scholarly journals Centroid migration on an impacted granular slope due to asymmetric ejecta deposition and landsliding

2020 ◽  
Author(s):  
Tomomi Omura ◽  
Shinta Takizawa ◽  
Hiroaki Katsuragi
Keyword(s):  
Oblique Impact ◽  
Minor Axis ◽  
Sand Layer ◽  
Migration Distance ◽  
Fundamental Information ◽  
Fundamental Understanding ◽  
Dry Sand ◽  
Two Parameters ◽  
Inclined Surface ◽  
Crater Shape

Abstract For a fundamental understanding of terrain relaxation occurring on sloped surfaces of terrestrial bodies, we analyze the crater shape produced by an impact on an inclined granular (dry-sand) layer. Owing to asymmetric ejecta deposition followed by landsliding, the slope of the impacted inclined surface can be relaxed. Using the experimental results of a solid projectile impact on an inclined dry-sand layer, we measure the distance of centroid migration induced by asymmetric cratering. We find that the centroid migration distance xmig normalized to the crater minor-axis diameter Dcy can be expressed as a function of the initial inclination of the target tan θ, the effective friction coefficient μ, and two parameters K and c that characterize the asymmetric ejecta deposition and oblique impact effect: xmig/Dcy = Ktan θ/(1 − (tan θ/μ)2) + c, where K = 0.6, μ = 0.8, and c = −0.1 to 0.3. This result is consistent with a previous study that considered the effect of asymmetric ejecta deposition. The obtained results provide fundamental information for analyzing the degradation of sloped terrain on planetary surfaces, such as crater-shape degradation due to the accumulation of micro-impacts.

scholarly journals Response of Different Machine Foundation Shapes Resting on Dry Sand to Dynamic Loading

2020 ◽  
Vol 27 (2) ◽  
pp. 29-39
Author(s):  
Khalid W. Abdul Kaream ◽  
Mohammed Y. Fattah ◽  
Zeyad S. M. Khaled
Keyword(s):  
Dynamic Loading ◽  
Pressure Sensors ◽  
Shaft Encoder ◽  
Supporting Soil ◽  
Different Depths ◽  
Dry Sand ◽  
Set Up ◽  
Two Parameters ◽  
College Of Engineering ◽  
Flexible Pressure Sensors

In this paper, the effect of footing shape resting on dry sand when subjected to machine dynamic loading is experimentally investigated. A laboratory set-up was prepared to simulate the case at different operating frequencies. Nine models were tested to examine the effects of the combinations of two parameters, including different frequencies of (0.5, 1, and 2 Hz) and different footing shapes (circular, square and rectangular). The tests were conducted under a load amplitude of (0.25 ton) using sand with medium and dense relative densities corresponding to (R.D. = 50% and 80%) having unit weights of (17.04 and 17.96 kN/m3) respectively. A shaft encoder and a vibration meter were used to measure the strain and amplitude displacement, while the stress in the soil at different depths was measured using flexible pressure sensors. It was found that the shape of footing has a considerable influence on the bearing capacity of the supporting soil under dynamic loading. For instance, the strain of dry sand under a circular footing was nearly (41%) higher, the amplitude displacement was nearly (17%) higher, and stress was nearly (12%) higher than square and rectangular footings, under the same conditions. @2019 TJES, College of Engineering, Tikrit University

scholarly journals THE INFLUENCE OF VISCOELASTICITY ON VELOCITY-DEPENDENT RESTITUTIONS IN THE OBLIQUE IMPACT OF SPHERES

2017 ◽  
Vol 15 (2) ◽  
pp. 269 ◽  
Author(s):  
Emanuel Willert ◽  
Stephan Kusche ◽  
Valentin L. Popov
Keyword(s):  
Coulomb Friction ◽  
Numerical Models ◽  
Oblique Impact ◽  
Analytic Expressions ◽  
Linear Viscoelastic ◽  
Sufficient Set ◽  
Full Solution ◽  
Two Parameters ◽  
The Impact ◽  
Impact Problem

We analyse the oblique impact of linear-viscoelastic spheres by numerical models based on the Method of Dimensionality Reduction and the Boundary Element Method. Thereby we assume quasi-stationarity, the validity of the half-space hypothesis, short impact times and Amontons-Coulomb friction with a constant coefficient for both static and kinetic friction. As under these assumptions both methods are equivalent, their results differ only within the margin of a numerical error. The solution of the impact problem written in proper dimensionless variables will only depend on the two parameters necessary to describe the elastic problem and a sufficient set of variables to describe the influence of viscoelastic material behaviour; in the case of a standard solid this corresponds to two additional variables. The full solution of the impact problem is finally determined by comprehensive parameter studies and partly approximated by simple analytic expressions.

scholarly journals Deep Brain Stimulation of Hemiparkinsonian Rats with Unipolar and Bipolar Electrodes for up to 6 Weeks: Behavioral Testing of Freely Moving Animals

2017 ◽  
Vol 2017 ◽  
pp. 1-18 ◽  
Author(s):  
Kathrin Badstuebner ◽  
Ulrike Gimsa ◽  
Immo Weber ◽  
Armin Tuchscherer ◽  
Jan Gimsa
Keyword(s):  
Deep Brain Stimulation ◽  
Open Field ◽  
Field Test ◽  
Brain Stimulation ◽  
Open Field Test ◽  
Initiation Time ◽  
Migration Distance ◽  
Bipolar Electrodes ◽  
Two Parameters ◽  
Deep Brain

Although the clinical use of deep brain stimulation (DBS) is increasing, its basic mechanisms of action are still poorly understood. Platinum/iridium electrodes were inserted into the subthalamic nucleus of rats with unilateral 6-OHDA-induced lesions of the medial forebrain bundle. Six behavioral parameters were compared with respect to their potential to detect DBS effects. Locomotor function was quantified by (i) apomorphine-induced rotation, (ii) initiation time, (iii) the number of adjusting steps in the stepping test, and (iv) the total migration distance in the open field test. Sensorimotor neglect and anxiety were quantified by (v) the retrieval bias in the corridor test and (vi) the ratio of migration distance in the center versus in the periphery in the open field test, respectively. In our setup, unipolar stimulation was found to be more efficient than bipolar stimulation for achieving beneficial long-term DBS effects. Performance in the apomorphine-induced rotation test showed no improvement after 6 weeks. DBS reduced the initiation time of the contralateral paw in the stepping test after 3 weeks of DBS followed by 3 weeks without DBS. Similarly, sensorimotor neglect was improved. The latter two parameters were found to be most appropriate for judging therapeutic DBS effects.

scholarly journals Compaction and Liquefaction of a Sandy Layer: Simulation of Shaking Table Experiments

2013 ◽  
Vol 59 (4) ◽  
pp. 509-521 ◽  
Author(s):  
A. Sawicki ◽  
W. Świdziński
Keyword(s):  
Experimental Data ◽  
Numerical Simulations ◽  
Shaking Table ◽  
Sand Layer ◽  
Saturated Sand ◽  
Shaking Table Tests ◽  
Horizontal Acceleration ◽  
Sandy Layer ◽  
Dry Sand ◽  
Model C

AbstractThis paper presents numerical simulations of the behavior of a sandy layer subjected to a cyclic horizontal acceleration in shaking table tests, with a particular attention focused on the settlements of a dry sand layer, and on the liquefaction of saturated sand. A compaction/liquefaction model (C/L) is applied to these simulations. The influence of specific parameters of the model on the compaction and liquefaction of a sandy layer is shown and discussed. The results of simulations are compared with selected experimental data.

OS1919 Crater Shape and Ejector Size in Oblique Impact

2013 ◽  
Vol 2013 (0) ◽  
pp. _OS1919-1_-_OS1919-2_
Author(s):  
Koichi HAYASHI ◽  
Masahiro NISHIDA ◽  
Kenta NOZAKI ◽  
Kazuki TOYA ◽  
Sunao HASEGAWA
Keyword(s):  
Oblique Impact ◽  
Crater Shape

scholarly journals Estimation of Stresses in a Dry Sand Layer Tested on Shaking Table

2012 ◽  
Vol 59 (3-4) ◽  
pp. 101-112 ◽  
Author(s):  
Andrzej Sawicki ◽  
Marek Kulczykowski ◽  
Robert Jankowski
Keyword(s):  
Stress Field ◽  
Boundary Conditions ◽  
Soil Layer ◽  
Experimental System ◽  
Shaking Table ◽  
Plastic State ◽  
Sand Layer ◽  
Equilibrium Equations ◽  
Limit States ◽  
Dry Sand

Abstract Theoretical analysis of shaking table experiments, simulating earthquake response of a dry sand layer, is presented. The aim of such experiments is to study seismic-induced compaction of soil and resulting settlements. In order to determine the soil compaction, the cyclic stresses and strains should be calculated first. These stresses are caused by the cyclic horizontal acceleration at the base of soil layer, so it is important to determine the stress field as function of the base acceleration. It is particularly important for a proper interpretation of shaking table tests, where the base acceleration is controlled but the stresses are hard to measure, and they can only be deduced. Preliminary experiments have shown that small accelerations do not lead to essential settlements, whilst large accelerations cause some phenomena typical for limit states, including a visible appearance of slip lines. All these problems should be well understood for rational planning of experiments. The analysis of these problems is presented in this paper. First, some heuristic considerations about the dynamics of experimental system are presented. Then, the analysis of boundary conditions, expressed as resultants of respective stresses is shown. A particular form of boundary conditions has been chosen, which satisfies the macroscopic boundary conditions and the equilibrium equations. Then, some considerations are presented in order to obtain statically admissible stress field, which does not exceed the Coulomb-Mohr yield conditions. Such an approach leads to determination of the limit base accelerations, which do not cause the plastic state in soil. It was shown that larger accelerations lead to increase of the lateral stresses, and the respective method, which may replace complex plasticity analyses, is proposed. It is shown that it is the lateral stress coefficient K0 that controls the statically admissible stress field during the shaking table experiments.

Vibrocompaction properties of dry sand

2014 ◽  
Vol 51 (4) ◽  
pp. 409-419 ◽  
Author(s):  
N. Denies ◽  
J. Canou ◽  
J.-N. Roux ◽  
A. Holeyman
Keyword(s):  
Free Surface ◽  
Volume Change ◽  
Vertical Vibration ◽  
Cohesionless Soil ◽  
Motion Pattern ◽  
Cohesionless Soils ◽  
Acceleration Amplitude ◽  
Fundamental Understanding ◽  
Experimental Works ◽  
Dry Sand

The fundamental understanding of the behaviour of dry sand as it is being vibrated is necessary to properly address a number of engineering issues, such as the vibrocompaction process. The present paper first summarizes experimental works focusing on the effects of vibrations on the volume change of dry cohesionless soils. Original experiments characterizing the behaviour of dry sand subjected to vertical vibration are then presented. The volume change and the motion pattern displayed by vertically vibrated sand particles are discussed. When cohesionless soil, placed in a cylindrical container, is vertically vibrated under the gravitational field (g), experiments performed on dry Fontainebleau sand allow the distinction between three types of dynamic behaviours depending on the acceleration amplitude (a): the densification behaviour (a/g < 1), the instability surface behaviour (a/g ≈ 1), and the vibrofluid behaviour (a/g > 1). In the densification range, the sand simply settles. When the acceleration amplitude is increased beyond 1g, granular convection is observed and there is an instability in the sand mass leading to the emergence of an inclined free surface. If the acceleration amplitude is further increased, the free surface progressively flattens. There is an impressive dilatation of the whole sample and grain saltation is observed. The sand becomes fully vibrofluidized. The efficiency of the vibrocompaction process is finally discussed especially with regard to these dynamic behaviours.

Dynamic Centrifugal Modeling of a Horizontal Dry Sand Layer

1985 ◽  
Vol 111 (3) ◽  
pp. 265-287 ◽  
Author(s):  
Philip C. Lambe ◽  
Robert V. Whitman
Keyword(s):  
Sand Layer ◽  
Dry Sand
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