A0-Wave and A-Wave in Cylindrical Shell Immersed in Water: Influence on the Acoustic Scattering

1999 ◽  
Author(s):  
Gérard Maze ◽  
Nicolas Touraine ◽  
André Baillard ◽  
Dominique Decultot ◽  
Véronique Latard ◽  
...  
Keyword(s):  
Cylindrical Shell ◽  
Lamb Wave ◽  
High Speed ◽  
Acoustic Scattering ◽  
Stoneley Wave ◽  
High Speed Camera ◽  
Low Frequencies ◽  
Schlieren Visualization ◽  
The Subject ◽  
Structure Inhomogeneity

Abstract In low frequencies (ka < 200), the A-wave (Scholte-Stoneley wave) and the S0-wave (first symmetrical Lamb wave) are the subject of a particular attention in the study of the acoustic scattering from empty cylindrical shells immersed in water. If the tube is in water, the A0-wave (flexural Lamb wave) which circumnavigates in the shell in vacuum, does not originate resonances in the backscattered pressure spectrum while the two others are active. Images of the acoustic scattering from cylindrical or spherical targets obtained from the “Schlieren” visualization using a high-speed camera show the typical re-radiation of the A0+-wave in water. Moreover, the backscattered signal recorded with one emitter-receiver transducer shows one echo which cannot attributed to the A- or S0-waves. In this paper, the propagation of the A0+-wave has been especially studied to explain the experimental results. This A0+-wave has a great impact if it crosses over a structure inhomogeneity after a short propagation in the shell, before its complete attenuation.

Visualization of the A0 Lamb Wave and a Scholte-Stoneley Wave Interaction

1999 ◽  
Author(s):  
V. Latard ◽  
A. Merlen ◽  
P. Pernod ◽  
A. Ahyi
Keyword(s):  
Lamb Wave ◽  
High Speed ◽  
Acoustic Pulse ◽  
Acoustic Scattering ◽  
Wave Interaction ◽  
Stoneley Wave ◽  
Visualization Technique ◽  
Single View ◽  
Wave Velocities ◽  
The Waves

Abstract Previous studies have shown the efficiency of the experimental impulsive acoustic approach for a fine understanding of acoustic scattering processes. The association of a high speed shadowgraph system and a spark generated acoustic pulse allowed the first visualization of the radiation into a fluid of a A0 Lamb wave travelling along an elastic plate (Ahyi and al., 1998) or the interaction of the A (Scholte Stoneley) and A0 on more complex geometries (Latard, 1998). Moreover it allows to follow the evolution in time and determine the generation points of the waves. It is shown in this paper that this visualization technique of impulsive scattering is a quantitative method providing not only wave velocities or frequencies, but also dispersion curves thanks to a single view of the phenomena. This paper presents also the visualization of the A wave by its interaction with the A0 radiation. Numerical simulations of this interaction are compared successfully with visualizations.

A0 Wave in a Submerged Stiffened Cylindrical Shell

1999 ◽  
Author(s):  
André Baillard ◽  
Jean-Marc Conoir ◽  
Dominique Décultot ◽  
Gérard Maze ◽  
Aleksander Klauson ◽  
...  
Keyword(s):  
Stainless Steel ◽  
Cylindrical Shell ◽  
Acoustic Wave ◽  
Lamb Wave ◽  
Wave Number ◽  
Stoneley Wave ◽  
Frequency Range ◽  
Wave Type ◽  
Stiffened Cylindrical Shell ◽  
Incident Plane

Abstract The backscattering of a normal incident plane acoustic wave by a stiffened cylindrical shell is considered. The studied cylindrical shell is made of stainless steel and its internal to external radius ratio is b/a = 0.98. The shell submerged in water is strengthened by an internal plate of the same material and thickness, which is diametrically soldered. As for the unstiffened shell, A wave (Scholte-Stoneley wave) and S0 wave (first symmetrical Lamb wave) are detected in the frequency range investigated (50–200 ka where k is the wave number in water). On the contrary, the presence of the plate into the tube allows the detection of A0 wave (flexural Lamb wave) whereas it is not observed for the unstiffened shell, owing to the attenuation of the wave during the propagation around the tube. In particularl, A0 wave could be reflected on the junction with enough energy to re-emit in water. Furthermore, wave type conversions are allowed by way of the junctions: S0–A0 wave conversions are observed.

scholarly journals Acoustic scattering from a stiffened finite cylindrical shell with external rings

2019 ◽  
Vol 283 ◽  
pp. 03002
Author(s):  
Fulin Zhou ◽  
Jun Fan ◽  
Bin Wang
Keyword(s):  
Cylindrical Shell ◽  
Acoustic Waves ◽  
Cylindrical Shells ◽  
Acoustic Scattering ◽  
Approximate Analytical Expression ◽  
Low Frequencies ◽  
Stiffened Cylindrical Shell ◽  
Layered Shells ◽  
Underwater Target ◽  
Finite Cylindrical Shell

Studying the interaction of sound with cylindrical shells immersed in water is essential and helpful to improving underwater target detection and classification algorithms. Elastic cylindrical shells often occur as part of double-layered shell and have been widely used in marine and aerospace area. Acoustic waves are easy to be transmitted through the outer shell to the interior especially at low frequencies, thus directly being scattered by the inner shell and the rings in water between double-layered shells. Therefore, the externally ring-stiffened cylindrical shell is investigated in this paper. An experiment was conducted that measured the acoustic scattering. A hybrid 2-D/3-D finite-element modelling technique is employed to numerically calculate the scattering characteristics. Good qualitative agreement is found between numerical calculations and experimental measurement. An approximate analytical expression is given explicitly to identify the Bragg wave trajectories in the frequency-angle spectrum. It also has been shown that the rings not only affect the dynamic response of shell and indirectly influence the exterior scattered field, but also become direct acoustic scatterers in water and increase the target cross section especially at oblique incidence.

scholarly journals Tracking by Deblatting

2021 ◽  
Author(s):  
Denys Rozumnyi ◽  
Jan Kotera ◽  
Filip Šroubek ◽  
Jiří Matas
Keyword(s):  
High Speed ◽  
High Performance ◽  
Motion Blur ◽  
Velocity Estimation ◽  
High Speed Camera ◽  
Trajectory Function ◽  
Novel Approach ◽  
Blind Deblurring ◽  
Object Trajectories ◽  
Complex Trajectories

AbstractObjects moving at high speed along complex trajectories often appear in videos, especially videos of sports. Such objects travel a considerable distance during exposure time of a single frame, and therefore, their position in the frame is not well defined. They appear as semi-transparent streaks due to the motion blur and cannot be reliably tracked by general trackers. We propose a novel approach called Tracking by Deblatting based on the observation that motion blur is directly related to the intra-frame trajectory of an object. Blur is estimated by solving two intertwined inverse problems, blind deblurring and image matting, which we call deblatting. By postprocessing, non-causal Tracking by Deblatting estimates continuous, complete, and accurate object trajectories for the whole sequence. Tracked objects are precisely localized with higher temporal resolution than by conventional trackers. Energy minimization by dynamic programming is used to detect abrupt changes of motion, called bounces. High-order polynomials are then fitted to smooth trajectory segments between bounces. The output is a continuous trajectory function that assigns location for every real-valued time stamp from zero to the number of frames. The proposed algorithm was evaluated on a newly created dataset of videos from a high-speed camera using a novel Trajectory-IoU metric that generalizes the traditional Intersection over Union and measures the accuracy of the intra-frame trajectory. The proposed method outperforms the baselines both in recall and trajectory accuracy. Additionally, we show that from the trajectory function precise physical calculations are possible, such as radius, gravity, and sub-frame object velocity. Velocity estimation is compared to the high-speed camera measurements and radars. Results show high performance of the proposed method in terms of Trajectory-IoU, recall, and velocity estimation.

Influence of Main Swirler Vane Angle on the Ignition Performance of TeLESS-II Combustor

2016 ◽  
Vol 139 (1) ◽  
Author(s):  
Bo Wang ◽  
Chi Zhang ◽  
Yuzhen Lin ◽  
Xin Hui ◽  
Jibao Li
Keyword(s):  
High Speed ◽  
Inlet Temperature ◽  
Main Stage ◽  
Ignition Process ◽  
High Speed Camera ◽  
Fuel Distribution ◽  
Fuel Droplets ◽  
Planar Laser ◽  
Cfd Method ◽  
Vane Angle

In order to balance the low emission and wide stabilization for lean premixed prevaporized (LPP) combustion, the centrally staged layout is preferred in advanced aero-engine combustors. However, compared with the conventional combustor, it is more difficult for the centrally staged combustor to light up as the main stage air layer will prevent the pilot fuel droplets arriving at igniter tip. The goal of the present paper is to study the effect of the main stage air on the ignition of the centrally staged combustor. Two cases of the main swirler vane angle of the TeLESS-II combustor, 20 deg and 30 deg are researched. The ignition results at room inlet temperature and pressure show that the ignition performance of the 30 deg vane angle case is better than that of the 20 deg vane angle case. High-speed camera, planar laser induced fluorescence (PLIF), and computational fluids dynamics (CFD) are used to better understand the ignition results. The high-speed camera has recorded the ignition process, indicated that an initial kernel forms just adjacent the liner wall after the igniter is turned on, the kernel propagates along the radial direction to the combustor center and begins to grow into a big flame, and then it spreads to the exit of the pilot stage, and eventually stabilizes the flame. CFD of the cold flow field coupled with spray field is conducted. A verification of the CFD method has been applied with PLIF measurement, and the simulation results can qualitatively represent the experimental data in terms of fuel distribution. The CFD results show that the radial dimensions of the primary recirculation zone of the two cases are very similar, and the dominant cause of the different ignition results is the vapor distribution of the fuel. The concentration of kerosene vapor of the 30 deg vane angle case is much larger than that of the 20 deg vane angle case close to the igniter tip and along the propagation route of the kernel, therefore, the 30 deg vane angle case has a better ignition performance. For the consideration of the ignition performance, a larger main swirler vane angle of 30 deg is suggested for the better fuel distribution when designing a centrally staged combustor.

scholarly journals Leader-chasing behavior in negative artificial triggered lightning flashes

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Fukun Wang ◽  
Jianguo Wang ◽  
Li Cai ◽  
Rui Su ◽  
Wenhan Ding ◽  
...  
Keyword(s):  
High Speed ◽  
The Other ◽  
Lightning Flash ◽  
High Speed Camera ◽  
Return Stroke ◽  
Catching Up ◽  
Special Cases ◽  
Triggered Lightning

AbstractTwo special cases of dart leader propagation were observed by the high-speed camera in the leader/return stroke sequences of a classical triggered lightning flash and an altitude-triggered lightning flash, respectively. Different from most of the subsequent return strokes preceded by only one leader, the return stroke in each case was preceded by two leaders occurring successively and competing in the same channel, which herein is named leader-chasing behavior. In one case, the polarity of the latter leader was opposite to that of the former leader and these two combined together to form a new leader, which shared the same polarity with the former leader. In the other case, the latter leader shared the same polarity with the former leader and disappeared after catching up with the former leader. The propagation of the former leader in this case seems not to be significantly influenced by the existence of the latter leader.

scholarly journals Influence of Hydrogeochemistry on Tunnel Drainage in Evaporitic Formations: El Regajal Tunnel Case Study (Aranjuez, Spain)

2021 ◽  
Vol 13 (3) ◽  
pp. 1505
Author(s):  
Ignacio Menéndez Pidal ◽  
Jose Antonio Mancebo Piqueras ◽  
Eugenio Sanz Pérez ◽  
Clemente Sáenz Sanz
Keyword(s):  
High Speed ◽  
Civil Engineering ◽  
Saturation Index ◽  
The Subject ◽  
Under Construction ◽  
Underground Flow ◽  
Very High ◽  
Over Time

Many of the large number of underground works constructed or under construction in recent years are in unfavorable terrains facing unusual situations and construction conditions. This is the case of the subject under study in this paper: a tunnel excavated in evaporitic rocks that experienced significant karstification problems very quickly over time. As a result of this situation, the causes that may underlie this rapid karstification are investigated and a novel methodology is presented in civil engineering where the use of saturation indices for the different mineral specimens present has been crucial. The drainage of the rock massif of El Regajal (Madrid-Toledo, Spain, in the Madrid-Valencia high-speed train line) was studied and permitted the in-situ study of the hydrogeochemical evolution of water flow in the Miocene evaporitic materials of the Tajo Basin as a full-scale testing laboratory, that are conforms as a whole, a single aquifer. The work provides a novel methodology based on the calculation of activities through the hydrogeochemical study of water samples in different piezometers, estimating the saturation index of different saline materials and the dissolution capacity of the brine, which is surprisingly very high despite the high electrical conductivity. The circulating brine appears unsaturated with respect to thenardite, mirabilite, epsomite, glauberite, and halite. The alteration of the underground flow and the consequent renewal of the water of the aquifer by the infiltration water of rain and irrigation is the cause of the hydrogeochemical imbalance and the modification of the characteristics of the massif. These modifications include very important loss of material by dissolution, altering the resistance of the terrain and the increase of the porosity. Simultaneously, different expansive and recrystallization processes that decrease the porosity of the massif were identified in the present work. The hydrogeochemical study allows the evolution of these phenomena to be followed over time, and this, in turn, may facilitate the implementation of preventive works in civil engineering.

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