Experiments on Dispersive Pulse Propagation in Laminated Composites and Comparison With Theory

1969 ◽  
Vol 36 (3) ◽  
pp. 485-490 ◽  
Author(s):  
J. S. Whittier ◽  
J. C. Peck
Keyword(s):  
Pulse Propagation ◽  
Laminated Composites ◽  
Rear Surface ◽  
Step Function ◽  
Surface Velocity ◽  
Flat Plates ◽  
Theoretical Predictions ◽  
Long Time ◽  
Capacitance Gauge ◽  
High Degree

Transient stress-wave experiments on laminated composites are described, and the results are compared with theoretical predictions. The composites are laminated from alternating layers of high and low-modulus material, which cause a high degree of geometric dispersion of waves propagating in the composite. Experiments were conducted in which waves propagated parallel to the laminations. Flat plates were subjected on one face to a uniform pressure with step-function time dependence induced by a gas-dynamic shock wave. Under this loading, the central portion of the specimen initially responds as if it were laterally unbounded. The average velocity over a 3/8-in-dia area of the backface of the plate was measured with a capacitance gauge. The results are in good agreement with theoretical predictions made with a long-time asymptotic approximation called the head-of-the-pulse approximation. The theory isolates the dominant character of the response and predicts timing and amplitude of oscillations in normalized rear surface velocity within a few percent.

Experiments on Pulse Propagation in an Obliquely Laminated Composite

1974 ◽  
Vol 41 (4) ◽  
pp. 1052-1056 ◽  
Author(s):  
C. Sve ◽  
S. Okubo
Keyword(s):  
Pulse Propagation ◽  
Rear Surface ◽  
Laminated Composite ◽  
Theoretical Work ◽  
Surface Velocity ◽  
Capacitive Transducer ◽  
Linear Elastic ◽  
Viscosity Effects ◽  
History Of ◽  
Velocity History

Experimental results are presented for the linear elastic dynamic response of periodically laminated composites. A shock tube-capacitive transducer technique is used to determine the rear surface velocity history of three laminated samples that have different lamination angles and are subjected to a step pressure loading. Viscosity effects are discussed, and comparisons are made with predictions based on previous theoretical work.

scholarly journals Triadic resonances in precessing rapidly rotating cylinder flows

2015 ◽  
Vol 778 ◽  
Author(s):  
T. Albrecht ◽  
H. M. Blackburn ◽  
J. M. Lopez ◽  
R. Manasseh ◽  
P. Meunier
Keyword(s):  
Rotating Cylinder ◽  
Direct Numerical Simulations ◽  
Mode Shapes ◽  
Resonance Model ◽  
Rapid Rotation ◽  
Nutation Angle ◽  
Resonant Instability ◽  
Theoretical Predictions ◽  
Long Time ◽  
Good Agreement

Direct numerical simulations of flows in cylinders subjected to both rapid rotation and axial precession are presented and analysed in the context of a stability theory based on the triadic resonance of Kelvin modes. For a case that was chosen to provide a finely tuned resonant instability with a small nutation angle, the simulations are in good agreement with the theory and previous experiments in terms of mode shapes and dynamics, including long-time-scale regularization of the flow and recurrent collapses. Cases not tuned to the most unstable triad, but with the nutation angle still small, are also in quite good agreement with theoretical predictions, showing that the presence of viscosity makes the physics of the triadic-resonance model robust to detuning. Finally, for a case with $45^{\circ }$ nutation angle for which it has been suggested that resonance does not occur, the simulations show that a slowly growing triadic resonance predicted by theory is in fact observed if sufficient evolution time is allowed.

scholarly journals Refined long-time asymptotics for Fisher–KPP fronts

2019 ◽  
Vol 21 (07) ◽  
pp. 1850072 ◽  
Author(s):  
James Nolen ◽  
Jean-Michel Roquejoffre ◽  
Lenya Ryzhik
Keyword(s):  
Travelling Waves ◽  
American Mathematical Society ◽  
Front Propagation ◽  
Step Function ◽  
Kolmogorov Equation ◽  
Compact Set ◽  
Kpp Equation ◽  
Branching Brownian Motion ◽  
Long Time ◽  
Unstable States

We study the one-dimensional Fisher–KPP equation, with an initial condition [Formula: see text] that coincides with the step function except on a compact set. A well-known result of Bramson in [Maximal displacement of branching Brownian motion, Comm. Pure Appl. Math. 31 (1978) 531–581; Convergence of Solutions of the Kolmogorov Equation to Travelling Waves (American Mathematical Society, Providence, RI, 1983)] states that, as [Formula: see text], the solution converges to a traveling wave located at the position [Formula: see text], with the shift [Formula: see text] that depends on [Formula: see text]. Ebert and Van Saarloos have formally derived in [Front propagation into unstable states: Universal algebraic convergence towards uniformly translating pulled fronts, Phys. D 146 (2000) 1–99; Front propagation into unstable states, Phys. Rep. 386 (2003) 29–222] a correction to the Bramson shift, arguing that [Formula: see text]. Here, we prove that this result does hold, with an error term of the size [Formula: see text], for any [Formula: see text]. The interesting aspect of this asymptotics is that the coefficient in front of the [Formula: see text]-term does not depend on [Formula: see text].

scholarly journals Low-frequency unsteadiness in the wake of a normal flat plate

1998 ◽  
Vol 370 ◽  
pp. 101-147 ◽  
Author(s):  
F. M. NAJJAR ◽  
S. BALACHANDAR
Keyword(s):  
Shear Layer ◽  
Flat Plate ◽  
Free Stream ◽  
Low Frequency ◽  
Separated Flow ◽  
Phase Mismatch ◽  
Streamwise Vortices ◽  
Long Time ◽  
Drag And Lift ◽  
High Degree

The separated flow past a zero-thickness flat plate held normal to a free stream at Re=250 has been investigated through numerical experiments. The long-time signatures of the drag and lift coefficients clearly capture a low-frequency unsteadiness with a period of approximately 10 times the primary shedding period. The amplitude and frequency of drag and lift variations during the shedding process are strongly modulated by the low frequency. A physical interpretation of the low-frequency behaviour is that the flow gradually varies between two different regimes: a regime H of high mean drag and a regime L of low mean drag. It is observed that in regime H the shear layer rolls up closer to the plate to form coherent spanwise vortices, while in regime L the shear layer extends farther downstream and the rolled-up Kármán vortices are less coherent. In the high-drag regime three-dimensionality is characterized by coherent Kármán vortices and reasonably well-organized streamwise vortices connecting the Kármán vortices. With a non-dimensional spanwise wavelength of about 1.2, the three-dimensionality in this regime is reminiscent of mode-B three-dimensionality. It is observed that the high degree of spanwise coherence that exists in regime H breaks down in regime L. Based on detailed numerical flow visualization we conjecture that the formation of streamwise and spanwise vortices is not in perfect synchronization and that the low-frequency unsteadiness is the result of this imbalance (or phase mismatch).

Reconstruction of the dynamics and origin of rock glaciers in an Alpine environment

2021 ◽  
Author(s):  
Benjamin Lehmann ◽  
Robert S. Anderson ◽  
Xavier Bodin ◽  
Pierre G. Valla ◽  
Julien Carcaillet
Keyword(s):  
Remote Sensing ◽  
Time Scales ◽  
Surface Velocity ◽  
Rock Glacier ◽  
Alpine Environment ◽  
Mountain Ranges ◽  
Long Time ◽  
Rock Glaciers ◽  
Alpine Environments ◽  
Alpine Valleys

<p>Rock glaciers are one of the most frequent cryospheric landform in mid-latitude mountain ranges. They influence the evolution of alpine environments on short (years to decades) and long (centuries to millennia) time scales. As a visible expression of mountain permafrost [1] as well as an important water reserve in the form of ground ice [2], rock glaciers are seen as increasingly important in the evolution of geomorphology and hydrology of mountain systems in the context of climate change and deglaciation [3, 4]. On longer time scales, rock glaciers transport boulders produced by the erosion of the headwall upstream and downstream and therefore participate in shaping mountain slopes [5]. Despite their importance, the dynamics and origin of rock glaciers are poorly understood.</p><p>In this study, we propose to address two questions:</p><p>1) How does the dynamics of rock glaciers change over time?</p><p>2) What is the origin of rock glaciers and what is their influence on the evolution of alpine environments?</p><p>These two questions require an evaluation of the surface velocity field of rock glaciers by relating short and long time scales. To solve this problem, we combine complementary methods including remote sensing, geochronology with a mechanical model of rock glacier dynamics. We apply this approach to the rock glacier complex of the Vallon de la Route in the Massif du Combeynot (French alps).</p><p>In order to reconstruct the displacement field of the rock glacier on modern time scales, we used remote sensing methods (i.e., image correlation and InSAR). Over longer periods (10<sup>3</sup> to 10<sup>4</sup> years), we used cosmogenic terrestrial nuclides (TCN) dating. By applying this methodology to boulder surfaces at different positions along the central flow line of the rock glacier, from the headwall to its terminus, we will be able to convert the exposure ages into surface displacement. The use of dynamic modelling of rock glaciers [6] will allow us to relate the surface kinematics to short to long time scales. It will then be possible to discuss the age, origin of rock glaciers and how topo-climatic and geomorphological processes control their evolution in Alpine environment.</p><p> </p><p>[1] Barsch, D.: Rockglaciers. Indicators for the Present and Former Geoecology in High Mountain Environments, Springer series in physical environment vol. 16, Springer, Berlin, Heidelberg, 1996.</p><p>[2] Jones, D. B., Harrison, S., Anderson, K., and Whalley, W. B.: Rock glaciers and mountain hydrology: A review, Earth-Sci Rev, 193, 66–90, 2019.</p><p>[3] Haeberli, W., Schaub, Y., and Huggel, C.: Increasing risks related to landslides from degrading permafrost into new lakes in deglaciating mountain ranges, Geomorphology, 293, 405–417, 2017.</p><p>[4] Knight, J., Harrison, S., and Jones, D. B.: Rock glaciers and the geomorphological evolution of deglacierizing mountains, Geomorphology, 324, 14–24, 2019.</p><p>[5] MacGregor, K.R., Anderson, R.S., Waddington, E.D.: Numerical modeling of glacial erosion and headwall processes in alpine valleys. Geomorphology 103 (2):189–204, 2009.</p><p>[6] Anderson, R. S., Anderson, L. S., Armstrong, W. H., Rossi, M. W., & Crump, S. E.: Glaciation of alpine valleys: The glacier–debris-covered glacier–rock glacier continuum. Geomorphology, 311, 127-142, 2018.</p>

Temperature Measurements in High-Velocity Air Streams

1945 ◽  
Vol 12 (1) ◽  
pp. A25-A32
Author(s):  
H. C. Hottel ◽  
A. Kalitinsky
Keyword(s):  
Axial Flow ◽  
Extensive Study ◽  
Recovery Factor ◽  
Scale Model ◽  
Kinetic Temperature ◽  
Flat Plates ◽  
Air Velocity ◽  
Theoretical Predictions ◽  
Air Streams ◽  
Thermocouple Junction

Abstract When a stream of air is partially stopped by an inserted temperature probe, the temperature increase due to the conversion of kinetic energy affects the reading of the probe. The fraction of the total kinetic temperature rise which is registered by the probe, i.e., the so-called “recovery factor” of the probe, is a function of a number of variables. Tests dealing with the effect of probe shape and air velocity on this recovery factor, and with the influence of radiation on the accuracy of the measurements, are reported in this paper. Bare-wire probes gave recovery factors of approximately 0.65 in transverse flow and, in axial flow, approached 0.87 as the air velocity increased (in good agreement with theoretical predictions for flow over flat plates). With a spherical enlargement at the thermocouple junction, recovery approached 0.75. Recovery of twisted-wire couples varied from 0.72 to 0.83. A reduced-scale model of the Franz probe was found unsatisfactory after extensive study. Two simpler probes were developed, having high recovery (above 0.98 as velocity approaches sonic) and satisfactory insensitivity to yaw and radiation errors.

scholarly journals Fast and Accurate Finite Transducer Analysis Method for Wireless Passive Impedance-Loaded SAW Sensors

Sensors ◽  
2018 ◽  
Vol 18 (11) ◽  
pp. 3988
Author(s):  
Wei Luo ◽  
Yang Yuan ◽  
Yi Wang ◽  
Qiuyun Fu ◽  
Hui Xia ◽  
...  
Keyword(s):  
Computation Time ◽  
Processing Unit ◽  
Bulk Wave ◽  
Analysis Method ◽  
Accurate Analysis ◽  
Central Processing ◽  
Finite Transducer ◽  
Long Time ◽  
High Degree ◽  
Element Method

An accurate and fast simulation tool plays an important role in the design of wireless passive impedance-loaded surface acoustic wave (SAW) sensors which have received much attention recently. This paper presents a finite transducer analysis method for wireless passive impedance-loaded SAW sensors. The finite transducer analysis method uses a numerically combined finite element method-boundary element method (FEM/BEM) model to analyze non-periodic transducers. In non-periodic transducers, FEM/BEM was the most accurate analysis method until now, however this method consumes central processing unit (CPU) time. This paper presents a faster algorithm to calculate the bulk wave part of the equation coefficient which usually requires a long time. A complete non-periodic FEM/BEM model of the impedance sensors was constructed. Modifications were made to the final equations in the FEM/BEM model to adjust for the impedance variation of the sensors. Compared with the conventional method, the proposed method reduces the computation time efficiently while maintaining the same high degree of accuracy. Simulations and their comparisons with experimental results for test devices are shown to prove the effectiveness of the analysis method.

scholarly journals X-Ray Observations of Elliptical Galaxies by ASCA Satellite

1996 ◽  
Vol 171 ◽  
pp. 412-412
Author(s):  
K. Matsushita ◽  
K. Makishima
Keyword(s):  
Low Temperature ◽  
Mass Loss ◽  
Elliptical Galaxies ◽  
Stellar Mass ◽  
Plasma Emission ◽  
X Ray ◽  
Theoretical Predictions ◽  
Long Time ◽  
Temperature Component ◽  
Hubble Time

Using ASCA, we have confirmed that the ISM of X-ray bright elliptical galaxies are surprisingly metal poor, as compared to the theoretical predictions. In fact the exact values of the derived metallicity depend considerably on the plasma emission codes. However, the overall metallicity cannot be larger than ∼ 1 solar. For low LX/LB galaxies, all the available plasma codes suggest abundances less than half a solar. The ASCA spectra may be compatible with somewhat higher metallicity if we assume there is an additional low-temperature component (e.g. kTe ∼ 0.3 keV). However, the derived abundance can not be over 1 solar. In particular, the Si abundance turns out to be < 1.5 solar, confirming the metal-poor nature of the ISM. These ASCA results are in severe contradiction with most of the SN Ia rate, particularly that of Tammann (1982). Considering further that a fairly long time (109–10yr) is needed for the stellar mass loss to accumulates into the ISM, it is suggested that the SN Ia rate has remained quite low throughout Hubble time.

scholarly journals Surface-velocity field of the northern Larsen Ice Shelf, Antarctica

1994 ◽  
Vol 20 ◽  
pp. 319-326 ◽  
Author(s):  
R. A. Bindschadler ◽  
M. A. Fahnestock ◽  
P. Skvarca ◽  
T. A. Scambos
Keyword(s):  
Satellite Images ◽  
Surface Velocity ◽  
Ice Shelf ◽  
Limited Region ◽  
Surface Survey ◽  
Degree Of Confidence ◽  
High Degree ◽  
The Antarctic ◽  
Larsen Ice Shelf ◽  
Measurement Period

Three satellite images of the northern Larsen Ice Shelf arc used to derive velocity fields for the periods 1975–86 and 1986 89. Substantial increases in the speed of the ice between these periods are detected to a high degree of confidence. Ice which entered the ice shelf between Fothergill Point and Cape Worsley and ice from Drygalski Glacier has accelerated by approximately 15% over the measurement period. Ice from Bombardier and Dinsmoor Glaciers also exhibits acceleration but by a lesser amount. These accelerations may be the result of either significant retreat experienced by the ice shelf during this period or warming in the Antarctic Peninsula region. Velocities measured by surface survey over a 15 d period in 1991 indicate a slower velocity than the image-derived velocities in the limited region of overlap. These differences appear to be systematic and may be the result of uncontrolled errors in the surface survey. Limited control of one image could also contribute to some of these differences.

scholarly journals Expectations, Coordination Failures and Macro Crises

2020 ◽  
Vol 0 (0) ◽  
Author(s):  
Daniel Heymann ◽  
Juan Pablo Brichetti ◽  
Pedro Juarros ◽  
Gustavo Montero
Keyword(s):  
Rational Expectations ◽  
Central Element ◽  
Critical Periods ◽  
Social Concern ◽  
Coordination Failures ◽  
Economic Changes ◽  
Macroeconomic Analysis ◽  
The People ◽  
Long Time ◽  
High Degree

AbstractDeep recessions and disruptions in credit markets have caused social concern and motivated research for a long time. They still challenge macroeconomic analysis. We map some observable features of a set of such episodes, trying to find common elements of the whole family of events. The different macroeconomic experiences show a high degree of heterogeneity. Given that, what emerges as a central element of crises is their character as a life-changing episode for the people concerned, which remains in their memory and triggers a search for lessons, as they frustrate past expectations and force widespread reevaluations of wealth and income prospects. Critical periods involve dynamics at different time scales, as economic changes with lasting implications take place in an environment of dramatic day-to-day variability. Crises tend to be associated with breaks in the growth trends of the economies in question, in a way that may surprise not only agents inclined to eccentric behavior, but also those who held beliefs based on prevalent economic analysis. Macroeconomic disturbances of this sort raise strong questions about the pertinence, and the logic, of usual rational expectations assumptions and modeling practices. These issues are briefly discussed in an opening section.

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