scholarly journals Models for Velocity Decrease in HH34

2019 ◽  
Vol 09 (03) ◽  
pp. 302-320
Author(s):  
Lorenzo Zaninetti
Keyword(s):  
Velocity Decrease

scholarly journals Wind Velocity Decreasing Effects of Windbreak Fence for Snowfall Measurement

2014 ◽  
Vol 2014 ◽  
pp. 1-20
Author(s):  
Ki-Pyo You ◽  
Young-Moon Kim
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Wind Velocity ◽  
Wind Tunnel Test ◽  
Field Measurements ◽  
Wind Flow ◽  
Dynamics Analysis ◽  
Computational Fluid Dynamics Analysis ◽  
Better Than ◽  
Velocity Decrease

Meteorological observatories use measuring boards on even ground in open areas to measure the amount of snowfall. In order to measure the amount of snowfall, areas unaffected by wind should be found. This study tried to determine the internal wind flow inside a windbreak fence, identifying an area unaffected by wind in order to measure the snowfall. We performed a computational fluid dynamics analysis and wind tunnel test, conducted field measurements of the type and height of the windbreak fence, and analyzed the wind flow inside the fence. The results showed that a double windbreak fence was better than a single windbreak fence for decreasing wind velocity. The double fence (width 4 m, height 60 cm, and fixed on the bottom) has the greatest wind velocity decrease rate at the central part of octagonal windbreak.

Differences in intersaccadic adaptation transfer between inward and outward adaptation

2011 ◽  
Vol 106 (3) ◽  
pp. 1399-1410 ◽  
Author(s):  
Fabian Schnier ◽  
Markus Lappe
Keyword(s):  
Peak Velocity ◽  
The Other ◽  
Saccade Target ◽  
Control Mechanisms ◽  
Saccadic Adaptation ◽  
Saccade Onset ◽  
Independent Parameters ◽  
Saccade Duration ◽  
Velocity Decrease

Saccadic adaptation is a mechanism to increase or decrease the amplitude gain of subsequent saccades, if a saccade is not on target. Recent research has shown that the mechanism of gain increasing, or outward adaptation, and the mechanism of gain decreasing, or inward adaptation, rely on partly different processes. We investigate how outward and inward adaptation of reactive saccades transfer to other types of saccades, namely scanning, overlap, memory-guided, and gap saccades. Previous research has shown that inward adaptation of reactive saccades transfers only partially to these other saccade types, suggesting differences in the control mechanisms between these saccade categories. We show that outward adaptation transfers stronger to scanning and overlap saccades than inward adaptation, and that the strength of transfer depends on the duration for which the saccade target is visible before saccade onset. Furthermore, we show that this transfer is mainly driven by an increase in saccade duration, which is apparent for all saccade categories. Inward adaptation, in contrast, is accompanied by a decrease in duration and in peak velocity, but only the peak velocity decrease transfers from reactive saccades to other saccade categories, i.e., saccadic duration remains constant or even increases for test saccades of the other categories. Our results, therefore, show that duration and peak velocity are independent parameters of saccadic adaptation and that they are differently involved in the transfer of adaptation between saccade categories. Furthermore, our results add evidence that inward and outward adaptation are different processes.

The effect of pressure on rock properties in the Gulf of Mexico: Comparison between compaction disequilibrium and unloading

2014 ◽  
Vol 2 (1) ◽  
pp. SB1-SB15 ◽  
Author(s):  
Hua Yu ◽  
Fred J. Hilterman
Keyword(s):  
Gulf Of Mexico ◽  
Rock Properties ◽  
Louisiana Shelf ◽  
Major Mechanism ◽  
Detailed Evaluation ◽  
Density Values ◽  
Pressure Regime ◽  
Relationship Of ◽  
The Relationship ◽  
Velocity Decrease

We used statistical methods on rock properties derived from more than 480 wells to catalog shale velocity and density trends in different pressure regimes in the Gulf of Mexico and evaluated the reasons for their variations. A detailed evaluation of the density and velocity trends revealed that in the northern part of the Louisiana shelf, unloading is the major mechanism of overpressure. The onset of overpressure occurs at depths around 3000 m where temperatures are normally greater than 70°C. The relationship of the temperature gradient increase and the velocity decrease to the smectite-illite transformation allowed us to believe that inelastic unloading may be the major mechanism for overpressure in this region. On the other hand, in the southern part of the Louisiana shelf, abnormal pore pressure is often caused by compaction disequilibrium where the sediment section has a low sand percentage. In this type of pressure regime, velocity and density values cease to change at the onset of overpressure and essentially remain at the same value below the onset.

Monitoring of damage processes in cemented granular materials with acoustic emissions and seismic velocity reduction

2020 ◽  
Author(s):  
Vincent Canel ◽  
Xiaoping Jia ◽  
Michel Campillo ◽  
Ioan R. Ionescu
Keyword(s):  
Acoustic Emission ◽  
Shear Band ◽  
Sound Velocity ◽  
Granular Materials ◽  
Fracture Process ◽  
Granular Media ◽  
Acoustic Emissions ◽  
Shear Band Formation ◽  
Band Formation ◽  
Velocity Decrease

<p>Earthquakes or fault core sliding occur naturally in response to long-term deformation produced by plate tectonics. However, the way the damage or fracture process of rocks control the frictional slip is not well understood. It involves indeed materials in very different states: from granular-like materials near the shear band within the highly cracked fault core [1] to almost cohesive state in distant host rocks. To address this issue, we perform controlled laboratory experiments and new numerical simulations of damage in cemented granular materials to study the material evolution from cohesive to granular-like states under external loading. Our synthetic rocks (porous media) are made of cemented glass beads in which the packing density and the cement property (ductile or brittle) as well its content are tunable [2,3]. Two mechanical tests have been conducted: i) under oedometric load in a cylindrical cell with rigid wall; and ii) under triaxial load in a cell with elastic membrane (confined by atmospheric pressure). The fracture processes are monitored by acoustic waves, measuring the longitudinal ultrasound velocity (active detection) [4] and the acoustic emission (passive detection) [5].</p><p>More precisely, in the case (i) the fracture process is likely associated with the crack increase, spatially diffused without shear-band formation. For a rock sample cemented by a ductile bond, the damage induced by load appears likely as an anomalous deviation in the master curve of stress-strain whereas the combined acoustic detection provides a very clear evidence with an important sound velocity decrease. Upon cyclic unloading-reloading, we recover a power-law scaling of the sound velocity with the pressure similar to the law in purely granular media but with a finite velocity at vanishing pressure which depends on the residual cohesion of the damaged material. When the drop stress occurs intermittently in fractured samples cemented with brittle materials, we measure not only the sound velocity decrease but also acoustic emissions. In the case (ii) under a triaxial load, we observe the formation of shear-bands, i.e. fractures on the scale of the sample at a load much smaller than those applied in the oedometric loading (i). Again, there is a strong elastic softening (velocity decrease) [4]. Finally, we also compare these experiments with the finite-element modelling of damage and wave propagation in 2D dense cemented disk packings with various cement contents and elasto-visco-plastic properties. This numerical simulation allows to characterize the heterogeneous damage of the material at a microscopic scale.</p><p> </p><p><strong>References</strong></p><p>[1] C. Marone, Laboratory-derived friction laws and their applications to seismic faulting, Annu. Rev. Earth Planet. Sci. 26 <strong>1998</strong>, 643-696.</p><p>[2] V. Langlois, X. Jia, Acoustic probing of elastic behavior and damage in weakly cemented granular media, Phys. Rev. E 89 <strong>2014, </strong>023206.</p><p>[3] A. Hemmerle, M. Schröter, L. Goehring, A cohesive granular material with tunable elasticity, Scientific reports <strong>2016.</strong></p><p>[4] Y. Khidas, X. Jia, Probing the shear-band formation in granular media with sound waves, Phys. Rev. E 85 <strong>2012, </strong>051302.</p><p>[5] P.A. Johnson et al., Acoustic emission and microslip precursors to stick-slip failure in sheared granular media, Geophys. Res. Lett. 40 <strong>2013</strong>, 5627-5631.</p>

Correlating Ultrasonic Velocity and Porosity Using FDTD Method Based on Random Pores Model

2011 ◽  
Vol 675-677 ◽  
pp. 1221-1224 ◽  
Author(s):  
Y. Zhao ◽  
Zhen Yue Ma ◽  
Li Lin ◽  
X.M. Li ◽  
M.K. Lei
Keyword(s):  
Finite Difference Time Domain ◽  
Ultrasonic Testing ◽  
Transverse Velocity ◽  
Fdtd Method ◽  
Thermal Barrier ◽  
Barrier Coating ◽  
Simulation Based ◽  
Plasma Sprayed ◽  
Difference Time ◽  
Velocity Decrease

Ultrasonic testing porosity of TBC (thermal barrier coating) has been investigated by numerical simulation based on the implementation of FDTD (Finite Difference Time Domain) method for the RPM (random pores model). Numerical simulations of measuring ultrasonic longitudinal and transverse velocities were carried out for the plasma sprayed ZrO2 coatings with porosities ranging from 0.5 % to 4 %. The results show both longitudinal and transverse velocity decrease with the increase of porosity, which is similar to the experimental results in the reference (J. Thermal Spray Technol 12 (2003) 530-535). The investigation proves that the combination of the RPM and FDTD method is available for simulating ultrasonic testing of TBC porosity.

Dynamic models for the contact analysis of a tensioned beam with a moving oscillator

2013 ◽  
Vol 228 (4) ◽  
pp. 676-689
Author(s):  
Kyuho Lee ◽  
Jintai Chung
Keyword(s):  
Natural Frequency ◽  
Nonlinear Model ◽  
Frequency Ratio ◽  
Dynamic Models ◽  
Equations Of Motion ◽  
Contact Analysis ◽  
Contact Forces ◽  
Accurate Analysis ◽  
Moving Oscillator ◽  
Velocity Decrease

Several dynamic models are proposed for the contact analysis of a tensioned beam with a moving oscillator. Depending on whether the strain and stress used to derive the equations of motion are nonlinear, four models are established to analyze the beam deflections and the contact force between the beam and moving oscillator. We find that the differences in the contact forces and deflections computed with the models become large as the beam tension and moving velocity decrease and the natural frequency ratio of the oscillator to the beam increases. The nonlinear model derived with nonlinear strain and stress is desirable for an accurate analysis.

Effect of TiO2 addition on the combustion synthesis in the Ti–B4C system

2008 ◽  
Vol 23 (5) ◽  
pp. 1327-1333 ◽  
Author(s):  
Ping Shen ◽  
Binglin Zou ◽  
Qichuan Jiang
Keyword(s):  
Combustion Temperature ◽  
Ignition Delay Time ◽  
Reaction Products ◽  
X Ray Diffraction ◽  
Reaction Behavior ◽  
X Ray ◽  
Tio2 Addition ◽  
Favorable Reaction ◽  
Addition Amount ◽  
Velocity Decrease

The effects of TiO2 addition on the reaction behavior, product, and mechanism in the Ti–B4C system were investigated in this study. The reaction could be self-sustaining for the TiO2 addition no more than ∼33% of the total weight of the reactants. With an increase in the TiO2 addition, the combustion temperature and wave velocity decrease progressively, the ignition delay time first decreases and then increases, while the constituents of the reaction products do not vary significantly unless the relative addition content of TiO2 exceeds ∼22 wt%. Therefore, TiO2 could be used as a favorable reaction regulator for the Ti–B4C system. The reaction mechanism, as determined by differential thermal analysis and combustion front quenching experiment in combination with subsequent x-ray diffraction examination, is changed more or less by the addition of TiO2 with the extent depending on the addition amount.

scholarly journals Numerical analysis of flow characteristics in diesel injector nozzles with convergent-divergent orifices

2017 ◽  
Vol 231 (14) ◽  
pp. 1935-1944 ◽  
Author(s):  
Francisco J. Salvador ◽  
Joaquin de la Morena ◽  
Marcos Carreres ◽  
David Jaramillo
Keyword(s):  
Fluid Dynamics ◽  
Experimental Data ◽  
Computational Fluid Dynamics ◽  
Steady State ◽  
Flow Characteristics ◽  
Mixing Processes ◽  
Effective Velocity ◽  
Air Mixing ◽  
Cavitation Intensity ◽  
Velocity Decrease

The geometry of diesel injector nozzles is known to significantly affect the characteristic spray behavior and emissions formation. In this paper, a novel nozzle concept, consisting of orifices with a convergent–divergent shape, is investigated through Computational Fluid Dynamics techniques. Three of these nozzles, characterized by different degrees of conicity, are compared to a nozzle with cylindrical orifices, which acts as a baseline. A homogeneous equilibrium model, validated against experimental data in previous works by the authors, is used to calculate the eventual cavitation formation inside these orifices. Additionally, the characteristics of the flow at the orifice outlet are analyzed for the four aforementioned nozzles in terms of their steady-state mass flow, effective outlet velocity and area coefficient. The results show that convergent-divergent nozzles exhibit a high cavitation intensity, located in the transition between the convergent and the divergent sections. This high cavitation intensity tends to compensate for the expected velocity decrease induced by the divergent shape, producing effective velocity values similar to those achieved by the cylindrical nozzle in many of the simulated conditions. The characteristics of the flow, together with the higher spray opening angles expected due to the divergent section of the nozzle, may improve atomization and fuel-air mixing processes.

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