scholarly journals Theoretical study of rut depth compaction of snow cover under influence of forest machine rover

2019 ◽  
Author(s):  
Е.Г. Хитров ◽  
Г.С. Тарадин ◽  
А.В. Андронов ◽  
Е.В. Котенев ◽  
Ю.Л. Пушков
Keyword(s):  
Mechanical Properties ◽  
Bearing Capacity ◽  
Snow Cover ◽  
Contact Pressure ◽  
Calculated Data ◽  
Compaction Process ◽  
Snow Layer ◽  
Contact Patch ◽  
Physical Pattern ◽  
Cover Thickness

Цель статьи разработать и исследовать математическую модель колееобразования и уплотнения снежной целины, вызванного действием движителя лесной машины. Теоретическую базу исследования составляют положения теории движения автомобильного транспорта в условиях бездорожья. Методы исследования включают в себя математический анализ, вычислительный эксперимент и аппроксимацию расчетных данных. Составлены интегральные уравнения для расчета глубины колеи и сжатия массива снежной поверхности под воздействием движителя. Уравнения составлены с учетом изменения механических свойств снега в процессе уплотнения. По результатам аппроксимации результатов численного решения предложенных уравнений получены упрощенные соотношения, позволяющие определить глубину колеи и сжатие снега как функции его начальной плотности, толщины снежного покрова, среднего давления по пятну контакта движителя с опорной поверхностью и геометрических параметров пятна контакта. Установлено, что несущая способность заснеженной опорной поверхности увеличивается вслед за возрастающим давлением по пятну контакта, что вызвано как уменьшением толщины деформируемого слоя снега, так и увеличением механических свойств снега при уплотнении, что отражает физическую картину колееобразования на заснеженной поверхности. При нормальном давлении в 50 от несущей способности глубина колеи составит ориентировочно 20 толщины деформируемого слоя опорной поверхности, а при давлении, близком к несущей способности 60 от толщины снежного покрова. Соотношение абсолютной деформации сжатия снега и глубины колеипри давлении до 10 от несущей способности опорной поверхности составляет ориентировочно 1:1. При возрастании давления до 20 от несущей способности соотношение составит 1:2, а при повышении среднего давления до 100 от несущей способности соотношение деформации сжатия и глубины колеи составит 1:4. The purpose of our article is developing and investigating a mathematical model of rutting and compaction of snowy virgin soil, caused by the action of forest machine rover. Theoretical basis of the study consists of theory of offtheroad locomotion. Research methods include mathematical analysis, computational experiment and approximation of the calculated data. The study compiles integral equations for calculating the rut depth and compression of snow surface under the rover influence. The equations take into account changes in mechanical properties of the snow in the compaction process. Basing to the results of approximation of numerical solution of the equations, simplified relations were obtained, allowing to determine the rut depth and snow compression as functions of the initial snow density, snow cover thickness, average contact pressure and geometric parameters of the contact patch. The study establishes that bearing capacity of snowcovered surface increases following the increasing pressure on the contact patch, which is caused by both a decrease in thickness of deformable snow layer and an increase in mechanical properties of snow during compaction, which reflects physical pattern of rutting on snowcovered surface. With a contact pressure of 50 of the bearing capacity, the rut depth will be approximately 20 of the thickness of the deformable layer, and at a pressure close to the bearing capacity 60 of snow cover thickness. The ratio of absolute compression deformation of snow and the rut depth at the pressure of up to 10 of the bearing capacity is approximately 1:1. With an increase in the pressure up to 20 of the bearing capacity, the ratio will be 1:2, and with an increase in the pressure up to 100 of the bearing capacity, the ratio will be 1:4.

scholarly journals Acoustic Emission Methods Applied to Avalanche-Formation Studies

1988 ◽  
Vol 34 (117) ◽  
pp. 232-235
Author(s):  
V. P. Yepifanov ◽  
V. P. Kuz'menko
Keyword(s):  
Mechanical Properties ◽  
Acoustic Emission ◽  
Snow Cover ◽  
Acoustic Emissions ◽  
Physical And Mechanical Properties ◽  
Snow Layer ◽  
Structural Investigations ◽  
Viscosity Coefficients ◽  
Acoustic Methods ◽  
Remote Identification

AbstractThe relationship between the intensity of snow acoustic emission impulses and snow-cover stability is revealed by measuring the physical and mechanical properties of the snow cover in the starting zones of avalanches. This relationship is fundamental to the remote identification of an avalanche-hazard period.In order to estimate the mechanical properties of a snow layer, a method of applying a rigid penetrometer equipped with a piezo-electric accelerometer is used. The viscosity coefficients of snow under destruction and the specific energy of destruction are determined. The overall effect of different elements of destruction is assessed using both structural investigations and acoustic methods (acoustic emissions).

scholarly journals Acoustic Emission Methods Applied to Avalanche-Formation Studies (Abstract)

1987 ◽  
Vol 9 ◽  
pp. 246-246
Author(s):  
V.P. Epifanov ◽  
V.P. Kuz’menko
Keyword(s):  
Mechanical Properties ◽  
Acoustic Emission ◽  
Snow Cover ◽  
Acoustic Emissions ◽  
Physical And Mechanical Properties ◽  
Snow Layer ◽  
Structural Investigations ◽  
Viscosity Coefficients ◽  
Acoustic Methods ◽  
Remote Identification

The relationship between the intensity of snow acoustic emission impulses and snow-cover stability is revealed by measuring the physical and mechanical properties of the snow cover in the starting zones of avalanches. This relationship is fundamental to the remote identification of an avalanche-hazard period.In order to estimate the mechanical properties of a snow layer, a method of applying a rigid penetrometer equipped with a piezoelectric accelerometer is used. The viscosity coefficients of snow under destruction and the specific energy of destruction are determined. The overall effect of the different elements of destruction is assessed using both structural investigations and acoustic methods (acoustic emissions).

scholarly journals Acoustic Emission Methods Applied to Avalanche-Formation Studies

1988 ◽  
Vol 34 (117) ◽  
pp. 232-235
Author(s):  
V. P. Yepifanov ◽  
V. P. Kuz'menko
Keyword(s):  
Mechanical Properties ◽  
Acoustic Emission ◽  
Snow Cover ◽  
Acoustic Emissions ◽  
Physical And Mechanical Properties ◽  
Snow Layer ◽  
Structural Investigations ◽  
Viscosity Coefficients ◽  
Acoustic Methods ◽  
Remote Identification

AbstractThe relationship between the intensity of snow acoustic emission impulses and snow-cover stability is revealed by measuring the physical and mechanical properties of the snow cover in the starting zones of avalanches. This relationship is fundamental to the remote identification of an avalanche-hazard period.In order to estimate the mechanical properties of a snow layer, a method of applying a rigid penetrometer equipped with a piezo-electric accelerometer is used. The viscosity coefficients of snow under destruction and the specific energy of destruction are determined. The overall effect of different elements of destruction is assessed using both structural investigations and acoustic methods (acoustic emissions).

scholarly journals Acoustic Emission Methods Applied to Avalanche-Formation Studies (Abstract)

1987 ◽  
Vol 9 ◽  
pp. 246
Author(s):  
V.P. Epifanov ◽  
V.P. Kuz’menko
Keyword(s):  
Mechanical Properties ◽  
Acoustic Emission ◽  
Snow Cover ◽  
Acoustic Emissions ◽  
Physical And Mechanical Properties ◽  
Snow Layer ◽  
Structural Investigations ◽  
Viscosity Coefficients ◽  
Acoustic Methods ◽  
Remote Identification

The relationship between the intensity of snow acoustic emission impulses and snow-cover stability is revealed by measuring the physical and mechanical properties of the snow cover in the starting zones of avalanches. This relationship is fundamental to the remote identification of an avalanche-hazard period. In order to estimate the mechanical properties of a snow layer, a method of applying a rigid penetrometer equipped with a piezoelectric accelerometer is used. The viscosity coefficients of snow under destruction and the specific energy of destruction are determined. The overall effect of the different elements of destruction is assessed using both structural investigations and acoustic methods (acoustic emissions).

Towards an Improved Parameter-Free Entrainment Model for Snow Avalanches

2021 ◽  
Author(s):  
Dieter Issler
Keyword(s):  
Snow Cover ◽  
Ad Hoc ◽  
Shear Stresses ◽  
Entrainment Rate ◽  
Snow Layer ◽  
Present Contribution ◽  
Weak Layer ◽  
Model Combining ◽  
The Difference ◽  
The 1960S

<p>On physical grounds, the rate of bed entrainment in gravity mass flows should be determined by the properties of the bed material and the dynamical variables of the flow. Due to the complexity of the process, most entrainment formulas proposed in the literature contain some ad-hoc parameter not tied to measurable snow properties. Among the very few models without free parameters are the Eglit–Grigorian–Yakimov (EGY) model of frontal entrainment from the 1960s and two formulas for basal entrainment, one from the 1970s due to Grigorian and Ostroumov (GO) and one (IJ) implemented in NGI’s flow code MoT-Voellmy. A common feature of these three approaches is their treating erosion as a shock and exploiting jump conditions for mass and momentum across the erosion front. The erosion or entrainment rate is determined by the difference between the avalanche-generated stress at the erosion front and the strength of the snow cover. The models differ with regard to how the shock is oriented and which momentum components are considered. The present contribution shows that each of the three models has some shortcomings: The EGY model is ambiguous if the avalanche pressure is too small to entrain the entire snow layer, the IJ model neglects normal stresses, and the GO model disregards shear stresses and acceleration of the eroded mass. As they stand, neither the GO nor the IJ model capture situations―observed experimentally by means of profiling radar―in which the snow cover is not eroded progressively but suddenly fails on a buried weak layer as the avalanche flows over it. We suggest a way to resolve the ambiguity in the EGY model and sketch a more comprehensive model combining all three approaches to capture gradual entrainment from the snow-cover surface together with erosion along a buried weak layer.</p>

Micro-mechanical modeling using DEM to study the effect of mechanical properties on crack propagation for snow slab avalanches

2021 ◽  
Author(s):  
Bobillier Gregoire ◽  
Bergfled Bastian ◽  
Gaume Johan ◽  
van Herwijnen Alec ◽  
Schweizer Jürg
Keyword(s):  
Mechanical Properties ◽  
Steady State ◽  
Crack Propagation ◽  
Sensitivity Study ◽  
Tensile Fracture ◽  
Crack Speed ◽  
Stress Concentrations ◽  
Snow Layer ◽  
Stress Regime ◽  
Weak Layer

<p>Dry-snow slab avalanche release is a multi-scale process starting with the formation of localized failure in a highly porous weak snow layer below a cohesive snow slab, which can be followed by rapid crack propagation within the weak layer. Finally, a tensile fracture through the slab leads to its detachment. About 15 years ago, the propagation saw test (PST) was developed. The PST is a fracture mechanical field test that provides information on crack propagation propensity in weak snowpack layers. It has become a valuable research tool to investigate the processes involved in crack propagation. While this has led to a better understanding of the onset of crack propagation, much less is known about the ensuing propagation dynamics. Here, we use the discrete element method to numerically simulate PSTs in 3D and analyze the fracture dynamics using a micro-mechanical approach. Our DEM model reproduced the observed PST behavior extracted from experimental analysis. We developed different indicators to define the crack tip that allowed deriving crack speed. Our results show that crack propagation in level terrain reaches a stationary speed if the snow column is long enough. Moreover, we define stress concentration sections. Their length evolution during crack propagation suggests the development of a steady-state stress regime. Slab and weak layer elastic modulus, as well as weak layer shear strength, are the key input parameters for modeling crack propagation; they affect stress concentrations, crack speed, and the critical length for the onset of crack propagation. The results of our sensitivity study highlight the effect of these mechanical parameters on the emergence of a steady-state propagation regime and consequences for dry-snow slab avalanche release. Our DEM approach opens the possibility for a comprehensive study on the influence of the snowpack mechanical properties on the fundamental processes for avalanche release.</p>

scholarly journals Specifics of boglands freezing in the north and northwest of the European part of Russia under climate change

2019 ◽  
Vol 59 (2) ◽  
pp. 233-244
Author(s):  
V. I. Batuev ◽  
I. L. Kalyuzhny
Keyword(s):  
Ambient Temperature ◽  
Snow Cover ◽  
Spatial And Temporal Variability ◽  
North West ◽  
The North ◽  
Climatic Period ◽  
European Part Of Russia ◽  
Freezing Depth ◽  
Main Factors ◽  
Cover Thickness

Long-term complex observations covering the period of 1949–2018 made possible to determine the average annual characteristics of the depth of freezing of wetlands in the North and Northwest of the European territory of Russia together with main factors of its formation, and spatial and temporal variability. The main factors that determine the depth of freezing of wetlands are ambient temperature, snow cover thickness, and a degree of watering of the micro landscape (water reserves of the micro landscape). At the initial stage of freezing, the major factor is the ambient temperature, when intensity of the freezing reaches 0.5–0.8 cm/day. As snow falls, the freezing rate becomes smaller, and when the snow cover thickness reaches 25–30 cm the depth amounts to 0.2–0.3 cm/day and smaller. It was found that the spatial variability of the freezing depth decreases from large values of the coefficient of variation (0.3–0.4) at the depth of 20–30 cm to less than 0.1 when the depth exceeds 60 cm. The largest values of the depth are recorded in the North of the Kola Peninsula, where sometimes they reach from 84 to 97 cm with the average values of 48–66. In large hummocky bogs, when the seasonal freezing comes down to 63–65 cm it links with the permafrost layer. On average, swamps of these bogs freeze down to a depth of 68 cm. The average climatic depth of freezing of oligotrophic bogs of the NorthWest is 21–24 cm; in some years, freezing of them reaches 32–40 cm. It has been shown that the relative warming of the climate resulted in decreasing in the depth of freezing of wetlands in the North and North-West of the European territory of Russia. Relative to the previous climatic period, the depth of frost penetration in the northern Ilasskoye bog decreased by 32%, and in north-western Lammin-Suo bog – by 31%.

scholarly journals Influence of the Direction of Mixture Compaction on the Selected Properties of a Hemp-Lime Composite

Materials ◽  
2021 ◽  
Vol 14 (16) ◽  
pp. 4629
Author(s):  
Przemysław Brzyski ◽  
Piotr Gleń ◽  
Mateusz Gładecki ◽  
Monika Rumińska ◽  
Zbigniew Suchorab ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Thermal Conductivity ◽  
Temperature Distribution ◽  
Preparation Method ◽  
Thermal And Mechanical Properties ◽  
Compaction Process ◽  
External Wall ◽  
Capillary Uptake ◽  
Parallel Direction ◽  
The Individual

The aim of the research presented in the article was to check the differences in the hygro-thermal and mechanical properties of hemp-lime composites with different shives fractions, depending on the direction of mixture compaction. The research part of the paper presents the preparation method and investigation on the composites. Thermal conductivity, capillary uptake, as well as flexural and compressive strengths were examined. Additionally, an analysis of the temperature distribution in the external wall insulated with the tested composites was performed. The results confirm that the direction of compaction influences the individual properties of the composites in a similar way, depending on the size of the shives. The differences are more pronounced in the case of the composite containing longer fractions of shives. Both thermal conductivity of the material and the capillary uptake ability are lower in the parallel direction of the compaction process. Composites exhibit greater stiffness, but they fail faster with increasing loads when loaded in the direction perpendicular to compaction.

scholarly journals HERMETIZATION OF VALVE SEALS FOR CRYOGENIC FLUIDS

2020 ◽  
Vol 6 (2) ◽  
pp. 12-19
Author(s):  
Yuri I. Kondrashov ◽  
Elena N. Ermilova ◽  
Anna N. Vidyaskina
Keyword(s):  
Mechanical Properties ◽  
Contact Pressure ◽  
Phase State ◽  
Working Fluid ◽  
Cryogenic Temperatures ◽  
Two Phase ◽  
Plastic Properties ◽  
Cryogenic Fluids ◽  
Specific Contact ◽  
Flow Through

For units providing flow control for cryogenic fluids and operating under conditions of a significant change in the temperature range from positive to cryogenic and in a two-phase state of the working fluid, the problem of sealing the closure members of the units (valve pairs) becomes urgent.Joint sealing is ensured by creating contact pressure in the joint through deforming the roughness peaks obtained by surface treatment of the valve pair.The mechanical properties of the materials of the contacting valve pairs change significantly under the influence of cryogenic temperatures. First of all, the plastic properties are reduced, therefore, the creation of increased contact pressure is required.The article presents a methodology for evaluation of changes in the microgeometry of contacting surfaces depending on the specific contact pressure. It also allows one to evaluate the conductivity of microgaps in the viscous and molecular regimes of fluid flow through contacting surfaces.

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