Pierre3D: a 3D stochastic rockfall simulator based on random ground roughness and hyperbolic restitution factors

2015 ◽  
Vol 52 (9) ◽  
pp. 1360-1373 ◽  
Author(s):  
Valentin S. Gischig ◽  
Oldrich Hungr ◽  
Andrew Mitchell ◽  
Franck Bourrier
Keyword(s):  
Stochastic Process ◽  
Slope Angle ◽  
Test Site ◽  
Fine Tuning ◽  
Model Parameters ◽  
Observation Data ◽  
Lumped Mass ◽  
Forest Road ◽  
Rockfall Hazard ◽  
The Impact

The use of dynamic computational methods has become indispensable for addressing problems related to rockfall hazard. Although a number of models with various degrees of complexity are available, model parameters are rarely calibrated against observations from rockfall experiments. A major difficulty lies in reproducing the apparent randomness of the impact process related to both ground and block irregularities. Calibration of rigorous methods capable of explicitly modeling trajectories and impact physics of irregular blocks is difficult, as parameter spaces become too vast and the quality of model input and observation data are insufficient. The model presented here returns to the simple “lumped-mass” approach and simulates the characteristic randomness of rockfall impact as a stochastic process. Despite similarities to existing approaches, the model presented here incorporates several novel concepts: (i) ground roughness and particle roughness are represented as a random change of slope angle at impact; (ii) lateral deviations of rebound direction from the trajectory plane at impact are similarly accounted for by perturbing the ground orientation laterally, thus inducing scatter of run-out directions; and (iii) a hyperbolic relationship connects restitution factors to impact deformation energy. With these features, the model is capable of realistically accounting for the influence of particle mass on dynamic behaviour. The model only requires four input parameters, rendering it flexible for calibration against observed datasets. In this study, we calibrate the model against observations from the rockfall test site at Vaujany in France. The model is able to reproduce observed distributions of velocity, jump heights, and runout at observation points. In addition, the spatial distribution of the trajectories and landing points has been successfully simulated. Different parameter sets have been used for different ground materials such as an avalanche channel, a forest road, and a talus cone. Further calibration of the new model against a range of field datasets is essential. This study is part of an extensive calibration program that is still in progress at this first presentation of the method, and focuses on fine-tuning the details of the stochastic process implemented both in two-dimensional (2D) and three-dimensional (3D) versions of the model.

scholarly journals Maximum Likelihood Estimation of the VAR(1) Model Parameters with Missing Observations

2013 ◽  
Vol 2013 ◽  
pp. 1-13 ◽  
Author(s):  
Helena Mouriño ◽  
Maria Isabel Barão
Keyword(s):  
Stochastic Process ◽  
Missing Data ◽  
Maximum Likelihood ◽  
Moving Average ◽  
Practical Importance ◽  
Likelihood Estimation ◽  
Model Parameters ◽  
Missing Observations ◽  
Data Set ◽  
The Impact

Missing-data problems are extremely common in practice. To achieve reliable inferential results, we need to take into account this feature of the data. Suppose that the univariate data set under analysis has missing observations. This paper examines the impact of selecting an auxiliary complete data set—whose underlying stochastic process is to some extent interdependent with the former—to improve the efficiency of the estimators for the relevant parameters of the model. The Vector AutoRegressive (VAR) Model has revealed to be an extremely useful tool in capturing the dynamics of bivariate time series. We propose maximum likelihood estimators for the parameters of the VAR(1) Model based on monotone missing data pattern. Estimators’ precision is also derived. Afterwards, we compare the bivariate modelling scheme with its univariate counterpart. More precisely, the univariate data set with missing observations will be modelled by an AutoRegressive Moving Average (ARMA(2,1)) Model. We will also analyse the behaviour of the AutoRegressive Model of order one, AR(1), due to its practical importance. We focus on the mean value of the main stochastic process. By simulation studies, we conclude that the estimator based on the VAR(1) Model is preferable to those derived from the univariate context.

scholarly journals Small dendritic synapses enhance temporal coding in a model of cochlear nucleus bushy cells

2020 ◽  
Author(s):  
Elisabeth Koert ◽  
Thomas Kuenzel
Keyword(s):  
Membrane Potential ◽  
Cochlear Nucleus ◽  
Temporal Coding ◽  
Fine Tuning ◽  
Model Parameters ◽  
Biophysical Parameters ◽  
Temporal Precision ◽  
Main Input ◽  
The Impact ◽  
Bushy Cells

AbstractSpherical bushy cells (SBC) in the the anteroventral cochlear nucleus can improve the temporal precision of the auditory nerve spiking activity despite receiving sometimes only a single suprathreshold axosomatic input. The interaction with small dendritic inputs could provide a possible explanation for this phenomenon. In a compartment model of spherical bushy cells with a stylized or realistic three-dimensional representation of the bushy dendrite we explored this proposal. Phase-locked dendritic inputs caused both a tonic depolarization and a modulation of the SBC membrane potential at the frequency of the stimulus but for plausible model parameters do not cause output action potentials (AP). The tonic depolarization increased the excitability of the SBC model. The modulation of the membrane potential caused a phase-dependent increase in the efficacy of the main axosomatic input to cause output AP. These effects increased the rate and the temporal precision of output AP. Rate was mainly increased for stimulus frequencies at and below the characteristic frequency of the main input. Precision mostly increased for higher frequencies above about 1 kHz. Dendritic morphological parameters, biophysical parameters of the dendrite and the synaptic inputs and tonotopic parameters of the inputs all affected the impact of dendritic synapses. This suggested the possibility of fine tuning of the effect the dendritic inputs have for different coding demands or input frequency ranges. Excitatory dendritic inputs modulate the processing of the main input and are thus a plausible mechanism for the improvement of temporal precision in spherical bushy cells.

Rockfall fragmentation simulations of real scale tests

2020 ◽  
Author(s):  
Gerard Matas ◽  
Nieves Lantada ◽  
Jordi Corominas ◽  
Josep Antoni Gili ◽  
Roger Ruiz-Carulla ◽  
...  
Keyword(s):  
Size Distribution ◽  
Block Size ◽  
Energy Conditions ◽  
Fragmentation Model ◽  
Model Parameters ◽  
Size Distributions ◽  
Lumped Mass ◽  
Fractal Fragmentation ◽  
The Impact ◽  
Real Scale

<p>Consideration of fragmentation during rockfalls is relevant for the assessment of hazard since it affects the number of generated blocks, their trajectories and impact energies, which also depends on the topography. Recently many scholars have paid attention to these phenomena since there are still many uncertainties around fragmentation regarding how mass and energy are distributed after fragmentation and how trajectory dispersion affects risk analysis. We developed a specific fragmentation model (Rockfall Fractal Fragmentation Model), as well as a 3D trajectory simulator called RockGIS with the fragmentation module implemented. In this contribution, we present the calibration of our rockfall trajectory simulator, based on real scale fragmentation tests performed on a quarry.</p><p>The RockGIS model considers a lumped mass approach and accounts block fragmentation upon impact with the terrain. Some improvements have been made on the simulator code regarding the consideration of rotation inside the kinematics of the model and restitution factors. The block size distributions obtained from natural rockfall events inventoried, as well as from the real scale fragmentation tests in a quarry, shows a fractal behaviour. On this way, the fractal fragmentation model implemented in the RockGIS simulator is able to reproduce the observed block size distributions.</p><p>To calibrate the model we used data gathered from a real scale rockfall test performed in a quarry. We calibrate the relations between the impact energy conditions and the fragmentation model parameters to generate the measured fragments size distribution. The initial volume of the tested blocks were measured manually using a tape and the release positions of the blocks were obtained with terrestrial photogrammetry. Both, the volume and spatial distribution of the fragments after each release were measured on the orthophotos obtained from UAV flights. Three calibration criteria were considered: runout distribution, volume distribution and cumulative volume as a function of the runout. Finally, the degree of fragmentation can be adjusted in the simulations allowing the comparison between different possible hazard scenarios (null, moderate, or severe fragmentation).</p><p>Finally, the results of the calibration shows that the RockGIS is able to reproduce the fragmentation behaviour in terms of block size distribution after breakage, as well as the spatial propagation, being a new tool with capabilities to assess the hazard related with fragmental rockfalls and the consequently risk associated.</p><p><span>The RockGIS tool and the fragmentation model based on the data collected from recent rockfall events have been developed within the RockRisk (2014-2016, BIA2013-42582-P) and RockModels (2016-2019, BIA2016-75668-P, AEI/FEDER, UE) projects. Both projects were funded by the Spanish Ministerio de Economía y Competitividad.</span></p>

scholarly journals Rockfall hazard in Greece.

2016 ◽  
Vol 47 (3) ◽  
pp. 1429 ◽  
Author(s):  
H. Saroglou
Keyword(s):  
Slope Angle ◽  
Block Size ◽  
Geological Structure ◽  
Archaeological Sites ◽  
Rainfall Events ◽  
Rockfall Hazard ◽  
Rock Formations ◽  
Specific Factors ◽  
The Impact ◽  
Of Greece

The geological structure of Greece (frequent occurrence of rock formations, existence of faults and fracturing of rocks), the steep topography and mountainous terrain as well as its high seismicity, creates a significant rockfall hazard. During the last decades, rockfalls in Greece are becoming a frequent phenomenon due to the increase of intense rainfall events but also due to the extension of human activities in mountainous areas.   The paper presents rockfall hazard in Greece trough an inventory of rockfalls and investigates  the  correlation  of  specific  factors,  namely:  a)  triggering  mechanism (rainfall, seismicity), b) slope angle, c) lithology, d) fault presence, e) block size in the  probability of occurrence of these, based on a statistical approach. The time and space frequency of the events is also investigated. Finally, the impact of the events on human and infrastructures (transportation infrastructure, inhabited areas, archaeological sites) is discussed.

scholarly journals Surface runoff simulation to mitigate the impact of soil erosion, case study of Třebsín (Czech Republic)

2012 ◽  
Vol 7 (No. 3) ◽  
pp. 85-96 ◽  
Author(s):  
P. Kovář ◽  
D. Vaššová ◽  
M. Janeček
Keyword(s):  
Shear Stress ◽  
Czech Republic ◽  
Soil Erosion ◽  
Surface Runoff ◽  
Model Simulation ◽  
Slope Angle ◽  
Model Parameters ◽  
Physically Based ◽  
The Impact ◽  
Experimental Plots

The relation between soil erosion and its redistribution on land strictly depends on the process of surface runoff formation during intensive rainfall. Therefore, interrupting and reducing continuous surface runoff, using adequate conservation measures, may be implemented in order to reduce the shear stress of flowing water. This paper describes the outcomes of the KINFIL model simulation in assessing the runoff from extreme rainfall on hill slopes. The model is a physically based and parameter distributed 3D model that was applied at the Třebsín experimental station in the Czech Republic. This model was used for the first time to simulate the impact of surface runoff caused by natural or sprinkler-made intensive rains on four of the seven different experimental plots. The plots involved in the analysis contain a variety of soils which are covered with different field crops. At this stage, the model parameters comprise saturated hydraulic conductivity, field capacity, sorptivity, plot geometry and surface roughness reflecting the Třebsín experimental plots. These parameters were verified on observed data. All seven plots had the same slope angle, but two of them were vulnerable to surface runoff due to their soil hydraulic parameters. There were rapidly increasing depths and velocities which consequently caused a higher shear stress for splashing soil particles downstream. The paper provides further information and data concerning the relationships between the depth of water and its velocity on the slopes of certain roughness. It also provides information concerning shear stress and shear velocity values, compared with their critical values depending on the soil particle distribution. This approach is more physically based than the traditional method of Universal Soil Loss Equation (USLE).

scholarly journals Cartographic analysis of the components of the agricultural landscape in the formation of sustainable land management in the context of land degradation Volgograd region

2021 ◽  
Vol 27 (4) ◽  
pp. 47-56
Author(s):  
Elena Denisova
Keyword(s):  
Agricultural Landscape ◽  
Arable Land ◽  
Slope Angle ◽  
Test Site ◽  
T Test ◽  
Test Plot ◽  
Forest Stands ◽  
Maximum Slope ◽  
Protective Forest ◽  
The Impact

Modern geoinformation studies of the structural components of the agricultural landscape allow us to quickly assess the state, the degree of preservation and the impact of its individual elements on the environment, and the sustainability of each land use. The preservation of the quality of land resources is the most important task for agricultural production and socio-economic development of the region. Mapping of the test site “Catchment area of the Kasarka River” made it possible to determine the agricultural landscape as a typical one, with an area of 78.55 thousand square meters. ha, with a predominance of arable land—60.3 %, woodlands—11.3 % and protective forest strips of artificial origin—3.6 %. The remaining area—19.39 thousand hectares—is occupied by hayfields and pastures, lands of settlements, roads and allotments. The terrain features a height difference of 86 m and a maximum slope angle of 7.5°. 456 plots of arable land were surveyed, the system of protective forest stands includes 581 forest strips and 21 forest stands, with a total area of 11.75 thousand hectares. 74.3 % of forest strips and massifs are degraded, the share of fallen forest belts was 34.3 %, the effectiveness of the protective action of forest stands is only 67 %, and this does not ensure the integrity of the agricultural landscape. The dependence of the slope angle (X) on the value of the potential washout (M) was determined, which made it possible to calculate the soil washout for each plot of arable land, which varies from 4.8 t/ha to 34.7 t/ha. The total flushing of the soil at the maximum values of the slope angles of the test site will be 823750.3 tons. For individual test plots of arable land, the spread of the calculated value of the average nutrient flushing is also significant from 3.1 t (test plot P67, area 0.943 ha), to 1655.5 t (test plot H142, area 296.86 ha).

Parameter Inversion of Tritium Migration Based on Parallel Genetic Algorithm

2012 ◽  
Vol 610-613 ◽  
pp. 1883-1888
Author(s):  
Yuan Cao ◽  
Wen Ke Wang ◽  
Tie Liang Wang ◽  
Ying Jie Wang
Keyword(s):  
Genetic Algorithm ◽  
Test Site ◽  
Tritium Concentration ◽  
Model Parameters ◽  
Observation Data ◽  
Parallel Genetic Algorithm ◽  
Radionuclide Migration ◽  
Parameter Inversion ◽  
Mainframe Computer ◽  
Manual Adjustment

To calibrate model parameters of tritium migration in a test site of China, an intelligent parameter inversion model based on parallel genetic algorithm is built, a forward and inverse coupling program of radionuclide migration is designed, and the values of key parameters like hydraulic conductivity, dispersity and porosity are inverted automatically on a mainframe computer, by means of abundant observation data of tritium concentration. The inversion results accord with observation data well on the whole. Compared to manual adjustment method, this method has better overall convergence, higher calculated precision and efficiency, and less manpower cost. The results show that parallel genetic algorithm is feasible and valid in application to parameter inversion of tritium migration.

scholarly journals The influence of grid resolution on the prediction of natural and road-related shallow landslides

2014 ◽  
Vol 18 (6) ◽  
pp. 2127-2139 ◽  
Author(s):  
D. Penna ◽  
M. Borga ◽  
G. T. Aronica ◽  
G. Brigandì ◽  
P. Tarolli
Keyword(s):  
High Resolution ◽  
Predictive Power ◽  
Shallow Landslide ◽  
Small Scale ◽  
Model Parameters ◽  
Full Potential ◽  
Forest Road ◽  
Terrain Attributes ◽  
The Impact ◽  
Landslide Model

Abstract. This work evaluates the predictive power of the quasi-dynamic shallow landslide model QD-SLaM to simulate shallow landslide locations in a small-scale Mediterranean landscape, namely, the lower portion (2.6 km2) of the Giampilieri catchment, located in Sicily (Italy). The catchment was impacted by a sequence of high-intensity storms over the years 2007–2009, resulting in widespread landsliding, with a total landslide initiation area amounting to 2.6% of the basin area. The effect of high-resolution digital terrain models (DTMs) on the quality of model predictions is tested by considering four DTM resolutions: 2, 4, 10 and 20 m. Moreover, the impact of the dense forest road network on the model performance is evaluated by separately considering road-related landslides and natural landslides. The landslide model does not incorporate the description of road-related failures and is applied without calibration of the model parameters. The model predictive power is shown to be DTM-resolution dependent. Use of coarser resolution has a smoothing effect on terrain attributes, with local slope angles decreasing and contributing areas becoming larger. The percentage of watershed area represented by the model as unconditionally unstable (i.e. failing even without the addition of water from precipitation) ranges between 6.3% at 20 m DTM and 13.8% at 2 m DTM, showing an overestimation of the mapped landslide area. We consider this prediction as an indication for likely failing sites in future storms rather than areas proved stable during previous storms. When assessed over the sample of mapped non-road-related landslides, better model performances are reported for 4 and 10 m DTM resolution, thus highlighting the fact that higher DTM resolution does not necessarily mean better model performances. Model performances over road-related failures are lower than for the natural cases, and slightly increase with decreasing DTM resolution. These findings indicate that to realize the full potential of high-resolution topography, more extensive work is needed aiming more specifically to identify the extent of the artificial structures and their impact on shallow landsliding processes.

Food Safety Security: A new Concept for Enhancing Food Safety Measures

2012 ◽  
Vol 82 (3) ◽  
pp. 216-222 ◽  
Author(s):  
Venkatesh Iyengar ◽  
Ibrahim Elmadfa
Keyword(s):  
Food Safety ◽  
Hazard Analysis ◽  
Warning System ◽  
Shared Responsibility ◽  
Fine Tuning ◽  
Strategic Action ◽  
Surveillance Network ◽  
Measurement Systems ◽  
Critical Control Points ◽  
The Impact

The food safety security (FSS) concept is perceived as an early warning system for minimizing food safety (FS) breaches, and it functions in conjunction with existing FS measures. Essentially, the function of FS and FSS measures can be visualized in two parts: (i) the FS preventive measures as actions taken at the stem level, and (ii) the FSS interventions as actions taken at the root level, to enhance the impact of the implemented safety steps. In practice, along with FS, FSS also draws its support from (i) legislative directives and regulatory measures for enforcing verifiable, timely, and effective compliance; (ii) measurement systems in place for sustained quality assurance; and (iii) shared responsibility to ensure cohesion among all the stakeholders namely, policy makers, regulators, food producers, processors and distributors, and consumers. However, the functional framework of FSS differs from that of FS by way of: (i) retooling the vulnerable segments of the preventive features of existing FS measures; (ii) fine-tuning response systems to efficiently preempt the FS breaches; (iii) building a long-term nutrient and toxicant surveillance network based on validated measurement systems functioning in real time; (iv) focusing on crisp, clear, and correct communication that resonates among all the stakeholders; and (v) developing inter-disciplinary human resources to meet ever-increasing FS challenges. Important determinants of FSS include: (i) strengthening international dialogue for refining regulatory reforms and addressing emerging risks; (ii) developing innovative and strategic action points for intervention {in addition to Hazard Analysis and Critical Control Points (HACCP) procedures]; and (iii) introducing additional science-based tools such as metrology-based measurement systems.

In-Plane Flexible Ring Tire Model—Part 1: Modeling and Parameter Identification

2018 ◽  
Vol 46 (3) ◽  
pp. 174-219 ◽  
Author(s):  
Bin Li ◽  
Xiaobo Yang ◽  
James Yang ◽  
Yunqing Zhang ◽  
Zeyu Ma
Keyword(s):  
Static Load ◽  
Model Parameters ◽  
Tire Model ◽  
Test Results ◽  
Lumped Mass ◽  
Virtual Test ◽  
Proposed Model ◽  
Particle Swarm Method ◽  
Vehicle Dynamic Simulation ◽  
Flexible Ring

ABSTRACT The tire model is essential for accurate and efficient vehicle dynamic simulation. In this article, an in-plane flexible ring tire model is proposed, in which the tire is composed of a rigid rim, a number of discretized lumped mass belt points, and numerous massless tread blocks attached on the belt. One set of tire model parameters is identified by approaching the predicted results with ADAMS® FTire virtual test results for one particular cleat test through the particle swarm method using MATLAB®. Based on the identified parameters, the tire model is further validated by comparing the predicted results with FTire for the static load-deflection tests and other cleat tests. Finally, several important aspects regarding the proposed model are discussed.

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