Tractive performance and compaction effect of a road roller running on a weak sandy soil

This study aims to investigate the tractive performance of a two-axle, two-wheel vehicle with rear-wheel drive or brake and the compaction of a decomposed granite soil. The effects of traction or braking, the change of sinkage, the slip ratio of the front and rear roller, and the number of passes of the road roller were studied. A number of tests were conducted and the experimental data were compared with the theoretical analysis results. It was observed that the amount of sinkage on the front and rear roller took the minimum value when the front roller was in the unpowered rolling state and the slip ratio of the rear roller was almost zero. When the absolute value of the slip ratio of rear roller increased, the amount of sinkage on the front and rear rollers, the absolute value of the driven or braking force of the rear roller and the absolute value of effective tractive or braking effort of the road roller increased. When the front roller was in the unpowered rolling state and the rear roller was in the braking state at −5% skid, the compaction density of the soil was at a maximum.     

Tractive performance of a driven rigid wheel on soft ground based on the analysis of soil-wheel interaction

A new analytical method has been presented to predict the tractive performance of a rigid wheel running on soft ground. The resultant stress of the normal stress and the shear resistance applied around the peripherical contact part of the rigid wheel should be calculated by use of the dynamic pressure-sinkage curve measured from the plate loading and unloading test, considering the rolling locus of the wheel in the direction of the external resultant force of the effective driving force and the axle load. The effective driving force could be calculated as the difference of the driving force, i.e. the integration of shear resistance and the locomotion resistance calculated from the total amount of sinkage. As a result, the analytical relations between the driving force, the effective driving force and the slip ratio, the amount of sinkage and the slip ratio, the amount of eccentricity of resultant force and the slip ratio, and the entry angle, the exit angle and the slip ratio could be verified experimentally.     

Tractive and braking performance of a flexible tracked tractor moving up and down weak sloped terrain

The objective of this study is to analyse the tractive and braking performance of a tractor travelling up and down a weak silty loam sloped terrain. The effects of track belt size on terrain-track system parameters were investigated experimentally, and the force and energy balances were clarified for the actual flexible tracked vehicle. The flexibility of the track belt has been precisely analysed as a function of track tension, loading and reloading properties of terrain, and contact pressure distributions. The results show that the optimum effective driving (or braking) force decreases with the increase of slope angle due to the decreasing vehicle weight component, while the thrust (or drag) decreases and the compaction resistance increases. The contact pressure distribution under the flexible track belt shows a triangular wavy pattern having peak values under each track roller. The shear resistance distribution has positive and negative peak values for the driving and braking states, respectively.     

Tractive performance of a tread design for improved flexibility

The tractive performance of an 18.4R38 radial-ply tractor tire with increased flexibility in the tread area was compared to that of a standard tread design. Normal soil-tire interface stresses were measured at four locations on the lug surfaces of both tires operating on Decatur clay loam and Norfolk sandy loam soils. There was a tendency for the increased flexibility in the tread area to provide a higher net traction ratio at the same tractive efficiency as the standard tread design, especially on Decatur clay loam soil. The more flexible tread design reduced the magnitude of peak normal contact stresses across the tire width, which may have implications for reducing soil compaction without compromising tractive performance. The more flexible tire reduced the average normal contact stress by approximately 15% in the sandy loam soil and 23% in the clay loam soil for the range of operating conditions investigated.     

Tractive performance analysis of a lugged wheel by open-source 3D DEM software

Open-source software (OSS) is free to use and has accessible source codes, thus, it can be modified by various users. By using OSS, it is possible to easily and economically develop a target program for interaction studies in terramechanics. Yet Another Dynamic Engine (YADE) is an OSS for the 3D discrete element method (DEM), but its applicability to various contact interaction problems in terramechanics is not well-known. To investigate the applicability of YADE in terramechanics, the tractive performance of a lugged wheel was analyzed in this study. An idea of a proportional-integral-differential control model was applied to realize the constant rotation of the wheel in YADE. Our previous experiments on the locomotion of a small lugged wheel on a lunar-soil simulant were analyzed by YADE, and the results were found to be qualitatively similar to the obtained experimental results when considering the effects of the lug height, lug thickness, lug number, and wheel diameter. By applying a quasi-2D analysis with the same soil bin width and wheel width, the computational load of 3D DEM by YADE can be reduced up to 36.8% with similar net traction behavior against the wheel slip in a 3D analysis.     

Travelling performance of a wheel on a finite thickness ground

Off-road terrain can often be regarded as a finite thickness ground consisting of a soft soil layer on a rigid base. Experiments for the traveling performance of a wheel in a dense sand layer on a rigid base revealed that as the soil layer thickness decreases under the condition of high constant slip, the drawbar pull does not increase monotonically but increases gradually to a maximal value, then decreases to a minimal value, and thereafter again increases rapidly to the highest value at zero soil layer thickness. The mechanical interpretation of the relationship between the drawbar pull and the soil layer thickness is given qualitatively from the aspects of the shear characteristics of dense sand and the rigid-body friction between the wheel and the rigid base of the soil layer. It is indicated that the relationship takes the same form as van der Waals' state equation for the pressure and the volume of an imperfect gas with a phase transition between gas and liquid. The equation representing the relationship of the drawbar pull to the soil layer thickness is proposed in accordance with van der Waals' equation.     

Analytical formulation of 2-D aeroelastic model in weak ground effect

This paper deals with the aeroelastic modeling and analysis of a 2-D oscillating airfoil in ground effect, elastically constrained by linear and torsional springs and immersed in an incompressible potential flow (typical section) at a finite distance from the ground. This work aims to extend Theodorsen theory, valid in an unbounded flow domain, to the case of weak ground effect, i.e., for clearances above half the airfoil chord. The key point is the determination of the aerodynamic loads, first in the frequency domain and then in the time domain, accounting for their dependence on the ground distance. The method of images is exploited in order to comply with the impermeability condition on the ground. The new integral equation in the unknown vortex distribution along the chord and the wake is solved using asymptotic expansions in the perturbation parameter defined as the inverse of the non-dimensional ground clearance of the airfoil. The mathematical model describing the aeroelastic system is transformed from the frequency domain into the time domain and then in a pure differential form using a finite-state aerodynamic approximation (augmented states). The typical section, which the developed theory is applied to, is obtained as a reduced model of a wing box finite element representation, thus allowing comparison with the corresponding aeroelastic analysis carried out by a commercial solver based on a 3-D lifting surface aerodynamic model. Stability (flutter margins) and response of the airfoil both in frequency and time domains are then investigated. In particular, within the developed theory, the solution of the Wagner problem can be directly achieved confirming an asymptotic trend of the aerodynamic coefficients toward the steady-state conditions different from that relative to the unbounded domain case. The dependence of flutter speed and the frequency response functions on ground clearance is highlighted, showing the usefulness of this approach in efficiently and robustly accounting for the presence of the ground when unsteady analysis of elastic lifting surfaces in weak ground effect is required.     

中间弱层对层合板性能影响分析

对于夹胶玻璃等结构,由于中间胶层很弱,层合板结构的层间剪切效应占主导地位。此时经典层合板理论以及整体高阶剪切位移场理论所预测的结果可能导致很大的实际误差,应采用更加精细的力学模型来分析弱层的效应。本文建立了分层位移场假设下的浅柱面层合板静力计算模型以及自振周期计算模型,并同经典层合板理论计算结果对比,分析了中间层的剪切模量、弹性模量、层合板曲率半径对层间剪切效应的影响。计算结果表明:中间层的剪切模量对层合板的受力性能有着决定性的影响,相对来说中间层的弹性模量对层合板性能的影响不太显著;当中间层与面层的剪切模量比值小于0.2时,随着中间层剪切模量的减小,两个模型的计算误差急剧增大。     

地冲击下新型脆断构件防护性能实验研究

为对地冲击作用下地下结构进行有效防护,提出一种泡沫混凝土材质的新型防护构件。与使用实心泡沫混凝土层的防护机理不同,本文中提出的构件在地冲击作用下,首先发生脆断破坏,然后破碎块体间搭接折断、挤压密实。通过构造设计,截断地冲击荷载,减弱荷载传递,改变被保护结构上的荷载形式。通过场地爆炸实验对比了不同防护措施下（无防护、实心泡沫混凝土层防护及新型构件防护）被保护结构的动力响应。实验结果表明：新型构件防护通过脆断、破碎块体的搭接、挤压密实表现出较实心泡沫混凝土层防护更好的防护效果;新型构件防护由于脆断特性,在较小荷载下即可显著削弱荷载传递,避免了实心泡沫混凝土层防护中负效果的出现;地冲击荷载较强时,构件防护层趋于压实,其防护效果逐渐接近实心泡沫混凝土层。

     

An experimental study on the thermal performance of ground heat exchanger

A knowledge of ground thermal properties is most important for the proper design of large GHE (ground heat exchanger) systems. Thermal response tests have so far been used primarily not only for in situ determination of design data for GHE systems, but also for the evaluation of grout material, heat exchanger types and groundwater effects. The main purpose has been to determine in situ values of effective ground thermal conductivity, including the effect of groundwater flow and natural convection in boreholes.     

Tractive rolling contact mechanics of graded coatings

In this study, the tractive rolling contact problem between a rigid cylinder and a graded coating is investigated. The main objective of this study is to investigate the effect of the stiffness ratio, the coefficient of friction and the coating thickness on the surface contact tractions, the surface in-plane stress, the stick zone length and the creep ratio parameter that may have a bearing on the fatigue life of the component. Assuming that the shear modulus varies exponentially through the thickness of the coating, the governing integral equations associated with the rolling contact problem are constructed. Furthermore, it is supposed that the contact patch is controlled by a central stick zone accompanied by two slip zones. The conventional Goodman approximation is employed in order to decouple the governing singular integral equations. Finally, the numerical solution of the integral equations is obtained by applying the Gauss–Chebyshev integration method.     

Tractive characteristics of radial ply and bias ply tyres in a California soil

Four tyres (18.4-38, 18.4R38, 14.9-28, 14.9R28) were tested using the UCD single wheel traction tester. Each tyre was tested at two different inflation pressures and three different vertical loads at each inflation pressure. All tests were conducted in a well tilled Yolo loam soil. A dimensional analysis procedure was used to design and analyse the experiment. Two models were considered: (A) using inflation pressure as a variable, and (B) using tyre deflection as a variable. The effect of tyre type, tyre size, tyre inflation pressure and dynamic load on (1) net traction ratio at 20% slip and (2) average tractive efficiency in the 0–30% slip range were investigated using an ANOVA technique. An estimate of the possible energy savings due to the use of radial ply tyres instead of bias ply tyres in California agriculture was made.     

Effects of non-smooth characteristics on bionic bulldozer blades in resistance reduction against soil

The phenomenon of soil adhesion occurs widely when terrain machines and construction machines work; this adhesion increases their working resistance. Bionics is one of the most effective methods to reduce resistance against soil. Several non-smooth convex form bulldozer blades were tested to study the effects of non-smooth characteristics on resistance reduction against soil. Under the same soil and test conditions, the draft forces of different non-smooth samples were obtained, and were lower than those of smooth samples. The sample with largest convex base diameter had the lowest draft force. The experiments with smooth and non-smooth samples were repeated to observe soil adhesion and test resistance. A minimum amount of soil adhered to the surface of the non-smooth sample, and the draft force varied smoothly. The smooth sample was different in soil adhesion and draft force.     

Numerical modelling and flow analysis of a centrifugal pump running as a turbine: Unsteady flow structures and its effects on the global performance

The purpose of this paper is to investigate the flow patterns in a centrifugal pump when it works as a centripetal turbine, with special interest in the unsteady behavior in order to explain the shape of the performance curves. Also, we focus on the determination of the radial thrust and other mechanical loads over a pump‐designed machine. The pump studied is commercial, with single axial suction and a vaneless spiral volute casing. A numerical study has been carried out in order to obtain more information about the flow into the volute and the impeller. A numerical three‐dimensional unsteady simulation has been developed using a commercial code that solves the URANS set of equations with a standard k–ε turbulence model. The results show the non‐axisymmetric flow developed in the volute, responsible for a significant radial thrust; the interaction between the tongue and the impeller, generating force fluctuations; the velocity and pressure distributions inside the impeller; and the exit flow, characterized with post‐rotation and low‐pressure. These flow results allow us to understand the behavior of the machine by comparing it with the pump mode. Complementarily, an experimental study was conducted to validate the numerical model and characterize the pump‐turbine performance curves at constant head. Fast‐response pressure taps and a three‐hole pneumatic pressure probe were employed to obtain a complete data set of non‐stationary and stationary measurements throughout the centrifugal machine. As a result, loss of efficiency or susceptibility to cavitation, detected numerically, was confirmed experimentally. The study demonstrates that the numerical methodology presented here has shown its reliability and possibilities to predict the unsteady flow and time‐mean characteristics of centrifugal pumps working as turbines. In particular, it is shown that the commercial design of the pump allows a reasonable use of the impeller as a turbine runner, due to the suitable adaptation of the inflow distributions to the volute casing. Moreover, the efficiency for the inverse mode is shown to be as high as achieved for the pumping operational mode. In addition, it is concluded that both axial and radial thrusts are controlled, though important unsteady fluctuations—up to 25%—clocked with the blade passing frequency appear beyond the nominal conditions. In that case, a moderate use of the pump as a turbine is recommended in order to minimize risks of fatigue failure of the bearings. Copyright © 2009 John Wiley & Sons, Ltd.     

Theory of weak turbulence of waves on a fluid surface

The nonlinear interaction of waves in a fluid of finite depth is discussed. Forbidden decay processes in the gravitational portion of the spectrum are eliminated from the Hamiltonian by means of a canonical transformation. This provides an opportunity to obtain a kinetic equation which takes into account scattering of capillary waves by gravitational waves, in addition to decays in the subsystem of gravitational waves. The distribution N_k P^1/2h^1/4k^–4 is obtained for capillary waves in shallow water with constant flow of energy P with respect to the spectrum in the space of the wave numbers k. The interaction of the gravitational and capillary turbulence spectra is discussed. An induced distribution of gravitational waves is found which results from their interaction with capillary waves. It is an increasing function of the wave numbers q in the region bounded by the capillary constant k_o, N_q q^9/4 (q < k_o). The coupling of spectra in the gravitational and capillary regions and the conversion from slightly turbulent distributions to universal distributions are discussed.Translated from Zhurnal Prikladnoi Mekhaniki i Tekhnicheskoi Fiziki, No. 6, pp. 97–106, November–December, 1974.     

3-D DEM simulation of cohesive soil-pushing behavior by bulldozer blade

A numerical simulation based on discrete element method (DEM) was conducted on the excavation and pushing processes of soil by a bulldozer blade. Soil contains water and the resistance acting on the bulldozer blade is largely influenced by the cohesive force due to liquid bridges formed among soil particles. In the present study, a cohesive bond force model proposed by Utili and Nova [5] was introduced in which the microscopic behavior of cohesive force was modeled analogously with macroscopic shear failure characteristics. The dependency on the magnitude of microscopic cohesive force was verified. The behavior of particles changed greatly by taking into account the cohesive bond force. The characteristic behavior of excavated soil aggregates, such as rolling motion and intermittent collapsing, were observed in front of the blade surface.     

On three dimensional transient wave motions on a running stream

Summary This paper considers the three-dimensional transient wave motions in a fluid produced by a moving oscillatory disturbance of frequency acting on the free surface of the fluid. The problem is treated as an initial value problem and is solved by the joint Laplace-Fourier transform method combined with the asymptotic treatment for the double Fourier inversion integrals. The explicit representation of the steady state as well as the transient solution of the problem is presented. It is shown that the ultimate steady is set up in the limit. A brief discussion on the principal behaviour of the wave motions is made.

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Sommario Si considerano i moti ondosi transitori tridimensionali prodotti in un fluido da una eccitazione oscillatoria, in movimento, di frequenza che agisce sulla superficie libera. Il problema è trattato come problema di valori iniziali e viene risolto con il metodo della trasformata congiunta di Laplace-Fourier combinata con il trattamento asintotico per gli integrali doppi di inversione di Fourier. Si espone la rappresentazione in forma esplicita della soluzione di regime e di quella transitoria. Si dimostra che la condizione finale di regime viene stabilita nel passaggio al limite. Si esegue una breve discussione del principale comportamento del moto ondoso.

     

Focusing of weak shock waves on a target in a parabolic chamber

Theoretical study of a weak shock focusing process in a confined chamber filled with liquid is presented. The chamber has a form of a thin cylinder with a parabolic cross-section, planar bottom and an arbitrary, although slowly varying, upper bounding surface. Analytical, numerical and experimental studies of weak shock wave focusing have been previously performed in the elliptic and ellipsoidal cases with a shock wave generated at one of the foci by means of an electric discharge or a microexplosion. In the present case a planar shock, perpendicular to the axis of the parabolic cross-section, sent in the inner of the chamber will converge at the focus after the reflection off the chamber wall, thus offering a different technical realization of the shock generation. The problem is solved within the frame of the geometrical acoustics approximation and a relation between the form of the upper bounding surface of the chamber and the pressure distribution behind the converging wavefront is obtained. It is shown that a desired pressure distribution may be obtained by an appropriate choice of the upper bounding surface.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.