Search

This paper aims to gain fundamental understanding of the microscopic mechanisms that control the transition between secondary and tertiary creep around salt caverns in typical geological storage conditions. We use a self-consistent inclusion-matrix model to homogenize the viscoplastic deformation of halite polycrystals and predict the number of broken grains in a Representative Elementary Volume of salt. We use this micro-macro modeling framework to simulate creep tests under various axial stresses, which gives us the critical viscoplastic strain at which grain breakage (i.e., tertiary creep) is expected to occur. The comparison of simulation results for short-term and long-term creep indicates that the initiation of tertiary creep depends on the stress and the viscoplastic strain. We use the critical viscoplastic deformation as a yield criterion to control the transition between secondary and tertiary creep in a phenomenological viscoplastic model, which we implement into the Finite Element Method program POROFIS. We model a 850-m-deep salt cavern of irregular shape, in axis-symmetric conditions. Simulations of cavern depressurization indicate that a strain-dependent damage evolution law is more suitable than a stress-dependent damage evolution law, because it avoids high damage concentrations and allows capturing the formation of a damaged zone around the cavity. The modeling framework explained in this paper is expected to provide new insights to link grain breakage to phenomenological damage variables used in Continuum Damage Mechanics. [ABSTRACT FROM AUTHOR]

The paper has considered the fractal flow in a dual media with fractal properties, where the media could be elastic, heterogeneous and visco-elastic. We argued that, the fractal flow within a geological formation with elastic property cannot be accurately described with the concept of differentiation with local operator, as this operator is unable to include into mathematical formulation the effect of elasticity. Thus to include into mathematical formula the observed facts, we have modified the model by replacing the local derivative with the non-local operator with power. A more complex problem was considered where the geological formation is considered to have visco-elastic and heterogeneity properties. We argued that, the flow within a matrix rock with these two properties cannot either be described with local derivative nor a non-local derivative with power law. In this case two non-local operators were considered, an operator with Mittag-Leffler kernel and Mittag-Leffler-Power law kernel [F. Ali et al., J. Magn. Magn. Mater. 423, 327 (2017); F. Ali et al., Eur. Phys. J. Plus 131, 310 (2016); F. Ali et al., Eur. Phys. J. Plus 131, 377 (2016); F. Ali et al., Nonlinear Sci. Lett. A 8, 101 (2017); N.A. Sheikh et al., Neural Comput. Appl. (2016) https://doi.org/10.1007/s00521-016-2815-5]. For each model, a detailed study of existence and uniqueness of the system solutions was presented using the fixed point theorem. We solved numerically each model using a more acculturate numerical scheme known as Upwind. Some numerical simulations are presented to underpin the effect of the suggested fractional differentiation. [ABSTRACT FROM AUTHOR]

Let M be a compact connected 3-submanifold of the 3-sphere S with one boundary component F such that there exists a collection of n pairwise disjoint connected orientable surfaces S = { S , · · ·, S } properly embedded in M, ∂ S = {∂ S , · · ·, ∂ S } is a complete curve system on F. We call S a complete surface system for M, and ∂ S a complete spanning curve system for M. In the present paper, the authors show that the equivalent classes of complete spanning curve systems for M are unique, that is, any complete spanning curve system for M is equivalent to ∂ S. As an application of the result, it is shown that the image of the natural homomorphism from the mapping class group M( M) to M( F) is a subgroup of the handlebody subgroup H . [ABSTRACT FROM AUTHOR]

This paper deals with the mathematical modelling of confinement of paralic ecosystems. It is based on the recent paper (Frénod and Goubert in Ecol. Model. 200(1-2):139-148, ) that presents a modelling procedure in order to compute the confinement field of a lagoon. Here, we improve the existing model in order to account for tide oscillations in any kind of geometry such as non-rectangular lagoons with a non-flat bottom. The new model, that relies on PDEs rather than ODEs, is then implemented thanks to the finite element method. Numerical results confirm the feasibility of confinement studies thanks to the introduced model. [ABSTRACT FROM AUTHOR]

The capacity to quickly and accurately simulate extracellular stimulation of neurons is essential to the design of next-generation neural prostheses. Existing platforms for simulating neurons are largely based on finite-difference techniques; due to the complex geometries involved, the more powerful spectral or differential quadrature techniques cannot be applied directly. This paper presents a mathematical basis for the application of a spectral element method to the problem of simulating the extracellular stimulation of retinal neurons, which is readily extensible to neural fibers of any kind. The activating function formalism is extended to arbitrary neuron geometries, and a segmentation method to guarantee an appropriate choice of collocation points is presented. Differential quadrature may then be applied to efficiently solve the resulting cable equations. The capacity for this model to simulate action potentials propagating through branching structures and to predict minimum extracellular stimulation thresholds for individual neurons is demonstrated. The presented model is validated against published values for extracellular stimulation threshold and conduction velocity for realistic physiological parameter values. This model suggests that convoluted axon geometries are more readily activated by extracellular stimulation than linear axon geometries, which may have ramifications for the design of neural prostheses. [ABSTRACT FROM AUTHOR]

Finite element simulations are being more and more applied when studying the crash-worthiness of vehicles during impact. This paper deals with setting up such a simulation and discusses several ways to simplify and verify a simulated crash. For this purpose, a notch impact-testing machine will be released from a certain angle and crash into a model constructed with three different wall thicknesses. The plastic and elastic deformation is measured in the front of the model and is then used for validation of the simulation. In the end, the simulation was found to be in good agreement with the real crash data. [ABSTRACT FROM AUTHOR]

This paper presents the results of calculations to determine the influence of the exciting force application point on the value of the vibration diagnostic parameter to identify the presence of a breathing crack at sub- and superharmonic resonances of the first flexural vibration mode in a cantilever beam of constant rectangular cross section using a three-dimensional finite element model. The investigation results are compared with the known data obtained by the analytical and numerical methods. [ABSTRACT FROM AUTHOR]

The need for computer modeling tools capable of precisely simulating multi-field interactions is increasing. The accurate modeling of an electrostatically actuated Micro-Electro-Mechanical-Systems speaker results in a system of coupled partial differential equations (PDEs), describing the interactions between electrostatic, mechanical and acoustic fields. A finite element (FE) method is applied to solve the PDEs efficiently and accurately. In the first part of this paper, we present the driving technology of an electrostatic actuated Micro-Electro-Mechanical-Systems speaker, where the electrostatic mechanical coupling is realized with reduced order electro mechanical transducer elements. The electrostatic attracting force is derived from the capacity to gap relation of our device. In a second investigation, we focus on generation of the generated sound including open domain characteristics and propagation region optimization. The sound pressure level is computed with Kirchhoff Helmholtz integral as well as with FEM by using CFS++. We use the Kirchhoff Helmholtz model to characterize the interactions of multiple speaker cells in arrays and the FE tool for single speaker cell investigations. At the acoustic FE model, the focus is on mesh generation and optimization of the propagation region using non-conforming grids (Mortar FEM) and in addition at the boundary region to model open domain characteristics. We apply a recently developed perfectly matched layer technique, which allows us to truncate the acoustic propagation domain with open domain characteristics. Finally, we present an optimization method taking advantage of stress induced self-raising realized with various merged layers with different intrinsic pre-stress. The buckling back plate concept can be compared to bimetal characteristics. [ABSTRACT FROM AUTHOR]

The development of precision machine tools requires an accurate understanding of the thermal behaviour of the tools. Therefore, by developing highly accurate machine tool thermal behaviour simulations, it can accurately forecast the functional performance of a machine tool at the prototype design stage and provide guidance on its design and performance optimization. To improve the accuracy of the thermal simulation of machine tools, it proposed whole-machine temperature field and thermal deformation modeling and a simulation method for vertical machining centers. Based on the studies of thermal-structure coupling finite-element data flow and its critical conditions, it also proposed design and computational methods for obtaining the heat-source power, when various rotational speeds, the forced convection heat transfer coefficient between a rotating surface and the air, the combined heat transfer coefficient between a stationary surface and the air/environment, and key contact surface thermal resistances were considered. Furthermore, this paper performed finite-element simulation analysis based on the constructed whole-machine thermal model, and the temperature characteristics and heat deformation mechanism/state were obtained. After comparing the simulation and experimental results, it verified the effectiveness of the finite-element simulation model and the relevant methods and confirmed that the simulation accuracy for both the temperature characteristics and the thermal deformation had been improved significantly, with a simulation error less than 10 %. [ABSTRACT FROM AUTHOR]

As a widely used engineering material, optical glass is very difficult to process because of its high hardness and brittleness. The material removal mechanism still needs further investigation. In this paper, a mesh-free simulation method—smooth particle hydrodynamics (SPH)—is introduced and an ultra-precision cutting model for K9 glass is provided. Compared with conventional finite element method, the SPH method can effectively avoid mesh distortion when dealing with large deformation problems such as cutting. Several numerical simulations were carried out to further investigate the critical value of transition. Simulation results indicate that when cutting depth is small enough, the K9 glass can be machined in ductile mode and a relatively smooth machined surface without crack can be obtained. The chip is always in irregular and discontinuous way no matter what the cutting mode is. Three cutting tools with different rake angle were used in simulation and the effect of rake angle is analyzed. [ABSTRACT FROM AUTHOR]

This paper presents the modeling and simulation of the thermal analysis on the hydrogenerator stator winding. The insulation aging is predetermined first by the insulation temperatures that, in turn, are influenced by the environmental conditions and second by the speed increase of the high temperature chemical reaction in materials. By increasing the temperature in the electro-insulated material, many molecules enter in chemical reaction accelerating the insulation aging. The heat transfer is a natural process, caused by inner energy, between bodies with high temperature and bodies with lower temperature. This process can also take place between parts of the same body that have different temperatures. The heat is transmitted by conduction, convection, and radiation. The heat transfer and especially the thermal conduction are a domain in which the finite element method is successfully applied. The thermal conduction problems will be solved by the finite elements method. The analysis of the thermal transfer process was made using the modeling and simulation program with finite elements ANSYS, and the results of the simulations were compared with measurement values. The analyzed stator winding is supplied with high voltage of 11 kV that is used for a high power hydrogenerator. To realize the thermal analysis of the winding stator, the coil will be supplied with 11 kV. The results of the analysis on a prototype model present the thermal transfer in coil-insulation-air system when the coil is hot. [ABSTRACT FROM AUTHOR]

This paper proposed an analytical model for the distributed magnetic field analysis of interior permanent magnet-type blush-less direct current motors under the stator-turn fault condition using the winding function theory. Stator-turn faults cause significant changes in electric and magnetic characteristic. Therefore, many studies on stator-turn faults have been performed by simulation of the finite element method because of its non-linear characteristic. However, this is difficult to apply to on-line fault detection systems because the processing time of the finite element method is very long. Fault-tolerant control systems require diagnostic methods that have simple processing systems and can produce accurate information. Thus analytical modeling of a stator-turn fault has been performed using the winding function theory, and the distributed magnetic characteristics have been analyzed under the fault condition. The proposed analytical model was verified using the finite element method. [ABSTRACT FROM AUTHOR]

Characterization of sound-absorbing materials is one of the investigation fields that is acquiring most interest in the last few years. As a consequence, there is an increase in investigators who are trying to obtain mathematical models to predict the acoustical behavior of the materials, as well as those who are looking for new materials to improve the acoustic isolation and acoustic conditioning. There are lots of applications, such as mufflers used in engines, in which it is of great interest to know the velocity of sound waves and the pressure distribution inside ducts. In this paper, the numerical simulation technique based on the finite element method is applied to study the propagation of the plane acoustic waves inside a standing wave tube by means of the application of a harmonic analysis, studying the distribution of pressures in an established frequency range. ANSYS software has been used to compare the numerical results with the theoretical ones. Then, comparing the numerical results with the experimental ones, the validity of the experimental method is evaluated. The experimental method follows the Standard ISO 10534-2 that is used for the determination of the absorption coefficient and acoustic impedance in porous and fibrous materials. [ABSTRACT FROM AUTHOR]

In this paper, temperature results obtained by numerical simulations based on three different methods of defining the heat flux load distribution are compared to directly measured temperatures acquired using infrared camera measurement techniques. The heat flux calculations are based on recorded instantaneous grinding power, average grinding power, and power calculated by multiplying the measured tangential forces and the cutting velocity (referred to as calculated power). The results show that the method applied to characterize the input flux load in the numerical model has a significant effect on the estimated grinding temperatures and that the calculated power data produce the best temperature results. [ABSTRACT FROM AUTHOR]

This paper proposes a numerical method to simulate hydrogen-assisted stress corrosion cracking, via coupled diffusion elastic-plastic finite element damage analyses based on phenomenological stress-modified fracture strain model. For validation, simulated results using the proposed method are compared with published experimental data of FeE 690T compact tension tests under air and hydrogen condition with various constant load-line displacement rates. The simulated results agree well with experimental data. [ABSTRACT FROM AUTHOR]

Train-induced ground vibration is numerically analyzed using the finite element method (FEM) in this paper. Varieties of open trenches including partial and full length systems with different geometries are employed as the vibration mitigation strategies. Ground is modeled by multiple soil layers and the train load pattern is simulated by series of successive moving loads. A parametric study is then carried out after verification of the numerical model. Effects of different parameters including the trench type, size and geometry and the train speed on the vibration mitigation level are investigated. The operational speeds are set to be in vicinity of the Rayleigh wave propagation velocity. Two types of active and passive trenches are considered with three different geometries consisting of rectangular, triangular (wedge) and circular cross sections. [ABSTRACT FROM AUTHOR]

This paper presents the results of vibro-acoustic modeling and simulation using the finite element and the boundary element methods for the free piston engine structure. A model of the engine was constructed through the use of finite element software to perform a normal mode analysis of the engine structure. The objective was to determine the mode shapes and the natural frequency that contribute to engine structure vibration. Theoretical development of the engine balance motion and frequency response was also conducted. From the simulation and finite element analysis, the force response pattern of the engine vibration was determined and then compared with its natural frequency. The vibration data were used as the input data for noise analysis using the boundary element method. The integration of the finite element and the boundary element determined the noise-frequency data of the engine structure toward the occurrence of engine noise. The information can be used by designers to analyze engine specifications and structure, especially at the preliminary design stage. [ABSTRACT FROM AUTHOR]

The existing numerical simulations of hydrodynamic characteristics of abrasive waterjet in a cutting head were mainly based on Eulerian grid or arbitrary Lagrange-Eulerian grid method to establish computational fluid dynamics models. However, using these two methods, the abrasive and water were premixed and given an identical initial velocity, which were different from the mixing and acceleration processes of abrasive in the cutting head. This paper presents a more suitable numerical model that the abrasive particle enters into the mixing chamber in a low velocity and is accelerated in the focus tube by a high-speed waterjet from the orifice. In order to model this mixing-and-acceleration process of abrasive and high-speed waterjet, the smooth particle hydrodynamics (SPH) coupled finite element method (FEM) is adopted, in which SPH particles are used to model the high-speed waterjet to adapt its extremely large deformation and FEM is applied to model the discrete abrasive particle, cutting head, and workpiece. As a result, evolution of abrasive and waterjet velocities along focus tube is analyzed; trajectory of single abrasive particle in focus tube is sighted; the relationships between abrasive particle velocities and different water pressures are described; the rule of outlet velocities of abrasive particle vs. dimensionless ratio of diameter is conducted; depth of penetration caused by single abrasive particle impact is obtained. The current model is validated by the existing theoretical and experimental data. [ABSTRACT FROM AUTHOR]

Welding deformations play an important role in sealing capabilities and service life of welded pipe-flange joints. A numerical procedure for modeling of tack welds in girth butt-welding of such joints is of vital importance for the prediction of transverse shrinkage and flange face deformation, which is directly related to the joint sealing capability. This paper presents a 3-D finite element simulation of a pipe-flange joint to describe the numerical procedure for modeling of tack welds in circumferential joints. Sequentially coupled nonlinear transient thermo-mechanical analysis is performed to simulate Metal Inert Gas (MIG) welding. Single pass butt weld geometry with single “V” for 100 mm nominal diameter pipe with same sized weld neck type ANSI flange of class no. 300 is used. Temperature dependent material properties are used and deposition of filler metal is obtained by element birth and death feature. The peak temperature of the tack during the butt-welding of the tacked model is concluded a key parameter for numerical prediction of deformations, whereas tack temperature has negligible effect on the residual stresses. [ABSTRACT FROM AUTHOR]