Low frequency motion measurement of spacecrafts and satellites with inertial monolithic sensors

2017 ◽  
Author(s):  
F. Barone ◽  
G. Giordano ◽  
F. Acernese ◽  
R. Romano
Keyword(s):  
Low Frequency ◽  
Motion Measurement ◽  
Low Frequency Motion

Unsteady measurements in a separated and reattaching flow

1984 ◽  
Vol 144 ◽  
pp. 13-46 ◽  
Author(s):  
N. J. Cherry ◽  
R. Hillier ◽  
M. E. M. P. Latour
Keyword(s):  
Shear Layer ◽  
Large Scale ◽  
Separation Bubble ◽  
Scale Up ◽  
Three Dimensional ◽  
Low Frequency ◽  
Vortical Structures ◽  
Large Scale Structures ◽  
Bubble Length ◽  
Low Frequency Motion

Measurements of fluctuating pressure and velocity, together with instantaneous smoke-flow visualizations, are presented in order to reveal the unsteady structure of a separated and reattaching flow. It is shown that throughout the separation bubble a low-frequency motion can be detected which appears to be similar to that found in other studies of separation. This effect is most significant close to separation, where it leads to a weak flapping of the shear layer. Lateral correlation scales of this low-frequency motion are less than the reattachment length, however; it appears that its timescale is about equal to the characteristic timescale for the shear layer and bubble to change between various shedding phases. These phases were defined by the following observations: shedding of pseudoperiodic trains of vortical structures from the reattachment zone, with a characteristic spacing between structures of typically 60% to 80% of the bubble length; a large-scale but irregular shedding of vorticity; and a relatively quiescent phase with the absence of any large-scale shedding structures and a significant ‘necking’ of the shear layer downstream of reattachment.Spanwise correlations of velocity in the shear layer show on average an almost linear growth of spanwise scale up to reattachment. It appears that the shear layer reaches a fully three-dimensional state soon after separation. The reattachment process does not itself appear to impose an immediate extra three-dimensionalizing effect upon the large-scale structures.

Nonlinear Wave Loads Acting on Cylinder Array Slowly Oscillating in Diffraction and Radiation Wave Fields

2005 ◽  
Author(s):  
Weiguang Bao ◽  
Takeshi Kinoshita ◽  
Motoki Yoshida
Keyword(s):  
Nonlinear Wave ◽  
Perturbation Expansion ◽  
Low Frequency ◽  
Added Mass ◽  
Wave Loads ◽  
Wave Fields ◽  
Wave Drift ◽  
Cylinder Array ◽  
Radiation Wave ◽  
Low Frequency Motion

The problem of a circular cylinder array slowly oscillating in both diffraction and radiation wave fields is considered in the present work. As a result of the interaction between the wave fields and the low-frequency motion, nonlinear wave loads may be separated into the so-called wave-drift added mass and damping. They are force components proportional to the square of the wave amplitude but in phase of the acceleration and velocity of the low-frequency motion respectively. The frequency of the slow oscillation is assumed to be much smaller than the wave frequency. Perturbation expansion based on two time scales and two small parameters is performed to the order to include the effects of the acceleration of the low-frequency motion. Solutions to these higher order potentials are suggested in the present work. Wave loads including the wave drift added mass and damping are evaluated by the integration of the hydrodynamic pressure over the instantaneous wetted body surface.

Biological membranes are rich in low-frequency motion

1983 ◽  
Vol 732 (2) ◽  
pp. 473-478 ◽  
Author(s):  
B.A. Cornell ◽  
R.G. Hiller ◽  
J. Raison ◽  
F. Separovic ◽  
R. Smith ◽  
...  
Keyword(s):  
Low Frequency ◽  
Biological Membranes ◽  
Low Frequency Motion

Contribution of the Mooring System to the Low-Frequency Motions of a Semisubmersible in Combined Wave and Current

2009 ◽  
Author(s):  
Amany M. A. Hassan ◽  
Martin J. Downie ◽  
Atilla Incecik ◽  
R. Baarholm ◽  
P. A. Berthelsen ◽  
...  
Keyword(s):  
Standard Deviation ◽  
Damping Ratio ◽  
Low Frequency ◽  
Scale Model ◽  
Mooring Line ◽  
Mooring System ◽  
Current Field ◽  
Mooring Lines ◽  
Mean Values ◽  
Low Frequency Motion

This paper presents the results of an experiment carried out on a semi-submersible model to measure the steady drift force and low frequency surge motions. In the experiments, the influence of mooring systems was also investigated in different combinations of current and sea state. The measurements were carried out with a 1/50 scale model which was moored using horizontal springs and catenary mooring lines. A comparative study of the mean values of steady drift motions and the standard deviation of the low frequency motion amplitudes is presented. In addition, the effect of current on the damping ratio is discussed. It is found that for both horizontal and catenary moorings, the presence of a current increases the damping ratio of the system. For the catenary mooring system, as expected, the presence of mooring lines and their interaction with waves and current increases the damping compared to the damping of the horizontal mooring system. The measured mean values of the surge motions in a wave–current field are compared to the superposed values of those obtained from waves and current separately. For the horizontal mooring, it is found that there is good agreement in moderate sea states, while in higher sea states the measured motion responses are larger. In the wave-current field, the standard deviation of the surge motion amplitudes is found to be less than that obtained in waves alone. This can be explained by the increased magnitude of the damping ratio. Only in the cases of high sea states with the horizontal mooring system, was it found that the standard deviation of the surge motions is slightly larger than those obtained for waves and current separately. This may be explained by the absence of catenary mooring line damping.

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