Experimental evaluation of cutting dynamic models in soil bin facility

Computer Aided Engineering methods in earthmoving machines design and their automation require the development of soil-cutting models. These models both in two or three dimensions, static or dynamic, fitted for frictional or cohesive soils, must be mutually compatible and must function with soil transportation models and with machine locomotion characteristic models. In this work two different methods of soil cutting have been evaluated, both of them based on the classical wedge method, in order to verify their applicability to test conditions in the new soil bin facility of CEMOTER. From experimental results the possibility of using dynamic models of soil cutting in the frequency domain is discussed, to improve earthmoving machinery performance by automation and implementation of open and closed-loop control. After a preliminary analysis of a plane blade under different test conditions in sandy soil, soil cutting theoretical models of a simple implement are compared with respective scale models by tests performed in a soil bin facility at various operating speeds and depths, in order to investigate their applicability and the dynamic behaviour of the soil cutting force.     

A framework for earthmoving blade/soil model development

This paper presents a framework for earthmoving blade/soil model development that combines the advantages of both the analytical and numerical methods. This framework greatly expands the limitations of traditional analytically formulated models and can be effectively used to tackle the technical issues that are faced with complex dozing. This model has a lot of new capabilities compared to other models that can be found in the open literatures. Some of the new capabilities are (1) it is a three-dimensional model and is able to account for the tilted and angled blade operations on different terrain conditions: level, uphill, and downhill; (2) uneven cutting can be effectively handled by the proposed model; (3) the transient soil piling, spillage process, and earthmoving productivity can be predicted and animated; (4) the forces and moments can be predicted as well as their centroids; (5) the cutting soil volumetric expansion and transient surcharge effect on resultant forces and moments acting on blade are well established; (6) many systematic relationships involving the dynamic dozing are well established through this framework. Numerical examples and qualitative validations are provided to demonstrate and verify the capabilities of this newly developed framework.     

The inception and evolution of earthmoving soil mechanics

Soil and test conditions important to earthmoving machinery have been found to be significantly different from all other fields of endeavour with the partial exception of tillage studies. This could be the subject of a long dissertation. Broadly, however, soil conditions which produce critical mobility problems are much too soft and/or wet to be of concern to the earthmoving contractor who has to meet rigid specifications on acceptable types and moisture contents of fill soils. Occasional soft spots are considered as nuisances instead of indicators of the need for major design compromises.

Civil engineers are concerned with the same types of soil, but in a vastly different context. They must design soil structures which will never reach initial soil failure. Earthmoving processes, on the other hand, must accept soil failures in many different forms and degrees and utilize post-failure soil strength to perform their tasks efficiently.

Tillage studies display many important similarities to earthmoving studies, particularly in regard to the types of soil failures of importance. They are, in reality, merely another form of earthmoving; by definition, if nothing more. Earthmoving processes can range into much stronger soils, but this alone is insufficient to set them apart.

The term Earthmoving Soil Mechanics was introduced in 1962⁽²⁰⁾. This paper more clearly defines the implications of the new terminology and illustrates the first successful application of soil mechanics and model analysis principles in the earthmoving industry.     

Ability of clay fill to support construction plant

Good ground conditions are required for the operation of modern earthmoving plants due to the higher contact pressures imposed by them on the supporting surface. The maximum allowable contact pressure has been arrived at by a simplified theory based on the bearing capacity of clay soils. From these considerations it appears that standards earthmoving tyres with inflation pressures of greater than 50 lb/in² should be used only on stiff or strong clays, but for firm clays it is necessary to reduce the inflation pressures to between 25 and 50 lb/in², depending on the shear strength of the soil. It would also seem desirable to replace the standard wheels on a particular plant with larger wheels capable of carrying the load under lower inflation pressures.     

Spectrum analysis of road roughness for earthmoving machinery

The power spectral density functions of roughness of road surfaces for earthmoving machines such as tractors, scrapers and dumpers were determined by use of an accelerometer mounted on a towed fifth wheel of which the frequency-response function had previously been known. From obtained data, a range of power spectral density curves of the road roughness for these earthmoving machines was derived and expressed mathematically.     

Soil parameters for estimating the rolling resistance of earthmoving plant on a compacted silty cohesive soil

The performance of earthmoving plant is currently estimated through experience, often with no more than a limited inspection of the site investigation report. On site, the absolute speed of the plant is seldom considered to be critical as long as the veheciles keep moving.The different factors which affect the speed of the plant on the haul roads are discussed. The various soils test which were carried out, as well as how they relate to the apparent rolling resistance of the driver-vehicle-haul-road system, are discussed. Also, the reasons why certain tests are inadequate for the estimation of the performance of earthmoving plant are discussed. It is shown that the speed of the plant can be estimated from the data contained within the site invesitigation report, and that it can be continually monitored throughout the life of the contract, by using the consistency index.     

The cutting of soil by narrow blades

The available models for predicting the forces acting on a narrow soil cutting blade have required separate measurements of the shape of the three-dimensional soil failure pattern ahead of the blade. It is proposed that a three-dimensional model consisting of straight line failure patterns in the soil can be used to predict both the draft forces and the volume of soil disturbed in front of a narrow blade. Limit equilibrium mechanics equations are written for the soil wedges in terms of an unknown angle of the failure zone and the theoretical draft force is minimized with respect to this angle. Force factors are thus found which are of the type to fit Reece's general earthmoving equation, but which vary with the width to depth ratio of the blade as well as with the rake angle of the blade and the friction angle of the soil. In addition the approximate geometry of the three-dimensional failure pattern in the soil is predicted for varying blade shapes and soil strengths. This allows the design of simple tools on the basis of their draft force requirements and their soil cutting efficiency. The draft force predictions and failure geometry calculations are shown to have considerable verification by experimental results.     

Evaluation of drawbar performance of winter tyres for special purpose vehicles

Driving on ice is still a risky activity. Research has investigated the factors contributing to the friction mechanism and has reported experimental studies of pneumatic tyres on ice in order to develop models that predict tractive and braking performance on ice/snow. Therefore, developing testing methods to obtain relevant experimental data for the validation of models is equally important.There are agricultural and industrial vehicles which are also designed for pulling but there are no specific studies reporting experimental tests on traction force of such machines in snowy conditions. However, this issue is very topical, as demonstrated by the appearance on the market of winter tyres for such vehicles.This study presents a method for testing winter tyres in outdoor test facilities with a focus on traction performance. The conclusions will serve in future investigations as a concise knowledge source to develop improved testing facilities and tyre–ice interaction models, aiding the development of better tyre designs and improved vehicle safety systems.The functional tests hereafter described have been carried out with the aim of evaluating the possibility of measuring the influences of different technique solutions on the performance of certain 17.5 R25 sized industrial tyres.     

Identification,design and kinematic analysis of an earthmoving mechanism

Earthmoving mechanisms in motor graders are critical components for earthwork, compaction and re-handling, and yet they have not received much attention by mechanical engineering research in recent times. In this paper, a comprehensive analysis, from mechanism identification and innovative design to kinematic analysis, is presented. First, the mechanism analysis and synthesis method based on multibody system dynamics is carried out through the analysis of the system topology and connectivity. We conclude that the earthmoving multibody system is a spatial hybrid mechanism, which consists of a spatial parallel mechanism and a spatial serial mechanism. Second, a number of new spatial parallel mechanisms, which are advantageous with respect to the original one under certain conditions, are generated. The kinematic characteristics of the parallel mechanism family are investigated in terms of constraint equations formulated in natural coordinates. Third and last, kinematic simulations and optimization processes are carried out to evaluate the advantages of the presented spatial parallel mechanisms. Simulation results show that these mechanisms can provide better kinematic performance.     

Nanoindentation of hyperelastic polymer layers at finite deformation and parameter re-identification

Thin polymer layers on substrates have a wide range of application in important areas. However, it is impossible to measure the mechanical properties with the traditional testing methods. Recently, nanoindentation became a new but primary testing technique of thin layers. In the present work, based on a finite element model of contact mechanics and hyperelastic materials, nanoindentation of polymer layers is simulated with the finite element code ABAQUS^?. Three often used hyperelastic models, that is, the neo-Hookean, Mooney–Rivlin and Yeoh models are investigated. The behaviour of these three models is compared to each other in different boundary value problems of nanoindentation in order to get some feeling of the different behaviour of various hyperelastic models under nanoindentation. In contrast to the traditional analytical method, the penetration depth is not restrained to avoid the influence of the substrate. A parameter re-identification strategy is employed to extract the parameters of the material models at small and finite deformation based on the principle of biological evolution. Furthermore, it is investigated how large the penetration depth has to be chosen in order to distinguish different models in reference to the load–displacement curves. Finally, the possibility is discussed of describing the data obtained by a non-linear complex model using the relatively simple approach based on the neo-Hookean model.     

Tests on microconcrete model of hyperbolic cooling tower

In the past 18 years following the collapse of three cooling towers on November 1, 1965 in Ferrybridge, England, a considerable interest has developed in determining the buckling behavior of these thin-walled shells under the loadings normally encountered. An extensive number of theories exist attempting to predict buckling response and failure. Numerous tests on small, elastic models of metals or plastics have also been reported. However, little work has been reported on the physical testing to failure of concrete models. This paper describes work on the construction, instrumentation and testing of a microconcrete model of a hyperboloid of revolution proportioned to exhibit buckling prior to collapse. This model is the first in a series of models which will be constructed and tested with a variety of load and support configurations. The shell model was tested to failure under the action of uniform pressure (vacuum loading). The failure was of a local nature so the model was repaired and tested a second time to failure. The results of these tests showed good agreement with membrane theory (modified to account for geometric imperfections) for measured strains but the buckling mode of failure was of an unexpected type. Paper was presented at 1982 SESA Fall Meeting held in Hartford, CT on November 7–10, 1982.     

The optimum height of application of force and eccentricity of a wheeled vehicle running on a loose sandy soil

In earthmoving sites, multi-wheeled vehicles are used to excavate a sandy soil or to pull other construction machinery. In this paper, the mechanism of a 5.88 kN weight, two-axle, four-wheel vehicle running on a loose sandy soil is theoretically analysed. For given terrain-wheel system constants, the combination of the effective braking force of the front wheel during pure rolling state and the effective driving force of the rear wheel during driving action will clarify the relation between effective effort of the vehicle and slip ratio and the relation between amounts of sinkage the front and rear wheels and slip ratio, etc. The maximum effective tractive effort of the vehicle varies with the height of application force and the position of the center of gravity of the vehicle. The optimum height of application of force and the eccentricity of the center of gravity to obtain the largest value of the maximum effective tractive effort can be explained with an analytical simulation program. Results of this study showed that the optimum height of application force should be 30 cm and the optimum eccentricity of the center of gravity is 0.05 for a vehicle considered for this study.     

MODAL RESPONSE OF A BEAM WITH IMPERFECT BOUNDARY CONDITIONS

The introduction of non-contacting dynamic measurement techniques such as holographic interferometry and laser vibrometry has led to increased usage of model testing. Without having to add mass, stiffness, or damping due to sensor attachment, small scale models can be employed, thus permitting the use of less expensive specimens, fixtures, and excitation sources. An additional driver towards model testing is the dynamic characterization of exotic materials for which only small samples are available. One of the disadvantages of small scale testing is the necessity to provide accurate placement of the specimen in a clamping fixture (the most often used boundary condition for beams and plates). This work is an effort to characterize the effect of imperfect boundary conditions on the resulting data.     

Erosion of oil&gas industry choke valves using computational fluid dynamics and experiment

As part of several years research activity with erosion in chokes, Norsk Hydro ASA has developed a model to estimate erosion and lifetime of chokes by incorporating erosion models into particulate flow models. This model has been verified with the results from flow and erosion testing of two different types of chokes, Needle&Seat and External Sleeve. The erosion tests with both the modified Needle&Seat choke and the External Sleeve choke gave peak erosion rates only two or three times larger than calculated. This is assumed to be near the uncertainty of the erosion model alone. This is very satisfactory for such complex flow geometries. The model and the experiments demonstrated that the External Sleeve choke is much more prone to erosion attack, at the given low pressure conditions.     

考虑地基-结构-散粒体相互作用时贮仓结构的静动力研究——[Ⅰ]实验研究

对贮仓结构的静、动力问题进行了系统的实验研究 :考虑到地基———结构———散粒体的相互作用 ,设计并完成了不同地基上的筒仓模型的静、动力试验 (包括模型制作、试验和测试方案 ,数据输入输出及处理 )。根据对多种工况试验的观察 ,得出结论 :在地基水平振动的情况下 ,贮仓内绝大部分的散粒体与仓壁没有相对运动 ,只有一小部分散粒体脱离仓壁与贮仓有相对运动     

优化跨音速自适应壁试验段设计的试验研究

分析了在矩形截面试验段中三元模型试验时的洞壁干扰分布。讨论了为扩大二元柔壁自适应壁风洞中进行飞机模型试验时的无干扰区，较合适的试验段宽高比。用两个翼身组合体模型，在西北工业大学高速二元柔壁自适应风洞中作了变试验段宽高比为Ｂ／Ｈ＝１．０，１．２，１．４时的测压试验。两个模型都在德国宇航院ＨＫＧ高速风洞中作了对比试验，研究结果表明，Ｂ／Ｈ＝１．４的柔壁试验段截面较为合适。     

Model analysis of box culverts subjected to highway loading

The strain distribution and the deflections of reinforced-concrete box culverts associated with highway loading are determined by testing scale models. Two types of scale models were constructured: 1/6-size concrete models and a 1/24-size photoelastic model. The concrete models were instrumented with electric-resistance strain gages, and the deflections were measured with dial indicators. Strain and deflection data due to live loading are compared with values from testing of prototypes. The results of testing indicate that box-culvert sections conforming to ASTM C 850 are overdesigned structurally. Testing of models of a redesigned box culvert indicates that they perform satisfactorily. Paper was presented in the Proceedings of the 1988 SEM Conference on Experimental Mechanics held in Portland, OR on June 5–10.     

基于基因表达式编程的数据驱动湍流建模

计算流体动力学是湍流研究的重要手段, 其中雷诺平均模拟在航空航天等实际工程中得到了广泛应用. 雷诺平均模拟的结果很大程度上依赖于湍流模型的预测精度, 而实际工程应用中常用的模型往往精度有限. 近年来, 数据驱动的湍流建模方法得到越来越多的关注. 本文介绍了基于基因表达式编程 (gene-expression programming, GEP) 方法的湍流建模相关进展. 本文首先讨论基因表达式编程应用于湍流建模的具体方法, 包括基本算法、显式代数应力模型和湍流传热两种建模框架、模型测试方法以及损失函数设置等. 在此基础上, 基因表达式编程方法被应用于涡轮叶栅尾流混合、竖直平板间自然对流、三维横向流中的射流等问题. 结果表明, GEP可以有效提升常用模型对于尾流混合损失、壁面热通量等关键参数的预测精度. 基因表达式编程方法可以显式给出模型方程, 因此模型具有可解释性强等特点. 基于双向耦合方法得到的模型还被证明具有较好的后验测试精度和鲁棒性. 基因表达式编程方法还被初步应用于大涡模拟亚格子应力和边界层转捩等问题的建模, 在不同湍流建模领域表现出很大的潜力.      

Advances in the embedded-strain-gage technique with an application to contact problems

Improvements in the embedded-strain-gage technique for the measurement of strains at internal points in models of machine components are described. A New measurement module permits an experimental determination of the strain in models of epoxy resin. By its construction, the centers of the rosettes may be accurately located in the model mold, before casting. A large number of gages may be embedded with accuracy in a systematic manner. Application to the study of rolling contact is discussed. The improved technique has permitted an accurate embedment of gages at 0.043 in. below the surface of a flat model of epoxy resin which is then pressed against a spherical model having a radsius of curvature machined to 75 in. A testing machine is described and preliminary test results are presented.     

The development of algebraic stress models using a novel evolutionary algorithm

This work presents developments to a novel evolutionary framework that symbolically regresses algebraic forms of the Reynolds stress anisotropy tensor. This work contributes to the growing trend in machine-learning for modelling physical phenomena. Our framework is shown to be computational inexpensive and produce accurate and robust models that are tangible mathematical expressions. This transparency in the result allows us to diagnose issues with the regressed formulae and appropriately make amendments, as we further understand the regression tools. Such models are created using hybrid RANS/LES flow field data and a passive solving of the RANS transport equations to obtain the modelled time scale. This process shows that models can be regressed from a qualitatively correct flow field and fully resolved DNS is not necessarily required. Models are trained and tested using rectangular ducts, an example flow genus that linear RANS models even qualitatively fail to predict correctly. A priori and a posteriori testing of the new models show that the framework is a viable methodology for RANS closure development. This a posteriori agenda includes testing on an asymmetric diffuser, for which the new models vastly outperform the baseline linear model. Therefore this study presents one of the most rigorous and complete CFD validation of machine learnt turbulent stress models to date.