Steady-State and Time-Harmonic Response in Micropolar Porous Thermoelastic Medium with Two Relaxation Times

2009 ◽  
Vol 12 (8) ◽  
pp. 791-800
Author(s):  
Rajneesh Kumar ◽  
Praveen Ailawalia
Keyword(s):  
Steady State ◽  
Relaxation Times ◽  
Thermoelastic Medium ◽  
Harmonic Response ◽  
Time Harmonic

Disorder and localization in ribbed structures with fluid loading

1994 ◽  
Vol 444 (1920) ◽  
pp. 73-89 ◽  
Keyword(s):  
Steady State ◽  
Band Structure ◽  
Transfer Matrix ◽  
Stop Band ◽  
Localization Length ◽  
Fluid Loading ◽  
Transfer Matrices ◽  
Matrix Solution ◽  
Harmonic Response ◽  
Irregular Case

The paper considers the steady-state harmonic response of an elastic fluid-loaded membrane supported by irregularly spaced ribs. Under the assumption of subsonic wave coupling, the solution is given exactly for any configuration as a product of 2 x 2 transfer matrices. It is well known that the response of a periodically ribbed membrane exhibits a pass/stop band structure. Although this structure is destroyed in the irregular case, we find that two distinct régimes remain: smooth and fluctuating exponential decay. The transfer matrix solution is used to explain these regions. The average transfer matrix is obtained exactly; where the decay is smooth its eigenvalues approximately determine the localization length.

scholarly journals Picosecond-Duration Vibrational Relaxation Kinetics in the Excited S1 State of Perylene and Anthracene Molecules

1983 ◽  
Vol 3 (1-6) ◽  
pp. 249-261 ◽  
Author(s):  
A. Freiberg ◽  
T. Tamm ◽  
K. Timpmann
Keyword(s):  
Steady State ◽  
Luminescence Spectrum ◽  
Vibrational Relaxation ◽  
Vibrational Energy ◽  
Streak Camera ◽  
Relaxation Times ◽  
Temporal Behavior ◽  
Vibrational Energy Relaxation ◽  
The Matrix ◽  
Measured Relaxation

We present and discuss the results of a direct observation of the picosecond range temporal behavior of vibronic lines in the luminescence spectrum of the matrix-isolated perylene and anthracene molecules. A novel subtractive dispersion mount of monochromators in conjunction with the synchroscan streak camera has been used. From spectrochronograms measured at different excitation wavelengths the vibrational energy relaxation times have been obtained. These are in the range of 20–30 ps and are most probably determined by the existence of the phonon bath of the matrix. A comparison of the measured relaxation constants with those estimated from the steady-state hot luminescence spectrum has been made.

Passive Stability and Active Control in a Rhythmic Task

2007 ◽  
Vol 98 (5) ◽  
pp. 2633-2646 ◽  
Author(s):  
Kunlin Wei ◽  
Tjeerd M. H. Dijkstra ◽  
Dagmar Sternad
Keyword(s):  
Steady State ◽  
Active Control ◽  
Human Performance ◽  
Passive Control ◽  
Basin Of Attraction ◽  
Relaxation Times ◽  
Passive Dynamics ◽  
Passive Stability ◽  
Set Up ◽  
Boundary Of Stability

Rhythmically bouncing a ball with a racket is a task that affords passively stable solutions as demonstrated by stability analyses of a mathematical model of the task. Passive stability implies that no active control is needed as errors die out without requiring corrective actions. Empirical results from human performance demonstrated that actors indeed exploit this passive dynamics in steady-state performance, thereby reducing computational demands of the task. The present study investigated the response to perturbations of different magnitudes designed on the basis of the model's basin of attraction. Humans performed the task in a virtual reality set-up with a haptic interface. Relaxation times of the performance errors showed significantly faster returns than predicted from the purely passive model, indicative of active error corrections. Systematic adaptations in the racket trajectories were a monotonic function of the perturbation magnitudes, indicating that active control was applied in proportion to the perturbation. These results did not indicate any sensitivity to the boundary of stability. Yet the influence of passive dynamics was also seen: the pattern of relaxation times in the major performance variable ball height was consistent with qualitative predictions derived from the basin of attraction and racket accelerations at contact were generally negative signaling use of passive stability. These findings suggest that the fast return back to steady state was assisted by passive properties of the task. It was concluded that actors used a blend of active and passive control for all sizes of perturbations.

scholarly journals Time-Harmonic Response of an Elastic Pile in a Radially Inhomogeneous Poroelastic Medium

2021 ◽  
Vol 2021 ◽  
pp. 1-14
Author(s):  
Xibin Li ◽  
Wenhui Xu ◽  
Zhiqing Zhang
Keyword(s):  
Twist Angle ◽  
Engineering Practice ◽  
Zone Model ◽  
Poroelastic Medium ◽  
Soil System ◽  
Harmonic Response ◽  
Disturbed Soil ◽  
Time Harmonic ◽  
Radially Inhomogeneous ◽  
Surrounding Soil

The time-harmonic response of an elastic pile embedded in a radially inhomogeneous poroelastic medium and subjected to a torsional loading is studied in the present article. In engineering practice, the surrounding soil may be weakened due to the disturbance effect caused by pile driving. To simulate the weakened surrounding soil, a boundary zone model with the complex shear modulus of the inner disturbed soil changing in a parabolic form along the radial direction is proposed. In view of the axis-symmetric deformation of the surrounding soil under torsional load, the equation of motion of the saturated soil is solved in the cylindrical coordinate system. The vibration displacement and shear stress solutions for the inner disturbed soil are gained by expanding the displacement as a power series, and those for the outer undisturbed soil are obtained by solving the partial differential equation. By virtue of continuity conditions at the interface between inner and outer soil regions, the torsional impedance of the radially inhomogeneous soil is solved. Then, via the boundary and continuity conditions of the pile-soil system, the twist angle and torque of the pile are obtained in the frequency domain. Finally, selected numerical results are conducted to investigate the influence of the material damping, softening degree, and softening range of the inner soil on the distribution of the twist angle and torque of the pile along the depth direction.

Steady State Dynamic Performance of the Slab with EPS-Blocks

2010 ◽  
Vol 168-170 ◽  
pp. 990-996 ◽  
Author(s):  
Da Ying Zhang ◽  
Lu Min Wang ◽  
Xing Pei Liang
Keyword(s):  
Steady State ◽  
Dynamic Performance ◽  
Response Analysis ◽  
Light Weight ◽  
Stress Distributions ◽  
Harmonic Response ◽  
State Dynamic ◽  
Harmonic Response Analysis ◽  
Stress Variations

In this paper, novel filled materials EPS-blocks of cast-in-situ slabs are presented. And EPS-blocks with light weight which are inexpensive are validated to be sufficient strong as filled materials to bring an innovation for the development of cast-in-situ slabs. Based on modal analysis, it is found that the decreased weight has a greater influence to the mode of the slab than the weakened stiffness. According to harmonic response analysis, tensile stress distributions of the slab with EPS-blocks are depicted in figures and explained. Typically, orifice stress distributions are expounded and stress variations of nodes in different places are illustrated. From these studies, it is concluded that the steady state dynamic performance of the slab with EPS-blocks is good.

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