints selection based on syndrome differentiation combined with pricking and cupping therapy is high pertinent and effective, the postherpetic neuralgia can be reduced significantly and the curative effect is superior to that of simple pricking and cupping.

The effect of convection and shear on the damping and propagation of pressure waves

NASA Astrophysics Data System (ADS)

Kiel, Barry Vincent

Combustion instability is the positive feedback between heat release and pressure in a combustion system. Combustion instability occurs in the both air breathing and rocket propulsion devices, frequently resulting in high amplitude spinning waves. If unchecked, the resultant pressure fluctuations can cause significant damage. Models for the prediction of combustion instability typically include models for the heat release, the wave propagation and damping. Many wave propagation models for propulsion systems assume negligible flow, resulting in the wave equation. In this research the effect of flow on wave propagation was studied both numerically and experimentally. Two experiential rigs were constructed, one with axial flow to study the longitudinal waves, the other with swirling flow to study circumferential waves. The rigs were excited with speakers and the resultant pressure was measured simultaneously at many locations. Models of the rig were also developed. Equations for wave propagation were derived from the Euler Equations. The resultant resembled the wave equation with three additional terms, two for the effect of the convection and a one for the effect of shear of the mean flow on wave propagation. From the experimental and numerical data several conclusions were made. First, convection and shear both act as damping on the wave propagation, reducing the magnitude of the Frequency Response Function and the resonant frequency of the modes. Second, the energy extracted from the mean flow as a result of turbulent shear for a given condition is frequency dependent, decreasing with increasing frequency. The damping of the modes, measured for the same shear flow, also decreased with frequency. Finally, the two convective terms cause the anti-nodes of the modes to no longer be stationary. For both the longitudinal and circumferential waves, the anti-nodes move through the domain even for mean flow Mach numbers less than 0.10. It was concluded that convection causes the spinning waves documented in inlets and exhausts of gas turbine engines, rocket combustion chambers, and afterburner chambers. As a result, the effects of shear must be included when modeling wave propagation, even for mean flows less than < Mach 0.10.

Beam dynamics issues in linear colliders

DOE Office of Scientific and Technical Information (OSTI.GOV)

Seeman, J.T.

1989-06-01

The primary goal of present and future linear colliders is to maximize the integrated luminosity for the experimental program. Beam dynamics plays a central role in the maximization of integrated luminosity. It is the major issue in the production of small beam sizes and low experimental backgrounds and is also an important factor in the production of particle numbers, in the acceleration process, and in the number of bunches. The beam dynamics effects on bunches which are extracted from the damping rings, accelerated in the linac, collimated, momentum analyzed, and finally delivered to the final focus are reviewed. The effectsmore » of bunch compression, transverse and longitudinal wakefields, BNS damping, energy definition, dispersion, emittance, bunch aspect ratio, feedback, and stability are all important. 11 refs., 1 tab.« less

Fluid Compressibility Effects on the Dynamic Response of Hydrostatic Journal Bearings

NASA Technical Reports Server (NTRS)

Sanandres, Luis A.

1991-01-01

A theoretical analysis for the dynamic performance characteristics of laminar flow, capillar/orifice compensated hydrostatic journal bearings is presented. The analysis considers in detail the effect of fluid compressibility in the bearing recesses. At high frequency excitations beyond a break frequency, the bearing hydrostatic stiffness increases sharply and it is accompanied by a rapid decrease in direct damping. Also, the potential of pneumatic hammer instability (negative damping) at low frequencies is likely to occur in hydrostatic bearing applications handling highly compressible fluids. Useful design criteria to avoid undesirable dynamic operating conditions at low and high frequencies are determined. The effect of fluid recess compressibility is brought into perspective, and found to be of utmost importance on the entire frequency spectrum response and stability characteristics of hydrostatic/hybrid journal bearings.

Capillary waves with surface viscosity

NASA Astrophysics Data System (ADS)

Shen, Li; Denner, Fabian; Morgan, Neal; van Wachem, Berend; Dini, Daniele

2017-11-01

Experiments over the last 50 years have suggested a correlation between the surface (shear) viscosity and the stability of a foam or emulsion. With recent techniques allowing more accurate measurements of the elusive surface viscosity, we examine this link theoretically using small-amplitude capillary waves in the presence of the Marangoni effect and surface viscosity modelled via the Boussinesq-Scriven model. The surface viscosity effect is found to contribute a damping effect on the amplitude of the capillary wave with subtle differences to the effect of the convective-diffusive Marangoni transport. The general wave dispersion is augmented to take into account the Marangoni and surface viscosity effects, and a first-order correction to the critical damping wavelength is derived. The authors acknowledge the financial support of the Shell University Technology Centre for fuels and lubricants.

A fully Galerkin method for the recovery of stiffness and damping parameters in Euler-Bernoulli beam models

NASA Technical Reports Server (NTRS)

Smith, R. C.; Bowers, K. L.

1991-01-01

A fully Sinc-Galerkin method for recovering the spatially varying stiffness and damping parameters in Euler-Bernoulli beam models is presented. The forward problems are discretized with a sinc basis in both the spatial and temporal domains thus yielding an approximate solution which converges exponentially and is valid on the infinite time interval. Hence the method avoids the time-stepping which is characteristic of many of the forward schemes which are used in parameter recovery algorithms. Tikhonov regularization is used to stabilize the resulting inverse problem, and the L-curve method for determining an appropriate value of the regularization parameter is briefly discussed. Numerical examples are given which demonstrate the applicability of the method for both individual and simultaneous recovery of the material parameters.

Constitution of traditional chinese medicine and related factors in women of childbearing age.

PubMed

Jiang, Qiao-Yu; Li, Jue; Zheng, Liang; Wang, Guang-Hua; Wang, Jing

2018-04-01

This study investigates the constitution of traditional Chinese medicine (TCM) among women who want to be pregnant in one year and explores factors related to TCM constitution. This study was conducted on women who participated in free preconception check-ups provided by the Zhabei District Maternity and Child Care Center in Shanghai, China. The information regarding the female demographic characteristics, physical condition, history of pregnancy and childbearing, diet and behavior, and social psychological factors was collected, and TCM constitution assessment was performed. The Chi-square test, t-test, logistic regression analysis, and multinomial logistic regression analysis were used to explore the related factors of TCM constitution. The participants in this study were aged 28.3 ± 3.0 years. Approximately fifty-five women in this study had Unbalanced Constitution. Logistic regression analysis showed that Shanghai residence, dysmenorrhea, gum bleeding, aversion to vegetables, preference for raw meat, job stress, and economic stress were significantly and negatively associated with Balanced Constitution. Multinomial logistic analysis showed that Shanghai residence was significantly associated with Yang-deficiency, Yin-deficiency, and Stagnant Qi Constitutions; gum bleeding was significantly associated with Yin-deficiency, Stagnant Blood, Stagnant Qi, and Inherited Special Constitutions; aversion to vegetables was significantly associated with Damp-heat Constitution; job stress was significantly associated with Yang-deficiency, Phlegm-dampness, Damp-heat, Stagnant Blood, and Stagnant Qi Constitutions; and economic stress was significantly associated with Yang-deficiency, and Stagnant Qi Constitutions. The application of TCM constitution to preconception care would be beneficial for early identification of potential TCM constitution risks and be beneficial for early intervention (e.g., health education, and dietary education), especially during the women who do not have a medical condition and those who have related factors found in this study. Copyright © 2018. Published by Elsevier Taiwan LLC.

Whistlers, Helicons, Lower Hybrid Waves: the Physics of RF Wave Absorption Without Cyclotron Resonances

NASA Astrophysics Data System (ADS)

Pinsker, R. I.

2014-10-01

In hot magnetized plasmas, two types of linear collisionless absorption processes are used to heat and drive noninductive current: absorption at ion or electron cyclotron resonances and their harmonics, and absorption by Landau damping and the transit-time-magnetic-pumping (TTMP) interactions. This tutorial discusses the latter process, i.e., parallel interactions between rf waves and electrons in which cyclotron resonance is not involved. Electron damping by the parallel interactions can be important in the ICRF, particularly in the higher harmonic region where competing ion cyclotron damping is weak, as well as in the Lower Hybrid Range of Frequencies (LHRF), which is in the neighborhood of the geometric mean of the ion and electron cyclotron frequencies. On the other hand, absorption by parallel processes is not significant in conventional ECRF schemes. Parallel interactions are especially important for the realization of high current drive efficiency with rf waves, and an application of particular recent interest is current drive with the whistler or helicon wave at high to very high (i.e., the LHRF) ion cyclotron harmonics. The scaling of absorption by parallel interactions with wave frequency is examined and the advantages and disadvantages of fast (helicons/whistlers) and slow (lower hybrid) waves in the LHRF in the context of reactor-grade tokamak plasmas are compared. In this frequency range, both wave modes can propagate in a significant fraction of the discharge volume; the ways in which the two waves can interact with each other are considered. The use of parallel interactions to heat and drive current in practice will be illustrated with examples from past experiments; also looking forward, this tutorial will provide an overview of potential applications in tokamak reactors. Supported by the US Department of Energy under DE-FC02-04ER54698.

Squeeze-film dampers for turbomachinery stabilization

NASA Technical Reports Server (NTRS)

Mclean, L. J.; Hahn, E. J.

1984-01-01

A technique for investigating the stability and damping present in centrally preloaded radially symmetric multi-mass flexible rotor bearing systems is presented. In general, one needs to find the eigenvalues of the linearized perturbation equations, though zero frequency stability maps may be found by solving as many simultaneous non-linear equations as there are dampers; and in the case of a single damper, such maps may be found directly, regardless of the number of degrees of freedom. The technique is illustrated for a simple symmetric four degree of freedom flexible rotor with an unpressurized damper. This example shows that whereas zero frequency stability maps are likely to prove to be a simple way to delineate multiple solution possibilities, they do not provide full stability information. Further, particularly for low bearing parameters, the introduction of an unpressurized squeeze film damper may promote instability in an otherwise stable system.

Attitude stability of spinning flexible spacecraft

NASA Technical Reports Server (NTRS)

Likins, P. W.; Barbera, F. J.

1971-01-01

The stability of spinning flexible satellites in a force-free environment was analyzed. The satellite was modeled as a rigid core having attached to it a flexible appendage idealized as a collection of particles (point masses) interconnected by springs. Both Liapunov and Routh-Hurwitz stability procedures are used. In the former, the Hamiltonian of the system, constrained through the angular momentum integral so as to admit complete damping, is used as a testing function. Equations of motion are written using the hybrid coordinate formulation, which readily accepts a modal coordinate transformation ultimately allowing truncation to a level amenable to literal stability analysis. Closed form stability criteria are generated for the first mode of a restricted appendage model lying in a plane containing the system center of mass and orthogonal to the spin axis. The effects of spin on flexible bodies are discussed by considering a very elementary particle model. Control of passively unstable spacecraft is briefly considered.

Optimal model of PDIG based microgrid and design of complementary stabilizer using ICA.

PubMed

Amini, R Mohammad; Safari, A; Ravadanegh, S Najafi

2016-09-01

The generalized Heffron-Phillips model (GHPM) for a microgrid containing a photovoltaic (PV)-diesel machine (DM)-induction motor (IM)-governor (GV) (PDIG) has been developed at the low voltage level. A GHPM is calculated by linearization method about a loading condition. An effective Maximum Power Point Tracking (MPPT) approach for PV network has been done using sliding mode control (SMC) to maximize output power. Additionally, to improve stability of microgrid for more penetration of renewable energy resources with nonlinear load, a complementary stabilizer has been presented. Imperialist competitive algorithm (ICA) is utilized to design of gains for the complementary stabilizer with the multiobjective function. The stability analysis of the PDIG system has been completed with eigenvalues analysis and nonlinear simulations. Robustness and validity of the proposed controllers on damping of electromechanical modes examine through time domain simulation under input mechanical torque disturbances. Copyright © 2016 ISA. Published by Elsevier Ltd. All rights reserved.

[Chinese classical formulas Ephedra associated prescriptions for treatment of skin diseases].

PubMed

Fan, Yi-Ping; Xiong, Xing-Jiang

2018-06-01

Chinese classical formulas, firstly recorded in Shanghan Zabing Lun by Zhang Zhongjing in the Han dynasty, have been widely used by traditional Chinese medicine physicians for thousands of years due to its good compatibility, strict structures, significant clinical efficacy and less adverse effects. Ephedra associated prescriptions, widely used in the treatment of skin diseases, are famous representative prescriptions in Chinese classical formulas. The commonly used Ephedra associated prescriptions include Mahuang Lianqiao Chixiaodou decoction, Maxing Shigan decoction, Maxing Yigan decoction, Mahuang decoction, Mahuang Jiazhu decoction, Guizhi Mahuang Geban decoction, and Guizhi Eryue Biyi decoction. Skin allergy is an allergic reaction, manifested as erythema, papules, and itching. It has been identified that Guizhi Mahuang Geban decoction (1/2 Guizhi decoction + 1/2 Mahuang decoction) is effective in dispersing wind and cold, relieving exterior syndrome and dredging the collaterals, so it can be used to treat skin allergy caused by pathogenic wind-cold. Guizhi Eryue Biyi decoction (1/4 Guizhi decoction + 1/8 Yuebi decoction) is effective in dispersing wind and cold, relieving exterior syndrome and clearing heat, so it is mainly used for the syndrome of wind-cold tightening superficies and heat transformed from wind-cold. Additionally, Mahuang Lianqiao Chixiaodou decoction can relieve exterior syndrome, clear heat and remove dampness, mainly for the dampness and heat depression in the muscle surface. It is found that Guizhi Mahuang Geban decoction and Guizhi Eryue Biyi decoction have certain efficacy for skin allergies, while Mahuang Lianqiao Chixiaodou decoction has significant efficacy for urticaria, acute and chronic eczema, etc. It has been identified that if the conditions of Ephedra associated prescriptions are well mastered by traditional Chinese medicine physicians, they could be widely applied to treat exogenous diseases and miscellaneous diseases. Copyright© by the Chinese Pharmaceutical Association.

Model Tests and Computer Simulations of a 15-Barge Tow for the Upper Mississippi River.

DTIC Science & Technology

1984-01-01

8217.* Damping lever ’v Static stability lever - S u’ - Mses of ship No Hf ...... ydrodynamic moment component jpUR about z axis (yawing moment) N Neem ...towboat designed to push an integrated oil barge tow. The second series of tests were performed using the "Exxon Nashville" and the Exxon Lake Charles

Sunrise seen from STS-77

NASA Image and Video Library

1996-05-22

S77-E-5073 (22 May 1996) --- From its position at 175 statute miles above Earth, the Space Shuttle Endeavour has encountered some colorful and attractive scenes heading into sunsets and sunrises. This particular encounter, captured with an Electronic Still Camera (ESC), occurred on flight day four, during which the six-member crew deployed the Passive Aerodynamically Stabilized Magnetically Damped Satellite (PAMS) - Satellite Test Unit (STU).

Rotor internal friction instability

NASA Technical Reports Server (NTRS)

Bently, D. E.; Muszynska, A.

1985-01-01

Two aspects of internal friction affecting stability of rotating machines are discussed. The first role of internal friction consists of decreasing the level of effective damping during rotor subsynchronous and backward precessional vibrations caused by some other instability mechanisms. The second role of internal frication consists of creating rotor instability, i.e., causing self-excited subsynchronous vibrations. Experimental test results document both of these aspects.

Riding and handling qualities of light aircraft: A review and analysis

NASA Technical Reports Server (NTRS)

Smetana, F. O.; Summery, D. C.; Johnson, W. D.

1972-01-01

Design procedures and supporting data necessary for configuring light aircraft to obtain desired responses to pilot commands and gusts are presented. The procedures employ specializations of modern military and jet transport practice where these provide an improvement over earlier practice. General criteria for riding and handling qualities are discussed in terms of the airframe dynamics. Methods available in the literature for calculating the coefficients required for a linearized analysis of the airframe dynamics are reviewed in detail. The review also treats the relation of spin and stall to airframe geometry. Root locus analysis is used to indicate the sensitivity of airframe dynamics to variations in individual stability derivatives and to variations in geometric parameters. Computer programs are given for finding the frequencies, damping ratios, and time constants of all rigid body modes and for generating time histories of aircraft motions in response to control inputs. Appendices are included presenting the derivation of the linearized equations of motion; the stability derivatives; the transfer functions; approximate solutions for the frequency, damping ratio, and time constants; an indication of methods to be used when linear analysis is inadequate; sample calculations; and an explanation of the use of root locus diagrams and Bode plots.

Handling qualities effects of display latency

NASA Technical Reports Server (NTRS)

King, David W.

1993-01-01

Display latency is the time delay between aircraft response and the corresponding response of the cockpit displays. Currently, there is no explicit specification for allowable display lags to ensure acceptable aircraft handling qualities in instrument flight conditions. This paper examines the handling qualities effects of display latency between 70 and 400 milliseconds for precision instrument flight tasks of the V-22 Tiltrotor aircraft. Display delay effects on the pilot control loop are analytically predicted through a second order pilot crossover model of the V-22 lateral axis, and handling qualities trends are evaluated through a series of fixed-base piloted simulation tests. The results show that the effects of display latency for flight path tracking tasks are driven by the stability characteristics of the attitude control loop. The data indicate that the loss of control damping due to latency can be simply predicted from knowledge of the aircraft's stability margins, control system lags, and required control bandwidths. Based on the relationship between attitude control damping and handling qualities ratings, latency design guidelines are presented. In addition, this paper presents a design philosophy, supported by simulation data, for using flight director display augmentation to suppress the effects of display latency for delays up to 300 milliseconds.