Optimization and numerical investigation of an excavator carrier

The excavator carrier is a device for moving the excavator. There are many operational benefits in using this carrier to transport excavators safely, easily, and efficiently. An earlier model of this carrier is manufactured and in tests showed that the design needs to be improved. In this paper, a finite element method is used to model and analyze this carrier and optimize the design for better performance. The static and dynamic analysis is done to optimizing carrier design for removing the defect that identified in practical test. The goal of optimization is to increase the carrier's life, increase the safety of transportation, decrease the cost, and finally, commercialize the product. The results show that the carrier's weight is decreased by up to 30%. Also, a holder and lock system in the back of the carrier is designed for increasing the transportation safety and the stiffness of the carrier chassis. The effect of increasing a suspension system is studied, the idea is using leaf spring. The numerical results show that using the suspension system increases the carrier's life by up to 30% while adding a suspension system increases manufacturing costs by up to 10%.     

Design of aluminium boom and arm for an excavator

The aim of this work is to study the boom and the arm of an excavator in order to replace the material, which they are usually made of, with another material. In particular, the study wants to substitute the steel alloy for an aluminium alloy. This change lightens the components of the arm, allows to increase the load capacity of the bucket and so it is possible to increase the excavator productivity per hour.For this purpose many different load conditions have been studied numerically on the original excavator in order to estimate a safety factor and the deformability or flexibility of each component. These parameters have been used in order to design a new arm.The excavator which has been analyzed is composed of three elements and the load conditions assumed, in order to evaluate the stress, are five (lifting at the maximum and minimum distance from the axis of rotation, maximum load induced by hydraulic cylinders, spin of the arm of the excavator and collision with an obstacle, etc.).As regards to the safety factor and deformability in order to maintain the original value the new geometry of the arm involves an increase of the dimension and so the lightness is not correlate only to the variation of the material density.The weight of the final geometry of the aluminium arm is 1080 kg whereas the one of the steel arm is 2050 kg and consequently it has been possible to increase the capacity of bucket from 1 m³ to the 1.35 m³.With reference to the manufacturing cycle of the aluminium arm with the new pins, the price increased about € 2.500-3.000 and this aspect could be justified if we consider that the productivity per hour increased about 35%.     

Dynamic modeling of marine boilers

Experimental investigation was performed on a simplified scale model of a typical marine boiler. Shaker-table tests were performed to determine natural frequencies, and impact tests were used to determine the structural shock response. The dynamic-response data have been used to verify analytical results obtained from a three-dimensional, beam-element model with the consideration of local flexibility at the nozzle-vessel intersections.     

Convective instability of an adsorption front

The monotonous instability of the adsorption front formed in a two-component gas filtered vertically through a fixed bed of adsorbent is demonstrated. A threshold value of the Archimedes adsorption criterion is calculated and the corresponding critical gas flow is considered.     

The flow structure in the front of a moving surface layer

Summary Behind the frontal wedge of a moving surface layer there is a zone of entrainment in which the flow is turbulent due to the onset of a Kelvin-Helmholtz instability. The entrainment coefficient is inversely proportional to the Richardson number. In the turbulent region the gradient Richardson number approached a constant value less than 1/4. The layer thickness and the mean velocity depend on the salt concentration of the underlying fluid. Finally the turbulence decayed leaving a stable interface and the layer behaved much like a free homogeneous flow over a solid boundary.

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Übersicht Hinter der keilförmigen Front einer fließenden Schicht gibt es eine Mischungszone, in der die Strömung turbulent ist. Die Turbulenz entsteht durch eine Kelvin-Helmholtz Instabilität. Der Ansaugbeiwert der turbulenten Strömung verhält sich umgekehrt zur Richardsonschen Zahl. In der turbulenten Strömung nähert sich die Richardsonsche Zahl einer konstanten Zahl kleiner als 1/4. Die Dicke und die mittlere Geschwindigkeit der Schicht hängt sehr von der Dichte der unteren Flüssigkeit ab. Schließlich stirbt die turbulente Strömung ab, und die Schicht fließt wie eine homogene Strömung längs einer ebenen Platte.

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The work described herein was carried out as part of a research programme of the Hydraulics Research Station, and the paper is published by permission of the Director of Hydraulics Research. The author wishes also to express his thanks to Mr. J. A. Weller for his help in measurement, and to a referee for his helpful comments.     

Electric structure of the combustion front in a homogeneous methane-air mixture

The electric structure of a plane laminar flame propagating through a homogeneous methane-air mixture in the absence of an external electric field is considered. The charged particle concentration and self-electric field distributions in the flame are found. The possibility of the ion-molecular reactions affecting the normal flame propagation velocity is estimated. Moscow. Translated from Izvestiya Rossiiskoi Akademii Nauk, Mekhanika Zhidkosti i Gaza, No. 1, pp. 3–7, January–February, 1998.     

大型渡槽动力建模研究

根据渡槽系薄壁杆件结构的特点,提出了渡槽薄壁结构空间动力分析模型。采用空间梁段单元进行离散,考虑渡槽横向、竖向、纵向、自由扭转和约束扭转变形,由能量原理推导给出了渡槽槽身结构的单元刚度矩阵、质量矩阵的显示表达式;渡槽支架采用空间梁单元模拟;渡槽支架与槽身联贯的盆式橡胶支认采用弹性元件单元模拟。文中具体计算了某大型渡槽的模态,计算结果表明：该模型计算渡槽结构的固有频率与理论解和用大型结构分析程序SAP计算的结果良好接近。本文模型计算简单,使用方便,是大型渡槽动力分析的实用模型。     

Wave propagation in an elastic structure modeling a split Hopkinson pressure bar

The Laplace transform with respect to time is used to study the problem of loading wave propagation in a composite elastic structure modeling a split Hopkinson pressure bar. Experiments were performed to compare the theoretical and experimental results. The obtained results can be used as a basis for justifying the split Hopkinson pressure bar technique.     

Approximate modeling of an elastic structure according to test data with various confidences

In this paper, an elastic structure model is constructed according to the test data with various confidences and properly selected analytical parameters (mass matrixM or stiffness matrixK). First, the modeling method is described, and second, the uniqueness of the result is strictly proved. Finally, a numerical example is given to show the reasonableness of this method and the superiority of the result to that in reference [4].     

Dynamic modeling of preloaded size-dependent nano-crystalline nano-structures

The vibration behavior of size-dependent nano-crystalline nano-beams is investigated based on nonlocal, couple stress and surface elasticity theories. A nanocrystalline nano-beam is composed of three phases which are nano-grains, nano-voids,and interface. Nano-voids or porosities inside the material have a stiffness-softening impact on the nano-beam. A Eringen's nonlocal elasticity theory is applied in the analysis of nano-crystalline nano-beams for the first time. Residual surface stresses which are usually neglected in modeling nano-crystalline nano-beams are incorporated into nonlocal elasticity to better understand the physics of the problem. Also, a modified couple stress theory is used to capture rigid rotations of grains. Applying a differential transform method(DTM) satisfying various boundary conditions, the governing equations obtained from the Hamilton's principle are solved. Reliability of the proposed approach is verified by comparing the obtained results with those provided in the literature. The effects of the nonlocal parameter, surface effect, couple stress, grain size, porosities, and interface thickness on the vibration characteristics of nano-crystalline nano-beams are explored.     

地下防护结构在冲击载荷作用下的动态破坏过程

通过数字高速摄影技术和动态电测技术,对马蹄形地下防护结构在冲击载荷作用下的动态破坏过 程进行了缩比模型实验研究。结果表明,底部是整个马蹄形结构最为脆弱的部分,需要重点防护。在结构内 层加装钢板或其他高强度防护材料会显著提高该种结构的抗冲击能力。结构的破坏是一个动态累积的过程, 而材料的抗拉强度直接影响这类结构的抗毁伤能力。通过获得的实验数据验证了采用LS-DYNA 有限元软 件对于地下防护结构在冲击载荷作用下破坏过程进行研究的可行性和准确性。     

Effect of initial disturbance on the detonation front structure of a narrow duct

The effect of an initial disturbance on the detonation front structure in a narrow duct is studied by three-dimensional numerical simulation. The numerical method used includes a high-resolution fifth-order weighted essentially non-oscillatory scheme for spatial discretization, coupled with a third-order total variation diminishing Runge-Kutta time-stepping method. Two types of disturbances are used for the initial perturbation. One is a random disturbance which is imposed on the whole area of the detonation front, and the other is a symmetrical disturbance imposed within a band along the diagonal direction on the front. The results show that the two types of disturbances lead to different processes. For the random disturbance, the detonation front evolves into a stable spinning detonation. For the symmetrical diagonal disturbance, the detonation front displays a diagonal pattern at an early stage, but this pattern is unstable. It breaks down after a short while and it finally evolves into a spinning detonation. The spinning detonation structure ultimately formed due to the two types of disturbances is the same. This means that spinning detonation is the most stable mode for the simulated narrow duct. Therefore, in a narrow duct, triggering a spinning detonation can be an effective way to produce a stable detonation as well as to speed up the deflagration to detonation transition process.     

Shock wave front from an underground explosion

Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, No. 6, pp. 23–30, November–December, 1991.