NASA Astrophysics Data System (ADS)
Burns, J. A.; Sharma, I.
2000-10-01
Motivated by the recent detection of complex rotational states for several asteroids and comets, as well as by the ongoing and planned spacecraft missions to such bodies, which should allow their rotational states to be accurately determined, we revisit the problem of the nutational damping of small solar system bodies. The nutational damping of asteroids has been approximately analyzed by Prendergast (1958), Burns and Safronov (1973), and Efroimsky and Lazarian (2000). Many other similar dynamical studies concern planetary wobble decay (e.g., Peale 1973; Yoder and Ward 1979), interstellar dust grain alignment (e.g., Purcell 1979; Lazarian and Efroimsky 1999) and damping of Earth's Chandler wobble (Lambeck 1980). Recall that rotational energy loss for an isolated body aligns the body's angular momentum vector with its axis of maximum inertia. Assuming anelastic dissipation, simple dimensional analysis determines a functional form of the damping timescale, on which all the above authors agree. However, the numerical coefficients of published results are claimed to differ by orders of magnitude. Differences have been ascribed to absent physics, to solutions that fail to satisfy boundary conditions perfectly, and to unphysical choices for the Q parameter. The true reasons for the discrepancy are unclear since, despite contrary claims, the full 3D problem (nutational damping of an anelastic ellipsoid) is analytically intractable so far. To move the debate forward, we compare the solution of a related 2D problem to the expressions found previously, and we present results from a finite element model. On this basis, we feel that previous rates for the decay of asteroidal tumbling (Harris 1994), derived from Burns and Safronov (1973), are likely to be accurate, at least to a factor of a few. Funded by NASA.
Solar attitude control including active nutation damping in a fixed-momentum wheel satellite
NASA Astrophysics Data System (ADS)
Azor, Ruth
1992-08-01
In geostationary cruise of a momentum biased satellite, it is necessary to stabilize the roll/yaw attitude due to disturbances, caused mainly by solar pressure. This work presents a roll/yaw control, which is obtained by the use of solar arrays and fixed flaps as actuators, with a horizon sensor for roll measurement. The design also includes an active nutation damping.
Solar sail attitude control including active nutation damping in a fixed-momentum wheel satellite
NASA Technical Reports Server (NTRS)
Azor, Ruth
1992-01-01
In geostationary cruise of a momentum biased satellite, it is necessary to stabilize the roll/yaw attitude due to disturbances, caused mainly by solar radiation pressure. This work presents a roll/yaw control which is obtained by the use of solar arrays and fixed flaps as actuators, with a horizon sensor for roll measurement. The design also includes an active nutation damping.
Solar sail attitude control including active nutation damping in a fixed-momentum wheel satellite
NASA Astrophysics Data System (ADS)
Azor, Ruth
1992-02-01
In the geostationary cruise of a momentum biased satellite, it is necessary to stabilize the roll/yaw attitude due to disturbances caused by solar radiation pressure. This work presents a roll/yaw control system with a horizon sensor for roll measurement. Roll/yaw control is obtained by the use of solar arrays and fixed flaps as actuators. The design also includes an active nutation damping method.
Damping Rotor Nutation Oscillations in a Gyroscope with Magnetic Suspension
NASA Technical Reports Server (NTRS)
Komarov, Valentine N.
1996-01-01
A possibility of an effective damping of rotor nutations by modulating the field of the moment transducers in synchronism with the nutation frequency is considered. The algorithms for forming the control moments are proposed and their application is discussed.
Variable structure controller design for spacecraft nutation damping
NASA Technical Reports Server (NTRS)
Sira-Ramirez, Hebertt; Dwyer, Thomas A. W., III
1987-01-01
Variable structure systems theory is used to design an automatic controller for active nutation damping in momentum biased stabilized spacecraft. Robust feedback stabilization of roll and yaw angular dynamics is achieved with prescribed qualitative characteristics which are totally independent of the spacecraft defining parameters.
Nutation damping in viscoelastic tumbling rotators
NASA Astrophysics Data System (ADS)
Frouard, Julien; Efroimsky, Michael
2015-11-01
Presently, 138 asteroids show signs of being in non-principal spin states (Warner et al. 2009, updated September 2015). Such spin is often called `tumble' or `wobble'. The instantaneous rotation axis of a wobbling body performs nutation about the direction of the (conserved) angular-momentum vector. Incited by collisions and YORP, wobble is mitigated by internal dissipation due to the nutation-caused alternating stresses inside the asteroid.The knowledge of the timescale related to the damping of the nutation angle is complementary to the knowledge of the timescales associated with collisions and YORP. Previous evaluations of the nutation relaxation rate were based on an inherently inconsistent approach that may be called "Q-model". First, the elastic energy in a periodically deforming rotator was calculated in assumption of the deformation being elastic. Therefrom, the energy dissipation rate was determined by introducing an ad hoc quality factor Q. This ignored the fact that friction (and the ensuing existence of Q) is due to deviation from elasticity.We use the viscoelastic Maxwell model which naturally implies dissipation (as any other viscoelastic model would). In this approach, we compute the power and damping time for an oblate ellipsoid and a prism. Now, the viscosity assumes the role of the product μQ in the empirical Q-model, with μ being the rigidity. Contrarily to the Q-model, our model naturally gives a null dissipation for a shape tending to a sphere. We also explore when the constant part of the stress can be ignored in the derivation of the damping time. The neglect of prestressing turns out to be legitimate for the mean viscosity exceeding a certain threshold value.
Backup nutation damping strategy for the Galileo spacecraft
NASA Technical Reports Server (NTRS)
Eke, Fidelis O.; Eke, Estelle M.
1989-01-01
A discussion is presented of the design and testing of remedial measures that can be taken to achieve reasonable nutation damping of the Galileo spacecraft in the event of failure of its boom damper in flight. One scheme exploits the effects of payload motion on the nutational stability of a spinning spacecraft. However, the spacecraft-motion-compensation algorithm can only be used if the scan platform bore sight is pointed in a direction chosen to produce rapid damping of spacecraft nutation. A second method suggested for nutation damping is a thruster-based open-loop control algorithm, utilizing a pair of thrusters as actuators.
Method of damping nutation motion with minimum spin axis attitude disturbance
NASA Technical Reports Server (NTRS)
Hoffman, H. C. (Inventor)
1983-01-01
In a method of and apparatus for damping nutation of a spinning spacecraft, spin axis attitude disturbances are substantially reduced by controlling at least one nutation damping gas thruster to fire with nonuniform gas pulses. During the beginning of a nutation control sequence, the duration of successive gas pulses is gradually increased (up pulsed) from zero to a predetermined maximum duration. The duration of successive pulses is then maintained constant for a time period. Finally, at the end of the nutation control sequence, the duration of successive gas pulses is gradually reduced to zero (down pulsed). Up pulsing of the gas thruster is initiated in response to a predetermined maximum nutation angle measured by an accelerometer. Down pulsing of the thruster is initiated in response to a predetermined minimum nutation angle.
Residual nutational activity of the sunflower hypocotyl in simulated weightlessness
NASA Technical Reports Server (NTRS)
Chapman, D. K.; Brown, A. H.
1979-01-01
The gravity dependence of circumnutational activity in the sunflower hypocotyl is investigated under conditions of simulated weightlessness. Seedling cultures of the sunflower Helianthus annuus were placed four days after planting in clinostats rotating at a rate of 1.0 rpm in the horizontal or somersaulting configurations, and plant movements around their growth axes were recorded in infrared light by a time-lapse closed-circuit video system. The amplitudes and mean cycle durations of the plant nutations in the horizontal and tumbling clinostats are observed to be 20% and 72%, and 32% and 74%, respectively, of the values observed in stationary plants; extrapolations to a state of zero g by the imposition of small centripetal forces on horizontally clinostated plants also indicate some nutational motion in the absence of gravity. It is concluded that the results are incompatible with the model of Israelsson and Johnsson (1967) of geotropic response with overshoot for sunflower circumnutation; however, results of the Spacelab 1 mission experiment are needed to unambiguously define the role of gravitation.
Spin-Down and Active Nutation Controller /SDANC/ for the Galileo project
NASA Technical Reports Server (NTRS)
Lin, H. S.
1980-01-01
The Spin-Down and Active Nutation Controller stabilizes the Galileo spacecraft during spin-down from approximately 70 to 1 rpm. Angular motion of the spacecraft is sensed through a pair of accelerometers and a sun sensor which is needed only at low spin rates. Spin and nutation information is derived by a set of 'loosely coupled' spin and transverse rate estimators. Spin rate is reduced by two spin-down thrusters. The transverse angular rate is compared with a variable threshold; exceeding the threshold activates axial thrusters which impart appropriate transverse torque to reduce the nutation. The scheme was verified by extensive computer simulations and has been demonstrated over a wide range of initial conditions.
NASA Technical Reports Server (NTRS)
Evans, J. (Inventor)
1973-01-01
A nutation damper for use on a spinning body is disclosed. The damper is positioned parallel to the spin axis of the body and radially displaced therefrom. The damper is partially filled with a fluid and contains a porous media to impede the flow of the fluid induced by nutation.
Active nutation control of an asymmetric spacecraft using an axial reaction wheel
NASA Astrophysics Data System (ADS)
Shahmohamadi Ousaloo, Hamed
2016-12-01
The focus of this paper is to develop a control scheme for overcoming the nutational motion of an asymmetric spin satellite regardless of its spin-to-transverse inertia ratio using a single reaction wheel mounted along the desired spin axis. In this strategy the basic Proportional-Derivative (PD) controller is acted on the precession angle error and, moreover, Lyapunov stability is applied for creating positive spin rate using proper precession command. A Monte Carlo type approach is used to verify the stability for various inertia ratios. The control system makes use of only angular velocity of wheel and spacecraft angular rates to stabilize spin. This active nutation controller globally and asymptotically stabilizes the spacecraft about a revolute motion and provides automatically logical recovery of desired positive spin from any initial state. This straightforward attitude recovery technique does not require accurate estimates of spacecraft inertias and various simulation results demonstrate that stability is not affected by various inertia ratios. Numerical simulations confirm that the approach has typically robust performance.
ALMA high performance nutating subreflector
NASA Astrophysics Data System (ADS)
Gasho, Victor L.; Radford, Simon J. E.; Kingsley, Jeffrey S.
2003-02-01
For the international ALMA project"s prototype antennas, we have developed a high performance, reactionless nutating subreflector (chopping secondary mirror). This single axis mechanism can switch the antenna"s optical axis by +/-1.5" within 10 ms or +/-5" within 20 ms and maintains pointing stability within the antenna"s 0.6" error budget. The light weight 75 cm diameter subreflector is made of carbon fiber composite to achieve a low moment of inertia, <0.25 kg m2. Its reflecting surface was formed in a compression mold. Carbon fiber is also used together with Invar in the supporting structure for thermal stability. Both the subreflector and the moving coil motors are mounted on flex pivots and the motor magnets counter rotate to absorb the nutation reaction force. Auxiliary motors provide active damping of external disturbances, such as wind gusts. Non contacting optical sensors measure the positions of the subreflector and the motor rocker. The principle mechanical resonance around 20 Hz is compensated with a digital PID servo loop that provides a closed loop bandwidth near 100 Hz. Shaped transitions are used to avoid overstressing mechanical links.
Active Damping Using Distributed Anisotropic Actuators
NASA Technical Reports Server (NTRS)
Schiller, Noah H.; Cabell, Randolph H.; Quinones, Juan D.; Wier, Nathan C.
2010-01-01
A helicopter structure experiences substantial high-frequency mechanical excitation from powertrain components such as gearboxes and drive shafts. The resulting structure-borne vibration excites the windows which then radiate sound into the passenger cabin. In many cases the radiated sound power can be reduced by adding damping. This can be accomplished using passive or active approaches. Passive treatments such as constrained layer damping tend to reduce window transparency. Therefore this paper focuses on an active approach utilizing compact decentralized control units distributed around the perimeter of the window. Each control unit consists of a triangularly shaped piezoelectric actuator, a miniature accelerometer, and analog electronics. Earlier work has shown that this type of system can increase damping up to approximately 1 kHz. However at higher frequencies the mismatch between the distributed actuator and the point sensor caused control spillover. This paper describes new anisotropic actuators that can be used to improve the bandwidth of the control system. The anisotropic actuators are composed of piezoelectric material sandwiched between interdigitated electrodes, which enables the application of the electric field in a preferred in-plane direction. When shaped correctly the anisotropic actuators outperform traditional isotropic actuators by reducing the mismatch between the distributed actuator and point sensor at high frequencies. Testing performed on a Plexiglas panel, representative of a helicopter window, shows that the control units can increase damping at low frequencies. However high frequency performance was still limited due to the flexible boundary conditions present on the test structure.
Improved analytic nutation model
NASA Technical Reports Server (NTRS)
Yoder, C. F.; Ivins, E. R.
1988-01-01
Models describing the earth's nutations are discussed. It is found that the simple model of Sasao et al., (1981) differs from Wahr's (1981) theory term by term by less than 0.3 marcsec if a modern earth structure model is used to evaluate the nutation structure constants. In addition, the effect of oceans is estimated.
Active damping of spacecraft structural appendage vibrations
NASA Technical Reports Server (NTRS)
Fedor, Joseph V. (Inventor)
1990-01-01
An active vibration damper system, for bending in two orthogonal directions and torsion, in each of three mutually perpendicular axes is located at the extremities of the flexible appendages of a space platform. The system components for each axis includes: an accelerometer, filtering and signal processing apparatus, and a DC motor-inertia wheel torquer. The motor torquer, when driven by a voltage proportional to the relative vibration tip velocity, produces a reaction torque for opposing and therefore damping a specific modal velocity of vibration. The relative tip velocity is obtained by integrating the difference between the signal output from the accelerometer located at the end of the appendage with the output of a usually carried accelerometer located on a relatively rigid body portion of the space platform. A selector switch, with sequential stepping logic or highest modal vibration energy logic, steps to another modal tip velocity channel and receives a signal voltage to damp another vibration mode. In this manner, several vibration modes can be damped with a single sensor/actuator pair. When a three axis damper is located on each of the major appendages of the platform, then all of the system vibration modes can be effectively damped.
NASA Technical Reports Server (NTRS)
Wahr, John; Bergen, Zachary
1986-01-01
The paper models the effects of mantle anelasticity on luni-solar nutations, on tidal deformation, on tidal variations in rotation rate, and on the eigenfrequency of the free core nutation. The results can be used to invert observations to solve for the anelastic contributions to the shear and bulk moduli of the upper and lower mantle. Specific anelastic models are used to numerically estimate the effects of anelasticity on these geodetic observables. The nutation estimates are compared with observational results. Among the conclusions: (1) mantle anelasticity is likely to be the most important source of damping for the free core nutation; (2) present VLBI nutation results are, in principle, accurate enough to usefully bound anelasticity at diurnal periods. But the discrepancy between the VLBI observed nutations and the 1984 IAU nutation model cannot be explained by anelasticity and is not yet well enough understood to allow anelasticity to be determined from the data.
Nutations of sunflower seedlings on tilted clinostats
NASA Technical Reports Server (NTRS)
Brown, A. H.; Chapman, D. K.
1977-01-01
The kinetics of hypocotyl nutations in Helianthus annuus L. were measured on plants which were rotated on clinostats with axes of rotation inclined at various angles, alpha, away from the vertical. The g-force component acting in the direction of the plant axis was taken as g cos alpha. The average period and average amplitude of nutation were constant for all such axially directed g-forces between 1.0 and 0.2 g (vertical to about 80 inclination). On the horizontal clinostat (90 inclination) nutation was neither initiated nor sustained. The g-force just sufficient fully to activate nutational oscillations should be sought for g-force parameter values ranging from 0 to 0.2.
Bridge feedback for active damping augmentation
NASA Technical Reports Server (NTRS)
Chen, G.-S.; Lurie, B. J.
1990-01-01
A method is described for broadband damping augmentation of a structural system in which the active members (with feedback control) were developed such that their mechanical input impedance can be electrically adjusted to maximize the energy dissipation rate in the structural system. The active member consists of sensors, an actuator, and a control scheme. A mechanical/electrical analogy is described to model the passive structures and the active members in terms of their impedance representation. As a result, the problem of maximizing dissipative power is analogous to the problem of impedance matching in the electrical network. Closed-loop performance was demonstrated for single- and multiple-active-member controlled truss structure.
Active damping of the SOFIA Telescope assembly
NASA Astrophysics Data System (ADS)
Keas, Paul J.; Dunham, Edward; Lampater, Ulrich; Pfüller, Enrico; Teufel, Stefan; Roeser, Hans-Peter; Wiedemann, Manuel; Wolf, Jürgen
2012-09-01
The NASA/DLR Stratospheric Observatory for Infrared Astronomy (SOFIA) employs a 2.5-meter reflector telescope in a Boeing 747SP. The telescope is housed in an open cavity and is subjected to aeroacoustic and inertial disturbances in flight. To meet pointing requirements, SOFIA must achieve a pointing stability of approximately 0.5 arcseconds RMS. An active damping control system is being developed for SOFIA to reduce image jitter and image degradation due to resonance of the telescope assembly. Our paper discusses the history of the active damping design for SOFIA, from early concepts to the current implementation which has recently completed a ground and flight testing for proof-of-concept. We describe some milestones in the analysis and testing of the telescope assembly which guided the development of the vibration control system. The control synthesis approach and current implementation of the active damping control system is presented. Finally, we summarize the performance observed in early flight tests and the steps that are currently foreseen to completing the development of this system.
Active Vibration Damping of Solar Arrays
NASA Astrophysics Data System (ADS)
Reinicke, Gunar; Baier, Horst; Grillebeck, Anton; Scharfeld, Frank; Hunger, Joseph; Abou-El-Ela, A.; Lohberg, Andreas
2012-07-01
Current generations of large solar array panels are lightweight and flexible constructions to reduce net masses. They undergo strong vibrations during launch. The active vibration damping is one convenient option to reduce vibration responses and limit stresses in facesheets. In this study, two actuator concepts are used for vibration damping. A stack interface actuator replaces a panel hold down and is decoupled from bending moments and shear forces. Piezoelectric patch actuators are used as an alternative, where the number, position and size of actuators are mainly driven by controllability analyses. Linear Quadratic Gaussian control is used to attenuate vibrations of selected mode shapes with both actuators. Simulations as well as modal and acoustic tests show the feasibility of selected actuator concepts.
NASA Astrophysics Data System (ADS)
Zharov, V.
2015-08-01
Time series of the Earth orientation parameters (EOP) were calculated. The ARIADNA software was used to analyze the corrections of the nutation angles. Main feature is un-modeled motion of the CIP in the GCRS that is known as the free core nutation (FCN). In contrast from theory the FCN motion is complex motion. Hypothesis of reason of this complex motion is based on amplitude modulation of the excitation that is connected with the atmospheric tide ψ_1.
Active member bridge feedback control for damping augmentation
NASA Technical Reports Server (NTRS)
Chen, Gun-Shing; Lurie, Boris J.
1992-01-01
An active damping augmentation approach using active members in a structural system is described. The problem of maximizing the vibration damping in a lightly damped structural system is considered using the analogy of impedance matching between the load and source impedances in an electrical network. The proposed active damping augmentation approach therefore consists of finding the desired active member impedances that maximize the vibration damping, and designing a feedback control in order to achieve desired active member impedances. This study uses a bridge feedback concept that feeds back a combination of signals from sensors of the axial force and relative velocity across the active member to realize the desired active member impedance. The proposed active damping augmentation approach and bridge feedback concept were demonstrated on a three-longeron softly suspended truss structure.
An analysis and intercomparison of VLBI nutation estimates
NASA Astrophysics Data System (ADS)
Eubanks, T. M.; Steppe, J. A.; Sovers, O. J.
Nutation estimates from long duration VLBI experiments conducted by the Deep Space Network and reduced at JPL were compared with similar estimates from the IRIS/Polaris data reduced at Harvard. The two series were found to have an rms difference of 1.6 milliarcsec or less, and both exhibited the existence of seasonal errors in the IAU 1980 nutation theory. Most of the observed seasonal discrepancies could be removed by changing the period of the free core resonance to 431.5 solar days. The VLBI data constrain the resonance damping time to be at least one decade, and possibly much longer. Any free core nutation has an amplitude of less than 1 milliarcsec. Crude estimates of the atmospheric forcing of this resonance indicate that meteorological forcing could easily explain the observed free core nutation.
Vibration control through passive constrained layer damping and active control
NASA Astrophysics Data System (ADS)
Lam, Margaretha J.; Inman, Daniel J.; Saunders, William R.
1997-05-01
To add damping to systems, viscoelastic materials (VEM) are added to structures. In order to enhance the damping effects of the VEM, a constraining layer is attached. When this constraining layer is an active element, the treatment is called active constrained layer damping (ACLD). Recently, the investigation of ACLD treatments has shown it to be an effective method of vibration suppression. In this paper, the treatment of a beam with a separate active element and passive constrained layer (PCLD) element is investigated. A Ritz- Galerkin approach is used to obtain discretized equations of motion. The damping is modeled using the GHM method and the system is analyzed in the time domain. By optimizing on the performance and control effort for both the active and passive case, it is shown that this treatment is capable of lower control effort with more inherent damping, and is therefore a better approach to damp vibration.
Active vibration damping using smart material
NASA Technical Reports Server (NTRS)
Baras, John S.; Yan, Zhuang
1994-01-01
We consider the modeling and active damping of an elastic beam using distributed actuators and sensors. The piezoelectric ceramic material (PZT) is used to build the actuator. The sensor is made of the piezoelectric polymer polyvinylidene fluoride (PVDF). These materials are glued on both sides of the beam. For the simple clamped beam, the closed loop controller has been shown to be able to extract energy from the beam. The shape of the actuator and its influence on the closed loop system performance are discussed. It is shown that it is possible to suppress the selected mode by choosing the appropriate actuator layout. It is also shown that by properly installing the sensor and determining the sensor shape we can further extract and manipulate the sensor signal for our control need.
NASA Astrophysics Data System (ADS)
Janssen, R.; Tijink, G. A. H.; Veeman, W. S.
1988-01-01
A two-dimensional solid state NMR experiment which combines rotary echoes and nutation NMR is investigated and used to study different sodium sites in zeolite NaA. It is shown that with this technique sodium ions with different relaxation rates in the rotating frame can be distinguished.
Microscale damping using thin film active materials
NASA Astrophysics Data System (ADS)
Kerrigan, Catherine A.; Ho, Ken K.; Mohanchandra, K. P.; Carman, Gregory P.
2007-04-01
This paper focuses on understanding and developing a new approach to dampen MEMS structures using both experiments and analytical techniques. Thin film Nitinol and thin film Terfenol-D are evaluated as a damping solution to the micro scale damping problem. Stress induced twin boundary motion in Nitinol is used to passively dampen potentially damaging vibrations. Magnetic domain wall motion is used to passively dampen vibration in Terfenol-D. The thin films of Nitinol, Nitinol/Silicon laminates and Nitinol/Terfenol-D/Nickel laminates have been produced using a sputter deposition process and damping properties have been evaluated. Dynamic testing shows substantial damping (tan δ) measurable in each case. Nitinol film samples were tested in the Differential Scanning Calorimetry (DSC) to determine phase transformation temperatures. The twin boundary mechanism by which energy absorption occurs is present at all points below the Austenite start temperature (approximately 69°C in our film) and therefore allows damping at cold temperatures where traditional materials fail. Thin film in the NiTi/Si laminate was found to produce substantially higher damping (tan δ = 0.28) due to the change in loading condition. The NiTi/Si laminate sample was tested in bending allowing the twin boundaries to be reset by cyclic tensile and compressive loads. The thin film Terfenol-D in the Nitinol/Terfenol-D/Nickel laminate was shown to produce large damping (tan δ = 0.2). In addition to fabricating and testing, an analytical model of a heterogeneous layered thin film damping material was developed and compared to experimental work.
Experiences with active damping and impedance-matching compensators
NASA Astrophysics Data System (ADS)
Betros, Robert S.; Alvarez, Oscar S.; Bronowicki, Allen J.
1993-09-01
TRW has been implementing active damping compensators on smart structures for the past five years. Since that time there have been numerous publications on the use of impedance matching techniques for structural damping augmentation. The idea of impedance matching compensators came about by considering the flow of power in a structure undergoing vibration. The goal of these compensators is to electronically dissipate as much of this flowing power as possible. This paper shows the performance of impedance matching compensators used in smart structures to be comparable to that of active damping compensators. Theoretical comparisons between active damping and impedance matching methods are made using PZT actuators and sensors. The effects of these collocated and non-collocated PZT sensors and actuators on the types of signals they sense and actuate are investigated. A method for automatically synthesizing impedance matching compensators is presented. Problems with implementing broad band active damping and impedance matching compensators on standard Digital Signal Processing (DSP) chips are discussed. Simulations and measurements that compare the performance of active damping and impedance matching techniques for a lightly damped cantilevered beam are shown.
An excitation mechanism for the free 'core nutation'
NASA Technical Reports Server (NTRS)
Sasao, T.; Wahr, J. M.
1981-01-01
The earth is believed to possess a free nutational mode due to its rotating, elliptical, fluid core, with an eigenfrequency of approximately (1 + 1/460) cycle per sidereal day as seen from the sidereally rotating earth. This free 'core nutation' has not yet been undisputably observed. Furthermore, there has been considerable doubt that any known mechanism could excite this mode to an observable level. It is shown here that diurnal atmospheric and oceanic loading of the earth's surface provides an efficient excitation mechanism which depends critically on the physical damping of the mode. Possible effects of the mode on geodetic measurements are discussed. The effects of 'wobble' and 'nutation' on astrometric observations are also considered.
Viscosity of the Earth's inner core: constraints from nutation observations
NASA Astrophysics Data System (ADS)
Koot, L.; Dumberry, M.
2010-12-01
Nutations are the variations in the orientation of the Earth’s rotation axis in a space-fixed reference frame. This motion shows two important normal modes, the Free Core Nutation (FCN) and the Free Inner Core Nutation (FICN), of which the frequencies and damping depend directly on the Earth’s interior structure and dynamics. The FICN is characterized by a differential rotation of the inner core relative to the mantle and outer core. Its natural frequency is thus directly affected both by the strength of the mechanical coupling at the inner core boundary (ICB) and by the way the inner core deforms due to centrifugal forces. Similarly, the damping of the mode reflects the energy dissipated both through the coupling at the ICB and through inner core deformation. Estimations of the ICB coupling strength and dissipation have been obtained previously from nutation observations by assuming a purely elastic inner core (Mathews et al. 2002, Koot et al. 2010). When interpreted in terms of a visco-magnetic coupling, these estimations lead to values of the magnetic field at the ICB around 6-7 mT and to a kinematic viscosity of the fluid core close to the ICB in the range of 10-30 m2 s-1. This value of the ICB fluid core viscosity is orders of magnitude larger than what is expected from laboratory measurements and ‘ab initio’ computations. In this work, we show that a visco-elastic inner core is able to reconcile the estimation of the outer core kinematic viscosity with that of laboratory measurements and ab initio computations. This reconciliation is achieved for a very narrow range of values of the inner core viscosity, which can be considered as a nutation constraint on this physical quantity. Finally, we show that this nutation constraint is in very good agreement with seismic observations of shear waves attenuation in the inner core.
An Active Damping at Blade Resonances Using Piezoelectric Transducers
NASA Technical Reports Server (NTRS)
Choi, Benjamin; Morrison, Carlos; Duffy, Kirsten
2008-01-01
The NASA Glenn Research Center (GRC) is developing an active damping at blade resonances using piezoelectric structure to reduce excessive vibratory stresses that lead to high cycle fatigue (HCF) failures in aircraft engine turbomachinery. Conventional passive damping work was shown first on a nonrotating beam made by Ti-6A1-4V with a pair of identical piezoelectric patches, and then active feedback control law was derived in terms of inductor, resister, and capacitor to control resonant frequency only. Passive electronic circuit components and adaptive feature could be easily programmable into control algorithm. Experimental active damping was demonstrated on two test specimens achieving significant damping on tip displacement and patch location. Also a multimode control technique was shown to control several modes.
Active damping performance of the KAGRA seismic attenuation system prototype
NASA Astrophysics Data System (ADS)
Fujii, Yoshinori; Sekiguchi, Takanori; Takahashi, Ryutaro; Aso, Yoichi; Barton, Mark; Erasmo Peña Arellano, Fabián; Shoda, Ayaka; Akutsu, Tomotada; Miyakawa, Osamu; Kamiizumi, Masahiro; Ishizaki, Hideharu; Tatsumi, Daisuke; Hirata, Naoatsu; Hayama, Kazuhiro; Okutomi, Koki; Miyamoto, Takahiro; Ishizuka, Hideki; DeSalvo, Riccardo; Flaminio, Raffaele
2016-05-01
The Large-scale Cryogenic Gravitational wave Telescope (formerly LCGT now KAGRA) is presently under construction in Japan. This May we assembled a prototype of the seismic attenuation system (SAS) for the beam splitter and the signal recycling mirrors of KAGRA, which we call Type-B SAS, and evaluated its performance at NAOJ (Mitaka, Toyko). We investigated its frequency response, active damping performance, vibration isolation performance and long-term stability both in and out of vacuum. From the frequency response test and the active damping performance test, we confirmed that the SAS worked as we designed and that all mechanical resonances which could disturb lock acquisition and observation are damped within 1 minute, which is required for KAGRA, by the active controls.
Geomagnetic excitation of nutation
NASA Astrophysics Data System (ADS)
Ron, C.; Vondrák, J.
2015-08-01
We tested the hypothesis of Malkin (2013), who demonstrated that the observed changes of Free Core Nutation parameters (phase, amplitude) occur near the epochs of geomagnetic jerks. We found that if the numerical integration of Brzeziński broad-band Liouville equations of atmospheric/oceanic excitations is re-initialized at the epochs of geomagnetic jerks, the agreement between the integrated and observed celestial pole offsets is improved (Vondrák & Ron, 2014). Nevertheless, this approach assumes that the influence of geomagnetic jerks leads to a stepwise change in the position of celestial pole, which is physically not acceptable. Therefore we introduce a simple continuous excitation function that hypothetically describes the influence of geomagnetic jerks, and leads to rapid but continuous changes of pole position. The results of numerical integration of atmospheric/oceanic excitations and this newly introduced excitation are then compared with the observed celestial pole offsets, and prove that the agreement is improved significantly.
Nutational Flows Inside Spinning Cylinders
1990-12-01
concentrations support nutational waves. Figure 10 shows a spiral wave travelling along a vortex . Such spiral waves actually nutate as they travel along the...direction, as shown in Figure 18. The spiral vortex flow was modelled by Dunlap, as shown in Figure 19, in accordance with the smoke visualizations. Based on...the pressure measurements at the centerline he further concluded that the onset of transition to the spiral vortex flow in the chamber occurred at a
Numerical simulation of Ulysses nutation
NASA Technical Reports Server (NTRS)
Marirrodriga, C. Garcia; Zeischka, J.; Boslooper, E. C.
1993-01-01
A numerical simulation has been performed on the in-orbit instability of the Ulysses Spacecraft. The thermal excitation from the solar flux, the flexible axial boom and its deployment mechanism have been modeled and analyzed. The simulation shows that the nutation build-up has been originated by the solar input on the axial boom coupled with the system nutation frequency of the spacecraft. The results agree with the observed behavior.
Active Constrained Layer Damping of Thin Cylindrical Shells
NASA Astrophysics Data System (ADS)
RAY, M. C.; OH, J.; BAZ, A.
2001-03-01
The effectiveness of the active constrained layer damping (ACLD) treatments in enhancing the damping characteristics of thin cylindrical shells is presented. A finite element model (FEM) is developed to describe the dynamic interaction between the shells and the ACLD treatments. Experiments are performed to verify the numerical predictions. The obtained results suggest the potential of the ACLD treatments in controlling the vibration of cylindrical shells which constitute the major building block of many critical structures such as cabins of aircrafts, hulls of submarines and bodies of rockets and missiles.
Six degree of freedom active vibration damping for space application
NASA Technical Reports Server (NTRS)
Haynes, Leonard S.
1993-01-01
Work performed during the period 1 Jan. - 31 Mar. 1993 on six degree of freedom active vibration damping for space application is presented. A performance and cost report is included. Topics covered include: actuator testing; mechanical amplifier design; and neural network control system development and experimental evaluation.
Counterspin nutation damper analysis and design
NASA Astrophysics Data System (ADS)
Clements, R. R.; Reece, G. J.; Tonkin, S. W.; Wright, J. H.
1982-08-01
A suitable counterspun nutation damping system was designed for IRIS, a combined spacecraft destined for geostationary orbit, and the perigee motor to put it into orbit after shuttle launch. A procedure is described for choosing a damper size, together with the number required, for any vehicle. For IRIS it is shown that two dampers, each with an angular momentum of 5 Nms, are sufficient, and that performance is adequate if one damper fails. Each damper would weigh just under 3 kg and require about 0.5 kg of batteries. The system can be operated immediately on ejection from the shuttle. Extensive computer simulations of damper performances show close agreement with predictions (for restricted cases) and reveal the effects of non-axisymmetry of the spacecraft, drive axle misalignment and Coulomb friction in the bearings.
Active vibration damping of the Space Shuttle remote manipulator system
NASA Technical Reports Server (NTRS)
Scott, Michael A.; Gilbert, Michael G.; Demeo, Martha E.
1991-01-01
The feasibility of providing active damping augmentation of the Space Shuttle Remote Manipulator System (RMS) following normal payload handling operations is investigated. The approach used in the analysis is described, and the results for both linear and nonlinear performance analysis of candidate laws are presented, demonstrating that significant improvement in the RMS dynamic response can be achieved through active control using measured RMS tip acceleration data for feedback.
Active vibration damping of the Space Shuttle Remote Manipulator System
NASA Technical Reports Server (NTRS)
Scott, Michael A.; Gilbert, Michael G.; Demeo, Martha E.
1991-01-01
The feasibility of providing active damping augmentation of the Space Shuttle Remote Manipulator System (RMS) following normal payload-handling operations is investigated. The approach used in the analysis is described and the results from both linear and nonlinear performance analyses of candidate laws are presented, demonstrating that significant improvement in the RMS dynamic response can be achieved through active control using measured RMS tip acceleration data for feedback.
Vibration control of cylindrical shells using active constrained layer damping
NASA Astrophysics Data System (ADS)
Ray, Manas C.; Chen, Tung-Huei; Baz, Amr M.
1997-05-01
The fundamentals of controlling the structural vibration of cylindrical shells treated with active constrained layer damping (ACLD) treatments are presented. The effectiveness of the ACLD treatments in enhancing the damping characteristics of thin cylindrical shells is demonstrated theoretically and experimentally. A finite element model (FEM) is developed to describe the dynamic interaction between the shells and the ACLD treatments. The FEM is used to predict the natural frequencies and the modal loss factors of shells which are partially treated with patches of the ACLD treatments. The predictions of the FEM are validated experimentally using stainless steel cylinders which are 20.32 cm in diameter, 30.4 cm in length and 0.05 cm in thickness. The cylinders are treated with ACLD patches of different configurations in order to target single or multi-modes of lobar vibrations. The ACLD patches used are made of DYAD 606 visco-elastic layer which is sandwiched between two layers of PVDF piezo-electric films. Vibration attenuations of 85% are obtained with maximum control voltage of 40 volts. Such attenuations are attributed to the effectiveness of the ACLD treatment in increasing the modal damping ratios by about a factor of four over those of conventional passive constrained layer damping (PCLD) treatments. The obtained results suggest the potential of the ACLD treatments in controlling the vibration of cylindrical shells which constitute the major building block of many critical structures such as cabins of aircrafts, hulls of submarines and bodies of rockets and missiles.
NASA Astrophysics Data System (ADS)
Zheng, Ling; Zhang, Dongdong; Wang, Yi
2011-02-01
In this paper, the application of active constrained layer damping (ACLD) treatments is extended to the vibration control of cylindrical shells. The governing equation of motion of cylindrical shells partially treated with ACLD treatments is derived on the basis of the constitutive equations of elastic, piezoelectric and visco-elastic materials and an energy approach. The damping of a visco-elastic layer is modeled by the complex modulus formula. A finite element model is developed to describe and predict the vibration characteristics of cylindrical shells partially treated with ACLD treatments. A closed-loop control system based on proportional and derivative feedback of the sensor voltage generated by the piezo-sensor of the ACLD patches is established. The dynamic behaviors of cylindrical shells with ACLD treatments such as natural frequencies, loss factors and responses in the frequency domain are further investigated. The effects of several key parameters such as control gains, location and coverage of ACLD treatments on vibration suppression of cylindrical shells are also discussed. The numerical results indicate the validity of the finite element model and the control strategy approach. The potential of ACLD treatments in controlling vibration and sound radiation of cylindrical shells used as major critical structures such as cabins of aircraft, hulls of submarines and bodies of rockets and missiles is thus demonstrated.
NASA Astrophysics Data System (ADS)
Gross, Richard; Schuh, Harald; Huang, Cheng-li
2011-01-01
Observing and Understanding Earth Rotation: A Joint GGOS/IAU Science Workshop; Shanghai, China, 25-28 October 2010 ; The Earth rotates about its axis once a day, but it does not do so uniformly. Instead, the rate of rotation fluctuates by as much as a millisecond a day, the Earth wobbles as it rotates because the Earth's mass is not balanced about its rotation axis, and the Earth's rotation axis precesses and nutates in space. These variations in the Earth's rotation are caused by processes acting within the interior of the Earth such as glacial isostatic adjustment and core-mantle interaction torques, by processes acting at the surface of the Earth such as fluctuations in the transport of mass within the atmosphere and oceans, and by processes acting external to the Earth such as torques due to the gravitational attraction of the Sun, the Moon, and the planets. These and other aspects of the Earth's rotation were discussed at a recent workshop in China that attracted 90 participants from 12 countries. The workshop was jointly organized by the Global Geodetic Observing System (GGOS) of the International Association of Geodesy and Commission 19 (Rotation of the Earth) of the International Astronomical Union (IAU). The objectives of the workshop were to (1) assess our ability to observe the Earth's time-varying rotation, (2) assess our understanding of the causes of the observed variations, (3) assess the consistency of Earth rotation observations with global gravity and shape observations, and (4) explore methods of combining rotation, gravity, and shape observations to gain greater understanding of the processes causing them to change on both the Earth and other planets, like Mars.
Consistency of IVS nutation time series
NASA Astrophysics Data System (ADS)
Gattano, César; Lambert, Sébastien; Bizouard, Christian
2016-04-01
We give a review of the various VLBI-derived nutation time series provided by the different operational analysis centers of the IVS and three combination centers (IVS, IERS EOP Center, and Rapid Service/Prediction Center). We focus on the stability of small nutation amplitudes, including the free core nutation and other atmospherically-driven nutations, that are of interest for improving Earth models. We discuss the possible origins of the differences (software packaged, inversion methods, analysis configuration including a priori and estimation strategy) and the consequences for scientific exploitation of the data, especially in terms of nutation modeling and inference of the Earth's internal structure.
Active vibration control using an inertial actuator with internal damping.
Paulitsch, Christoph; Gardonio, Paolo; Elliott, Stephen J
2006-04-01
Collocated direct velocity feedback with ideal point force actuators mounted on structures is unconditionally stable and generates active damping. When inertial actuators are used to generate the control force, the system can become unstable even for moderate velocity feedback gains due to an additional -180 degree phase lag introduced by the fundamental axial resonant mode of the inertial actuator. In this study a relative velocity sensor is used to implement an inner velocity feedback loop that generates internal damping in a lightweight, electrodynamic, inertial actuator. Simulation results for a model problem with the actuator mounted on a clamped plate show that, when internal relative velocity feedback is used in addition to a conventional external velocity feedback loop, there is an optimum combination of internal and external velocity feedback gains, which, for a given gain margin, maximizes vibration reduction. These predictions are validated in experiments with a specially built lightweight inertial actuator.
Modeling active constrained-layer damping using Golla-Hughes-McTavish approach
NASA Astrophysics Data System (ADS)
Lam, Margaretha J.; Saunders, William R.; Inman, Daniel J.
1995-05-01
Viscoelastic material (VEM) adds damping to structures. In order to enhance the damping effects of the viscoelastic material, a constraining layer is attached. If this constraining layer is a piezoelectric patch, the system is said to have active constrained layer damping (ACLD). In this paper, the damping effects due to viscoelastic material which has an active constraining layer is modeled using the Golla-Hughes-McTavish (GHM) damping method. The piezoelectric patch and structure are modeled using a Galerkin approach in order to account for the effect of the constraining layer on the beam.
NASA Astrophysics Data System (ADS)
Koot, L.
2012-12-01
The gravitational torque applied on the Earth by the other celestial bodies generates periodic variations in the orientation of the Earth's rotation axis in space which are called nutations. This motion has two normal modes, the Free Core Nutation (FCN) and the Free Inner Core Nutation (FICN), of which the frequencies and dampings depend directly on the Earth's interior structure and dynamics (e.g. Mathews et al. 1991a, 1991b, Mathews & Shapiro 1992). Both normal modes are characterized by differential rotations of the inner core, the outer core, and the mantle. Their natural frequencies are thus directly affected both by the strength of the mechanical coupling at the outer core boundaries and by the way the three regions deform due to the action of centrifugal forces. Similarly, the damping of the modes reflects the energy dissipated both through the couplings at the outer core boundaries and through anelastic deformation. The mechanical coupling can be of several physical origins such as gravitational, electromagnetic, viscous, or pressure/topographic couplings. Due to the high precision of the nutation observations, obtained from the Very Long Baseline Interferometry (VLBI) technique, the frequency and damping of the normal modes can be estimated from the resonance effect they induce on the forced nutations (Mathews et al. 2002, Koot et al. 2008, 2010). Interpretation of these estimated natural frequencies and dampings allows then for insights into the deep Earth's physical properties. In this talk, we review the constraints that have been inferred from nutation observations on deep Earth's properties such as the intensity of the magnetic field at the outer core boundaries (Buffett et al. 2002, Koot et al. 2010, Buffett 2010a), the viscosity of the core fluid close to those boundaries (Mathews & Guo 2005, Deleplace & Cardin 2006, Koot et al. 2010), the chemical stratification at the top of the core (Buffett 2010b), and the viscosity of the inner core (Koot
The earth's forced nutations - Geophysical implications
NASA Technical Reports Server (NTRS)
Wahr, J. M.; De Vries, D.
1990-01-01
Theories of nutation are examined critically to develop an extension of the theoretical description based on an earth in nonhydrostatic equilibrium. The estimation of nutation amplitude as a function of frequency is reviewed with reference to contributing variables such as the oceans, mantle anelasticity, and nonhydrostatic structure. Theoretical results by Wahr (1981) are compared to those of VLBI observations, and other VLBI data are used to discuss Wahr and Bergen's (1986) theoretical nutation admittances for an anelastic earth. The contributions associated with the tilt-over mode and with free-core nutations (FCN) are discussed, and the contribution of anelasticity is examined. The VLBI data show that nutation data are important sources of information regarding the earth's interior. Nutation amplitudes are derived with a model for a nonhydrostatically prestressed earth to determine the FCN contributions.
Viscosity of the Earth's inner core: Constraints from nutation observations
NASA Astrophysics Data System (ADS)
Koot, Laurence; Dumberry, Mathieu
2011-08-01
The gravitational torque applied on the Earth by the other celestial bodies generates periodic variations in the orientation of the Earth's rotation axis in space which are called nutations. Observations of Earth's nutations allow for insights into the physical properties of the inner core because of the presence of a normal mode, the Free Inner Core Nutation (FICN), which is characterized by a tilt of the inner core figure and rotation axes with respect to the mantle and outer core. The frequency of the FICN is controlled by the strength of the mechanical coupling acting at the inner core boundary (ICB) and by the ability of the inner core to deform under the action of centrifugal and gravitational forces. Attenuation of the FICN reflects energy dissipated by electromagnetic (EM) and viscous friction at the ICB and through viscous relaxation of the inner core. Here, we show that it is possible to explain the observed frequency and damping of the FICN by a combination of EM coupling at the ICB and viscoelastic deformation of the inner core. This imposes a strong constraint on the viscosity of the inner core which has to be in the range ~ 2-7 × 10 14 Pa s. We also obtain an estimate of the RMS strength of the radial magnetic field at the ICB, which has to be between 4.5 and 6.7 mT. Interestingly, if a viscoelastic Maxwell rheology is assumed for the inner core, our estimated inner core viscosity is in very good agreement with the shear quality factor inferred from seismic normal modes observations. This suggests that the viscous deformation of the inner core at the nutation (diurnal) time scale and at the seismic normal modes time scale may be due to the same physical mechanisms.
Nutation determination using the Global Positioning System
NASA Astrophysics Data System (ADS)
Yao, Kunliang; Capitaine, Nicole; Umnig, Elke; Weber, Robert
2012-08-01
VLBI observation of extragalactic radio sources is the only technique that allows high accuracy determination of nutation on a regular basis. However, this is limited to periods of nutation greater than about 30 days due to the current resolution of VL BI estimation. It is there fore important to use another technique to improve nutation at shorter periods. It has been shown by Rothacher et al. (1999) and Weber & Rothacher (2001) that GPS is a potential technique for the determination of the short period terms of nutation. The met hod, which is based on the estimation of nutation rates with respect to an a priori model, is limited to nutation terms in the higher frequency range (with periods up to about 21 days) due to deficiencies in the modeling of the satellite orbits. The high accuracy and high time resolution of the GPS observations that are now achieved give us the possibility to estimate the nutation variations with respect to the IAU2000A nutation, with an expected precision of 10 microarcseconds (μas ). The purpose of our study is to use recent GPS observations obtained by 140 IGS stations (IGS08 Core Reference Frame sites included) to estimate the short period nutations. Two methods are applied: one is to investigate the retrograde diurnal term of polar motion with nutation fixed to the IAU 2006/2000 precession - nutation, using CNES/GRGS software GINS/DYNAMO at Observatoire de Paris; another one is to investigate the nutation time derivative, with polar motion fixed, using Bernese GPS software at University of Technology in Vienna. In this poster, we report on our preliminary results with data set covering a period of 3 years (2009 - 2011), with appropriate time resolutions and on the comparison between the two approaches.
NASA Astrophysics Data System (ADS)
Getino, J.; Escapa, A.
2015-08-01
This is the mid-term report of the Sub-WG1 of the IAU/IAG Joint Working Group on Theory of Earth Rotation (JWG ThER). The main objectives are (1) to provide some feasible enhancements of current precession/nutation model; (2) to give a list of potential future improvements of that model provided by the contributors of the subgroup, and (3) to raise out some open questions which should be discussed within the JWG ThER.
An a priori model for the reduction of nutation observations: KSV(1994.3) nutation series
NASA Technical Reports Server (NTRS)
Herring, T. A.
1995-01-01
We discuss the formulation of a new nutation series to be used in the reduction of modern space geodetic data. The motivation for developing such a series is to develop a nutation series that has smaller short period errors than the IAU 1980 nutation series and to provide a series that can be used with techniques such as the Global Positioning System (GPS) that have sensitivity to nutations but can directly separate the effects of nutations from errors in the dynamical force models that effect the satellite orbits. A modern nutation series should allow the errors in the force models for GPS to be better understood. The series is constructed by convolving the Kinoshita and Souchay rigid Earth nutation series with an Earth response function whose parameters are partly based on geophysical models of the Earth and partly estimated from a long series (1979-1993) of very long baseline interferometry (VLBI) estimates of nutation angles. Secular rates of change of the nutation angles to represent corrections to the precession constant and a secular change of the obliquity of the ecliptic are included in the theory. Time dependent amplitudes of the Free Core Nutation (FCN) that is most likely excited by variations in atmospheric pressure are included when the geophysical parameters are estimated. The complex components of the prograde annual nutation are estimated simultaneously with the geophysical parameters because of the large contribution to the nutation from the S(sub 1) atmospheric tide. The weighted root mean square (WRMS) scatter of the nutation angle estimates about this new model are 0.32 mas and the largest correction to the series when the amplitudes of the ten largest nutations are estimated is 0.18 +/- 0.03 mas for the in phase component of the prograde 18. 6 year nutation.
Local structural modeling for implementation of optimal active damping
NASA Astrophysics Data System (ADS)
Blaurock, Carl A.; Miller, David W.
1993-09-01
Local controllers are good candidates for active control of flexible structures. Local control generally consists of low order, frequency benign compensators using collocated hardware. Positive real compensators and plant transfer functions ensure that stability margins and performance robustness are high. The typical design consists of an experimentally chosen gain on a fixed form controller such as rate feedback. The resulting compensator performs some combination of damping (dissipating energy) and structural modification (changing the energy flow paths). Recent research into structural impedance matching has shown how to optimize dissipation based on the local behavior of the structure. This paper investigates the possibility of improving performance by influencing global energy flow, using local controllers designed using a global performance metric.
Active damping of capillary oscillations on liquid columns
NASA Astrophysics Data System (ADS)
Thiessen, David B.; Wei, Wei; Marston, Philip L.
2002-05-01
Active control of acoustic radiation pressure and of electrostatic stresses on liquid columns has been demonstrated to overcome the Rayleigh-Plateau instability that normally causes long liquid columns to break [M. J. Marr-Lyon et al., J. Fluid Mech. 351, 345 (1997); Phys. Fluids 12, 986-995 (2000)]. Though originally demonstrated for liquid-liquid systems in plateau tanks, the electrostatic method also works on columns in air in reduced gravity [D. B. Thiessen, M. J. Marr-Lyon, and P. L. Marston, ``Active electrostatic stabilization of liquid bridges in low gravity,'' J. Fluid Mech. (in press)]. In new research, the electrostatic stresses are applied in proportion to the velocity of the surface of the column so as to actively dampen capillary oscillations of the surface. The mode amplitude is optically sensed and the rate-of-change is electronically determined. Plateau tank measurements and theory both show that the change in damping rate is proportional to the feedback gain. The results suggest that either active control of electrostatic stresses or of acoustic radiation stresses can be used to suppress the response of interfaces to vibration. [Work supported by NASA.
Damping MEMS Devices in Harsh Environments Using Active Thin Films
2008-06-17
properties of the layers was developed. Damping properties in Nitinol thin film due only to residual stresses was measured to be as high as tan delta...0.17 for large strain (0.9%). At lower strain levels a Nitinol /Silicon laminate was tested in a cantilever load frame. The damping value of the...film was measured to be 0.28 (at 0.27% strain). A Nitinol /Terfenol-D/Nickel laminate was fabricated and tested in a cantilever loading. The damping
Smart actuators: a novel technique for active damping
NASA Astrophysics Data System (ADS)
Muth, Michael; Moldovan, Klaus; Goetz, Bernt
1995-05-01
Sensors are important components for any automatic process. Their function is to measure physical variables, and thus to allow automatic actions in a technical process, for example in a manufacturing sequence or a measurement. Selecting a sensor for a process, it is mostly overlooked that actuators used in a process also have sensory properties. The reactions of actuators to the state of a process give the possibility to extract relevant information out of the process with actuators. In using the sensory properties of actuators the costs for additional sensors can be saved. Even more important, under some circumstances it may not even be possible to place a special sensor directly at the location of interest: In that case the information about the physical variable is only accessible by analyzing the return signal of the actuator. An example of such a smart actuator combining active and sensory properties is demonstrated in a simple experiment. This experiment shows a steel ball supported as a pendulum. The steel ball can be pushed off, and on swinging back it can be caught in a single pass without any bounce. The actuator uses the piezoelectric effect which shows the underlying principle most clearly: Application of the reversibility of physical effects. In this case mechanical energy can either be produced or absorbed. This experiment is means as a demonstration model for students. It is also used for preliminary investigations developing a fast, actively damped tipping mechanism (optical scanner).
Nutation control during precession of a spin-stabilized spacecraft
NASA Technical Reports Server (NTRS)
Taylor, J. M.; Donner, R. J.
1973-01-01
The effects of precession thrust pulses and energy dissipation upon nutation of a spin-stabilized spacecraft are studied. Methods for controlling nutation during a precession maneuver are proposed and examined. A precession modulation control law is developed which uses precession thrust pulses to control nutation. Digital simulations show that precession control with separate nutation control is the fastest precessing system; however, the precession modulation method is only fractionally slower while not requiring a separate nutation control system.
VLBI studies of the nutations of the earth
NASA Technical Reports Server (NTRS)
Herring, T. A.
1988-01-01
The analysis of six years of VLBI data has yielded corrections to the coefficients of the seven largest terms in the IAU 1980 nutation series with periods of one year or less, with accuracies approaching the truncation error of this nutation series (0.1 mas). This paper examines the methods used to extract the nutation information from the VLBI data, the calculation of the uncertanties of the resultant corrections to the nutation-series coefficients, and current research on the earth's nutations.
NASA Astrophysics Data System (ADS)
Puthanpurayil, Arun M.; Reynolds, Paul; Nyawako, Donald
2013-04-01
The mathematical model of a vibrating structure includes mass, damping and stiffness; out of which mass and stiffness could be defined as a function of the system geometry, whereas damping is more of an observed phenomenon. Despite having a large literature on the subject, the underlying physics is only known in a phenomenological ad-hoc manner, making damping an overall mystery in the general dynamic analysis of structures. A major reason of this could be the fact that there is no single universally accepted model for damping. Common practice is to use the classical viscous damping model originated by Rayleigh, through his famous `Rayleigh dissipation function', with a preconceived damping ratio, irrespective of the purpose or type of analysis involved. This paper investigates the effect of this modelling uncertainty on the analytical prediction of the required control force in a semi-active control application for civil structures. Global classical Rayleigh damping models and global non-viscous damping models are used in the present study. Responses of a laboratory slab strip are simulated and are compared with experimental responses. The comparisons emphasises the fact that the choice of in-structure damping models has a significant effect in the computation of the required control force. The comparison also clearly indicates that mathematically sophisticated models have better prediction capability as compared to the classical Rayleigh model.
Real-time RMS active damping augmentation: Heavy and very light payload evaluations
NASA Technical Reports Server (NTRS)
Demeo, Martha E.; Gilbert, Michael G.; Lepanto, Janet A.; Flueckiger, Karl W.; Bains, Elizabeth M.; Jensen, Mary C.
1994-01-01
Controls-Structures Integration Technology has been applied to the Space Shuttle Remote Manipulator System (RMS) to improve on-orbit performance. The objective was to actively damp undesired oscillatory motions of the RMS following routine payload maneuvering and Shuttle attitude control thruster firings. Simulation of active damping was conducted in the real-time, man-in-the-loop Systems Engineering Simulator at NASA's Johnson Space Center. The simulator was used to obtain qualitative and quantitative data on active damping performance from astronaut operators. Using a simulated three-axis accelerometer mounted on the RMS, 'sensed' vibration motions were used to generate joint motor commands that reduced the unwanted oscillations. Active damping of the RMS with heavy and light attached payloads was demonstrated in this study. Five astronaut operators examined the performance of active damping following operator commanded RMS maneuvers and Shuttle thruster firings. Noticeable improvements in the damping response of the RMS with the heavy, Hubble Space Telescope payload and the very light, astronaut in Manipulator Foot Restraint payload were observed. The potential of active damping to aid in precisely maneuvering payloads was deemed significant.
Precession and Nutation of the Earth
NASA Astrophysics Data System (ADS)
Souchay, Jean; Capitaine, Nicole
Precession and nutation of the Earth originate in the tidal forces exerted by the Moon, the Sun, and the planets on the equatorial bulge of the Earth. Discovered respectively in the 2nd century B.C. by Hipparcus and in the 18th century by Bradley, their existence and characteristics were deduced theoretically by Newton for the precession and by d'Alembert for the nutation. After a historical review we explain, both in an intuitive manner and by simple calculations, the gravitational origin and the main characteristics of the precession-nutation. Then we describe in detail two fundamental theories, one using the Lagrangian formalism, the other the Hamiltonian one. A large final part is devoted to successive improvements of the precession-nutation theory in the last decades, both when considering the Earth as a rigid body and when taking into account the small effects of non-rigidity.
NASA Astrophysics Data System (ADS)
Badre Alam, Askari
This thesis presents a study conducted to explore the feasibility of employing Enhanced Active Constrained Layer (EACL) damping treatment in helicopter rotor systems to alleviate aeromechanical instability. The central idea is to apply the EACL treatment on the flexbeams of soft in-plane bearingless main rotors (BMRs) and increase the damping of the first lag mode. In this research, it is explored whether EACL damping treatment can provide sufficient damping in rotor system without exceeding the physical design limits of actuators. To study the feasibility of the EACL damping treatment, a finite element based mathematical model of a rotor with EACL damping treatment on flexbeam is developed. A bench top experiment is conducted to verify the mathematical model. It is shown that the experimental results correlate well with the analytical results. A derivative controller, with control voltage based on the flexbeam tip transverse velocity, is used in this investigation. A filter is developed to remove 1/rev component of the feedback signal. An optimization study is conducted to understand the influence of EACL design parameters on the performance of the damping treatment. A study is conducted to analyze delamination of EACL damping treatment. In this study, a new finite element model is developed that is capable of accurately predicting both, the performance and interlaminar stresses in EACL damping treatment. A new configuration of PCL damping treatment is developed by tapering the constraining layer at the free ends. As compared to a conventional PCL, this configuration has significantly lower interlaminar stresses and similar damping performance. A study is conducted to compare ACL with purely active configuration. It was shown that in ACL configuration, the interlaminar stresses are an-order-of-magnitude lower than the purely active configuration for similar damping levels. A new ACL configuration is designed by changing the poling direction of the PZT constraining
VLBI Observations of the Free Core Nutations
NASA Astrophysics Data System (ADS)
Smylie, D. E.
2012-12-01
At core scale lengths with periods from a few hours to days, the Coriolis acceleration dominates the Lorentz force density and core modes can be considered as purely mechanical. One of the most interesting core modes is the spin-over mode, which reflects the ability of the outer core to rotate about an axis different from that of either the inner core or the shell. It has a nearly diurnal period. In the Earth frame of reference, this mode produces the nearly diurnal retrograde wobble. In the space frame of reference it is accompanied by the free core nutations. When the flattening of the boundaries of the fluid outer core and the figure-figure gravitational coupling are taken into account, as well as the deformability of the boundaries, both a retrograde free core nutation and a prograde free core nutation are found. The retrograde free core nutation was first predicted by Poincare (1910) for a completly fluid, incompressible core bounded by a rigid shell. In a variational calculation of wobble-nutation modes in realistic Earth models, Jiang (1993) found the classical retrograde free core nutation (RFCN) but discovered a prograde free core nutation (PFCN) as well. VLBI residuals in longitude and obliquity compared to the 1980 IAU nutation series, and their standard errors, were downloaded from the Goddard Space Flight Center website, for the period August 3, 1979 to March 6, 2003, giving 3343 points over a span of 8617 days. In an overlapping segment analysis, the discrete Fourier transform (DFT) for each segment was found for the corresponding series of unequally spaced nutation residuals by singular value decomposition (SVD), with the number of singular values eliminated determined by the satisfaction of Parseval's theorem. Both the RFCN and the PFCN resonances were found in the resulting power spectrum. The nutation resonances were found to be in free decay, the half-life of the PFCN at 2620 days and that of the RFCN at 2229 days, with Ekman boundary layer
Human-in-the-loop evaluation of RMS Active Damping Augmentation
NASA Technical Reports Server (NTRS)
Demeo, Martha E.; Gilbert, Michael G.; Scott, Michael A.; Lepanto, Janet A.; Bains, Elizabeth M.; Jensen, Mary C.
1993-01-01
Active Damping Augmentation is the insertion of Controls-Structures Integration Technology to benefit the on-orbit performance of the Space Shuttle Remote Manipulator System. The goal is to reduce the vibration decay time of the Remote Manipulator System following normal payload maneuvers and operations. Simulation of Active Damping Augmentation was conducted in the realtime human-in-the-loop Systems Engineering Simulator at the NASA Johnson Space Center. The objective of this study was to obtain a qualitative measure of operational performance improvement from astronaut operators and to obtain supporting quantitative performance data. Sensing of vibratory motions was simulated using a three-axis accelerometer mounted at the end of the lower boom of the Remote Manipulator System. The sensed motions were used in a feedback control law to generate commands to the joint servo mechanisms which reduced the unwanted oscillations. Active damping of the Remote Manipulator System with an attached 3990 lb. payload was successfully demonstrated. Six astronaut operators examined the performance of an Active Damping Augmentation control law following single-joint and coordinated six-joint translational and rotational maneuvers. Active Damping Augmentation disturbance rejection of Orbiter thruster firings was also evaluated. Significant reductions in the dynamic response of the 3990 lb. payload were observed. Astronaut operators recommended investigation of Active Damping Augmentation benefits to heavier payloads where oscillations are a bigger problem (e.g. Space Station Freedom assembly operators).
Active damping of modal vibrations by force apportioning. [for spacecraft structures
NASA Technical Reports Server (NTRS)
Hallauer, W. L., Jr.; Barthelemy, J.-F. M.
1980-01-01
The theory and numerical simulation of active structural damping is described which requires few discrete control thrusters positioned on the structure. A particular apportioning of coherently phased control forces is applied for each vibration mode which is to be damped; this strongly affects the damped vibration mode, while minimally exciting all other modes. The force apportioning used is that which would tune a target mode if the structure was being shaken in a model vibration test. In contrast to model testing, the forces are varied temporally so as to dampen, rather than excite, the target mode(s).
The Earth's nutation: VLBI versus IAU 2000A
NASA Astrophysics Data System (ADS)
Lambert, S.; Rosat, S.; Capitaine, N.; Souchay, J.
2014-12-01
The nutation measured by VLBI is compared with the IAU 2000A model. The differences are modeled empirically by adjusting the free core nutation and a number of tidal terms. The signal remaining in the residuals is discussed.
Fedorov's attempt to solve the nutation problem
NASA Astrophysics Data System (ADS)
Yatskiv, Ya. S.
First of all a brief history of the investigation of nutation carried out before Fedorov's first studies of this problem is presented. Afterwards the main attention is paid to the Fedorov's determination of corrections to nutation coefficients from latitude observations and to the Fedorov's theory of nutation of a perfectly elastic Earth. Fedorov showed that elastic deformations do not virtually affect the motion of the axis of angular momentum in space, i.e. the nutation of this axis. At the same time they diminish the coefficients of the expression of forced nearly diurnal motion of the pole, the so-called Oppolzer terms. Therefore Fedorov compared the expression of these terms for a perfectly elastic Earth with observations and stated: - the Earth as a whole is not a perfectly elastic body: - the theory of nutation of the Earth consisting of an elastic mantle and a fluid core has not been developed to a degree such that it is possible to test this theory by observations.
Numerical derivation of forced nutation terms for a rigid earth
NASA Technical Reports Server (NTRS)
Schastok, J.; Soffel, M.; Ruder, H.
1990-01-01
The results of a numerical integration of the Euler equations for a rigid earth model covering a time span of 250 years are compared with Kinoshita's (1977) theory for the forced nutations and with a new nutation series by Kinoshita and Souchay. Numerical corrections to some of the analytically derived nutation terms are presented.
Spectral damping scaling factors for shallow crustal earthquakes in active tectonic regions
Rezaeian, Sanaz; Bozorgnia, Yousef; Idriss, I.M.; Campbell, Kenneth; Abrahamson, Norman; Silva, Walter
2012-01-01
Ground motion prediction equations (GMPEs) for elastic response spectra, including the Next Generation Attenuation (NGA) models, are typically developed at a 5% viscous damping ratio. In reality, however, structural and non-structural systems can have damping ratios other than 5%, depending on various factors such as structural types, construction materials, level of ground motion excitations, among others. This report provides the findings of a comprehensive study to develop a new model for a Damping Scaling Factor (DSF) that can be used to adjust the 5% damped spectral ordinates predicted by a GMPE to spectral ordinates with damping ratios between 0.5 to 30%. Using the updated, 2011 version of the NGA database of ground motions recorded in worldwide shallow crustal earthquakes in active tectonic regions (i.e., the NGA-West2 database), dependencies of the DSF on variables including damping ratio, spectral period, moment magnitude, source-to-site distance, duration, and local site conditions are examined. The strong influence of duration is captured by inclusion of both magnitude and distance in the DSF model. Site conditions are found to have less significant influence on DSF and are not included in the model. The proposed model for DSF provides functional forms for the median value and the logarithmic standard deviation of DSF. This model is heteroscedastic, where the variance is a function of the damping ratio. Damping Scaling Factor models are developed for the “average” horizontal ground motion components, i.e., RotD50 and GMRotI50, as well as the vertical component of ground motion.
Active damping of oscillations in a long compliant manipulator link
NASA Astrophysics Data System (ADS)
Baker, C. P.; Evans, M. S.; Trudnowski, D. J.; Magee, D. P.
1993-07-01
A flexible manipulator test bed consisting of a fifteen foot long fixed-free compliant beam (representing a compliant manipulator link) with a Shilling Titan II dextrous manipulator mounted on its free end has been constructed at Pacific Northwest Laboratory (PNL). A comprehensive dynamic model which includes flexible body effects has been developed at PNL using a commercially available multibody dynamics code. A linearized version of the model is used to develop control strategies which use inertial forces generated by movements of the dextrous manipulator to damp out induced oscillations in the beam. These control strategies are tested on the model and shown to be feasible, and then implemented in the flexible manipulator testbed. Results from the hardware experiments are analyzed and compared with the model results.
Active/Passive Control of Sound Radiation from Panels using Constrained Layer Damping
NASA Technical Reports Server (NTRS)
Gibbs, Gary P.; Cabell, Randolph H.
2003-01-01
A hybrid passive/active noise control system utilizing constrained layer damping and model predictive feedback control is presented. This system is used to control the sound radiation of panels due to broadband disturbances. To facilitate the hybrid system design, a methodology for placement of constrained layer damping which targets selected modes based on their relative radiated sound power is developed. The placement methodology is utilized to determine two constrained layer damping configurations for experimental evaluation of a hybrid system. The first configuration targets the (4,1) panel mode which is not controllable by the piezoelectric control actuator, and the (2,3) and (5,2) panel modes. The second configuration targets the (1,1) and (3,1) modes. The experimental results demonstrate the improved reduction of radiated sound power using the hybrid passive/active control system as compared to the active control system alone.
An Early Nutation-Driven Lunar Dynamo
NASA Astrophysics Data System (ADS)
Dwyer, C. A.; Stevenson, D. J.; Nimmo, F.
2010-12-01
Paleointensity data have long been adduced as evidence of an ancient lunar magnetic dynamo and recent paleomagnetic measurements have strengthened this argument [1]. However, a driving mechanism for the dynamo has been hard to find. We investigate here the possibility of a mechanically-stirred dynamo driven by nutation. Nutation results in the stirring of a liquid core by the differential motion of the solid outer mantle. Lunar laser ranging supports a small (≈335 km) liquid core and provides an estimate of the energy dissipated at the lunar core/mantle boundary at the present-day [2]. While the current energy dissipation rate is not enough to power a dynamo, the energy available would have been much larger earlier in lunar history, when the moon was closer to Earth and the spin axis was more offset from the orbital plane. As a first step investigating the feasibility of a nutation-driven lunar paleodynamo, we considered the energy budget likely available to power a dynamo. Model A used a simple scaling argument based on the terrestrial dynamo. Model B was based on the energy flux model of [3]. For lunar semi-major axes less than ≈42 REarth (≈3 Ga), both models produce comparable results and predict surface fields greater than 1 µT (comparable to the paleointensity estimates of [1]). Furthermore, a nutation-driven dynamo would have naturally ceased to operate as the lunar orbit expanded; it would have failed when the available power (which strongly depends on semi-major axis) was no longer able to overcome the tendency of the core to cool to a subadiabatic state. Thus, mechanical stirring via nutation is a viable potential driver of a lunar dynamo and deserves further study. [1] Garrick-Bethell et al. (2009) Science 323, 356-359. [2] Williams et al. (2001) JGR-P 106, 27933-27968. [3] Christensen et al. (2009) Nature 457, 167-169.
NASA Astrophysics Data System (ADS)
Leuva, Dhawal
2011-07-01
Motion of propellant in the liquid propellant tanks due to inertial forces transferred from actions like stage separation and trajectory correction of the launch vehicle is known as propellant slosh. If unchecked, propellant slosh can reach resonance and lead to complete loss of the spacecraft stability, it can change the trajectory of the vehicle or increase consumption of propellant from the calculated requirements, thereby causing starvation of the latter stages of the vehicle. Predicting the magnitude of such slosh events is not trivial. Several passive mechanisms with limited operating range are currently used to mitigate the effects of slosh. An active damping mechanism concept developed here can operate over a large range of slosh frequencies and is much more effective than passive damping devices. Spherical and cylindrical tanks modeled using the ANSYS CFX software package considers the free surface of liquid propellant exposed to atmospheric pressure. Hydrazine is a common liquid propellant and since it is toxic, it cannot be used in experiment. But properties of hydrazine are similar to the properties of water; therefore water is substituted as propellant for experimental study. For close comparison of the data, water is substituted as propellant in CFD simulation. The research is done in three phases. The first phase includes modeling free surface slosh using CFD and validation of the model by comparison to previous experimental results. The second phase includes developing an active damping mechanism and simulating the behavior using a CFD model. The third phase includes experimental development of damping mechanism and comparing the CFD simulation to the experimental results. This research provides an excellent tool for low cost analysis of damping mechanisms for propellant slosh as well as proves that the concept of an active damping mechanism developed here, functions as expected.
Active Damping of the E-P Instability at the Los Alamos Proton Storage Ring
Macek, R.J.; Assadi, S.; Byrd, J.M.; Deibele, C.E.; Henderson, S.D.; Lee, S.Y.; McCrady, R.C.; Pivi, M.F.T.; Plum, M.A.; Walbridge, S.B.; Zaugg, T.J.; /Los Alamos
2008-03-17
A prototype of an analog, transverse (vertical) feedback system for active damping of the two-stream (e-p) instability has been developed and successfully tested at the Los Alamos Proton Storage Ring (PSR). This system was able to improve the instability threshold by approximately 30% (as measured by the change in RF buncher voltage at instability threshold). The feedback system configuration, setup procedures, and optimization of performance are described. Results of several experimental tests of system performance are presented including observations of instability threshold improvement and grow-damp experiments, which yield estimates of instability growth and damping rates. A major effort was undertaken to identify and study several factors limiting system performance. Evidence obtained from these tests suggests that performance of the prototype was limited by higher instability growth rates arising from beam leakage into the gap at lower RF buncher voltage and the onset of instability in the horizontal plane, which had no feedback.
Active damping of the e-p instability at the Los Alamos Proton Storage Ring
Macek, R. J.; Assadi, S.; Byrd, J. M.; Deibele, C. E.; Henderson, S. D.; Lee, S. Y.; McCrady, R. C.; Pivi, M. F. T.; Plum, M. A.; Walbridge, S. B.; Zaugg, T. J.
2007-12-15
A prototype of an analog, transverse (vertical) feedback system for active damping of the two-stream (e-p) instability has been developed and successfully tested at the Los Alamos Proton Storage Ring (PSR). This system was able to improve the instability threshold by approximately 30% (as measured by the change in RF buncher voltage at instability threshold). The feedback system configuration, setup procedures, and optimization of performance are described. Results of several experimental tests of system performance are presented including observations of instability threshold improvement and grow-damp experiments, which yield estimates of instability growth and damping rates. A major effort was undertaken to identify and study several factors limiting system performance. Evidence obtained from these tests suggests that performance of the prototype was limited by higher instability growth rates arising from beam leakage into the gap at lower RF buncher voltage and the onset of instability in the horizontal plane, which had no feedback.
Effects of Active Sting Damping on Common Research Model Data Quality
NASA Technical Reports Server (NTRS)
Acheson, Michael J.; Balakrishna, S.
2011-01-01
Recent tests using the Common Research Model (CRM) at the Langley National Transonic Facility (NTF) and the Ames 11-foot Transonic Wind Tunnel (11' TWT) produced large sets of data that have been used to examine the effects of active damping on transonic tunnel aerodynamic data quality. In particular, large statistically significant sets of repeat data demonstrate that the active damping system had no apparent effect on drag, lift and pitching moment repeatability during warm testing conditions, while simultaneously enabling aerodynamic data to be obtained post stall. A small set of cryogenic (high Reynolds number) repeat data was obtained at the NTF and again showed a negligible effect on data repeatability. However, due to a degradation of control power in the active damping system cryogenically, the ability to obtain test data post-stall was not achieved during cryogenic testing. Additionally, comparisons of data repeatability between NTF and 11-ft TWT CRM data led to further (warm) testing at the NTF which demonstrated that for a modest increase in data sampling time, a 2-3 factor improvement in drag, and pitching moment repeatability was readily achieved not related with the active damping system.
DESIGN AND ANALYSIS OF AN FPGA-BASED ACTIVE FEEDBACK DAMPING SYSTEM
Xie, Zaipeng; Schulte, Mike; Deibele, Craig Edmond
2010-01-01
The Spallation Neutron Source (SNS) at the Oak Ridge National Laboratory is a high-intensity proton-based accelerator that produces neutron beams for neutronscattering research. As the most powerful pulsed neutron source in the world, the SNS accelerator has experienced an unprecedented beam instability that has a wide bandwidth (0 to 300MHz) and fast growth time (10 to100 s). In this paper, we propose and analyze several FPGA-based designs for an active feedback damping system. This signal processing system is the first FPGA-based design for active feedback damping of wideband instabilities in high intensity accelerators. It can effectively mitigate instabilities in highintensity protons beams, reduce radiation, and boost the accelerator s luminosity performance. Unlike existing systems, which are designed using analog components, our FPGA-based active feedback damping system offers programmability while maintaining high performance. To meet the system throughput and latency requirements, our proposed designs are guided by detailed analysis of resource and performance tradeoffs. These designs are mapped onto a reconfigurable platform that includes Xilinx Virtex-II Pro FPGAs and high-speed analog-to-digital and digital-toanalog converters. Our results show that our FPGA-based active feedback damping system can provide increased flexibility and improved signal processing performance that are not feasible with existing analog systems.
Design analysis for a nutating plate drive 4
NASA Technical Reports Server (NTRS)
Loewenthal, S. H.; Townsend, D. P.
1972-01-01
A simplified design analysis was conducted on a nutating plate type drive system for a 2500 horsepower helicopter main rotor gear box. A drive system that split the output torque evenly between two nutating plates for the purpose of reducing the load on each nutating plate was analyzed. Needle bearings were used on the nutating plate pins. The results of the analysis indicate that the required load capacity of the pin bearings and the speed of the nutating plate bearings were beyond the state-of-the-art capacity of rolling-element bearings. The analysis further indicates that the nutating plate drive is less efficient, and results in a higher weight per horsepower than a conventional planetary helicopter transmission with similar design specifications.
Regularization of Nutation Time Series at GSFC
NASA Astrophysics Data System (ADS)
Le Bail, K.; Gipson, J. M.; Bolotin, S.
2012-12-01
VLBI is unique in its ability to measure all five Earth orientation parameters. In this paper we focus on the two nutation parameters which characterize the orientation of the Earth's rotation axis in space. We look at the periodicities and the spectral characteristics of these parameters for both R1 and R4 sessions independently. The study of the most significant periodic signals for periods shorter than 600 days is common for these four time series (period of 450 days), and the type of noise determined by the Allan variance is a white noise for the four series. To investigate methods of regularizing the series, we look at a Singular Spectrum Analysis-derived method and at the Kalman filter. The two methods adequately reproduce the tendency of the nutation time series, but the resulting series are noisier using the Singular Spectrum Analysis-derived method.
Precession, Nutation and Wobble of the Earth
NASA Astrophysics Data System (ADS)
Dehant, V.; Mathews, P. M.
2015-04-01
Covering both astronomical and geophysical perspectives, this book describes changes in the Earth's orientation, specifically precession and nutation, and how they are observed and computed in terms of tidal forcing and models of the Earth's interior. Following an introduction to key concepts and elementary geodetic theory, the book describes how precise measurements of the Earth's orientation are made using observations of extra-galactic radio-sources by Very Long Baseline Interferometry techniques. It demonstrates how models are used to accurately pinpoint the location and orientation of the Earth with reference to the stars and how to determine variations in its rotation speed. A theoretical framework is also presented that describes the role played by the structure and properties of the Earth's deep interior. Incorporating suggestions for future developments in nutation theory for the next generation models, this book is ideal for advanced-level students and researche! rs in solid Earth geophysics, planetary science and astronomy.
Planetary-Induced Nutation of the Earth: Direct Terms
NASA Technical Reports Server (NTRS)
Williams, James G.
1995-01-01
Small torques by the planets can alter the direction of the Earth's rotation axis in space. These direct planetary-induced nutations have been computed using a numerical technique. 62 nutation terms with periods between 0.2 and 883 yr are presented. The maximum,nutation is 0.5 marcsec. Also given are planetary-induced rates and accelerations of precession and obliquity.
Improved Models for Precession and Nutation
2000-03-01
in the process of constructing the series. A series due to Shirai and Fukushima (2000) also gives a somewhat comparable t to data, improving on the...IERS 1996 have been e ected recently by Shirai and Fukushima (2000) through re nements of the method and the use of more extensive data, in their...once these series are implemented in the software used for estimation of nutation amplitudes from VLBI data. It is known ( Fukushima , 1991) that general
Rabi nutations in a ferromagnetic film
NASA Astrophysics Data System (ADS)
Capua, Amir; Rettner, Charles; Parkin, Stuart
When electromagnetic radiation interacts with a two-level system, energy is transferred back and forth between the quantum system and the electromagnetic radiation at a rate defined by the Rabi frequency. This process takes place as long as coherence prevails, until steady state is reached. Rabi nutations have been observed in a variety of quantum systems (atomic vapors, semiconductors, superconducting qubits, etc.). Here, we observe Rabi nutations in an ultrathin ~10 Å perpendicularly magnetized CoFeB film. A hybrid ferromagnetic resonance (FMR) - time resolved magneto optical Kerr effect (TRMOKE) system is used for this observation. Namely, a strong optical pump pulse perturbs the precessing spin system after which a weak optical probe pulse is sent at different times to map its recovery until steady precessional motion is reached again. The responses at the different detunings of magnetic field away from resonance conditions readily indicate the occurrence of the Rabi nutations which are initiated by the pump arriving at t =0. Excellent agreement with the prediction given by the Rabi formula is found. The method we report presents a new approach to study dynamical phenomena in magnetic materials.
Nutation of Helianthus Annuus in a microgravity environment
NASA Technical Reports Server (NTRS)
Brown, A. H.
1981-01-01
An experiment to gather evidence to decide between the Darwinian concept of endogenously motivated nutation and the more mechanistic concept of gravity dependent nutation is described. If nutation persists in weightlessness, parameters describing the motion will be measured by recording in time lapse mode the video images of a population of seedlings that were grown at 1-g, but which will be observed at virtual zero gravity. Later, the plant images will be displayed on a video monitor in a laboratory, photographed on 16 millimeter film, and analyzed frame by frame to determine the kinetics of nutation for each specimen tested.
Damping Control of Liquid Container by Swing-type Active Vibration Reducer on Mobile Robot
NASA Astrophysics Data System (ADS)
Hamaguchi, Masafumi; Taniguchi, Takao
This paper proposes a damping control of sloshing in a cylindrical container with a swing-type active vibration reducer on a wheeled mobile robot (WMR). The WMR runs along a straight path on a horizontal plane. The container is mounted on the active vibration reducer. A laser displacement sensor is used to observe the liquid level in the container. The container can be tilted in the running direction by the active vibration reducer. A sloshing model is obtained from a spherical pendulum-type sloshing model, which approximately expresses (1, 1)-mode sloshing. The sloshing model is used to design a damping control system. The control system of the active vibration reducer is designed with an inverse model of sloshing and an optimal regulator with a Kalman filter. The WMR is driven by an acceleration pattern designed with an input shaping method. The usefulness of the proposed method is demonstrated through simulation and experimental results.
High-damping-performance magnetorheological material for passive or active vibration control
NASA Astrophysics Data System (ADS)
Liu, Taixiang; Yang, Ke; Yan, Hongwei; Yuan, Xiaodong; Xu, Yangguang
2016-10-01
Optical assembly and alignment system plays a crucial role for the construction of high-power or high-energy laser facility, which attempts to ignite fusion reaction and go further to make fusion energy usable. In the optical assembly and alignment system, the vibration control is a key problem needs to be well handled and a material with higher damping performance is much desirable. Recently, a new kind of smart magneto-sensitive polymeric composite material, named magnetorheological plastomer (MRP), was synthesized and reported as a high-performance magnetorheological material and this material has a magneto-enhanced high-damping performance. The MRP behaves usually in an intermediate state between fluid-like magnetorheological fluid and solid-like magnetorheological elastomer. The state of MRP, as well as the damping performance of MRP, can be tuned by adjusting the ratio of hard segments and soft segments, which are ingredients to synthesize the polymeric matrix. In this work, a series of MRP are prepared by dispersing micron-sized, magneto-sensitive carbonyl iron powders with related additives into polyurethane-based, magnetically insensitive matrix. It is found that the damping performance of MRP depends much on magnetic strength, shear rate, carbonyl iron content and shear strain amplitude. Especially, the damping capacity of MRP can be tuned in a large range by adjusting external magnetic field. It is promising that the MRP will have much application in passive and active vibration control, such as vibration reduction in optical assembly and alignment system, vibration isolation or absorption in vehicle suspension system, etc.
NASA Astrophysics Data System (ADS)
Beri, Rajan; Chattopadhyay, Aditi; Nam, Changho
2000-06-01
A rigorous multi-objective optimization procedure, is developed to address the integrated structures/control design of composite plates with surface bonded segmented active constrained layer (ACL) damping treatment. The Kresselmeier- Steinhauser function approach is used to formulate this multidisciplinary problem. The goal is to control vibration without incorporating a weight penalty. Objective functions and constraints include damping ratios, structural weight and natural frequencies. Design variables include the ply stacking sequence, dimensions and placement of segmented ACL. The optimal designs show improved plate vibratory characteristics and reduced structural weight. The results of the multi- objective optimization problem are compared to those of a single objective optimization with vibration control as the objective. Results establish the necessity for developing the integrated structures/controls optimization procedure.
NASA Technical Reports Server (NTRS)
Choi, Benjamin; Morrison, Carlos; Min, James
2009-01-01
The Structural Dynamics and. Mechanics branch (RXS) is developing smart adaptive structures to improve fan blade damping at resonances using piezoelectric (PE) transducers. In this presentation, only one shunted PE transducer was used to demonstrate active control of multi-mode blade resonance damping on a titanium alloy (Ti-6A1-4V) flat plate model, regardless of bending, torsion, and 2-stripe modes. This work would have a significant impact on the conventional passive shunt damping world because the standard feedback control design tools can now be used to design and implement electric shunt for vibration control. In other words, the passive shunt circuit components using massive inductors and. resistors for multi-mode resonance control can be replaced with digital codes. Furthermore, this active approach with multi patches can simultaneously control several modes in the engine operating range. Dr. Benjamin Choi presented the analytical and experimental results from this work at the Propulsion-Safety and. Affordable Readiness (P-SAR) Conference in March, 2009.
Multilayer Active Control For Structural Damping And Optical-Path Regulation
NASA Technical Reports Server (NTRS)
Rahman, Zahidul H.; Spanos, John T.; Fanson, James L.
1995-01-01
Two active-control concepts incorporated into system for suppression of vibrations in truss structure and regulation of length of optical path on structure to nanometer level. Optical-path-length-control subsystem contains two feedback control loops to obtain active damping in wide amplitude-and-frequency range. Concept described in more detail in number of previous articles, including "Stabilizing Optical-Path Length on a Vibrating Structure" (NPO-19040), "Controllable Optical Delay Line for Stellar Interferometry" (NPO-18686), "Test Bed for Control of Optical-Path Lengths" (NPO-18487).
A study on actuation power flow produced in an active damping system
NASA Astrophysics Data System (ADS)
Horodinca, Mihaita
2013-08-01
This paper aims to present some new features of the experimental research in dynamics of a closed-loop actively controlled mechanical system with collocated PZT sensor and actuator and a proportional-derivative regulator. The evolution of active electrical power absorbed by the actuator is mainly used. A fraction of this power is converted into mechanical real power and delivered by the actuator to the mechanical system. This paper highlights the fact that derivative gain in the regulator produces a directly proportional synthetic damping (positive or negative) in the mechanical system, due to the fact that a directly proportional flow of active electrical power (negative or positive) absorbed by the actuator is generated. The paper proves that the active power flow evolution is very useful to describe the behavior of the actuator for some dynamic regimes (more useful than the magnitude of the electrical impedance). The research was done on a setup that consists of an aluminium cantilever beam equipped with two PZT collocated transducers - rectangular laminar design - closely glued by the rigidly fixed end of the beam. The feedback between sensor and actuator is provided by a regulator which produces a tunable phase difference between input and output (equivalent to a proportional-derivative feedback). The electrical current and the voltage generated by the regulator and applied to the actuator are used for finding the values of the active electrical power absorbed by the actuator, the magnitude of the electrical impedance and the values of some dynamic parameters of the cantilever (e.g. damping ratio, damped modal frequency, etc.) due to an external excitation of first bending mode. A computer assisted data acquisition system and some new data processing techniques are used for these purposes.
Rezaeian, Sanaz; Bozorgnia, Yousef; Idriss, I.M.; Abrahamson, Norman; Campbell, Kenneth; Silva, Walter
2014-01-01
Ground motion prediction equations (GMPEs) for elastic response spectra are typically developed at a 5% viscous damping ratio. In reality, however, structural and nonstructural systems can have other damping ratios. This paper develops a new model for a damping scaling factor (DSF) that can be used to adjust the 5% damped spectral ordinates predicted by a GMPE for damping ratios between 0.5% to 30%. The model is developed based on empirical data from worldwide shallow crustal earthquakes in active tectonic regions. Dependencies of the DSF on potential predictor variables, such as the damping ratio, spectral period, ground motion duration, moment magnitude, source-to-site distance, and site conditions, are examined. The strong influence of duration is captured by the inclusion of both magnitude and distance in the DSF model. Site conditions show weak influence on the DSF. The proposed damping scaling model provides functional forms for the median and logarithmic standard deviation of DSF, and is developed for both RotD50 and GMRotI50 horizontal components. A follow-up paper develops a DSF model for vertical ground motion.
Nutation damper for the AMPTE-IRM satellite: Final Report
NASA Technical Reports Server (NTRS)
Truckenbrodt, A.; Schultysik, B.; Mehltretter, J. P.
1983-01-01
The design, computations, and testing of the nutation damper for the AMPTE-IRM satellite are described. The nutation motions of the satellite excite fluid oscillations in the closed tube system; kinetic energy is destroyed (converted to heat) through tube/fluid friction, constriction of the stream by cross sectional change, and formation of turbulence by stream enlargement. This energy is extracted from the satellite such that nutation is reduced. Tests were carried out in a pendulum testing device and the time constants were calculated. Findings showed that the damper remained within the originally specified values and provided for good dynamic behavior of the satellite.
Piezoelectric Stewart platform for general purpose active damping interface and precision control
NASA Astrophysics Data System (ADS)
Abu Hanieh, A.; Preumont, A.; Loix, N.
2001-09-01
This paper discloses a stiff active interface wherein a six degree of freedom Stewart platform, a standard hexapod with a cubic architecture, is used to actively increase the structural damping of flexible systems attached to it. It can also be used to rigidly connect arbitrary substructures while damping them. Each leg of the active interface consists of a linear piezo electric actuator, a collocated force sensor and flexible tips for the connections with the two end plates. By providing the legs with strain or elongation sensors, this active interface can also be used as an interface with infinite stiffness at low frequency (i.e. for machine tools), a 6 d.o.f. positioning and steering device for space applications as well as a microvibration isolator. The translation and rotation strokes of the interface are 90, 103 and 95 μm in the x, y and z directions respectively and 1300, 1150 and 700 μrad around the x, y and z directions respectively.
Testing of an actively damped boring bar featuring structurally integrated PZT stack actuators
Redmond, J.; Barney, P.
1998-06-01
This paper summarizes the results of cutting tests performed using an actively damped boring bar to minimize chatter in metal cutting. A commercially available 2 inch diameter boring bar was modified to incorporate PZT stack actuators for controlling tool bending vibrations encountered during metal removal. The extensional motion of the actuators induce bending moments in the host structure through a two-point preloaded mounting scheme. Cutting tests performed at various speeds and depths of cuts on a hardened steel workpiece illustrate the bar`s effectiveness toward eliminating chatter vibrations and improving workpiece surface finish.
Implementation of an active vibration damping system for the SOFIA telescope assembly
NASA Astrophysics Data System (ADS)
Janzen, Paul C.; Keas, Paul J.
2014-07-01
The NASA/DLR Stratospheric Observatory for Infrared Astronomy (SOFIA) employs a 2.5-meter reflector telescope in a Boeing 747SP. The image stability goal for SOFIA is 0.2 arc-seconds. An active damping control system is being developed for SOFIA to reduce image jitter and degradation due to resonance of the telescope assembly. We describe the vibration control system design and implementation in hardware and software. The system's unique features enabling system testing, control system design, and online health monitoring will also be presented.
Temperature-activated interfacial friction damping in carbon nanotube polymer composites.
Suhr, Jonghwan; Zhang, Wei; Ajayan, Pulickel M; Koratkar, Nikhil A
2006-02-01
Effect of temperature on interfacial sliding in single-walled carbon nanotube polycarbonate composites is investigated experimentally. We show that interfacial slip at the tube-polymer interfaces can be activated at relatively low dynamic strain levels ( approximately 0.35%) by raising temperature to approximately 90 degrees C. We attribute this to increased mobility of the polymer chain backbones at elevated temperatures and thermal relaxation of the radial compressive stresses at the tube-polymer interfaces. These results show the potential of polymer nanocomposites as high-temperature damping materials for vibration and acoustic suppression in a variety of dynamic systems.
Semi-active control of helicopter vibration using controllable stiffness and damping devices
NASA Astrophysics Data System (ADS)
Anusonti-Inthra, Phuriwat
Semi-active concepts for helicopter vibration reduction are developed and evaluated in this dissertation. Semi-active devices, controllable stiffness devices or controllable orifice dampers, are introduced; (i) in the blade root region (rotor-based concept) and (ii) between the rotor and the fuselage as semi-active isolators (in the non-rotating frame). Corresponding semi-active controllers for helicopter vibration reduction are also developed. The effectiveness of the rotor-based semi-active vibration reduction concept (using stiffness and damping variation) is demonstrated for a 4-bladed hingeless rotor helicopter in moderate- to high-speed forward flight. A sensitivity study shows that the stiffness variation of root element can reduce hub vibrations when proper amplitude and phase are used. Furthermore, the optimal semi-active control scheme can determine the combination of stiffness variations that produce significant vibration reduction in all components of vibratory hub loads simultaneously. It is demonstrated that desired cyclic variations in properties of the blade root region can be practically achieved using discrete controllable stiffness devices and controllable dampers, especially in the flap and lag directions. These discrete controllable devices can produce 35--50% reduction in a composite vibration index representing all components of vibratory hub loads. No detrimental increases are observed in the lower harmonics of blade loads and blade response (which contribute to the dynamic stresses) and controllable device internal loads, when the optimal stiffness and damping variations are introduced. The effectiveness of optimal stiffness and damping variations in reducing hub vibration is retained over a range of cruise speeds and for variations in fundamental rotor properties. The effectiveness of the semi-active isolator is demonstrated for a simplified single degree of freedom system representing the semi-active isolation system. The rotor
Nutation and precession control of the High Energy Solar Physics (HESP) satellite
NASA Technical Reports Server (NTRS)
Jayaraman, C. P.; Robertson, B. P.
1993-01-01
The High Energy Solar Physics (HESP) spacecraft is an intermediate class satellite proposed by NASA to study solar high-energy phenomena during the next cycle of high solar activity in the 1998 to 2005 time frame. The HESP spacecraft is a spinning satellite which points to the sun with stringent pointing requirements. The natural dynamics of a spinning satellite includes an undesirable effect: nutation, which is due to the presence of disturbances and offsets of the spin axis from the angular momentum vector. The proposed Attitude Control System (ACS) attenuates nutation with reaction wheels. Precessing the spacecraft to track the sun in the north-south and east-west directions is accomplished with the use of torques from magnetic torquer bars. In this paper, the basic dynamics of a spinning spacecraft are derived, control algorithms to meet HESP science requirements are discussed and simulation results to demonstrate feasibility of the ACS concept are presented.
NASA Technical Reports Server (NTRS)
Spalding, E. P.; Cosgrove, D. J.
1993-01-01
A variety of electrolytes (10-30 mol m-3) increased the relative growth rate of etiolated cucumber (Cucumis sativus L. cv. Burpee's Pickler) hypocotyls by 20-50% relative to water-only controls. The nonelectrolyte mannitol inhibited growth by 10%. All salts tested were effective, regardless of chemical composition or valence. Measurements of cell-sap osmolality ruled out an osmotic mechanism for the growth stimulation by electrolytes. This, and the nonspecificity of the response, indicate that an electrical property of the solutions was responsible for their growth-stimulating activity. Measurements of surface electrical potential supported this reasoning. Treatment with electrolytes also enhanced nutation and altered the pattern of phototropic curvature development. A novel analytical method for quantitating these effects on growth was developed. The evidence indicates that electrolytes influence an electrophysiological parameter that is involved in the control of cell expansion and the coordination of growth underlying tropisms and nutations.
NASA Technical Reports Server (NTRS)
Beck, Benjamin; Schiller, Noah
2013-01-01
This paper outlines a direct, experimental comparison between two established active vibration control techniques. Active vibration control methods, many of which rely upon piezoelectric patches as actuators and/or sensors, have been widely studied, showing many advantages over passive techniques. However, few direct comparisons between different active vibration control methods have been made to determine the performance benefit of one method over another. For the comparison here, the first control method, velocity feedback, is implemented using four accelerometers that act as sensors along with an analog control circuit which drives a piezoelectric actuator. The second method, negative capacitance shunt damping, consists of a basic analog circuit which utilizes a single piezoelectric patch as both a sensor and actuator. Both of these control methods are implemented individually using the same piezoelectric actuator attached to a clamped Plexiglas window. To assess the performance of each control method, the spatially averaged velocity of the window is compared to an uncontrolled response.
Effects of increased gravity force on nutations of sunflower hypocotyls
NASA Technical Reports Server (NTRS)
Brown, A. H.; Chapman, D. K.
1977-01-01
A centrifuge was used to provide sustained acceleration in order to study the hypocotyl nutation of 6-day-old Helianthus annuus L. over a range of g-forces, up to 20 times normal g. At the upper end of this g-range, nutation was impeded and at times was erratic evidently because the weight of the cotyledons exceeded the supportive abilities of the hypocotyls. Over the range 1 to 9 g, the period of nutation was independent of the resultant force vector. Over the same g-range, the amplitude of nutation was nearly independent of the chronic g-force. If nutation in sunflower seedlings is an oscillation caused by a succession of geotropic responses which continue to overshoot the equilibrium position (plumb line), its amplitude might be expected to be more sensitive to changes in magnitude of the sustained g-force. In order to preserve the geotropic model, in which nutation is considered to be a sustained oscillation driven by geotropic reactions, it is necessary to assume that geotropic response must increase with increasing g most rapidly in the region of the g-parameter below the terrestrial value of 1 g.
NASA Astrophysics Data System (ADS)
Perfetto, S.; Rohlfing, J.; Infante, F.; Mayer, D.; Herold, S.
2016-09-01
Piezoelectric transducers can be used to harvest electrical energy from structural vibrations in order to power continuously operating condition monitoring systems local to where they operate. However, excessive vibrations can compromise the safe operation of mechanical systems. Therefore, absorbers are commonly used to control vibrations. With an integrated device, the mechanical energy that otherwise would be dissipated can be converted via piezoelectric transducers. Vibration absorbers are designed to have high damping factors. Hence, the integration of transducers would lead to a low energy conversion. Efficient energy harvesters usually have low damping capabilities; therefore, they are not effective for vibration suppression. Thus, the design of an integrated device needs to consider the two conflicting requirements on the damping. This study focuses on the development of a laboratory test rig with a host structure and a vibration absorber with tunable damping via an active relative velocity feedback. A voice coil actuator is used for this purpose. To overcome the passive damping effects of the back electromagnetic force a novel voltage feedback control is proposed, which has been validated both in simulation and experimentally. The aim of this study is to have a test rig ready for the introduction of piezo-transducers and available for future experimental evaluations of the damping effect on the effectiveness of vibration reduction and energy harvesting efficiency.
NASA Astrophysics Data System (ADS)
Lin, J.; Huang, Z. Z.; Huang, P. H.
2007-07-01
This paper deals with active damping control problems of robot manipulators with oscillatory bases. A first investigation of two-time scale fuzzy logic controller with vibration stabilizer for such structures has been proposed, where the dynamics of a robotic system is strongly affected by disturbances due to the base oscillation. Under the assumption of two-time scale, its stability and design procedures are presented for a multiple link manipulator with multiple dimension oscillation. The fast-subsystem controller will damp out the vibration of the oscillatory bases using a PD control method. Hence, the slow-subsystem fuzzy logic controller dominates the trajectory tracking. It can be guaranteed the stability of the internal dynamics by adding a boundary-layer correction based on singular perturbations approach. Experimental results have shown that the proposed control model offers several implementation advantages such as reduced effect of overshoot and chattering, smaller steady state error, and a fast convergent rate. The results of this study can be feasible to various mechanical systems, such as mobile robot, gantry cranes, underwater robot, and other dynamic systems mounted on oscillatory bases.
The Modelling and Vibration Control of Beams with Active Constrained Layer Damping
NASA Astrophysics Data System (ADS)
SHI, Y. M.; LI, Z. F.; HUA, H. X.; FU, Z. F.; LIU, T. X.
2001-08-01
The finite element method (FEM) is combined with the Golla-Hughes-McTavish (GHM) model of viscoelastic materials (VEM) to model a cantilever beam with active constrained layer damping treatments. This approach avoids time-consuming iteration in solving modal frequencies, modal damping ratios and responses. But the resultant finite element (FE) model has too many degrees of freedom (d.o.f.s) from the point of view of control, nor is it observable and controllable. A new model reduction procedure is proposed. An iterative dynamic condensation is performed in the physical space, and Guyan condensation is taken as an initial iteration approximation. A reduced order model (ROM) of suitable size emerges, but it is still not observable and controllable. Accordingly, a robust model reduction method is then employed in the state space. A numerical example proves that this procedure reduces the model and assures the stability, controllability and observability of the final reduced order model (FROM). Finally, a controller is designed by linear-quadratic Gaussian (LQG) method based on the FROM. The vibration attenuation is evident
Active Damping of a Piezoelectric Tube Scanner using Self-Sensing Piezo Actuation
Kuiper, S.; Schitter, G.
2010-01-01
In most Atomic Force Microscopes (AFM), a piezoelectric tube scanner is used to position the sample underneath the measurement probe. Oscillations stemming from the weakly damped resonances of the tube scanner are a major source of image distortion, putting a limitation on the achievable imaging speed. This paper demonstrates active damping of these oscillations in multiple scanning axes without the need for additional position sensors. By connecting the tube scanner in a capacitive bridge circuit the scanner oscillations can be measured in both scanning axes, using the same piezo material as an actuator and sensor simultaneously. In order to compensate for circuit imbalance caused by hysteresis in the piezo element, an adaptive balancing circuit is used. The obtained measurement signal is used for feedback control, reducing the resonance peaks in both scanning axes by 18 dB and the cross-coupling at those frequencies by 30 dB. Experimental results demonstrate a significant reduction in scanner oscillations when applying the typical triangular scanning signals, as well as a strong reduction in coupling induced oscillations. Recorded AFM images show a considerable reduction in image distortion due to the proposed control method, enabling artifact free AFM imaging at a speed of 122 lines per second with a standard piezoelectric tube scanner. PMID:26412944
Active Damping of a Piezoelectric Tube Scanner using Self-Sensing Piezo Actuation.
Kuiper, S; Schitter, G
2010-09-01
In most Atomic Force Microscopes (AFM), a piezoelectric tube scanner is used to position the sample underneath the measurement probe. Oscillations stemming from the weakly damped resonances of the tube scanner are a major source of image distortion, putting a limitation on the achievable imaging speed. This paper demonstrates active damping of these oscillations in multiple scanning axes without the need for additional position sensors. By connecting the tube scanner in a capacitive bridge circuit the scanner oscillations can be measured in both scanning axes, using the same piezo material as an actuator and sensor simultaneously. In order to compensate for circuit imbalance caused by hysteresis in the piezo element, an adaptive balancing circuit is used. The obtained measurement signal is used for feedback control, reducing the resonance peaks in both scanning axes by 18 dB and the cross-coupling at those frequencies by 30 dB. Experimental results demonstrate a significant reduction in scanner oscillations when applying the typical triangular scanning signals, as well as a strong reduction in coupling induced oscillations. Recorded AFM images show a considerable reduction in image distortion due to the proposed control method, enabling artifact free AFM imaging at a speed of 122 lines per second with a standard piezoelectric tube scanner.
NASA Astrophysics Data System (ADS)
Lam, Margaretha J.; Inman, Daniel J.; Saunders, William R.
1998-06-01
Damping is important to structures and can be achieved through the addition of viscoelastic materials (VEM). The damping of the VEM is enhanced if a constraining layer is attached to the VEM. If this constraining layer is active, the treatment is called active constrained layer damping (ACLD). In the last few years, ACLD has proven to be superior in vibration control to active or passive damping. The active element makes ACLD more effective than passive constrained layer damping. It also provides a fail-safe in case of breakdown of the active element that is not present for purely active control. It is shown that the control effort needed to damp vibration using ACLD can be significantly higher than purely active control. In order to combine the inherent damping of passive control with the effectiveness of the active element, this paper will explore different variations of active, passive and hybrid damping. Some of the variations include: passive constrained layer damping (PCLD) separate from active element but on the same side of beam, PCLD separate from active on the opposite side of the beam, and active element underneath PCLD. The discretized system equations will be obtained using assumed modes method and Lagrange's equation. The damping will be modeled using the Golla-Hughes-McTavish (GHM) method. The optimal placement and size of the active, passive, ACLD and hybrid treatments will be found using different schemes. The issue of overshoot and settling time of the output and control force using LQR will be addressed, as well as the control effort, passive and active vibration suppression, and LQR cost function. It will be shown that the hybrid treatments are capable of greater vibration control for lower control effort for different optimization schemes. 31
Active sensor/actuator assemblies for vibration damping, compensation, measurement, and testing
NASA Astrophysics Data System (ADS)
Ryaboy, Vyacheslav M.; Kasturi, Prakash S.
2010-04-01
The vibration control module known as IQ damper had been developed as part of active vibration damping system for optical tables and other precision vibration isolated platforms. The present work describes steps to expand the application of these units to other tasks, namely, (1) dynamic testing of structures and (2) compensation of forced vibration in local areas. The sensor-actuator assembly, including signal conditioning circuits, is designed as a compact dynamically symmetric module with mechanical interface to an optical table. The test data show that the vibration control modules can be used to measure dynamic compliance characteristics of optical tables with precision comparable to that of dedicated vibration measurement systems. Stable concerted work of active vibration control modules compensating forced harmonic vibration is demonstrated experimentally.
NASA Technical Reports Server (NTRS)
McElrath, T. P.; Cangahuala, L. A.; Miller, K. J.; Stravert, L. R.; Garcia-Perez, Raul
1995-01-01
Ulysses is a spin-stabilized spacecraft that experienced significant nutation after its launch in October 1990. This was due to the Sun-spacecraft-Earth geometry, and a study of the phenomenon predicted that the nutation would again be a problem during 1994-95. The difficulty of obtaining nutation estimates in real time from the spacecraft telemetry forced the ESA/NASA Ulysses Team to explore alternative information sources. The work performed by the ESA Operations Team provided a model for a system that uses the radio signal strength measurements to monitor the spacecraft dynamics. These measurements (referred to as AGC) are provided once per second by the tracking stations of the DSN. The system was named ARGOS (Attitude Reckoning from Ground Observable Signals) after the ever-vigilant, hundred-eyed giant of Greek Mythology. The ARGOS design also included Doppler processing, because Doppler shifts indicate thruster firings commanded by the active nutation control carried out onboard the spacecraft. While there is some visibility into thruster activity from telemetry, careful processing of the high-sample-rate Doppler data provides an accurate means of detecting the presence and time of thruster firings. DSN Doppler measurements are available at a ten-per-second rate in the same tracking data block as the AGC data.
Passive damping to enhance active positioning of a prototype lithography platen
Segalman, D.J.; Kipp, R.L.; Gregory, D.L.
1994-12-31
A viscoelastic tuned-mass damper was used to suppress specific structural modes of a prototype lithography platen. The platen is magnetically levitated and it is repositioned and held in position by a closed-loop feedback control system. Important capabilities of the platen control system are precise positioning and rapid repositioning, which tend to require high frequency bandwidth. The high bandwidth excites structural vibration modes which are disruptive to the control system. The present work was to develop and demonstrate a means to suppress these modes using passive vibration damping techniques. The motivation is to increase the robustness of the platen positioning and control system by reducing unwanted modal accelerations excited by high control system bandwidth. Activities performed and discussed in this paper include the analytical design of viscoelastic tuned-mass dampers and the demonstration/testing of their effectiveness on the platen while levitated and controlled.
Non-symmetrical semi-active vibration control based on synchronized switching damping
NASA Astrophysics Data System (ADS)
Ji, Hongli; Qiu, Jinhao; Zhang, Jin; Nie, Hong; Cheng, Li
2014-04-01
An unsymmetrical switch circuit is designed for semi-active control method based on synchronized switching damping principle of piezoelectric actuators. A bypass capacitor and an additional switch are used to realize unsymmetrical bipolar voltage. The control logic of the switches is introduced in detail and the switched voltages, which directly influence the control performance, are derived as functions of the vibration amplitude and the outputs of the voltage sources. Simulations were carried out to verify the design circuit and the theoretical results of the switched voltage. The voltage ratio increases with increasing bypass capacitance, but its increasing rate decreases. The results show that large bypass capacitor is needed to realize a voltage ratio of 3, which is common in some piezoelectric actuator such as MFC.
Active Damping of the E-P Instability at the LANL PSR
McCrady, R.; Macek, R.J.; Zaugg, T.; Assadi, S.; Deibele, C.; Henderson, S.; Plum, M.; Lee, S.V.; Walbridge, S.; Byrd, J.M.; Pivi, M.; /SLAC
2007-11-14
A prototype of an analog, transverse (vertical) feedback system for active damping of the two-stream (e-p) instability has been developed and successfully tested at the Los Alamos National Laboratory Proton Storage Ring (PSR). This system was able to improve the instability threshold by approximately 30% (as measured by the change in RF buncher voltage at instability threshold). Evidence obtained from these tests suggests that further improvement in performance is limited by beam leakage into the gap at lower RF buncher voltage and the onset of instability in the horizontal plane, which had no feedback. Here we describe the present system configuration, system optimization, results of several recent experimental tests, and results from studies of factors limiting its performance.
NASA Common Research Model Test Envelope Extension With Active Sting Damping at NTF
NASA Technical Reports Server (NTRS)
Rivers, Melissa B.; Balakrishna, S.
2014-01-01
The NASA Common Research Model (CRM) high Reynolds number transonic wind tunnel testing program was established to generate an experimental database for applied Computational Fluid Dynamics (CFD) validation studies. During transonic wind tunnel tests, the CRM encounters large sting vibrations when the angle of attack approaches the second pitching moment break, which can sometimes become divergent. CRM transonic test data analysis suggests that sting divergent oscillations are related to negative net sting damping episodes associated with flow separation instability. The National Transonic Facility (NTF) has been addressing remedies to extend polar testing up to and beyond the second pitching moment break point of the test articles using an active piezoceramic damper system for both ambient and cryogenic temperatures. This paper reviews CRM test results to gain understanding of sting dynamics with a simple model describing the mechanics of a sting-model system and presents the performance of the damper under cryogenic conditions.
Simultaneous active and passive control for eigenstructure assignment in lightly damped systems
NASA Astrophysics Data System (ADS)
Richiedei, Dario; Trevisani, Alberto
2017-02-01
The assignment of the eigenstructure (i.e. eigenvalues and eigenvectors) in vibrating systems is an effective way to improve their dynamic performances. System controllability ensures that the poles of the controlled system are exactly assigned but it does not allow to assign arbitrary desired eigenvectors. To this purpose, this paper proposes a novel method for vibration control in lightly damped systems through the concurrent synthesis of passive structural modifications and active state (or state derivative) feedback control gains. Indeed, the suitable modification of the inertial and elastic parameters allows to enlarge the range of assignable eigenvectors. The problem is formulated as an optimization problem, where constraints are introduced to assure the feasibility of the physical system modifications while avoiding spillover phenomena. The experimental application to the eigenstructure assignment on a manipulator proves the method effectiveness.
ERIC Educational Resources Information Center
Fay, Temple H.
2012-01-01
Quadratic friction involves a discontinuous damping term in equations of motion in order that the frictional force always opposes the direction of the motion. Perhaps for this reason this topic is usually omitted from beginning texts in differential equations and physics. However, quadratic damping is more realistic than viscous damping in many…
NASA Astrophysics Data System (ADS)
Jiang, Kejian; Zhu, Changsheng; Chen, Liangliang; Qiao, Xiaoli
2015-08-01
To represent the support characteristic of active magnetic bearings (AMB), the commonly used parameters are the equivalent stiffness and the equivalent damping, which inherit the parameters of the stiffness and the damping from traditional mechanical bearings. First, by analyzing the diversity and the similarity between traditional mechanical bearing and AMB, the prior condition for applying the parametric representation of equivalent stiffness and equivalent damping to AMB is illuminated. Then, a method for measuring the equivalent stiffness and the equivalent damping of AMB-rotor system is proposed with multi-frequency excitation. One of its outstanding features is that the proposed method is based on the multi-degree of freedom (DOF) rotor model, not the single- DOF model, because the single DOF model cannot be suitably applied to the multi-DOF AMB-rotor systems. Otherwise, in order to decrease the identification error, the multi-frequency excitation can achieve the lowest peak value by means of appropriate selection for the relative phasing of each component, so that the possibility of the rotor displacement exceeding clearances of AMB and the magnetic force reaching saturation is minimized. Finally, the experiments, which are carried out on an AMB-rotor test rig with a vertical shaft, indicate that the proposed method can efficiently reduce the peak value for the superimposed multi-frequency excitation and correctly identify the equivalent stiffness and equivalent damping of AMB-rotor system.
NASA Astrophysics Data System (ADS)
Yuan, Li-Yun; Xiang, Yu; Lu, Jing; Jiang, Hong-Hua
2015-12-01
Based on the transfer matrix method of exploring the circular cylindrical shell treated with active constrained layer damping (i.e., ACLD), combined with the analytical solution of the Helmholtz equation for a point source, a multi-point multipole virtual source simulation method is for the first time proposed for solving the acoustic radiation problem of a submerged ACLD shell. This approach, wherein some virtual point sources are assumed to be evenly distributed on the axial line of the cylindrical shell, and the sound pressure could be written in the form of the sum of the wave functions series with the undetermined coefficients, is demonstrated to be accurate to achieve the radiation acoustic pressure of the pulsating and oscillating spheres respectively. Meanwhile, this approach is proved to be accurate to obtain the radiation acoustic pressure for a stiffened cylindrical shell. Then, the chosen number of the virtual distributed point sources and truncated number of the wave functions series are discussed to achieve the approximate radiation acoustic pressure of an ACLD cylindrical shell. Applying this method, different radiation acoustic pressures of a submerged ACLD cylindrical shell with different boundary conditions, different thickness values of viscoelastic and piezoelectric layer, different feedback gains for the piezoelectric layer and coverage of ACLD are discussed in detail. Results show that a thicker thickness and larger velocity gain for the piezoelectric layer and larger coverage of the ACLD layer can obtain a better damping effect for the whole structure in general. Whereas, laying a thicker viscoelastic layer is not always a better treatment to achieve a better acoustic characteristic. Project supported by the National Natural Science Foundation of China (Grant Nos. 11162001, 11502056, and 51105083), the Natural Science Foundation of Guangxi Zhuang Autonomous Region, China (Grant No. 2012GXNSFAA053207), the Doctor Foundation of Guangxi
NASA Astrophysics Data System (ADS)
BALAMURUGAN, V.; NARAYANAN, S.
2002-01-01
This work deals with the active vibration control of beams with smart constrained layer damping (SCLD) treatment. SCLD design consists of viscoelastic shear layer sandwiched between two layers of piezoelectric sensors and actuator. This composite SCLD when bonded to a vibrating structure acts as a smart treatment. The sensor piezoelectric layer measures the vibration response of the structure and a feedback controller is provided which regulates the axial deformation of the piezoelectric actuator (constraining layer), thereby providing adjustable and significant damping in the structure. The damping offered by SCLD treatment has two components, active action and passive action. The active action is transmitted from the piezoelectric actuator to the host structure through the viscoelastic layer. The passive action is through the shear deformation in the viscoelastic layer. The active action apart from providing direct active control also adjusts the passive action by regulating the shear deformation in the structure. The passive damping component of this design eliminates spillover, reduces power consumption, improves robustness and reliability of the system, and reduces vibration response at high-frequency ranges where active damping is difficult to implement. A beam finite element model has been developed based on Timoshenko's beam theory with partially covered SCLD. The Golla-Hughes-McTavish (GHM) method has been used to model the viscoelastic layer. The dissipation co-ordinates, defined using GHM approach, describe the frequency-dependent viscoelastic material properties. Models of PCLD and purely active systems could be obtained as a special case of SCLD. Using linear quadratic regulator (LQR) optimal control, the effects of the SCLD on vibration suppression performance and control effort requirements are investigated. The effects of the viscoelastic layer thickness and material properties on the vibration control performance are investigated.
Specific features of two-photon optical nutation in a system of biexcitons in semiconductors
Khadzhi, P. I. Vasil'ev, V. V.
2007-05-15
Specific features of two-photon nutation in a system of coherent biexcitons in CuCl-type semiconductors are studied. It is shown that, depending on the parameters of the system, nutation represents a process of periodic conversion of photon pairs into biexcitons and vice versa. The possibility of phase control of optical nutation is predicted.
Governance of the Nutation Line Contour in Nuclear-Magnetic Flowmeters
NASA Astrophysics Data System (ADS)
Davydov, V. V.; Dudkin, V. I.; Karseev, A. Yu.
2015-06-01
A new method of nutation line shaping under conditions of modulation of the permanent magnetic field В0 by an alternating magnetic field is considered. The dependence is investigated of the amplitude and width of the nutation line on the parameters of the modulation field and of the magnetic field in the region where the nutation coil is located.
Chandler wobble and free core nutation of single pulsar
NASA Astrophysics Data System (ADS)
Gusev, A.
2011-10-01
PSR B1828-11 has long-term, highly periodic and correlated variations pulse shape and of the rate of slow-down with period variations approximately 1000, 500 and 250 days (Stairs et al., 2000). There are three potential explanations of pulses time-of-arrival from pulsar concerned with the interior of the neutron star, planetary bodies, free precession and nutation. We use the Hamiltonian canonical method of Getino et al. (1999) for the dynamically symmetrical pulsar consisting of the rigid crust, elliptical liquid outer core and solid inner core of PSR B1828-11. Correctly extending theory of differential rotation of a pulsar, we investigated dependence on Chandler wobble period, Inner Chandler Wobble, retrograde Free Core Nutation and prograde Free Inner Core Nutation from ellipticity of inner crystal core, outer liquid core and total pulsar.
NASA Astrophysics Data System (ADS)
Balamurugan, V.; Narayanan, S.
2003-10-01
In the present paper, the active-passive hybrid vibration control performance due to Enhanced Smart Constrained Layer Damping (ESCLD) treatment as proposed by Liao and Wang on plate like structures has been considered. This treatment consists of a viscoelastic layer constrained between a smart piezoelectric layer and the base structure being controlled. Also, the smart constraining layer is clamped to the base structure. This type of damping treatment has got both active and passive component of damping. The passive damping is through cyclic shearing of viscoelastic constrained layer which is further enhanced by activating the smart piezoelectric constraining layer and the active component of the damping is through the transfer of control moments from the piezoelectric layer to the base structure through the viscoelastic layer and also bypassed through the clamps. A plate finite element has been formulated using first order shear deformation theory, including the effect of transverse shear and rotary inertia. The effect of the viscoelastic shear layer and piezoelectric constraining layer on the mass and stiffness has been included in the model. The viscoelastic shear layer is modeled usig Golla-Hughes-McTavish (GHM) method, which is a time domain approach. The clamps (edge elements) are modeled as equivalent springs connecting the smart piezoelectric constraining layer with the structure to be controlled. LQR optimal control strategy is used to obtain optimal control gains. The effect of the viscoelastic material properties (shear modulus and loss factor) on the hybrid vibration control performance is studied for both SCLD (without edge elements) and ESCLD systems.
A robust active control system for shimmy damping in the presence of free play and uncertainties
NASA Astrophysics Data System (ADS)
Orlando, Calogero; Alaimo, Andrea
2017-02-01
Shimmy vibration is the oscillatory motion of the fork-wheel assembly about the steering axis. It represents one of the major problem of aircraft landing gear because it can lead to excessive wear, discomfort as well as safety concerns. Based on the nonlinear model of the mechanics of a single wheel nose landing gear (NLG), electromechanical actuator and tire elasticity, a robust active controller capable of damping shimmy vibration is designed and investigated in this study. A novel Decline Population Swarm Optimization (PDSO) procedure is introduced and used to select the optimal parameters for the controller. The PDSO procedure is based on a decline demographic model and shows high global search capability with reduced computational costs. The open and closed loop system behavior is analyzed under different case studies of aeronautical interest and the effects of torsional free play on the nose landing gear response are also studied. Plant parameters probabilistic uncertainties are then taken into account to assess the active controller robustness using a stochastic approach.
An enhanced nonlinear damping approach accounting for system constraints in active mass dampers
NASA Astrophysics Data System (ADS)
Venanzi, Ilaria; Ierimonti, Laura; Ubertini, Filippo
2015-11-01
Active mass dampers are a viable solution for mitigating wind-induced vibrations in high-rise buildings and improve occupants' comfort. Such devices suffer particularly when they reach force saturation of the actuators and maximum extension of their stroke, which may occur in case of severe loading conditions (e.g. wind gust and earthquake). Exceeding actuators' physical limits can impair the control performance of the system or even lead to devices damage, with consequent need for repair or substitution of part of the control system. Controllers for active mass dampers should account for their technological limits. Prior work of the authors was devoted to stroke issues and led to the definition of a nonlinear damping approach, very easy to implement in practice. It consisted of a modified skyhook algorithm complemented with a nonlinear braking force to reverse the direction of the mass before reaching the stroke limit. This paper presents an enhanced version of this approach, also accounting for force saturation of the actuator and keeping the simplicity of implementation. This is achieved by modulating the control force by a nonlinear smooth function depending on the ratio between actuator's force and saturation limit. Results of a numerical investigation show that the proposed approach provides similar results to the method of the State Dependent Riccati Equation, a well-established technique for designing optimal controllers for constrained systems, yet very difficult to apply in practice.
Gol'dshtein, B N; Aksirov, A M; Zakrzhevskaia, D T
2007-01-01
Plasma membrane Ca2+-ATPase is the calcium pump that extrudes calcium ions from cells using ATP hydrolisis for the maintenance of low Ca2+ concentrations in the cell. Calmodulin stimulates Ca2+-ATPase by binding to the autoinhibitory enzyme domain, which allows the access of cytoplasmic ATP and Ca2+ to the active and transport cites. Our kinetic model predicts damped oscillations in the enzyme activity and interprets the known nonmonotonous kinetic behavior of the enzyme in the presence of calmodulin. For the parameters close to the experimental ones, the kinetic model explains the changes in frequency and damping factor of the oscillatory enzyme activity, as dependent on calmodulin concentration. The calculated pre-steady-state curves fit well the known experimental data. The kinetic analysis allows us to assign Ca2+-ATPase to the hysteretic enzymes exhibiting activity oscillations in open systems.
Liu, Yong; Zhu, Lin; Zhan, Lingwei; ...
2015-06-23
Because of zero greenhouse gas emission and decreased manufacture cost, solar photovoltaic (PV) generation is expected to account for a significant portion of future power grid generation portfolio. Because it is indirectly connected to the power grid via power electronic devices, solar PV generation system is fully decoupled from the power grid, which will influence the interconnected power grid dynamic characteristics as a result. In this study, the impact of solar PV penetration on large interconnected power system frequency response and inter-area oscillation is evaluated, taking the United States Eastern Interconnection (EI) as an example. Furthermore, based on the constructedmore » solar PV electrical control model with additional active power control loops, the potential contributions of solar PV generation to power system frequency regulation and oscillation damping are examined. The advantages of solar PV frequency support over that of wind generator are also discussed. Finally, simulation results demonstrate that solar PV generations can effectively work as ‘actuators’ in alleviating the negative impacts they bring about.« less
Liu, Yong; Zhu, Lin; Zhan, Lingwei; Gracia, Jose R.; King, Thomas Jr.; Liu, Yilu
2015-06-23
Because of zero greenhouse gas emission and decreased manufacture cost, solar photovoltaic (PV) generation is expected to account for a significant portion of future power grid generation portfolio. Because it is indirectly connected to the power grid via power electronic devices, solar PV generation system is fully decoupled from the power grid, which will influence the interconnected power grid dynamic characteristics as a result. In this study, the impact of solar PV penetration on large interconnected power system frequency response and inter-area oscillation is evaluated, taking the United States Eastern Interconnection (EI) as an example. Furthermore, based on the constructed solar PV electrical control model with additional active power control loops, the potential contributions of solar PV generation to power system frequency regulation and oscillation damping are examined. The advantages of solar PV frequency support over that of wind generator are also discussed. Finally, simulation results demonstrate that solar PV generations can effectively work as ‘actuators’ in alleviating the negative impacts they bring about.
Non-linear modelling and control of semi-active suspensions with variable damping
NASA Astrophysics Data System (ADS)
Chen, Huang; Long, Chen; Yuan, Chao-Chun; Jiang, Hao-Bin
2013-10-01
Electro-hydraulic dampers can provide variable damping force that is modulated by varying the command current; furthermore, they offer advantages such as lower power, rapid response, lower cost, and simple hardware. However, accurate characterisation of non-linear f-v properties in pre-yield and force saturation in post-yield is still required. Meanwhile, traditional linear or quarter vehicle models contain various non-linearities. The development of a multi-body dynamics model is very complex, and therefore, SIMPACK was used with suitable improvements for model development and numerical simulations. A semi-active suspension was built based on a belief-desire-intention (BDI)-agent model framework. Vehicle handling dynamics were analysed, and a co-simulation analysis was conducted in SIMPACK and MATLAB to evaluate the BDI-agent controller. The design effectively improved ride comfort, handling stability, and driving safety. A rapid control prototype was built based on dSPACE to conduct a real vehicle test. The test and simulation results were consistent, which verified the simulation.
Characterization of the active Tollmien-Schlichting wave damping process using phase-locked PIV
NASA Astrophysics Data System (ADS)
Kurz, Armin; Duchmann, Alexander; Widmann, Alexander; Grundmann, Sven; Tropea, Cameron
2011-11-01
The interaction of artificially excited 2-dimensional Tollmien-Schlichting (TS) waves and a body force, in this case created by a DBD plasma actuator, has been investigated experimentally. To enable the visualization of TS-waves in a laminar boundary layer, which have an amplitude in the order of the measured background noise, a phase-locked particle image velocimetry (PIV) method has been developed. The experiments were carried out on a flat plate setup with negligible pressure gradient at a free-stream velocity of 16 m/s. Active wave control (AWC) is applied by driving the actuator in a pulsed mode of operation. The field data is obtained using a conventional PIV system. It could be demonstrated successfully that the spatial and the temporal evolution of the velocity fluctuations in the flow, as well as the flow structures induced by the body force, can be reconstructed for discrete phase angles with respect to the wave-excitation signal. Therefore the wave damping process can be analyzed. With this technique a tool is at hand to simultaneously measure two velocity components in close vicinity of any flow control actuator subject to periodic flow conditions.
Active lower order mode damping for the four rod LHC crab cavity
NASA Astrophysics Data System (ADS)
Dexter, A. C.; Burt, G.; Apsimon, R.
2017-02-01
The high luminosity upgrade planned for the LHC requires crab cavities to rotate bunches into alignment at the interaction points. They compensate for a crossing angle near 500 μ r ad . It is anticipated that four crab cavities in succession will be utilized to achieve this rotation on either side of each IP in a local crossing scheme. A crab cavity operates in a dipole mode but always has an accelerating mode that may be above or below the frequency of the operating mode. Crab cavities are given couplers to ensure that unwanted acceleration modes are strongly damped however employing standard practice these unwanted modes will always have some level of excitation. Where this excitation has a random phase it might promote bunch growth and limit beam lifetime. This paper sets out a method for active control of the phase and amplitude of the unwanted lowest accelerating mode in the crab cavities. The paper investigates the level of suppression that can be achieved as a function cavity quality factor and proximity to resonance.
Double panel with skyhook active damping control units for control of sound radiation.
Gardonio, Paolo; Alujević, Neven
2010-09-01
This paper presents an experimental study on decentralized velocity feedback control on a double panel consisting of an external aluminum panel and a honeycomb trim panel. The decentralized feedback loops are formed by a 3x3 array of coil-magnet electrodynamic actuators that react off the trim panel and a lightweight stiff frame structure located in the air gap between the two panels. Microelectromechanical systems (MEMS) accelerometers are located on the opposite side of the trim panel in correspondence to the electrodynamic actuators. The grid structure is designed to provide an inertial reference to the actuators. In this way the velocity feedback control loops produce skyhook active damping on the double panel, which minimizes the vibrational response and sound radiation of the trim panel at low audio frequencies. Two configurations are considered where the grid structure is either weakly coupled or strongly coupled to the external panel. Both stability and control performance of the two configurations are analyzed experimentally. The study shows that the control configuration with the weakly coupled grid structure enables the implementation of larger stable feedback control gains, which lead to reductions of the sound radiated by the trim panel between 10 and 30 dB for the first seven resonance peaks.
ERIC Educational Resources Information Center
Fay, Temple H.
2012-01-01
Viscous damping is commonly discussed in beginning differential equations and physics texts but dry friction or Coulomb friction is not despite dry friction being encountered in many physical applications. One reason for avoiding this topic is that the equations involve a jump discontinuity in the damping term. In this article, we adopt an energy…
The global S1 tide and Earth's nutation
NASA Astrophysics Data System (ADS)
Schindelegger, M.; Böhm, J.; Salstein, D. A.
2015-08-01
Diurnal S1 tidal atmospheric oscillations induced by the cyclic heating of air masses through solar radiation elicit a small contribution to Earth's prograde annual nutation at a level of 100 μas (microarcseconds). Previously published estimates of this Sun-synchronous perturbation based on angular momentum series from global geophysical fluid models have however diverged, and within the present conventional nutation theory, the effect has been instead accounted for in an empirical manner based on analyzing residual spectra of observed celestial pole offsets. This study constitutes a first, tentative reassessment of the S1 signal in nutation by resorting to modern-day atmospheric reanalyses as well as available hydrodynamic solutions for diurnal oceanic angular momentum changes that are driven by daily air pressure variations at the water surface. We elucidate the global character of the S1 tide with particular regard to Earth rotation variations and investigate to which extent atmospheric and oceanic excitation terms from various sources can be superimposed. The combined influence of the principal diurnal tide on Earth's nutation, associated with both atmosphere and ocean dynamics, is found to yield a sound agreement with its observational evidence from geodetic VLBI (Very Long Baseline Interferometry) measurements.
Refinements on precession, nutation, and wobble of the Earth
NASA Astrophysics Data System (ADS)
Dehant, V. Folgueira M.; Puica, M.; Van Hoolst, T.
2015-08-01
Most of the essential elements of the theory of nutation of the nonrigid Earth have been presented in the IAU adopted model MHB2000 (Mathews et al., 2002) considering an ellipsoidal rotating Earth, with a solid inner core, a liquid outer core, and an ellipsoidal inelastic mantle, and with a magnetic field. However in the meantime, the observed nutation amplitudes have been redetermined with a better precision. A number of relatively small significant effects have to be taken into account before one can expect to have a theoretical framework that can yield numerical results matching the precession and nutation observations. The adopted model already accounts for the existence of a geomagnetic field passing through the mantle and the fluid core regions and beyond. The model MHB2000 considers an electromagnetic torque generated by this field when the core and the mantle are moving relative to each other, which can in turn affect some nutation amplitudes (both in phase and out-of-phase) to the extent of a few hundreds of microarcsecond (μas), playing thus a significant role. The paper revisits the last adopted model in order to incorporate potential additional coupling effects at the core-mantle boundary, that can be at an observable level, such as the existence of a non-hydrostatic core-mantle boundary topography, the viscosity of the liquid core, the existence of stratification in the core, the existence of boundary layers at both sides of the core-mantle boundary.
Excitation of nutation by the global radiational S1 tide
NASA Astrophysics Data System (ADS)
Schindelegger, M.; Salstein, D. A.; Einspigel, D.; Boehm, J.
2014-12-01
Cyclic mass redistributions in the atmosphere and oceans related to the global radiational S1 tide elicit seasonal perturbations of Earth's nutation at a level of 0.1 mas (milliarcseconds). The present study provides an up-to-date assessment of these excitation effects on the basis of 10-year surface and isobaric level data from three, previously unavailable global atmospheric reanalysis systems. We retrieve numerical values of in- and out-of-phase nutation corrections for seasonally modulated S1 variations and indicate how model improvements, specifically in terms of the representation of tidal oscillations, lead to different estimates with respect to earlier reanalyses. Motion term signals in nutation display a close agreement across all probed datasets, whereas larger disparities remain among mass term excitation estimates due to their dependency on small-scale diurnal surface pressure oscillations. A simple time-stepping model for barotropic ocean dynamics, based on the shallow water equations and driven by air pressure tide climatologies, represents an appropriate means to determine global S1 estimates of sea level heights and currents that are consistent with the respective forcing fields from each reanalysis. We address the intricacies of constructing such a model and compare our preliminary oceanic angular momentum solutions to those from more established hydrodynamic forward integrations. The combined influence of the S1 tide on Earth's nutation, associated with both atmosphere and ocean dynamics, is found to yield a rough agreement with observations from geodetic VLBI (Very Long Baseline Interferometry) measurements.
Fluid logic control circuit operates nutator actuator motor
NASA Technical Reports Server (NTRS)
1966-01-01
Fluid logic control circuit operates a pneumatic nutator actuator motor. It has no moving parts and consists of connected fluid interaction devices. The operation of this circuit demonstrates the ability of fluid interaction devices to operate in a complex combination of series and parallel logic sequence.
Nutation determination by means of GNSS - Comparison with VLBI .
NASA Astrophysics Data System (ADS)
Capitaine, N.; Yao, K.
2014-12-01
Space geodetic techniques cannot be used for a direct determination of the nutation offsets due to deficiencies in the modeling of the satellite orbits. However, as shown first by Rothacher et al. 1999 and then Weber and Rothacher (2001), GPS can be used to estimate the time derivatives of nutation quantities, similarly to what is done on a regular basis for UT1-UTC rates (or LOD) estimation. We have revisited the potential of GNSS observations for nutation estimation with the high precision currently achieved by this technique. The computations have been carried out by means of a new software, which has been developed in Matlab in the framework of K. Yao's PhD (2013), based on the GPS observations analysis strategy of CNES-GRGS GINS software, but with a few specific characteristics. The reference system for orbit computations is different from that generally used in order to minimize the influence of the a priori values of precession-nutation and UT1-UTC. The method is based on the determination of the time derivatives of the GCRS CIP coordinates (X, Y) with high temporal resolution. The observations used are 3 years of GPS measurements from 1 January 2009, obtained from a dense and globally distributed reference station network. The Xdot and Ydot time series so obtained are then analyzed in order to determine the corrections to the amplitudes of the short periodic terms of the IAU 2000 nutation model. The methodology, time series and results of this analysis are compared with those obtained from Very Long Baseline Interferometry (VLBI) observations of extragalactic radio sources.
Analysis of active damping of LCL filter used in single-phase PV system in discrete domain
NASA Astrophysics Data System (ADS)
Zhang, Ningyun; Tang, Houjun; Yao, Chen
2015-06-01
Sampling and computational delay are necessary in digital control, though they may alter the characteristics of the actual controlled plant when considered in the discrete domain. Accordingly, this article establishes a mathematical model of a single-phase grid-connected inverter with an LCL filter in the discrete domain. Three active damping control delay times: 0, ?, ? are analysed, considering the influences introduced by digital control of the plant. Further, the range of the capacitor current feedback coefficient used in active damping control is derived to guarantee that the controlled plant does not have poles outside the unit circle. Using Nyquist diagrams, the proper proportional-resonant (PR) controller parameters can be intuitively determined. The theoretical analysis is verified using MATLAB and a 3 kW laboratory prototype based on a digital signal processor (TMS320F2808).
NASA Astrophysics Data System (ADS)
Goldin, Nikolas; King, Rudibert; Pätzold, Andreas; Nitsche, Wolfgang; Haller, Daniel; Woias, Peter
2013-03-01
Control strategies for laminar flow control above an unswept wing are investigated. An actuation method based on a flexible membrane displaced by multiple piezo-polymer composite elements is developed for wind tunnel experiments. A model predictive control algorithm is applied to control the multi-bar actuator. The direct negative superposition method of damping Tollmien-Schlichting waves is compared to a biomimetic approach imitating the damping mechanisms of a compliant skin. In both cases, a model predictive control algorithm is applied to control the multi-bar actuator segments. For the biomimetic approach, reduced, real-time solvable models of compliant surfaces are developed and parametrized by direct optimization and according to numerically generated optimal wall properties. Damping results of up to 85 % RMS value are achieved, shifting the onset of transition about 100 mm downstream with a single actuation membrane. Additional experiments with cascaded multiple membranes show the potential for a further shift.
Contributions to the Earth's Obliquity Rate, Precession, and Nutation
NASA Technical Reports Server (NTRS)
Williams, James G.
1994-01-01
The precession and nutation of the Earth's equator arise from solar, lunar, and planetary torques on the oblate Earth. The mean lunar orbit plane is nearly coincident with the ecliptic plane. A small tilt out of the ecliptic is caused by planetary perturbations and the Earth's gravitational harmonic J(sub 2). These planetary perturbations on the lunar orbit result in torques on the oblate Earth which contribute to precession, obliquity rate, and nutation while the J(sub 2) perturbations contribute to precession and nutation. Small additional contributions to the secular rates arise from tidal effects and planetary torques on the Earth's bulge. The total correction to the obliquity rate is -0.024 sec/century, it is an observable motion in space (the much larger conventional obliquity rate is wholly from the motion of the ecliptic, not the equator), and it is not present in the IAU-adopted expressions for the orientation of the Earth's equator. The effects have generally been allowed for in past nutation theories and some precession theories. For the planetary effect, the contributions to the 18.6 yr nutation are -0.03 mas (milliarcseconds) for the in-phase Delta(psi) plus out-of-phase contributions of 0.14 mas in Delta(psi) and -0.03 mas in Delta(sub epsilon). The latter terms demonstrate that out-of-phase contributions can arise by means other than dissipation. The sum of the contributions to the precession rate is considered and the inferred value of the moment of inertia combination (C-A)/C, which is used to scale the coefficients in the nutation series, is evaluated. Using an updated value for the precession rate, the rigid body (C-A)/C =0.003 273 763 4 which, in combination with a satellite-derived J(sub 2), gives a normalized polar moment of inertia C/MR(exp 2) = 0.330 700 7. The planetary contributions to the precession and obliquity rates are not constant for long times causing accelerations in both quantities. Acceleration in precession also arises from
Contributions to the Earth's obliquity rate, precession, and nutation
NASA Technical Reports Server (NTRS)
Williams, James G.
1994-01-01
The precession and nutation of the Earth's equator arise from solar, lunar, and planetary torques on the oblate Earth. The mean lunar orbit plane is nearly coincident with the ecliptic plane. A small tilt out of the ecliptic is caused by planetary perturbations and the Earth's gravitational harmonic J(sub2). These planetary perturbations on the lunar orbit result in torques on the oblate Earth which contribute to precession, obliquity rate, and nutation while the J(sub 2) perturbations contribute to precession and nutation. Small additional contributions to the secular rates arise from tidal effects and planetary torques on the Earth's bulge. The total correction to the obliquity rate is -0.024sec/century, it is an observable motion in space (the much larger conventional obliquity rate is wholly from the motion of the ecliptic, not the equator), and it is not present in the IAU-adopted expressions for the orientation of the Earth's equator. The J(sub2) effects have generally been allowed for in past nutation theories and some procession theories. For the planetary effect, the contributions to the 18.6 yr nutation are -0.03 mas (milliarcseconds) for the in-phase Delta phi plus out-of-phase contributions of 0.14 mas in Delta phi and -0.03 mas in Delta epsilon. The latter terms demonstrate that out-of-phase contributions can arise by means other than dissipation. The sum of the contributions to the precession rate is considered and the inferred value of the moment of inertia combination (C-A)/C, which is used to scale the coefficients in the nutation series, is evaluated. Using an updated value for the precession rate, the rigid body (C-A)/C = 0.003 273 763 4 which, in combination with a satellite-derived J(sub2), gives a normalized polar moment of inertia C/MR(exp2) = 0.330 700 7. The planetary contributions to the precession and obliquity rates are not constant for long times causing accelerations in both quantities. Acceleration in precession also arises from tides
NASA Astrophysics Data System (ADS)
Ji, Hongli; Qiu, Jinhao; Cheng, Li; Nie, Hong
2016-05-01
In semi-active synchronized switch damping (SSD) approaches for structural vibration control, the damping effect is achieved by properly switching the voltage on the piezoelectric actuators. Unsymmetrical SSD switch circuit has been designed in the previous paper to increase the effective voltage range on the PZT actuator for improvement of the control performance. In this study, analysis and experimental validation of control performance of a synchronized switch damping system based on the unsymmetrical switch circuit are carried out. First the model of an unsymmetrical SSD system is presented and the working principle is introduced. The general expression of the switched voltage on the piezoelectric actuator is derived. Based on its periodicity in steady-state control, the harmonic components of the actuator voltage are derived using Fourier series expansion. Next, the displacement response of the system is derived under combined actions of the excitation and switched voltage. Finally, a setup of a flexible beam with unsymmetrical switch circuit is used to demonstrate the control performance under different voltage sources and to verify the theoretical results. The results show that the control performance mainly depends on the voltage range on the PZT. A higher effective voltage range can be generated in unsymmetrical SSDV than in symmetrical SSDV and better control performance can be achieved at the same negative actuator voltage. The unsymmetrical SSDV makes better utilization of the actuator capability.
Spin nutation induced by atomic motion in a magnetic lattice
Kobayashi, Y.; Shiraishi, Y.; Hatakeyama, A.
2010-12-15
An atom moving in a spatially periodic field experiences a temporally periodic perturbation and undergoes a resonance transition between atomic internal states when the transition frequency is equal to the atomic velocity divided by the field period. We demonstrated that spin nutation was induced by this resonant transition in a polarized rubidium (Rb) atomic beam passing through a magnetic lattice. The lattice was produced by current flowing through an array of parallel wires crossing the beam. This array structure, reminiscent of a multiwire chamber for particle detection, allowed the Rb beam to pass through the lattice at a variety of incident angles. The dephasing of spin nutation was reduced by varying the incident angle.
NASA Technical Reports Server (NTRS)
Charlot, P.; Sovers, O. J.; Williams, J. G.; Newhall, X. X.
1995-01-01
24 years of Lunar Laser Ranging (LLR) observations and 16 years of Very Long Baseline Interferometry (VLBI) observations are combined in a global analysis to yield improved estimates of the Earth's precession and nutation. The correction to the International Astronomical Union (IAU) (1976) precession constant inferred from this joint VLBI/LLR analysis is -3.00 +/- 0.20 milliarcsec/yr (mas/yr). A significant obliquity rate correction of -0.20 +/- 0.08 mas/yr is also found. In all, 32 forced nutation coefficients are estimated. These coefficients confirm that the IAU (1980) nutation theory is in error by several mas. The estimated nutation coeficients are found to vary by as much as several tenths of mas, depending on the a priori nutation model used to analyze the VLBI and LLR data. Forced circular nutations derived from this analysis agree with the ZMOA-1990-2 nutation theory at the 0.2 mas level for the 18.6 yr terms, and at the 0.05 mas level for the other terms (periods less than or = 1 yr). A retrograde free core nutation with an amplitude of 0.20 mas is also detected. Its phase is found to be very sensitive to the precise value of the free core nutation period used in the solution. Separate analyses of four independent subsets of the LVBI data indicate no significant variations of the free core nutation since 1988. The pre-1988 estimates of the free core nutation are consistent with the post-1988 estimates but are not accurate enough to rule out possible variations of the free core nutation at these earlier epochs.
Possible detection of the earth's free-core nutation
NASA Technical Reports Server (NTRS)
Robertson, D. S.; Carter, W. E.; Wahr, J. M.
1986-01-01
The 5.5 years of VLBI observations primarily collected under project IRIS are used to search for evidence of the free-core nutation (FCN). The observations are consistent with an irregular excitation process, and a model which assumes a step excitation in the FCN amplitude to about 2.0 milliseconds of arc in late 1985 fits the data well. Theoretical analysis appears to rule out the strong Mexican earthquake of September 19, 1985, as a cause of the excitation.
The Global S_1 Tide in Earth's Nutation
NASA Astrophysics Data System (ADS)
Schindelegger, Michael; Einšpigel, David; Salstein, David; Böhm, Johannes
2016-05-01
Diurnal S_1 tidal oscillations in the coupled atmosphere-ocean system induce small perturbations of Earth's prograde annual nutation, but matching geophysical model estimates of this Sun-synchronous rotation signal with the observed effect in geodetic Very Long Baseline Interferometry (VLBI) data has thus far been elusive. The present study assesses the problem from a geophysical model perspective, using four modern-day atmospheric assimilation systems and a consistently forced barotropic ocean model that dissipates its energy excess in the global abyssal ocean through a parameterized tidal conversion scheme. The use of contemporary meteorological data does, however, not guarantee accurate nutation estimates per se; two of the probed datasets produce atmosphere-ocean-driven S_1 terms that deviate by more than 30 μ as (microarcseconds) from the VLBI-observed harmonic of -16.2+i113.4 μ as. Partial deficiencies of these models in the diurnal band are also borne out by a validation of the air pressure tide against barometric in situ estimates as well as comparisons of simulated sea surface elevations with a global network of S_1 tide gauge determinations. Credence is lent to the global S_1 tide derived from the Modern-Era Retrospective Analysis for Research and Applications (MERRA) and the operational model of the European Centre for Medium-Range Weather Forecasts (ECMWF). When averaged over a temporal range of 2004 to 2013, their nutation contributions are estimated to be -8.0+i106.0 μ as (MERRA) and -9.4+i121.8 μ as (ECMWF operational), thus being virtually equivalent with the VLBI estimate. This remarkably close agreement will likely aid forthcoming nutation theories in their unambiguous a priori account of Earth's prograde annual celestial motion.
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.
A New Approach on Computing Free Core Nutation
NASA Astrophysics Data System (ADS)
Zhang, Mian; Huang, Chengling
2015-04-01
Free core nutation (FCN) is a rotational modes of the earth related to non-alignment of the rotation axis of the core and of the mantle. FCN period by traditional theoretical methods is near 460 days with PREM, while the precise observations (VLBI + SG tides) say it should be near 430 days. In order to fill this big gap, astronomers and geophysicists give various assumptions, e.g., increasing core-mantle-boundary (CMB) flattening by about 5%, a strong coupling between nutation and geomagnetic field near CMB, viscous coupling, or topographical coupling etc. Do we really need these unproved assumptions? or is it only the problem of these traditional theoretical methods themselves? Earth models (e.g. PREM) provide accurate and robust profiles of physical parameters, like density and Lame parameters, but their radial derivatives, which are also used in all traditional methods to calculate normal modes (e.g.. FCN), nutation and tides of non-rigid earth theoretically, are not so trustable as the parameters themselves. A new stratified Galerkin method is proposed and applied to the computation of rotational modes, to avoid these problems. This new method can solve not only one order ellipsoid but also irregular asymmetric 3D earth model. Our primary result of the FCN period is 435 sidereal days.
Next step in Earth interior modeling for nutation
NASA Astrophysics Data System (ADS)
Dehant, V.; Folgueira, M.; Puica, M.; Koot, L.; Van Hoolst, T.; Trinh, A.
2014-12-01
Accurate reference systems are important for many geophysical applications and satellite observations. It is therefore necessary to know the Earth rotation and orientation with high precision. Interactions between the solid Earth and its fluid layers (liquid core, atmosphere, ocean) induce variations in the Earth's speed of rotation. In addition, because the Earth is not a perfect sphere, but rather an ellipsoid flattened at its poles, the combined gravitational forces acting upon it produce changes in the orientation of its spin axis. Precession describes the long-term trend in the orientation of the Earth, while nutation refers to shorter-term periodic variations. The nutations of the Earth are the prime focus of the present paper. Models are used to predict the real-time Earth rotation and orientation, based on past observations and theoretical considerations of geophysical processes. In particular, the coupling mechanisms at the internal boundaries have been shown to be important for rotation. We here address the coupling mechanisms at the core boundaries such as the topographic, electromagnetic and viscous couplings, and discuss improvements in their computation and observation. The study uses and compares numerical and semi-analytical approaches, with the objective of both improving the nutation model and the rotation, and better understanding the interior of the Earth.
Constraints on magnetic energy and mantle conductivity from the forced nutations of the earth
NASA Technical Reports Server (NTRS)
Buffett, Bruce A.
1992-01-01
The possibility of a presence of a conducting layer at the base of the mantle, as suggested by Knittle and Jeanloz (1986, 1989), was examined using observations of the earth's nutations. Evidence favoring the presence of a conducting layer is found in the effect of ohmic dissipation, which can cause the amplitude of the earth's nutation to be out-of-phase with tidal forcings. It is shown that the earth's magnetic field can produce observable signatures in the forced nutations of the earth when a thin conducting layer is located at the base of the mantle. The present theoretical calculations are compared with VLBI determinations of forced nutations.
Martinez-Villalpando, Ernesto C; Mooney, Luke; Elliott, Grant; Herr, Hugh
2011-01-01
This paper examines the impact of a biomimetic active knee prosthesis on the metabolic costs associated with a unilateral transfemoral amputee walking at self selected speed. In this study we compare the antagonistic active knee prosthesis developed at MIT to an electronically controlled, variable-damping commercial knee prosthesis, the Otto Bock C-leg. Use of the active knee prosthesis resulted in both, a 17% increase in an amputee's average self selected walking speed from 1.12 m/s to 1.31 m/s, and a 6.8% reduction in metabolic cost. The results of this study suggest that an agonist-antagonist active knee prosthesis design with variable impedance control can offer walking energetic advantages over commercially available systems.
NASA Technical Reports Server (NTRS)
Heeg, Jennifer; Miller, Jonathan M.; Doggett, Robert V., Jr.
1993-01-01
Dynamic response and damping data obtained from buffet studies conducted in a low-speed wind tunnel by using a simple, rigid model attached to spring supports are presented. The two parallel leaf spring supports provided a means for the model to respond in a vertical translation mode, thus simulating response in an elastic first bending mode. Wake-induced buffeting flow was created by placing an airfoil upstream of the model of that the wake of the airfoil impinged on the model. Model response was sensed by a strain gage mounted on one of the springs. The output signal from the strain gage was fed back through a control law implemented on a desktop computer. The processed signals were used to 'actuate' a piezoelectric bending actuator bonded to the other spring in such a way as to add damping as the model responded. The results of this 'proof-of-concept' study show that the piezoelectric actuator was effective in attenuating the wake-induced buffet response over the range of parameters investigated.
Bhalla, Amneet Pal Singh; Griffith, Boyce E; Patankar, Neelesh A
2013-01-01
A fundamental issue in locomotion is to understand how muscle forcing produces apparently complex deformation kinematics leading to movement of animals like undulatory swimmers. The question of whether complicated muscle forcing is required to create the observed deformation kinematics is central to the understanding of how animals control movement. In this work, a forced damped oscillation framework is applied to a chain-link model for undulatory swimming to understand how forcing leads to deformation and movement. A unified understanding of swimming, caused by muscle contractions ("active" swimming) or by forces imparted by the surrounding fluid ("passive" swimming), is obtained. We show that the forcing triggers the first few deformation modes of the body, which in turn cause the translational motion. We show that relatively simple forcing patterns can trigger seemingly complex deformation kinematics that lead to movement. For given muscle activation, the forcing frequency relative to the natural frequency of the damped oscillator is important for the emergent deformation characteristics of the body. The proposed approach also leads to a qualitative understanding of optimal deformation kinematics for fast swimming. These results, based on a chain-link model of swimming, are confirmed by fully resolved computational fluid dynamics (CFD) simulations. Prior results from the literature on the optimal value of stiffness for maximum speed are explained.
NASA Technical Reports Server (NTRS)
Anderson, W. J.
1974-01-01
The equations for the displacement, velocity, and acceleration of a point in a nutating body are developed. These are used to derive equations for the inertial moment developed by a nutating body of arbitrary shape. Calculations made for a previously designed nutating plate transmission indicate that that device is severely speed limited because of the very high magnitude inertial moment.
Precession and Nutation from the Analysis of Positions of Extragalactic Radio Sources
NASA Technical Reports Server (NTRS)
Walter, H. G.; Sovers, O. J.
1995-01-01
Corrections to the Earth's precession and nutation have been derived from VLBI observations of extragalactic sources carried out by JPL's Deep Space Network between 1978 and 1994. The analysis is based on the source right ascensions and declinations given in annual position catalogues. These catalogues result from adopting specific conventions on precession and a nutation model, using VLBI data.
Testing a satellite automatic nutation control system. [on synchronous meteorological satellite
NASA Technical Reports Server (NTRS)
Hrasiar, J. A.
1974-01-01
Testing of a particular nutation control system for the synchronous meteorological satellite (SMS) is described. The test method and principles are applicable to nutation angle control for other satellites with similar requirements. During its ascent to synchronous orbit, a spacecraft like the SMS spins about its minimum-moment-of-inertia axis. An uncontrolled spacecraft in this state is unstable because torques due to fuel motion increase the nutation angle. However, the SMS is equipped with an automatic nutation control (ANC) system which will keep the nutation angle close to zero. Because correct operation of this system is critical to mission success, it was tested on an air-bearing table. The ANC system was mounted on the three-axis air-bearing table which was scaled to the SMS and equipped with appropriate sensors and thrusters. The table was spun up in an altitude chamber and nutation induced so that table motion simulated spacecraft motion. The ANC system was used to reduce the nutation angle. This dynamic test of the ANC system met all its objectives and provided confidence that the ANC system will control the SMS nutation angle.
Proton decoupling and recoupling under double-nutation irradiation in solid-state NMR
NASA Astrophysics Data System (ADS)
Takeda, Kazuyuki; Wakisaka, Asato; Takegoshi, K.
2014-12-01
The effect of 1H decoupling in magic-angle spinning solid-state NMR is studied under radiofrequency irradiation causing simultaneous nutations around a pair of orthogonal axes. Double-nutation with an arbitrary pair of nutation frequencies is implemented through modulation of the amplitude, phase, and frequency of the transmitting pulses. Similarity and difference of double-nutation decoupling and two-pulse phase-modulation decoupling schemes [A. E. Bennett, C. M. Rienstra, M. Auger, K. V. Lakshmi, and R. G. Griffin, J. Chem. Phys. 103, 6951-6958 (1995) and I. Scholz, P. Hodgkinson, B. H. Meier, and M. Ernst, J. Chem. Phys. 130, 114510 (2009)] are discussed. The structure of recoupling bands caused by interference of the 1H spin nutation with sample spinning is studied by both experiments and numerical simulations.
Proton decoupling and recoupling under double-nutation irradiation in solid-state NMR
Takeda, Kazuyuki Wakisaka, Asato; Takegoshi, K.
2014-12-14
The effect of {sup 1}H decoupling in magic-angle spinning solid-state NMR is studied under radiofrequency irradiation causing simultaneous nutations around a pair of orthogonal axes. Double-nutation with an arbitrary pair of nutation frequencies is implemented through modulation of the amplitude, phase, and frequency of the transmitting pulses. Similarity and difference of double-nutation decoupling and two-pulse phase-modulation decoupling schemes [A. E. Bennett, C. M. Rienstra, M. Auger, K. V. Lakshmi, and R. G. Griffin, J. Chem. Phys. 103, 6951–6958 (1995) and I. Scholz, P. Hodgkinson, B. H. Meier, and M. Ernst, J. Chem. Phys. 130, 114510 (2009)] are discussed. The structure of recoupling bands caused by interference of the {sup 1}H spin nutation with sample spinning is studied by both experiments and numerical simulations.
Testing a new Free Core Nutation empirical model
NASA Astrophysics Data System (ADS)
Belda, Santiago; Ferrándiz, José M.; Heinkelmann, Robert; Nilsson, Tobias; Schuh, Harald
2016-03-01
The Free Core Nutation (FCN) is a free mode of the Earth's rotation caused by the different material characteristics of the Earth's core and mantle. This causes the rotational axes of those layers to slightly diverge from each other, resulting in a wobble of the Earth's rotation axis comparable to nutations. In this paper we focus on estimating empirical FCN models using the observed nutations derived from the VLBI sessions between 1993 and 2013. Assuming a fixed value for the oscillation period, the time-variable amplitudes and phases are estimated by means of multiple sliding window analyses. The effects of using different a priori Earth Rotation Parameters (ERP) in the derivation of models are also addressed. The optimal choice of the fundamental parameters of the model, namely the window width and step-size of its shift, is searched by performing a thorough experimental analysis using real data. The former analyses lead to the derivation of a model with a temporal resolution higher than the one used in the models currently available, with a sliding window reduced to 400 days and a day-by-day shift. It is shown that this new model increases the accuracy of the modeling of the observed Earth's rotation. Besides, empirical models determined from USNO Finals as a priori ERP present a slightly lower Weighted Root Mean Square (WRMS) of residuals than IERS 08 C04 along the whole period of VLBI observations, according to our computations. The model is also validated through comparisons with other recognized models. The level of agreement among them is satisfactory. Let us remark that our estimates give rise to the lowest residuals and seem to reproduce the FCN signal in more detail.
NASA Astrophysics Data System (ADS)
Hau, L. C.; Fung, E. H. K.; Yau, D. T. W.
2006-12-01
This paper describes the use of the multi-objective genetic algorithm (MOGA) to solve an integrated optimization problem of a rotating flexible arm with active constrained layer damping (ACLD) treatment. The arm is rotating in a horizontal plane with triangular velocity profiles. The ACLD patch is placed at the clamped end of the arm. The design objectives are to minimize the total treatment weight, the control voltage and the tip displacement of the arm, as well as to maximize the passive damping characteristic of the arm. Design variables include the control gains, the maximum angular velocity, the shear modulus of the viscoelastic layer, the thickness of the piezoelectric constraining and viscoelastic layers, and the length of the ACLD patch. In order to evaluate the effect of different combinations of design variables on the system, the finite element method, in conjunction with the Golla-Hughes-McTavish (GHM) method, is employed to model the flexible arm with ACLD treatment to predict its dynamic behavior, in which the effects of centrifugal stiffening due to the rotation of flexible arm are taken into account. As a result of optimization, reasonable Pareto solutions are successfully obtained. It is shown that the MOGA is applicable to the present integrated optimization problem.
NASA Astrophysics Data System (ADS)
Panda, Satyajit; Ray, M. C.
2008-04-01
In this paper, a geometrically nonlinear dynamic analysis has been presented for functionally graded (FG) plates integrated with a patch of active constrained layer damping (ACLD) treatment and subjected to a temperature field. The constraining layer of the ACLD treatment is considered to be made of the piezoelectric fiber-reinforced composite (PFRC) material. The temperature field is assumed to be spatially uniform over the substrate plate surfaces and varied through the thickness of the host FG plates. The temperature-dependent material properties of the FG substrate plates are assumed to be graded in the thickness direction of the plates according to a power-law distribution while the Poisson's ratio is assumed to be a constant over the domain of the plate. The constrained viscoelastic layer of the ACLD treatment is modeled using the Golla-Hughes-McTavish (GHM) method. Based on the first-order shear deformation theory, a three-dimensional finite element model has been developed to model the open-loop and closed-loop nonlinear dynamics of the overall FG substrate plates under the thermal environment. The analysis suggests the potential use of the ACLD treatment with its constraining layer made of the PFRC material for active control of geometrically nonlinear vibrations of FG plates in the absence or the presence of the temperature gradient across the thickness of the plates. It is found that the ACLD treatment is more effective in controlling the geometrically nonlinear vibrations of FG plates than in controlling their linear vibrations. The analysis also reveals that the ACLD patch is more effective for controlling the nonlinear vibrations of FG plates when it is attached to the softest surface of the FG plates than when it is bonded to the stiffest surface of the plates. The effect of piezoelectric fiber orientation in the active constraining PFRC layer on the damping characteristics of the overall FG plates is also discussed.
A global model of electromagnetic coupling for nutations
NASA Astrophysics Data System (ADS)
Dumberry, Mathieu; Koot, Laurence
2012-09-01
Nutations are small variations in the orientation of the Earth's rotation axis in space. They are caused by the gravitational torque that the Moon, the Sun, and other planets exert on the equatorial bulge. As nutations involve differential rotations between the mantle, fluid core and inner core, the motion of each of these internal regions depends on the coupling between them. In particular, a coupling of a dissipative nature is required to match observations. One possibility is electromagnetic (EM) coupling at the inner and outer core boundaries, the focus of our study. Existing EM coupling models are based on a formulation where the perturbation variables and the equations they must satisfy are defined at local geographic points on the boundary. Here, we show how EM coupling models can be cast under a global formalism, where all variables are expanded in spherical harmonics. This formulation allows a separation of the contribution from the poloidal and toroidal parts of the EM torque, and we show that, under certain conductivity scenarios, this separation is important.
Optical nutation in the exciton range of spectrum
Khadzhi, P. I.; Vasiliev, V. V.
2013-08-15
Optical nutation in the exciton range of spectrum is studied in the mean field approximation taking into account exciton-photon and elastic exciton-exciton interactions. It is shown that the features of nutation development are determined by the initial exciton and photon densities, the resonance detuning, the nonlinearity parameter, and the initial phase difference. For nonzero initial exciton and photon concentrations, three regimes of temporal evolution of excitons and photons exist: periodic conversion of excitons to photons and vice versa, aperiodic conversion of photons to excitons, and the rest regime. In the rest regime, the initial exciton and photon densities are nonzero and do not change with time. The oscillation amplitudes and periods of particle densities determined by the system parameters are found. The exciton self-trapping and photon trapping appearing in the system at threshold values of the nonlinearity parameter were predicted. As this parameter increases, the oscillation amplitudes of the exciton and photon densities sharply change at the critical value of the nonlinearity parameter. These two phenomena are shown to be caused by the elastic exciton-exciton interaction, resulting in the dynamic concentration shift of the exciton level.
High radio-frequency field strength nutation NMR of quadrupolar nuclei
NASA Astrophysics Data System (ADS)
Franssen, W. M. J.; Rezus, Y. L. A.; Kentgens, A. P. M.
2016-12-01
Owing to the introduction of microcoils, high RF field strength nutation NMR is a viable candidate for the study of quadrupolar nuclei with strong quadrupolar couplings, not accessible using contemporary NMR techniques. We show powder 23 Na nutation spectra on sodium nitrite for RF field strengths of up to 1170 kHz, that conform to theoretical predictions. For lanthanum fluoride powder, 139 La nutation spectra taken at elevated RF field amplitudes show clear discrepancies when compared to the theory. These errors are shown to be mainly caused by pulse transients at the end of the pulse, which proved to be detrimental to the shape of the nutation spectra. Using a nutation pulse which ends in a sudden frequency jump, we show that these errors can be reduced, and nutation spectra that conform to theory can be readily acquired. This enables nutation NMR for the study of quadrupolar nuclei with a strong quadrupolar coupling, bridging the gap between NMR, which can only analyse nuclei with a weak to medium quadrupolar coupling, and NQR, were extensive searching for the right quadrupolar frequency is the limiting factor.
An updated set of nutations derived from the reanalysis of 3.5 decades VLBI observations
NASA Astrophysics Data System (ADS)
Zhu, Ping; Koot, Laurence; Rivoldini, Attilio; Dehant, Veronique
2016-04-01
The global VLBI observation started in the 1979. After that the qualities of the measurements are continuously improving by taking into account various instrumental and environmental effects. The MHB2000 models was introduced in 2002 (Mathews, et.al. 2002, [1]) and it has a good agreement (5 μas) on the short period nutation series (<400 days) with the values derived from 2 decades (1979-2000) VLBI data while a higher uncertainties up to 56 μas for those longer periods (>400 days) nutation series (Herring et.al. 2002). In MHB2000, the forcing frequencies of the nutation series are solved by least-squares fitting to the VLBI data in frequency domain. Koot et al. (2008), have processed another similar set of nutation series by inversing the time series of VLBI data (1984-2005) using a Bayesian approach. In the present work, we will repeat both approaches using the up-to-date 3.5 decades VLBI observations (1980-2014) meanwhile paying more attention on the results of longer period (>400 days). Finally some features of Earth's interior structure will be discussed based on the determined nutation series. [1] Mathews, P.M., Herring, T.A. & Buffett, B.A., 2002. Modeling of nutation and precession: new nutation series for nonrigid Earth and insights into the Earth's interior, J. Geophys. Res., 107, 2068, doi: 10.1029/2001JB000390. [2] Herring, T. A., P. M. Mathews, and B. A. Buffett, Modeling of nutation and precession: Very long baseline interferometry results, J. Geophys. Res., 107, B4, 2069, doi: 10.1029/2001JB000165, 2002 [3] Koot, L., Rivoldini, A., de Viron, O. & Dehant, V., 2008. Estimation of Earth interior parameters from a Bayesian inversion of very long baseline interferometry nutation time series, J. Geophys. Res., 113, 8414, doi: 10.1029/2007JB005409.
Hybrid Damping System for an Electronic Equipment Mounting Shelf
NASA Technical Reports Server (NTRS)
Voracek, David; Kolkailah, Faysal A.; Cavalli, J. R.; Elghandour, Eltahry
1997-01-01
The objective of this study was to design and construct a vibration control system for an electronic equipment shelf to be evaluated in the NASA Dryden FTF-11. The vibration control system was a hybrid system which included passive and active damping techniques. Passive damping was fabricated into the equipment shelf using ScothDamp(trademark) damping film and aluminum constraining layers. Active damping was achieved using a two channel active control circuit employing QuickPack(trademark) sensors and actuators. Preliminary Chirp test results indicated passive damping smoothed the frequency response while active damping reduced amplitudes of the frequency response for most frequencies below 500Hz.
Hybrid Damping System for an Electronic Equipment Mounting Shelf
NASA Technical Reports Server (NTRS)
Voracek, David; Kolkailah, Faysal A.; Cavalli, J. R.; Elghandour, Eltahry
1997-01-01
The objective of this study was to design and construct a vibration control system for an electronic equipment shelf to be evaluated in the NASA Dryden FTF-II. The vibration control system was a hybrid system which included passive and active damping techniques. Passive damping was fabricated into the equipment shelf using ScothDamp(trademark) damping film and aluminum constraining layers. Active damping was achieved using a two channel active control circuit employing QuickPack(trademark) sensors and actuators. Preliminary Chirp test results indicated passive damping smoothed the frequency response while active damping reduced amplitudes of the frequency response for most frequencies below 500Hz.
The use of precession modulation for nutation control in spin-stabilized spacecraft
NASA Technical Reports Server (NTRS)
Taylor, J. M.; Donner, R. J.; Tasar, V.
1974-01-01
The relations which determine the nutation effects induced in a spinning spacecraft by periodic precession thrust pulses are derived analytically. By utilizing the idea that nutation need only be observed just before each precession thrust pulse, a difficult continuous-time derivation is replaced by a simple discrete-time derivation using z-transforms. The analytic results obtained are used to develop two types of modulated precession control laws which use the precession maneuver to concurrently control nutation. Results are illustrated by digital simulation of an actual spacecraft configuration.
Errors in the J(sub 3) Part of Nutation Series
NASA Technical Reports Server (NTRS)
Hartmann, Torsten; Williams, James G.; Soffel, Michael
1996-01-01
This paper points out that the nutation terms of Zhu & Groten due to the tidal potential of degree 3 are erroneous. Correct values are deduced here and they coincide very well with those given in Kinoshita & Souchay. These errors explain the discrepancies between the evaluation of the theories of Zhu & Groten and Kinoshita & Souchay, which can reach values up to 165 micro arc second. Also the two leading nutation terms due to the tidal potential of degree 4 are given. Finally, some of the computer programs (NUTC.F, KSV_1994.F) for evaluating the,13 nutation terms are also erroneous.
NASA Astrophysics Data System (ADS)
Yan, Zhang; Tao, Ma; Yongyi, Huang
2016-07-01
The first Chinese space observatory DAMPE (DArk Matter Particle Explorer) was successfully launched on Dec. 17th, 2015. One major scientific object of DAMPE is to measure electrons between 5GeV to 10TeV with excellent energy resolution (1.5% at 800GeV) to search for possible dark matter signatures. The detector consists of four subsystems: a plastic scintillator detector (PSD), a silicon-tungsten tracker (STK), a BGO calorimeter (BGO), and a neutron detector (NUD). The NUD on board DAMPE is designed to detect moderated neutrons via the boron capture of thermal neutrons in boron-doped plastics. Given the fact that hadron showers initiated in the BGO calorimeter by incident nuclei tend to be followed by significantly more neutron activities comparing to electromagnetic cascades triggered by electrons, the NUD provides an additional order of magnitude hadron rejection capability to improve the overall e/p discrimination of DAMPE up to 10 ^{5}. Preliminary analysis of the in-orbit data is given, together with comparisons to the results obtained by a detailed GEANT4 simulation of the NUD instrument.
Book Review: Precession, Nutation, and Wobble of the Earth
NASA Astrophysics Data System (ADS)
Sterken, Christiaan; Dehant, V.; Mathews, P. M.
2016-10-01
This great book describes and explains observational and computational aspects of three apparently tiny changes in the Earth's motion and orientation, viz., precession, nutation, and wobble. The three introductory chapters of this book present fundamental definitions, elementary geodetic theory, and celestial/terrestrial reference systems - including transformations between reference frames. The next chapter on observational techniques describes the principle of accurate measurements of the orientation of the Earth's axis, as obtained from measurements of extra-galactic radio sources using Very Long Baseline Interferometry and GPS observations. Chapter 5 handles precession and nutation of the rigid Earth (i.e., a celestial body that cannot, by definition, deform) and the subsequent chapter takes deformation into consideration, viz., the effect of a centrifugal force caused by a constant-rate rotation that causes the Earth's shape and structure to become ellipsoidal. Deformations caused by external solar-system bodies are discussed in terms of deformability parameters. The next three chapters handle additional complex deviations: non-rigid Earth and more general Earth models, anelastic Earth parameters, and the effects of the fluid layers (i.e., ocean and atmosphere) on Earth rotation. Chapter 10 complements Chapter 7 with refinements that take into account diverse small effects such as the effect of a thermal conductive layer at the top of the core, Core Mantle and Inner Boundary coupling effects on nutation, electromagnetic coupling, and so-called topographic coupling. Chapter 11 covers comparison of observation and theory, and tells us that the present-date precision of the nutation theory is at the level of milliarcseconds in the time domain, and of a tenth of a microsecond in the frequency domain (with some exceptions). This chapter is followed by a 25-page chapter of definitions of equator, equinox, celestial intermediate pole and origin, stellar angle
Effects of increased G-force on the nutations of sunflower seedlings
NASA Technical Reports Server (NTRS)
Brown, A. H.; Chapman, D. K.; Dahl, A. O.
1975-01-01
A centrifuge was used to provide chronic acceleration in order to study the nutation of six-day old sunflower hypocotyls at 1 to 20 times normal gravity (g). At the upper end of the g-range nutational movement was impeded and at times erratic evidently because the weight of the cotyledons exceeded the supportive abilities of the hypocotyls. Over the range from 1 to 9 g the period of nutation was independent of the resultant g-force. That finding is interpreted as evidence that the geotropic response time -- i.e., the time needed for growth hormone transport from the region of g-sensing to the region of bending response --was not influenced significantly by substantial increments of the g-level, since geotropic response time is related to the period of nutation.
Analytical description of the I = 5/2 quadrupole nutation experiment
NASA Astrophysics Data System (ADS)
van der Mijden, J. A. M.; Janssen, R.; Veeman, W. S.
The theory of nutation N.M.R. for a quadrupolar nucleus with spin quantum I = 5/2 is presented in an exact, analytical way. It is shown that the nutation spectrum is described by 9 different frequencies each dependent on the orientation of the quadrupole tensor relative to the external field. The frequencies are calculated from the eigenvalues of a 6th-degree secular equation that is reduced to 2 secular equations of order 3. This reduction is obtained by a transformation of bases. An extension of the nutation experiment, x&(x)macr;-nutation, is compared with the standard technique. The theoretical spectra are compared with experimental 27Al spectra of NH4Al(SO4)2 · 12H2O and zeolite NaA.
NASA Astrophysics Data System (ADS)
Shao, Xinxin; Naghdy, Fazel; Du, Haiping
2017-03-01
A fault-tolerant fuzzy H∞ control design approach for active suspension of in-wheel motor driven electric vehicles in the presence of sprung mass variation, actuator faults and control input constraints is proposed. The controller is designed based on the quarter-car active suspension model with a dynamic-damping-in-wheel-motor-driven-system, in which the suspended motor is operated as a dynamic absorber. The Takagi-Sugeno (T-S) fuzzy model is used to model this suspension with possible sprung mass variation. The parallel-distributed compensation (PDC) scheme is deployed to derive a fault-tolerant fuzzy controller for the T-S fuzzy suspension model. In order to reduce the motor wear caused by the dynamic force transmitted to the in-wheel motor, the dynamic force is taken as an additional controlled output besides the traditional optimization objectives such as sprung mass acceleration, suspension deflection and actuator saturation. The H∞ performance of the proposed controller is derived as linear matrix inequalities (LMIs) comprising three equality constraints which are solved efficiently by means of MATLAB LMI Toolbox. The proposed controller is applied to an electric vehicle suspension and its effectiveness is demonstrated through computer simulation.
Vibration damping method and apparatus
Redmond, James M.; Barney, Patrick S.; Parker, Gordon G.; Smith, David A.
1999-01-01
The present invention provides vibration damping method and apparatus that can damp vibration in more than one direction without requiring disassembly, that can accommodate varying tool dimensions without requiring re-tuning, and that does not interfere with tool tip operations and cooling. The present invention provides active dampening by generating bending moments internal to a structure such as a boring bar to dampen vibration thereof.
Vibration damping method and apparatus
Redmond, J.M.; Barney, P.S.; Parker, G.G.; Smith, D.A.
1999-06-22
The present invention provides vibration damping method and apparatus that can damp vibration in more than one direction without requiring disassembly, that can accommodate varying tool dimensions without requiring re-tuning, and that does not interfere with tool tip operations and cooling. The present invention provides active dampening by generating bending moments internal to a structure such as a boring bar to dampen vibration thereof. 38 figs.
NASA Technical Reports Server (NTRS)
Herring, T. A.; Gwinn, C. R.; Shapiro, I. I.
1986-01-01
Very long baseline interferometry (VLBI) observations of compact extragalactic radio sources collected in North America and Europe between July 1980-December 1984 are analyzed. The nutations derived from VLBI data are compared with the nutations in the Wahr series (1981). Good correlation of the data is observed; however, it is detected that a correction of -1.80 + or - 0.18-i(0.42 + or - 0.18) is required for the amplitude of the retrograde annual nutation in the Wahr series. The change in free core nutation resonance frequency is calculated to explain the derivation in the retrograde annual nutation. It is concluded that VLBI earth nutation measurements have sufficient accuracy to be sensitive to core-mantle boundary properties.
Application of Semi Active Control Techniques to the Damping Suppression Problem of Solar Sail Booms
NASA Technical Reports Server (NTRS)
Adetona, O.; Keel, L. H.; Whorton, M. S.
2007-01-01
Solar sails provide a propellant free form for space propulsion. These are large flat surfaces that generate thrust when they are impacted by light. When attached to a space vehicle, the thrust generated can propel the space vehicle to great distances at significant speeds. For optimal performance the sail must be kept from excessive vibration. Active control techniques can provide the best performance. However, they require an external power-source that may create significant parasitic mass to the solar sail. However, solar sails require low mass for optimal performance. Secondly, active control techniques typically require a good system model to ensure stability and performance. However, the accuracy of solar sail models validated on earth for a space environment is questionable. An alternative approach is passive vibration techniques. These do not require an external power supply, and do not destabilize the system. A third alternative is referred to as semi-active control. This approach tries to get the best of both active and passive control, while avoiding their pitfalls. In semi-active control, an active control law is designed for the system, and passive control techniques are used to implement it. As a result, no external power supply is needed so the system is not destabilize-able. Though it typically underperforms active control techniques, it has been shown to out-perform passive control approaches and can be unobtrusively installed on a solar sail boom. Motivated by this, the objective of this research is to study the suitability of a Piezoelectric (PZT) patch actuator/sensor based semi-active control system for the vibration suppression problem of solar sail booms. Accordingly, we develop a suitable mathematical and computer model for such studies and demonstrate the capabilities of the proposed approach with computer simulations.
Khadzhi, P I; Vasiliev, V V
2010-12-09
The peculiarities of two-photon nutation in a system of coherent biexcitons in CuCl semiconductors are considered taking into account the elastic biexciton - biexciton interaction. It is shown that depending on the system parameters, optical nutation represents a process of periodic transformation of photon pairs into biexcitons and vice versa. The possibility of exercising the phase control of the optical nutation process is predicted. (nonlinear optical phenomena)
NASA Astrophysics Data System (ADS)
Hau, L. C.; Fung, E. H. K.
2004-08-01
This work presents the use of a multi-objective genetic algorithm (MOGA) to solve an integrated optimization problem for the shape control of flexible beams with an active constrained layer damping (ACLD) treatment. The design objectives are to minimize the total weight of the system, the input voltages and the steady-state error between the achieved and desired shapes. Design variables include the thickness of the constraining and viscoelastic layers, the arrangement of the ACLD patches, as well as the control gains. In order to set up an evaluator for the MOGA, the finite element method (FEM), in conjunction with the Golla-Hughes-McTavish (GHM) method, is employed to model a clamped-free beam with ACLD patches to predict the dynamic behaviour of the system. As a result of the optimization, reasonable Pareto solutions are successfully obtained. It is shown that ACLD treatment is suitable for shape control of flexible structures and that the MOGA is applicable to the present integrated optimization problem.
Wu, Chijui; Lee, Yuangshung )
1993-03-01
An active and reactive power (P-Q) simultaneous control scheme which is based on a superconducting magnetic energy storage (SMES) unit is designed to damp out the subsynchronous resonant (SSR) oscillations of a turbine-generator unit. In order to suppress unstable torsional mode oscillations, a proportional-integral-derivative (PID) controller is employed to modulate the active and reactive power input/output of the SMES unit according to speed deviation of the generator shaft. The gains of the proposed PID controller are determined by pole assignment approach based on modal control theory. Eigenvalue analysis of the studied system shows that the PID controller is quite effective over a wide range of operating conditions. Dynamic simulations using the nonlinear system model are also performed to demonstrate the damping effect of the proposed control scheme under disturbance conditions.
Influence of Nutation of the Projectile on Fracture of the Anisotropic Target
NASA Astrophysics Data System (ADS)
Radchenko, Andrey; Radchenko, Pavel
2012-02-01
In actual practice the direction of the vector of velocity, as a rule, doesn't coincide with the direction of a longitudinal axis of a moving body, and makes with it some angle named the angle of nutation. The nutation influence on process of interaction of the projectile and a target is defined not only by its size, but also geometrical and kinematic parameters of the process. It is obvious that for a case of the prolonged projectile the angle of nutation influence is more considerable, than for the compact projectile because in this case the nutation angle presence changes not only a picture of strain-stress state of interaction bodies, but also leads to loss of stability in the projectile. The three-dimensional problem of oblique high-velocity interaction of the prolonged cylindrical projectile from steel with an anisotropic target from organoplastic is considered. Lengthening of the projectile makes from 15 to 30 calibers, the range of initial velocities of the projectile from 700 to 3000 m/sec is researched. Modeling is carried out numerically by a method of finite elements. Influence of nutation angle and rotation of the projectile on fracture of target and stability of the projectile is analyzed.
NASA Astrophysics Data System (ADS)
Rosat, S.; Lambert, S. B.; Gattano, C.; Calvo, M.
2017-01-01
Geophysical parameters of the deep Earth's interior can be evaluated through the resonance effects associated with the core and inner-core wobbles on the forced nutations of the Earth's figure axis, as observed by very long baseline interferometry (VLBI), or on the diurnal tidal waves, retrieved from the time-varying surface gravity recorded by superconducting gravimeters (SGs). In this paper, we inverse for the rotational mode parameters from both techniques to retrieve geophysical parameters of the deep Earth. We analyse surface gravity data from 15 SG stations and VLBI delays accumulated over the last 35 yr. We show existing correlations between several basic Earth parameters and then decide to inverse for the rotational modes parameters. We employ a Bayesian inversion based on the Metropolis-Hastings algorithm with a Markov-chain Monte Carlo method. We obtain estimates of the free core nutation resonant period and quality factor that are consistent for both techniques. We also attempt an inversion for the free inner-core nutation (FICN) resonant period from gravity data. The most probable solution gives a period close to the annual prograde term (or S1 tide). However the 95 per cent confidence interval extends the possible values between roughly 28 and 725 d for gravity, and from 362 to 414 d from nutation data, depending on the prior bounds. The precisions of the estimated long-period nutation and respective small diurnal tidal constituents are hence not accurate enough for a correct determination of the FICN complex frequency.
NASA Astrophysics Data System (ADS)
Rosat, S.; Lambert, S. B.; Gattano, C.; Calvo, M.
2016-10-01
Geophysical parameters of the deep Earth's interior can be evaluated through the resonance effects associated with the core and inner-core wobbles on the forced nutations of the Earth's figure axis, as observed by very long baseline interferometry (VLBI), or on the diurnal tidal waves, retrieved from the time-varying surface gravity recorded by superconducting gravimeters (SGs). In this paper, we inverse for the rotational mode parameters from both techniques to retrieve geophysical parameters of the deep Earth. We analyze surface gravity data from 15 SG stations and VLBI delays accumulated over the last 35 years. We show existing correlations between several basic Earth parameters and then decide to inverse for the rotational modes parameters. We employ a Bayesian inversion based on the Metropolis-Hastings algorithm with a Markov Chain Monte Carlo method. We obtain estimates of the free core nutation (FCN) resonant period and quality factor that are consistent for both techniques. We also attempt an inversion for the free inner core nutation (FICN) resonant period from gravity data. The most probable solution gives a period close to the annual prograde term (or S1 tide). However the 95% confidence interval extend the possible values between roughly 28 days and 725 days for gravity, and from 362 to 414 days from nutation data, depending on the prior bounds. The precisions of the estimated long-period nutation and respective small diurnal tidal constituents are hence not accurate enough for a correct determination of the FICN complex frequency.
Observation of the Earth's nutation by the VLBI: how accurate is the geophysical signal
NASA Astrophysics Data System (ADS)
Gattano, César; Lambert, Sébastien B.; Bizouard, Christian
2016-09-01
We compare nutation time series determined by several International VLBI Service for geodesy and astrometry (IVS) analysis centers. These series were made available through the International Earth Rotation and Reference Systems Service (IERS). We adjust the amplitudes of the main nutations, including the free motion associated with the free core nutation (FCN). Then, we discuss the results in terms of physics of the Earth's interior. We find consistent FCN signals in all of the time series, and we provide corrections to IAU 2000A series for a number of nutation terms with realistic errors. It appears that the analysis configuration or the software packages used by each analysis center introduce an error comparable to the amplitude of the prominent corrections. We show that the inconsistencies between series have significant consequences on our understanding of the Earth's deep interior, especially for the free inner core resonance: they induce an uncertainty on the FCN period of about 0.5 day, and on the free inner core nutation (FICN) period of more than 1000 days, comparable to the estimated period itself. Though the FCN parameters are not so much affected, a 100 % error shows up for the FICN parameters and prevents from geophysical conclusions.
Damped transverse oscillations of interacting coronal loops
NASA Astrophysics Data System (ADS)
Soler, Roberto; Luna, Manuel
2015-10-01
Damped transverse oscillations of magnetic loops are routinely observed in the solar corona. This phenomenon is interpreted as standing kink magnetohydrodynamic waves, which are damped by resonant absorption owing to plasma inhomogeneity across the magnetic field. The periods and damping times of these oscillations can be used to probe the physical conditions of the coronal medium. Some observations suggest that interaction between neighboring oscillating loops in an active region may be important and can modify the properties of the oscillations. Here we theoretically investigate resonantly damped transverse oscillations of interacting nonuniform coronal loops. We provide a semi-analytic method, based on the T-matrix theory of scattering, to compute the frequencies and damping rates of collective oscillations of an arbitrary configuration of parallel cylindrical loops. The effect of resonant damping is included in the T-matrix scheme in the thin boundary approximation. Analytic and numerical results in the specific case of two interacting loops are given as an application.
NASA Technical Reports Server (NTRS)
Cabell, Randolph H.; Gibbs, Gary P.
2000-01-01
make the controller adaptive. For example, a mathematical model of the plant could be periodically updated as the plant changes, and the feedback gains recomputed from the updated model. To be practical, this approach requires a simple plant model that can be updated quickly with reasonable computational requirements. A recent paper by the authors discussed one way to simplify a feedback controller, by reducing the number of actuators and sensors needed for good performance. The work was done on a tensioned aircraft-style panel excited on one side by TBL flow in a low speed wind tunnel. Actuation was provided by a piezoelectric (PZT) actuator mounted on the center of the panel. For sensing, the responses of four accelerometers, positioned to approximate the response of the first radiation mode of the panel, were summed and fed back through the controller. This single input-single output topology was found to have nearly the same noise reduction performance as a controller with fifteen accelerometers and three PZT patches. This paper extends the previous results by looking at how constrained layer damping (CLD) on a panel can be used to enhance the performance of the feedback controller thus providing a more robust and efficient hybrid active/passive system. The eventual goal is to use the CLD to reduce sound radiation at high frequencies, then implement a very simple, reduced order, low sample rate adaptive controller to attenuate sound radiation at low frequencies. Additionally this added damping smoothes phase transitions over the bandwidth which promotes robustness to natural frequency shifts. Experiments were conducted in a transmission loss facility on a clamped-clamped aluminum panel driven on one side by a loudspeaker. A generalized predictive control (GPC) algorithm, which is suited to online adaptation of its parameters, was used in single input-single output and multiple input-single output configurations. Because this was a preliminary look at the potential
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.
NASA Astrophysics Data System (ADS)
Chen, Zhong; Chen, Guisheng; Zhang, Xianmin
2015-05-01
Flexure-based mechanism like compliant actuation system embeds complex dynamics that will reduce the control bandwidth and limits their dynamic positioning precision. This paper presents a theoretical model of a leaf flexure hinge with damping layers using strain energy method and Kelvin damping model. The modified loss factor of the damped leaf flexure hinge is derived, and the equivalent viscous damping coefficient of the damped leaf hinge is obtained, which could be used to improve the pseudo-rigid-model. The free vibration signals of the hinge in three different damping configurations are measured. The experimental modal analysis also is performed on the three kinds of damped leaf flexure hinges in order to evaluate their 1st order bending natural frequency and vibration-suppressing effects. The evaluation of modified loss factor model also is performed. The experimental results indicate that the constrained layer damping can enhance the structure damping of the hinge even if only single damping layer each side, the modified loss factor model can get good predicts of a damped leaf flexure hinge in the frequency range below 1st order natural frequency, and it is necessary that the dimensional parameters of the damping layers and basic layer of the hinge should be optimized for simplification at the mechanism's design stage.
Estimation of Nutation Time Constant Model Parameters for On-Axis Spinning Spacecraft
NASA Technical Reports Server (NTRS)
Schlee, Keith; Sudermann, James
2008-01-01
Calculating an accurate nutation time constant for a spinning spacecraft is an important step for ensuring mission success. Spacecraft nutation is caused by energy dissipation about the spin axis. Propellant slosh in the spacecraft fuel tanks is the primary source for this dissipation and can be simulated using a forced motion spin table. Mechanical analogs, such as pendulums and rotors, are typically used to simulate propellant slosh. A strong desire exists for an automated method to determine these analog parameters. The method presented accomplishes this task by using a MATLAB Simulink/SimMechanics based simulation that utilizes the Parameter Estimation Tool.
Interactions between SAS-C spacecraft nutations and spin control system
NASA Technical Reports Server (NTRS)
Tossman, B. E.; Thayer, D. L.
1974-01-01
The SAS-C spacecraft is stabilized by a momentum biased reaction wheel and passive nutation damper. A closed-loop low-speed spacecraft spin rate control system is included which uses a single-axis gyro and a variable speed range on the reaction wheel. Dynamic instability can result from interactions among the gyro, damper, and spacecraft dynamic unbalance. This instability may be aggravated by gyro angular misalignment, gyro error signals, and spacecraft nutations. Analytic eigenvector, and digital computer analyses of the coupled systems are presented. Mechanisms for instability are described as well as the effects that gyro error signal, tilt, and spacecraft dynamic unbalance produce on control system performance.
The theory of the earth's orientation, with some new results for nutation
NASA Technical Reports Server (NTRS)
Wahr, John M.
1988-01-01
The rotation of the earth is variable at a number of time scales, from a few days to thousands of years and longer. Variations occur in the rotation rate, in the geographical position of the rotation axis (referred to as polar motion), and in the position of the axis relative to inertial space (referred to as nutation and precession). The interpretations of the various observations have implications for the dynamical behavior and structure of the earth's deep interior, and for various aspects of meteorology and oceanography. These are reviewed below. A model of the diurnal resonance in nutation for a nonhydrostatically pre-stressed earth is also presented.
The Nutating Engine-Prototype Engine Progress Report and Test Results
NASA Technical Reports Server (NTRS)
Meitner, Peter L.; Boruta, Mike
2006-01-01
A prototype of a new, internal combustion (IC) engine concept has been completed. The Nutating Engine features an internal disk nutating (wobbling) on a Z-shaped power shaft. The engine is exceedingly compact, and several times more power dense than any conventional (reciprocating or rotary) IC engine. This paper discusses lessons learned during the prototype engine's development and provides details of its construction. In addition, results of the initial performance tests of the various components, as well as the complete engine, are summarized.
Damping of the wrist joint during voluntary movement.
Milner, T E; Cloutier, C
1998-10-01
Damping characteristics of the musculoskeletal system were investigated during rapid voluntary wrist flexion movements. Oscillations about the final position were induced by introducing a load with the characteristics of negative damping, which artificially reduced the damping of the wrist. Subjects responded to increases in the negatively damped load by stronger cocontraction of wrist flexor and extensor muscles during the stabilization phase of the movement. However, their ability to counteract the effects of the negatively damped load diminished as the negative damping increased. Consequently, the number and frequency of oscillations increased. The oscillations were accompanied by phase-locked muscle activity superimposed on underlying tonic muscle activation. The wrist stiffness and damping coefficient increased with the increased cocontraction that accompanied more negatively damped loads, although changes in the damping coefficient were less systematic than the stiffness. Analysis of successive half-cycles of the oscillation revealed that the wrist stiffness and damping coefficient increased, despite decreasing muscle activation, as oscillation amplitude and velocity declined. This indicates that the inverse dependence of the damping coefficient on oscillation velocity contributes significantly to damping of joint motion. It is suggested that this property helps to offset a negative contribution to damping from the stretch reflex.
Red cell DAMPs and inflammation.
Mendonça, Rafaela; Silveira, Angélica A A; Conran, Nicola
2016-09-01
Intravascular hemolysis, or the destruction of red blood cells in the circulation, can occur in numerous diseases, including the acquired hemolytic anemias, sickle cell disease and β-thalassemia, as well as during some transfusion reactions, preeclampsia and infections, such as those caused by malaria or Clostridium perfringens. Hemolysis results in the release of large quantities of red cell damage-associated molecular patterns (DAMPs) into the circulation, which, if not neutralized by innate protective mechanisms, have the potential to activate multiple inflammatory pathways. One of the major red cell DAMPs, heme, is able to activate converging inflammatory pathways, such as toll-like receptor signaling, neutrophil extracellular trap formation and inflammasome formation, suggesting that this DAMP both activates and amplifies inflammation. Other potent DAMPs that may be released by the erythrocytes upon their rupture include heat shock proteins (Hsp), such as Hsp70, interleukin-33 and Adenosine 5' triphosphate. As such, hemolysis represents a major inflammatory mechanism that potentially contributes to the clinical manifestations that have been associated with the hemolytic diseases, such as pulmonary hypertension and leg ulcers, and likely plays a role in specific complications of sickle cell disease such as endothelial activation, vaso-occlusive processes and tissue injury.
NASA Technical Reports Server (NTRS)
2008-01-01
Calculating an accurate nutation time constant (NTC), or nutation rate of growth, for a spinning upper stage is important for ensuring mission success. Spacecraft nutation, or wobble, is caused by energy dissipation anywhere in the system. Propellant slosh in the spacecraft fuel tanks is the primary source for this dissipation and, if it is in a state of resonance, the NTC can become short enough to violate mission constraints. The Spinning Slosh Test Rig (SSTR) is a forced-motion spin table where fluid dynamic effects in full-scale fuel tanks can be tested in order to obtain key parameters used to calculate the NTC. We accomplish this by independently varying nutation frequency versus the spin rate and measuring force and torque responses on the tank. This method was used to predict parameters for the Genesis, Contour, and Stereo missions, whose tanks were mounted outboard from the spin axis. These parameters are incorporated into a mathematical model that uses mechanical analogs, such as pendulums and rotors, to simulate the force and torque resonances associated with fluid slosh.
Interactions Between SAS-C Spacecraft Nutations and Spin-Rate Control System.
The SAS-C spacecraft is stabilized by a momentum biased reaction wheel and passive nutation damper. A closed-loop low-speed spacecraft spin rate...control system is included which uses a single-axis gyro and a variable speed range on the reaction wheel . Dynamic instability can result from
On estimation of the free core nutation parameters from analysis of the VLBI celestial pole offsets
NASA Astrophysics Data System (ADS)
Brzezinski, A.
2013-12-01
The free core nutation (FCN) resonance influences Earth rotation in two different ways: 1) through resonant enhancement of the amplitudes of those forced nutation components which are close to the FCN frequency (indirect effect); 2) it gives rise to the free oscillation of the pole in response to the irregular nearly-diurnal geophysical forcing (direct effect). It is commonly believed that the best estimate of the FCN parameters, the space-referred period T and the quality factor Q, is that from the VLBI determination of the nutation amplitudes. The estimated values corresponding to the MHB2000 precession-nutatin model are T=-430 days and Q=20 000 with quite narrow uncertainty limits (429.93,430.48) and (18 870,21 280), respectively. Here we focus attention on determination of T and Q from analysis of the FCN signal observed by VLBI since 1984. The underlying stochastic model is similar to that applied since decades for analysis of the Chandler wobble, the so-called "pea-shooter" model proposed by Jeffreys (1940). We discuss here different ways of implementation of such model based on the methods of time series analysis. We also show and compare the FCN parameters derived from various available VLBI nutation data sets.
NASA Astrophysics Data System (ADS)
Oh, J.; Ray, Manas C.; Baz, Amr M.
2001-07-01
Engineered Damping Treatments (EDT) that have high damping characteristics per unit volume are presented. The EDT's under consideration, consist of cellular viscoelastic damping matrices with optimally selected cell configuration, size and distribution. The cellular topology of the EDT's is designed using Computer-Aided-Design (CAD) strategies and the obtained optimal configurations will be manufactured using the state-of-the-art technology of Rapid Prototyping (RP). The EDT's are modeled using the finite element method in an attempt to determine the optimal topologies that maximize the strain energy, maximize the damping characteristics and minimize the total weight. The CAD files of the prototypes of the EDT's. The damping characteristics of the manufactured EDT's are evaluated and compared with the corresponding characteristics obtained by conventional solid damping treatments in order to emphasize the importance of using optimally configured damping treatment to achieve high damping characteristics. The presented procedures are invaluable for designing efficient damping treatments for many military and civilian structures whose vibrations and noise must be effectively controlled.
Critically damped quantum search.
Mizel, Ari
2009-04-17
Although measurement and unitary processes can accomplish any quantum evolution in principle, thinking in terms of dissipation and damping can be powerful. We propose a modification of Grover's algorithm in which the idea of damping plays a natural role. Remarkably, we find that there is a critical damping value that divides between the quantum O(sqrt[N]) and classical O(N) search regimes. In addition, by allowing the damping to vary in a fashion we describe, one obtains a fixed-point quantum search algorithm in which ignorance of the number of targets increases the number of oracle queries only by a factor of 1.5.
DAMPs from Cell Death to New Life
Vénéreau, Emilie; Ceriotti, Chiara; Bianchi, Marco Emilio
2015-01-01
Our body handles tissue damage by activating the immune system in response to intracellular molecules released by injured tissues [damage-associated molecular patterns (DAMPs)], in a similar way as it detects molecular motifs conserved in pathogens (pathogen-associated molecular patterns). DAMPs are molecules that have a physiological role inside the cell, but acquire additional functions when they are exposed to the extracellular environment: they alert the body about danger, stimulate an inflammatory response, and finally promote the regeneration process. Beside their passive release by dead cells, some DAMPs can be secreted or exposed by living cells undergoing a life-threatening stress. DAMPs have been linked to inflammation and related disorders: hence, inhibition of DAMP-mediated inflammatory responses is a promising strategy to improve the clinical management of infection- and injury-elicited inflammatory diseases. However, it is important to consider that DAMPs are not only danger signals but also central players in tissue repair. Indeed, some DAMPs have been studied for their role in tissue healing after sterile or infection-associated inflammation. This review is focused on two exemplary DAMPs, HMGB1 and adenosine triphosphate, and their contribution to both inflammation and tissue repair. PMID:26347745
Decoherence and Landau-Damping
Ng, K.Y.; /Fermilab
2005-12-01
The terminologies, decoherence and Landau damping, are often used concerning the damping of a collective instability. This article revisits the difference and relation between decoherence and Landau damping. A model is given to demonstrate how Landau damping affects the rate of damping coming from decoherence.
A Resonant Damping Study Using Piezoelectric Materials
NASA Technical Reports Server (NTRS)
Min, J. B.; Duffy, K. P.; Choi, B. B.; Morrison, C. R.; Jansen, R. H.; Provenza, A. J.
2008-01-01
Excessive vibration of turbomachinery blades causes high cycle fatigue (HCF) problems requiring damping treatments to mitigate vibration levels. Based on the technical challenges and requirements learned from previous turbomachinery blade research, a feasibility study of resonant damping control using shunted piezoelectric patches with passive and active control techniques has been conducted on cantilever beam specimens. Test results for the passive damping circuit show that the optimum resistive shunt circuit reduces the third bending resonant vibration by almost 50%, and the optimum inductive circuit reduces the vibration by 90%. In a separate test, active control reduced vibration by approximately 98%.
NASA Technical Reports Server (NTRS)
Dominic, R. J.
1984-01-01
Research results and progress on the performance of bladed systems is reported the different topics discussed include: the study of turbine blade damping; forced vibrations of friction damped beam moistures in two dimensions; and a users manual for a computer program for dynamic analysis of bladed systems.
NASA Technical Reports Server (NTRS)
Srinivasan, A. V.; Cutts, D. G.; Sridhar, S.
1981-01-01
The potentials of various sources of nonaerodynamic damping in engine blading are evaluated through a combination of advanced analysis and testing. The sources studied include material hysteresis, dry friction at shroud and root disk interfaces as well as at platform type external dampers. A limited seris of tests was conducted to evaluate damping capacities of composite materials (B/AL, B/AL/Ti) and thermal barrier coatings. Further, basic experiments were performed on titanium specimens to establish the characteristics of sliding friction and to determine material damping constants J and n. All the tests were conducted on single blades. Mathematical models were develthe several mechanisms of damping. Procedures to apply this data to predict damping levels in an assembly of blades are developed and discussed.
NASA Technical Reports Server (NTRS)
Alfriend, K. T.
1973-01-01
A ring partially filled with a viscous fluid has been analyzed as a nutation damper for a spinning satellite. The fluid has been modelled as a rigid slug of finite length moving in a tube and resisted by a linear viscous force. It is shown that there are two distinct modes of motion, called the spin synchronous mode and the nutation synchronous mode. Time constants for each mode are obtained for both the symmetric and asymmetric satellite. The effects of a stop in the tube and an offset of the ring from the spin axis are also investigated. An analysis of test results is also given including a determination of the effect of gravity on the time constants in the two modes.
Constraint on the 1D earth model near core-mantle boundary by free core nutation
NASA Astrophysics Data System (ADS)
Huang, Chengli; Zhang, Mian
2015-04-01
Free core nutation (FCN) is a normal mode of the rotating earth with fluid outer core (FOC). Its period depends on the physics of the mantle and FOC, especially the parameters near core-mantle boundary (CMB), like the density and elastic (Lame) parameters. FCN period can be determined very accurately by VLBI and superconductive tidal gravimetry, but the theoretical calculation results of FCN period from traditional approaches and 1D earth model (like PREM) deviate significantly from the accurate observation. Meanwhile, the influence of the uncertainty of a given earth model on nutation has never been studied before. In this work, a numerical experiment is presented to check this problem, and we want to see whether FCN can provide a constraint on the construction of a 1D earth model, especially on the gradient of material density near CMB.
Estimation of nutation rates from combination of ring laser and VLBI data
NASA Astrophysics Data System (ADS)
Tercjak, M.; Böhm, J.; Brzeziński, A.; Gebauer, A.; Klügel, T.; Schreiber, U.; Schindelegger, M.
2015-08-01
Ring laser gyroscopes (RLG) are instruments measuring inertial rotations locally and in real-time without the need for an external reference system. They are sensitive to variations in the instantaneous rotation vector, therefore they are considered as a potential complement to space geodetic techniques for studying Earth rotation. In this work we examine the usability of ring laser observations for estimation of nutation rates. We investigate possibilities of computing those parameters from only one ring laser and we simulate the usage of several instruments. We also combine simulated RLG observations with actual Very Long Baseline Interferometry VLBI data and compare them with real Wettzell RLG data. Our results attest to the theoretical possibility of estimating nutation rates, albeit with a number of restrictive assumptions.
Constraint on the earth density near core-mantle boundary by free core nutation
NASA Astrophysics Data System (ADS)
Huang, Cheng-Li; Zhang, Mian
2015-08-01
Free core nutation (FCN) is a normal mode of the rotating earth with fluid outer core (FOC). Its period depends on the physics of the mantle and FOC, especially the parameters near core-mantle boundary (CMB), like the density and elastic (Lame) parameters. FCN period can be determined very accurately by VLBI and superconductive tidal gravimetry, but the theoretical calculation results of FCN period from traditional approaches and 1D earth model (like PREM) deviate significantly from the accurate observation. Meanwhile, the influence of the uncertainty of a given earth model on nutation has never been studied before. In this work, a numerical experiment is presented to check this problem, and we want to see whether FCN can provide a constraint on the construction of a 1D earth model, especially on the gradient of material density near CMB.
A Numerical Experiment to Test the Influence of the Uncertainty of Earth Model on Nutation
NASA Astrophysics Data System (ADS)
Huang, C. L.; Zhang, M.
2014-12-01
From an infinite set of coupled ordinary differential equations that govern the infinitesimal elastic-gravitational oscillations of a rotating, slightly elliptical Earth, as well as a set of boundary conditions on displacement vector, stress tensor and gravity potential, the theoretical nutation model of non-rigid earth can be numerically obtained. In these differential equations and the boundary conditions, the distributions of density and elastic (Lame) parameters interior the Earth are key parameters and are usually input from 1D earth model like PREM. However, the influence of the uncertainty of a given earth model on nutation has never been checked. In this work, we made a numerical experiment to test it, and some primary results will be presented.
The Global S[Formula: see text] Tide in Earth's Nutation.
Schindelegger, Michael; Einšpigel, David; Salstein, David; Böhm, Johannes
Diurnal S[Formula: see text] tidal oscillations in the coupled atmosphere-ocean system induce small perturbations of Earth's prograde annual nutation, but matching geophysical model estimates of this Sun-synchronous rotation signal with the observed effect in geodetic Very Long Baseline Interferometry (VLBI) data has thus far been elusive. The present study assesses the problem from a geophysical model perspective, using four modern-day atmospheric assimilation systems and a consistently forced barotropic ocean model that dissipates its energy excess in the global abyssal ocean through a parameterized tidal conversion scheme. The use of contemporary meteorological data does, however, not guarantee accurate nutation estimates per se; two of the probed datasets produce atmosphere-ocean-driven S[Formula: see text] terms that deviate by more than 30 [Formula: see text]as (microarcseconds) from the VLBI-observed harmonic of [Formula: see text] [Formula: see text]as. Partial deficiencies of these models in the diurnal band are also borne out by a validation of the air pressure tide against barometric in situ estimates as well as comparisons of simulated sea surface elevations with a global network of S[Formula: see text] tide gauge determinations. Credence is lent to the global S[Formula: see text] tide derived from the Modern-Era Retrospective Analysis for Research and Applications (MERRA) and the operational model of the European Centre for Medium-Range Weather Forecasts (ECMWF). When averaged over a temporal range of 2004 to 2013, their nutation contributions are estimated to be [Formula: see text] [Formula: see text]as (MERRA) and [Formula: see text] [Formula: see text]as (ECMWF operational), thus being virtually equivalent with the VLBI estimate. This remarkably close agreement will likely aid forthcoming nutation theories in their unambiguous a priori account of Earth's prograde annual celestial motion.
Effects of the observed J2 variations on the Earth's precession and nutation
NASA Astrophysics Data System (ADS)
Ferrándiz, José M.; Baenas, Tomás; Belda, Santiago
2016-04-01
The Earth's oblateness parameter J2 is closely related to the dynamical ellipticity H, which factorizes the main components of the precession and the different nutation terms. In most theoretical approaches to the Earth's rotation, with IAU2000 nutation theory among them, H is assumed to be constant. The precession model IAU2006 supposes H to have a conventional linear variation, based on the J2 time series derived mainly from satellite laser ranging (SLR) data for decades, which gives rise to an additional quadratic term of the precession in longitude and some corrections of the nutation terms. The time evolution of J2 is, however, too complex to be well approximated by a simple linear model. The effect of more general models including periodic terms and closer to the observed time series, although still unable to reproduce a significant part of the signal, has been seldom investigated. In this work we address the problem of deriving the effect of the observed J2 variations without resorting to such simplified models. The Hamiltonian approach to the Earth rotation is extended to allow the McCullagh's term of the potential to depend on a time-varying oblateness. An analytical solution is derived by means of a suitable perturbation method in the case of the time series provided by the Center for Space Research (CSR) of the University of Texas, which results in non-negligible contributions to the precession-nutation angles. The presentation focuses on the main effects on the longitude of the equator; a noticeable non-linear trend is superimposed to the linear main precession term, along with some periodic and decadal variations.
Introduction to the scientific application system of DAMPE (On behalf of DAMPE collaboration)
NASA Astrophysics Data System (ADS)
Zang, Jingjing
2016-07-01
The Dark Matter Particle Explorer (DAMPE) is a high energy particle physics experiment satellite, launched on 17 Dec 2015. The science data processing and payload operation maintenance for DAMPE will be provided by the DAMPE Scientific Application System (SAS) at the Purple Mountain Observatory (PMO) of Chinese Academy of Sciences. SAS is consisted of three subsystems - scientific operation subsystem, science data and user management subsystem and science data processing subsystem. In cooperation with the Ground Support System (Beijing), the scientific operation subsystem is responsible for proposing observation plans, monitoring the health of satellite, generating payload control commands and participating in all activities related to payload operation. Several databases developed by the science data and user management subsystem of DAMPE methodically manage all collected and reconstructed science data, down linked housekeeping data, payload configuration and calibration data. Under the leadership of DAMPE Scientific Committee, this subsystem is also responsible for publication of high level science data and supporting all science activities of the DAMPE collaboration. The science data processing subsystem of DAMPE has already developed a series of physics analysis software to reconstruct basic information about detected cosmic ray particle. This subsystem also maintains the high performance computing system of SAS to processing all down linked science data and automatically monitors the qualities of all produced data. In this talk, we will describe all functionalities of whole DAMPE SAS system and show you main performances of data processing ability.
Research on measurement of flying object nutation angle based on double linear CCD intersection
NASA Astrophysics Data System (ADS)
Ma, Weihong; Pang, Qiuhong; Ni, Jinping
2012-01-01
The importance of space scale matching of flying direction and object long axis is presented when we measure nutation angle of flying object with slit photography, and a new method to measure nutation angle of flying object combined slit photography and double linear CCD intersection is examined. A brief methodology of nutation angle computing by series double linear image analysis is discussed, and a nunation angle measurement system is designed. A series linear image analysis method is developed to obtain the image position of series point on object long axis at pixel scale, and then the double linear CCD intersection theory is used to find the space coordinate position of various points at actual space scale. They are also put forward in this paper that invalid coordinate data are rejected by line detecting and flying direction data space is decided by perpendicular flying distance of object at CCD sampling interval. At final, a practical test sample is given, and the feasibility of measurement method is proved.
Spin rotation, Chandler wobble and free core nutation of isolated multi-layer pulsars
NASA Astrophysics Data System (ADS)
Gusev, Alexander; Kitiashvili, Irina
2013-03-01
At present time there are investigations of precession and nutation for very different celestial multi-layer bodies: the Earth (Getino 1995), Moon (Gusev 2010), planets of Solar system (Gusev 2010) and pulsars (Link et al. 2007). The long-periodic precession phenomenon was detected for few pulsars: PSR B1828-11, PSR B1557-50, PSR 2217+47, PSR 0531+21, PSR B0833-45, and PSR B1642-03. Stairs, Lyne & Shemar (2000) have found that the arrival-time residuals from PSR B1828-11 vary periodically with a different periods. According to our model, the neutron star has the rigid crust (RC), the fluid outer core (FOC) and the solid inner core (SIC). The model explains generation of four modes in the rotation of the pulsar: two modes of Chandler wobble (CW, ICW) and two modes connecting with free core nutation (FCN, FICN) (Gusev & Kitiashvili 2008). We are propose the explanation for all harmonics of Time of Arrival (TOA) pulses variations as precession of a neutron star owing to differential rotation of RC, FOC and crystal SIC of the pulsar PSR B1828-11: 250, 500, 1000 days. We used canonical method for interpretation TOA variations by Chandler Wobble (CW) and Free Core Nutation (FCN) of pulsar.
Consistency problems associated to the improvement of precession-nutation theories
NASA Astrophysics Data System (ADS)
Ferrandiz, J. M.; Escapa, A.; Baenas, T.; Getino, J.; Navarro, J. F.; Belda, S.
2014-12-01
The complexity of the modelling of the rotational motion of the Earth in space has produced that no single theory has been adopted to describe it in full. Hence, it is customary using at least a theory for precession and another one for nutation. The classic approach proceeds by deriving some of the fundamentals parameters from the precession theory at hand, like, e.g. the dynamical ellipticity H, and then using that valuesin the nutation theory. The former IAU1976 precession and IAU1980 nutation theories followed that scheme. Along with the improvement of the accuracy of the determination of EOP (Earth orientation parameters), IAU1980 was superseded by IAU2000, based on the application of the MHB2000 (Mathews et al 2002) transfer function to the previous rigid earth analytical theory REN2000 (Souchay et al 1999). The latter was derived while the precession model IAU1976 was still in force therefore it used the corresponding values for some of the fundamental parameters, as the precession rate, associated to the dynamical ellipticity, and the obliquity of the ecliptic at the reference epoch. The new precession model P03 was adopted as IAU2006. That change introduced some inconsistency since P03 used different values for some of the fundamental parameters that MHB2000 inherited from REN2000. Besides, the derivation of the basic earth parameters of MHB2000 itself comprised a fitted variation of the dynamical ellipticity adopted in the background rigid theory. Due to the strict requirements of accuracy of the present and coming times, the magnitude of the inconsistencies originated by this two-fold approach is no longer negligible as earlier. Some corrections have been proposed by Capitaine et al (2005) and Escapa et al (2014) in order to reach a better level of consistency between precession and nutation theories and parameters. In this presentation we revisit the problem taking into account some of the advances in precession theory not accounted for yet, stemming
Truncation effects in computing free wobble/nutation modes explored using a simple Earth model
NASA Astrophysics Data System (ADS)
Seyed-Mahmoud, Behnam; Rochester, Michael G.; Rogers, Christopher M.
2017-03-01
The displacement field accompanying the wobble/nutation of the Earth is conventionally represented by an infinite chain of toroidal and spheroidal vector spherical harmonics, coupled by rotation and ellipticity. Numerical solutions for the eigenperiods require truncation of that chain, and the standard approaches using the linear momentum description (LMD) of deformation during wobble/nutation have truncated it at very low degrees, usually degree 3 or 4, and at most degree 5. The effects of such heavy truncation on the computed eigenperiods have hardly been examined. We here investigate the truncation effects on the periods of the free wobble/nutation modes using a simplified Earth model consisting of a homogeneous incompressible inviscid liquid outer core with a rigid (but not fixed) inner core and mantle. A novel Galerkin method is implemented using a Clairaut coordinate system to solve the classic Poincaré problem in the liquid core and, to close the problem, we use the Lagrangean formulation of the Liouville equation for each of the solid parts of the Earth model. We find that, except for the free inner core nutation (FICN), the periods of the free rotational modes converge rather quickly. The period of the tiltover mode (TOM) is found to excellent accuracy. The computed periods of the Chandler wobble (CW) and free core nutation (FCN) are nearly identical to the values cited in the literature for similar Earth models, but that for the inner core wobble (ICW) is slightly different. Truncation at low-degree harmonics causes the FICN period to fluctuate over a range as large as 90 sd, with different values at different truncation levels. For example, truncation at degree 6 gives a period of 752 sd (almost identical with the value cited in the literature for such an Earth model) but truncation at degree 24 is required to obtain convergence, and the resulting period is 746 ± 1 sd, as more terms are included, with no guarantee that its proximity to earlier values
NASA Astrophysics Data System (ADS)
Jiménez-Reyes, S. J.; García, R. A.; Jiménez, A.; Chaplin, W. J.
2003-09-01
We have used observations made by the Global Oscillations at Low Frequency (GOLF) and the Variability of Irradiance and Gravity Oscillations Sun Photometer (VIRGO/SPM) instruments on board the ESA/NASA Solar and Heliospheric Observatory satellite to study variations in the excitation and damping of low angular degree (low-l) solar p-modes on the rising phase of activity cycle 23. Our analysis includes a correction procedure that for the first time allows GOLF data to be ``treated'' as a single homogeneous set, thereby compensating for the change of operational configuration partway through the mission. Over the range 2.5<=ν<=3.5mHz, we uncover an increase in damping and decrease in mode power that is consistent with previous findings. Furthermore, an excellent level of agreement is found between the variations extracted from the GOLF and VIRGO/SPM data. We find no net long-term changes to the modal energy supply rate. However, an analysis of the residuals uncovers the presence of a quasi-periodic signature of period ~1.5 yr (most pronounced for SPM). While it is true that several workers claim to have uncovered similar periodicities in other phenomena related to the near-surface layers of the Sun here, we are at present more inclined to attribute our finding to an artifact of the mode-fitting procedure. We also uncover a significant change in the asymmetry of mode peaks in the GOLF data, as found in previous studies of much longer data sets. These assumed that the dominant contribution to this arose from the switch in operating configuration partway through the mission (which altered the depth in the solar atmosphere sampled by the instrument). However, our preliminary analysis of data collected over the 100 day period beginning 2002 November 19-when the instrument switched back to its original configuration-suggests that this change may have a solar cycle component.
Modification of spastic gait through mechanical damping.
Maki, B E; Rosen, M J; Simon, S R
1985-01-01
The effect of dissipative mechanical loads on spastic gait has been studied, to evaluate the feasibility of using mechanically damped orthoses to effect functional improvements in the gait of spastic patients. This concept is based on a hypothesis citing uninhibited, velocity-dependent stretch reflexes as a possible causal factor in spastic gait abnormalities, such as equinus and back-kneeing. In order to screen potential experimental subjects and to quantify velocity-dependent reflex behaviour, ankle rotation experiments and filmed gait analysis were performed. The results supported the existence of a velocity threshold. Orthosis simulation experiments were performed with one spastic subject, using a wearable, computer-controlled, electromechanical, below-knee orthosis simulator to apply a variety of damping loads to the ankle as the subject walked. Results indicated that appropriate damping can improve local joint kinematics. The damping causes a reduction in muscle stretch velocity which apparently results in reduced spastic reflex activity.
Duxbury, Geoffrey; Kelly, James F.; Blake, Thomas A.; Langford, Nigel
2012-05-07
Free induction decay (FID), optical nutation and rapid passage induced (RP) signals in nitrous oxide, under both optically thin and optically thick conditions, have been observed using a rapid current pulse modulation, or chirp, applied to the slow current ramp of a quantum cascade (QC) laser. The variation in optical depth was achieved by increasing the pressure of nitrous oxide in a long pathlength multipass absorption cell. This allows the variation of optical depth to be achieved over a range of low gas pressures. Since, even at the highest gas pressure used in the cell, the chirp rate of the QC laser is faster than the collisional reorientation time of the molecules, there is minimal collisional damping, allowing a large macroscopic polarization of the molecular dipoles to develop. This is referred to as rapid passage induced gain. The resultant FID signals are enhanced due to the constructive interference between the field within the gas generated by the slow ramp of the laser (pump), and the fast chirp of the laser (probe) signal generated by pulse modulation of the continuously operating QC laser. The FID signals obtained at large 2 optical depth have not been observed previously in the mid-infrared regions, and unusual oscillatory signals have been observed at the highest gas pressures used.
Acoustic transducer with damping means
Smith, Richard W.; Adamson, Gerald E.
1976-11-02
An ultrasonic transducer specifically suited to high temperature sodium applications is described. A piezoelectric active element is joined to the transducer faceplate by coating the faceplate and juxtaposed active element face with wetting agents specifically compatible with the bonding procedure employed to achieve the joint. The opposite face of the active element is fitted with a backing member designed to assure continued electrical continuity during adverse operating conditions which can result in the fracturing of the active element. The fit is achieved employing a spring-loaded electrode operably arranged to electrically couple the internal transducer components, enclosed in a hermetically sealed housing, to accessory components normally employed in transducer applications. Two alternative backing members are taught for assuring electrical continuity. The first employs a resilient, discrete multipoint contact electrode in electrical communication with the active element face. The second employs a resilient, elastomeric, electrically conductive, damped member in electrical communication with the active element face in a manner to effect ring-down of the transducer. Each embodiment provides continued electrical continuity within the transducer in the event the active element fractures, while the second provides the added benefit of damping.
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.
Ishima, Rieko
2016-01-01
Abundant solvent nuclear spins, such as water protons in aqueous solution, cause radiation damping in NMR experiments. It is important to know how the effect of radiation damping appears in high-resolution protein NMR because macromolecular studies always require very high magnetic field strengths with a highly sensitive NMR probe that can easily cause radiation damping. Here, we show the behavior of water magnetization after a pulsed-field gradient (PFG) using nutation experiments at 900 MHz with a cryogenic probe: when water magnetization is located in the upper hemisphere (having +Z component, parallel to the external magnetic field), dephasing of the magnetization by a PFG effectively suppresses residual water magnetization in the transverse plane. In contrast, when magnetization is located in the lower hemisphere (having −Z component), the small residual transverse component remaining after a PFG is still sufficient to induce radiation damping. Based on this observation, we designed 1H-15N HSQC experiments in which water magnetization is maintained in the upper hemisphere, but not necessarily along Z, and compared them with the conventional experiments, in which water magnetization is inverted during the t1 period. The result demonstrates moderate gain of signal-to-noise ratio, 0–28%. Designing the experiments such that water magnetization is maintained in the upper hemisphere allows shorter pulses to be used compared to the complete water flip-back and, thereby, is useful as a building block of protein NMR pulse programs in solution. PMID:27524944
Ishima, Rieko
2015-09-01
Abundant solvent nuclear spins, such as water protons in aqueous solution, cause radiation damping in NMR experiments. It is important to know how the effect of radiation damping appears in high-resolution protein NMR because macromolecular studies always require very high magnetic field strengths with a highly sensitive NMR probe that can easily cause radiation damping. Here, we show the behavior of water magnetization after a pulsed-field gradient (PFG) using nutation experiments at 900 MHz with a cryogenic probe: when water magnetization is located in the upper hemisphere (having +Z component, parallel to the external magnetic field), dephasing of the magnetization by a PFG effectively suppresses residual water magnetization in the transverse plane. In contrast, when magnetization is located in the lower hemisphere (having -Z component), the small residual transverse component remaining after a PFG is still sufficient to induce radiation damping. Based on this observation, we designed (1)H-(15)N HSQC experiments in which water magnetization is maintained in the upper hemisphere, but not necessarily along Z, and compared them with the conventional experiments, in which water magnetization is inverted during the t1 period. The result demonstrates moderate gain of signal-to-noise ratio, 0-28%. Designing the experiments such that water magnetization is maintained in the upper hemisphere allows shorter pulses to be used compared to the complete water flip-back and, thereby, is useful as a building block of protein NMR pulse programs in solution.
DuBois, Neil J.; Amaral, Antonio M.
1992-10-27
A damped flexible seal assembly for a torpedo isolates the tailcone thereof rom vibrational energy present in the drive shaft assembly. A pair of outside flanges, each of which include an inwardly facing groove and an O-ring constrained therein, provide a watertight seal against the outer non-rotating surface of the drive shaft assembly. An inside flange includes an outwardly-facing groove and an O-ring constrained therein, and provides a watertight seal against the inner surface of the tail cone. Two cast-in-place elastomeric seals provide a watertight seal between the flanges and further provide a damping barrier between the outside flanges and the inside flanges for damping vibrational energy present in the drive shaft assembly before the energy can reach the tailcone through the seal assembly.
NASA Technical Reports Server (NTRS)
Wahr, J. M.; Sasao, T.
1981-01-01
The effects of the oceans, which are subject to a resonance due to a free rotational eigenmode of an elliptical, rotating earth with a fluid outer core having an eigenfrequency of (1 + 1/460) cycle/day, on the body tide and nutational response of the earth to the diurnal luni-tidal force are computed. The response of an elastic, rotating, elliptical, oceanless earth with a fluid outer core to a given load distribution on its surface is first considered, and the tidal sea level height for equilibrium and nonequilibrium oceans is examined. Computations of the effects of equilibrium and nonequilibrium oceans on the nutational and deformational responses of the earth are then presented which show small but significant perturbations to the retrograde 18.6-year and prograde six-month nutations, and more important effects on the earth body tide, which is also resonant at the free core notation eigenfrequency.
NASA Astrophysics Data System (ADS)
Gattano, César; Lambert, Sébastien; Bizouard, Christian; Souchay, Jean
2015-08-01
Very Large Baseline Interferometry (VLBI) is the only technique which permits to determine Earth's precession-nutation at submilliarcsecond accuracy. With its 35 years of observations, at the rate of 2 observing sessions a week during the last decade, it allows to estimate nutation over periods from 14 days to 20 years. But VLBI data analysis is of such a complexity that there are as much different nutation time series that there are analysis center working on it. So, it is worthful to investigate the nature of these differences in relation with the choices in the analysis strategy.Differences between the operationnal nutation time series are considered as composed of a signal and a noise, determined by mean of wavelets and Allan variance analysis. We try to explain them by the choices made on the Celestial Reference Frame. In particulary, the ICRF2 catalog is perturbed by introducting random shifts on all the 3414 sources, and we investigate the consequences on nutation.
NASA Astrophysics Data System (ADS)
Rouyer, C.; Heimbolt, G.; Lange, T.
1981-11-01
The problem of the nutation divergence of a 3 axis stablized satellite equipped with hydrodynamic bearing momentum wheels is discussed. The magnetic bearing momentum wheels, having a relatively low transverse rigidity and dissipating energy in the rotor (due to eddy currents), are likely to present an inconvenience of the same nature, if not of the same magnitude. A physical explanation of the phenomenon is given. The results of tests carried out on an air-bearing table are presented and it is shown that phenomenon cannot be detected on a satellite of the INTELSAT size.
Obliquity, precession rate, and nutation coefficients for a set of 100 asteroids
NASA Astrophysics Data System (ADS)
Lhotka, C.; Souchay, J.; Shahsavari, A.
2013-08-01
Context. Thanks to various space missions and the progress of ground-based observational techniques, the knowledge of asteroids has considerably increased in the recent years. Aims: Due to this increasing database that accompanies this evolution, we compute for a set of 100 asteroids their rotational parameters: the moments of inertia along the principal axes of the object, the obliquity of the axis of rotation with respect to the orbital plane, the precession rates, and the nutation coefficients. Methods: We select 100 asteroids for which the parameters for the study are well-known from observations or space missions. For each asteroid, we determine the moments of inertia, assuming an ellipsoidal shape. We calculate their obliquity from their orbit (instead of the ecliptic) and the orientation of the spin-pole. Finally, we calculate the precession rates and the largest nutation components. The number of asteroids concerned leads to some statistical studies of the output. Results: We provide a table of rotational parameters for our set of asteroids. The table includes the obliquity, their axes ratio, their dynamical ellipticity Hd, and the scaling factor K. We compute the precession rate ψ˙ and the leading nutation coefficients Δψ and Δɛ. We observe similar characteristics, as observed by previous authors that is, a significantly larger number of asteroids rotates in the prograde mode (≈ 60%) than in the retrograde one with a bimodal distribution. In particular, there is a deficiency of objects with a polar axis close to the orbit. The precession rates have a mean absolute value of 18″/y, and the leading nutation coefficients have an average absolute amplitude of 5.7″ for Δψ and 5.2″ for Δɛ. At last, we identify and characterize some cases with large precession rates, as seen in 25143 Itokawa, with has a precession rate of about - 475''/y. Tables 1 and 2 are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130
Recent developments in the theory of the Earth’s precession and nutation
NASA Astrophysics Data System (ADS)
Escapa, Alberto; Getino, Juan; Ferrándiz, Jose Manuel; Navarro, Juan F.; Baenas, Tomás
2015-08-01
We report on recent advances in the theoretical modelling of the precession and nutation of the non-rigid Earth, with especial emphasis in those obtained by the authors following the Hamiltonian approach. We focus in second order components of the approximate solutions that come from various origins of physical and mathematical nature. They have been neglected in the available models up to now. Their contribution to the solutions, however, has a non-negligible magnitude, which in some cases reaches some tens of micro arcseconds.
Spin nutation in the quasi-isotropic A-like superfluid phase of {sup 3}He
Fomin, I. A.
2006-06-15
The order parameter of the quasi-isotropic A-like superfluid phase of {sup 3}He has been reduced to a simple form. The frequencies of the spatially homogeneous oscillations of the spin and the spin part of the order parameter of this phase have been obtained taking into account the anisotropy of its magnetic susceptibility. It has been shown that the anisotropy of susceptibility strongly affects the low-frequency oscillation mode, which is similar to the nutation of an asymmetric top. The possibility of observing this mode using the NMR method is discussed.
NASA Technical Reports Server (NTRS)
De Vries, Dan; Wahr, John M.
1991-01-01
This paper computes the effects of the solid inner core (IC) on the forced nutations and earth tides, and on certain of the earth's rotational normal modes. The theoretical results are extended to include the effects of a solid IC and of nonhydrostatic structure. The presence of the IC is responsible for a new, almost diurnal, prograde normal mode which involves a relative rotation between the IC and fluid outer core about an equatorial axis. It is shown that the small size of the IC's effects on both nutations and tides is a consequence of the fact that the IC's moments of inertia are less than 1/1000 of the entire earth's.
Palmer, R.B.
1987-05-01
This paper looks at, and compares three types of damping ring lattices: conventional, wiggler lattice with finite ..cap alpha.., wiggler lattice with ..cap alpha.. = 0, and observes the attainable equilibrium emittances for the three cases assuming a constraint on the attainable longitudinal impedance of 0.2 ohms. The emittance obtained are roughly in the ratio 4:2:1 for these cases.
Radiation damping on cryoprobes.
Shishmarev, Dmitry; Otting, Gottfried
2011-12-01
Radiation damping on 600 and 800 MHz cryoprobes was investigated. The phase angle β between a vector 90° phase shifted to the precessing magnetization and the rf field induced in the coil was found to depend markedly on whether an FID was being acquired or not. The magnitude of the radiation damping field was sufficiently strong to restore 95% of the equilibrium water magnetization of a 90% H2O sample in a 5 mm sample tube within about 5 ms following a 165° pulse. This can be exploited in water flip-back versions of NOESY and TOCSY experiments of proteins, but care must be taken to limit the effect of the radiation damping field from the water on the Ha protons. Long water-selective pulses can be applied only following corrections. We developed a program for correcting pulse shapes if β is non-zero. The WATERGATE scheme is shown to be insensitive to imperfections introduced by radiation damping.
NASA Astrophysics Data System (ADS)
Zhu, Sheng-Yuan; Mueller, Ivan I.
1983-03-01
First, the paper is devoted to the effects of adopting new definitive precession and equinox corrections on the terrestrial reference frame: The effect on polar motion is a diurnal periodic term with an amplitude increasing linearly in time; on UT1 it is a linear term. Second, general principles are given the use of which can determine the effects of small rotations (such as precession, nutation or equinox corrections) of the frame of a Conventional Inertial Reference System (CIS) on the frame of the Conventional Terrestrial Reference System (CTS). Next, seven CTS options are presented, one of which is necessary to accommodate such rotations (corrections). The last of these options requiring no changes in the origin of terrestrial longitudes and in UT1 is advocated; this option would be maintained by eventually referencing the Greenwich Mean Sidereal Time to a fixed point on the equator, instead of to the mean equinox of date, the current practice. Accommodating possible future changes in the astronomical nutation is discussed in the last section. The Appendix deals with the effects of differences which may exist between the various CTS's and CIS's (inherent in the various observational techniques) on earth rotation parameters (ERP) and how these differences can be determined. It is shown that the CTS differences can be determined from observations made at the same site, while the CIS differences by comparing the ERP's determined by the different techniques during the same time period.
Signature analysis of ballistic missile warhead with micro-nutation in terahertz band
NASA Astrophysics Data System (ADS)
Li, Ming; Jiang, Yue-song
2013-08-01
In recent years, the micro-Doppler effect has been proposed as a new technique for signature analysis and extraction of radar targets. The ballistic missile is known as a typical radar target and has been paid many attentions for the complexities of its motions in current researches. The trajectory of a ballistic missile can be generally divided into three stages: boost phase, midcourse phase and terminal phase. The midcourse phase is the most important phase for radar target recognition and interception. In this stage, the warhead forms a typical micro-motion called micro-nutation which consists of three basic micro-motions: spinning, coning and wiggle. This paper addresses the issue of signature analysis of ballistic missile warhead in terahertz band via discussing the micro-Doppler effect. We establish a simplified model (cone-shaped) for the missile warhead followed by the micro-motion models including of spinning, coning and wiggle. Based on the basic formulas of these typical micro-motions, we first derive the theoretical formula of micro-nutation which is the main micro-motion of the missile warhead. Then, we calculate the micro-Doppler frequency in both X band and terahertz band via these micro-Doppler formulas. The simulations are given to show the superiority of our proposed method for the recognition and detection of radar micro targets in terahertz band.
Optimization of a nutation damper attached to a spin-stabilized satellite
NASA Astrophysics Data System (ADS)
Hauboldt, Brady P.
1994-12-01
This study uses linearized equations of motion for a rigid body with an attached spring-mass-damper to maximize the decay rate of a satellite's coning motion. An analysis of the numerical eigenvalues is presented which leads to an optimal relationship between relevant parameters: damper placement, spring constant, damping coefficient, system moments of inertia, and damper mass fraction. The coupled system's eigenvalues do not provide true critical damping, thus the real eigenvalue parts are minimized in order to achieve damping which requires the minimum amount of time. A comparison between this optimal design method and a classical method concludes with a noticeable improvement in damping performance for the optimized systems.
Samelko, Lauryn; Landgraeber, Stefan; McAllister, Kyron; Jacobs, Joshua; Hallab, Nadim James
2016-01-01
Cobalt alloy debris has been implicated as causative in the early failure of some designs of current total joint implants. The ability of implant debris to cause excessive inflammation via danger signaling (NLRP3 inflammasome) vs. pathogen associated pattern recognition receptors (e.g. Toll-like receptors; TLRs) remains controversial. Recently, specific non-conserved histidines on human TLR4 have been shown activated by cobalt and nickel ions in solution. However, whether this TLR activation is directly or indirectly an effect of metals or secondary endogenous alarmins (danger-associated molecular patterns, DAMPs) elicited by danger signaling, remains unknown and contentious. Our study indicates that in both a human macrophage cell line (THP-1) and primary human macrophages, as well as an in vivo murine model of inflammatory osteolysis, that Cobalt-alloy particle induced NLRP3 inflammasome danger signaling inflammatory responses were highly dominant relative to TLR4 activation, as measured respectively by IL-1β or TNF-α, IL-6, IL-10, tissue histology and quantitative bone loss measurement. Despite the lack of metal binding histidines H456 and H458 in murine TLR4, murine calvaria challenge with Cobalt alloy particles induced significant macrophage driven in vivo inflammation and bone loss inflammatory osteolysis, whereas LPS calvaria challenge alone did not. Additionally, no significant increase (p<0.05) in inflammation and inflammatory bone loss by LPS co-challenge with Cobalt vs. Cobalt alone was evident, even at high levels of LPS (i.e. levels commiserate with hematogenous levels in fatal sepsis, >500pg/mL). Therefore, not only do the results of this investigation support Cobalt alloy danger signaling induced inflammation, but under normal homeostasis low levels of hematogenous PAMPs (<2pg/mL) from Gram-negative bacteria, seem to have negligible contribution to the danger signaling responses elicited by Cobalt alloy metal implant debris. This suggests the
Inertia-Wheel Vibration-Damping System
NASA Technical Reports Server (NTRS)
Fedor, Joseph V.
1990-01-01
Proposed electromechanical system would damp vibrations in large, flexible structure. In active vibration-damping system motors and reaction wheels at tips of appendages apply reaction torques in response to signals from accelerometers. Velocity signal for vibrations about one axis processes into control signal to oppose each of n vibrational modes. Various modes suppressed one at a time. Intended primarily for use in spacecraft that has large, flexible solar panels and science-instrument truss assembly, embodies principle of control interesting in its own right and adaptable to terrestrial structures, vehicles, and instrument platforms.
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.
Vibrational modes and damping in the cochlear partition
NASA Astrophysics Data System (ADS)
O'Maoiléidigh, Dáibhid; Hudspeth, A. J.
2015-12-01
It has been assumed in models of cochlear mechanics that the primary role of the cochlear active process is to counteract the damping of the basilar membrane, the vibration of which is much larger in a living animal than post mortem. Recent measurements of the relative motion between the reticular lamina and basilar membrane imply that this assumption is incorrect. We propose that damping is distributed throughout the cochlear partition rather than being concentrated in the basilar membrane. In the absence of significant damping, the cochlear partition possesses three modes of vibration, each associated with its own locus of Hopf bifurcations. Hair-cell activity can amplify any of these modes if the system's operating point lies near the corresponding bifurcation. The distribution of damping determines which mode of vibration predominates. For physiological levels of damping, only one mode produces a vibration pattern consistent with experimental measurements of relative motion and basilar-membrane motion.
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.
On damping mechanisms in beams
NASA Technical Reports Server (NTRS)
Banks, H. T.; Inman, D. J.
1989-01-01
A partial differential equation model of a cantilevered beam with a tip mass at its free end is used to study damping in a composite. Four separate damping mechanisms consisting of air damping, strain rate damping, spatial hysteresis and time hysteresis are considered experimentally. Dynamic tests were performed to produce time histories. The time history data is then used along with an approximate model to form a sequence of least squares problems. The solution of the least squares problem yields the estimated damping coefficients. The resulting experimentally determined analytical model is compared with the time histories via numerical simulation of the dynamic response. The procedure suggested here is compared with a standard modal damping ratio model commonly used in experimental modal analysis.
On damping mechanisms in beams
NASA Technical Reports Server (NTRS)
Banks, H. T.; Inman, D. J.
1991-01-01
A partial differential equation model of a cantilevered beam with a tip mass at its free end is used to study damping in a composite. Four separate damping mechanisms consisting of air damping, strain rate damping, spatial hysteresis and time hysteresis are considered experimentally. Dynamic tests were performed to produce time histories. The time history data is then used along with an approximate model to form a sequence of least squares problems. The solution of the least squares problem yields the estimated damping coefficients. The resulting experimentally determined analytical model is compared with the time histories via numerical simulation of the dynamic response. The procedure suggested here is compared with a standard modal damping ratio model commonly used in experimental modal analysis.
Magnetically Damped Furnace (MDF)
NASA Technical Reports Server (NTRS)
1998-01-01
The Magnetically Damped Furnace (MDF) breadboard is being developed in response to NASA's mission and goals to advance the scientific knowledge of microgravity research, materials science, and related technologies. The objective of the MDF is to dampen the fluid flows due to density gradients and surface tension gradients in conductive melts by introducing a magnetic field during the sample processing. The MDF breadboard will serve as a proof of concept that the MDF performance requirements can be attained within the International Space Station resource constraints.
NASA Technical Reports Server (NTRS)
Zhu, S. Y.; Mueller, I. I.
1982-01-01
The effect of adopting definitive precession and equinox corrections on the terrestrial reference frame was investigated. It is noted that the effect on polar motion is a diurnal periodic term with an amplitude increasing linearly in time whole on UT1 it is a linear term: general principles are given to determine the effects of small rotations of the frame of a conventional inertial reference system (CIS) on the frame of the conventional terrestrial reference system (CTS); seven CTS options are presented, one of which is necessary to accommodate such rotation. Accommodating possible future changes in the astronomical nutation is discussed. The effects of differences which may exist between the various CTS's and CIS's on Earth rotation parameters (ERP) and how these differences can be determined are examined. It is shown that the CTS differences can be determined from observations made at the same site. The CIS differences by comparing the ERP's are determined by the different techniques during the same time period.
NASA Technical Reports Server (NTRS)
Cummins, Phil R.; Wahr, John M.
1993-01-01
In this study we consider the influence of the earth's free core nutation (FCN) on diurnal tidal admittance estimates for 11 stations of the globally distributed International Deployment of Accelerometers network. The FCN causes a resonant enhancement of the diurnal admittances which can be used to estimate some properties of the FCN. Estimations of the parameters describing the FCN (period, Q, and resonance strength) are made using data from individual stations and many stations simultaneously. These yield a result for the period of 423-452 sidereal days, which is shorter than theory predicts but is in agreement with many previous studies and suggests that the dynamical ellipticity of the core may be greater than its hydrostatic value.
On the changes of IAU 2000 nutation theory stemming from IAU 2006 precession theory
NASA Astrophysics Data System (ADS)
Escapa, A.; Getino, J.; Ferrándiz, J. M.; Baenas, T.
2014-12-01
The adoption of IAU 2006 precession theory (Capitaine et al. 2003) introduced some small changes in IAU 2000A nutation theory, relevant at the mircroarcsecond level. These adjustments were derived in Capitaine et al. (2005) and are currently considered in international standards like, for example, IERS Conventions (2010) or in the Explanatory Supplement to the Astronomical Almanac (2013). We reexamine the issue, working out the induced modifications due to a change in the value of the obliquity of the ecliptic and to the secular variation of the Earth dynamical flattening. In particular, within the framework of the Hamiltonian theory of the rotation of the Earth we derive analytical expressions of those changes for the motion of the figure axis. These expressions and their corresponding numerical contributions will be compared with those obtained in Capitaine et al. (2005).
Joint analysis of celestial pole offset and free core nutation series
NASA Astrophysics Data System (ADS)
Malkin, Zinovy
2016-10-01
Three combined celestial pole offset (CPO) series computed at the Paris Observatory (C04), the United States Naval Observatory (USNO), and the International VLBI Service for Geodesy and Astrometry (IVS), as well as six free core nutation (FCN) models, were compared from different perspectives, such as stochastic and systematic differences, and FCN amplitude and phase variations. The differences between the C04 and IVS CPO series were mostly stochastic, whereas a low-frequency bias at the level of several tens of μ as was found between the C04 and USNO CPO series. The stochastic differences between the C04 and USNO series became considerably smaller when computed at the IVS epochs, which can indicate possible problems with the interpolation of the IVS data at the midnight epochs during the computation of the C04 and USNO series. The comparison of the FCN series showed that the series computed with similar window widths of 1.1-1.2 years were close to one another at a level of 10-20 μ as, whereas the differences between these series and the series computed with a larger window width of 4 and 7 years reached 100 μ as. The dependence of the FCN model on the underlying CPO series was investigated. The RMS differences between the FCN models derived from the C04, USNO, and IVS CPO series were at a level of approximately 15 μ as, which was considerably smaller than the differences among the CPO series. The analysis of the differences between the IVS, C04, and USNO CPO series suggested that the IVS series would be preferable for both precession-nutation and FCN-related studies.
The Joint Damping Experiment (JDX)
NASA Technical Reports Server (NTRS)
Folkman, Steven L.; Bingham, Jeff G.; Crookston, Jess R.; Dutson, Joseph D.; Ferney, Brook D.; Ferney, Greg D.; Rowsell, Edwin A.
1997-01-01
The Joint Damping Experiment (JDX), flown on the Shuttle STS-69 Mission, is designed to measure the influence of gravity on the structural damping of a high precision three bay truss. Principal objectives are: (1) Measure vibration damping of a small-scale, pinjointed truss to determine how pin gaps give rise to gravity-dependent damping rates; (2) Evaluate the applicability of ground and low-g aircraft tests for predicting on-orbit behavior; and (3) Evaluate the ability of current nonlinear finite element codes to model the dynamic behavior of the truss. Damping of the truss was inferred from 'Twang' tests that involve plucking the truss structure and recording the decay of the oscillations. Results are summarized as follows. (1) Damping, rates can change by a factor of 3 to 8 through changing the truss orientation; (2) The addition of a few pinned joints to a truss structure can increase the damping by a factor as high as 30; (3) Damping is amplitude dependent; (4) As gravity induced preloads become large (truss long axis perpendicular to gravity vector) the damping is similar to non-pinjointed truss; (5) Impacting in joints drives higher modes in structure; (6) The torsion mode disappears if gravity induced preloads are low.
NASA Technical Reports Server (NTRS)
Mathews, P. M.; Buffett, Bruce A.; Herring, Thomas A.; Shapiro, Irwin I.
1991-01-01
A treatment is presented of the nutation problem for an oceanless, elastic, spheroidally stratified earth, with the dynamical role of the inner core explicitly included in the formulation. Solving the enlarged system of equations shows that a new almost diurnal eigenfrequency emerges. A rough estimate places it not far from the prograde annual tidal excitation frequency, so that possible resonance effects on nutation amplitudes need careful consideration. Tables are provided that exhibit the sensitivities of various relevant quantities, the eigenfrequencies and the coefficients which appear in the resonance expansion, as well as the nutation amplitudes at important tidal frequencies, to possible errors in the earth parameters which enter the theory set forth. Finally, the analysis of 798 VLBI experiments performed between July 1980 and February 1989 and the determination from this analysis of corrections to selected coefficients in the International Astronomical Union 1980 theory of the nutations of the earth are discussed.
Nonlinear damping model for flexible structures. Ph.D. Thesis
NASA Technical Reports Server (NTRS)
Zang, Weijian
1990-01-01
The study of nonlinear damping problem of flexible structures is addressed. Both passive and active damping, both finite dimensional and infinite dimensional models are studied. In the first part, the spectral density and the correlation function of a single DOF nonlinear damping model is investigated. A formula for the spectral density is established with O(Gamma(sub 2)) accuracy based upon Fokker-Planck technique and perturbation. The spectral density depends upon certain first order statistics which could be obtained if the stationary density is known. A method is proposed to find the approximate stationary density explicitly. In the second part, the spectral density of a multi-DOF nonlinear damping model is investigated. In the third part, energy type nonlinear damping model in an infinite dimensional setting is studied.
Vibration damping for the Segmented Mirror Telescope
NASA Astrophysics Data System (ADS)
Maly, Joseph R.; Yingling, Adam J.; Griffin, Steven F.; Agrawal, Brij N.; Cobb, Richard G.; Chambers, Trevor S.
2012-09-01
The Segmented Mirror Telescope (SMT) at the Naval Postgraduate School (NPS) in Monterey is a next-generation deployable telescope, featuring a 3-meter 6-segment primary mirror and advanced wavefront sensing and correction capabilities. In its stowed configuration, the SMT primary mirror segments collapse into a small volume; once on location, these segments open to the full 3-meter diameter. The segments must be very accurately aligned after deployment and the segment surfaces are actively controlled using numerous small, embedded actuators. The SMT employs a passive damping system to complement the actuators and mitigate the effects of low-frequency (<40 Hz) vibration modes of the primary mirror segments. Each of the six segments has three or more modes in this bandwidth, and resonant vibration excited by acoustics or small disturbances on the structure can result in phase mismatches between adjacent segments thereby degrading image quality. The damping system consists of two tuned mass dampers (TMDs) for each of the mirror segments. An adjustable TMD with passive magnetic damping was selected to minimize sensitivity to changes in temperature; both frequency and damping characteristics can be tuned for optimal vibration mitigation. Modal testing was performed with a laser vibrometry system to characterize the SMT segments with and without the TMDs. Objectives of this test were to determine operating deflection shapes of the mirror and to quantify segment edge displacements; relative alignment of λ/4 or better was desired. The TMDs attenuated the vibration amplitudes by 80% and reduced adjacent segment phase mismatches to acceptable levels.
Bullock, Jack C.; Kelly, Benjamin E.
1980-01-01
A valve having a mechanism for damping out flow surges in a vacuum system which utilizes a slotted spring-loaded disk positioned adjacent the valve's vacuum port. Under flow surge conditions, the differential pressure forces the disk into sealing engagement with the vacuum port, thereby restricting the flow path to the slots in the disk damping out the flow surge.
Utilising HVDC to damp power oscillations
Smed, T.; Andersson, G. . Dept. of Electric Power Systems)
1993-04-01
In this paper, damping of slow oscillations with active and reactive power modulation of HVDC-links is analyzed with the aim of gaining a physical insight into the problem. The analysis shows that active power modulation is efficient when applied to a short mass-scaled electrical distance from one of the swinging machines, and reactive power modulation is most efficient when there exists a well-defined power flow direction and the modulation is made at a point close to the electrical midpoint between the swinging machines. It is shown that the intuitively appealing feedback signals frequency and derivative of the voltage are appropriate for active and reactive power modulation, respectively. The impact of the constraints imposed by the HVDC equations are analyzed, and it is determined when the implicit reactive power modulation resulting from constant [gamma] control may be detrimental for the damping.
Damping measurements using operational data
James, G.H.; Carne, T.G.; Veers, P.S.
1996-08-01
The authors have measured modal damping using strain-gauge data from an operating wind turbine. This new technique for measuring modal damping is easier and less expensive than previously used methods. Auto-correlation and cross-correlation functions of the strain-gauge data have been shown to consist of decaying sinusoids which correspond to the modal frequencies and damping ratios of the wind turbine. The authors have verified the method by extracting damping values from an analytically generated data set. Actual operating response data from the DOE/Sandia 34-m Test Bed has been used to calculate modal damping ratios as a function of rotor rotation rate. This capability will allow more accurate fatigue life prediction and control.
Bastien, Renaud; Meroz, Yasmine
2016-01-01
Nutation is an oscillatory movement that plants display during their development. Despite its ubiquity among plants movements, the relation between the observed movement and the underlying biological mechanisms remains unclear. Here we show that the kinematics of the full organ in 3D give a simple picture of plant nutation, where the orientation of the curvature along the main axis of the organ aligns with the direction of maximal differential growth. Within this framework we reexamine the validity of widely used experimental measurements of the apical tip as markers of growth dynamics. We show that though this relation is correct under certain conditions, it does not generally hold, and is not sufficient to uncover the specific role of each mechanism. As an example we re-interpret previously measured experimental observations using our model. PMID:27923062
NASA Technical Reports Server (NTRS)
Buffett, B. A.; Mathews, P. M.; Herring, T. A.; Shapiro, I. I.
1993-01-01
We determine the deformation produced by the lunisolar tidal potential in a rotating, spheroidal model Earth. We proceed by decomposing the equations of motion into separate, though coupled, equations for the nutational and deformational parts of the Earth's response. Using this scheme, we derive a simpler set of equations for the deformational displacements, where the driving forces include not only the tidal terms but also inertial forces and gravitational perturbations associated with the nutational motions. We show that the deformations are affected only to a very small extent by the Earth's asphericity and rotation. This fact is exploited to set up a perturbative procedure, whereby the equation governing the deformation is separated into equations of zeroth and first orders in the perturbation.
NASA Astrophysics Data System (ADS)
Escapa, Alberto; Ferrándiz, José M.; Baenas, Tomás; Getino, Juan; Navarro, Juan F.; Belda-Palazón, Santiago
2016-03-01
The complexity of the modeling of the rotational motion of the Earth in space has produced that no single theory has been adopted to describe it in full. Hence, it is customary using at least a theory for precession and another one for nutation. The classic approach proceeds by deriving some of the fundamental parameters from the precession theory, like, e.g., the dynamical ellipticity Hd, and then using those values in the nutation theory. The former IAU 1976 precession and IAU 1980 nutation theories followed that scheme. Along with the improvement of the accuracy of the determination of Earth orientation parameters, IAU 1980 was superseded by IAU2000, based on the application of the MHB2000 transfer function to the previous rigid Earth analytical theory REN2000. The latter was derived while the precession model IAU 1976 was still in force, therefore it used the corresponding values for some of the fundamental parameters, as the precession rate, associated to the dynamical ellipticity. The new precession model P03 was adopted as IAU 2006. That change introduced some inconsistency since P03 used different values for some of the fundamental parameters that MHB2000 inherited from REN2000. Besides, the derivation of the basic Earth parameters of MHB2000 itself comprised a fitted variation of the dynamical ellipticity adopted in the background rigid theory. Due to the strict requirements of accuracy of the present and coming times, the magnitude of the inconsistencies originated by this twofold approach is no longer negligible as earlier, hence the need of discussing the effects of considering slightly different values for H_d in precession and nutation theories.
NASA Astrophysics Data System (ADS)
Dumberry, M.; Koot, L.
2010-12-01
The nutations are daily variations in the Earth's rotation caused by the torque that the Moon, the Sun and, to a lesser extent, other planets exert on the equatorial bulge. In this motion, the mantle, fluid core and inner core are in slight differential rotation. This is both because they would, in isolation, react differently to the imposed torque, and also because the forced nutations excite free rotational modes characterized by differential rotation. The overall nutational response of the Earth depends then on the coupling between its internal regions. In particular, a coupling of a dissipative nature is required in order to match observations. One possibility is electromagnetic coupling at the inner and outer core boundaries and in this work, we take a fresh look at this hypothesis. Existing models are based on a local approach, in which the amplitude of the secondary toroidal magnetic field at a point on the core surface is directly proportional to the amplitude of the local background radial magnetic field. However, this cannot be the case everywhere because toroidal magnetic field lines must form closed loops on spherical surfaces. We show that taking this into account in a global approach reduces the amplitude of the toroidal torque by a factor 2. We also show that the poloidal part of the torque, previously neglected, is approximately equal in amplitude to the toroidal torque. In the weak-field approximation (when the feedback from the Lorentz force can be neglected in the computation of the coupling), these two effects result in an overall electromagnetic torque that is not very different from previous estimates. However, a larger discrepancy is found when Lorentz forces are important. In particular a weaker field at the inner core boundary is required to explain the nutation observations.
Resistor-damped electromechanical lever blocks
NASA Astrophysics Data System (ADS)
Zago, Lorenzo; Genequand, Pierre M.; Kjelberg, Ivar
1998-06-01
The paper presents an innovative technical solution which provides a combined damping and isolation interface with the appropriate transmissibility characteristics between a vibrating base and a sensitive payload, typically an optical terminal/telescope. The novelty of the solution is primarily found in the implementation of uncoupling and magnification of the incurred vibrations by means of flexures combined with the implementation of energy dissipation by means of a linear electro-magnetic actuator to constitute a passive integrated resistor-damped electromechanic lever block. By means of frictionless flexible lever systems, the amplitude of the payload vibrations is adapted to the optimal range of the actuator with a magnification by a factor ranging typically between 10 and 30. Passive viscous damping is obtained by simply short-circuiting the electro-magnetic motor and can be adapted by setting the impedance of the shorting connection. The desired stiffness is provided by the passive springs of the elastic motor suspension and by the stiffness of the lever flexure blades. The mobile mass of the motors also provide a reaction mass which, like damping and stiffness, is amplified by the square of the lever factor. A theoretical model of resistor-damped electromechanical lever blocks has been established. A particular property is it the good attenuation of excited vibrations only over a set frequency range. Above this range the interface properties rejoin the ones of a rigid connection. This performance makes this type of isolators particularly suitable for integration into multi-layer vibration control systems where sensitive equipment is protected by a mix of passive and active damping/isolation devices acting optimally at different frequency ranges. Experiments performed with a dummy load (80 Kg) representative of a satellite based optical terminal demonstrated the efficiency of the system in protecting the payload by passive damping for vibration excitations
NASA Technical Reports Server (NTRS)
Weddendorf, Bruce
1993-01-01
Self-damping sprung wheel provides shock-absorbing suspension for wheelchair, reducing user's discomfort when traversing rough terrain or obstacles. Pair of self-damping sprung wheels installed in place of conventional large rear wheels of standard wheelchair, which user operates in conventional manner. Rim deflects in vicinity of contact with ground or floor. Includes inner and outer hoops bending when obstacle encountered. Shear deformation of elastomeric hoop between them absorbs energy. Thus, three hoops act together as damping spring. Alternative version of wheel designed for bicycle.
Bearing-Cartridge Damping Seal
NASA Technical Reports Server (NTRS)
Goggins, David G.; Scharrer, Joseph K.; Chen, Wei C.
1991-01-01
In proposed design for improved ball-bearing cartridge, damping seal in form of thin-layer fluid journal bearing incorporated into cartridge. Damping seal acts as auxiliary bearing, relieving bearing balls of significant portions of both static and dynamic bearing loads. Damping from seal reduces dynamic loads even further by reducing amplitude of vibrations in second vibrational mode of rotor, which mode occurs when rotor turning at nearly full operating speed. Intended for use in high-pressure-oxygen turbopump of Space Shuttle main engine, also applicable to other turbomachinery bearings.
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.
A quantum description of radiation damping and the free induction signal in magnetic resonance
Tropp, James
2013-07-07
We apply the methods of cavity quantum electrodynamics (CQED), to obtain a microscopic and fully quantum-mechanical picture of radiation damping in magnetic resonance, and the nascent formation of the free induction signal. Numerical solution of the Tavis-Cummings model - i.e., multiple spins 1/2 coupled to a lossless single-mode cavity - shows in fine detail the transfer of Zeeman energy, via spin coherence, to excite the cavity - represented here by a quantized LC resonator. The case of a single spin is also solved analytically. Although the motion of the Bloch vector is non-classical, we nonetheless show that the quantum mechanical Rabi nutation frequency (as enhanced by cavity coupling and stimulated emission) gives realistic estimates of macroscopic signal strength and the radiation damping constant in nuclear magnetic resonance. We also show how to introduce dissipation: cavity losses by means of a master equation, and relaxation by the phenomenological method of Bloch. The failure to obtain the full Bloch equations (unless semi-classical conditions are imposed on the cavity) is discussed in light of similar issues arising in CQED (and in earlier work in magnetic resonance as well), as are certain problems relative to quantization of the electromagnetic near-field.
A quantum description of radiation damping and the free induction signal in magnetic resonance.
Tropp, James
2013-07-07
We apply the methods of cavity quantum electrodynamics (CQED), to obtain a microscopic and fully quantum-mechanical picture of radiation damping in magnetic resonance, and the nascent formation of the free induction signal. Numerical solution of the Tavis-Cummings model - i.e., multiple spins 1∕2 coupled to a lossless single-mode cavity - shows in fine detail the transfer of Zeeman energy, via spin coherence, to excite the cavity - represented here by a quantized LC resonator. The case of a single spin is also solved analytically. Although the motion of the Bloch vector is non-classical, we nonetheless show that the quantum mechanical Rabi nutation frequency (as enhanced by cavity coupling and stimulated emission) gives realistic estimates of macroscopic signal strength and the radiation damping constant in nuclear magnetic resonance. We also show how to introduce dissipation: cavity losses by means of a master equation, and relaxation by the phenomenological method of Bloch. The failure to obtain the full Bloch equations (unless semi-classical conditions are imposed on the cavity) is discussed in light of similar issues arising in CQED (and in earlier work in magnetic resonance as well), as are certain problems relative to quantization of the electromagnetic near-field.
Electrorheologically damped impact system
NASA Astrophysics Data System (ADS)
Hardt, Lee R.
1991-05-01
An impact switch is described having a housing containing a rigid coaxial conductor entering one end. An inner cylindrical contact extends axially inward from and beyond the in housing end of an outer tubular contact which has a spiral spring extending axially from within a recess therein. The free end of the spring supports a mass spaced from the end of the inner contact. The contacts, spring and mass are enclosed within a flexible shroud spaced from the inner wall of the housing. The space between the shroud and housing contains an electrorheological fluid, the viscosity of which is a function of the voltage supplied by two electrodes extending through the housing and into the fluid. The voltage controlled viscosity permits control of damping of the shroud, mass, and spring movements in response to impact caused switch deceleration and control of time for switch closure and fuze delay by means of mass contact with the inner cylindrical contact, or spring contact with the outer tubular contact.
Landau damping in space plasmas
NASA Technical Reports Server (NTRS)
Thorne, Richard M.; Summers, Danny
1991-01-01
The Landau damping of electrostatic Langmuir waves and ion-acoustic waves in a hot, isotropic, nonmagnetized, generalized Lorentzian plasma is analyzed using the modified plasma dispersion function. Numerical solutions for the real and imaginary parts of the wave frequency omega sub 0 - (i)(gamma) have been obtained as a function of the normalized wave number (k)(lambda sub D), where lambda sub D is the electron Debye length. For both particle distributions the electrostatic modes are found to be strongly damped at short wavelengths. At long wavelengths, this damping becomes less severe, but the attenuation of Langmuir waves is much stronger for a generalized Lorentzian plasma than for a Maxwellian plasma. It is concluded that Landau damping of ion-acoustic waves is only slightly affected by the presence of a high energy tail, but is strongly dependent on the ion temperature.
Damping measurements using operational data
James, G.H.; Carne, T.G.; Veers, P.S.
1991-01-01
We have measured modal damping using strain-gauge data from an operating wind turbine. Previously, such measurements were difficult and expensive. Auto-correlation and cross-correlation functions of the strain-gauge data have been shown to consist of decaying sinusoids which correspond to the modal frequencies and damping ratios of the wind turbine. We have verified the method by extracting damping values from an analytically generated data set. Actual operating response data from the DOE/Sandia 34-meter Test Bed has been used to calculate modal damping ratios as a function of rotor rotation rate. This capability will allow more accurate fatigue life prediction and control. 16 refs., 3 figs., 2 tabs.
NASA Technical Reports Server (NTRS)
Zhu, S. Y.; Mueller, I. I.
1982-01-01
The effects of adopting new definitive precession and equinox corrections on the terrestrial reference frame was investigated. It is noted that: (1) the effect on polar motion is a diurnal periodic term with an amplitude increasing linearly in time whole on UT1 it is a linear term; (2) general principles are given to determine the effects of small rotations of the frame of a conventional inertial reference system (CIS) on the frame of the conventional terrestrial reference system (CTS); (3) seven CTS options are presented, one of which is necessary to accommodate such rotation. Accommodating possible future changes in the astronomical nutation is discussed. The effects of differences which may exist between the various CTS's and CIS's on Earth rotation parameters (ERP) and how these differences can be determined are examined. It is shown that the CTS differences can be determined from observations made at the same site, while the CIS differences by comparing the ERP's determined by the different techniques during the same time period.
Triaxial Earth's rotation: Chandler wobble, free core nutation and diurnal polar motion (Abstract)
NASA Astrophysics Data System (ADS)
Sun, R.; Shen, W.-B.
2015-08-01
In this study, we formulate two-layered triaxial Earth rotation theory, focusing on the influence of the triaxiality on the Chandler wobble (CW), free core nutation (FCN) and diurnal polar motion. We estimate the frequencies of the normal modes CW and FCN, and results show that though the influence of two-layer triaxiality on the CW and FCN frequencies are very small, there appear some new natures. The response of the Earth's polar motion to the excitation consists of two parts. One is in response to the same frequency excitation and the other is in response to the opposite frequency excitation. For an Earth model with triaxial mantle and core, both of these two parts have four resonant frequencies rather than two that are suggested by rotational symmetric Earth model. However, due to the small strength of these new resonances, the effects of these resonances are only significant when the excitation frequencies are very near to these resonance frequencies. In addition, compared to the biaxial case, the influences of the triaxiality on the prograde and retrograde diurnal polar motions excited by ocean tide component K1 are estimated as - 1.4 μas and - 0.9 μas respectively, which should be taken into account in theory. This study is supported by National 973 Project China (grant No. 2013CB733305), NSFC (grant Nos. 41174011, 41210006, 41128003, 41021061).
Determination of nutation offsets by combining VLBI/GPS-produced normal equations
NASA Astrophysics Data System (ADS)
Kudryashova, Maria; Lambert, Sebastien; Dehant, Veronique; Bruyninx, Carine
2010-05-01
Longstanding routing operation of individual geodetic space- and ground-based techniques (like, for instance, VLBI, GNSS, LLR, etc.) revealed their strong and weak aspects. More effective use of these strengths as well as reduction of their weaknesses is possible by incorporating of the information collected by each individual technique into combined products. Such a consistent combination can be performed either by combination at the observational level or at the level of normal equations. We concentrate on the combination of normal equations gathered during VLBI/GPS-data processing. The main goal of this combination is to construct a time series of nutation offsets in the most consistent way. The objective of this presentation is to describe the developed strategy of combination and to present the current status of tits implementation. For the purpose of step-by-step validation of our procedure we use two-month-long time series of normal equations produced from VLBI and GPS observations by means of CALC/SOLVE and BERNESE v.5.0 software, respectively. Earth orientation parameter determination will, in our procedure, benefit from angle and rate observation for a unique estimation.
Driben, R.; Konotop, V. V.; Meier, T.
2016-01-01
Nonlinearity is the driving force for numerous important effects in nature typically showing transitions between different regimes, regular, chaotic or catastrophic behavior. Localized nonlinear modes have been the focus of intense research in areas such as fluid and gas dynamics, photonics, atomic and solid state physics etc. Due to the richness of the behavior of nonlinear systems and due to the severe numerical demands of accurate three-dimensional (3D) numerical simulations presently only little knowledge is available on the dynamics of complex nonlinear modes in 3D. Here, we investigate the dynamics of 3D non-coaxial matter wave vortices that are trapped in a parabolic potential and interact via a repulsive nonlinearity. Our numerical simulations demonstrate the existence of an unexpected and fascinating nonlinear regime that starts immediately when the nonlinearity is switched-on and is characterized by a smooth dynamics representing torque-free precession with nutations. The reported motion is proven to be robust regarding various effects such as the number of particles, dissipation and trap deformations and thus should be observable in suitably designed experiments. Since our theoretical approach, i.e., coupled nonlinear Schrödinger equations, is quite generic, we expect that the obtained novel dynamical behavior should also exist in other nonlinear systems. PMID:26964759
Nonlinear and detuning effects of the nutation angle in precessionally forced rotating cylinder flow
NASA Astrophysics Data System (ADS)
Lopez, Juan M.; Marques, Francisco
2016-06-01
The flow in a rapidly rotating cylinder forced to precess through a nutation angle α is investigated numerically, keeping all parameters constant except α , and tuned to a triadic resonance at α =1∘ . When increasing α , the flow undergoes a sequence of well-characterized bifurcations associated with triadic resonance, involving heteroclinic and homoclinic cycles, for α up to about 4∘. For larger α , we identify two chaotic regimes. In the first regime, with α between about 4∘ and 27∘, the bulk flow retains remnants of the helical structures associated with the triadic resonance, but there are strong nonlinear interactions between the various azimuthal Fourier components of the flow. For the larger α regime, large detuning effects lead to the triadic resonance dynamics being completely swamped by boundary layer eruptions. The azimuthal mean flow at large angles results in a large mean deviation from solid-body rotation and the flow is characterized by strong shear at the boundary layers with temporally chaotic eruptions.
Simple suppression of radiation damping.
Khitrin, A K; Jerschow, Alexej
2012-12-01
Radiation damping is known to cause line-broadening and frequency shifts of strong resonances in NMR spectra. While several techniques exist for the suppression of these effects, many require specialized hardware, or are only compatible with the presence of few strong resonances. We describe a simple pulse sequence for radiation damping suppression in spectra with many strong resonances. The sequence can be used as-is to generate simple spectra or as a signal excitation part in more advanced experiments.
Turbomachinery rotor support with damping
NASA Technical Reports Server (NTRS)
Vonpragenau, George L. (Inventor)
1990-01-01
Damping seals, damping bearings, and a support sleeve are presented for the ball bearings of a high speed rotor. The ball bearings consist of a duplex set having the outer races packaged tightly within the sleeve while the sleeve provides a gap with a support member so that the bearings may float with the sleeve. The sleeve has a web extending radially between the pair of outer races and acts in conjunction with one or more springs to apply an axial preload to the outer races. The sleeves have a series of slits which provide the sleeve with a spring-like quality so that the spring acts to center the rotor upon which the bearings are mounted during start up and shut down. A damping seal or a damping bearing may be used in conjunction with the ball bearings and supporting sleeve, the damping seal and damping bearing having rotor portions including rigid outer surfaces mounted within the bore of a stator portion having triangular shaped pockets on the surface facing the rotor. Axial gates are provided between adjacent pockets in sections of the stator permitting fluid to flow with less resistance axially relative to the flow of fluids circumferentially between the rotor and the stator.
Damping characterization in large structures
NASA Technical Reports Server (NTRS)
Eke, Fidelis O.; Eke, Estelle M.
1991-01-01
This research project has as its main goal the development of methods for selecting the damping characteristics of components of a large structure or multibody system, in such a way as to produce some desired system damping characteristics. The main need for such an analytical device is in the simulation of the dynamics of multibody systems consisting, at least partially, of flexible components. The reason for this need is that all existing simulation codes for multibody systems require component-by-component characterization of complex systems, whereas requirements (including damping) often appear at the overall system level. The main goal was met in large part by the development of a method that will in fact synthesize component damping matrices from a given system damping matrix. The restrictions to the method are that the desired system damping matrix must be diagonal (which is almost always the case) and that interbody connections must be by simple hinges. In addition to the technical outcome, this project contributed positively to the educational and research infrastructure of Tuskegee University - a Historically Black Institution.
The effect of mechanical damping loads on disabling action tremor.
Aisen, M L; Arnold, A; Baiges, I; Maxwell, S; Rosen, M
1993-07-01
Patients with severe action tremor have uncontrollable, relatively rapid oscillatory motion super-imposed on otherwise useable slower voluntary motor activity. Because a mechanical damper produces an opposing force proportional to velocity, applying damping loads to tremorous limbs should attenuate the (high-velocity) tremor component of movement while permitting the slower purposeful portion to proceed relatively unopposed. In this study, the effect of upper extremity damping in three degrees of freedom was examined in 10 patients with cerebellar action tremor due to multiple sclerosis or traumatic brain injury. Variable amounts of damping were applied by prototype energy-dissipating orthoses which generated resistive viscous loads by means of computer-controlled magnetic particle brakes. All patients experienced statistically and functionally significant tremor reduction with the application of damping.
Damping mechanisms of a pendulum
NASA Astrophysics Data System (ADS)
Dolfo, Gilles; Castex, Daniel; Vigué, Jacques
2016-11-01
In this paper, we study the damping mechanisms of a pendulum. The originality of our setup is the use of a metal strip suspension and the development of extremely sensitive electric measurements of the pendulum velocity and position. Their sensitivity is absolutely necessary for a reliable measurement of the pendulum damping time constant because this measurement is possible only for very low oscillation amplitudes, when air friction forces quadratic in velocity have a negligible contribution to the observed damping. We have thus carefully studied damping by air friction forces, which is the dominant mechanism for large values of the Reynolds number Re but which is negligible in the Stokes regime, {Re} ∼ 1. In this last case, we have found that the dominant damping is due to internal friction in the metal strip, a universal effect called anelasticity, and, for certain frequencies, to resonant coupling to the support of the pendulum. All our measurements are well explained by theory. We believe this paper would be of interest to students in an undergraduate classical mechanics course.
NASA Astrophysics Data System (ADS)
Vitzthum, Veronika; Caporini, Marc A.; Ulzega, Simone; Trébosc, Julien; Lafon, Olivier; Amoureux, Jean-Paul; Bodenhausen, Geoffrey
2012-10-01
In solids that are spinning about the magic angle, trains of short pulses in the manner of Delays Alternating with Nutations for Tailored Excitation (DANTE) allow one to improve the efficiency of the excitation of magnetization compared to rectangular pulses. By interleaving N pulse trains with N > 1, one obtains 'DANTE-N' sequences comprising N pulses per rotor period that extend over K rotor periods. Optimized interleaved DANTE schemes with N > 1 are shorter than basic DANTE-1 sequences with N = 1. Therefore, they are less affected by coherent or incoherent decays, thus leading to higher signal intensities than can be obtained with basic DANTE-1 or with rectangular pulses. Furthermore, the shorter length of DANTE-N with N > 1 increases the width of the spikelets in the excitation profile, allowing one to cover the range of isotropic chemical shifts and second-order quadrupolar effects typical for side-chain and backbone amide 14N sites in peptides at B0 = 18.8 T. In DANTE-N, spinning sidebands only appear at multiples of the spinning frequency νrot, as if the samples were rotating at Nνrot. We show applications to direct detection of nitrogen-14 nuclei with spin I = 1 subject to large quadrupole interactions, using fast magic angle spinning (typically νrot ⩾ 60 kHz), backed up by simulations that provide insight into the properties of basic and interleaved DANTE sequences. When used for indirect detection, we show by numerical simulations that even basic DANTE-1 sequences can lead to a four-fold boost of efficiency compared to standard rectangular pulses.
Vitzthum, Veronika; Caporini, Marc A; Ulzega, Simone; Trébosc, Julien; Lafon, Olivier; Amoureux, Jean-Paul; Bodenhausen, Geoffrey
2012-10-01
In solids that are spinning about the magic angle, trains of short pulses in the manner of Delays Alternating with Nutations for Tailored Excitation (DANTE) allow one to improve the efficiency of the excitation of magnetization compared to rectangular pulses. By interleaving N pulse trains with N>1, one obtains 'DANTE-N' sequences comprising N pulses per rotor period that extend over K rotor periods. Optimized interleaved DANTE schemes with N>1 are shorter than basic DANTE-1 sequences with N=1. Therefore, they are less affected by coherent or incoherent decays, thus leading to higher signal intensities than can be obtained with basic DANTE-1 or with rectangular pulses. Furthermore, the shorter length of DANTE-N with N>1 increases the width of the spikelets in the excitation profile, allowing one to cover the range of isotropic chemical shifts and second-order quadrupolar effects typical for side-chain and backbone amide (14)N sites in peptides at B(0)=18.8 T. In DANTE-N, spinning sidebands only appear at multiples of the spinning frequency ν(rot), as if the samples were rotating at Nν(rot). We show applications to direct detection of nitrogen-14 nuclei with spin I=1 subject to large quadrupole interactions, using fast magic angle spinning (typically ν(rot)≥60 kHz), backed up by simulations that provide insight into the properties of basic and interleaved DANTE sequences. When used for indirect detection, we show by numerical simulations that even basic DANTE-1 sequences can lead to a four-fold boost of efficiency compared to standard rectangular pulses.
Damping filter method for obtaining spatially localized solutions.
Teramura, Toshiki; Toh, Sadayoshi
2014-05-01
Spatially localized structures are key components of turbulence and other spatiotemporally chaotic systems. From a dynamical systems viewpoint, it is desirable to obtain corresponding exact solutions, though their existence is not guaranteed. A damping filter method is introduced to obtain variously localized solutions and adapted in two typical cases. This method introduces a spatially selective damping effect to make a good guess at the exact solution, and we can obtain an exact solution through a continuation with the damping amplitude. The first target is a steady solution to the Swift-Hohenberg equation, which is a representative of bistable systems in which localized solutions coexist and a model for spanwise-localized cases. Not only solutions belonging to the well-known snaking branches but also those belonging to isolated branches known as "isolas" are found with continuation paths between them in phase space extended with the damping amplitude. This indicates that this spatially selective excitation mechanism has an advantage in searching spatially localized solutions. The second target is a spatially localized traveling-wave solution to the Kuramoto-Sivashinsky equation, which is a model for streamwise-localized cases. Since the spatially selective damping effect breaks Galilean and translational invariances, the propagation velocity cannot be determined uniquely while the damping is active, and a singularity arises when these invariances are recovered. We demonstrate that this singularity can be avoided by imposing a simple condition, and a localized traveling-wave solution is obtained with a specific propagation speed.
Increased damping in irregular resonators
NASA Astrophysics Data System (ADS)
Sapoval, Bernard; Asch, Mark; Felix, Simon; Filoche, Marcel
2005-04-01
The relation between shape and damping of shallow acoustical cavities has been studied numerically in the case where the dissipation occurs only on the cavity walls. It is first found that whatever the type of geometrical irregularity, many, but not all the modes are localized. It is shown that the localization mechanism is what is called weak localization. The more irregular, the smaller the quality factors are found. However this effect is very different for the non-localized and the localized modes. For non-localized modes the damping increases roughly proportionally to the cavity surface. The localized modes are even more damped. These results generalize the results already obtained both numerically and experimentally on prefractal acoustical cavities. [B. Sapoval, O. Haeberle, and S. Russ, J. Acoust. Soc. Am. 102, 2014-2019 (1997); B. Hebert, B. Sapoval, and S. Russ, ibid. 105, 1567-1576 (1999)].
Increased damping of irregular resonators.
Russ, S; Sapoval, B
2002-03-01
It is shown that fractal drums and jagged geometry resonators may be more damped than ordinary Euclidean systems. Several damping mechanisms are examined and studied by numerical calculations. The results depend on the dissipation mechanisms but globally they increase with localization, frequency, and the irregularity of the resonator. The increased dissipation is due to the uneven spatial distribution of the vibrational amplitude in two different ways. First, it is related to the partial confinement of the vibrational modes. Secondly, increased dissipation may be due to singularities in the amplitude distribution. This is the case when a few points exist where the vibration is pinned to zero inducing local logarithmic singularities. This last effect can be spectacular: a single defect can dominate the surface damping by viscous forces of a square drum.
Landau damping of auroral hiss
NASA Technical Reports Server (NTRS)
Morgan, D. D.; Gurnett, D. A.; Menietti, J. D.; Winningham, J. D.; Burch, J. L.
1994-01-01
Auroral hiss is observed to propagate over distances comparable to an Earth radius from its source in the auroral oval. The role of Landau damping is investigated for upward propagating auroral hiss. By using a ray tracing code and a simplified model of the distribution function, the effect of Landau damping is calculated for auroral hiss propagation through the environment around the auroral oval. Landau damping is found to be the likely mechanism for explaining some of the one-sided auroral hiss funnels observed by Dynamics Explorer 1. It is also found that Landau damping puts a lower limit on the wavelength of auroral hiss. Poleward of the auroral oval, Landau damping is found in a typical case to limit omega/k(sub parallel) to values of 3.4 x 10(exp 4) km/s or greater, corresponding to resonance energies of 3.2 keV or greater and wavelengths of 2 km or greater. For equatorward propagation, omega/k(sub parallel) is limited to values greater than 6.8 x 10(exp 4) km/s, corresponding to resonance energies greater than 13 keV and wavelengths greater than 3 km. Independent estimates based on measured ratios of the magnetic to electric field intensity also show that omega/k(sub parallel) corresponds to resonance energies greater than 1 keV and wavelengths greater than 1 km. These results lead to the difficulty that upgoing electron beams sufficiently energetic to directly generate auroral hiss of the inferred wavelength are not usually observed. A partial transmission mechanism utilizing density discontinuities oblique to the magnetic field is proposed for converting auroral hiss to wavelengths long enough to avoid damping of the wave over long distances. Numerous reflections of the wave in an upwardly flared density cavity could convert waves to significantly increased wavelengths and resonance velocities.
Kobori, Nilce N; Mascarin, Gabriel M; Jackson, Mark A; Schisler, David A
2015-04-01
Media and culturing protocols were identified that supported the formation of submerged conidia and microsclerotia (MS) by Trichoderma harzianum Rifai strain T-22 using liquid culture fermentation. Liquid media with a higher carbon concentration (36 g L(-1)) promoted MS formation at all C:N ratios tested. Hyphae aggregated to form MS after 2 d growth and after 7 d MS were fully melanized. This is the first report of MS formation by T. harzianum or any species of Trichoderma. Furthermore, submerged conidia formation was induced by liquid culture media, but yields, desiccation tolerance, and storage stability varied with C:N ratio and carbon rate. Air-dried MS granules (<4% moisture) retained excellent shelf life under cool and unrefrigerated storage conditions with no loss in conidial production. A low-cost complex nitrogen source based on cottonseed flour effectively supported high MS yields. Amending potting mix with dried MS formulations reduced or eliminated damping-off of melon seedlings caused by Rhizoctonia solani. Together, the results provide insights into the liquid culture production, stabilization process, and bioefficacy of the hitherto unreported MS of T. harzianum as a potential biofungicide for use in integrated management programs against soilborne diseases.
Anand, V; Narendran, R
2016-09-01
In this paper, a technique for estimation of state variables and control of a class of electromechanical system is proposed. Initially, an attempt is made on rudimentary pole placement technique for the control of rotor position and angular velocity profiles of Permanent Magnet Stepper Motor. Later, an alternative approach is analyzed using feedback linearization method to reduce the error in tracking performances. A damping control scheme was additionally incorporated into the feedback linearization system in order to nullify the persistent oscillations present in the system. Furthermore, a robust backstepping controller with high efficacy is put forth to enhance the overall performance and to carry out disturbance rejection. The predominant advantage of this control technique is that it does not require the DQ Transformation of the motor dynamics. A Lyapunov candidate was employed to ensure global asymptotical stability criterion. Also, a nonlinear observer is presented to estimate the unknown states namely load torque and rotor angular velocity, even under load uncertainty conditions. Finally, the performances of all the aforementioned control schemes and estimation techniques are compared and analyzed extensively through simulation.
Estimation of the free core nutation period by the sliding-window complex least-squares fit method
NASA Astrophysics Data System (ADS)
Zhou, Yonghong; Zhu, Qiang; Salstein, David A.; Xu, Xueqing; Shi, Si; Liao, Xinhao
2016-05-01
Estimation of the free core nutation (FCN) period is a challenging prospect. Mostly, two methods, one direct and one indirect, have been applied in the past to address the problem by analyzing the Earth orientation parameters observed by the very long baseline interferometry. The indirect method estimates the FCN period from resonance effects of the FCN on forced nutation terms, whereas the direct method estimates the FCN period using the Fourier Transform (FT) approach. However, the FCN period estimated by the direct FT technique suffers from the non-stationary characteristics of celestial pole offsets (CPO). In this study, the FCN period is estimated by another direct method, i.e., the sliding-window complex least-squares fit method (SCLF). The estimated values of the FCN period for the full set of 1984.0-2014.0 and four subsets (1984.0-2000.0, 2000.0-2014.0, 1984.0-1990.0, 1990.0-2014.0) range from -428.8 to -434.3 mean solar days. From the FT to the SCLF method, the estimate uncertainty of the FCN period falls from several tens of days to several days. Thus, the SCLF method may serve as an independent direct way to estimate the FCN period, complementing and validating the indirect resonance method that has been frequently used before.
Vibration Damping Circuit Card Assembly
NASA Technical Reports Server (NTRS)
Hunt, Ronald Allen (Inventor)
2016-01-01
A vibration damping circuit card assembly includes a populated circuit card having a mass M. A closed metal container is coupled to a surface of the populated circuit card at approximately a geometric center of the populated circuit card. Tungsten balls fill approximately 90% of the metal container with a collective mass of the tungsten balls being approximately (0.07) M.
Surfactant damping of water waves
NASA Astrophysics Data System (ADS)
Lapham, Gary S.; Dowling, David R.; Schultz, William W.
1997-11-01
The most well known and perhaps most important distinguishing characteristic of a water surface laden with surfactant is the profound increase in small-wave damping with the addition of even small amounts of surfactant material. It would seem to follow that damping increases with increasing surfactant concentration. This is undoubtedly true for some surfactants, however our experiments with a soluble surfactant show that it is possible to increase surfactant concentration and measure a decrease in damping. While the increased concentration is accompanied by a dramatic decrease in measured static surface tension, some of the capillary-wave frequency regime is less damped. Experimental measurements of the real and imaginary parts of the wave speed are compared with existing theory where at least one other physical quantity besides surface tension is needed to properly model the interface. Our on-going work with insoluble surfactants may also provide an example of this type of behavior for materials that do not readily transfer to and from the bulk water. [Supported by the Office of Naval Research
Technology Transfer Automated Retrieval System (TEKTRAN)
Damping-off is a common disease that rots and kills both seeds and recently germinated seedlings. The disease is caused by number of different soilborne pathogens, including true fungi (Botrytis, Fusarium, and Rhizoctonia species) and oomycetes (Phytophthora and Pythium species). The seedlings of mo...
Damped Oscillator with Delta-Kicked Frequency
NASA Technical Reports Server (NTRS)
Manko, O. V.
1996-01-01
Exact solutions of the Schrodinger equation for quantum damped oscillator subject to frequency delta-kick describing squeezed states are obtained. The cases of strong, intermediate, and weak damping are investigated.
Squeezed states of damped oscillator chain
NASA Technical Reports Server (NTRS)
Manko, O. V.
1993-01-01
The Caldirola-Kanai model of one-dimensional damped oscillator is extended to the chain of coupled parametric oscillators with damping. The correlated and squeezed states for the chain of coupled parametric oscillators with damping are constructed. Based on the concept of the integrals of motion, it is demonstrated how squeezing phenomenon arises due to parametric excitation.
Cocured damped layers in composite structure
Rotz, C.A. ); Barrett, D.J. )
1992-01-01
A study was made on the feasibility of laminating and cocuring graphite fiber-epoxy prepreg with plies of commercially available damping materials for form beams and hat-stiffened panels. Experiments showed that cocuring did not adversely affect the damping materials and that excellent structural damping properties could be obtained. The construction of the hat-stiffened panels proved that complex parts containing damping materials could be fabricated. Dynamic testing of these components showed that internal architectural features could be designed to promote damping in primary structure.
Pre-emergence Damping Off of Beta vulgaris by Rhizopus stolonifer
Technology Transfer Automated Retrieval System (TEKTRAN)
Rhizopus stolonifer (Rs), a cool temperature zygomycete that can cause a post-harvest rot on sugarbeet (Beta vulgaris), also causes pre-emergence damping off in other crops. We are interested in its potential pre-emergence damping off activity in sugarbeet. Sugarbeets are quite susceptible to seedli...
NASA Astrophysics Data System (ADS)
Koot, L.; Dumberry, M.
2011-12-01
Nutations are periodic variations in the orientation of the Earth's rotation axis in space. This motion is generated by the gravitational torque applied on the Earth's equatorial bulge by the Moon, the Sun, and the other planets. Because the mantle, the fluid outer core and the solid inner core react differently to the applied torque, the nutation motion is characterized by differential rotations between these three regions. Since the boundaries of the fluid outer core are permeated by a background magnetic field (the geodynamo field), the differential rotation at the fluid core boundaries induces a secondary magnetic field by shear and advection of the background field. The associated electric currents produce Lorentz forces and torques between the outer core, inner core, and mantle, that tend to oppose the differential rotation. A previous study has shown that the magnitude of the electromagnetic (EM) torque is mainly determined by the electrical conductivities on both sides of the outer core boundaries and by the mean RMS strength of the background magnetic field, with the spatial distribution of this magnetic field being unimportant to first order. The goal of the present work is to reassess the role of the magnetic field spatial distribution on the strength of the EM torque using a new model of the EM coupling for nutations that we have recently developed. Our model differs from previous ones in that we use a global approach to describe the induced magnetic field. Moreover, we also include in the torque the contribution from the poloidal component of the induced field, an effect neglected in previous models. In addition, we do not assume a priori that the non-dipolar components of the background magnetic field can be represented by a uniform field with the same power but instead we calculate the torque on the basis of the full geometry of the field. This is particularly important for the poloidal torque as it depends directly on the surface gradient of the
NASA Astrophysics Data System (ADS)
Han, Y. H.; Park, B. J.; Jung, S. Y.; Han, S. C.; Lee, W. R.; Bae, Y. C.
2013-02-01
A 35 kWh Superconductor Flywheel Energy Storage system (SFES) using hybrid bearing sets, which is composed of a high temperature superconductor (HTS) bearing and an active magnet damper (AMD), has been developed at KEPCO Research Institute (KEPRI). Damping is a source of energy loss but necessary for the stability of the flywheel system. We found that the damping of HTS bearings can be improved by thermal insulating bolts, which play a role of passive type external damper. To investigate the source of the increased damping, damping coefficients were measured with HTS bearings using insulating bolts made of three kinds of polymer materials. The damping coefficient was raised over 3000 N s/m in the case of PEEK bolts. The value was almost a quarter of the AMD. In this study, thermoelastic and Coulomb friction damping mechanisms are discussed. The main damping mechanism was the thermoelastic damping of the bolts themselves. And interfacial gap between the insulating bolt and metal chamber, which increased during the cooling process, was considered to be the cause of the anisotropic damping coefficients. Finally, the effects of the HTS bearings on the first critical speed are shown.
Radiation damping in real time.
Mendes, A C; Takakura, F I
2001-11-01
We study the nonequilibrium dynamics of a charge interacting with its own radiation, which originates the radiation damping. The real-time equation of motion for the charge and the associated Langevin equation is found in classical limit. The equation of motion for the charge allows one to obtain the frequency-dependent coefficient of friction. In the lowest order we find that although the coefficient of static friction vanishes, there is dynamical dissipation represented by a non-Markovian dissipative kernel.
Spin-Damping in an RF atomic magnetometer
NASA Astrophysics Data System (ADS)
Alem, Orang; Romalis, Michael V.; Sauer, Karen L.
2009-05-01
Optically pumped atomic magnetometers have demonstrated an improved sensitivity over standard tuned coils for frequencies less than 50 MHz, making these radio-frequency (RF) magnetometers attractive for low-field NMR (for example, Budker and Romalis, Nature Physics 3, April 2007). Such magnetometers are often plagued by transient effects resulting in decreased sensitivity. The decay time of these transients, or ringing, can last for milliseconds, which is particularly detrimental for rapidly decaying NMR signals. We have found that actively damping the ringing of the atomic spins can significantly reduce such dead time. This spin-damping of the atomic transients is achieved through a negative feedback mechanism in which part of the optical signal during ringing is used to apply an RF field forcing the realignment of the atomic spins with the static magnetic field. We have successfully implemented spin-damping in 100 μs and recovered our femto-Tesla signal previously obscured by the ringing.
Quantifying acoustic damping using flame chemiluminescence
NASA Astrophysics Data System (ADS)
Boujo, E.; Denisov, A.; Schuermans, B.; Noiray, N.
2016-12-01
Thermoacoustic instabilities in gas turbines and aeroengine combustors falls within the category of complex systems. They can be described phenomenologically using nonlinear stochastic differential equations, which constitute the grounds for output-only model-based system identification. It has been shown recently that one can extract the governing parameters of the instabilities, namely the linear growth rate and the nonlinear component of the thermoacoustic feedback, using dynamic pressure time series only. This is highly relevant for practical systems, which cannot be actively controlled due to a lack of cost-effective actuators. The thermoacoustic stability is given by the linear growth rate, which results from the combination of the acoustic damping and the coherent feedback from the flame. In this paper, it is shown that it is possible to quantify the acoustic damping of the system, and thus to separate its contribution to the linear growth rate from the one of the flame. This is achieved by post-processing in a simple way simultaneously acquired chemiluminescence and acoustic pressure data. It provides an additional approach to further unravel from observed time series the key mechanisms governing the system dynamics. This straightforward method is illustrated here using experimental data from a combustion chamber operated at several linearly stable and unstable operating conditions.
NASA Astrophysics Data System (ADS)
Lhotka, C.; Reimond, S.; Souchay, J.; Baur, O.
2016-02-01
The aim of this study is first to determine the gravity field of the comet 67P/Churyumov-Gerasimenko and second to derive the solar component of the precession rate and nutation coefficients of the spin-axis of the comet nucleus, i.e. without the direct, usually larger, effect of outgassing. The gravity field and related moments of inertia are obtained from two polyhedra, which are provided by the Optical, Spectroscopic, and Infrared Remote Imaging System (OSIRIS) and NAVigation CAMera (NAVCAM) experiments on Rosetta, and are based on the assumption of uniform density for the comet nucleus. We also calculate the forced precession rate as well as the nutation coefficients on the basis of Kinoshita's theory of rotation of the rigid Earth and adapted it to be able to indirectly include the effect of outgassing on the rotational parameters. The second degree denormalized Stokes coefficients of comet 67P/C-G turn out to be (bracketed numbers refer to second shape model) C20 ≃ -6.74 [-7.93] × 10-2, C22 ≃ 2.60 [2.71] × 10-2, consistent with normalized principal moments of inertia A/MR2 ≃ 0.13 [0.11], B/MR2 ≃ 0.23 [0.22], with polar moment c = C/MR2 ≃ 0.25, depending on the choice of the polyhedron model. The obliquity between the rotation axis and the mean orbit normal is ε ≃ 52°, and the precession rate only due to solar torques becomes dot{ψ }in [20,30] arcsec yr^{-1}. Oscillations in longitude caused by the gravitational pull of the Sun turn out to be of the order of Δψ ≃ 1 arcmin, and oscillations in obliquity can be estimated to be of the order of Δε ≃ 0.5 arcmin.
Nonlinear damping identification from transient data
NASA Astrophysics Data System (ADS)
Smith, Clifford B.; Wereley, Norman M.
1999-06-01
To study new damping augmentation methods for helicopter rotor systems, accurate and reliable nonlinear damping identification techniques are needed. For example, current studies on applications of magnetorheological (MR) dampers for rotor stability augmentation suggest that a strong Coulomb damping characteristic will be manifested as the field applied to the MR fluid is maximized. Therefore, in this work, a single degree of freedom (SDOF) system having either nonlinear Coulomb or quadratic damping is considered. This paper evaluates three analyses for identifying damping from transient test data; an FFT-based moving block analysis, an analysis based on a periodic Fourier series decomposition, and a Hilbert transform based technique. Analytical studies are used to determine the effects of block length, noise, and error in identified modal frequency on the accuracy of the identified damping level. The FFT-based moving block has unacceptable performance for systems with nonlinear damping. These problems were remedied in the Fourier series based analysis and acceptable performance is obtained for nonlinear damping identification from both this technique and the Hilbert transform based method. To more closely simulate a helicopter rotor system test, these techniques were then applied to a signal composed of two closely spaced modes. This data was developed to simulate a response containing the first lag and 1/rev modes. The primary mode of interest (simulated lag mode) had either Coulomb or quadratic damping, and the close mode (1/rev) was either undamped or had a specified viscous damping level. A comprehensive evaluation of the effects of close mode amplitude, frequency, and damping level was performed. A classifier was also developed to identify the dominant damping mechanism in a signal of 'unknown' composition. This classifier is based on the LMS error of a fit of the analytical envelope expression to the experimentally identified envelope signal. In most
NASA Astrophysics Data System (ADS)
Lam, Margaretha J.; Inman, Daniel J.; Saunders, William R.
2000-06-01
Viscoelastic materials (VEMs) are used to increase passive damping in structures. The damping capabilities of the VEM can be enhanced by attaching a constraining layer to the VEM. If this constraining layer is active, the treatment is called active constrained layer damping (ACLD). In the last few years, ACLD has proven to be superior in vibration control to active or passive damping. The active element allows for more effective vibration suppression than purely passive constrained layer damping. On the other hand, the VEM provides a fail-safe in case of breakdown of the active element that is not present for purely active control. It has been shown that the control effort needed to damp vibration using ACLD can be significantly higher than purely active control. In order to combine the inherent damping of passive control with the effectiveness of the active element, different variations of active, passive and hybrid damping are explored. Some of the variations included in this paper are passive constrained layer damping (PCLD) separate from the active element, but on the same side of beam and PCLD separate from the active element on the opposite side of the beam. The discretized system equations are obtained using the assumed modes method and Lagrange's equation. The damping is modeled using the Golla-Hughes-McTavish (GHM) method. This method adds `dissipation coordinates' to the structure in order to account for the damping present. These additional modes are eliminated using a reduction method, rendering the method more practical. A linear quadratic regulator and output feedback are used to actively control vibration.
ICAN/DAMP-integrated composite analyzer with damping analysis capabilities: User's manual
NASA Technical Reports Server (NTRS)
Saravanos, Dimitrious A.; Sanfeliz, Jose G.
1992-01-01
This manual describes the use of the computer code ICAN/DAMP (Integrated Composite Analyzer with Damping Analysis Capabilities) for the prediction of damping in polymer-matrix composites. The code is written in FORTRAN 77 and is a version of the ICAN (Integrated Composite ANalyzer) computer program. The code incorporates a new module for synthesizing the material damping from micromechanics to laminate level. Explicit micromechanics equations based on hysteretic damping are programmed relating the on-axis damping capacities to the fiber and matrix properties and fiber volume ratio. The damping capacities of unidirectional composites subjected to off-axis loading are synthesized from on-axis damping values. The hygrothermal effect on the damping performance of unidirectional composites caused by temperature and moisture variation is modeled along with the damping contributions from interfacial friction between broken fibers and matrix. The temperature rise is continuously vibrating composite plies and composite laminates is also estimated. The ICAN/DAMP user's manual provides descriptions of the damping analysis module's functions, structure, input requirements, output interpretation, and execution requirements. It only addresses the changes required to conduct the damping analysis and is used in conjunction with the 'Second Generation Integrated Composite Analyzer (ICAN) Computer Code' user's manual (NASA TP-3290).
Introduction to DAMPE event reconstruction (On behalf of DAMPE collaboration)
NASA Astrophysics Data System (ADS)
Zang, Jingjing
2016-07-01
The Dark Matter Particle Explorer (DAMPE) is a high energy particle physics experiment satellite, launched on 17 Dec 2015. To measure basic attributes of cosmic ray particles, DAMPE is equipped with four sub-detectors, BGO calorimeter (BGO), plastic scintillator detector (PSD), silicon tungsten tracker (STK) and neutron detector (NUD). On orbit, the high energy particle data are acquired and recorded by well-designed Data Acquisition system. After that, a series of elaborate event reconstruction algorithms are implemented to determine the energy, direction and particle ID of each event. The energy reconstruction algorithm firstly treats the sum of the BGO crystal energy as the overall energy estimator and various corrections are performed to calculate energy leakage from side and back of the calorimeter. The track reconstruction starts with cluster finding in STK, then shower axis of BGO and barycentre of clusters are used to extract seed of tracks. These seeds will be projected on the next layer by Kalman Filter method which will finally give location and direction of particle tracks. Based on shower development in BGO and tracks reconstructed by STK, we also combine data from PSD and NUD and developed a series of algorithms to evaluate particle's charge and identification. In this talk, we will describe technical strategies of event reconstruction and provide their basic performance.
Vitreous Enamel Damping Material Development.
1982-11-01
PROCEDURES 3 2.1. EXPERIMENTAL 3 2.1.1. GLASS PREPARATION 3 2.1.2. METHOD OF COATING APPLICATION 3 2.1.3. VIBRATION DAMPING MEASUREMENTS 3 2.2. CALCULATION OF...discussion in this report. fL 2 SECTION II TECHNICAL PROCEDURES 2.1 EXPERIMENTAL 2.1.1 Glass Preparation All of the compositions, except the standard...After heat treatments of composition "B", a- cristobalite and devitrite (Na20.3CaO-6SiO 2) appear as crystalline phases; a- cristobalite being the major
CHARACTERIZATION OF DAMPING IN BOLTED LAP JOINTS
C. MALONEY; D. PEAIRS; ET AL
2000-08-01
The dynamic response of a jointed beam was measured in laboratory experiments. The data were analyzed and the system was mathematically modeled to establish plausible representations of joint damping behavior. Damping is examined in an approximate, local linear framework using log decrement and half power bandwidth approaches. in addition, damping is modeled in a nonlinear framework using a hybrid surface irregularities model that employs a bristles-construct. Experimental and analytical results are presented.
Radiation damping in metal nanoparticle pairs.
Dahmen, Christian; Schmidt, Benjamin; von Plessen, Gero
2007-02-01
The radiation damping rate of plasmon resonances in pairs of spherical gold nanoparticles is calculated. The radiative line width of the plasmon resonance indicates significant far-field coupling between the nanoparticles over distances many times the particle diameter. The radiation damping of the coupled particle-plasmon mode alternates between superradiant and subradiant behavior when the particle spacing is varied. At small particle spacings where near-field coupling occurs, the radiation damping rate lies far below that of an isolated particle.
Hysteretic damping in rotordynamics: An equivalent formulation
NASA Astrophysics Data System (ADS)
Genta, Giancarlo; Amati, Nicola
2010-10-01
The hysteretic damping model cannot be applied to time domain dynamic simulations: this is a well-known feature that has been discussed in the literature since the time when analog computers were widespread. The constant equivalent damping often introduced to overcome this problem is also discussed, and its limitations are stated, in particular those linked with its application in rotordynamics to simulate rotating damping. An alternative model based on the nonviscous damping (NVD) model, but with a limited number of additional degrees of freedom, is proposed, and the relevant equations are derived. Some examples show applications to the rotordynamics field.
Viscous damped space structure for reduced jitter
NASA Technical Reports Server (NTRS)
Wilson, James F.; Davis, L. Porter
1987-01-01
A technique to provide modal vibration damping in high performance space structures was developed which uses less than one once of incompressible fluid. Up to 50 percent damping can be achieved which can reduce the settling times of the lowest structural mode by as much as 50 to 1. This concept allows the designers to reduce the weight of the structure while improving its dynamic performance. Damping by this technique is purely viscous and has been shown by test to be linear over 5 orders of input magnitude. Amplitudes as low as 0.2 microinch were demonstrated. Damping in the system is independent of stiffness and relatively insensitive to temperature.
Damping constant estimation in magnetoresistive readers
Stankiewicz, Andrzej Hernandez, Stephanie
2015-05-07
The damping constant is a key design parameter in magnetic reader design. Its value can be derived from bulk or sheet film ferromagnetic resonance (FMR) line width. However, dynamics of nanodevices is usually defined by presence of non-uniform modes. It triggers new damping mechanisms and produces stronger damping than expected from traditional FMR. This work proposes a device-level technique for damping evaluation, based on time-domain analysis of thermally excited stochastic oscillations. The signal is collected using a high bandwidth oscilloscope, by direct probing of a biased reader. Recorded waveforms may contain different noise signals, but free layer FMR is usually a dominating one. The autocorrelation function is a reflection of the damped oscillation curve, averaging out stochastic contributions. The damped oscillator formula is fitted to autocorrelation data, producing resonance frequency and damping constant values. Restricting lag range allows for mitigation of the impact of other phenomena (e.g., reader instability) on the damping constant. For a micromagnetically modeled reader, the technique proves to be much more accurate than the stochastic FMR line width approach. Application to actual reader waveforms yields a damping constant of ∼0.03.
Material Damping Experiments at Cryogenic Temperatures
NASA Technical Reports Server (NTRS)
Levine, Marie; White, Christopher
2003-01-01
A unique experimental facility has been designed to measure damping of materials at cryogenic temperatures. The test facility pays special attention to removing other sources of damping in the measurement by avoiding frictional interfaces, decoupling the test specimen from the support system, and by using a non-contacting measurement device; Damping data is obtained for materials (AI, GrEp, Be, Fused Quartz), strain amplitudes (less than 10-6 ppm), frequencies (20Hz-330Hz) and temperatures (20K-293K) relevant to future precision optical space missions. The test data shows a significant decrease in viscous damping at cryogenic temperatures and can be as low as 10-4%, but the amount of the damping decrease is a function of frequency and material. Contrary to the other materials whose damping monotonically decreased with temperature, damping of Fused Quartz increased substantially at cryo, after reaching a minimum at around l50 K. The damping is also shown to be insensitive to strain for low strain levels. At room temperatures, the test data correlates well to the analytical predictions of the Zener damping model. Discrepancies at cryogenic temperatures between the model predictions and the test data are observed.
NASA Technical Reports Server (NTRS)
Dolgin, Benjamin P. (Inventor)
1994-01-01
A superconductive load bearing support without a mechanical contact and vibration damping for cryogenic instruments in space is presented. The levitation support and vibration damping is accomplished by the use of superconducting magnets and the 'Meissner' effect. The assembly allows for transfer of vibration energy away from the cryogenic instrument which then can be damped by the use of either an electronic circuit or conventional vibration damping mean.
Magnetomechanical damping and magnetoelastic hysteresis in permalloy
NASA Astrophysics Data System (ADS)
Ercuta, A.; Mihalca, I.
2002-11-01
The inverse Wiedemann effect (IWE) consisting in longitudinal magnetization reversals was detected with a cylindrical permalloy layer subjected to circular DC magnetic fields while performing low frequency (~1 Hz) free torsion oscillations. Hysteresis occurring in the magnetization vs elastic strain dependence (the `magnetoelastic hysteresis') suggested irreversible processes activated mechanically. Joint vibration and magnetization time records were carried out by means of an experimental set-up including inverted pendulum and conventional integrating fluxmeter, in order to compare the relative energy losses ascribed to the magnetomechanical damping (MMD) and to the magnetoelastic hysteresis, respectively. The experimental results clearly pointed out a close connection between IWE and MMD providing evidence that, when simultaneously examined, both effects reflect the same basic phenomenon: the irreversible magnetization changes induced by the elastic strain.
NASA Astrophysics Data System (ADS)
Petitjean, P.; Ledoux, C.
Recently, Prochaska & Wolfe (1997) have used Keck spectra of 17 DLA absorbers to investigate the kinematics of the neutral gas using unsaturated low excitation transitions such as Si iiλ 1808. They show that the absorption profiles are inconsistent with models of galactic haloes with random motions, spherically infalling gas and slowly rotating hot disks. The CDM model (Kauffmann 1996) is rejected as it produces disks with rotation velocities too small to account for the large observed velocity broadening of the absorption lines. Models of thick disks (h ~0.3 R, where h is the vertical scale and R the radius) with large rotational velocity (v 225kms-1) can reproduce the data. By combining new data on five damped systems with information gathered in the literature, we study the kinematics of the low and high-ionization phases in a sample of 26 damped Lyman-α systems in the redshift range 1.17 - 4.38. We show that the broader the line the more asymmetric, as expected in case rotation dominates the line broadening. However this correlation does not hold for velocities larger than 150 km/s indicating that evidence for rotational motions if any is restricted to velocity broadenings Δ V < 150kms-1. The systems with Δ V > 200kms-1 are peculiar with kinematics consistent with random motions. They show sub-systems as those expected if the objects are in the process of merging.
Relaxation damping in oscillating contacts
Popov, M.; Popov, V.L.; Pohrt, R.
2015-01-01
If a contact of two purely elastic bodies with no sliding (infinite coefficient of friction) is subjected to superimposed oscillations in the normal and tangential directions, then a specific damping appears, that is not dependent on friction or dissipation in the material. We call this effect “relaxation damping”. The rate of energy dissipation due to relaxation damping is calculated in a closed analytic form for arbitrary axially-symmetric contacts. In the case of equal frequency of normal and tangential oscillations, the dissipated energy per cycle is proportional to the square of the amplitude of tangential oscillation and to the absolute value of the amplitude of normal oscillation, and is dependent on the phase shift between both oscillations. In the case of low frequency tangential oscillations with superimposed high frequency normal oscillations, the dissipation is proportional to the ratio of the frequencies. Generalization of the results for macroscopically planar, randomly rough surfaces as well as for the case of finite friction is discussed. PMID:26549011
Tuned vibration absorbers with nonlinear viscous damping for damped structures under random load
NASA Astrophysics Data System (ADS)
Shum, K. M.
2015-06-01
The classical problem for the application of a tuned vibration absorber is to minimize the response of a structural system, such as displacement, velocity, acceleration or to maximize the energy dissipated by tuned vibration absorber. The development of explicit optimal absorber parameters is challenging for a damped structural system since the fixed points no longer exist in the frequency response curve. This paper aims at deriving a set of simple design formula of tuned vibration absorber with nonlinear viscous damping based on the frequency tuning for harmonic load for a damped structural system under white noise excitation. The vibration absorbers being considered include tuned mass damper (TMD) and liquid column vibration absorber (LCVA). Simple approximate expression for the standard deviation velocity response of tuned vibration absorber for damped primary structure is also derived in this study to facilitate the estimation of the damping coefficient of TMD with nonlinear viscous damping and the head loss coefficient of LCVA. The derived results indicate that the higher the structural inherent damping the smaller the supplementary damping provided by a tuned vibration absorber. Furthermore, the optimal damping of tuned vibration absorber is shown to be independent of structural damping when it is tuned using the frequency tuning for harmonic load. Finally, the derived closed-form expressions are demonstrated to be capable of predicting the optimal parameters of tuned vibration absorbers with sufficient accuracy for preliminary design of tuned vibration absorbers with nonlinear viscous damping for a damped primary structure.
Yoo, Won-Gyu
2015-01-01
[Purpose] We investigated the effects of individual strengthening exercises for the stabilization muscles on the nutation torque of the sacroiliac joint in a sedentary worker with nonspecific sacroiliac joint pain. [Subject] A 36-year-old female complained of pain in the sacroiliac joints. [Methods] The subject performed individual strengthening exercises for the stabilization muscles for nutation torque of the sacroiliac joint for 3 weeks. Pain-provocation tests and visual analog scale (VAS) scores were evaluated before and after the exercises. [Results] After performing the individual strengthening exercises for the erector spinae, rectus abdominis, and biceps femoris muscles for 3 weeks, the subject displayed no pain in the pain provocation tests, and the VAS score was 2/10. [Conclusion] The individual strengthening exercises for the stabilization muscles of the sacroiliac joint performed in the present study appear to be effective for sedentary workers with sacroiliac joint pain.
Quasienergy formulation of damped response theory.
Kristensen, Kasper; Kauczor, Joanna; Kjaergaard, Thomas; Jørgensen, Poul
2009-07-28
We present a quasienergy-based formulation of damped response theory where a common effective lifetime parameter has been introduced for all excited states in terms of complex excitation energies. The introduction of finite excited state lifetimes leads to a set of (complex) damped response equations, which have the same form to all orders in the perturbation. An algorithm is presented for solving the damped response equations in Hartree-Fock theory and Kohn-Sham density functional theory. The use of the quasienergy formulation allows us to obtain directly the computationally simplest expressions for damped response functions by applying a set of response parameter elimination rules, which minimize the total number of damped response equations to be solved. In standard response theory broadened absorption spectra are obtained by ad hoc superimposing lineshape functions onto the absorption stick spectra, whereas an empirical lineshape function common to all excitations is an integrated part of damped response theory. By superimposing the lineshape functions inherent in damped response theory onto the stick spectra of standard response theory, we show that the absorption spectra obtained in standard and damped response theory calculations are identical. We demonstrate that damped response theory may be applied to obtain absorption spectra in all frequency ranges, also those that are not readily addressed using standard response theory. This makes damped response theory an effective tool, e.g., for determining absorption spectra for large molecules, where the density of the excited states may be very high, and where standard response theory therefore is not applicable in practice. A thorough comparison is given between our formulation of damped response theory and the formulation by Norman et al. [J. Chem. Phys. 123, 194103 (2005)].
Study for ILC Damping Ring at KEKB
Flanagan, J.W.; Fukuma, H.; Kanazawa, K.I.; Koiso, H.; Masuzawa, M.; Ohmi, Kazuhito; Ohnishi, Y.; Oide, Katsunobu; Suetsugu, Y.; Tobiyama, M.; Pivi, M.; /SLAC
2011-11-04
ILC damping ring consists of very low emittance electron and positron storage rings. It is necessary for ILC damping ring to study electron cloud effects in such low emittance positron ring. We propose a low emittance operation of KEKB to study the effects.
Understanding the Damped SHM without ODEs
ERIC Educational Resources Information Center
Ng, Chiu-king
2016-01-01
Instead of solving ordinary differential equations (ODEs), the damped simple harmonic motion (SHM) is surveyed qualitatively from basic mechanics and quantitatively by the instrumentality of a graph of velocity against displacement. In this way, the condition b ? [square root]4mk for the occurrence of the non-oscillating critical damping and…
Bending rate damping in elastic systems
NASA Technical Reports Server (NTRS)
Banks, H. T.; Wang, Y.; Fabiano, R. H.
1989-01-01
Preliminary results of an investigation of the bending rate damping model for elastic structures are presented. A model for which the internal damping term is physically plausible and which can accomodate cantilevered boundary conditions is discussed. The model formulation and mathematical foundations are given, and numerical results are discussed.
Damping device for a stationary labyrinth seal
NASA Technical Reports Server (NTRS)
El-Aini, Yehia M. (Inventor); Mitchell, William S. (Inventor); Roberts, Lawrence P. (Inventor); Montgomery, Stuart K. (Inventor); Davis, Gary A. (Inventor)
2010-01-01
A stationary labyrinth seal system includes a seal housing having an annular cavity, a plurality of damping devices, and a retaining ring. The damping devices are positioned within the annular cavity and are maintained within the annular cavity by the retaining ring.
Magnetic dipole oscillations and radiation damping
NASA Astrophysics Data System (ADS)
Stump, Daniel R.; Pollack, Gerald L.
1997-01-01
We consider the problem of radiation damping for a magnetic dipole oscillating in a magnetic field. An equation for the radiation reaction torque is derived, and the damping of the oscillations is described. Also discussed are runaway solutions for a rotating magnetic dipole moving under the influence of the reaction torque, with no external torque.
Landau damping in a turbulent setting
Plunk, G. G.
2013-03-15
To address the problem of Landau damping in kinetic turbulence, we consider the forcing of the linearized Vlasov equation by a stationary random source. It is found that the time-asymptotic density response is dominated by resonant particle interactions that are synchronized with the source. The energy consumption of this response is calculated, implying an effective damping rate, which is the main result of this paper. Evaluating several cases, it is found that the effective damping rate can differ from the Landau damping rate in magnitude and also, remarkably, in sign. A limit is demonstrated in which the density and current become phase-locked, which causes the effective damping to be negligible; this result offers a fresh perspective from which to reconsider recent observations of kinetic turbulence satisfying critical balance.
Damping characteristics of damaged fiber composite components
NASA Technical Reports Server (NTRS)
Eberle, K.
1986-01-01
Defects in fiber composite components produce changes with respect to the vibrational characteristics of the material. These changes can be recognized in the form of a frequency shift or an alteration of the damping process. The present investigation is concerned with questions regarding the possibility of a utilization of the changes in suitable defect-detecting inspection procedures. A description is given of a method for measuring the damping characteristics of a specimen. This method provides a spectrum of the damping coefficients of the sample as a basis for a comprehensive evaluation of the damping behavior. The correlation between defects and change in the damping characteristics is demonstrated with the aid of results obtained in measurements involving specimens of carbon-fiber composites and a component consisting of glass-fiber-reinforced plastics.
Magnetic damping of rotation. [in satellites
NASA Technical Reports Server (NTRS)
Opik, E. J.
1977-01-01
Based on Wilson's (1977) article on the magnetic effects on space vehicles and other celestial bodies, the magnetic damping of rotation is considered. The inadequacy of the interstellar magnetic field in overcoming solar wind shielding and thus influencing the rotation of bodies is described. The ionospheric shielding of the interstellar field is discussed along with the permeability and magnetic damping by the solar or stellar wind. Star formation and angular momentum is discussed and attention is given to the magnetic damping of unshielded small bodies. Calculations of the rate for damping through random particle impact are made. Theories concerning the rotation of asteroids and the origin of meteorites are reviewed. The shielding process of ionospheric plasmas is outlined and the damping effect of the geomagnetic field on the rotation of artificial satellites is evaluated.
VIBRATION DAMPING AND SHOCK MOUNT
Stevens, D.J.; Forman, G.W.
1963-12-10
A shock absorbing mount in which vibrations are damped by an interference fit between relatively movable parts of the mount is described. A pair of generally cup-shaped parts or members have skirt portions disposed in an oppositely facing nesting relationship with the skirt of one member frictionally engaging the skirt of the other. The outermost skirt may be slotted to provide spring-like segments which embrace the inner skirt for effecting the interference fit. Belleville washers between the members provide yieldable support for a load carried by the mount. When a resonant frequency of vibration forces acting upon the moumt attains a certain level the kinetic energy of these forces is absorbed by sliding friction between the parts. (AEC)
Large space structure damping design
NASA Technical Reports Server (NTRS)
Pilkey, W. D.; Haviland, J. K.
1983-01-01
Several FORTRAN subroutines and programs were developed which compute complex eigenvalues of a damped system using different approaches, and which rescale mode shapes to unit generalized mass and make rigid bodies orthogonal to each other. An analytical proof of a Minimum Constrained Frequency Criterion (MCFC) for a single damper is presented. A method to minimize the effect of control spill-over for large space structures is proposed. The characteristic equation of an undamped system with a generalized control law is derived using reanalysis theory. This equation can be implemented in computer programs for efficient eigenvalue analysis or control quasi synthesis. Methods to control vibrations in large space structure are reviewed and analyzed. The resulting prototype, using electromagnetic actuator, is described.
NASA Technical Reports Server (NTRS)
Miller, G.; Heimann, Paula J.; Scheiman, Daniel A.; Duffy, Kirsten P.; Johnston, J. Chris; Roberts, Gary D.
2013-01-01
Vibration mitigation in composite structures has been demonstrated through widely varying methods which include both active and passive damping. Recently, nanomaterials have been investigated as a viable approach to composite vibration damping due to the large surface available to generate energy dissipation through friction. This work evaluates the influence of dispersed nanoparticles on the damping ratio of an epoxy matrix. Limited benefit was observed through dispersion methods, however nanoparticle application as a coating resulting in up to a three-fold increase in damping.
Shunted Piezoelectric Vibration Damping Analysis Including Centrifugal Loading Effects
NASA Technical Reports Server (NTRS)
Min, James B.; Duffy, Kirsten P.; Provenza, Andrew J.
2011-01-01
Excessive vibration of turbomachinery blades causes high cycle fatigue problems which require damping treatments to mitigate vibration levels. One method is the use of piezoelectric materials as passive or active dampers. Based on the technical challenges and requirements learned from previous turbomachinery rotor blades research, an effort has been made to investigate the effectiveness of a shunted piezoelectric for the turbomachinery rotor blades vibration control, specifically for a condition with centrifugal rotation. While ample research has been performed on the use of a piezoelectric material with electric circuits to attempt to control the structural vibration damping, very little study has been done regarding rotational effects. The present study attempts to fill this void. Specifically, the objectives of this study are: (a) to create and analyze finite element models for harmonic forced response vibration analysis coupled with shunted piezoelectric circuits for engine blade operational conditions, (b) to validate the experimental test approaches with numerical results and vice versa, and (c) to establish a numerical modeling capability for vibration control using shunted piezoelectric circuits under rotation. Study has focused on a resonant damping control using shunted piezoelectric patches on plate specimens. Tests and analyses were performed for both non-spinning and spinning conditions. The finite element (FE) shunted piezoelectric circuit damping simulations were performed using the ANSYS Multiphysics code for the resistive and inductive circuit piezoelectric simulations of both conditions. The FE results showed a good correlation with experimental test results. Tests and analyses of shunted piezoelectric damping control, demonstrating with plate specimens, show a great potential to reduce blade vibrations under centrifugal loading.
Simulation Study of Electronic Damping of Microphonic Vibrations in Superconducting Cavities
Alicia Hofler; Jean Delayen
2005-05-01
Electronic damping of microphonic vibrations in superconducting rf cavities involves an active modulation of the cavity field amplitude in order to induce ponderomotive forces that counteract the effect of ambient vibrations on the cavity frequency. In lightly beam loaded cavities, a reduction of the microphonics-induced frequency excursions leads directly to a reduction of the rf power required for phase and amplitude stabilization. Jefferson Lab is investigating such an electronic damping scheme that could be applied to the JLab 12 GeV upgrade, the RIA driver, and possibly to energy-recovering superconducting linacs. This paper discusses a model and presents simulation results for electronic damping of microphonic vibrations.
Validation Of Equivalent Viscous Damping Methodologies
NASA Astrophysics Data System (ADS)
Vaquer Araujo, Xavier; Fransen, S. H. J. A.; Germes, S.; Thiry, N.
2012-07-01
An important step in the design and verification process of spacecraft structures is the coupled dynamic analysis with the launch vehicle in the low-frequency domain. To obtain accurate predictions of the satellite’s dynamic environment it is essential that the damping of the system is correctly defined and taken into account within the resolution methodologies for the Coupled Loads Analysis (CLA). When working with finite element models, the materials’ damping is characterized by structural damping ratios. In addition, most of the load cases present in the CLA are transient excitations so the resolution of the equations of motion must be done in the time domain. Unfortunately, transient analyses cannot be carried out using structural damping models. Thus, a transformation from a structural to a viscous damping characterization is necessary. Nevertheless, this transformation is not trivial. There exist many methodologies aiming at computing an equivalent viscous damping matrix of the system so it can be used in transient analyses. This paper describes the results obtained in the validation of equivalent viscous damping methodologies used in the European Space Agency. This work permitted to identify the limitations of these methodologies and to come up with an enhanced methodology that predicts more reliable results.
SLC positron damping ring optics design
Delahaye, J.P.; Rivkin, L.
1984-12-01
The basic SLAC Linear Collider operation scheme assumes the use of two damping rings, one for the e/sup -/, one for the e/sup +/, in order to reduce the colliding beam normalized emittances to 30..pi.. ..mu..radm hence raising the corresponding luminosity by a factor 170. The e/sup -/ damping ring which optics was designed by H. Wiedemann, has been extensively studied and modelled since it's completion at the end of 1982. The e/sup +/ damping ring to be built soon will be based on the same design except for some modifications resulting from the studies on the e/sup -/ damping ring which clearly pointed out two major optics weak points: the extracted normalized emittances are 30 to 60% bigger than the design values, which already left no margin for unavoidable blow-up between the damping rings and the SLC interaction point, and the chromaticity correction based on distributed sextupole components provided by shaping the ends of the bending magnet poles was insufficient. Moreover the QDI quadrupoles introduce a strong coupling between transverse planes due to an undesirable skew component. The present note describes the basic modifications of the ring lattice and main equipment positions in order to improve the first two points in the Positron Damping Ring. The QDI quadrupole design has already been modified and magnets of a new type will be implemented in both damping rings.
Material damping experiments at cryogenic temperatures
NASA Astrophysics Data System (ADS)
Levine, Marie B.; White, Christopher
2003-12-01
NASA's James Webb Space Telescope (JWST) will be operating at temperatures below 40K to image in the infrared. The 7-m class telescope will require nanometric jitter stability of the optical elements such as the primary and secondary mirrors. Of particular concern is the vibration response of these cryogenic systems when subjected to on-board disturbance sources such as the reaction wheels, the amplitude of which is governed by damping. Unfortunately there is relatively little data available for flight grade materials at these temperatures and within the frequency bands of interest. The paper will describe the experimental setup designed to measure viscous damping to values as low 10^-4%. The tests measure damping from room temperature all the way down to 20K in a controlled thermal and disturbance free environment. Data is obtained for strain levels of about 0.1 micro-strain down to nano-strains to verify vibration level effects on material damping. Damping is also measured for several frequencies in the range of 20Hz to 300Hz to assess the trend of damping as a function of vibrational frequency. Data for several materials, such as Aluminum, Beryllium, Quartz, and various composites are presented. The data is compared to analytical predictions using the Zener damping theory and is shown to match well at room temperature but to disagree at colder temperatures.
Vitzthum, Veronika; Caporini, Marc A; Ulzega, Simone; Bodenhausen, Geoffrey
2011-09-01
A train of short rotor-synchronized pulses in the manner of Delays Alternating with Nutations for Tailored Excitation (DANTE) applied to nitrogen-14 nuclei (I=1) in samples spinning at the magic angle at high frequencies (typically νrot=62.5 kHz so that τrot=16 μs) allows one to achieve uniform excitation of a great number of spinning sidebands that arise from large first-order quadrupole interactions, as occur for aromatic nitrogen-14 nuclei in histidine. With routine rf amplitudes ω1(14N)/(2π)=60 kHz and very short pulses of a typical duration 0.5<τp<2 μs, efficient excitation can be achieved with 13 rotor-synchronized pulses in 13 τrot=208 μs. Alternatively, with 'overtone' DANTE sequences using 2, 4, or 8 pulses per rotor period one can achieve efficient broadband excitation in fewer rotor periods, typically 2-4 τrot. These principles can be combined with the indirect detection of 14N nuclei via spy nuclei with S=½ such as 1H or 13C in the manner of Dipolar Heteronuclear Multiple-Quantum Correlation (D-HMQC).
NASA Astrophysics Data System (ADS)
Vitzthum, Veronika; Caporini, Marc A.; Ulzega, Simone; Bodenhausen, Geoffrey
2011-09-01
A train of short rotor-synchronized pulses in the manner of Delays Alternating with Nutations for Tailored Excitation (DANTE) applied to nitrogen-14 nuclei ( I = 1) in samples spinning at the magic angle at high frequencies (typically νrot = 62.5 kHz so that τrot = 16 μs) allows one to achieve uniform excitation of a great number of spinning sidebands that arise from large first-order quadrupole interactions, as occur for aromatic nitrogen-14 nuclei in histidine. With routine rf amplitudes ω1( 14N)/(2 π) = 60 kHz and very short pulses of a typical duration 0.5 < τp < 2 μs, efficient excitation can be achieved with 13 rotor-synchronized pulses in 13 τrot = 208 μs. Alternatively, with 'overtone' DANTE sequences using 2, 4, or 8 pulses per rotor period one can achieve efficient broadband excitation in fewer rotor periods, typically 2-4 τrot. These principles can be combined with the indirect detection of 14N nuclei via spy nuclei with S = ½ such as 1H or 13C in the manner of Dipolar Heteronuclear Multiple-Quantum Correlation (D-HMQC).
Electromagnetic induction and damping: Quantitative experiments using a PC interface
NASA Astrophysics Data System (ADS)
Singh, Avinash; Mohapatra, Y. N.; Kumar, Satyendra
2002-04-01
A bar magnet, attached to an oscillating system, passes through a coil periodically, generating a series of electromotive force pulses. A novel method for the quantitative verification of Faraday's law is described which eliminates all errors associated with angular measurements, thereby revealing subtle features of the underlying mechanics. When electromagnetic damping is activated by short-circuiting the coil, a distinctly linear decay of the oscillation amplitude is observed. A quantitative analysis reveals an interesting interplay of the electromagnetic and mechanical time scales.
Experimental verification of damping mechanisms in a composite beam
NASA Technical Reports Server (NTRS)
Cudney, Harley H.; Inman, Daniel J.
1989-01-01
A method of estimating the distributed damping parameters based on the measured modal parameters (frequency and damping ratios) was derived. Three different mathematical models were used to model the damping mechanism of a quasi-isotropic pultruded cantilevered beam. These three models were (1) viscous (air) damping, (2) strain rate damping, and (3) both viscous and strain rate damping. The eigenvalues of the partial differential equation model were found to be uninfluenced by any of the three assumed damping models. Values were obtained for each of the damping models as well as the modulus of elasticity of the beam. It was found that the two-parameter damping model provided the best fit to measured modal data. However, the two-parameter damping model could only reproduce the measured damping ratios to within 85 percent.
Investigation on the mechanism of damping behavior of magnetorheological elastomers
NASA Astrophysics Data System (ADS)
Yang, Jie; Gong, Xinglong; Deng, Huaxia; Qin, Lijun; Xuan, Shouhu
2012-12-01
Magnetorheological elastomers (MREs) are a group of smart materials which have many applications such as dynamic vibration absorbers, engine mounts, and so on. The damping behavior is important for applications of MREs. However, the mechanism of the damping of MREs has not been investigated thoroughly. In this study, MREs are modeled as special particle reinforced composites with magneto-induced properties and the mechanism of the damping behavior of MREs is investigated theoretically and experimentally. It has been found that there are three types of damping property in MREs: the intrinsic damping, the interface damping and the magneto-mechanical damping. The presented damping model is successfully validated by damping tests on a series of MRE samples. Furthermore, the relationships between the damping properties and formulas of MREs are discussed; this provides guidance for the manufacture of MREs with various damping properties.
Nonlinear Landau damping of Alfven waves.
NASA Technical Reports Server (NTRS)
Hollweg, J. V.
1971-01-01
Demonstration that large-amplitude linearly or elliptically polarized Alfven waves propagating parallel to the average magnetic field can be dissipated by nonlinear Landau damping. The damping is due to the longitudinal electric field associated with the ion sound wave which is driven (in second order) by the Alfven wave. The damping rate can be large even in a cold plasma (beta much less than 1, but not zero), and the mechanism proposed may be the dominant one in many plasmas of astrophysical interest.
Oscillation damped movement of suspended objects
Jones, J.F.; Petterson, B.J.
1988-01-01
Transportation of objects using overhead cranes or manipulators can induce pendulum motion of the object. Residual oscillation from transportation typically must be damped or allowed to decay before the next process can take place. By properly programming the acceleration of the transporting device (e.g., crane) an oscillation damped transport and swing free stop is obtainable. This paper reviews the theory associated with oscillation damped trajectories for simply suspended objects and describes a particular implementation using a CIMCORP XR 6100 gantry robot. 8 refs., 7 figs., 1 tab.
Swept sine testing of rotor-bearing system for damping estimation
NASA Astrophysics Data System (ADS)
Chandra, N. Harish; Sekhar, A. S.
2014-01-01
Many types of rotating components commonly operate above the first or second critical speed and they are subjected to run-ups and shutdowns frequently. The present study focuses on developing FRF of rotor bearing systems for damping estimation from swept-sine excitation. The principle of active vibration control states that with increase in angular acceleration, the amplitude of vibration due to unbalance will reduce and the FRF envelope will shift towards the right (or higher frequency). The frequency response function (FRF) estimated by tracking filters or Co-Quad analyzers was proved to induce an error into the FRF estimate. Using Fast Fourier Transform (FFT) algorithm and stationary wavelet transform (SWT) decomposition FRF distortion can be reduced. To obtain a theoretical clarity, the shifting of FRF envelope phenomenon is incorporated into conventional FRF expressions and validation is performed with the FRF estimated using the Fourier Transform approach. The half-power bandwidth method is employed to extract damping ratios from the FRF estimates. While deriving half-power points for both types of responses (acceleration and displacement), damping ratio (ζ) is estimated with different approximations like classical definition (neglecting damping ratio of order higher than 2), third order (neglecting damping ratios with order higher than 4) and exact (no assumptions on damping ratio). The use of stationary wavelet transform to denoise the noise corrupted FRF data is explained. Finally, experiments are performed on a test rotor excited with different sweep rates to estimate the damping ratio.
Circulating Mitochondrial DAMPs Cause Inflammatory Responses to Injury
Zhang, Qin; Raoof, Mustafa; Chen, Yu; Sumi, Yuka; Sursal, Tolga; Junger, Wolfgang; Brohi, Karim; Itagaki, Kiyoshi; Hauser, Carl J.
2009-01-01
Injury causes a systemic inflammatory response syndrome (SIRS) clinically much like sepsis 1. Microbial pathogen-associated molecular patterns (PAMPs) activate innate immunocytes through pattern recognition receptors 2. Similarly, cellular injury can release endogenous damage-associated molecular patterns (DAMPs) that activate innate immunity 3. Mitochondria are evolutionary endosymbionts that were derived from bacteria 4 and so might bear bacterial molecular motifs. We show here that injury releases mitochondrial DAMPs (MTD) into the circulation with functionally important immune consequences. MTD include formyl peptides and mitochondrial DNA. These activate human neutrophils (PMN) through formyl peptide receptor-1 and TLR9 respectively. MTD promote PMN Ca2+ flux and phosphorylation of MAP kinases, thus leading to PMN migration and degranulation in vitro and in vivo. Circulating MTD can elicit neutrophil-mediated organ injury. Cellular disruption by trauma releases mitochondrial DAMPs with evolutionarily conserved similarities to bacterial PAMPs into the circulation. These can then signal through identical innate immune pathways to create a sepsis-like state. The release of such mitochondrial ‘enemies within’ by cellular injury is a key link between trauma, inflammation and SIRS. PMID:20203610
Turbine blade friction damping study
NASA Technical Reports Server (NTRS)
Dominic, R. J.
1985-01-01
A lumped parameter method, implemented on a VAX 11/780 computer shows that the primary parameters affecting the performance of the friction damper of the first stage turbine of the SSME high pressure fuel pump are: the damper-blade coefficient of friction; the normal force applied to the friction interface; the amplitude of the periodic forcing function; the relative phase angle of the forcing functions for adjacent blades bridged by a damper (effectively, the engine order of the forcing function); and the amount of hysteretic damping that acts to limit the vibration amplitude of the blade in its resonance modes. The low order flexural resonance vibration modes of HPFTP blades without dampers, with production dampers, and with two types of lightweight experimental dampers were evaluated in high speed spin pit tests. Results agree with those of the analytical study in that blades fitted with production friction dampers experienced the airfoil-alone flexural resonance mode, while those without dampers or with lighter weight dampers did not. No blades fitted with dampers experienced the whole blade flexural resonance mode during high speed tests, while those without dampers did.
Eigensolutions of non-proportionally damped systems based on continuous damping sensitivity
NASA Astrophysics Data System (ADS)
Lázaro, Mario
2016-02-01
The viscous damping model has been widely used to represent dissipative forces in structures under mechanical vibrations. In multiple degree of freedom systems, such behavior is mathematically modeled by a damping matrix, which in general presents non-proportionality, that is, it does not become diagonal in the modal space of the undamped problem. Eigensolutions of non-proportional systems are usually estimated assuming that the modal damping matrix is diagonally dominant (neglecting the off-diagonal terms) or, in the general case, using the state-space approach. In this paper, a new closed-form expression for the complex eigenvalues of non-proportionally damped system is proposed. The approach is derived assuming small damping and involves not only the diagonal terms of the modal damping matrix, but also the off-diagonal terms, which appear under higher order. The validity of the proposed approach is illustrated through a numerical example.
The Influence of Damping Changes on Vertical Dynamic Loads of Wheel - Experimental Investigations
NASA Astrophysics Data System (ADS)
Ślaski, Grzegorz; Pikosz, Hubert
2011-06-01
In this paper the results of tests of vertical dynamic wheel loads due to changes in suspension damping level are presented. The changes in damping level were performed using semi-active shock absorbers with by-pass valve. The article presents suspension goals, the definition of dynamic loads of vehicle wheel, testing methods with the information on the used apparatus and sensors. In the end the results are presented, interpreted and compared with other researchers' results.
NASA Technical Reports Server (NTRS)
Sireteanu, T.
1974-01-01
An oscillating system with quadratic damping subjected to white noise excitation is replaced by a nonlinear, statistically equivalent system for which the associated Fokker-Planck equation can be exactly solved. The mean square responses are calculated and the optimum damping coefficient is determined with respect to the minimum mean square acceleration criteria. An application of these results to the optimization of automobile suspension damping is given.
Simplified Model of Nonlinear Landau Damping
N. A. Yampolsky and N. J. Fisch
2009-07-16
The nonlinear interaction of a plasma wave with resonant electrons results in a plateau in the electron distribution function close to the phase velocity of the plasma wave. As a result, Landau damping of the plasma wave vanishes and the resonant frequency of the plasma wave downshifts. However, this simple picture is invalid when the external driving force changes the plasma wave fast enough so that the plateau cannot be fully developed. A new model to describe amplification of the plasma wave including the saturation of Landau damping and the nonlinear frequency shift is proposed. The proposed model takes into account the change of the plasma wave amplitude and describes saturation of the Landau damping rate in terms of a single fluid equation, which simplifies the description of the inherently kinetic nature of Landau damping. A proposed fluid model, incorporating these simplifications, is verified numerically using a kinetic Vlasov code.
Roll Damping Characterisation Program: User Guide
2014-06-01
sallying test. The Defence Science and Technology Organisation (DSTO) have developed a software-based tool called the Roll Damping Characterisation...Murray Riding Maritime Division Murray obtained a Bachelor of Science (Honours) Degree from the
Electron beam depolarization in a damping ring
Minty, M.
1993-04-01
Depolarization of a polarized electron beam injected into a damping ring is analyzed by extending calculations conventionally applied to proton synchrotrons. Synchrotron radiation in an electron ring gives rise to both polarizing and depolarizing effects. In a damping ring, the beam is stored for a time much less than the time for self polarization. Spin flip radiation may therefore be neglected. Synchrotron radiation without spin flips, however, must be considered as the resonance strength depends on the vertical betatron oscillation amplitude which changes as the electron beam is radiation damped. An expression for the beam polarization at extraction is derived which takes into account radiation damping. The results are applied to the electron ring at the Stanford Linear Collider and are compared with numerical matrix formalisms.
Oscillation damping means for magnetically levitated systems
Post, Richard F.
2009-01-20
The present invention presents a novel system and method of damping rolling, pitching, or yawing motions, or longitudinal oscillations superposed on their normal forward or backward velocity of a moving levitated system.
Collisional damping of the geodesic acoustic mode
Gao Zhe
2013-03-15
The frequency and damping rate of the geodesic acoustic mode (GAM) is revisited by using a gyrokinetic model with a number-conserving Krook collision operator. It is found that the damping rate of the GAM is non-monotonic as the collision rate increases. At low ion collision rate, the damping rate increases linearly with the collision rate; while as the ion collision rate is higher than v{sub ti}/R, where v{sub ti} and R are the ion thermal velocity and major radius, the damping rate decays with an increasing collision rate. At the same time, as the collision rate increases, the GAM frequency decreases from the (7/4+{tau})v{sub ti}/R to (1+{tau})v{sub ti}/R, where {tau} is the ratio of electron temperature to ion temperature.
Mechanical loading, damping, and load-driven bone formation in mouse tibiae.
Dodge, Todd; Wanis, Mina; Ayoub, Ramez; Zhao, Liming; Watts, Nelson B; Bhattacharya, Amit; Akkus, Ozan; Robling, Alexander; Yokota, Hiroki
2012-10-01
Mechanical loads play a pivotal role in the growth and maintenance of bone and joints. Although loading can activate anabolic genes and induce bone remodeling, damping is essential for preventing traumatic bone injury and fracture. In this study we investigated the damping capacity of bone, joint tissue, muscle, and skin using a mouse hindlimb model of enhanced loading in conjunction with finite element modeling to model bone curvature. Our hypothesis was that loads were primarily absorbed by the joints and muscle tissue, but that bone also contributed to damping through its compression and natural bending. To test this hypothesis, fresh mouse distal lower limb segments were cyclically loaded in axial compression in sequential bouts, with each subsequent bout having less surrounding tissue. A finite element model was generated to model effects of bone curvature in silico. Two damping-related parameters (phase shift angle and energy loss) were determined from the output of the loading experiments. Interestingly, the experimental results revealed that the knee joint contributed to the largest portion of the damping capacity of the limb, and bone itself accounted for approximately 38% of the total phase shift angle. Computational results showed that normal bone curvature enhanced the damping capacity of the bone by approximately 40%, and the damping effect grew at an accelerated pace as curvature was increased. Although structural curvature reduces critical loads for buckling in beam theory, evolution apparently favors maintaining curvature in the tibia. Histomorphometric analysis of the tibia revealed that in response to axial loading, bone formation was significantly enhanced in the regions that were predicted to receive a curvature-induced bending moment. These results suggest that in addition to bone's compressive damping capacity, surrounding tissues, as well as naturally-occurring bone curvature, also contribute to mechanical damping, which may ultimately affect
Spatial versus time hysteresis in damping mechanisms
NASA Technical Reports Server (NTRS)
Banks, H. T.; Fabiano, R. H.; Wang, Y.; Inman, D. J.; Cudney, H., Jr.
1988-01-01
A description is given of continuing investigations on the task of estimating internal damping mechanisms in flexible structures. Specifically, two models for internal damping in Euler-Bernoulli beams are considered: spatial hysteresis and time hysteresis. A theoretically sound computational algorithm for estimation is described, and experimental results are discussed. It is concluded that both models perform well in the sense that they accurately predict response for the experiments conducted.
Turbine blade with tuned damping structure
Campbell, Christian X.; Messmann, Stephen J.
2015-09-01
A turbine blade is provided comprising: a root; an airfoil comprising an external wall extending radially from the root and having a radially outermost portion; and a damping structure. The external wall may comprise first and second side walls joined together to define an inner cavity of the airfoil. The damping structure may be positioned within the airfoil inner cavity and coupled to the airfoil so as to define a tuned mass damper.
Analysis of nonlinear damping properties of carbon
NASA Astrophysics Data System (ADS)
Kazakova, Olga I.; Smolin, Igor Yu.; Bezmozgiy, Iosif M.
2016-11-01
This paper describes research results of nonlinear damping properties of carbon fiber reinforced plastics. The experimental and computational research is performed on flat composite specimens with the gradual structure complication (from 1 to 12 layers). Specimens are subjected to three types of testing which are modal, harmonic and transient analyses. Relationships between the amplitude response and damping ratio are obtained by means of the analysis of variance as the result of this research.
Quantum damped oscillator I: Dissipation and resonances
Chruscinski, Dariusz
2006-04-15
Quantization of a damped harmonic oscillator leads to so called Bateman's dual system. The corresponding Bateman's Hamiltonian, being a self-adjoint operator, displays the discrete family of complex eigenvalues. We show that they correspond to the poles of energy eigenvectors and the corresponding resolvent operator when continued to the complex energy plane. Therefore, the corresponding generalized eigenvectors may be interpreted as resonant states which are responsible for the irreversible quantum dynamics of a damped harmonic oscillator.
Aerospace Structures Technology Damping Design Guide. Volume 3. Damping Material Data
1985-12-01
1.1 DAMPING MATERIAL PROPERTIES 1 3 1.2 THE STANDARIZED MATERIAL DATA I 1.2.1 Nomogram Cover Sheet 3 ’ 1.2.2 The Reduced Nomogram 4 1.2.3 Reading...MATERIALS 6 2 DAMPING MATERIAL PROPERTY DATA 14 3 STRUCTURAL EPOXIES AND OTHER MATERIALS 469 3.1 STRUCTURAL EPOXIES 469 3.2 STRUCTURAL PLASTICS 477 3.3...Data Listing II 6 Temperature Shift Function and Its Properties 12 7 Typical TCA Plot 13 8 Quick Reference Chart for Damping Materials 15 9 Damping vs
NASA Astrophysics Data System (ADS)
Smith, Clifford B.; Wereley, Norman M.
1996-10-01
The first objective of this paper is to evaluate the performance of damping identification algorithms. The second objective is to determine the feasibility of damping augmentation in rotating composite beams via passive constrained layer damping (PCLD). Damping identification schemes were applied to four rectangular cross-section laminated composite beams with cocured integral damping layers over the span of the beam. The cocured beam consisted of a twenty-ply balanced and symmetric cross-ply Gr/Ep composite host structure, a top and bottom damping layer of viscoelastic material (VEM), and a 2-ply Gr/Ep constraining layer sandwiching the viscoelastic material to the host structure. Four VEM thicknesses were considered: 0, 5, 10, and 15 mils. The cantilevered beams were tested at rotational speeds ranging from 0 to 900 RPM in a vacuum chamber. Excitation in bending was provided using piezo actuators, and the bending response was measured using full strain gauge bridges. Transient data were analysed using logarithmic decrement, a Hilbert transform technique, and an FFT- based moving block analysis. When compared to the beam with no VEM, a 19.2% volume fraction (15 mil layer) of viscoelastic in the beam produced a 400% increase in damping ratio in the non-rotating case, while at 900 RPM, the damping ratio increased only 360%. Overall structural damping was reduced as a function of RPM, due to centrifugal stiffening.
Validation of equivalent viscous damping methodologies
NASA Astrophysics Data System (ADS)
Vaquer Araujo, Xavier; Fransen, Sebastiaan H. J. A.; Germès, Sylvain; Thiry, Nicolas
2013-06-01
An important step in the design and verification process of spacecraft structures is the coupled dynamic analysis with the launch vehicle in the low-frequency domain. To obtain accurate predictions of the satellite's dynamic environment, it is essential that the damping of the system is correctly defined and taken into account within the resolution methodologies for the coupled loads analysis (CLA). When working with finite element models, the materials' damping is characterized by structural damping ratios. In addition, most of the load cases present in the CLA are transient excitations, and so the resolution of the equations of motion must be done in the time domain. Unfortunately, in the CLA, transient analyses cannot be carried out using structural damping models. Thus, a transformation from a structural to a viscous damping characterization is necessary in this case. Nevertheless, this transformation is not trivial. There exist many methodologies for computing an equivalent viscous damping (EqVD) matrix of the system which can be used in transient analyses. This paper describes the results obtained from the validation of EqVD methodologies used in the European Space Agency. This work identifies the limitations of these methodologies and comes up with an enhanced methodology that predicts more reliable results.
Xia, Hong; Liang, Yaojun; Wang, Xiao; Bao, Wenduona; Yun, Shifeng; Ye, Yuting; Zheng, Chunxia; Liu, Zhihong; Shi, Shaolin
2015-01-01
Mitochondria in eukaryotic cells are derived from bacteria in evolution. Like bacteria, mitochondria contain DNA with unmethylated CpG motifs and formyl peptides, both of which have recently been shown to be damage associated molecular patterns (DAMPs) and induce immune response and cell injury. Based on the facts that circulating mitochondrial DAMPs (mtDAMPs) are increased in the patients of trauma or burn injury who also have proteinuria, that mtDAMPs can activate immune cells which in turn secrete glomerular permeability factors, that renal intrinsic cells express a variety of DAMP receptors, and that mtDAMPs can directly increase endothelial cell permeability in vitro, we hypothesized that mtDAMPs may be novel circulating factors inducing proteinuria and kidney injury. We tested this hypothesis by directly injecting mtDAMPs into rodents and examining urinary protein and kidney histology. We prepared mtDAMP samples, including mitochondrial DNA (mtDNA) and mitochondrial debris (MTD), from rodent liver. In mice, injection of mtDNA for 20 μg/ml initial concentration in circulation (much higher than the clinical range), did not cause any renal manifestations. However, an increased dose leading to 45 μg/ml initial concentration in circulation resulted in a transient, slight increase in urinary albumin. In rats, MTD injection resulting in 450 μg/ml initial concentration of MTD protein in circulation, which was much higher than the clinical range, caused mild, transient proteinuria and lung lesions. Multiple injections of such large amount of either mtDNA or MTD into rodents on 3 consecutive days also failed in inducing proteinuria and kidney injury. In summary, clinical levels of circulating mtDAMPs do not induce proteinuria and clinically irrelevant high levels of mtDAMPs cause only a transient and slight increase in urinary protein in rodents, suggesting that circulating mtDAMPs may not be responsible for the proteinuria and kidney injury in patients with trauma
Robust time-domain identification of mass stiffness, and damping matrices
NASA Technical Reports Server (NTRS)
Roemer, Michael J.; Mook, D. Joseph
1990-01-01
Accurate estimates of the mass, stiffness, and damping characteristics of a structure is necessary for determining the control laws best suited for active control methodologies. There are several modal identification techniques available for determining the frequencies, damping ratios, and mode shapes of a structure. However, modal identification methods in both the frequency and time domains have difficulties for certain circumstances. Frequency domain techniques which utilize the steady-state response from various harmonic inputs often encounter difficulties when the frequencies are closely distributed, the structure exhibits a high degree of damping, or the steady-state condition is hard to establish. Time domain techniques have produced successful results, but lack robustness with respect to measurement noise. In this paper, two identification techniques and an estimation method are combined to form a time-domain technique to accurately identify the mass, stiffness, and damping matrices from noisy measurements.
Tracing Plant Defense Responses in Roots upon MAMP/DAMP Treatment.
Hiruma, Kei; Saijo, Yusuke
2016-01-01
This chapter describes how to apply microbe-associated molecular pattern (MAMP) or damage-associated molecular pattern (DAMP) solutions to Arabidopsis roots to trace defense responses in the root. Plants sense the presence of microbes via the perception of MAMPs or DAMPs by surface-localized pattern recognition receptors. The mechanisms governing plant root immunity are poorly characterized compared with those underlying plant immunity in the leaf, despite the fact that plant roots constantly interact with countless microbes living in soils that carry potential MAMPs and could stimulate the production of plant-derived DAMPs during colonization. To understand how a plant root immune system detects and reacts to the potential sources of a stimulus, we describe a simple method to monitor activation of root immunity upon MAMP/DAMP treatment by measuring relative expression of defense-related genes by RT-qPCR.
NASA Astrophysics Data System (ADS)
Strain, K. A.; Shapiro, B. N.
2012-04-01
The mirrors of laser interferometric gravitational wave detectors hang from multi-stage suspensions. These support the optics against gravity while isolating them from external vibration. Thermal noise must be kept small so mechanical loss must be minimized and the resulting structure has high-Q resonances rigid-body modes, typically in the frequency range between about 0.3 Hz and 20 Hz. Operation of the interferometer requires these resonances to be damped. Active damping provides the design flexibility required to achieve rapid settling with low noise. In practice there is a compromise between sensor performance, and hence cost and complexity, and sophistication of the control algorithm. We introduce a novel approach which combines the new technique of modal damping with methods developed from those applied in GEO 600. This approach is predicted to meet the goals for damping and for noise performance set by the Advanced LIGO project.
Zajączkowska, U; Barlow, P W
2017-03-03
Orbital movement of the Moon generates a system of gravitational fields that periodically alter the gravitational force on Earth. This lunar tidal acceleration (Etide) is known to act as an external environmental factor affecting many growth and developmental phenomena in plants. Our study focused on the lunar tidal influence on stem elongation growth, nutations and leaf movements of peppermint. Plants were continuously recorded with time-lapse photography under constant illumination as well in constant illumination following 5 days of alternating dark-light cycles. Time courses of shoot movements were correlated with contemporaneous time courses of the Etide estimates. Optical microscopy and SEM were used in anatomical studies. All plant shoot movements were synchronised with changes in the lunisolar acceleration. Using a periodogram, wavelet analysis and local correlation index, a convergence was found between the rhythms of lunisolar acceleration and the rhythms of shoot growth. Also observed were cyclical changes in the direction of rotation of stem apices when gravitational dynamics were at their greatest. After contrasting dark-light cycle experiments, nutational rhythms converged to an identical phase relationship with the Etide and almost immediately their renewed movements commenced. Amplitudes of leaf movements decreased during leaf growth up to the stage when the leaf was fully developed; the periodicity of leaf movements correlated with the Etide rhythms. For the fist time, it was documented that lunisolar acceleration is an independent rhythmic environmental signal capable of influencing the dynamics of plant stem elongation. This phenomenon is synchronised with the known effects of Etide on nutations and leaf movements.
NASA Astrophysics Data System (ADS)
Chao, B. F.; Hsieh, Y.
2015-12-01
The free-core nutation (FCN) is a rotational normal mode of the Earth's outer core. We derive the equations of motion for FCN w.r.t. both the inertia space F0 and the uniformly rotating frame FΩ, and show that the two sets of equations are invariant in form under the reference frame transformation, as required by physics. The frequency-domain formulation describes the FCN resonance (to nearby tidal signals), which has been exploited to estimate the complex eigenfrequency of FCN, or its eigenperiod P and quality factor Q. On the other hand, our time-domain formulation in terms of temporal convolution describes the response of the free FCN under a (continual) excitation. The convolution well explains the dynamic behaviors of FCN in the observed very-long-baseline interferometry (VLBI) data (in F0), including the undulation of the FCN amplitude and the apparent fluctuations in the period and phase over time, as well as the temporal concurrence of a large phase jump with the near-zero amplitude during ∼ 1998- 2000, in complete analogy to the observed behavior of the Chandler wobble (in FΩ). The reverse, deconvolution process is further exploited to yield optimal estimates for FCN's eigenfrequency using the VLBI data, following the approach of Furuya and Chao (1996) of locating minimum excitation power. While this method is found to be insensitive to Q owing to the short timespan of the data, we obtain the estimate of P = 441 ± 4.5 sidereal days (sd) where the 1-sigma uncertainty is assessed via extensive Monte Carlo simulations. This value is closer to the theoretical value of ∼460 sd predicted by Earth models assuming hydrostatic equilibrium than do the prior estimates (425-435 sd) by the resonance method. The deconvolution process also yields the excitation function as a by-product, the physical sources of which await further studies.
NASA Astrophysics Data System (ADS)
Carnevale, Diego; Vitzthum, Veronika; Lafon, Olivier; Trébosc, Julien; Amoureux, Jean-Paul; Bodenhausen, Geoffrey
2012-11-01
This Letter shows that interleaved sequences of short pulses in the manner of 'Delays Alternating with Nutation for Tailored Excitation' (DANTE) with N = 1, 2, 3 … equidistant pulses per rotor period extending over K rotor periods can be used to excite, invert or refocus a large number of spinning sidebands of spin-1/2 nuclei in paramagnetic samples where hyperfine couplings lead to very broad spectra that extend over more than 1 MHz. The breadth of the response is maintained for rf-field amplitudes as low as 30 kHz since it results from cumulative effects of individual pulses with very short durations.
NASA Astrophysics Data System (ADS)
Petit, A.; Souchay, J.; Lhotka, C.
2014-05-01
Context. Several asteroids have recently been visited by spacecrafts that give us precious information and new constraints on their physical and rotational properties. In parallel, there are already several well-established theories to model the rotational motion of a rigid body, but accurate models of the rotational motion of asteroids have been poorly investigated so far. Aims: We aim to model the rotational motion of the asteroids (1) Ceres, (4) Vesta, (433) Eros, (2867) Steins, and (25143) Itokawa with high precision. Their physical parameters have been or will be (in the case of Ceres) better constrained by data from space missions. We concentrate in particular on the motion of their spin axis in space, a component that is generally not studied. Methods: We used Kinoshita's theory, based on a Hamiltonian approach for the rotation of a rigid body. We deduced an analytical model for determining the precession rate and the nutation coefficients for the set of five asteroids selected above. Results: For each asteroid considered we make a summary of the rotational and physical characteristics necessary for our calculations, and we give both the precession rate and accurate tables of nutation. Results show a very high precession rate for (25143) Itokawa, of more than one degree per decade (˙ψ = - (461.52 ± 6.57)'' /yr), and rather high ones for (433) Eros and (2867) Steins. We present the complete tables of nutation for both (1) Ceres and (4) Vesta, and give the peak-to-peak amplitudes for the five asteroids. At last, we show the curves described by the spin axis in space. Results agree with previous ones for (4)Vesta and (433) Eros. Conclusions: In this paper we show that it is possible to accurately compute the combined precession-nutation motion of asteroids that are well constrained by observational data as we do for a set of five asteroids. This enables one to understand the rotational behavior of their spin axis in space and constitutes an interesting step
On the modal damping ratios of shear-type structures equipped with Rayleigh damping systems
NASA Astrophysics Data System (ADS)
Trombetti, T.; Silvestri, S.
2006-04-01
The effects of added manufactured viscous dampers upon shear-type structures are analytically investigated here for the class of Rayleigh damping systems. The definitions of mass proportional damping (MPD) and stiffness proportional damping (SPD) systems are briefly recalled and their physical counterpart is derived. From basic physics, a detailed mathematical demonstration that the first modal damping ratio of a structure equipped with the MPD system is always larger than the first modal damping ratio of a structure equipped with the SPD system is provided here. All results are derived for the class of structures characterised by constant values of lateral stiffness and storey mass, under the equal "total size" constraint. The paper also provides closed form demonstrations of other properties of modal damping ratios which further indicate that the MPD and the SPD systems are respectively characterised by the largest and the smallest damping efficiency among Rayleigh damping systems subjected to base excitation. A numerical application with realistic data corresponding to an actual seven-storey building structure is presented to illustrate and verify the theoretical findings.
Damping of Electron Density Structures and Implications for Interstellar Scintillation
NASA Astrophysics Data System (ADS)
Smith, K. W.; Terry, P. W.
2011-04-01
The forms of electron density structures in kinetic Alfvén wave (KAW) turbulence are studied in connection with scintillation. The focus is on small scales L ~ 108-1010 cm where the KAW regime is active in the interstellar medium, principally within turbulent H II regions. Scales at 10 times the ion gyroradius and smaller are inferred to dominate scintillation in the theory of Boldyrev et al. From numerical solutions of a decaying KAW turbulence model, structure morphology reveals two types of localized structures, filaments and sheets, and shows that they arise in different regimes of resistive and diffusive damping. Minimal resistive damping yields localized current filaments that form out of Gaussian-distributed initial conditions. When resistive damping is large relative to diffusive damping, sheet-like structures form. In the filamentary regime, each filament is associated with a non-localized magnetic and density structure, circularly symmetric in cross section. Density and magnetic fields have Gaussian statistics (as inferred from Gaussian-valued kurtosis) while density gradients are strongly non-Gaussian, more so than current. This enhancement of non-Gaussian statistics in a derivative field is expected since gradient operations enhance small-scale fluctuations. The enhancement of density gradient kurtosis over current kurtosis is not obvious, yet it suggests that modest density fluctuations may yield large scintillation events during pulsar signal propagation. In the sheet regime the same statistical observations hold, despite the absence of localized filamentary structures. Probability density functions are constructed from statistical ensembles in both regimes, showing clear formation of long, highly non-Gaussian tails.
Effects of damping wigglers on beam dynamics in the NLC damping rings
Wolski, Andrzej; Wu, Ying
2001-06-16
To achieve the required damping time in the main damping rings for the Next Linear Collider (NLC), a wiggler will be required in each ring with integrated squared field strength up to 110 T{sup 2}m. There are concerns that nonlinear components of the wiggler field will damage the dynamic aperture of the ring, leading to poor injection efficiency. Severe effects from an insertion device have been observed and corrected in SPEAR 2. In this paper, we describe a model that we have developed to study the effects of the damping wiggler, compare the predictions of the model with actual experience in the case of the SPEAR 2 wiggler, and consider the predicted effects of current damping wiggler design on the NLC main damping rings.
Gilbert damping in magnetic layered systems
NASA Astrophysics Data System (ADS)
Barati, E.; Cinal, M.; Edwards, D. M.; Umerski, A.
2014-07-01
The Gilbert damping constant present in the phenomenological Landau-Lifshitz-Gilbert equation describing the dynamics of magnetization is calculated for ferromagnetic metallic films as well as Co/nonmagnet (NM) bilayers. The calculations are done within a realistic nine-orbital tight-binding model including spin-orbit coupling. The convergence of the damping constant expressed as a sum over the Brillouin zone is remarkably improved by introducing finite temperature into the electronic occupation factors and subsequent summation over the Matsubara frequencies. We investigate how the Gilbert damping constant depends on the ferromagnetic film thickness as well as on the thickness of the nonmagnetic cap in Co/NM bilayers (NM=Cu, Pd, Ag, Pt, and Au). The obtained theoretical dependence of the damping constant on the electron-scattering rate, describing the average lifetime of electronic states, varies substantially with the ferromagnetic film thickness and it differs significantly from the dependence for bulk ferromagnetic metals. The presence of nonmagnetic caps is found to largely enhance the magnetic damping in Co/NM bilayers in accordance with experimental data. Unlike Cu, Ag, and Au a particularly strong enhancement is obtained for Pd and Pt caps. This is attributed to the combined effect of the large spin-orbit couplings of Pd and Pt and the simultaneous presence of d states at the Fermi level in these two metals. The calculated Gilbert damping constant also shows an oscillatory dependence on the thicknesses of both ferromagnetic and nonmagnetic parts of the investigated systems which is attributed to quantum-well states. Finally, the expression for contributions to the damping constant from individual atomic layers is derived. The obtained distribution of layer contributions in Co/Pt and Co/Pd bilayers proves that the enhanced damping which affects the dynamics of the magnetization in the Co film originates mainly from a region within the nonmagnetic part of the
Damping and spectral formation of upstream whistlers
Orlowski, D.S.; Russell, C.T.; Krauss-Varban, D.
1995-09-01
Previous studies have indicated that damping rates of upstream whistlers strongly depend on the details of the electron distribution function. Moreover, detailed analysis of Doppler shift and the whistler dispersion relation indicate that upstream whistlers propagate obliquely in a finite band of frequencies. In this paper we present results of a kinetic calculation of damping lengths of wideband whistlers using the sum of seven drifting bi-Maxwellian electron distributions as a best fit to the ISEE 1 electron data. For two cases, when upstream whistlers are observed, convective damping lengths derived from ISEE magnetic field and ephemeris data are compared with theoretical results. We find that the calculated convective damping lengths are consistent with the data and that upstream whistlers remain marginally stable. We also show that the slope of plasma frame spectra of upstream whistlers, obtained by direct fitting of the observed spectra, is between 5 and 7. The overall spectral, wave, and particle characteristics, proximity to the shock, as well as propagation and damping properties indicated that these waves cannot be generated locally. Instead, the observed upstream whistlers arise in the shock ramp, most likely by a variety of cross-field drift and/or anisotropy driven instabilities. 57 refs., 11 figs.
Radiation damping in microcoil NMR probes
NASA Astrophysics Data System (ADS)
Krishnan, V. V.
2006-04-01
Radiation damping arises from the field induced in the receiver coil by large bulk magnetization and tends to selectively drive this magnetization back to equilibrium much faster than relaxation processes. The demand for increased sensitivity in mass-limited samples has led to the development of microcoil NMR probes that are capable of obtaining high quality NMR spectra with small sample volumes (nL-μL). Microcoil probes are optimized to increase sensitivity by increasing either the sample-to-coil ratio (filling factor) of the probe or quality factor of the detection coil. Though radiation damping effects have been studied in standard NMR probes, these effects have not been measured in the microcoil probes. Here a systematic evaluation of radiation damping effects in a microcoil NMR probe is presented and the results are compared with similar measurements in conventional large volume samples. These results show that radiation-damping effects in microcoil probe is much more pronounced than in 5 mm probes, and that it is critically important to optimize NMR experiments to minimize these effects. As microcoil probes provide better control of the bulk magnetization, with good RF and B0 inhomogeneity, in addition to negligible dipolar field effects due to nearly spherical sample volumes, these probes can be used exclusively to study the complex behavior of radiation damping.
Radiation damping in microcoil NMR probes.
Krishnan, V V
2006-04-01
Radiation damping arises from the field induced in the receiver coil by large bulk magnetization and tends to selectively drive this magnetization back to equilibrium much faster than relaxation processes. The demand for increased sensitivity in mass-limited samples has led to the development of microcoil NMR probes that are capable of obtaining high quality NMR spectra with small sample volumes (nL-microL). Microcoil probes are optimized to increase sensitivity by increasing either the sample-to-coil ratio (filling factor) of the probe or quality factor of the detection coil. Though radiation damping effects have been studied in standard NMR probes, these effects have not been measured in the microcoil probes. Here a systematic evaluation of radiation damping effects in a microcoil NMR probe is presented and the results are compared with similar measurements in conventional large volume samples. These results show that radiation-damping effects in microcoil probe is much more pronounced than in 5 mm probes, and that it is critically important to optimize NMR experiments to minimize these effects. As microcoil probes provide better control of the bulk magnetization, with good RF and B0 inhomogeneity, in addition to negligible dipolar field effects due to nearly spherical sample volumes, these probes can be used exclusively to study the complex behavior of radiation damping.
Anti-damping effect of radiation reaction
NASA Astrophysics Data System (ADS)
Wang, G.; Li, H.; Shen, Y. F.; Yuan, X. Z.; Zi, J.
2010-01-01
The anti-damping effect of radiation reaction, which means the radiation reaction does non-negative work on a radiating charge, is investigated at length by using the Lorentz-Dirac equation (LDE) for the motion of a point charge respectively acted on by (a) a pure electric field, (b) a pure magnetic field and (c) the fields of an electromagnetic wave. We found that the curvature of the charge's trajectory plays an important role in the radiation reaction force, and the anti-damping effect cannot take place for the real macroscopic motions of a point charge. The condition for this anti-damping effect to take place is that the gradient of the external force field must exceed a certain value over the region of magnitude of the classical radius of massive charges (~10-15 m). Our results are potentially helpful to lessen the controversy on LDE and justify it as the correct classical equation describing the radiating charge's motion. If this anti-damping effect of LDE were a real existing physical process, it could serve as a mechanism within the context of classical electrodynamics for the stability of hydrogen atoms. Using the picture of an electron in quantum electrodynamics, namely the negative bare charge surrounded by the polarized positive charges of vacuum, we can obtain a reasonable explanation for the energy transferred to the electron during the occurrence of the anti-damping effect, on which the venerable work of Wheeler and Feynman has thrown some light.
Damping by branching: a bioinspiration from trees.
Theckes, B; Langre, E de; Boutillon, X
2011-12-01
Man-made slender structures are known to be sensitive to high levels of vibration due to their flexibility which often cause irreversible damage. In nature, trees repeatedly endure large amplitudes of motion, mostly caused by strong climatic events, yet with minor or no damage in most cases. A new damping mechanism inspired by the architecture of trees is identified here and characterized in the simplest tree-like structure, a Y-shaped branched structure. Through analytical and numerical analyses of a simple two-degree-of-freedom model, branching is shown to be the key ingredient in this protective mechanism that we call damping-by-branching. It originates in the geometrical nonlinearities so that it is specifically efficient to damp out large amplitudes of motion. A more realistic model, using flexible beam approximation, shows that the mechanism is robust. Finally, two bioinspired architectures are analyzed, showing significant levels of damping achieved via branching with typically 30% of the energy being dissipated in one oscillation. This concept of damping-by-branching is of simple practical use in the design of very slender and flexible structures subjected to extreme dynamical loadings.
Passive damping concepts for slender columns in space structures
NASA Technical Reports Server (NTRS)
Razzaq, Z.; Ekhelikar, R. K.
1985-01-01
An experimental and theoretical study of three different passive damping concepts is conducted for a slender member with partial rotational end restraints. Over a hundred full-scale natural vibration experiments were conducted to evaluate the effectiveness of mass-string, polyethylene tubing, and chain damping concepts. The damping properties obtained from the experiments were used in the approximate analyses based on the partial differential equation of motion for the problem. The comparison of the experimental and the theoretical deflection-time relations shows that the velocity-dependent damping model used in the theory is adequate. From the experimental results, the effect of end connection friction and induced axial forces on damping is identified. The definition of an efficiency index is proposed based on the damping ratio and the mass of a given passive damping device. Using this definition, the efficiencies of the three damping devices are compared. The polyethylene tubing concept resulted into a low damping efficiency.
Liu, Yong; Gracia, Jose R,; King, Jr, Thomas J.; ...
2014-05-16
The U.S. Eastern Interconnection (EI) is one of the largest electric power grids in the world and is expected to have difficulties in dealing with frequency regulation and oscillation damping issues caused by the increasing wind power. On the other side, variable-speed wind generators can actively engage in frequency regulation or oscillation damping with supplementary control loops. This paper creates a 5% wind power penetration simulation scenario based on the 16 000-bus EI system dynamic model and developed the user-defined wind electrical control model in PSS (R) E that incorporates additional frequency regulation and oscillation damping control loops. We evaluatedmore » the potential contributions of variable-speed wind generations to the EI system frequency regulation and oscillation damping, and simulation results demonstrate that current and future penetrations of wind power are promising in the EI system frequency regulation and oscillation damping.« less
Liu, Yong; Gracia, Jose R,; King, Jr, Thomas J.; Liu, Yilu
2014-05-16
The U.S. Eastern Interconnection (EI) is one of the largest electric power grids in the world and is expected to have difficulties in dealing with frequency regulation and oscillation damping issues caused by the increasing wind power. On the other side, variable-speed wind generators can actively engage in frequency regulation or oscillation damping with supplementary control loops. This paper creates a 5% wind power penetration simulation scenario based on the 16 000-bus EI system dynamic model and developed the user-defined wind electrical control model in PSS (R) E that incorporates additional frequency regulation and oscillation damping control loops. We evaluated the potential contributions of variable-speed wind generations to the EI system frequency regulation and oscillation damping, and simulation results demonstrate that current and future penetrations of wind power are promising in the EI system frequency regulation and oscillation damping.
Thin-layer magnetostrictive composite films for turbomachinery fan blade damping
NASA Astrophysics Data System (ADS)
Pulliam, Wade J.; Lee, Donggun; Carman, Gregory P.; McKnight, Geoffrey P.
2003-08-01
Recently, there have been significant advances in using magnetostrictive particles in a polymer matrix; finding uses in many applications, both as an active transducer and a passive dumper. Termed magnetostrictive particulate composites (MPC), the material provides capabilities identical or superior to the monolithic material. Fortis Technologies has been pursuing improvements in the applications and fabrication of this innovative material. Specifically, this MPC technology provides a passive, broadband, large temperature range, high stiffness, damping material to be used where current technologies fall short. A novel manufacturing technique based on magnetic fields has been developed to distribute magnetostrictive particulates in a polymer resin and apply it in thin-layer on surfaces for vibration damping in environments typical of turbomachinery fan blades. These magnetostrictive particulates provide damping through domain wall switching, a non-conservative action which provides a high loss factor, and, in turn, significant vibration mitigation. The magnetostrictive damping composites can be easily fabricated into thin films, provide stiffness and strength while also incorporating damping capabilities which exceed in performance and temperature range viscoelastic materials, the current state of the art for applied blade damping. Analytical studies, a finite element analysis and experimental study of the new material in a typical turbomachinery blade loading condition has been conducted and has demonstrated the benefits of this technology.
Highly damped kinematic coupling for precision instruments
Hale, Layton C.; Jensen, Steven A.
2001-01-01
A highly damped kinematic coupling for precision instruments. The kinematic coupling provides support while causing essentially no influence to its nature shape, with such influences coming, for example, from manufacturing tolerances, temperature changes, or ground motion. The coupling uses three ball-cone constraints, each combined with a released flexural degree of freedom. This arrangement enables a gain of higher load capacity and stiffness, but can also significantly reduce the friction level in proportion to the ball radius divided by the distance between the ball and the hinge axis. The blade flexures reduces somewhat the stiffness of the coupling and provides an ideal location to apply constrained-layer damping which is accomplished by attaching a viscoelastic layer and a constraining layer on opposite sides of each of the blade flexures. The three identical ball-cone flexures provide a damped coupling mechanism to kinematically support the projection optics system of the extreme ultraviolet lithography (EUVL) system, or other load-sensitive apparatus.
Measurement of damping of graphite epoxy materials
NASA Technical Reports Server (NTRS)
Crocker, M. J.
1985-01-01
The design of an experiment to measure the damping of a cylindrical graphite-epoxy specimen with a three point support and a knife edge support is described as well as equipment used in tests conducted to determine the influence of the support at the two ends of the specimen and to simulate an idealized free-free boundary condition at the two edges. A curve fitting technique is being used to process the frequency response data obtained. Experiments conducted on the thin plate specimen also reveal the influence of the end support condition on the damping ratio of the specimen. The damping ratio values measured for both specimens appear to be strongly influenced by the shape of the specimen and appear to depend on length and fiber orientation as well as the presence of discontinuities such as sharp bends, corners, and notches.
Turbine blade damping device with controlled loading
Marra, John J
2013-09-24
A damping structure for a turbomachine rotor. The damping structure including an elongated snubber element including a first snubber end rigidly attached to a first blade and extending toward an adjacent second blade, and an opposite second snubber end positioned adjacent to a cooperating surface associated with the second blade. The snubber element has a centerline extending radially inwardly in a direction from the first blade toward the second blade along at least a portion of the snubber element between the first and second snubber ends. Rotational movement of the rotor effects relative movement between the second snubber end and the cooperating surface to position the second snubber end in frictional engagement with the cooperating surface with a predetermined damping force determined by a centrifugal force on the snubber element.
Radiation damping in focusing-dominated systems
Huang, Zhirong; Chen, Pisin; Ruth, R.D.
1995-06-01
A quasi-classical method is developed to calculate the radiation damping of a relativistic particle in a straight, continuous focusing system. In one limiting case where the pitch angle of the particle {theta}{sub p} is much larger than the radiation opening angle 1/{gamma}, the radiation power spectrum is similar to synchrotron radiation and the relative damping rate of the transverse action is proportional to the relative energy loss rate. In the other limiting case where {theta}{sub p} {much_lt} 1/{gamma}, the radiation is dipole in nature and the relative damping rate of the transverse action is energy-independent and is much faster than the relative energy rate. Quantum excitation to the transverse action is absent in this focusing channel. These results can be extended to bent systems provided that the focusing field dominates over the bending field.
Resolving photons from cosmic ray in DAMPE
NASA Astrophysics Data System (ADS)
Xu, Zunlei; Chang, Jin; Li, Xiang; Dong, TieKuang; Zang, Jingjing
2016-07-01
The Dark Matter Particle Explorer(DAMPE), which took to the skies on 17 December, is designed for high energy cosmic ray ion detection. The proportion of photons in the cosmic ray is very small, so it's difficult to distinguish between photons and 'background', but necessary for any DAMPE gamma-ray science goals.The paper present a algorithm to identify photons from 'background' mainly by the tracker/converter, which promote pair conversion and measure the directions of incident particles, and an anticoincidence detector,featuring an array of plastic scintillator to detect the charged particles.The method has been studied by simulating using the GEANT4 Monte Carlo simulation code and adjusted by the BeamTest at CERN in December,2014.In addition,DAMPE photon detection capabilities can be checked using the flight data.
Turbine blade damping device with controlled loading
Marra, John J.
2015-09-29
A damping structure for a turbomachine rotor. The damping structure including an elongated snubber element including a first snubber end rigidly attached to a first blade and extending toward an adjacent second blade, and an opposite second snubber end positioned adjacent to a cooperating surface associated with the second blade. The snubber element has a centerline extending radially inwardly in a direction from the first blade toward the second blade along at least a portion of the snubber element between the first and second snubber ends. Rotational movement of the rotor effects relative movement between the second snubber end and the cooperating surface to position the second snubber end in frictional engagement with the cooperating surface with a predetermined damping force determined by a centrifugal force on the snubber element.
Viscous damping of perforated planar micromechanical structures
Homentcovschi, D.; Miles, R.N.
2008-01-01
The paper gives an analytical approximation to the viscous damping coefficient due to the motion of a gas between a pair of closely spaced fluctuating plates in which one of the plates contains a regular system of circular holes. These types of structures are important parts of many microelectromechanical devices realized in MEMS technology as microphones, microaccelerometers, resonators, etc. The pressure satisfies a Reynolds’ type equation with coefficients accounting for all the important effects: compressibility of the gas, inertia and possibly slip of the gas on the plates. An analytical expression for the optimum number of circular holes which assure a minimum value of the total damping coefficient is given. This value realizes an equilibrium between the squeeze-film damping and the viscous resistance of the holes. The paper also provides analytical design formulas to be used in the case of regular circular perforated plates. PMID:19365579
Passively damped vibration welding system and method
Tan, Chin-An; Kang, Bongsu; Cai, Wayne W.; Wu, Tao
2013-04-02
A vibration welding system includes a controller, welding horn, an anvil, and a passive damping mechanism (PDM). The controller generates an input signal having a calibrated frequency. The horn vibrates in a desirable first direction at the calibrated frequency in response to the input signal to form a weld in a work piece. The PDM is positioned with respect to the system, and substantially damps or attenuates vibration in an undesirable second direction. A method includes connecting the PDM having calibrated properties and a natural frequency to an anvil of an ultrasonic welding system. Then, an input signal is generated using a weld controller. The method includes vibrating a welding horn in a desirable direction in response to the input signal, and passively damping vibration in an undesirable direction using the PDM.
Biomimetic Gradient Polymers with Enhanced Damping Capacities.
Wang, Dong; Zhang, Huan; Guo, Jing; Cheng, Beichen; Cao, Yuan; Lu, Shengjun; Zhao, Ning; Xu, Jian
2016-04-01
Designing gradient structures, mimicking biological materials, such as pummelo peels and tendon, is a promising strategy for developing advanced materials with superior energy damping capacities. Here a facile and effective approach for fabricating polymers with composition gradients at millimeter length scale is presented. The gradient thiol-ene polymers (TEPs) are created by the use of density difference of ternary thiol-ene-ene precursors and the subsequent photo-crosslinking via thiol-ene reaction. The compositional gradients are analyzed via differential scanning calorimeter (DSC), compressive modulus testing, atomic force microscopy (AFM) indentation, and swelling measurements. In contrast to homogeneous TEPs networks, the resultant gradient polymer shows a broader effective damping temperature range combining with good mechanical properties. The present result provides an effective route toward high damping materials by the fabrication of gradient structures.
Fluid damping of cylindrical liquid storage tanks.
Habenberger, Joerg
2015-01-01
A method is proposed in order to calculate the damping effects of viscous fluids in liquid storage tanks subjected to earthquakes. The potential equation of an ideal fluid can satisfy only the boundary conditions normal to the surface of the liquid. To satisfy also the tangential interaction conditions between liquid and tank wall and tank bottom, the potential flow is superimposed by a one-dimensional shear flow. The shear flow in this boundary layer yields to a decrease of the mechanical energy of the shell-liquid-system. A damping factor is derived from the mean value of the energy dissipation in time. Depending on shell geometry and fluid viscosity, modal damping ratios are calculated for the convective component.
Dirken, P J; Nachtegaal, G H; Kentgens, A P
1995-11-01
Framework aluminosilicate glasses with varying charge-balancing cation (Li, Na, K, Rb and Cs) have been studied with 27Al and 29Si magic-angle spinning nuclear magnetic resonance (MAS NMR) and 27Al on-resonance and off-resonance nutation NMR spectroscopy. This first application of off-resonance nutation NMR to disordered samples proves that it is a promising technique for the determination of mean quadrupole interactions in amorphous systems. Linewidths for Al decrease systematically with increasing size of the cation, due to a decrease in the quadrupole interaction from 5.0 MHz for the Li glass to 2.8 MHz for the Cs glass. A simple point-charge model effectively predicts the decrease in the quadrupole interaction. This indicates that the alkali ion is located close to aluminum. Looking at the residual linewidth after subtraction of the quadrupole broadening, the Al chemical shift distribution does not change significantly with the type of alkali ion. The same is true for the observed Si linewidth.
Radiation Damping in a Focusing Channel
NASA Astrophysics Data System (ADS)
Ruth, Ronald D.
1996-05-01
In electron storage rings synchrotron radiation leads to the damping of the three degrees of freedom of the particle trajectory towards a stable closed orbit transversely and a fixed stable phase longitudinally. At the same time, the emission of discrete quanta leads to diffusion in all three degrees of freedom. These two competing effects result in an equilibrium beam emittance that depends upon the parameters of the storage ring. In the case above, the radiation in the bending fields dominates, and the radiation due to the focusing fields is either neglected or taken into account perturbatively. In this talk we study the opposite case, a continuous focusing channel in which the radiation and its reaction are dominated by the strong focusing field. If there is a bending field, it is much weaker than the focusing field. In such focusing systems, we find that the radiation is synchrotron-like for larger betatron oscillation amplitudes and undulator-like for smaller amplitudes. However, quantum excitation is absent for any oscillation amplitude, and the damping exhibits asymmetry in favor of the transverse degree of freedom as the amplitude becomes smaller. In the undulator regime, the damping turns into exponential in the transverse direction, much faster than the total energy damping in this system. In principle, the particle could damp to the transverse ground state of the harmonic oscillator, reaching a minimum normalized emittance, γ ɛ_min = hbar/2mc, limited only by the uncertainty principle. In the case of a bent focusing system, we find that the lack of quantum excitation and asymmetric damping still hold provided that the bending field is sufficiently weak.
Lag-stabilized force feedback damping
Petterson, B.J.; Robinett, R.D.; Werner, J.C.
1991-05-01
A lag-stabilized, force feedback controller for damping initial and residual oscillations of a planar, cantilevered flexible arm has been analytically developed and experimentally implemented on a commercial robot. The controller feeds back force sensor measurements that are delayed in time and proportional to the displacement (angular orientation) of the arm in order to damp the oscillation. As a result of the lag (contrary to popular belief), the controlled robot system is stable and provides tunable performance on a Cincinnati Milacron T3-786 robot. 3 refs., 9 figs., 2 tabs.
Particle systems and nonlinear Landau damping
Villani, Cédric
2014-03-15
Some works dealing with the long-time behavior of interacting particle systems are reviewed and put into perspective, with focus on the classical Kolmogorov–Arnold–Moser theory and recent results of Landau damping in the nonlinear perturbative regime, obtained in collaboration with Clément Mouhot. Analogies are discussed, as well as new qualitative insights in the theory. Finally, the connection with a more recent work on the inviscid Landau damping near the Couette shear flow, by Bedrossian and Masmoudi, is briefly discussed.
Optimal piezoelectric switching technique for vibration damping
NASA Astrophysics Data System (ADS)
Neubauer, Marcus; Oleskiewicz, Robert
2007-04-01
This paper describes piezoelectric switching techniques for vibration damping. The dynamical behaviour of a piezoceramics connected to a switching LR shunt and the dissipated energy are obtained using a fundamental piezoelectric model. All calculations are performed in a normalized way and highlight the influence of the electromechanical coupling coefficient of the piezoceramics and the shunt parameters. For the first time, a precise result for the dynamics of a shunted piezoceramics is derived. The analytic results are used to determine the optimal switching sequence and external branch parameters in order to maximize the damping performance. The results are validated by measurements of a clamped beam.
Wind turbine blade with viscoelastic damping
Sievers, Ryan A.; Mullings, Justin L.
2017-01-10
A wind turbine blade (60) damped by viscoelastic material (54, 54A-F) sandwiched between stiffer load-bearing sublayers (52A, 52B, 56A, 56B) in portions of the blade effective to damp oscillations (38) of the blade. The viscoelastic material may be located in one or more of: a forward portion (54A) of the shell, an aft portion (54D) of the shell, pressure and suction side end caps (54B) of an internal spar, internal webbing walls (54C, 54E), and a trailing edge core (54F).
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.
Mechanical Design of the DAMPE BGO Calorimeter
NASA Astrophysics Data System (ADS)
Hu, Yiming; Wu, Jian; Feng, Changqing; Zhang, Yunlong; Chen, Dengyi; Chang, Jin
The Dark Matter Particle Explorer, DAMPE, is a new designed satellite developed for the CASs new Innovation 2020 program. As the main component of DAMPE, the new designed BGO calorimeter consists of 308 BGO Crystals coupled with photomultiplier tube.The reliability and safety of the BGO Calorimeter structure play a very important role in the operation of whole detector. During the rocket launch, the calorimeter structure should be stable against vibration and environmental factors to ensure detector works in good conditions. In this article, we make the BGO calorimeter structure design, and then prove that it will work in the environments of rocket launch and flight.
Arrangement for damping the resonance in a laser diode
NASA Technical Reports Server (NTRS)
Katz, J.; Yariv, A.; Margalit, S. (Inventor)
1985-01-01
An arrangement for damping the resonance in a laser diode is described. This arrangement includes an additional layer which together with the conventional laser diode form a structure (35) of a bipolar transistor. Therein, the additional layer serves as the collector, the cladding layer next to it as the base, and the active region and the other cladding layer as the emitter. A capacitor is connected across the base and the collector. It is chosen so that at any frequency above a certain selected frequency which is far below the resonance frequency the capacitor impedance is very low, effectively shorting the base to the collector.
Nonlinear Landau damping and Alfven wave dissipation
NASA Technical Reports Server (NTRS)
Vinas, Adolfo F.; Miller, James A.
1995-01-01
Nonlinear Landau damping has been often suggested to be the cause of the dissipation of Alfven waves in the solar wind as well as the mechanism for ion heating and selective preacceleration in solar flares. We discuss the viability of these processes in light of our theoretical and numerical results. We present one-dimensional hybrid plasma simulations of the nonlinear Landau damping of parallel Alfven waves. In this scenario, two Alfven waves nonresonantly combine to create second-order magnetic field pressure gradients, which then drive density fluctuations, which in turn drive a second-order longitudinal electric field. Under certain conditions, this electric field strongly interacts with the ambient ions via the Landau resonance which leads to a rapid dissipation of the Alfven wave energy. While there is a net flux of energy from the waves to the ions, one of the Alfven waves will grow if both have the same polarization. We compare damping and growth rates from plasma simulations with those predicted by Lee and Volk (1973), and also discuss the evolution of the ambient ion distribution. We then consider this nonlinear interaction in the presence of a spectrum of Alfven waves, and discuss the spectrum's influence on the growth or damping of a single wave. We also discuss the implications for wave dissipation and ion heating in the solar wind.
The Stochastic Nonlinear Damped Wave Equation
Barbu, V. Da Prato, G.
2002-12-19
We prove the existence of an invariant measure for the transition semigroup associated with a nonlinear damped stochastic wave equation in R{sup n} of the Klein-Gordon type. The uniqueness of the invariant measure and the structure of the corresponding Kolmogorov operator are also studied.
Radiation damping in pulsed Gaussian beams
NASA Astrophysics Data System (ADS)
Harvey, Chris; Marklund, Mattias
2012-01-01
We consider the effects of radiation damping on the electron dynamics in a Gaussian-beam model of a laser field. For high intensities, i.e., with dimensionless intensity a0≫1, it is found that the dynamics divides into three regimes. For low-energy electrons (low initial γ factor, γ0) the radiation damping effects are negligible. At higher energies, but still at 2γ0
Scattering Theory of Mesoscopic Gilbert Damping
NASA Astrophysics Data System (ADS)
Brataas, Arne
2010-03-01
Magnetic damping determines the performance of magnetic devices including high-frequency oscillators, hard drives, magnetic random access memories, magnetic logic devices, and magnetic field sensors. The drive to improve these devices, to reduce the response time of sensors and the physical dimensions has led to a greater focus on studying the friction force a changing magnetization experiences. We study the magnetization dynamics of single domain ferromagnets and domain walls in contact with a thermal bath by scattering theory. We recover the Landau-Lifshitz-Gilbert equation and express the Gilbert damping tensor in terms of the scattering matrix [1,2]. Dissipation of magnetic energy equals energy current pumped out of the system by the time-dependent magnetization, with separable spin-relaxation induced bulk and spin-pumping generated interface contributions [3]. The scattering theory of Gilbert damping is suitable for first-principles calculations that include disorder and spin-orbit coupling on an equal footing [4]. In linear response, our scattering theory for the Gilbert damping tensor is equivalent with the Kubo formalism. [4pt] [1] A. Brataas, Y. Tserkovnyak, and G. E. W. Bauer, Phys. Rev. Lett. 101, 037207 (2008). [0pt] [2] K. M. D. Hals, A. K. Nguyen, and A. Brataas, Phys. Rev. Lett. 102, 256601 (2009). [0pt] [3] Y. Tserkovnyak, A. Brataas, G. E. W. Bauer, and B. I. Halperin, Rev. Mod. Phys. 77, 1375 (2005). [0pt] [4] A. A. Starikov, P. J. Kelly, A. Brataas, Y. Tserkovnyak, and G. E. W. Bauer, unpublished.
The DAMPE experiment: first data from space
NASA Astrophysics Data System (ADS)
De Mitri, Ivan
2017-03-01
The DAMPE satellite has been successfully launched in orbit on December 2015. The science goals of the mission include the study of high energy cosmic ray electrons, photons, protons and nuclei in a wide energy range: 109 - 1014 eV. A report on the mission status will be presented, together with on-orbit detector performance and first data coming from space.
The DAMPE silicon-tungsten tracker
NASA Astrophysics Data System (ADS)
Azzarello, P.; Ambrosi, G.; Asfandiyarov, R.; Bernardini, P.; Bertucci, B.; Bolognini, A.; Cadoux, F.; Caprai, M.; De Mitri, I.; Domenjoz, M.; Dong, Y.; Duranti, M.; Fan, R.; Fusco, P.; Gallo, V.; Gargano, F.; Gong, K.; Guo, D.; Husi, C.; Ionica, M.; La Marra, D.; Loparco, F.; Marsella, G.; Mazziotta, M. N.; Mesa, J.; Nardinocchi, A.; Nicola, L.; Pelleriti, G.; Peng, W.; Pohl, M.; Postolache, V.; Qiao, R.; Surdo, A.; Tykhonov, A.; Vitillo, S.; Wang, H.; Weber, M.; Wu, D.; Wu, X.; Zhang, F.
2016-09-01
The DArk Matter Particle Explorer (DAMPE) is a spaceborne astroparticle physics experiment, launched on 17 December 2015. DAMPE will identify possible dark matter signatures by detecting electrons and photons in the 5 GeV-10 TeV energy range. It will also measure the flux of nuclei up to 100 TeV, for the study of the high energy cosmic ray origin and propagation mechanisms. DAMPE is composed of four sub-detectors: a plastic strip scintillator, a silicon-tungsten tracker-converter (STK), a BGO imaging calorimeter and a neutron detector. The STK is composed of six tracking planes of 2 orthogonal layers of single-sided micro-strip detectors, for a total detector surface of ca. 7 m2. The STK has been extensively tested for space qualification. Also, numerous beam tests at CERN have been done to study particle detection at silicon module level, and at full detector level. After description of the DAMPE payload and its scientific mission, we will describe the STK characteristics and assembly. We will then focus on some results of single ladder performance tests done with particle beams at CERN.
Chiral damping of magnetic domain walls.
Jué, Emilie; Safeer, C K; Drouard, Marc; Lopez, Alexandre; Balint, Paul; Buda-Prejbeanu, Liliana; Boulle, Olivier; Auffret, Stephane; Schuhl, Alain; Manchon, Aurelien; Miron, Ioan Mihai; Gaudin, Gilles
2016-03-01
Structural symmetry breaking in magnetic materials is responsible for the existence of multiferroics, current-induced spin-orbit torques and some topological magnetic structures. In this Letter we report that the structural inversion asymmetry (SIA) gives rise to a chiral damping mechanism, which is evidenced by measuring the field-driven domain-wall (DW) motion in perpendicularly magnetized asymmetric Pt/Co/Pt trilayers. The DW dynamics associated with the chiral damping and those with Dzyaloshinskii-Moriya interaction (DMI) exhibit identical spatial symmetry. However, both scenarios are differentiated by their time reversal properties: whereas DMI is a conservative effect that can be modelled by an effective field, the chiral damping is purely dissipative and has no influence on the equilibrium magnetic texture. When the DW motion is modulated by an in-plane magnetic field, it reveals the structure of the internal fields experienced by the DWs, allowing one to distinguish the physical mechanism. The chiral damping enriches the spectrum of physical phenomena engendered by the SIA, and is essential for conceiving DW and skyrmion devices owing to its coexistence with DMI (ref. ).
Apparatus and method of preloading vibration-damping bellows
Cutburth, Ronald W.
1988-01-01
An improved vibration damping bellows mount or interconnection is disclosed. In one aspect, the bellows is compressively prestressed along its length to offset vacuum-generated tensile loads and thereby improve vibration damping characteristics.
Experimental determination of material damping using vibration analyzer
NASA Technical Reports Server (NTRS)
Chowdhury, Mostafiz R.; Chowdhury, Farida
1990-01-01
Structural damping is an important dynamic characteristic of engineering materials that helps to damp vibrations by reducing their amplitudes. In this investigation, an experimental method is illustrated to determine the damping characteristics of engineering materials using a dual channel Fast Fourier Transform (FFT) analyzer. A portable Compaq III computer which houses the analyzer, is used to collect the dynamic responses of three metal rods. Time-domain information is analyzed to obtain the logarithmic decrement of their damping. The damping coefficients are then compared to determine the variation of damping from material to material. The variations of damping from one point to another of the same material, due to a fixed point excitation, and the variable damping at a fixed point due to excitation at different points, are also demonstrated.
Nonlinear damping and quasi-linear modelling.
Elliott, S J; Ghandchi Tehrani, M; Langley, R S
2015-09-28
The mechanism of energy dissipation in mechanical systems is often nonlinear. Even though there may be other forms of nonlinearity in the dynamics, nonlinear damping is the dominant source of nonlinearity in a number of practical systems. The analysis of such systems is simplified by the fact that they show no jump or bifurcation behaviour, and indeed can often be well represented by an equivalent linear system, whose damping parameters depend on the form and amplitude of the excitation, in a 'quasi-linear' model. The diverse sources of nonlinear damping are first reviewed in this paper, before some example systems are analysed, initially for sinusoidal and then for random excitation. For simplicity, it is assumed that the system is stable and that the nonlinear damping force depends on the nth power of the velocity. For sinusoidal excitation, it is shown that the response is often also almost sinusoidal, and methods for calculating the amplitude are described based on the harmonic balance method, which is closely related to the describing function method used in control engineering. For random excitation, several methods of analysis are shown to be equivalent. In general, iterative methods need to be used to calculate the equivalent linear damper, since its value depends on the system's response, which itself depends on the value of the equivalent linear damper. The power dissipation of the equivalent linear damper, for both sinusoidal and random cases, matches that dissipated by the nonlinear damper, providing both a firm theoretical basis for this modelling approach and clear physical insight. Finally, practical examples of nonlinear damping are discussed: in microspeakers, vibration isolation, energy harvesting and the mechanical response of the cochlea.
Mendell, Mark J.
2015-06-01
This report briefly summarizes, based on recent review articles and selected more recent research reports, current scientific knowledge on two topics: assessing unhealthy levels of indoor D/M in homes and remediating home dampness-related problems to protect health. Based on a comparison of current scientific knowledge to that required to support effective, evidence-based, health-protective policies on home D/M, gaps in knowledge are highlighted, prior questions and research questions specified, and necessary research activities and approaches recommended.
Mendell, Mark J.
2015-05-28
This report briefly summarizes, based on recent review articles and selected more recent research reports, current scientific knowledge on two topics: assessing unhealthy levels of indoor D/M in homes and remediating home dampness-related problems to protect health. Based on a comparison of current scientific knowledge to that required to support effective, evidence-based, health-protective policies on home D/M, gaps in knowledge are highlighted, prior questions and research questions specified, and necessary research activities and approaches recommended.
Spectroscopic Evidence of Alfvén Wave Damping in the Off-limb Solar Corona
NASA Astrophysics Data System (ADS)
Gupta, G. R.
2017-02-01
We investigate the off-limb active-region and quiet-Sun corona using spectroscopic data. The active region is clearly visible in several spectral lines formed in the temperature range of 1.1–2.8 MK. We derive the electron number density using the line ratio method, and the nonthermal velocity in the off-limb region up to the distance of 140 Mm. We compare density scale heights derived from several spectral line pairs with expected scale heights per the hydrostatic equilibrium model. Using several isolated and unblended spectral line profiles, we estimate nonthermal velocities in the active region and quiet Sun. Nonthermal velocities obtained from warm lines in the active region first show an increase and then later either a decrease or remain almost constant with height in the far off-limb region, whereas nonthermal velocities obtained from hot lines show consistent decrease. However, in the quiet-Sun region, nonthermal velocities obtained from various spectral lines show either a gradual decrease or remain almost constant with height. Using these obtained parameters, we further calculate Alfvén wave energy flux in both active and quiet-Sun regions. We find a significant decrease in wave energy fluxes with height, and hence provide evidence of Alfvén wave damping. Furthermore, we derive damping lengths of Alfvén waves in the both regions and find them to be in the range of 25–170 Mm. Different damping lengths obtained at different temperatures may be explained as either possible temperature-dependent damping or by measurements obtained in different coronal structures formed at different temperatures along the line of sight. Temperature-dependent damping may suggest some role of thermal conduction in the damping of Alfvén waves in the lower corona.
Enhanced damping for bridge cables using a self-sensing MR damper
NASA Astrophysics Data System (ADS)
Chen, Z. H.; Lam, K. H.; Ni, Y. Q.
2016-08-01
This paper investigates enhanced damping for protecting bridge stay cables from excessive vibration using a newly developed self-sensing magnetorheological (MR) damper. The semi-active control strategy for effectively operating the self-sensing MR damper is formulated based on the linear-quadratic-Gaussian (LQG) control by further considering a collocated control configuration, limited measurements and nonlinear damper dynamics. Due to its attractive feature of sensing-while-damping, the self-sensing MR damper facilitates the collocated control. On the other hand, only the sensor measurements from the self-sensing device are employed in the feedback control. The nonlinear dynamics of the self-sensing MR damper, represented by a validated Bayesian NARX network technique, are further accommodated in the control formulation to compensate for its nonlinearities. Numerical and experimental investigations are conducted on stay cables equipped with the self-sensing MR damper operated in passive and semi-active control modes. The results verify that the collocated self-sensing MR damper facilitates smart damping for inclined cables employing energy-dissipative LQG control with only force and displacement measurements at the damper. It is also demonstrated that the synthesis of nonlinear damper dynamics in the LQG control enhances damping force tracking efficiently, explores the features of the self-sensing MR damper, and achieves better control performance over the passive MR damping control and the Heaviside step function-based LQG control that ignores the damper dynamics.
Damped and zero-damped quasinormal modes of charged, nearly extremal black holes
NASA Astrophysics Data System (ADS)
Zimmerman, Aaron; Mark, Zachary
2016-02-01
Despite recent progress, the complete understanding of the perturbations of charged, rotating black holes as described by the Kerr-Newman metric remains an open and fundamental problem in relativity. In this study, we explore the existence of families of quasinormal modes of Kerr-Newman black holes whose decay rates limit to zero at extremality, called zero-damped modes in past studies. We review the nearly extremal and WKB approximation methods for spin-weighted scalar fields (governed by the Dudley-Finley equation) and give an accounting of the regimes where scalar zero-damped and damped modes exist. Using Leaver's continued fraction method, we verify that these approximations give accurate predictions for the frequencies in their regimes of validity. In the nonrotating limit, we argue that gravito-electromagnetic perturbations of nearly extremal Reissner-Nordström black holes have zero-damped modes in addition to the well-known spectrum of damped modes. We provide an analytic formula for the frequencies of these modes, verify their existence using a numerical search, and demonstrate the accuracy of our formula. These results, along with recent numerical studies, point to the existence of a simple universal equation for the frequencies of zero-damped gravito-electromagnetic modes of Kerr-Newman black holes, whose precise form remains an open question.
Effect of chemical exchange on radiation damping in aqueous solutions of the osmolyte glycine.
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.
Fast damping in mismatched high intensity beam transportation
NASA Astrophysics Data System (ADS)
Variale, V.
2001-08-01
A very fast damping of beam envelope oscillation amplitudes was recently observed in simulations of high intensity beam transport, through periodic FODO cells, in mismatched conditions [V. Variale, Nuovo Cimento Soc. Ital. Fis. 112A, 1571-1582 (1999) and T. Clauser et al., in Proceedings of the Particle Accelerator Conference, New York, 1999 (IEEE, Piscataway, NJ, 1999), p. 1779]. A Landau damping mechanism was proposed at the origin of observed effect. In this paper, to further investigate the source of this fast damping, extensive simulations have been carried out. The results presented here support the interpretation of the mechanism at the origin of the fast damping as a Landau damping effect.
Determining material damping type by comparing modal frequency estimators.
Anthony, D K; Simón, F; Juan, Jesús
2009-09-01
The accuracy of modal frequency and damping estimators for non-lightly damped single degree of freedom systems depend on the response parameter used as well as the damping mechanism. Therefore, in order to make accurate modal parameter measurements, the damping mechanism at play must be known to be either viscous or hysteretic a priori. Here, comparisons between the evaluated frequency values are used to glean this information. The damping mechanism of an experimental system (consisting of resilient layer and mass plate) is then determined using two simple modal parameter estimators and applying statistical methods.
Effects of Landau-Lifshitz-Gilbert damping on domain growth.
Kudo, Kazue
2016-12-01
Domain patterns are simulated by the Landau-Lifshitz-Gilbert (LLG) equation with an easy-axis anisotropy. If the Gilbert damping is removed from the LLG equation, it merely describes the precession of magnetization with a ferromagnetic interaction. However, even without the damping, domains that look similar to those of scalar fields are formed, and they grow with time. It is demonstrated that the damping has no significant effects on domain growth laws and large-scale domain structure. In contrast, small-scale domain structure is affected by the damping. The difference in small-scale structure arises from energy dissipation due to the damping.
Effects of damping on mode shapes, volume 1
NASA Technical Reports Server (NTRS)
Gates, R. M.
1977-01-01
Displacement, velocity, and acceleration admittances were calculated for a realistic NASTRAN structural model of space shuttle for three conditions: liftoff, maximum dynamic pressure and end of solid rocket booster burn. The realistic model of the orbiter, external tank, and solid rocket motors included the representation of structural joint transmissibilities by finite stiffness and damping elements. Methods developed to incorporate structural joints and their damping characteristics into a finite element model of the space shuttle, to determine the point damping parameters required to produce realistic damping in the primary modes, and to calculate the effect of distributed damping on structural resonances through the calculation of admittances.
Koopmans, Peter J; Boyacioğlu, Rasim; Barth, Markus; Norris, David G
2013-06-01
A method for simultaneous multislice (SMS) inversion contrast imaging is presented using a combination of the delays alternating with nutation for tailored excitation (DANTE) and the power independent of the number of slices (PINS) techniques. In SMS imaging, simultaneously excited slices result in an aliased image that is disentangled using parallel imaging reconstruction techniques. At high-magnetic field strengths, the peak amplitude and specific absorption rate of conventional (summed) SMS radio frequency pulses can be prohibitively high. Using the PINS approach, specific absorption rate is independent of the number of slices allowing high SMS acceleration factors even at high fields. Using DANTE, adiabatic SMS radio frequency pulses can be created to be combined with PINS. This allows 2D imaging protocols that employ adiabatic pulses to also reap the benefits of low specific absorption rate SMS acceleration. As a proof-of-concept, simulations and measurements using hyperbolic secant inversion pulses are shown.
NASA Astrophysics Data System (ADS)
Brzeziński, A.; Wielgosz, A.; Bóhm, S.
2015-08-01
In the recent work (Bóhm et al., J. Geodynamics, 62(2012), 56-68) we demonstrated the application of the complex demodulation (CD) technique for VLBI estimation of the Earth orientation parameters (EOP). This technique enables simultaneous determination of the long period components of polar motion (x,y), universal time (dUT1=UT1 UTC) and nutation (celestial pole offsets dX,dY) as well as the high frequency (diurnal, semidiurnal, ...) components of polar motion and dUT1. In this work we perform analysis of the retrograde diurnal component of polar motion and the low frequency component of dUT1 estimated by the VieVS CD software. By comparison to the results based on the celestial pole offsets and dUT1 series from the combined solutions IVS and IERS we demonstrate consistency of the CD parametrization with the standard approach.
Landau damping of magnetospherically reflected whistlers
NASA Technical Reports Server (NTRS)
Thorne, Richard M.; Horne, Richard B.
1994-01-01
Unducted VLF signals produced by lightning activity can form a population of magnetospherically reflected (MR) whistlers in the inner magnetosphere. It has been suggested recently that in the absence of significant attenuation such waves could merge into a broadband continuum with sufficient intensity to account for plasmaspheric hiss. To test this conjecture we have evaluated the path-integrated attenuation of MR whistlers along representative ray paths using the HOTRAY code. Using a realistic plasma distribution modeled on in-situ data, we find that the majority of MR waves experience significant damping after a few transits across the equator. This is primarily due to Landau resonance with suprathermal (0.1-1 keV) electrons. The attenuation is most pronounced for waves that propagate through the outer plasmasphere; this can readily account for the infrequent occurrence of multiple-hop MR waves for L greater than or equal to 3.5. Selected waves that originate at intermediate latitudes (15 deg is less than or equal to lambda is less than or equal to 35 deg) and whose ray paths are confined to the inner plasma- sphere may experience up to 10 magnetospheric reflections before substantial attentuation occurs. These waves should form the population of observed MR waves. Wave attenuation becomes more pronounced at higher frequencies; this can account for the absence of multiple-hop waves above 5 kHz. Weakly attenuated MR waves tend to migrate outward to the L shell, where their frequency is comparable to the equatorial lower hybrid frequency. The enhanced concentration of waves due to a merging of ray paths would produce a spectral feature that rises in frequency at lower L. This is quite distinct from the reported properties of plasmaspheric hiss, which maintains a constant frequency band throughout the entire plasmasphere. Furthermore, in the absence of mode conversion, waves below 500 Hz, which often form an important if not dominant part of the spectral properties
A soft damping function for dispersion corrections with less overfitting.
Ucak, Umit V; Ji, Hyunjun; Singh, Yashpal; Jung, Yousung
2016-11-07
The use of damping functions in empirical dispersion correction schemes is common and widespread. These damping functions contain scaling and damping parameters, and they are usually optimized for the best performance in practical systems. In this study, it is shown that the overfitting problem can be present in current damping functions, which can sometimes yield erroneous results for real applications beyond the nature of training sets. To this end, we present a damping function called linear soft damping (lsd) that suffers less from this overfitting. This linear damping function damps the asymptotic curve more softly than existing damping functions, attempting to minimize the usual overcorrection. The performance of the proposed damping function was tested with benchmark sets for thermochemistry, reaction energies, and intramolecular interactions, as well as intermolecular interactions including nonequilibrium geometries. For noncovalent interactions, all three damping schemes considered in this study (lsd, lg, and BJ) roughly perform comparably (approximately within 1 kcal/mol), but for atomization energies, lsd clearly exhibits a better performance (up to 2-6 kcal/mol) compared to other schemes due to an overfitting in lg and BJ. The number of unphysical parameters resulting from global optimization also supports the overfitting symptoms shown in the latter numerical tests.
A soft damping function for dispersion corrections with less overfitting
NASA Astrophysics Data System (ADS)
Ucak, Umit V.; Ji, Hyunjun; Singh, Yashpal; Jung, Yousung
2016-11-01
The use of damping functions in empirical dispersion correction schemes is common and widespread. These damping functions contain scaling and damping parameters, and they are usually optimized for the best performance in practical systems. In this study, it is shown that the overfitting problem can be present in current damping functions, which can sometimes yield erroneous results for real applications beyond the nature of training sets. To this end, we present a damping function called linear soft damping (lsd) that suffers less from this overfitting. This linear damping function damps the asymptotic curve more softly than existing damping functions, attempting to minimize the usual overcorrection. The performance of the proposed damping function was tested with benchmark sets for thermochemistry, reaction energies, and intramolecular interactions, as well as intermolecular interactions including nonequilibrium geometries. For noncovalent interactions, all three damping schemes considered in this study (lsd, lg, and BJ) roughly perform comparably (approximately within 1 kcal/mol), but for atomization energies, lsd clearly exhibits a better performance (up to 2-6 kcal/mol) compared to other schemes due to an overfitting in lg and BJ. The number of unphysical parameters resulting from global optimization also supports the overfitting symptoms shown in the latter numerical tests.
Relativity Damps OPEP in Nuclear Matter
NASA Astrophysics Data System (ADS)
Banerjee, Manoj K.
1998-09-01
Using a relativistic Dirac--Brueckner analysis the OPEP contribution to the ground state energy of nuclear matter is studied. In the study the pion is derivative-coupled. We find that the role of the tensor force in the saturation mechanism is substantially reduced compared to its dominant role in a usual nonrelativistic treatment. We show that the damping of derivative-coupled OPEP is actually due to the decrease of M*/M with increasing density. We point out that if derivative-coupled OPEP is the preferred form of nuclear effective Lagrangian nonrelativistic treatment of nuclear matter is in trouble. Lacking the notion of M* it cannot replicate the damping. We suggest an examination of the feasibility of using pseudoscalar coupled πN interaction before reaching a final conclusion about nonrelativistic treatment of nuclear matter.
Nonlinear Landau damping in the ionosphere
NASA Technical Reports Server (NTRS)
Kiwamoto, Y.; Benson, R. F.
1978-01-01
A model is presented to explain the non-resonant waves which give rise to the diffuse resonance observed near 3/2 f sub H by the Alouette and ISIS topside sounders, where f sub H is the ambient electron cyclotron frequency. In a strictly linear analysis, these instability driven waves will decay due to Landau damping on a time scale much shorter than the observed time duration of the diffuse resonance. Calculations of the nonlinear wave particle coupling coefficients, however, indicate that the diffuse resonance wave can be maintained by the nonlinear Landau damping of the sounder stimulated 2f sub H wave. The time duration of the diffuse resonance is determined by the transit time of the instability generated and nonlinearly maintained diffuse resonance wave from the remote short lived hot region back to the antenna. The model is consistent with the Alouette/ISIS observations, and clearly demonstrates the existence of nonlinear wave-particle interactions in the ionosphere.
Harmonic cavities for the NLC damping rings
de Santis, S.; Wolski, A.
2003-05-29
To achieve high luminosity, a linear collider needs damping rings to produce beams with very small transverse emittances. In the NLC, design constraints place the Main Damping Rings in a parameter regime where intrabeam scattering (IBS) is likely to be a limitation on the emittance, and hence on the final luminosity. It is possible to mitigate the effects of IBS by lengthening the bunch: this may be achieved by redesigning the lattice with higher momentum compaction, or by use of higher harmonic cavities. Here, we consider the latter approach. We estimate the required bunch lengthening that might be needed, outline some appropriate parameters for the harmonic cavities, and discuss some of the effects that might be introduced or exacerbated by the cavities, such as synchronous phase variation along the bunch train.
Movers and shakers: granular damping in microgravity.
Bannerman, M N; Kollmer, J E; Sack, A; Heckel, M; Mueller, P; Pöschel, T
2011-07-01
The response of an oscillating granular damper to an initial perturbation is studied using experiments performed in microgravity and granular dynamics simulations. High-speed video and image processing techniques are used to extract experimental data. An inelastic hard sphere model is developed to perform simulations and the results are in excellent agreement with the experiments. In line with previous work, a linear decay of the amplitude is observed. Although this behavior is typical for a friction-damped oscillator, through simulation it is shown that this effect is still present even when friction forces are absent. A simple expression is developed which predicts the optimal damping conditions for a given amplitude and is independent of the oscillation frequency and particle inelasticities.
Relativity damps OPEP in nuclear matter
Banerjee, M.K.
1998-06-01
Using a relativistic Dirac-Brueckner analysis the OPEP contribution to the ground state energy of nuclear matter is studied. In the study the pion is derivative-coupled. The author finds that the role of the tensor force in the saturation mechanism is substantially reduced compared to its dominant role in a usual nonrelativistic treatment. He shows that the damping of derivative-coupled OPEP is actually due to the decrease of M{sup *}/M with increasing density. He points out that if derivative-coupled OPEP is the preferred form of nuclear effective lagrangian nonrelativistic treatment of nuclear matter is in trouble. Lacking the notion of M{sup *} it cannot replicate the damping. He suggests an examination of the feasibility of using pseudoscalar coupled {pi}N interaction before reaching a final conclusion about nonrelativistic treatment of nuclear matter.
Enthalpy damping for the steady Euler equations
NASA Technical Reports Server (NTRS)
Jespersen, D. C.
1984-01-01
For inviscid steady flow problems where the enthalpy is constant at steady state, it was previously proposed to use the difference between the local enthalpy and the steady state enthalpy as a driving term to accelerate convergence of iterative schemes. This idea is analyzed, both on the level of the partial differential equation and on the level of a particular finite difference scheme. It is shown that for the two-dimensional unsteady Euler equations, a hyperbolic system with eigenvalues on the imaginary axis, there is no enthalpy damping strategy which moves all the eigenvalues into the open left half plane. For the numerical scheme, however, the analysis shows and examples verify that enthalpy damping is potentially effective in accelerating convergence to steady state.
Enthalpy damping for the steady Euler equations
NASA Technical Reports Server (NTRS)
Jespersen, D. C.
1985-01-01
For inviscid steady flow problems where the enthalpy is constant at steady state, it was previously proposed to use the difference between the local enthalpy and the steady state enthalpy as a driving term to accelerate convergence of iterative schemes. This idea is analyzed, both on the level of the partial differential equation and on the level of a particular finite difference scheme. It is shown that for the two-dimensional unsteady Euler equations, a hyperbolic system with eigenvalues on the imaginary axis, there is no enthalpy damping strategy which moves all the eigenvalues into the open left half plane. For the numerical scheme, however, the analysis shows and examples verify that enthalpy damping is potentially effective in accelerating convergence to steady state.
On the damping capacity of cast irons
NASA Astrophysics Data System (ADS)
Golovin, S. A.
2012-07-01
The treatment of experimental data on the amplitude-dependent internal friction (ADIF) in terms of various theoretical models has revealed a staged character and the main mechanisms of the processes of energy dissipation in graphite with increasing amplitude of vibrations upon cyclic loading. It is shown that the level of the damping capacity of lamellar cast iron depends on the relationship between the elastic and strength characteristics of graphite and the matrix phase. In cast irons with a rigid matrix structure (pearlite, martensite), the energy dissipation is determined by the volume fraction and morphology of the initial graphite phase. In cast irons with a softer metallic phase (ferrite), the contact interaction of graphite inclusions with the matrix and the properties of the matrix introduce additional sources of high damping.
Pressurized fluid damping of nanoelectromechanical systems.
Svitelskiy, Oleksiy; Sauer, Vince; Liu, Ning; Cheng, Kar-Mun; Finley, Eric; Freeman, Mark R; Hiebert, Wayne K
2009-12-11
Interactions of nanoscale structures with fluids are of current interest both in the elucidation of fluid dynamics at these small scales, and in determining the ultimate performance of nanoelectromechanical systems outside of vacuum. We present a comprehensive study of nanomechanical damping in three gases (He, N2, CO2), and liquid CO2. Resonant dynamics in multiple devices of varying size and frequency is measured over 10 decades of pressure (1 mPa-20 MPa) using time-domain stroboscopic optical interferometry. The wide pressure range allows full exploration of the regions of validity of Newtonian and non-Newtonian flow damping models. Observing free molecular flow behavior extending above 1 atm, we find a fluid relaxation time model to be valid throughout, but not beyond, the non-Newtonian regime, and a Newtonian flow vibrating spheres model to be valid in the viscous limit.
Development of Transverse Modes Damped DLA Structure
Jing, C.; Kanareykin, A.; Schoessow, P.; Gai, W.; Konecny, R.; Power, J. G.; Conde, M.
2009-01-22
As the dimensions of accelerating structures become smaller and beam intensities higher, the transverse wakefields driven by the beam become quite large with even a slight misalignment of the beam from the geometric axis. These deflection modes can cause inter-bunch beam breakup and intra-bunch head-tail instabilities along the beam path, and thus BBU control becomes a critical issue. All new metal based accelerating structures, like the accelerating structures developed at SLAC or power extractors at CLIC, have designs in which the transverse modes are heavily damped. Similarly, minimizing the transverse wakefield modes (here the HEMmn hybrid modes in Dielectric-Loaded Accelerating (DLA) structures) is also very critical for developing dielectric based high energy accelerators. In this paper, we present the design of a 7.8 GHz transverse mode damped DLA structure currently under construction, along with plans for the experimental program.
Plasmon damping in graphene out of equilibrium
NASA Astrophysics Data System (ADS)
Sun, Zhiyuan; Basov, Dimitri; Fogler, Michael
Motivated by recent experiments with graphene under high photoexcitation, we study theoretically plasmons of graphene in the two-temperature regime, i.e., the regime where electrons are much hotter than the lattice. We calculate the plasmon damping due to scattering of electrons by acoustic phonons, which is the dominant intrinsic contribution in clean graphene. As the system relaxes to equilibrium, the plasmon frequency adiabatically changes with time. We show that this causes a partial compensation of the plasmon damping. A similar mechanism may apply to another collective mode (the energy wave) predicted to exist in graphene in the low-frequency hydrodynamic regime. Implications for infrared and THz pump-probe experiments are discussed.
Wakefield Damping for the CLIC Crab Cavity
Ambattu, P.K.; Burt, G.; Dexter, A.C.; Carter, R.G.; Khan, V.; Jones, R.M.; Dolgashev, V.; /SLAC
2011-12-01
A crab cavity is required in the CLIC to allow effective head-on collision of bunches at the IP. A high operating frequency is preferred as the deflection voltage required for a given rotation angle and the RF phase tolerance for a crab cavity are inversely proportional to the operating frequency. The short bunch spacing of the CLIC scheme and the high sensitivity of the crab cavity to dipole kicks demand very high damping of the inter-bunch wakes, the major contributor to the luminosity loss of colliding bunches. This paper investigates the nature of the wakefields in the CLIC crab cavity and the possibility of using various damping schemes to suppress them effectively.
Turner, Neil A
2016-05-01
Cardiac fibroblasts (CF) are well-established as key regulators of extracellular matrix (ECM) turnover in the context of myocardial remodelling and fibrosis. Recently, this cell type has also been shown to act as a sensor of myocardial damage by detecting and responding to damage-associated molecular patterns (DAMPs) upregulated with cardiac injury. CF express a range of innate immunity pattern recognition receptors (TLRs, NLRs, IL-1R1, RAGE) that are stimulated by a host of different DAMPs that are evident in the injured or remodelling myocardium. These include intracellular molecules released by necrotic cells (heat shock proteins, high mobility group box 1 protein, S100 proteins), proinflammatory cytokines (interleukin-1α), specific ECM molecules up-regulated in response to tissue injury (fibronectin-EDA, tenascin-C) or molecules modified by a pathological environment (advanced glycation end product-modified proteins observed with diabetes). DAMP receptor activation on fibroblasts is coupled to altered cellular function including changes in proliferation, migration, myofibroblast transdifferentiation, ECM turnover and production of fibrotic and inflammatory paracrine factors, which directly impact on the heart's ability to respond to injury. This review gives an overview of the important role played by CF in responding to myocardial DAMPs and how the DAMP/CF axis could be exploited experimentally and therapeutically.
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.
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.
The impact damped harmonic oscillator in free decay
NASA Technical Reports Server (NTRS)
Brown, G. V.; North, C. M.
1987-01-01
The impact-damped oscillator in free decay is studied by using time history solutions. A large range of oscillator amplitude is covered. The amount of damping is correlated with the behavior of the impacting mass. There are three behavior regimes: (1) a low amplitude range with less than one impact per cycle and very low damping, (2) a useful middle amplitude range with a finite number of impacts per cycle, and (3) a high amplitude range with an infinite number of impacts per cycle and progressively decreasing damping. For light damping the impact damping in the middle range is: (1) proportional to impactor mass, (2) additive to proportional damping, (3) a unique function of vibration amplitude, (4) proportional to 1-epsilon, where epsilon is the coefficient of restitution, and (5) very roughly inversely proportional to amplitude. The system exhibits jump phenomena and period doublings. An impactor with 2 percent of the oscillator's mass can produce a loss factor near 0.1.
Damping in Ferrous Shape Memory Alloys
1993-08-01
time it has been proposed that the solution lies in the approach of energy dissipation by using metallic structural materials which have inherent...and automotive manufacturing plants, has never achieved commercial producton . 1-b. Ferromagnetic alloys, such as Fe-Cr alloys High damping Fe-Cr alloys...Pre-exsiring mar~en-si,ýe worms orwie treenred orieL a ion ! A Lr cow s SL AL 14- L AL Figure 26. Schematic illustration of various processes involved
Fluidic Technology Investigation - Suspension Damping Simulations
1977-01-01
IF (w (I LT’ CVM)~4$1 IF ( Wrf 1 0 i CmpY MX2)V?1112wW~ CALL ORPArIP:(Pcx) pP,i.,IERR) .......-or pi i v~,R4p CAlLA (QAI)Rr7,4,?,T.ERR) T F Z (I ~LT C V...Damper Damping Devices Suspension Systems Shock Absorbers Adaptive Suspension Systems Hydro -Fluidics 20. ABSTRACT (Continue on reverse side if necessary
Robot vibration control using inertial damping forces
NASA Technical Reports Server (NTRS)
Lee, Soo Han; Book, Wayne J.
1991-01-01
This paper concerns the suppression of the vibration of a large flexible robot by inertial forces of a small robot which is located at the tip of the large robot. A controller for generating damping forces to a large robot is designed based on the two time scale model. The controller does not need to calculate the quasi-steady variables and is efficient in computation. Simulation results show the effectiveness of the inertial forces and the controller designed.
Robot vibration control using inertial damping forces
NASA Technical Reports Server (NTRS)
Lee, Soo Han; Book, Wayne J.
1989-01-01
The suppression is examined of the vibration of a large flexible robot by inertial forces of a small robot which is located at the tip of the large robot. A controller for generating damping forces to a large robot is designed based on the two time scale mode. The controller does not need to calculate the quasi-steady state variables and is efficient in computation. Simulation results show the effectiveness of the inertial forces and the controller designed.
Damping Materials, Finite Elements and Special Projects.
1982-12-01
made of either Haynes Alloy Number 188, Hastalloy C, Hastalloy X, or 17 - 4PH stainless steel Hastalloy X. Figure 1.26 is a schematic of the test...Motors Corporation (DDA), conducted a cooperative effort to characterize a DDA proprietary temperature damping material. The UDRI supplied two 17 - 4PH ...range at which the 17 - 4PH stainless steel beams could be tested. Serious discrepancy was noted between the structural loss factors derived from the room
Vibration Damping Response of Composite Materials
1991-04-01
to predict the vibration damping of these coposites. L lein Irauu, .. rii. se i-s foi tesi specimel gC-miLtrics oSl0y, so that - material...manner that the strain in the x direction was determined. This development results in the transverse strain given as av (x,y,z) avO (x,y)ei~ t a 2wO(xy) ei
Collisional damping rates for plasma waves
NASA Astrophysics Data System (ADS)
Tigik, S. F.; Ziebell, L. F.; Yoon, P. H.
2016-06-01
The distinction between the plasma dynamics dominated by collisional transport versus collective processes has never been rigorously addressed until recently. A recent paper [P. H. Yoon et al., Phys. Rev. E 93, 033203 (2016)] formulates for the first time, a unified kinetic theory in which collective processes and collisional dynamics are systematically incorporated from first principles. One of the outcomes of such a formalism is the rigorous derivation of collisional damping rates for Langmuir and ion-acoustic waves, which can be contrasted to the heuristic customary approach. However, the results are given only in formal mathematical expressions. The present brief communication numerically evaluates the rigorous collisional damping rates by considering the case of plasma particles with Maxwellian velocity distribution function so as to assess the consequence of the rigorous formalism in a quantitative manner. Comparison with the heuristic ("Spitzer") formula shows that the accurate damping rates are much lower in magnitude than the conventional expression, which implies that the traditional approach over-estimates the importance of attenuation of plasma waves by collisional relaxation process. Such a finding may have a wide applicability ranging from laboratory to space and astrophysical plasmas.
Synchrosqueezed wavelet transform for damping identification
NASA Astrophysics Data System (ADS)
Mihalec, Marko; Slavič, Janko; Boltežar, Miha
2016-12-01
Synchrosqueezing is a procedure for improving the frequency localization of a continuous wavelet transform. This research focuses on using a synchrosqueezed wavelet transform (SWT) to determine the damping ratios of a vibrating system using a free-response signal. While synchrosqueezing is advantageous due to its localisation in the frequency, damping identification with the original SWT is not sufficiently accurate. Here, the synchrosqueezing was researched in detail, and it was found that an error in the frequency occurs as a result of the numerical calculation of the preliminary frequencies. If this error were to be compensated, a better damping identification would be expected. To minimize the frequency-shift error, three different strategies are investigated: the scale-dependent coefficient method, the shifted-coefficient method and the autocorrelated-frequency method. Furthermore, to improve the SWT, two synchrosqueezing criteria are introduced: the average SWT and the proportional SWT. Finally, the proposed modifications are tested against close modes and the noise in the signals. It was numerically and experimentally confirmed that the SWT with the proportional criterion offers better frequency localization and performs better than the continuous wavelet transform when tested against noisy signals.
A comparison of viscoelastic damping models
NASA Technical Reports Server (NTRS)
Slater, Joseph C.; Belvin, W. Keith; Inman, Daniel J.
1993-01-01
Modern finite element methods (FEM's) enable the precise modeling of mass and stiffness properties in what were in the past overwhelmingly large and complex structures. These models allow the accurate determination of natural frequencies and mode shapes. However, adequate methods for modeling highly damped and high frequency dependent structures did not exist until recently. The most commonly used method, Modal Strain Energy, does not correctly predict complex mode shapes since it is based on the assumption that the mode shapes of a structure are real. Recently, many techniques have been developed which allow the modeling of frequency dependent damping properties of materials in a finite element compatible form. Two of these methods, the Golla-Hughes-McTavish method and the Lesieutre-Mingori method, model the frequency dependent effects by adding coordinates to the existing system thus maintaining the linearity of the model. The third model, proposed by Bagley and Torvik, is based on the Fractional Calculus method and requires fewer empirical parameters to model the frequency dependence at the expense of linearity of the governing equations. This work examines the Modal Strain Energy, Golla-Hughes-McTavish and Bagley and Torvik models and compares them to determine the plausibility of using them for modeling viscoelastic damping in large structures.
Metallic materials for mechanical damping capacity applications
NASA Astrophysics Data System (ADS)
Crăciun, R. C.; Stanciu, S.; Cimpoeșu, R.; (Dragoș Ursanu, A. I.; Manole, V.; Paraschiv, P.; Chicet, D. L.
2016-08-01
Some metallic materials exhibit good damping capacity of mechanical energy into thermal energy. This property along with the others metallic characteristics make this materials interesting for a big number of applications. These materials can be used as bumpers in different applications including automotive field. Beside grey cast iron and shape memory alloys few new metallic materials are presented for the supposition of high damping capacity. We analyze the causes that increase the internal friction of some metallic materials and possibilities to enhance this property through different mechanical, physical or chemical methods. Shape memory alloys, especially those based on copper, present a different damping capacity on martensite, austenite or transition state. In the transformation range M ↔A, which in case of copper base shape memory alloys is quite large, the metallic intelligent materials present a high internal friction, almost comparable with natural rubber behavior that can transform mechanical energy into thermal energy till a certain value of the external solicitation. These materials can be used as noise or small vibrations bumpers or even as shock absorbers in automotive industry.
Random Response of Linear Hysteretic Damping
Floris, Claudio
2008-07-08
The probabilistic characterization of the response of a single-degree-of-freedom (SDOF) oscillator with linear hysteretic damping excited by ground motion described by zero mean stationary Gaussian processes is achieved by profiting from a steady-state solution of the motion equation, valid when the excitation is given by the superposition of harmonics. The model of linear hysteretic damping has been introduced to fit damping mechanisms in which the dissipation rate is independent of frequency, and mathematically it is described by the Hilbert transform of the response. Though this model is debated since it violates the principle of causality, its intrinsic simplicity makes it preferable to other models. The steady-state solution of the motion equation proposed in this paper allows a closed form evaluation of the respone mean square value. However, the numerical examples show that this quantity is affected by the mechanism of energy dissipation only when this is large. On the contrary, for a low capacity of dissipation the response mean square value is rather insensitive to the dissipation mechanism.
Intelligent damping layer under a plate subjected to a pair of masses moving in opposite directions
NASA Astrophysics Data System (ADS)
Bajer, Czesław; Pisarski, Dominik; Szmidt, Tomasz; Dyniewicz, Bartłomiej
2017-04-01
Reducing displacements of a plate vibrating under a pair of masses traveling in opposite directions can be improved by adding a smart subsoil instead of a classical damping layer. We propose a material that acts according to the instantaneous state of the plate, i.e., its displacements and velocity. Such an intelligent damping layer reduces vertical displacements even by 40%-60%, depending on the type of load and the assumed objective function. Existing materials enable the application of the proposed layer in a semi-active mode. The passive mode can be applied with materials exhibiting direction-dependent viscosity.
Controllable damping of high-Q violin modes in fused silica suspension fibers
NASA Astrophysics Data System (ADS)
Dmitriev, A. V.; Mescheriakov, S. D.; Tokmakov, K. V.; Mitrofanov, V. P.
2010-01-01
Fused silica fiber suspension of the test masses will be used in the interferometric gravitational wave detectors of the next generation. This allows a significant reduction of losses in the suspension and thermal noise associated with the suspension. Unfortunately, unwanted violin modes may be accidentally excited in the suspension fibers. The Q-factor of the violin modes also exceeds 108. They have a ring-down time that is too long and may complicate the stable control of the interferometer. Results of the investigation of a violin mode active damping system are described. An original sensor and actuator were especially developed to realize the effective coupling of a thin, optically transparent, non-conducting fused silica fiber with an electric circuit. The damping system allowed the changing of the violin mode's damping rate over a wide range.
NASA Technical Reports Server (NTRS)
Ham, N. D.; Behal, B. L.; Mckillip, R. M., Jr.
1982-01-01
A new, advanced type of active control for helicopters and its application to a system for blade lag damping augmentation is described. The system, based on previously developed M.I.T. Individual-Blade-Control hardware, employs blade-mounted accelerometers to sense blade lag motion and feeds back rate information to increase the damping of the first lag mode. A linear model of the blade and control system dynamics is used to give guidance in the design process as well as to aid in analysis of experimental results. System performance in wind tunnel tests is described, and evidence is given of the system's ability to provide substantial additional damping to blade lag motion.
NASA Technical Reports Server (NTRS)
Sutton, M. A.; Davis, P. K.
1976-01-01
Numerical solutions of the governing equations of motion of a liquid squeeze film damped forced vibration system were carried out to examine the feasibility of using a liquid squeeze film to cushion and protect large structures, such as buildings, located in areas of high seismic activity. The mathematical model used was that for a single degree of freedom squeeze film damped spring mass system. The input disturbance was simulated by curve fitting actual seismic data with an eleventh order Lagranging polynomial technique. Only the normal component of the seismic input was considered. The nonlinear, nonhomogeneous governing differential equation of motion was solved numerically to determine the transmissibility over a wide range of physical parameters using a fourth-order Runge-Kutta technique. It is determined that a liquid squeeze film used as a damping agent in a spring-mass system can significantly reduce the response amplitude for a seismic input disturbance.
Nembach, Hans T; Shaw, Justin M; Boone, Carl T; Silva, T J
2013-03-15
We demonstrate a strong dependence of the effective damping on the nanomagnet size and the particular spin-wave mode that can be explained by the theory of intralayer transverse-spin pumping. The effective Landau-Lifshitz damping is measured optically in individual, isolated nanomagnets as small as 100 nm. The measurements are accomplished by use of a novel heterodyne magneto-optical microwave microscope with unprecedented sensitivity. Experimental data reveal multiple standing spin-wave modes that we identify by use of micromagnetic modeling as having either localized or delocalized character, described generically as end and center modes. The damping parameter of the two modes depends on both the size of the nanomagnet as well as the particular spin-wave mode that is excited, with values that are enhanced by as much as 40% relative to that measured for an extended film. Contrary to expectations based on the ad hoc consideration of lithography-induced edge damage, the damping for the end mode decreases as the size of the nanomagnet decreases. The data agree with the theory for damping caused by the flow of intralayer transverse spin currents driven by the magnetization curvature. These results have serious implications for the performance of nanoscale spintronic devices such as spin-torque-transfer magnetic random access memory.
Paredes-Juarez, Genaro A.; Sahasrabudhe, Neha M.; Tjoelker, Reina S.; de Haan, Bart J.; Engelse, Marten A.; de Koning, Eelco J. P.; Faas, Marijke M.; de Vos, Paul
2015-01-01
In between the period of transplantation and revascularization, pancreatic islets are exposed to low-oxygen and low-nutrient conditions. In the present study we mimicked those conditions in vitro to study the involvement of different cell death processes, release of danger-associated molecular patterns (DAMP), and associated in vitro immune activation. Under low-oxygen and low-nutrient conditions, apoptosis, autophagy and necroptosis occur in human islets. Necroptosis is responsible for DAMP-release such as dsDNA, uric acid, and HMGB1. The sensors of the innate immune system able to recognize these DAMPs are mainly TLR, NOD receptors, and C-type lectins. By using cell-lines with a non-functional adaptor molecule MyD88, we were able to show that the islet-derived DAMPs signal mainly via TLR. Immunoisolation in immunoprotective membranes reduced DAMP release and immune activation via retention of the relative large DAMPs in the capsules. Another effective strategy was suppressing necroptosis using the inhibitor nec-1. Although the effect on cell-survival was minor, nec-1 was able to reduce the release of HMGB1 and its associated immune activation. Our data demonstrate that in the immediate post-transplant period islets release DAMPs that in vitro enhance responses of innate immune cells. DAMP release can be reduced in vitro by immunoisolation or intervention with nec-1. PMID:26419792
Inertially excited beam vibrations damped by Vacuum Packed Particles
NASA Astrophysics Data System (ADS)
Szmidt, T.; Zalewski, R.
2014-10-01
The dynamics of an inertially excited steel cantilever beam encapsulated in a hermetic sleeve filled with polypropylene grains is investigated experimentally and theoretically. An electric motor rotating an unbalanced mass is attached at the end of the beam to generate forced vibrations of the system. Changing the underpressure in the sleeve results in changes of the stiffness and dissipative properties of the composite structure, which allow one to control the resonant characteristics of the system. Is is shown that the amplitude of vibrations can be reduced in this way. This innovative semi-active method of vibration damping is based on the jamming mechanism of the granules, and proved to be efficient in the reduction of the free vibrations of the beam, which was studied in the authors’ latest paper. In the present work, it is confirmed that the classical Bernoulli-Euler beam model with Kelvin-Voigt damping provides a satisfactory explanation of the observed relation between the vibrations amplitude and underpressure.
Piezoelectric Vibration Damping Study for Rotating Composite Fan Blades
NASA Technical Reports Server (NTRS)
Min, James B.; Duffy, Kirsten P.; Choi, Benjamin B.; Provenza, Andrew J.; Kray, Nicholas
2012-01-01
Resonant vibrations of aircraft engine blades cause blade fatigue problems in engines, which can lead to thicker and aerodynamically lower performing blade designs, increasing engine weight, fuel burn, and maintenance costs. In order to mitigate undesirable blade vibration levels, active piezoelectric vibration control has been investigated, potentially enabling thinner blade designs for higher performing blades and minimizing blade fatigue problems. While the piezoelectric damping idea has been investigated by other researchers over the years, very little study has been done including rotational effects. The present study attempts to fill this void. The particular objectives of this study were: (a) to develop and analyze a multiphysics piezoelectric finite element composite blade model for harmonic forced vibration response analysis coupled with a tuned RLC circuit for rotating engine blade conditions, (b) to validate a numerical model with experimental test data, and (c) to achieve a cost-effective numerical modeling capability which enables simulation of rotating blades within the NASA Glenn Research Center (GRC) Dynamic Spin Rig Facility. A numerical and experimental study for rotating piezoelectric composite subscale fan blades was performed. It was also proved that the proposed numerical method is feasible and effective when applied to the rotating blade base excitation model. The experimental test and multiphysics finite element modeling technique described in this paper show that piezoelectric vibration damping can significantly reduce vibrations of aircraft engine composite fan blades.
Damping and isolation of the GHM mini-oscillators
NASA Astrophysics Data System (ADS)
Liao, Wei-Hsin
2000-04-01
Golla-Hughes-McTavish (GHM) method has been shown to be an effective approach to model viscoelastic materials (VEMs). In the GHM model, a mini-oscillator has been used as the mechanical analogy to illustrate the relation of GHM parameters. However, the GHM mini-oscillators have not been studied in depth so far. In this paper, the damping and isolation characteristics of this two degree-of-freedom mini- oscillator are analyzed. Those characteristics are crucial to the effectiveness and limitations of the passive and hybrid (active-passive) vibration suppression techniques employing VEMs. Under harmonic excitations, the corresponding nondimensional relationships among parameters are derived. The transmissibility due to force and base excitations is investigated with respect to various parameters. The damping ability of the mini-oscillator is also evaluated. For those critical points and special cases, their conditions are identified and discussed. Several unique distinctions are observed when compared to previous studies on vibration absorbers and isolators. The analysis results of this research provide more understanding and physical insight to designers when considering VEM-based configurations including passive and hybrid systems for the purpose of vibration isolation and control.
Discrete-layered damping model of multilayer plate with account of internal damping
NASA Astrophysics Data System (ADS)
Paimushin, V. N.; Gazizullin, R. K.
2016-11-01
Construction of discrete-layered damping model of multilayer plate in small displacement and deformations with account of internal damping of layers of Thompson- Kelvin-Voight model is presented. Based on derived equations, analytical solution is given to the static damping problem of simply supported single-layer rectangular plate subjected to uniformly distributed pressure, which is applied to one of its boundary planes. Convergence to the three-dimensional case is analysed for the obtained solution with respect to the dependence on dimension of mesh in the thickness direction of plate. For thin plates, dimension reduction of the formulated problem is set on the basis of simplifying hypothesis applied for each layer.
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
Damping in high-temperature superconducting levitation systems
Hull, John R.
2009-12-15
Methods and apparatuses for improved damping in high-temperature superconducting levitation systems are disclosed. A superconducting element (e.g., a stator) generating a magnetic field and a magnet (e.g. a rotor) supported by the magnetic field are provided such that the superconducting element is supported relative to a ground state with damped motion substantially perpendicular to the support of the magnetic field on the magnet. Applying this, a cryostat housing the superconducting bearing may be coupled to the ground state with high damping but low radial stiffness, such that its resonant frequency is less than that of the superconducting bearing. The damping of the cryostat may be substantially transferred to the levitated magnetic rotor, thus, providing damping without affecting the rotational loss, as can be derived applying coupled harmonic oscillator theory in rotor dynamics. Thus, damping can be provided to a levitated object, without substantially affecting the rotational loss.
Research on damping properties optimization of variable-stiffness plate
NASA Astrophysics Data System (ADS)
Wen-kai, QI; Xian-tao, YIN; Cheng, SHEN
2016-09-01
This paper investigates damping optimization design of variable-stiffness composite laminated plate, which means fibre paths can be continuously curved and fibre angles are distinct for different regions. First, damping prediction model is developed based on modal dissipative energy principle and verified by comparing with modal testing results. Then, instead of fibre angles, the element stiffness and damping matrixes are translated to be design variables on the basis of novel Discrete Material Optimization (DMO) formulation, thus reducing the computation time greatly. Finally, the modal damping capacity of arbitrary order is optimized using MMA (Method of Moving Asymptotes) method. Meanwhile, mode tracking technique is employed to investigate the variation of modal shape. The convergent performance of interpolation function, first order specific damping capacity (SDC) optimization results and variation of modal shape in different penalty factor are discussed. The results show that the damping properties of the variable-stiffness plate can be increased by 50%-70% after optimization.
Dynamic analyses of viscoelastic dielectric elastomers incorporating viscous damping effect
NASA Astrophysics Data System (ADS)
Zhang, Junshi; Zhao, Jianwen; Chen, Hualing; Li, Dichen
2017-01-01
In this paper, based on the standard linear solid rheological model, a dynamics model of viscoelastic dielectric elastomers (DEs) is developed with incorporation of viscous damping effect. Numerical calculations are employed to predict the damping effect on the dynamic performance of DEs. With increase of damping force, the DEs show weak nonlinearity and vibration strength. Phase diagrams and Poincaré maps are utilized to detect the dynamic stability of DEs, and the results indicate that a transition from aperiodic vibration to quasi-periodic vibration occurs with enlargement of damping force. The resonance properties of DEs including damping effect are subsequently analyzed, demonstrating a reduction of resonant frequency and resonance peak with increase of damping force.
Higher order mode damping in an ALS test cavity
Jacob, A.F.; Lamberston, G.R. ); Barry, W. )
1990-06-01
The higher order mode attenuation scheme proposed for the Advanced Light Source accelerating cavities consists of two broad-band dampers placed 90{degrees} apart on the outer edge. In order to assess the damping efficiency a test assembly was built. The HOM damping was obtained by comparing the peak values of the transmission through the cavity for both the damped and the undamped case. Because of the high number of modes and frequency shifts due to the damping gear, the damping was assessed statistically, by averaging over several modes. In the frequency range from 1.5 to 5.5 GHz, average damping greater than 100 was obtained. 1 ref., 6 figs.
Imaging of Damped Ly-alpha Absorbers
NASA Astrophysics Data System (ADS)
Jim, K. T. C.; Roth, K. C.
1998-05-01
Intervening H I gas clouds toward QSOs give rise to damped Ly-alpha absorption. Because of the high column density (N(H I)>= 2*E(20) cm(-2) ) these systems have been thought to be galactic disks in some stage of formation. However, because potential optical counterparts have not been identified for most damped Ly-alpha systems, it is possible that some of the absorbing systems could be dwarf irregular galaxies or low surface brightness galaxies, and are thus difficult to image. In any case, the absorbers are expected to have small angular separation from the QSOs, and so high resolution imaging is required to differentiate the absorbers from the QSOs. Because previous studies have not shown any dominant morphological form for the few candidate objects known, our images are obtained with the Hawaii tip-tilt system in order to achieve the best possible morphological classification. By imaging in the NIR and optical bands that bracket the 4000 Angstroms break of these Ly-alpha absorbers, we can more readily select candidate objects by photometrically constraining their redshifts. In our sample of 14 QSOs with abosorbers from 1
Researches on Track Reconstruction for DAMPE
NASA Astrophysics Data System (ADS)
Lu, T. S.; Lei, S. J.; Zang, J. J.; Chang, J.; Wu, J.
2016-05-01
The Dark Matter Particle Explorer (DAMPE) is aimed to study the existence and distribution of dark matter via observation of high energy particles in space with unprecedented large energy bandwidth, high energy resolution, and high space resolution. The track reconstruction is to restore the positions and angles of the incident particles using the multiple observations of different channels at different positions, and its accuracy determines the angular resolution of the detector. The track reconstruction is mainly based on the observations of two sub-detectors, namely, the Silicon Tracker (STK) detector and the BGO (Bi_4Ge_3O12) calorimeter. In accordance with the design and structure of the two sub-detectors and using the data collected during the beam tests and ground tests, we provide a detailed introduction of the track reconstruction of DAMPE data, including three basic steps, the selection of track hits, the fitting of track hits, and the judgement of the best track among (most probably) many of them. Since a high energy particle most probably leaves more than one hit in each level of the STK and BGO, we first provide a method to constrain the STK clusters for the track reconstruction using the rough result of the BGO reconstruction. We apply two different algorithms, the Kalman filter and the least square linear fitting, to fit the track hits. The consistency of the results obtained independently via the two algorithms confirms the validity of our track reconstruction results, and we discuss the advantages/disadvantages of each method. Several criteria combining the BGO and STK detection are discussed for picking out the most possible track among all the tracks found in the track reconstruction. Using the track reconstruction methods mentioned in this article and the beam test data, we confirm that the angular resolution of DAMPE satisfies the requirement in design.
Status of the SLC damping rings
Hutton, A.M.; Davies-White, W.A.; Delahaye, J.P.; Fieguth, T.H.; Hofmann, A.; Jager, J.; Kloeppel, P.K.; Lee, M.J.; Linebarger, W.A.; Rivkin, L.
1985-06-01
Electron beams of full design energy 1.21 GeV and nearly full design intensity 4 x 10/sup 10/ particles/pulse (design 5 x 10/sup 10/) have been extracted from the Stanford Linac and successfully stored in the electron damping ring. Beams of less intensity have been extracted from the ring and reinjected into the Linac. The present intensity limits are not thought to be fundamental. The operating experience with the electron ring and the status of the construction of the positron ring will be discussed. 11 refs., 1 fig., 2 tabs.
HVDC system control for damping subsynchronous oscillations
Piwko, R.J.; Larsen, E.V.
1982-07-01
A method for designing a supplemental subsynchronous damping control (SSDC) for an HVDC transmission system is described. The SSDC eliminates torsional instabilities caused by interaction between conventional HVDC controls and turbine-generator rotor torsional modes of vibration. Results of digital simulation used in the design process are compared with measurements made on an HVDC simulator. Results of both digital simulations and HVDC simulator tests which demonstrate SSDC performance are shown. This research and development effort was sponsored by EPRI under RP1425-1.
Radiation damping in closed expanding universes
NASA Astrophysics Data System (ADS)
Bernui, Armando
The dynamics of a coupled model (harmonic oscillator-relativistic scalar field) in Conformal Robertson-Walker (k = +1) spacetimes is investigated. The exact radiation-reaction equation of the source-including the retarded radiation terms due to the closed space geometry - is obtained and analyzed. A suitable family of Lyapunov functions is constructed to show that, if the spacetime expands monotonely, then the source's energy damps. A numerical simulation of this equation for expanding Universes, with and without Future Event Horizon, is performed.
System for damping vibrations in a turbine
Roberts, III, Herbert Chidsey; Johnson, Curtis Alan; Taxacher, Glenn Curtis
2015-11-24
A system for damping vibrations in a turbine includes a first rotating blade having a first ceramic airfoil, a first ceramic platform connected to the first ceramic airfoil, and a first root connected to the first ceramic platform. A second rotating blade adjacent to the first rotating blade includes a second ceramic airfoil, a second ceramic platform connected to the second ceramic airfoil, and a second root connected to the second ceramic platform. A non-metallic platform damper has a first position in simultaneous contact with the first and second ceramic platforms.
Coatings for High-Temperature Vibration Damping of Turbines
2009-10-01
damping is provided by both the thin bond- coat and thermal barrier coating (TBC) in TBC coated superalloy system, (ii) the damping from each component...bond- coat and the TBC itself, and (iii) damping from EB-PVD deposited TBCs and platinum-modified nickel aluminide bond- coats occur at the same...closer to chemical equilibrium with existing superalloys than those currently used as bond- coats . Also, depending on the platinum content, the nickel
Test particle study of Landau damping of steepening magnetosonic waves
NASA Technical Reports Server (NTRS)
Matsumoto, H.; Barnes, A.
1982-01-01
A test particle study of Landau damping of steepening large-amplitude magnetosonic waves is made. Motions of test particles in a model of a steepening large-amplitude magnetosonic wave are traced. The kinetic energy change of the ensemble of test particles is computed to estimate the effective Landau damping rate of the magnetosonic wave. The numerical results are compared with the linear kinetic theory of Landau damping and interpreted in terms of a simple physical picture for particle trapping.
Critical damping constant of microwave-assisted magnetization switching
NASA Astrophysics Data System (ADS)
Yamaji, Toshiki; Arai, Hiroko; Matsumoto, Rie; Imamura, Hiroshi
2016-02-01
Microwave-assisted switching of magnetization in a perpendicularly magnetized disk was theoretically studied and special attention was paid to the effect of a damping constant on the switching field. We found that there exists a critical damping constant above which the switching field suddenly increases. We derived an analytical expression of the critical damping constant and showed that it decreases with increasing frequency of the microwave field, while it increases with increasing amplitude of the microwave field and the effective anisotropy field.
Existence and damping of toroidicity-induced Alfven eigenmodes
Mahajan, S.M.; Mett, R.R.
1991-12-01
A new method of analyzing the toroidicity-induced Alfven eigenmode (TAE) from kinetic theory is presented. The analysis includes electron parallel dynamics non-perturbatively, an effect which is found to strongly influence the character and damping of the TAE -- contrary to previous theoretical predictions. The normal electron Landau damping of the TAE is found to be higher than previously expected, and may explain recent experimental measurements of the TAE damping coefficient. 11 refs., 1 fig., 1 tab.
Confinement-dependent damping in a layered liquid.
de Beer, Sissi; van den Ende, Dirk; Mugele, Frieder
2011-03-23
We present atomic force microscopy (AFM) measurements of the conservative oscillatory solvation forces and the damping in confined films of octamethylcyclotetrasiloxane using small amplitude modulation with magnetic driving. We find distinct maxima in the interaction damping upon probing the discrete molecular layers, supporting earlier observations of the same phenomenon using AFM with an acoustic driving scheme. The maxima in the damping are located at the same tip-surface separation as the maxima in the conservative oscillatory interaction stiffness.
Damping element for reducing the vibration of an airfoil
Campbell, Christian X; Marra, John J
2013-11-12
An airfoil (10) is provided with a tip (12) having an opening (14) to a center channel (24). A damping element (16) is inserted within the opening of the center channel, to reduce an induced vibration of the airfoil. The mass of the damping element, a spring constant of the damping element within the center channel, and/or a mounting location (58) of the damping element within the center channel may be adjustably varied, to shift a resonance frequency of the airfoil outside a natural operating frequency of the airfoil.
Design and fabrication of integrally damped composite fan blades
NASA Astrophysics Data System (ADS)
Kosmatka, John B.; Appuhn, Geoffrey
1999-06-01
The design, analysis, and fabrication methods of embedding small viscoelastic damping patches into scaled composite fan blades is presented, where the goal is to improve the blade fatigue characteristics by increasing the damping in the chord-wise modes. This discussion concentrates on improving the damping levels in a research composite shell/titanium spar fan blade, developed by NASA-Lewis and Pratt and Whitney. First, the geometry and material definition of the existing composite fan blade are presented. Second, methods for sizing and locating the damping patch are presented based upon the modal strain energy method. The layered damping patch is composed of outer layers of a TEDLAR (or KAPTON) barrier film, which encompasses a viscoelastic damping material and loose- weave scrim cloth (creep protection). Two different patch sizes and locations are discussed to provide maximum damping as well as optimal damping. Finally, procedures are outlined for fabricating the integrally damped composite fan blades. Fabricated blades will be tested at the NASA-Lewis vacuum facility.
Dependence of Kambersky damping on Fermi level and spin orientation
Qu, T.; Victora, R. H.
2014-05-07
Kambersky damping represents the loss of magnetic energy from the electrons to the lattice through the spin orbit interaction. It is demonstrated that, for bcc Fe-based transition metal alloys, the logarithm of the energy loss is proportional to the density of states at the Fermi level. Both inter and intraband damping are calculated for spins at arbitrary angle to the previously examined [001] direction. Although the easy axis 〈100〉 shows isotropic relaxation and achieves the minimum damping value of 0.002, other directions, such as 〈110〉, show substantial anisotropic damping.
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.
Development of Composite Materials with High Passive Damping Properties
2006-05-15
SPONSOR/MONITOR’S REPORT NUMBER(S) 12. DISTRIBUTION/AVAILABILITY STATEMENT 13. SUPPLEMENTARY NOTES 14 . ABSTRACT The structures studied in this ONR...2.1.2 Measures of damping 8 2.1.3 Measurement methods 9 2.2 Damping in Sandwich Structures. 9 2.2.1 Analytical models 10 2.2.2 Damping and damage 14 ...2.2.3 Finite element models 14 2.2.4 Statistical energy analysis method 15 CHAPTER 3 ANALYSIS OF DAMPING IN SANDWICH MATERIALS. 24 3.1 Equation of
Damping of superfluid flow by a thermal cloud.
Meppelink, R; Koller, S B; Vogels, J M; Stoof, H T C; van der Straten, P
2009-12-31
One of the principal signatures of superfluidity is the frictionless flow of a superfluid through another substance. Here, we study the flow of a Bose-Einstein condensate through a thermal cloud and study its damping for different harmonic confinements and temperatures. The damping rates close to the collisionless regime are found to be in good agreement with Landau damping and become smaller for more homogeneous systems. In the hydrodynamic regime, we observe additional damping due to collisions, and we discuss the implications of these findings for superfluidity in this system.
Excitation of magnetization using a modulated radiation damping field.
Walls, Jamie D; Huang, Susie Y; Lin, Yung-Ya
2006-10-12
In this work, pulsed-field gradients are used to modulate the radiation damping field generated by the detection coil in an NMR experiment in order that spins with significantly different chemical shifts can affect one another via the radiation damping field. Experiments performed on solutions of acetone/water and acetone/DMSO/water demonstrate that spins with chemical shift differences much greater than the effective radiation damping field strength can still be coupled by modulating the radiation damping field. Implications for applications in high-field NMR and for developing sensitive magnetization detectors are discussed.
Damping and power spectra of quasi-periodic intensity disturbances above a solar polar coronal hole
NASA Astrophysics Data System (ADS)
Jiao, Fang-Ran; Xia, Li-Dong; Huang, Zheng-Hua; Li, Bo; Fu, Hui; Yuan, Ding; Chandrashekhar, Kalugodu
2016-06-01
We study intensity disturbances above a solar polar coronal hole that can be seen in the AIA 171 Å and 193 Å passbands, aiming to provide more insights into their physical nature. The damping and power spectra of the intensity disturbances with frequencies from 0.07 mHz to 10.5 mHz are investigated. The damping of the intensity disturbances tends to be stronger at lower frequencies, and their damping behavior below 980″ (for comparison, the limb is at 945″) is different from what happens above. No significant difference is found between the damping of the intensity disturbances in the AIA 171 Å and that in the AIA 193 Å. The indices of the power spectra of the intensity disturbances are found to be slightly smaller in the AIA 171 Å than in the AIA 193 Å, but the difference is within one standard deviation. An additional enhanced component is present in the power spectra in a period range of 8-40 min at lower heights. The power spectra of a spicule is highly correlated with its associated intensity disturbance, which suggests that the power spectra of the intensity disturbances might be a mixture of spicules and wave activities. We suggest that each intensity disturbance in the polar coronal hole is possibly a series of independent slow magnetoacoustic waves triggered by spicular activities.
Characterization of damping in microfibrous material
NASA Astrophysics Data System (ADS)
Soobramaney, Pregassen; Flowers, George T.; Dean, Robert N.
2012-04-01
MEMS gyroscopes are used in many applications including harsh environments such as high-power, high-frequency acoustic noise. If the latter is at the natural frequency of the gyroscope, the proof mass will be overexcited giving rise to a corrupted gyroscope output. To mitigate the effect of the high-power, high-frequency acoustic noise, it is proposed to use nickel microfibrous sheets as an acoustic damper. For this purpose, the characterization of vibration damping in Nickel microfibrous sheets was examined in the present research effort. The sheets were made from nickel fibers with cellulose as a binding agent using a wet-lay papermaking technique. Sintering was done at 1000 °C to remove all the cellulose giving rise to a porous material. Square sheets of 20 cm were made from three diameters of nickel fibers namely 4, 8, and 12 microns. The sheets were cut into smaller pieces to fit the requirements of a fixture specially designed for this study. The fixture was attached to a LDS V408 shaker with a mass resting on a stack of the microfibrous sheets to simulate transmitted vibration by base motion with the sheet stack acting as a damper. A series of experiments was conducted using these 3 fiber diameters, different number of layers of microfibrous sheets and varying the vibration amplitude. From the collected vibration data, the stiffness and damping ratio of the microfibrous material was characterized.
Damping of Crank-Nicolson error oscillations.
Britz, D; Østerby, O; Strutwolf, J
2003-07-01
The Crank-Nicolson (CN) simulation method has an oscillatory response to sharp initial transients. The technique is convenient but the oscillations make it less popular. Several ways of damping the oscillations in two types of electrochemical computations are investigated. For a simple one-dimensional system with an initial singularity, subdivision of the first time interval into a number of equal subintervals (the Pearson method) works rather well, and so does division with exponentially increasing subintervals, where however an optimum expansion parameter must be found. This method can be computationally more expensive with some systems. The simple device of starting with one backward implicit (BI, or Laasonen) step does damp the oscillations, but not always sufficiently. For electrochemical microdisk simulations which are two-dimensional in space and using CN, the use of a first BI step is much more effective and is recommended. Division into subintervals is also effective, and again, both the Pearson method and exponentially increasing subintervals methods are effective here. Exponentially increasing subintervals are often considerably more expensive computationally. Expanding intervals over the whole simulation period, although capable of satisfactory results, for most systems will require more cpu time compared with subdivision of the first interval only.
Vibrational resonance in Duffing systems with fractional-order damping.
Yang, J H; Zhu, H
2012-03-01
The phenomenon of vibrational resonance (VR) is investigated in over- and under-damped Duffing systems with fractional-order damping. It is found that the factional-order damping can induce change in the number of the steady stable states and then lead to single- or double-resonance behavior. Compared with vibrational resonance in the ordinary systems, the following new results are found in the fractional-order systems. (1) In the overdamped system with double-well potential and ordinary damping, there is only one kind of single-resonance, whereas there are double-resonance and two kinds of single-resonance for the case of fractional-order damping. The necessary condition for these new resonance behaviors is the value of the fractional-order satisfies α > 1. (2) In the overdamped system with single-well potential and ordinary damping, there is no resonance, whereas there is a single-resonance for the case of fractional-order damping. The necessary condition for the new result is α > 1. (3) In the underdamped system with double-well potential and ordinary damping, there are double-resonance and one kind of single-resonance, whereas there are double-resonance and two kinds of single-resonance for the case of fractional-order damping. The necessary condition for the new single-resonance is α < 1. (4) In the underdamped system with single-well potential, there is at most a single-resonance existing for both the cases of ordinary and fractional-order damping. In the underdamped systems, varying the value of the fractional-order is equivalent to change the damping parameter for some cases.
Energy harvesting using parametric resonant system due to time-varying damping
NASA Astrophysics Data System (ADS)
Scapolan, Matteo; Tehrani, Maryam Ghandchi; Bonisoli, Elvio
2016-10-01
In this paper, the problem of energy harvesting is considered using an electromechanical oscillator. The energy harvester is modelled as a spring-mass-damper, in which the dissipated energy in the damper can be stored rather than wasted. Previous research provided the optimum damping parameter, to harvest maximum amount of energy, taking into account the stroke limit of the device. However, the amount of the maximum harvested energy is limited to a single frequency in which the device is tuned. Active and semi-active strategies have been suggested, which increases the performance of the harvester. Recently, nonlinear damping in the form of cubic damping has been proposed to extend the dynamic range of the harvester. In this paper, a periodic time-varying damper is introduced, which results in a parametrically excited system. When the frequency of the periodic time-varying damper is twice the excitation frequency, the system internal energy increases proportionally to the energy already stored in the system. Thus, for certain parametric damping values, the system can become unstable. This phenomenon can be exploited for energy harvesting. The transition curves, which separate the stable and unstable dynamics are derived, both analytically using harmonic balance method, and numerically using time simulations. The design of the harvester is such that its response is close to the transition curves of the Floquet diagram, leading to stable but resonant system. The performance of the parametric harvester is compared with the non-parametric one. It is demonstrated that performances and the frequency bandwidth in which the energy can be harvested can be both increased using time-varying damping.
The role of magnetic damping in the r-mode evolution of accreting neutron stars
NASA Astrophysics Data System (ADS)
Cao, GuoJie; Zhou, Xia; Wang, Na
2015-03-01
The magnetic damping rate was introduced in the evolution equations of r-modes, which shows that r-modes can generate strong toroidal magnetic fields in the core of accreting millisecond pulsars inducing by differential rotation. With consideration of the coupling evolution of r-modes, spin and thermal evolution, we investigated the influence of the magnetic damping on the differential rotation of nonlinear r-modes of accreting neutron stars. We derived the coupling evolution equations of the star involving the magnetic damping rate in the framework of second-order r-mode theory. The numerical results show that the magnetic damping suppressed the nonlinear evolution of r-modes since the saturation amplitude is reduced to a great extent. In particular, because of the presence of the generated toroidal magnetic field, the spin-down of the stars is terminated and the viscous heating effects are also weakened. Moreover, we could obtain a stronger generated toroidal magnetic field in the second-order r-mode theory. The gravitational radiation may be detected by the advanced laser interferometer detector LIGO if the amount of differential rotation is small when the r-mode instability becomes active and the accretion rate is not very high.
Design of the magnetorheological mount with high damping force for medium speed diesel generators
NASA Astrophysics Data System (ADS)
Kang, O.-H.; Kim, W.-H.; Joo, W. H.; Park, J.-H.
2013-04-01
This paper investigates the controllable magnetorheological (MR) mount for the marine diesel-generator (D/G) sets. Sometimes, significant vibrations over the allowable limit are observed on the D/G sets due to their huge excitation forces. Because the severe vibration can lead to structural damages to the D/G sets, it should be reduced to below the limit. Although passive mounts with rubber isolators are usually used, the vibration reduction performance is not always sufficient. In addition, expecting that the vibration levels required by customers will get more severe, semi-active vibration isolation system needs to be developed. To the aim, the valve (flow) mode type of MR mount has been designed. Especially, the annular-radial configuration was adopted to enhance the damping force within the restricted space. The geometry of the mount has been optimized to obtain the required damping force and the magnetic field analysis has been carried out using ANSYS APDL. To verify the performance of the developed MR mount, excitation test was conducted and the dynamic characteristics were identified. Since damping property of the MR fluid is changed by the applied magnetic field strength and excitation frequency, responses to changing applied currents and frequencies were obtained. From the results, damping performance of the MR mount was evaluated.
Biomolecular ligands screening using radiation damping difference WaterLOGSY spectroscopy.
Sun, Peng; Jiang, Xianwang; Jiang, Bin; Zhang, Xu; Liu, Maili
2013-07-01
Water-ligand observed via gradient spectroscopy (WaterLOGSY) is a widely used nuclear magnetic resonance method for ligand screening. The crucial procedure for the effectiveness of WaterLOGSY is selective excitation of the water resonance. The selective excitation is conventionally achieved by using long selective pulse, which causes partial saturation of the water magnetization leading to reduction of sensitivity, in addition to time consuming and error prone. Therefore, many improvements have been made to enhance the sensitivity and robustness of the method. Here we propose an alternative selective excitation scheme for WaterLOGSY by utilizing radiation damping effect. The pulse scheme starts simply with a hard inversion pulse, instead of selective pulse or pulse train, followed by a pulse field gradient to control the radiation damping effect. The rest parts of the pulse scheme are similar to conventional WaterLOGSY. When the gradient pulse is applied immediately after the inversion pulse, the radiation damping effect is suppressed, and all of the magnetization is inversed. When the gradient pulse and the inversion pulse are about 10-20 ms apart, the radiation damping effect remains active and drives the water magnetization toward +z-axis, resulting in selective non-inversion of the water magnetization. By taking the differences of the spectra obtained under these two conditions, one should get the result of WaterLOGSY. The method is demonstrated to be simple, robust and sensitive for ligand screening.
Metallic adhesion layer induced plasmon damping and molecular linker as a nondamping alternative.
Habteyes, Terefe G; Dhuey, Scott; Wood, Erin; Gargas, Daniel; Cabrini, Stefano; Schuck, P James; Alivisatos, A Paul; Leone, Stephen R
2012-06-26
Drastic chemical interface plasmon damping is induced by the ultrathin (∼2 nm) titanium (Ti) adhesion layer; alternatively, molecular adhesion is implemented for lithographic fabrication of plasmonic nanostructures without significant distortion of the plasmonic characteristics. As determined from the homogeneous linewidth of the resonance scattering spectrum of individual gold nanorods, an ultrathin Ti layer reduces the plasmon dephasing time significantly, and it reduces the plasmon scattering amplitude drastically. The increased damping rate and decreased plasmon amplitude are due to the dissipative dielectric function of Ti and the chemical interface plasmon damping where the conduction electrons are transferred across the metal-metal interface. In addition, a pronounced red shift due to the Ti adhesion layer, more than predicted using electromagnetic simulation, suggests the prevalence of interfacial reactions. By extending the experiment to conductively coupled ring-rod nanostructures, it is shown that a sharp Fano-like resonance feature is smeared out due to the Ti layer. Alternatively, vapor deposition of (3-mercaptopropyl)trimethoxysilane on gently cleaned and activated lithographic patterns functionalizes the glass surface sufficiently to link the gold nanostructures to the surface by sulfur-gold chemical bonds without observable plasmon damping effects.
The Study of Damped Harmonic Oscillations Using an Electronic Counter
ERIC Educational Resources Information Center
Wadhwa, Ajay
2009-01-01
We study damped harmonic oscillations in mechanical systems like the loaded spring and simple pendulum with the help of an oscillation measuring electronic counter. The experimental data are used in a software program that solves the differential equation for damped vibrations of any system and determines its position, velocity and acceleration as…
Interdigitated interdigital transducer for surface elastometry of soft damping tissue.
Danicki, Eugene; Nowicki, Andrzej; Tasinkevych, Yuriy
2013-06-01
Measurement of the shear elastic constant of soft and highly damping tissue of high Poisson ratio is quite a challenging task. It is proposed to evaluate shear wave velocity and damping of tissue by measuring the shear skimming bulk waves using one interdigitated interdigital transducer on a piezoelectric layer, such as polyvinylidene fluoride, applied to the surface of the small tissue sample.
Nonlinear Landau damping in quark-gluon plasma
NASA Astrophysics Data System (ADS)
Xiaofei, Zhang; Jiarong, Li
1995-08-01
The semiclassical kinetic equations for the quark-gluon plasma (QGP) are discussed by the multiple time-scale method. The mechanism of nonlinear Landau damping owing to non-Abelian and nonlinear wave-particle interactions in QGP is investigated, and the nonlinear Landau damping rate for the longitudinal color eigenwaves in the long-wavelength limit is calculated.