Oscillatory Moment Research Articles

Effects of blade configuration parameters on helicopter rotor structural dynamics and whirl tower loads

ABSTRACTThe influence of the blade geometric parameters on the structural dynamic characteristics, response and loads of a helicopter rotor under hover condition in a whirl tower was investigated. A general geometry was considered for the rotor blade which included configuration parameters like root offset, torque offset, pre-twist, pre-cone, pre-droop, pre-sweep, tip-sweep and tip-anhedral. The option of placing concentrated masses at any location on the blade was also included. Natural frequencies and the corresponding mode shapes of the rotating blade were obtained by solving the linear, undamped structural dynamics model in the finite element domain. For calculating the response and loads on the rotor, the complete aeroelastic equation was solved in modal space. Aerodynamic models used in the aeroelastic loads calculations were Peters-He dynamic wake theory for inflow and themodifiedONERA dynamic stall theory for airloads calculations. From the study, the blade structural dynamic characteristics are found to be sensitive to variation in blade geometric parameters. Tip-sweep was found to have significant effects on root oscillatory moments. The moments at the tip junction with the straight portion of the blade were found to be substantially affected by tip-sweep and tip-anhedral.

Factorial correlators and oscillatory multiplicity moments of ring-like and jet-like events in 16O–Ag/Br interactions at 60 A GeV1Supported by Department of Science and Technology, Government of India through SERC Fast Track Scheme for Young Scientists Project.

The analysis of ring-like and jet-like events in 16O–Ag/Br interactions at 60 A GeV is performed using the methods of factorial correlators and oscillatory multiplicity moments. The investigation reveals that the correlators increase with a decrease of the size of bin separation interval, following the power law, and suggest the presence of the intermittent nature of the dynamical fluctuations measured. The analysis shows the signal of the intermittency to be stronger in the ring-like events. However, both the ring-like and jet-like events are found to be consistent with the α-model predictions. The oscillatory moments are found to follow a different behavior in ring-like events and jet-like events. In most cases, the simulation fails to reproduce the measurements.

Intermittency and related issues in 16O-Ag/Br collision at 200A GeV/c

In this paper we present some results on the nonstatistical fluctuation in the 1-dimensional (1-d) density distribution of singly charged produced particles in the framework of the intermittency phenomenon. A set of nuclear emulsion data on 16O-Ag/Br interactions at an incident momentum of 200A GeV/c, was analyzed in terms of different statistical methods that are related to the self-similar fractal properties of the particle density function. A comparison of the present experiment with a similar experiment induced by the 32S nuclei and also with a set of results simulated by the Lund Monte Carlo code FRITIOF is presented. A similar comparison between this experiment and a pseudo-random number generated simulated data set is also made. The analysis reveals the presence of a weak intermittency in the 1-d phase space distribution of the produced particles. The results also indicate the occurrence of a nonthermal phase transition during emission of final-state hadrons. Our results on factorial correlators suggests that short-range correlations are present in the angular distribution of charged hadrons, whereas those on oscillatory moments show that such correlations are not restricted only to a few particles. In almost all cases, the simulated results fail to replicate their experimental counterparts.

Measurement of Lumbar Spine Loads and Motions During Rotational Mobilization

Objectives To measure the loads acting at the lumbar spine and the resulting motions during rotational mobilization. Methods Twenty healthy subjects were subjected to right rotational mobilization of different grades. The magnitude and frequency of mobilization loads were decided by an experienced manipulative therapist to be appropriate for each mobilization grade. Subjects were positioned on a specially constructed plinth capable of measuring forces and moments about 3 axes. The 3-dimensional movements of the lumbar spine were captured by an electromagnetic tracking device. Results In the starting positions, the lumbar spines were found to be flexed, axially rotated to the right, and laterally bent to the left. As the mobilization grade increased, the spine was axially rotated further into the range. Rotational mobilization was found to induce oscillatory moments and movements of the spine in all 3 anatomical planes. The twisting moment and movement were generally accompanied by lateral bending moment and movement in the opposite direction. The mean amplitudes of the moment and movement oscillations were small and found to be largest for grade III mobilization. Conclusion The mechanical effects of rotational mobilization are not restricted to axial rotation of the spine as the name may have suggested. Rotational mobilization may be able to restore lost movements of the lumbar spine in any of the 3 planes. The method developed in this study showed good reliability and may be considered to assess treatment outcome and changes in spinal stiffness after therapy.

Hydrodynamical models for W Vir pulsating variables

We have calculated a grid of hydrodynamical models for W Vir pulsating variable stars with mass M = 0.6M⊙ and bolometric luminosity 200 ≤ Lbol/L⊙ ≤ 1.2 × 103. The positions of the blue edge of the instability strip and the boundary separating the domains of periodic and semi-regular pulsation in the H-R diagram were determined. These two boundaries converge for Lbol ≈ 103L⊙. Two different groups of models can be distinguished in the region of periodic solutions, characterized by oscillations with alternating amplitude and duration of the pulsation cycle. For the first group of models, the alternation of the pulsations occurs over a time interval of two periods of the fundamental mode; this is due to the 2П0=3П1 resonance between the fundamental mode and first overtone. The models of the second group have larger luminosities and are located near the boundary separating the domains of periodic and semiregular pulsations. A discrete Fourier transformation analysis shows that, as we approach the region of semiregular pulsations, additional peaks appear in the spectra of the oscillatory moment of inertia and kinetic energy. These peaks correspond to period doubling bifurcations (a Feigenbaum sequence) of order n≤4. Approximate formulas are presented for the pulsation constant Q as a function of the mass-to-radius ratio (M/M⊙)/(R/R⊙) and the luminosity of the star Lbol.

On properties of the fourier harmonics in the limit-cycle models of classical cepheids

The Fourier coefficients of the hydrodynamic variables are calculated for the limit-cycle models of classical Cepheids having periods from 7.2 to 10.9 days. In adiabatically pulsating layers of the stellar envelope, each Fourier harmonic of orderk ≤ 8 is shown to be identified with a corresponding standing wave, so that the pulsation motions of the adiabatic layers may be represented as a superposition of standing waves. Each Fourier harmonic of orderk may also be identified with the eigenfunction of orderl of the linear adiabatic wave equation when the resonance condition Ωl/Ω0 =k is fulfilled. The spectra of the oscillatory moment of inertia and the spectra of kinetic energy obey the power law for the Fourier harmonics of orderk ≤ 15, the spectrum slope being steeper for shorter pulsation periods. In the helium and hydrogen ionizing regions all of the Fourier harmonics drive the pulsation instability, whereas in the radiative damping region the mechanical work done by each Fourier harmonic is negative. In classical Cepheids having periods shorter than 10 days the period dependence of the secondary bump is due to phase changes of the second order Fourier harmonic in the outer nonadiabatic layers of the stellar envelope. At a pulsation period of II ≈ 9.7 days the second order Fourier harmonic is identified with the second overtone. At periods II > 10 days the second order Fourier harmonic tends to be attracted by the fundamental mode in such a way that their phases coincide in the outer layers of the stellar envelope.

Fourier Analysis of the Hydrodynamic Limit-Cycle Models of Pulsating Stars

AbstractThe pulsation motions of the limit-cycle model can be described as a superposition of the Fourier harmonics, in the adiabatic layers each harmonics being identified with the corresponding standing wave. Near the resonance Π0/Πl = k the harmonics of order k is also identified with the overtone of order l The spectra of the oscillatory moment of inertia obey to the power dependence on the Fourier harmonics order k. In cepheids with periods shorter than 9 days the bump is due to the wave packet generated by the second overtone, whereas at periods longer than 10 days the bump feature is due to the traveling pulse reflected off the stellar core.

Persistent currents in mesoscopic copper rings

At sufficiently low temperature, the total magnetization of an ensemble of 10 7 isolated mesoscopic copper rings oscillates as a function of the enclosed magnetic flux with a period of half a flux quantum, h/2 e. The amplitude of the oscillatory moment is ≈1.2×10 -15 A m 2 and decreases exponentially with increasing temperature on the scale of the correlation energy E c = π 2ℏ D/ L 2. This isevidence for a flux periodic persistent current in each ring of average value 3×10 -3 ev F/ L. Single-particle effects only give rise to an h/2 e periodicity in a closed system where the variations of the chemical potential are correlated to the variation of the density of states with magnetic flux. On the other hand, electron-electron interactions always give rise to persistent currents periodic in h/2 e whether the system is open or closed.

Magnetization of mesoscopic copper rings: Evidence for persistent currents.

We have measured the low-temperature magnetization response of ${10}^{7}$ isolated mesoscopic copper rings to a slowly varying magnetic flux. At sufficiently low temperature, the total magnetization response oscillates as a function of the enclosed magnetic flux on the scale of half of a flux quantum. The amplitude of the oscillatory moment is \ensuremath{\approxeq}1.2\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}15}$ ${\mathrm{Am}}^{2}$ and decreases exponentially with increasing temperature on the scale of the correlation energy ${\mathit{E}}_{\mathit{c}}$=hD/(2L${)}^{2}$\ensuremath{\approxeq}80 mK. This is evidence for a flux-periodic persistent current in each ring of average value 3\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}3}$e${\ensuremath{\nu}}_{\mathit{F}}$/L.

Mössbauer spectroscopy study of composition modulated [110] Fe-V films

Conversion electron Mössbauer spectra of composition modulated Fe-V films have been analysed within the framework of an additive hyperfine-field perturbation model. A single parameter fit to spectra of 3 to 11 atomic planes of Fe gives confidence in the deduced values of 0.85 to 1.2 for the diffusion-length, implying strong composition modulation. The theoretical prediction of a reduced moment at the interface is verified, the antiferromagnetic moment on the V atoms near the interface is supported, but the predicted oscillatory moment of the inner iron layers is ruled out.

Input and transfer admittances of thick plates driven by a uniform line moment

The response of an infinite homogeneous elastic plate to an external oscillatory moment, applied uniformly along a straight line, is analyzed within the framework of the Mindlin model for the dynamics of a thick plate. That model includes the two antisymmetric modes of lowest order. Expressions for the input and transfer admittances in vacuo are found in closed form. Pressure distributions that lead to precisely the same response as the line moment are shown not to exist, except in a limiting sense for the classical, low-frequency limit.

A Study on the Rolling Characteristics of Ship by a Forced Oscillation Model Experiment

The forced oscillation method is a very suitable method to find out the characteristics of oscillations, and several types of forced oscillation generater have been developed. However, most of them are designed for the model towed by or running under the tank carriage, which can be used as a platform to endue the force. For the investigation of the rolling characteristics, it is desirable to use a completely free running model, for example in a square shaped basin, because the experiments by the model can be carried out without any wall effects and any complicated techniques. For the completely free running model, very few oscillation generater can be used except the weight shifting type. At first, we also used this type, however, the oscillater produces the movement of the centre of gravity together with the inclining moment, that makes the scope of analysis of the oscillation characteristics limited.Recently, we have completed a new type forced oscillation generater to use on the free running model test. As is shown in Fig. 2, the new oscillater is composed of two gyroscopes, which have their axis vertical and are turning in opposite direction. The angular velocity is given to the gyroscope around the y axis oscillatory, then the forced oscillatory moment is produced around the x axis as the precession moment. As the direction of rotation and the given angular velocity of each gyroscope is reverse each other, only the forced moment on the same direction around the lateral axis x is produced, while the reaction moments are cancelled each other. Moreover, even if the model perform the pitching motion, the rolling moment is not produced. The superior character of this method to Gerritsma's and Golovato, s methods is that the oscillation can produce the pure sinusoidal forced moment by giving the sinusoidal angular velocity to the gyroscopes. The characteristics of oscillation can be obtained by measuring and analysing the motion of the model.Here, as the first attempt, we have carried out the forced rolling experiments by the free running model to obtain the rolling characteristics, especially when she is advancing with forward speed. The results are summarized as follows ;1. The rolling characteristics of ship while she is advancing are essentially the same with that while she is drifting. Even in rolling, it is sufficient to consider the effect of the nonlinearity of damping term in the equation of motion, and the non-linearity of restoring term can be neglected, so far as the amplitude is modelate.2. Comparing the forced rolling tests in still water with the rolling tests in regular beam waves, it is concluded that the amount of forced moment of the wave affecting on the ship with advance speed is almost the same as that affecting on the ship in drift condition.3. The effects of forward advance speed on the roll damping of the ship were made clear quantatively as well as qualitatively. The damping of roll increases with the increase of the advanced speed of ship, and around the service speed of the ordinary ships, say at Froude number of 0.2 to 0.3 it becomes about 1.5-1. 8 times the damping in drift condition. It is very interesting to find that the damping of ship has usually a hump and a hollow at the same range of the Froude number.