Experimental considerations for steady state edge excavation under a constant cutting depth for a mortar specimen using a disk cutter bit

This paper aims to investigate experimentally steady state excavation performance under a constant cutting depth, especially the specific cutting energy of a disk cutter bit in the free edge part of a mortar specimen. Here, the tangential, lateral and normal forces acting on a disk cutter bit having three tip angles and the amount of debris were measured for several cutting spaces and cutting depths. As a result, it was observed that the specific cutting energy, i.e. the ratio of the excavation power of the disk cutter bit to the amount of debris, showed a minimum value of the ratio of cutting space to cutting depth of five, at which ratio the most efficient excavation could be attained.     

基于OpenMP的三维显式物质点法并行化研究

基于OpenMP技术开发了三维显式物质点并行程序MPM3DMP。为了避免节点更新阶段的数据竞争,采用区域分解法将背景网格分解为均匀的子域,每个线程负责一个子域的节点变量更新,然后将更新后的节点变量装配到整体。在质点更新阶段采用了循环分解方法进行并行。针对Taylor杆碰撞的三种计算模型,在双Intel Woodcrest 4核CPU服务器下进行了测试:粗模型在4核下加速比为3.82,在8核下为6.23,中模型在4核下加速比为3.79,在8核下加速比为6.23;细模型在4核下加速比为3.75,8核下加速比为6.26。因此,本文的并行程序具有较好的并行效率和可扩展性。     

On the motion of a material point on a moving surface

Summary Sufficient conditions are given for the stability and instability of the equilibrium position x=y=z=0 in the mechanical system consisting of a material point constrained to move on the moving surface z=−λ(t)(x²+y²) (λ(t)>0) in a constant field of gravity (the axis 0z is directed vertically upward) under the action of viscous friction of total dissipation.

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Sommario Si danno condizioni sufficienti per la stabilità e la instabilità della posizione di equilibrio x=y=z=0 nel sistema meccanico che consiste di un punto materiale vincolato a muoversi sulla superficie mobile z=−λ(t)(x²+y²) (λ(t)>0) in un campo di gravità costante (l'asse 0z è diretto verticalmente e orientato verso l'alto) sotto l'azione di attriti viscosi con dissipazione completa.

     

Solving time‐dependent PDEs using the material point method,a case study from gas dynamics

The material point method (MPM) developed by Sulsky and colleagues is currently being used to solve many challenging problems involving large deformations and/or fragementations with some success. In order to understand the properties of this method, an analysis of the considerable computational properties of MPM is undertaken in the context of model problems from gas dynamics. The MPM method in the form used here is shown both theoretically and computationally to have first‐order accuracy for a standard gas dynamics test problem. Copyright © 2009 John Wiley & Sons, Ltd.     

Oscillatory regimes of the complex motion of a material point in a variable mass

S. P. Timoshenko Institute of Mechanics, National Academy of Sciences of the Ukraine, Kiev. A. Navoi Samarkand University, Republic of Uzbekistan. Translated from Prikladnaya Mekhanika, Vol. 31, No. 4, pp. 59–64, April, 1995.     

Nonlinear 3D vibrations of a heavy material point on a spring at resonance

We consider the problem of nonlinear 3D vibrations of a heavy material point suspended on a weightless spring at a 1:1:2 frequency resonance. To construct an asymptotic solution, we use the Hamiltonian normal form method. Just as in the plane problem, this asymptotic solution describes the periodic process in which the vertical vibration energy passes into the horizontal vibration energy. For an arbitrarily small nonzero angular momentum with respect to the vertical axis, an effect typical of 3D systems manifests itself. The projection of the trajectory of the point onto the horizontal plane (xy) is an ellipse of constant area with axes varying in time. For certain initial conditions, the ellipse almost degenerates into straight-line segments. The direction of the straight line does not vary on the time interval where the vibration energy is in the horizontal mode and then varies almost by a jump on the interval where the vibration energy is transferred into the vertical mode. The analytic results are in good agreement with numerical solutions of equations of motion of the system.     

Impact of a hydroabrasive jet on material: Hydroabrasive wear

The wear of steel plates under the impact of a hydroabrasive jet was studied experimentally by varying the distance between the sample surface and the nozzle, the angle of impingement of the jet on the plate, and the abrasive concentrations in water and in the ambient medium (jet in air, submerged jet). The results are compared with available data on the structure of the jet and jet flow around an obstacle. It is shown that the addition of abrasive particles to the liquid can be used to study the liquid jet flow around an obstacle because the form of surface wear allows one to determine the region of impact of the jet core, the deceleration region, and the near-wall flow region before flow separation.     

Optimal impulse space trajectories of a material point in the field of two bodies

Kiev Civil Engineering Institute. Translated from Prikladnaya Mekhanika, Vol. 26, No. 9, pp. 102–109, September, 1990.     

无网格MPM法三维前处理系统设计

无网格法在解决爆炸冲击、裂纹扩展、高速碰撞以及大变形等问题时,由于与网格无关,能够避免有限元法因网格畸变计算精度降低或计算终止的矛盾,是目前求解固体力学问题的有效方法之一,也是近年来研究的热点。前处理对于无网格法数值计算是非常重要的环节,基于面向对象程序设计思想,应用C 和OpenGL开发了三维图形交互方式的MPM法前处理系统,提出了应用递归四叉树法、扫描表示法和CSG法划分任意形状非等间距的MPM法质点单元,为建立通用的无网格前处理平台提出了有效的解决方案。     

Instantaneous pressure and material acceleration measurements using a four-exposure PIV system

This paper describes a non-intrusive technique for measuring the instantaneous spatial pressure distribution over a sample area in a flow field. A four-exposure PIV system is used for measuring the distribution of material acceleration by comparing the velocity of the same group of particles at different times and then integrating it to obtain the pressure distribution. Exposing both cameras to the same particle field at the same time and cross-correlating the images enables precision matching of the two fields of view. Application of local image deformation correction to velocity vectors measured by the two cameras reduces the error due to relative misalignment and image distortion to about 0.01 pixels in synthetic images. An omni-directional virtual boundary integration scheme is introduced to integrate the acceleration while minimizing the effect of the local random errors in acceleration. Further improvements are achieved by iterations to correct the pressure along the boundary. Typically 3–5 iterations are sufficient for reducing the incremental mean pressure change in each iteration to less than 0.1% of the dynamic pressure. Validation tests of the principles of the technique using synthetic images of rotating and stagnation point flows show that the standard deviation of the measured pressure from the exact value is about 1.0%. This system is used to measure the instantaneous pressure and acceleration distributions of a 2D cavity turbulent flow field and sample results are presented.     

Three-dimensional quasi-static Green's function for an infinite transversely isotropic pyroelectric material under a step point heat source

Based on the three-dimensional quasi-static general solution of the transversely isotropic pyroelectric material, the Green's function for an infinite transversely isotropic pyroelectric material under a step point heat source is presented in this paper. Firstly, a suitable function with an undetermined constant is constructed. Secondly, the Green's function can be obtained by substituting this function into the general solution. The undetermined constant can be determined by the heat conservation equation. Finally, the numerical results are shown in form of contours at the different times.     

Experimental study of underwater rock drilling using a pulsed Ho:YAG laser-induced jets

This paper is primarily an assessment of laser-induced water jets for boring rock surfaces. It also reports the result of preliminary experiments of pulsed Ho:YAG laser-induced jets applied to drill a submerged rock specimen. The irradiation of pulsed Ho:YAG laser beams at 3 Hz inside a thin metal tube produces intermittent water vapor bubbles which result in liquid jet discharge from the exit of the metal tube. The laser-induced water jets are visualized by shadowgraphs and images are recorded by a high-speed digital video camera. High stagnation pressures were eventually generated by the jet impingements. Simultaneously shock waves of about 22.7 MPa were generated at bubble collapse, which effectively cracked the surface of the rock specimens. Repeated exposures of these laser-induced jets against submerged rock specimens have a potential to practically bore holes on rock surfaces.     

Analysis of a three-dimensional dissimilar material joint with one real singularity using a conservative integral

In the present study, a conservative integral based on the Betti reciprocal principle is formulated to determine the intensity of singularity at a vertex of the interface in three-dimensional dissimilar material joints with one real singularity. Eigenanalysis formulated using a three-dimensional finite element method (FEM) is used to calculate the order of stress singularity, angular functions of displacements and stresses. Models with various element sizes and various integral areas are used to investigate the effect of the integration area on the accuracy of the results. The results are compared with those obtained from the boundary element method (BEM) using a curve-fitting technique to calculate the intensity of singularity. In addition, models of various lengths and various material combinations are used to investigate the stress singularity characteristics in three-dimensional dissimilar material joints. The results of the present study indicate that the conservative integral can be used to determine the intensity of singularity in three-dimensional bi-material joints. The accuracy of the results can be improved by mesh refinement. Finally, the relationships among the intensity of singularity, the order of stress singularity and the model geometry are discussed.     

Determining plastic properties of a material with residual stress by using conical indentation

Instrumented indentation is a popular method for determining mechanical properties in engineering materials. However, there are several shortcomings and challenges involved with correctly interpreting the test results. We propose here a unified method for evaluating instrumented indentation testing conducted on a material that exhibits both strain hardening under yielding and which is subjected to uniform, equi-biaxial residual stresses. The proposed method is based on extensive finite element simulations that relate the parameter-space spanned by Young’s modulus, yield strength, strain hardening and residual stress, to the response from the indentation test. Based on reverse analysis, the proposed method can be used to determine two unknown quantities, such as yield strength and strain hardening. The technique involves utilizing the concept of representative strain and plural indenter-shapes.     

Microfluidic-based single cell trapping using a combination of stagnation point flow and physical barrier

Single cell trapping in vitro by microfluidic device is an emerging approach for the study of the rela-tionship between single cells and their dynamic biochemical microenvironments. In this paper, a hydrodynamic-based microfluidic device for single cell trapping is designed using a combination of stagnation point flow and physical barrier. The microfluidic device overcomes the weakness of the tra-ditional ones, which have been only based upon either stag-nation point flows or physical barriers, and can conveniently load dynamic biochemical signals to the trapped cell. In addi-tion, it can connect with a programmable syringe pump and a microscope to constitute an integrated experimental system. It is experimentally verified that the microfluidic system can trap single cells in vitro even under flow disturbance and con-veniently load biochemical signals to the trapped cell. The designed micro-device would provide a simple yet effective experimental platform for further study of the interactions between single cells and their microenvironments.     

The measurement of the material parameters of viscoelastic fluids using a rotating sphere and a rheogoniometer

Summary In this work, measurement of the flow field around a rotating sphere has been used to obtain the material parameters of a second-order Rivlin-Ericksen fluid. Experiments were carried out with a Laser-Doppler anemometer to obtain the velocity distribution and usingGiesekus' analysis, the material parameters for the second-order fluid were obtained.

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Zusammenfassung In dieser Untersuchung wird die Ausmessung des Strömungsfeldes um eine rotierende Kugel dazu verwendet, um die Stoffparameter einer Rivlin-Ericksen-Flüssigkeit zweiter Ordnung zu erhalten. Die Experimente zur Bestimmung der Geschwindigkeitsverteilung werden mit einem Laser-Doppler-Anemometer durchgeführt, und zur Auswertung der Parameter der Flüssigkeit zweiter Ordnung wird eine Analyse vonGiesekus benutzt.

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Notations A ₁,A₂ Rivlin-Ericksen tensor - A ² Parameter used in eq. [12] - a Radius of the sphere - B Parameter used in eq. [12] - I Unit tensor - m ₀(₁ – ₂)/a², parameter used by ref. (8) - N ₁,N₂ First and second normal stress difference - p Isotropic pressure - Radial distance from the centre of the rotating body - S ₁,S₂ Stress tensor - v _r,v,v Velocity components in a spherical coordinate system - ₀,₁,₂ Material parameters used in eq. [2] - Shear rate - _a Apparent voscosity - ₀ Zero-shear viscosity - Angle measured from the axis of rotation - Fluid density - Stream function - Shear stress - Angular velocity With 3 figures     

Optimal control of material concentration using Fourier series

This paper presents an optimal control of the material concentration using Fourier series and finite element method. It is assumed that the optimal control value can be expanded into a Fourier series. The Fourier coefficient is identified to minimize the performance function and the optimal control value is determined. The Sakawa–Shindo algorithm is used for the minimization algorithm. The advection–diffusion equation and shallow water equation are used for the analysis of material concentration and water flow. The Crank–Nicolson scheme and finite element method using bubble function element with stabilized control parameter are employed as temporal and special discretization. Copyright © 2004 John Wiley & Sons, Ltd.