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A computer model is constructed and numerical experiment is performed for the investigation of phenomenological regularities of contact melting. Adequate agreement is obtained with the results of real experiment. 相似文献
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Szymon Nosewicz Jerzy Rojek Marcin Chmielewski Katarzyna Pietrzak 《Advanced Powder Technology》2017,28(7):1745-1759
This paper presents the numerical and experimental analysis of hot pressing of NiAl powder with an emphasis on the best possible representation of its main stages: initial powder compaction and pressure-assisted sintering. The numerical study has been performed within the discrete element framework. In the paper, an original viscoelastic model of hot pressing has been used. In order to ensure that the applied values of material parameters in numerical simulations are appropriate, the reference literature has been reviewed. It produced the relations and equations to estimate the values of all required sintering material parameters of the considered viscoelastic model. Numerical simulations have employed the geometrical model of the initial dense specimen generated by a special algorithm which uses the real grain distribution of powder. The numerical model has been calibrated and validated through simulations of the real process of hot pressing of intermetallic NiAl material. The kinetics of compaction, sintering and cooling stage indicated by the evolution of density, shrinkage and densification rate have been studied. The comparison of numerical and experimental results has shown a good performance of the developed numerical model. 相似文献
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Jihoon Kim Eric L. Sonnenthal Jonny Rutqvist 《International journal for numerical methods in engineering》2012,92(5):425-456
We extend constitutive relations of coupled flow and geomechanics for the isothermal elastic double porosity model by Berryman [Journal of Engineering Mechanics ASCE 2002; 128(8):840–847] in the previous study to those for the nonisothermal elastic/elastoplastic multiple porosity model, finding coupling coefficients and constraints of the multiple porosity model and determining the upscaled elastic/elastoplastic moduli as well as relations between the local strains of all materials within a gridblock and the global strain of the gridblock. Furthermore, the coupling equations and relations between local and global variables provide well‐posed problems, implying that they honor the dissipative mechanism of coupled flow and geomechanics. For numerical implementation, we modify the fixed‐stress sequential method for the multiple porosity model. From the a priori stability estimate, the sequential method provides numerical stability when an implicit time‐stepping algorithm is used. This sequential scheme can easily be implemented by using a modified porosity function and its porosity correction. In numerical examples, we observe clear differences among the single, double, and multiple porosity systems, and the multiple porosity model can reflect the substantial heterogeneity that exists within a gridblock. We also identify considerably complicated physics in coupled flow and geomechanics of the multiple porosity systems, which cannot accurately be detected in the uncoupled flow simulation. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
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V. A. F. Costa 《Materialwissenschaft und Werkstofftechnik》2005,36(10):578-585
Diffusion is often used as the model for real diffusion phenomena, as well as the used approach for non‐diffusive phenomena, the latter due to its relative simplicity, to the existence of many mathematical tools to solve the resulting differential equations, and to its robustness if a numerical solution is to be obtained. When searching for the solution of a practical problem, the involved phenomena and processes are usually complex or/and the real phenomena is other than diffusion, and some comments need to be addressed if a diffusive model is adopted. This work concerns mainly on the author’s experience on the transport phenomena field (fluid dynamics and heat and mass transfer), including the numerical simulation of systems and processes, where the diffusive model is often used even to model non‐diffusive phenomena. It is thus a report of some ill‐answered questions that the author has experienced, related with the use of the diffusion model. Different ill‐answered questions, related with the diffusion modeling, in different fields or problems, could be equally founded. 相似文献
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型钢混凝土结构ANSYS数值模拟技术研究 总被引:15,自引:0,他引:15
采用ANSYS程序对6个型钢混凝土梁试件的受力性能进行非线性有限元数值分析,对型钢混凝土结构数值模拟中混凝土和钢材材料模型定义、有限元建模、钢筋单元生成及后处理等关键技术进行系统研究。着重对型钢混凝土粘结滑移性能的数值模拟技术进行了研究。采用由ANSYS程序单元库中非线性弹簧单元combination-39组成的三维连接单元模拟型钢混凝土在不同部位及不同方向上的界面相互作用,建议了非线性弹簧单元粘结力-滑移曲线与型钢混凝土粘结滑移本构关系的转换技术,并提出了生成非线性弹簧单元的实用方法。最终形成考虑粘结滑移的型钢混凝土数值模拟技术。型钢混凝土梁数值模拟结果与试验结果吻合较好,表明所建立型钢混凝土结构ANSYS数值模拟技术合理、可行,可适用于基于ANSYS程序的型钢混凝土结构有限元数值模拟和受力性能深入研究。 相似文献
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L. A. Merzhievsky A. D. Resnyansky 《International Journal of Impact Engineering》1995,17(4-6):559-570
The issue of the role of numerical simulation in solving the high-velocity impact problems is discussed. The applicability of some most often used models to describe the shock wave processes is analyzed. The model of deformation and fracture of materials under the action of dynamic loading, which combines the macro- and microstructural representations of the deformation and fracture mechanisms, is described. The solutions of some problems which demonstrate the posibilities of the model in studying physical regularities of the high-velocity impact process are presented. 相似文献
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A detailed technique has been developed in terms of a molecular dynamics method, which allows for the detailed investigation of a wide range of phenomena occurring in crystals as a result of different thermal and mechanical influences. This method has been applied to the numerical simulation of several types of real thermo-mechanical treatment (TMT) and to the qualitative and quantitative comparison of the course of recrystallization, structure and stability of the crystals obtained. Possible reasons and methods of the loss of stability of the systems are discussed. Two model methods of stabilization were observed. 相似文献
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We study the stress-strain state formed in a plate containing a stationary crack of finite length subjected to pulsed loading, develop a model of quasibrittle fracture caused by loads of this type, and deduce analytic expressions for the stress-strain state near the tip of the stationary crack in the plate. The proposed model admits rigorous physical justification and enables one to describe the development of brittle and quasibrittle fracture processes in materials with cracklike defects under dynamic and static loads within the framework of the same approach. The results of numerical simulation are in good qualitative agreement with the experimentally established regularities of the behavior of the critical parameters of fracture processes. 相似文献
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Summary Observations are reported on a thermoplastic elastomer (ethylene-octene copolymer) in uniaxial cyclic tensile tests with a
strain-controlled program and maximum elongation ratios up to λmax = 2.0. A constitutive model is derived for the viscoplastic behavior of a polymer network with constrained chains at three-dimensional
deformations with finite strains. The stress–strain relations involve five adjustable parameters that are found by fitting
the experimental data. Good agreement is demonstrated between the observations and the results of numerical simulation. It
is shown that the model correctly predicts the mechanical response, and its parameters are affected by amplitude of cyclic
deformation in a physically plausible way. 相似文献
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紧缩场高精度蜂窝夹层结构反射面板由经特殊工艺处理的铝蜂窝芯和表层铝板胶接而成 , 解析计算和材料力学性能试验很难准确获得该夹层板的材料性能参数。本文中采用数值2试验混合模型方法对该种夹层板的等效材料性能参数进行了优化反求。正向分析采用有限元方法 , 逆向分析采用遗传算法和梯度法组合优化算法。正、 逆分析过程的无缝集成和组合优化算法策略使反求效率明显提高。试验验证表明 , 采用反求方法获得的材料性能参数能够精确反应该夹层板的弹性本构关系 , 建立在该材料参数基础上的有限元模型具有理想的精度。 相似文献
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针对对称间隙单自由度振动系统,为了解决仿真速度慢、实验设计难度大的问题,设计了一种在数学模型上完全等效的电子电路,该电路仅使用了运放、电阻和电容等简单的电子器件。通过Multi Sim12.0软件进行仿真,结果和数值计算完全吻合。在仿真的基础上,通过对非线性模块的设计,搭建了硬件PCB电路,应用信号发生器和示波器进行了实验,进一步验证了应用等效电子电路进行非线性振动实验的合理性和正确性,并且具有数值仿真无可比拟的高速运算和动态参数调整的优良特性,为非线性系统的仿真和实验提供了一种参考。 相似文献
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This paper presents a new method to describe, analyse and estimate production system performances. Work-in-process (units), lead time (number of time units spent in the production system for each unit) and throughput (number of produced units per time unit) are basic performance measures, also used in this article. It is essential for industry to know about relations between system parameters and system performances in existing systems, and in not yet implemented system alternatives. Different performances are achieved by adjusting system parameters. Trade-offs between system parameters and its different performances are necessary to stay efficient and competitive in today's market. Queuing theory and simulation can help the decision makers to estimate system performances of existing and not yet implemented systems. When the complexity increases queuing theory becomes cumbersome, very difficult and eventually impossible to use. A single simulation presents limited information. Multiple simulations are necessary to ensure that the best alternative is chosen. A high number of simulations demand a lot of computer time and resources. Reduction of runs is desirable even with cheaper computer equipment. Currently, traditional two-dimensional charts are the only tools to present and analyse system performances. This article presents a new surrogate model for easier estimation and presentation of system performances, their internal relations, and relations to the system parameters. With the new surrogate model, system performances based on simulations are presented as positions in a three-dimensional environment. Parametric curves and surfaces of Bezier type are generated and adapted to these positions. System performances of other system alternatives can then be estimated without explicit simulation. The number of simulation calculations can thereby be moderated. The method is illustrated with a small production line system. 相似文献
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为研究地表粗糙度对山区峡谷地形桥址区风环境的影响,通过计算流体力学数值模拟的方法,对不同粗糙度下理想峡谷与真实峡谷模型中主梁跨中位置的风剖面进行了研究。通过理想模型的计算分析,确定了不同风向角下主梁跨中风剖面随粗糙度变化的一般规律,结合对峡谷内流场特点的分析,揭示了粗糙度对峡谷内风速造成影响的原因,并在真实地形模型中进行了验证,根据地表种类细化了粗糙度设置方案。研究表明,在峡谷地形条件下,粗糙度对风速的影响与常规地形有明显差异,在主梁高度处,随着粗糙度的增加,主梁跨中风速可能会有不同程度的增加。研究结论为山区峡谷地形处桥梁设计风速确定提供了依据。 相似文献
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Simulation of acoustic wave propagation in dispersive media with relaxation losses by using FDTD method with PML absorbing boundary condition 总被引:1,自引:0,他引:1
Yuan X Borup D Wiskin J Berggren M Johnson SA 《IEEE transactions on ultrasonics, ferroelectrics, and frequency control》1999,46(1):14-23
We present a method to incorporate the relaxation dominated attenuation into the finite-difference time-domain (FDTD) simulation of acoustic wave propagation in complex media. A dispersive perfectly matched layer (DPML) boundary condition, which is suitable for boundary matching to such a dispersive media whole space, is also proposed to truncate the FDTD simulation domain. The numerical simulation of a Ricker wavelet propagating in a dispersive medium, described by second-order Debye model, shows that the Ricker wavelet is attenuated in amplitude and expanded in time in its course of propagation, as required by Kramers-Kronig relations. The numerical results also are compared to exact solution showing that the dispersive FDTD method is accurate and that the DPML boundary condition effectively dampens reflective waves. The method presented here is applicable to the simulation of ultrasonic instrumentation for medical imaging and other nondestructive testing problems with frequency dependent, attenuating media. 相似文献
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Summary. A constitutive model is derived for the viscoplastic behavior of rubbery polymers at finite strains. A polymer is treated as an equivalent network of chains bridged by permanent junctions. The elastic response of the network is attributed to the elongation of strands, whereas its plastic behavior is associated with the sliding of nodes with respect to their initial positions. Unlike conventional stress–strain relations in finite viscoplasticity, the rate-of-strain tensor for the sliding of junctions is expressed in terms of the rate-of-strain tensor for macro-deformation. Constitutive equations are developed by using the laws of thermodynamics. These relations are simplified for simple shear of an incompressible medium with finite strains. The governing equations are determined by 3 material constants. To verify the model, a series of shear tests is performed on polycarbonate melts reinforced with short glass fibers. Adjustable parameters in the stress–strain relations are found by fitting the experimental data. Fair agreement is demonstrated between the observations and the results of numerical simulation. It is shown that the material constants change with the filler content in a physically plausible way.Department of Chemical Engineering, Kuwait University, Safat 13060, Kuwait 相似文献