scholarly journals Discussion: “Thermomechanical Cracking in the Vicinity of a Near-Surface Void Due to High-Speed Friction Load” (Chen, T. Y., and Ju, F. D., 1988, ASME J. Tribol., 110, pp. 306–311)

1988 ◽  
Vol 110 (2) ◽  
pp. 311-311
Author(s):  
F. E. Kennedy
Keyword(s):  
High Speed ◽  
Near Surface

scholarly journals About mathematical simulation of processes for high-speed loading of materials on Department of Physical Mechanics of St. Petersburg State University

2020 ◽  
Vol 65 (4) ◽  
pp. 699-713
Author(s):  
Victor A. Morozov ◽  
◽  
Vsevolod I. Bogatko ◽  
Andrey B. Yakovlev ◽  
◽  
...  
Keyword(s):  
Mathematical Simulation ◽  
High Speed ◽  
Surface Region ◽  
Pulse Method ◽  
Magnetic Pulse ◽  
State University ◽  
Natural Experiments ◽  
Near Surface ◽  
Metal Rings ◽  
Physical Mechanics

The researches of shock-wave processes in the constructional materials are actual, but carrying out of natural experiments is extremely inconvenient and expensive, and sometimes it is even impossible to replicate. Therefore basically all researches of these problems are reduced to various cases of simulation of processes for high-speed loading of materials in the laboratory circumstances. In the paper we consider following directions of mathematical simulation of processes for high-speed loading of materials that were made on department of physical mechanics of St. Petersburg State University: the simulation of shock-loaded media by using of dynamics of dislocations; the simulation of high-speed loading of media with the account of the relaxation phenomena in a near-surface region; the simulation of propagation of the short elastoplastic impulse in medium under the condition of influence of a weak magnetic field; the generation of mathematical models of deformation and destruction of thin metal rings by a magnetic-pulse method; the simulation of crack propagation during the short-term pulse loading.

The infrared measurement cascade: Connecting large scale meteorologically induced surface temperature perturbations to local spatial velocity structures

2020 ◽  
Author(s):  
Benjamin Schumacher ◽  
Marwan Katurji ◽  
Jiawei Zhang
Keyword(s):  
Boundary Layer ◽  
Velocity Field ◽  
Brightness Temperature ◽  
High Speed ◽  
Surface Brightness ◽  
Large Scale ◽  
Mean Velocity ◽  
Near Surface ◽  
Multi Scale ◽  
Infrared Cameras

<p>The evolution of micrometeorological measurements has been recently manifested by developments in methodological and analytical techniques using spatial surface brightness temperature captured by infrared cameras (Schumacher et al. 2019, Katurji and Zawar-Reza 2016). The Thermal Image Velocimetry (TIV) method can now produce accurate 2D advection-velocities using high speed (>20Hz) infrared imagery (Inagaki 2013, Schumacher 2019). However, to further develop TIV methods and achieve a novel micrometeorological measurement technique, all scales of motion within the boundary layer need to be captured.</p><p>Spatial observations of multi-frequency and multi-scale temperature perturbations are a result from the turbulent interaction of the overlying atmosphere and the surface. However, these surface signatures are connected to the larger scales of the atmospheric boundary layer (McNaughton 2002, Träumner 2015). When longer periods (a few hours to a few days) of spatial surface brightness temperatures are observed, the larger scale information needs to be accounted for to build a comprehensive understanding of surface-atmospheric spatial turbulent interactions. Additionally, the time-frequency decomposition of brightness temperature perturbations shows longer periods of 4-15 minutes superimposed over shorter periods of ~ 4–30 seconds. This suggests that that boundary layer dynamic scales (of longer periods) can influence brightness temperature perturbations on the local turbulent scale. An accurate TIV algorithm needs to account for all scales of motion when analysing the time-space variability of locally observed spatial brightness temperature patterns.</p><p>To analyse these propositions temporally high resolved geostationary satellite infrared data from the Himawari 8 satellite was compared to near-surface and high speed (20 Hz) measured air and brightness temperature using thermocouple measurements and infrared cameras. The satellite provides a temporal resolution of 10-minutes and a horizontal resolution of 2 by 2 km per pixel and therefore captures the atmospheric meso γ and micro α scale which signals are usually active for ~10 minutes to < 12 hours. Moreover, the Himawari 8 brightness temperature was used to create the near-surface mean velocity field using TIV. Afterwards, the velocity field was compared to the in-situ measured wind velocity over several days during January 2019.</p><p>The results show that the atmospheric forcing from the micro α scale to lower atmospheric scales has a major impact on the near-surface temperature over several minutes. A significant (p-value: 0.02) positive covariance between the Himawari 8 measurement and the local measured temperature 1.5 cm above the ground on a 10 minute average, specifically concerning cooling and heating patterns, has been found.</p><p>Further analysis demonstrates that the retrieved near-surface 2-D velocity field calculated from the Himawari 8 brightness temperature perturbations is correctly representing the mean velocity. This finding allows the classification of meso-scale atmospheric forcing and its direct connection to local scale turbulent 2-D velocity measurements. This extends the TIV algorithm by a multi-scale component which allows to address inter-scale boundary layer analysis from a new point of view. In respect to the current findings a new experiment will focus on the repeated induced local velocity patterns from large scale forcing which will be measured through the surface brightness temperature.</p>

High-Speed Frictional Heating of an Elastic Medium With a Near-Surface Horizontal Line Crack

1993 ◽  
Vol 115 (1) ◽  
pp. 56-60 ◽  
Author(s):  
T. Y. Chen ◽  
Frederick D. Ju
Keyword(s):  
Temperature Field ◽  
Stress Intensity ◽  
Stress Intensity Factors ◽  
High Speed ◽  
Frictional Heating ◽  
Crack Tip ◽  
Horizontal Line ◽  
Intensity Factors ◽  
Near Surface ◽  
Line Crack

This paper studies the effect of high-speed frictional heating over the surface of an elastic material, which has a near surface horizontal line crack. The frictional heating is represented by a high-speed moving heat source, since the mechanical loading effect is much smaller than the thermal effect in the resulting stress field. Finite difference methods are employed to compute the temperature field and the displacement field, taking into consideration the characteristic singularity at the crack tip. The temperature field solutions are first computed, using the method of heat balance. The thermo-mechanical solutions follow with particular interest in the vicinity of the line crack as represented by the stress intensity factors at the crack tip. It was found that both the open mode and the shear mode occur, as a result of the excitation of the moving thermal load. The paper also presents effects on the stress intensity factors from varying the thermal and the mechanical properties of the medium, and the location of the line crack from the wear surface. The depth at which the maximum thermal stress occurs is an exponential function of the Peclet number, as in the cases when there is no defect in the wear material and when there is a near surface cavity. Albeit, the “critical depth” reduces with increasing Peclet number and severity of the defect.

The water entry of a sphere in a jet

2019 ◽  
Vol 863 ◽  
pp. 956-968 ◽  
Author(s):  
Nathan B. Speirs ◽  
Jesse Belden ◽  
Zhao Pan ◽  
Sean Holekamp ◽  
George Badlissi ◽  
...  
Keyword(s):  
Structural Damage ◽  
High Speed ◽  
Early Time ◽  
Water Entry ◽  
Rigid Sphere ◽  
High Speed Imaging ◽  
Near Surface ◽  
Image Velocimetry ◽  
Surface Particle ◽  
Force Reduction

The forces on an object impacting the water are extreme in the early moments of water entry and can cause structural damage to biological and man-made bodies alike. These early-time forces arise largely from added mass, peaking when the submergence is much less than one body length. We experimentally investigate a means of reducing impact forces on a rigid sphere by placing the sphere inside a jet of water so that the jet strikes the quiescent water surface prior to entry of the sphere into the pool. The water jet accelerates the pool liquid and forms a cavity into which a sphere falls. Through on-board accelerometer measurements and high-speed imaging, we quantify the force reduction compared to the case of a sphere entering a quiescent pool. Finally, we find the emergence of a critical jet volume required to maximize force reduction; the critical volume is rationalized using scaling arguments informed by near-surface particle image velocimetry (PIV) data.

Packets of Capillary and Acoustic Waves of Drop Impact

2021 ◽  
pp. 73-91
Author(s):  
Yu.D. Chashechkin
Keyword(s):  
Acoustic Waves ◽  
High Speed ◽  
Large Scale ◽  
Video Camera ◽  
Acoustic Signals ◽  
Capillary Waves ◽  
Near Surface ◽  
Large Scale Analysis ◽  
High Speed Video Camera ◽  
Hydro Phone

Flows, capillary waves, and acoustic signals generated by a drop of water falling into a pool of degassed liquid were recorded by a high-speed video camera, hydro-phone, and microphone. A large-scale analysis of the system of equations was performed. The fast conversion of available surface potential energy is traced. The converted energy is stored in a thin layer in the vicinity of the merged free surfaces and creates large perturbations of temperature, pressure and flow velocity. Capillary waves start to radiate simultaneously with the formation of a cavity and the rise of the crown. New groups of capillary waves arise with all changes in the flow structure --- the formation and immersion of a splash, come back of secondary drops, the formation of cavities, the immersion of a streamer and droplets. Simultaneously with the waves, ligaments --- thin near-surface flows are formed that affect the transport and rupture of gas cavities. Thin flows quickly decay and form again when a new group of capillary waves is generated. A comparison of flow patterns and acoustic signals indicates that the generation of resonant sound packets is synchronized with the pinch-off gas fragments from the cavity or their breaking. The duration of the sound depends on the initial heterogeneity of the geometry of the sounding cavity, gradually transforming into a smooth spheroidal form

scholarly journals Dynamics of Bubble Motion and Gas-Liquid Interfacial Phenomena

2003 ◽  
Author(s):  
Katsumi Tsuchiya
Keyword(s):  
Mass Transfer ◽  
Surface Wave ◽  
High Speed ◽  
Bubble Surface ◽  
Liquid Interface ◽  
Oscillatory Motion ◽  
Wave Formation ◽  
High Speed Imaging ◽  
Vertical Projection ◽  
Near Surface

Two aspects of the dynamics associated with oscillating bubbles are discussed in this paper: oscillatory motion of bubble itself and bubble-surface wave. The primary issue here is whether it is the case that the surface wave occurs in sychronization with the bubble’s oscillatory motion. The dynamic process of wave formation and propagation along the surface of an oscillating bubble is studied based on high-speed imaging, through which the wave characteristics such as wavelength and phase/propagation speed are evaluated as mostly the vertical projection of rather regularly generated bubble-surface ripples. The bubble oscillating motion is characterized quantitatively by the bubble-gyration (or edge-rotation) frequency, diameter and velocity. In addition, dynamics of mass transfer across gas–liquid interface in a gas-dispersed (continuous liquid) system are examined via high-sensitivity, high-speed imaging. The dispersive dynamics of the dissolved component from the gas into the liquid phase are visualized using laser-induced fluorescence (LIF) with pH-sensitive pyrene (HPTS) for both a single and multi-bubble systems. The coupling between these dynamics of surface/interfacial flow and mass transfer is attempted towards better understanding of such complex phenomena prevailing in the vicinity of the fluctuating gas–liquid interface. Enhancement of the mass transfer is found to be associated with the (nonlinear) wave formation, influence of which could be included in modeling the mass-transfer coefficient, apart from an physical account of the near-surface concentration gradient. Due to significant bubble–bubble interactions in a multi-bubble system, the dispersive pattern of low-pH region arising from gas dissolution becomes extremely complex; the visual estimate of time variation in fluorescence level is then mainly made over a fixed space in the gas–liquid flow system.

An Analysis of the Secondary Flow Around a Tandem Blade Under the Presence of a Tip Gap in a High-Speed Linear Compressor Cascade

2021 ◽  
pp. 1-20
Author(s):  
Liesbeth Konrath ◽  
Dieter Peitsch ◽  
Alexander Heinrich
Keyword(s):  
Flow Field ◽  
High Speed ◽  
Tip Clearance ◽  
Compressor Cascade ◽  
Complex Flow ◽  
Flow Topology ◽  
Linear Compressor ◽  
Near Surface ◽  
Oil Flow ◽  
Linear Compressor Cascade

Abstract Tandem blades have often been under investigation, experimentally as well as numerically, but most studies have been about tandem blade stators without tip gap. This work analyzes the influence of a tip gap on the flow field of a tandem blade for engine core compressors. Experiments have been conducted in a high-speed linear compressor cascade on a tandem and a reference geometry. The flow is analyzed using five-hole probe measurements in the wake of the blades and oil flow visualization to show the near surface stream lines. First, the results for design conditions (tandem and conventional blade) are compared to measurements on corresponding blades without tip gap. Similarities and differences in the flow topology due to the tip clearance are analyzed, showing that the introduction of the tip clearance has a similar influence on the loss and turning development for the tandem and the conventional blade. The tandem blade features two tip clearance vortices with a complex flow interaction and the possible formation of a third counter-rotating vortex between them. An incidence variation from 0deg to 5deg for both blades indicates at first a similar behavior. After a separation of the flow field into gap and non-gap half it becomes apparent that the tandem blade shows higher losses on the gap side, while featuring a close-to-constant behavior on the non-gap side. Further investigation of the flow on the gap side shows indicators of the front blade exhibiting tip clearance vortex break down.

THE APPLICATION OF THE REFLECTION SEISMOGRAPH TO NEAR‐SURFACE EXPLORATION

Geophysics ◽  
1952 ◽  
Vol 17 (4) ◽  
pp. 859-866 ◽  
Author(s):  
C. F. Allen ◽  
L. V. Lombardi ◽  
W. M. Wells
Keyword(s):  
High Speed ◽  
Seismic Profile ◽  
Resolving Power ◽  
Mining Engineering ◽  
Stanford Research Institute ◽  
Near Surface ◽  
Surface Exploration ◽  
Water Problems ◽  
And Control ◽  
Special Instrumentation

The geophysical approach to very shallow exploration problems has been limited, in the main, to electrical, magnetic, electromagnetic, and refraction methods. The reflection seismograph, with its clear advantages of decreased ambiguity and increased resolving power, can be applied to many of these problems. In the fall of 1951, a Stanford Research Institute crew conducted an experimental reflection survey in Minnesota, mapping with correlation spreads the glacial drift‐bedrock interface along seventy miles of line. The interface varied from a few hundred to several hundred feet in depth below surface, and control core holes showed the seismic profile to be essentially correct, where checked. Over‐all velocities, determined by shooting core holes, varied from 3,800 feet per second to 5,500 feet per second. Special instrumentation included a high speed camera and a filter peaked at 100 cps. All shots were fired in the air. The method has obvious applications to mining, engineering, and ground‐water problems, and to difficult weathering problems involving thick alluvial, eolian, or glacial debris.

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