Dynamic model for landsliding monitoring under rigid body assumption

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Simulations of Self-Expanding Braided Stent Using Macroscopic Model of NiTi Shape Memory Alloys Covering R-Phase

Self-expanding stents or stentgrafts made from Nitinol superelastic alloy are widely used for a less invasive treatment of disease-induced localized flow constriction in the cardiovascular system. The therapy is based on insertion of a stent into a blood vessel to maintain the inner diameter of the vessel; it provides highly effective results at minimal cost and with reduced hospital stays. However, since stent is an external mechanical healing tool implemented into human body for quite a long time, information on the mechanical performance of it is of fundamental importance with respect to patient’s safety and comfort. Advantageously, computational structural analysis can provide valuable information on the response of the product in an environment where in vivo experimentation is extremely expensive or impossible. With this motivation, a numerical model of a particular braided self-expanding stent was developed. As a reasonable approximation substantially reducing computational demands, the stent was considered to be composed of a set of helical springs with specific constrains reflecting geometry of the structure. An advanced constitutive model for NiTi-based shape memory alloys including R-phase transition was employed in analysis. Comparison to measurements shows a very good match between the numerical solution and experimental results. Relation between diameter of the stent and uniform radial pressure on its surface is estimated. Information about internal phase and stress state of the material during compression loading provided by the model is used to estimate fatigue properties of the stent during cyclic loading.     

Numerical Implementation and Application of an Extended Model for Diffusion and Precipitation of Chemical Elements in Metallic Matrices

A model for simultaneous and coupled diffusion and precipitation of chemical elements in metallic matrices is proposed, together with a scheme for its numerical solution and some applications to problems of internal oxidation. This model extends over a previous one of the authors, which itself stood as a generalization of many earlier ones. It includes the possibility that precipitates may be present in large fractions; if so, they may affect diffusion in the matrix phase by acting as “barriers”, and/or by distorting this matrix. The possible re-dissolution of some or all precipitates may also be prohibited for kinetic reasons. A simple but robust numerical scheme based on 1D finite differences in space coupled with explicit integration in time is proposed to solve the equations of the problem. This scheme notably contains an efficient Newton–Raphson algorithm used to solve the laws of mass action. Numerical simulations of internal oxidation processes close to those encountered in actual industrial practice are finally presented. It is first shown that in simple cases, the simulations reproduce Wagner’s classical analytical solution and related ones. More complex cases not amenable to analytic solutions are then envisaged.     

Experimental and numerical modelling of the flow field in a CuxSny direct chill caster

Abstract

To investigate the influence of the casting speed on the flow field and the shape of the solidification front in an industrial bronze caster, numerical calculations have been performed and experimental flow field measurements were used to validate the numerical model. Both numerical and experimental model represented 1:1 the real caster geometry of 820 × 250 × 800 mm³. A steady-state calculation, considering solidification and turbulent flow, was performed. Furthermore, a 1:1 water model of the industrial bronze caster has been built and combined with a Particle Image Velocity (PIV) setup to measure the apparent flow fields. Amongst other parameters, the numerical model provided information on the influence of the casting speed on the solidification front shape. The water model gave the experimentalist the facility to adjust the shape of the solidification front to the one predicted by the numerical model and compare the resulting flow field with the numerical prediction. This work presents a comparison of the results of both numerical and experimental models for different casting speeds with the same numerical parameters and boundary conditions.     

Investigation of heat pipe cooling in drilling applications.: part I: preliminary numerical analysis and verification

A combined numerical and experimental study is performed to analyze the feasibility of using heat pipe cooling in drilling applications. A parametric study is conducted to analyze the effect of different geometrical parameters expected for a heat pipe drill configuration, such as depth of the heat pipe within the drill, heat pipe diameter, heat flux input magnitude and length of the heat input zone. In this model, it is assumed that the drill is subjected to a static heat source which verifies the analysis and feasibility of using heat pipe cooling in drilling operations. The performance of the heat pipe drill model is approximated using a solid cylinder model of pure conduction. To validate the assumptions, numerical results are compared with experimental data that are based on the solid cylinder model. Both the numerical and experimental studies show that the use of a heat pipe in a drill can reduce the temperature field significantly. The results of this study can be used to define geometrical parameters for ‘optimal’ design and the setup for further analysis.     

水电厂气象水文综合预报调度模型的建立与应用

水电厂气象水文综合预报调度模型整合了降雨预报方案、中长期水文预报方案、洪水预报方案、水库优化调度方案等现有模型系统。降雨数值预报接入水库预报调度系统后,延长了来水预报预见期,结合文中研究的优化调度模型,使水电厂能够提前调整发电计划、调度方案,增加了水电厂的发电效益和水库的防洪减灾社会效益。     

Application of numerical simulation to flow induced corrosion in flowing seawater system

An established model was presented as a new kind of means for investigating flow induced corrosion. In this method the near-wall hydrodynamic parameters including wall shear stress τ and mass transfer coefficient k near the wall of materials can be numerically calculated, and combining corrosive kinetics tested by experiments, the corrosion rates can be also calculated accurately. The flow induced corrosion mechanism was further verified by numerical results in this model, and the various corrosion phenomena were explained. The modelled results also show that the ability to accurately utilize numerical method to study flow induced corrosion strongly to some extent depends on material corrosive kinetics processes tested by experiments.     

On the proper characterization of tooling motions and initial conditions in powder die compaction modeling

The present paper is concerned with the finite element modeling of Powder Metallurgy (P/M) cold die compaction process. Rather than on material constitutive theories or on numerical algorithmic issues, attention is confined exclusively on an scarcely addressed issue in the P/M modeling literature: the proper characterization of the boundary (tooling motions) and initial conditions of the problem. A case study of the compaction of an axially symmetric multilevel adapter in an advanced CNC press machine is used to convey the relevance of the accurate representation of these input data in the quality of model predictions. It is shown that unawareness or deliberate simplification of apparently insignificant details in this respect may cause errors far overshadowing those introduced by deficiencies in either the constitutive model or in the corresponding algorithmic solution procedure. The discussion of this case study serves also to provide useful modeling guidelines; illustrate frequent difficulties, as the unavailability of some information when guessing starting conditions; and reveal subtle, yet relevant for modeling purposes, technical details of advanced CNC press machines.     

Coupled thermomechanical analysis of friction stir welding process using simplified models

Abstract

It is widely recognised that the fundamental mechanisms associated with the weld formation process and their relationships with welding parameters are complex and remain to be fully understood. The present paper reports a series of general findings based on a set of simplified numerical models that were designed to elucidate various aspects of the complex thermomechanical phenomena associated with friction stir welding. The following phenomena were investigated in separate numerical models: (i) coupled friction heat generation; (ii) plastic flow slip zone development; and (iii) three-dimensional heat and material flow. The friction induced heat generation model was used to quantify the contributions of coupled thermomechanical friction heating, including non-linear interfacial phenomena between the tooling (e.g. stir pin) and material being welded. The plastic work induced heating effects were also examined. The plastic slip formation mechanisms were then investigated by considering contributions from various heating mechanisms. Finally, a simplified three-dimensional heat and material flow model, based on the observations from the coupled friction heat generation model, was used to establish some initial insight regarding the heat and material flow. The results from the three subproblem areas were then generalised in the form of a simple parametric relationship between welding variables (i.e. travel and rotating speeds) and weld formation conditions. A series of assumptions were made in constructing these individual models since there exists little information on actual material behaviour under friction stir welding conditions. However, the findings from the present study not only illuminate some of the important weld formation mechanisms in friction stir welding, but also provide an effective framework for more focused investigations into some of the fundamental phenomena identified in the three subproblem areas: such investigations will be reported separately in a future publication.     

Information model for the integration of inspection activity in a concurrent engineering framework

The basis of the integration of activities related to the product life cycle is, mainly, the creation of a unique and coherent information model along all the stages in the cycle. Up to date, dimensional inspection activities have not been deeply analysed, possibly due to the fact that, their work influences are smaller than others, such us numerical analysis, materials or numerical control. However, the integration of dimensional inspection is very important for several reasons: the need of specifying the design and planning of the inspection process from the conceptual part design; the increase of use of high speed coordinate measuring machine (CMM) in the production lines; and finally, for the interest of a feedback between data inspection and manufacturing processes. This paper is a detailed proposal of an information model for inspection based on operations for CMM, which represents a consistent structure of the necessary data in an integrated product setting.     

3D simulations and experiments of guided wave propagation in adhesively bonded multi-layered structures

Understanding guided wave propagation in multi-layered plates and interaction with discontinuities can be difficult, as well as the interpretation of the ultrasonic signals. Propagation of guided waves can be studied analytically solving the equations of motion with the proper boundary conditions; nevertheless analytical models can be difficult to solve for complex multi-layered structures or having inner discontinuities. The problem can be efficiently studied using numerical techniques. Simulation of guided wave propagation in multi-layered structures, for ultrasonic waves in the MHz range, is solved here with the finite element analysis based on an explicit integration rule to solve the equations of motion in a dynamic analysis. Simulation allows a better understanding of propagation and interference phenomena by creating a window of observation in the multi-layered plate. Numerical results determined for a three-layer Al plate, without or with discontinuities, matched very well with experiments, providing an efficient tool to visualize and extract significant information in the transmitted waves and to optimize wave mode and configuration for a rigorous ultrasonic inspection.     

镁合金半固态流变压铸充型凝固过程数值模拟及试验研究

在前期平板模型流变压铸充型凝固过程数值分析的基础上,利用所建立的数学模型对镁合金压铸件中间轴螺塞进行了数值分析和实验研究,对比分析了零件成形时镁合金牛顿流体与镁合金半固态流体的充型特征及零件中存在缺陷的位置和大小。结果表明,与牛顿流体相比半固态流体更易实现铸液充型时的顺序填充,有利于铸型中的气体的排出和铸件成形质量的提高。模拟结果与试验结果吻合较好。     

基于Web的生产过程信息管理系统设计与实现

根据企业在生产经营理念上的变化和发展方向,结合计算机网络技术的迅速发展以及数控设备的特点,采用ASP.NET技术研制开发了基于Web的生产过程信息管理系统PIMS.该系统通过PCI数据采集卡实现了数控设备运行状态信号的采集和分析,同时将生产过程中产生的其它信息在系统网络中进行传输、管理和分析.通过试运行,证明了该系统的可行性和有效性.     

Experimental and numerical study of an AlMgSc sheet formed by an incremental process

A recently developed AlMgSc alloy is studied since this material, which is well adapted to the aeronautic domain, is poorly known.The first objective is to reach a better knowledge of this alloy to provide the missing useful information to the aeronautic industry and to help research institutes who want to simulate sheet forming processes by Finite Element (FE) simulations. A set of experimental tests has been performed on the as-received sheets, material laws have been chosen and the corresponding material parameters have been adjusted to correctly describe the material behaviour.The second objective is to study the applicability of the Single Point Incremental Forming process (SPIF) on this material. Truncated cones with different geometries were formed and the maximum forming angle was determined. A numerical model was developed and proved to be able to predict both the force evolution during the process and the final geometrical shape. Moreover, the model helps reaching a better understanding of the process.The characterisation method described in this research and applied on the AlMgSc alloy can be extended to other alloys. In addition, the numerical simplified model, able to accurately describe the SPIF process with a reduced computation time, can be used to study more complex geometries.     

有限元数值模拟在汽车覆盖件设计和制造中的应用

汽车覆盖件成形同时包含大变形、（粘）塑性、接触、摩擦等多种非线性因素耦合，利用有限元法在计算机上模拟出板材从坯件到成品的全过程并加以图形显示，进而研究影响成形的各种因素，可以为板材成形的设计和生产提供可靠的依据。本文主要介绍有限元数值模拟技术的现状，并讨论了其在汽车覆盖设计和制造上的应用。     

Material flow in FSW of AA7075–T6 butt joints: numerical simulations and experimental verifications

Abstract

Friction stir welding (FSW) has reached a large interest in the scientific community and in the recent years also in the industrial environment, owing to the advantages of such solid state welding process with respect to the classic ones. Advanced finite element method tools are needed in order to develop an effective engineering of the processes; quantitative results can be acquired from numerical simulations once the basic information such as the material flow is certain. A 3D Lagrangian implicit coupled rigid viscoplastic model has already been developed by the authors to simulate FSW of butt joints. In the present paper the material flow in the FSW of AA7075–T6 butt joints is investigated on the varying of the most relevant technological and geometrical parameters with numerical simulations and experiments. In particular to investigate the metal flow a wide campaign of experimental tests and observations has been developed utilising a thin foil of copper as marker.     

基于以太网的异构数控机床集成实现

实现DNC系统的核心问题是解决数控机床与计算机之间的信息交换和互联.文章介绍了一种基于以太网的DNC通信技术.实现了将中央计算机的加工信息传递给机床;然后由计算机在线监视并处理机床反馈的实时信息;并且通过中央计算机协调数控机床进行协同加工.     

Numerical procedure for simulation of multicomponent and multi-layered phase diffusion

A mass balance error-free numerical procedure for simulation of multicomponent and multi-layered phase diffusional reactions has been suggested, based on an explicit fixed grid finite difference method. Basically, a local equilibrium was assumed at each phase interface and one dimensional movement of interfaces was considered. Attention was paid to the treatments of newly formed thin phase layers and different molar volumes among interacting phases, together with the removal of a mass balance error. Specially derived finite difference forms were used to treat phase layers thinner than two inter-grid distances. A new flux balance equation which is independent from the molar volume differences among phases and leaves no mass balance error was developed by a transformation of space variable system and by a systematic analysis of sources of mass balance error, respectively. Through some model simulations, it could be shown that the present numerical procedure cantreat multi-layered phase diffusion including thin layered phases and can reproduce transitions of layer sequences during diffusional reactions successfully, leaving no mass balance error.     

Rapid computation of eddy current signals from narrow cracks

An existing boundary element method model for eddy current inspection of ideal or narrow cracks is revised. Using some lately devised concepts on efficiently and rapidly simulating canonical eddy current geometries, we show how this model can be made easier to implement and faster to calculate. The approach is largely based on a novel method for rapidly calculating the Green's function and reducing the matrix fill-time, and also on a similar method for rapidly computing the incident electric field. As a result, the model has been made an order of magnitude faster than the existing one without sacrificing accuracy. We pay attention to numerical analysis details and analyze issues that so far have not been clarified. The validity of our approach is also verified by the experiment. Although we have tested the model against published data, we have also produced our own precision measurements for surface and through-the-thickness slots in plates with the coils performing scans along and across the slots at various frequencies.     

Simulation of PYSZ particle impact and solidification in atmospheric plasma spraying coating process

In this work a numerical model of the impact and solidification of partially yttria stabilized zirconia particles on flat and rough substrate surfaces under plasma spraying conditions and the simulation results are presented. Results of the numerical simulation showed the influence of particle diameter and particle state prior to impact on splats spreading behavior and final morphology. The particles have a diameter range from 20 µm to 60 µm. Particle initial conditions prior to impact: speed, temperature and melting state are taken from previous simulation approaches of particle acceleration and heating. Simulations of fluid dynamics, heat transfer and solidification during the particle impact were performed using computational fluid dynamics. Tracing of free surfaces was determined by the volume of fluid method. The simulation results are compared with several numerical and experimental studies of other scientists and showed good agreement. Simulated splat morphologies are compared with experimentally obtained splats. The numerical model shows good results under real coating conditions and is suitable for the implementation in industrial applications. This model builds a basis for calculation of microstructure during real coating processes and can be used not only for coating under atmospheric plasma spraying conditions but also for similar coating processes and diverse materials.