scholarly journals Investigating the Effect of Preimpact Energy Dissipation on Coefficient of Restitution regarding the Slope-Boulder Interaction

2021 ◽  
Vol 2021 ◽  
pp. 1-11
Author(s):  
Ran Bi ◽  
Shaoying Li ◽  
Gou Liu ◽  
Jianxi Ren ◽  
Yongjun Song
Keyword(s):  
Energy Dissipation ◽  
Linear Function ◽  
Initial Velocity ◽  
Slope Angle ◽  
Coefficient Of Restitution ◽  
Small Scale ◽  
Surface Type ◽  
Velocity Surface ◽  
Increasing Trend ◽  
Kinematic Coefficient

Coefficient of restitution is regarded as a dominating parameter in rockfall research. Generally, small-scale experiments were developed without considering interactions between boulder and slope. However, preimpact moving statuses are essential to evaluate rockfall behaviors. To reveal the effect of preimpact interactions on coefficient of restitution, energy dissipation considering initial velocity, surface type, and slope angle is executed based on medium-scale tests. The results show that (1) as the inclination of initial velocity, higher rebound height, and the declining normal coefficient of restitution occur, a determinable linear function could demonstrate relationships among energy dissipation and all coefficient of restitution; when initial velocity exceeds 5 m/s, the recovery ability shows and produces an increasing trend with respect to the variation of kinematic coefficient of restitution and kinetic energy coefficient of restitution. (2) As the surface material varies, slope hardness and rebound ability influence normal coefficient of restitution, and the surface roughness and rotation feature dominate tangential coefficient of restitution; considering preimpact slope and boulder interactions, four types of coefficient of restitution follow declining trend with different material sequence. (3) Slope angle affects normal coefficient of restitution, and tangential coefficient of restitution relatively descends 18% and inclines 10% when the angle ranges from 30° to 75°; regarding preimpact moving status, it differs from bounce times. The correlation between preimpact energy dissipation and four coefficients of restitution can be represented by the same decreasing linear function, when increasing the slope angle.

Observations of Small-Scale Turbulence and Energy Dissipation Rates in the Cloudy Boundary Layer

2006 ◽  
Vol 63 (5) ◽  
pp. 1451-1466 ◽  
Author(s):  
Holger Siebert ◽  
Katrin Lehmann ◽  
Manfred Wendisch
Keyword(s):  
Boundary Layer ◽  
Energy Dissipation ◽  
Wind Velocity ◽  
Turbulence Theory ◽  
Horizontal Wind ◽  
Inertial Subrange ◽  
Intermittent Flow ◽  
Small Scale ◽  
Dissipation Rates ◽  
Wide Range

Abstract Tethered balloon–borne measurements with a resolution in the order of 10 cm in a cloudy boundary layer are presented. Two examples sampled under different conditions concerning the clouds' stage of life are discussed. The hypothesis tested here is that basic ideas of classical turbulence theory in boundary layer clouds are valid even to the decimeter scale. Power spectral densities S( f ) of air temperature, liquid water content, and wind velocity components show an inertial subrange behavior down to ≈20 cm. The mean energy dissipation rates are ∼10−3 m2 s−3 for both datasets. Estimated Taylor Reynolds numbers (Reλ) are ∼104, which indicates the turbulence is fully developed. The ratios between longitudinal and transversal S( f ) converge to a value close to 4/3, which is predicted by classical turbulence theory for local isotropic conditions. Probability density functions (PDFs) of wind velocity increments Δu are derived. The PDFs show significant deviations from a Gaussian distribution with longer tails typical for an intermittent flow. Local energy dissipation rates ɛτ are derived from subsequences with a duration of τ = 1 s. With a mean horizontal wind velocity of 8 m s−1, τ corresponds to a spatial scale of 8 m. The PDFs of ɛτ can be well approximated with a lognormal distribution that agrees with classical theory. Maximum values of ɛτ ≈ 10−1 m2 s−3 are found in the analyzed clouds. The consequences of this wide range of ɛτ values for particle–turbulence interaction are discussed.

Estimating energy dissipation in internal solitary waves breaking on slopes

2021 ◽  
Author(s):  
Kateryna Terletska ◽  
Vladіmir Maderich ◽  
Tatiana Talipova
Keyword(s):  
Energy Dissipation ◽  
Solitary Waves ◽  
Wave Breaking ◽  
Wave Amplitude ◽  
Hot Spot ◽  
Slope Angle ◽  
Bottom Layer ◽  
Internal Solitary Waves ◽  
Coastal Zones ◽  
Waves Interaction

<p>The shoaling mechanisms of internal solitary waves that propagate horizontally are an important source of mixing and transport in the coastal zones. Numerical modelling, llaboratory experiments and observations are needed for understanding wave energetics, especially energy transformation during waves interaction with the slopes. Two shoaling mechanisms are important during interaction with the slope: (i) wave breaking that results in mixing and dissipation, (ii) changing of the polarity of the initial wave of depression on the slope. Classification based on regimes of interaction with the slope was presented in [1]. Four zones were separated in αβγ (γ - is slope angle, α-  is the non-dimensional wave amplitude (wave amplitude normalized on the thermocline thickness) and β – is the blocking parameter that is the ratio of the height of the bottom layer on the shelf to the incident wave amplitude) classification diagram: (I) without changing polarity and wave breaking, (II) changing polarity without breaking; (III) wave breaking without changing polarity; (IV) wave breaking with changing polarity. It was shown that results of field, laboratory and numerical experiments are in good agreement with proposed classification.  In the present study we estimate energy dissipation for all the types of interaction and present the algorithm for building a zone map with a ‘hot spot’ of energy dissipation for real slopes in the ocean.</p><p> </p><p>[1] K Terletska, BH Choi, V Maderich, T Talipova  Classification of internal waves shoaling over slope-shelf topography RUSSIAN JOURNAL OF EARTH SCIENCES vol. 20, 4, 2020, doi: 10.2205/2020ES000730</p>

Evaluation of Turbulent Kinetic Energy Dissipation Rate in a Free Jet Flow from PIV Measurements

2012 ◽  
Vol 7 (1) ◽  
pp. 53-69
Author(s):  
Vladimir Dulin ◽  
Yuriy Kozorezov ◽  
Dmitriy Markovich
Keyword(s):  
Energy Dissipation ◽  
Kinetic Energy ◽  
Turbulent Kinetic Energy ◽  
Dissipation Rate ◽  
Energy Dissipation Rate ◽  
Turbulent Velocity ◽  
Small Scale ◽  
Velocity Fluctuations ◽  
Piv Measurements ◽  
Free Jet

The present paper reports PIV (Particle Image Velocimetry) measurements of turbulent velocity fluctuations statistics in development region of an axisymmetric free jet (Re = 28 000). To minimize measurement uncertainty, adaptive calibration, image processing and data post-processing algorithms were utilized. On the basis of theoretical analysis and direct measurements, the paper discusses effect of PIV spatial resolution on measured statistical characteristics of turbulent fluctuations. Underestimation of the second-order moments of velocity derivatives and of the turbulent kinetic energy dissipation rate due to a finite size of PIV interrogation area and finite thickness of laser sheet was analyzed from model spectra of turbulent velocity fluctuations. The results are in a good agreement with the measured experimental data. The paper also describes performance of possible ways to account for unresolved small-scale velocity fluctuations in PIV measurements of the dissipation rate. In particular, a turbulent viscosity model can be efficiently used to account for the unresolved pulsations in a free turbulent flow

Flume investigation of cylindrical baffles for dissipation of debris flow energy

2021 ◽  
Author(s):  
Chan-Young Yune ◽  
Beom-Jun Kim
Keyword(s):  
Energy Dissipation ◽  
Debris Flow ◽  
Debris Flows ◽  
High Speed ◽  
Flow Characteristics ◽  
Digital Camera ◽  
Major Effect ◽  
Small Scale ◽  
Design Guideline ◽  
Flow Energy

<p>A debris flow with a high speed along valleys has been reported to cause serious damages to urban area or infrastructure. To prevent debris flow disaster, countermeasures for flow-impeding structures are installed on the flow path of debris flows. Recently, an installation of cylindrical baffles which are open-type countermeasures has increased because of a low construction cost, filtering out rocks, and an increased hydraulic continuity. However, a comprehensive design guideline for specification and arrangement on cylindrical baffles has not yet been suggested. Moreover, the design of baffle installation is mainly based on empirical approaches as the influence of baffle array on debris mobility is not well understood. In this study, to investigate the effect of cylindrical baffles on the flow characteristics of debris flow, a series of small-scale flume tests were performed according to the varying baffle height and row numbers of installed baffles. High-speed cameras and digital camera to record the flow interaction with baffles were installed at the top and side of the channel. To reproduce the viscosity of debris flows caused by fine-grained soil in the flume, glycerin was mixed with debris materials (sand and gravel). After the test, the velocity and energy dissipation according to various baffle arrays were estimated. Test results showed that the installation of baffles reduced the frontal velocity of debris flows. Furthermore, taller baffles also increased the effect of the energy dissipation in debris flows, but additional rows of the baffle did not have a major effect on the energy dissipation. Thus, increasing the height of baffle led to an increased efficiency of energy dissipation of debris flows.</p>

scholarly journals Anisotropic Characteristics of Turbulence Dissipation in Swirling Flow: A Direct Numerical Simulation Study

2015 ◽  
Vol 2015 ◽  
pp. 1-9 ◽  
Author(s):  
Xingtuan Yang ◽  
Nan Gui ◽  
Gongnan Xie ◽  
Jie Yan ◽  
Jiyuan Tu ◽  
...  
Keyword(s):  
Numerical Simulation ◽  
Energy Dissipation ◽  
Direct Numerical Simulation ◽  
Large Scale ◽  
Isotropic Turbulence ◽  
Vortex Breakdown ◽  
Swirling Flow ◽  
Turbulent Energy ◽  
Swirling Flows ◽  
Small Scale

This study investigates the anisotropic characteristics of turbulent energy dissipation rate in a rotating jet flow via direct numerical simulation. The turbulent energy dissipation tensor, including its eigenvalues in the swirling flows with different rotating velocities, is analyzed to investigate the anisotropic characteristics of turbulence and dissipation. In addition, the probability density function of the eigenvalues of turbulence dissipation tensor is presented. The isotropic subrange of PDF always exists in swirling flows relevant to small-scale vortex structure. Thus, with remarkable large-scale vortex breakdown, the isotropic subrange of PDF is reduced in strongly swirling flows, and anisotropic energy dissipation is proven to exist in the core region of the vortex breakdown. More specifically, strong anisotropic turbulence dissipation occurs concentratively in the vortex breakdown region, whereas nearly isotropic turbulence dissipation occurs dispersively in the peripheral region of the strong swirling flows.

Analysis of mechanical properties of different volleyballs

2019 ◽  
Vol 233 (2) ◽  
pp. 292-300
Author(s):  
Florian Schneider ◽  
Kerry MacDonald ◽  
Doug Reimer ◽  
Angela D Melnyk ◽  
Thomas R Oxland
Keyword(s):  
Mechanical Properties ◽  
Energy Dissipation ◽  
Significant Influence ◽  
High Velocity ◽  
Testing Machine ◽  
Sampling Frequency ◽  
Coefficient Of Restitution ◽  
Materials Testing ◽  
Compression Force ◽  
Gauge Pressure

Concussions are becoming an increasingly important issue in sports, especially in an area like volleyball that, until recently, seemed less prone to such injuries. The purpose of this study was to determine the coefficient of restitution and basic mechanical properties of standardized volleyballs, including stiffness and hysteresis, dependent on different influencing factors. A drop test was performed to calculate the coefficient of restitution based on the time of flight of the ball between the first and second bounce. This was detected using a microphone with a sampling frequency of 44.1 kHz. To determine the mechanical properties, a materials testing machine applied a compression force until a deformation of 50 mm was achieved. These data were sampled with a frequency of 12.5 kHz. The results showed that the three analysed factors in this study, including the ball model, gauge pressure, and incident velocity, had a significant influence on the coefficient of restitution. Therefore, the amount of energy dissipation during an impact situation at low velocities was significantly different within the tested sample of official standardized volleyballs. The stiffness and hysteresis of the volleyballs also varied significantly. These basic mechanical findings raise an interesting question as to whether the investigated factors are appropriate to predict forces acting on the head during a high velocity collision (25–30 m/s), ultimately resulting in a risk of concussion.

scholarly journals Seismic Behavior of Concrete-Filled Circular Steel Tubular Column–Reinforced Concrete Beam Frames with Recycled Aggregate Concrete

2020 ◽  
Vol 10 (7) ◽  
pp. 2609 ◽  
Author(s):  
Zongping Chen ◽  
Ji Zhou ◽  
Zhibin Li ◽  
Xinyue Wang ◽  
Xingyu Zhou
Keyword(s):  
Reinforced Concrete ◽  
Energy Dissipation ◽  
Seismic Behavior ◽  
Recycled Aggregate Concrete ◽  
Recycled Aggregate ◽  
Scale Model ◽  
Hysteresis Curve ◽  
Small Scale ◽  
Skeleton Curve ◽  
Aggregate Concrete

The application of recycled aggregate concrete (RAC) in concrete filled steel tubular (CFST) structures can eliminate the deterioration of concrete performance caused by the original defects of the recycled aggregate, which also provides an effective way for the recycling of waste concrete. In this paper, a test of a small scale model of a circular CFST column-reinforced concrete (RC) beam frame with RACs under low cyclic loading was presented in order to investigate its seismic behavior. The failure modes, plastic hinges sequence, hysteresis curve, skeleton curve, energy dissipation capacity, ductility and stiffness degeneration of the frame were presented and analyzed in detail. The test results show that the design method of the recycled aggregate concrete filled circular steel tube (RACFCST) frame complies with the seismic design requirements of a stronger joint followed by the stronger column and the weaker beam. The hysteresis curve of the frame is symmetrical, showing a relatively full shuttle shape; at the same time, the ductility coefficient of the frame is greater than 2.5, showing good deformation performance. In addition, when the frame is damaged, the displacement angle is greater than 1/38, and the equivalent damping ratios coefficient is 0.243, which indicates that the frame has excellent anti-collapse and energy dissipation abilities. In summary, the RACFCST frame has good seismic behavior, which can be applied to high-rise buildings in high-intensity seismic fortification areas.

scholarly journals Diffusional and accretional growth of water drops in a rising adiabatic parcel: effects of the turbulent collision kernel

2009 ◽  
Vol 9 (7) ◽  
pp. 2335-2353 ◽  
Author(s):  
W. W. Grabowski ◽  
L.-P. Wang
Keyword(s):  
Energy Dissipation ◽  
Kinetic Energy ◽  
Turbulent Kinetic Energy ◽  
Collision Kernel ◽  
Small Scale ◽  
Large Set ◽  
Initiation Time ◽  
Cloud Droplets ◽  
Dissipation Rates ◽  
Speedup Factor

Abstract. A large set of rising adiabatic parcel simulations is executed to investigate the combined diffusional and accretional growth of cloud droplets in maritime and continental conditions, and to assess the impact of enhanced droplet collisions due to small-scale cloud turbulence. The microphysical model applies the droplet number density function to represent spectral evolution of cloud and rain/drizzle drops, and various numbers of bins in the numerical implementation, ranging from 40 to 320. Simulations are performed applying two traditional gravitational collection kernels and two kernels representing collisions of cloud droplets in the turbulent environment, with turbulent kinetic energy dissipation rates of 100 and 400 cm2 s−3. The overall result is that the rain initiation time significantly depends on the number of bins used, with earlier initiation of rain when the number of bins is low. This is explained as a combination of the increase of the width of activated droplet spectrum and enhanced numerical spreading of the spectrum during diffusional and collisional growth when the number of model bins is low. Simulations applying around 300 bins seem to produce rain at times which no longer depend on the number of bins, but the activation spectra are unrealistically narrow. These results call for an improved representation of droplet activation in numerical models of the type used in this study. Despite the numerical effects that impact the rain initiation time in different simulations, the turbulent speedup factor, the ratio of the rain initiation time for the turbulent collection kernel and the corresponding time for the gravitational kernel, is approximately independent of aerosol characteristics, parcel vertical velocity, and the number of bins used in the numerical model. The turbulent speedup factor is in the range 0.75–0.85 and 0.60–0.75 for the turbulent kinetic energy dissipation rates of 100 and 400 cm2 s−3, respectively.

Forest edges and the soil-vegetation- atmosphere interaction at the landscape scale: the state of affairs

1996 ◽  
Vol 20 (3) ◽  
pp. 292-310 ◽  
Author(s):  
Arthur W. L. Veen ◽  
Wim Klaassen ◽  
Bart Kruijt ◽  
Ronald W.A. Hutjes
Keyword(s):  
Experimental Evidence ◽  
Forest Edge ◽  
Landscape Scale ◽  
Small Scale ◽  
Forest Edges ◽  
Surface Type ◽  
Heterogeneous Landscape ◽  
Atmosphere Interaction ◽  
State Of Affairs ◽  
The Impact

Although the soil-vegetation-atmosphere exchange of momentum and heat is fairly well understood for many types of homogeneous surfaces, the disturbances created by tran sitions of one surface type to another remain to be analysed more fully. This is especially true for the impact which a large transition such as the forest edge has on the average fluxes in a small-scale heterogeneous landscape with forest. Recently acquired experimental evidence appears to some extent contradictory and at variance with conventional concepts.

SEISMIC MODEL EXPERIMENTS WITH SHEAR WAVES

Geophysics ◽  
1959 ◽  
Vol 24 (1) ◽  
pp. 40-48 ◽  
Author(s):  
J. F. Evans
Keyword(s):  
Field Experiments ◽  
Shear Waves ◽  
High Amplitude ◽  
Homogeneous Layer ◽  
Small Scale ◽  
Seismic Model ◽  
Low Velocity ◽  
Model Experiments ◽  
Velocity Surface ◽  
Seismic Models

The experimental study of shear waves in the earth has been limited by the difficulty of producing them in sufficient strength. However, sensitive piezoelectric shear plates can now be made which enable experimentation with shear waves using small‐scale seismic models. Seismic model experiments serve to demonstrate the simplicity of SH‐shear wave reflections in a single homogeneous layer, the production of SH waves by an impulsive horizontal thrust, and the development of relatively high amplitude Love waves in a low‐velocity surface layer. The results of these model experiments with shear waves are in general agreement with and confirm theory. They also agree with the results of field experiments in the scattered cases for which comparison is available.

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