Study on the efficiency of the digging process using the model of excavator bucket

In the first part of the paper, an experimental program is presented investigating the soil cutting problem, with the application of vertical rigid walls at various widths as the working tools. It was found that when the tool width equalled the width of the soil bin, the soil cutting problems might be treated as plane strain processes. For the tools for which no interaction with the sidewalls of the bin was observed, the zone of the plane strain deformations occurred in the central part of the tools. In the second part of this paper a new experimental program of laboratory tests is presented, for a tool model in the shape of an excavator’s bucket equipped with teeth. The experimental verification of the influence of teeth (number of teeth and the position of teeth on the bucket’s inside lip) on the efficiency of the digging cycle is the aim of this paper. For high values of teeth spacing, the superposition of the plane strain deformation mechanism with three-dimensional failure modes within the soil was observed. For the low values of teeth spacing, the teeth did not act as separate three-dimensional objects but as one wide tool built up from several modules. As a consequence, the deformation pattern in front of such an assembly of teeth was again the plane strain deformation pattern.     

Comparison between centrifugal and vertical vibro-compaction of high-lifted decomposed weathered granite sandy soil using a tracked vehicle

The aim of this research was to develop a new vibro-compaction machine by comparing experimentally and theoretically the effects of a tracked vehicle of total weight 9.8 kN mounted with a centrifugal or vertical oscillator on a high lifted decomposed weathered granite sandy soil. By measuring the amount of sinkage of the terrain surface, the dry density distribution with depth, the normal earth pressure distribution with depth, and the vertical and horizontal acceleration distribution with depth, the compacting effect of centrifugal and vertical vibro-tracked vehicles on the increment of dry density in a deep soil stratum were compared for a frequency of about 54 Hz. It was observed that the centrifugal vibro-tracked vehicle showed a 25% increase in the final amount of sinkage and a 11.3% increase in the maximum dry density of compacted soil compared to the vertical vibro-tracked vehicle. We believe that the centrifugal vibro-tracked vehicle can be shown from the analysis of the stress and acceleration propagation to be a better compaction machine at a high frequency of oscillation for a high lifted soil stratum when compared to conventional vertical vibro-tracked vehicles.     

Discrete and continuum modelling of excavator bucket filling

Two-dimensional discrete and continuum modelling of excavator bucket filling is presented. The discrete element method (DEM) is used for the discrete modelling and the material-point method (MPM) for continuum modelling. MPM is a so-called particle method or meshless finite element method. Standard finite element methods have difficulty in modelling the entire bucket filling process due to large displacements and distortions of the mesh. The use of a meshless method overcomes this problem. DEM and MPM simulations (plane strain) of bucket filling are compared to two-dimensional experimental results. Cohesionless corn grains were used as material and the simulated force acting on the bucket and flow patterns were compared with experimental results. The corn macro (continuum) and micro (DEM) properties were obtained from shear and oedometer tests. As part of the MPM simulations, both the classic (nonpolar) and the Cosserat (polar) continuums were used. Results show that the nonpolar continuum is the most accurate in predicting the bucket force while the polar and DEM methods predict lower forces. The DEM model does not accurately predict the material flow during filling, while the polar and nonpolar methods are more accurate. Different flow zones develop during filling and it is shown that DEM, the polar and the nonpolar methods can accurately predict the position and orientation of these different flow zones.     

Dynamics of digging in wet soil

Numerous animals live in, and locomote through, subsea soils. To move in a medium dominated by frictional interactions, many of these animals have adopted unique burrowing strategies. This paper presents a burrowing model inspired by the Atlantic razor clam (Ensis directus), which uses deformations of its body to cyclically loosen and re-pack the surrounding soil in order to locally manipulate burrowing drag. The model reveals how an anisotropic body - composed of a cylinder and sphere varying sinusoidally in size and relative displacement - achieves unidirectional motion through a medium with variable frictional properties. This net displacement is attained even though the body kinematics are reciprocal and inertia of both the model organism and the surrounding medium are negligible. Our results indicate that body aspect ratio has a strong effect on burrowing velocity and efficiency, with a well-defined maximum for given kinematics and soil material properties.     

工程结构优化的进化策略-高斯过程协同优化方法

针对采用仿生全局优化方法进行复杂工程结构优化时数值计算量浩大导致的计算代价过高的公开问题,将自适应协方差矩阵进化策略(CMAES)全局优化算法、高斯过程(GP)机器学习技术与有限元方法相结合,提出了基于自适应协方差矩阵进化策略-高斯过程协同优化算法(CMAES-GP)的结构优化方法。该方法利用全局寻优性好且寻优效率高的CMAES算法进行全局最优搜索,当搜索进入局部寻优阶段时,采用回归性能优秀的GP模型对适应度函数进行动态拟合,进而利用GP模型替代有限元分析进行个体适应度评价,以减小局部寻优阶段的有限元重分析次数,从而实现有效降低工程结构优化计算代价的目的。算例研究表明,与传统结构优化方法相比较,本文方法具有全局性好、计算效率高的优点。     

Mathematical modelling of the soil desalinization process

Of the many physical and chemical factors influencing the migration of salt in the ground, only molecular-filtration diffusion, convective transport, and salt exchange between the porous soil skeleton and the moving solution are usually taken into account [1]. The salt-exchange process is of a diffusion nature (“internal” diffusion) and depends on the types of soil and the nature of their salinization. We may assume that soils of a heavy mechanical composition (clay, heavy loam) possessing high moisture-retention capacity are most appropriately modelled by a heterogeneous porous medium with porosity m = m₁ + m₂, where m₁ denotes the volume of transit pores occupied by the moving solution and m₂, the volume of terminal pores, filled with a stationary solution (“bound” moisture). In this case, the internal diffusion mass-exchange process between both types of pores is described [2, 3] in the form of Freundlich-type isotherms, (0.1) $$\alpha {{\partial N} \mathord{\left/ {\vphantom {{\partial N} {\partial t}}} \right. \kern-\nulldelimiterspace} {\partial t}} = c - N,$$ where c (x, t) and N (x, t) are the concentrations of solutions in the transit and terminal pores, respectively, t is the time, x is a coordinate, and α is the kinetic parameter. Salinization of soil of light mechanical composition (sand, light loam) with low moisture-retention capacity is associated with the presence of salts in the solid phase. We must write kinetic equations for salt dissolution in place of Eq. (0.1). Some types of these equations have been previously presented [1–5]. In this work, three problems modelling the soil desalinization process and admitting analytic solutions for arbitrarily given initial salinization are considered. It is assumed here that the “internal” diffusion process occurs sufficiently rapidly (or infinitely rapidly) in comparison with the “external” diffusion process and convection.     

Laboratory astrophysics and non-ideal equations of state: the next challenges for astrophysical MHD simulations

Laboratory astrophysics holds great promise not only as a highly effective validation tool for astrophysical magneto-hydrodynamics (MHD) codes but it also presents a unique challenge for these codes. The high-density plasmas found in these experiments are not well modeled by the ideal equations of state (EOS) found in most astrophysical simulation codes. To solve this problem, we replaced the ideal EOS scheme in an existing MHD code, AstroBEAR, with a non-ideal EOS method and validated our implementation with van der Waals shock tube tests. The improved code is also able to model flows that contain more than one material, as required in laboratory experiments. Simulations of jet experiments performed at the OMEGA Laser reproduce the morphology of the jet much better than when the code used a single material and an ideal EOS.     

Study of the non-isothermal glass fibre drawing process

The glass fibre drawing process is simulated using a finite-element method. The two-dimensional energy and momentum equations are solved in their fully non-linear forms. These are coupled via the temperature-sensitive viscosity function. Both convective and radiative cooling mechanisms are taken into account on the filament surface. An effective emissivity of about 0.2 is found to be applicable to the drawing conditions in this paper. Even at this fairly low effective emissivity, radiation is found to be the dominant mode of cooling. The material thermal conductivity is found to have a small but definite influence on the filament profiles. Two-dimensionsl effects of the kinematic field are only significant up to a distance of about two orifice radii from the nozzle exit.The symbols in the square brackets show the dimensions of the parameters;M Mass,L Length,T Temperature,t Time. a Constant radius of a uniform cylinder [L] - A Local cross-sectional area of the filament [L ² ] - b _i Total tension applied on the filament boundary surface in thei ^th direction [ML/t ² ] - c Specific heat [L ² /t ² T] - D Local filament diameter [L] - f _i i ^th component of the body-force vector [L/t ² ] - h Surface convective heat transfer coefficient of the filament [M/t ³ T] - H Total equivalent heat transfer coefficient due to both convection and radiation [M/t ³ T] - k Thermal conductivity [ML/t ³ T] - M Mass-flow rate [M/t] - n Coordinate normal to the local filament surface [L] - Nu Local Nusselt number [–] - Average Nusselt number [–] - Q Rate of heat transfer [ML ² /t ³ ] - Volume-flow rate [ ³ /t] - r Radial coordinate [L] - R Local radius of the filament [L] - Re _x Reynolds number based on characteristic length scalex [–] - s Coordinate along the filament surface [L] - T Temperature [T] - u Radial component of the velocity [T/t] - U Free-stream velocity of a uniform flow [L/t] - v Local speed of a fluid particle defined by v = ;[L/t] - V Volume [L ³ ] - v _f Constant velocity of a filament with a uniform radius [L/t] - w Axial component of the velocity [L/t] - Average axial velocity of the fluid inside the tube [L/t] - z Axial coordinate, i.e. axial distance from the orifice exit [L] - Exponential coefficient of the viscosity function [T ^–1 ] - _ij Kronecker delta [–] - Emissivity or total hemispherical emissivity [–] - µ Viscosity [M/Lt] - µ ₀ Reference viscosity defined byµ = µ ₀ e ^–T [M/Lt] - Fluid density [M/L ³ ] - Stefan-Boltzmann constant [M/t ³ T ⁴ ] - Viscous dissipation function [M/Lt ³ ] - a Of air - a Based on the (constant) filament radius - C.L. Referred to the centre line of the filament - conv Referred to convection - D Dased on the diameter - f Referred to the filament local condition - g Referred to glass - i,j Species in multi-component systems - o Quantity evaluated at the orifice exit - R Based on the radius - rad Referred to radiation - s Evaluated at the filament surface - tot Referred to the total heat transfer from the filament surface - w Evaluated at the tube wall - Ambient condition - * Refers to non-dimensional quantities - — Indicating quantities averaged over the filament cross-section     

Effects of dry density and thickness of sandy soil on impact response due to rockfall

Sand cushions against impact force are widely used for rockfall prevention covers. The objective of this paper is to investigate the effects of the dry density and thickness of a sand cushion on an impact response due to a falling weight likened to a rockfall. A series of laboratory experiments for a decomposed granite soil was executed in the combination of the mass and drop height of the weight. As a result, the impact pressure applied to the soil surface increases with the dry density, but it does not depend on the thickness of the soil. The earth pressure at the bottom of the mold increases with the dry density, and it decreases with the thickness of the soil. Therefore, the transmissibility of the impact pressure decreases rapidly with the thickness of the soil.     

Indentation tests and rolling simulations of a compliant wheel on soil at different consistencies

The investigation presented addresses the response of a compliant wheel in interaction with deformable soil dependent on the water content, and accordingly on soil consistency. Two fine soils are considered. The basic soil properties and the soil shear strength are obtained from routine tests. A non-pneumatic Tweel in full size is tested in a loading device against a rigid base and against soil placed in a container in order to assess its stiffness and the compressional behavior of the soil, respectively. The measured pressure sinkage curves are then utilized in conjunction with a standard explicit FEM code to calibrate a hyperelastic model for the Tweel and an elasto-plastic constitutive model for the soil. Soil-tire interface strength is obtained from shear tests on a flat tire section embedded in soil. The numerical model is then applied to investigate how the water content affects the global response of the tire-soil system under different scenarios of free rolling, braking and driving. The methodology followed, complemented by appropriate soil testing, can be used as guide for the implementation of more elaborate models.     

On the compression process in a free-piston shock-tunnel

Preliminary results in the Marseille free-piston shock-tunnel facility are presented. The compression of the driver gas by the piston is studied experimentally for two different geometries of the end of the compression tube. Peak pressures obtained with the end of the compression tube closed, and with bursting of the diaphragm separating the high pressure from the low pressure chamber, are compared with calculated values in the cases of N₂ and He as driver gases. A phenomenon of accoustic resonance has been uncovered, generating strong pressure oscillations which, if not properly dealt with, could impair the quality of the useful flow in such a facility.This article was processed using Springer-Verlag T_EX Shock Waves macro package 1.0 and the AMS fonts, developed by the American Mathematical Society.     

复杂结构高层建筑火灾坍塌过程研究

为了探究具有多核心筒和中空结构的复杂高层建筑受火灾后的坍塌特征,采用颗粒流方法对建筑进行建模并实施火灾模拟。建筑为中空-四核心筒-框架结构,根据其特点设置了单侧火场和双侧火场两种方案,模拟温度为1000℃,1200℃,1400℃和1600℃。模拟上述情况下该建筑的坍塌过程,分析其坍塌特点和时间。总结坍塌现象发现,该类建筑在一侧受火灾作用坍塌情况下,较结构简单的高层建筑更易出现坐塌破坏,有利于坍塌范围控制;主要坐塌位置为两处,31m高变阶位置和火区上部;前期坍塌是由于火灾,后期是由于底部结构破坏而失稳坐塌;双侧火区与单侧相比,坍塌明显较快,因火灾坍塌的阶段时间较短,后期失稳坐塌时间较长。     

Regression analysis of the characteristics of vibro-cutting blade for tuffaceous rock

The vibro-cutting mechanism of a blade was experimentally tested for tuffaceous rock material. The influences of frequency and amplitude of displacement of vibro-cutting, the cutting velocity and the wave shape of vibration on the maximum excavation force were investigated. It was observed that the ratio of maximum horizontal component of excavation force of vibro-cutting to that of non-vibration tended to decrease hyperbolically with the increment of frequency for a constant amplitude of displacement. The specific energy decreased hyperbolically with the increment of the velocity ratio. The energy for the sinusoidal wave of vibration was always smaller than that for triangular wave. The ratio of specific energy at vibro-cutting to that at non-vibration decreased hyperbolically with the increment of mutual velocity. The sinusoidal wave of vibration of a blade was evaluated as more efficient for cutting tuffaceous rock than the triangular wave of vibration.     

Numerical path integration of a non-homogeneous Markov process

The numerical path integration method, based on Gauss-Legendre integration scheme, is applied to a Duffing oscillator subject to both sinusoidal and white noise excitations. The response of the system is a Markov process with one of the drift coefficients being periodic. It is a non-homogeneous Markov process that does not have a stationary probability distribution. When applying the numerical procedure, the values of transition probability density at the Gaussian-Legendre quadrature points need only be calculated for time steps of the first period of the sinusoidal excitation, and they can be saved for use in all subsequent periods. The numerical procedure is capable of capturing the evolution of the probability density from an initial distribution to one that is changing and rotating periodically in the phase space.     

Simulation of a soil loosening process by means of the modified distinct element method

We apply the Distinct Element Method (DEM) to analyze the dynamic behavior of soil. However, the conventional DEM model for calculation of contact forces between elements has some problems; for example, the movement of elements is too discrete to simulate real soil particle movement. Therefore, we modify the model to solve the difficulties. To investigate the validity of the modified model, we conduct an experiment in which soil is cut with a pendulum-typeblade, and simulate the soil loosening process with the modified DEM model. This paper presents details of the experimental apparatus and the comparison of soil behavior and energy absorption between the simulation and the experiment. Some characteristic phenomena of the experiment are reproduced in the simulation giving us confidence that the modified model is better than the conventional model for the simulation of soil behavior.     

基于RAGA的模糊层次分析方法在爆破方案优选中的应用

探讨了应用实码加速遗传算法,直接检验和修正模糊优先关系矩阵的爆破方案模糊层次分析改进优选方法。实例应用表明,该法可合理确定指标权重,能提高评价结果的精度和优度值的离散度。     

Numerical investigations on dynamic process of muzzle flow

The integrative process of a quiescent projectile accelerated by high-pressure gas to shoot out at a supersonic speed and beyond the range of a precursor flow field was simulated numerically. The calculation was based on ALE equations and a second-order precision Roe method that adopted chimera grids and a dynamic mesh. From the predicted results, the coupling and interaction among the precursor flow field, propellant gas flow field and high-speed projectile were discussed in detail. The shock-vortex interaction, shockwave reflection, shock-projectile interaction with shock diffraction, and shock focus were clearly demonstrated to explain the effect on the acceleration of the projectile.