Analytical and numerical study of the densification of carbon/carbon composites by a film-boiling chemical vapor infiltration process

The film-boiling chemical vapor infiltration (CVI) process is a fast process developed for composite material fabrication, and especially carbon/carbon composites. In order to help define optimal conditions, a local 1D model has been developed to study the densification front which establishes itself during the processing of a carbon/carbon fibrous preform. The model features heat conduction, precursor gas diffusion, densification reactions and structural evolution of the porous medium. The effects of total mass flux, Thiele modulus, porous medium geometry on front behavior parameters such as width, velocity and residual porosity are presented as semi-analytical correlations. An existence criterion is produced, which involves a minimal heat flux. Comparison between process-scale experiments and simulation is then possible by inserting the semi-analytical results achieved in the local study of the front into a light numerical model involving the entire preform. The model has been validated with respect to previous experimental and numerical data.     

多孔介质模型在核电蒸汽发生器设计中的应用

对基于多孔介质模型开发的核电蒸汽发生器三维热工水力分析程序ATHOS进行介绍．并应用ATHOS对核电蒸汽发生器二次侧的复杂传热传质现象进行数值模拟。获得蒸汽发生器二次侧的流动换热状态,以及二次侧三维两相流场分布,分析结果可作为传热管流致振动、磨损分析及结构设计的输入数据。研究工作表明,多孔介质模型在核电蒸汽发生器设计中具有重要的应用价值。     

全波场地震波数值模拟中的边界处理实践研究

在用有限差分法或有限元法模拟无界区域中的波动时,需要对计算区域的边界做特殊处理,以消除由于把地震波的传播设定在有限区域而产生的边界反射。为了这一目的,人们研究出了多种人工边界处理方法,完全匹配层（PML）吸收边界条件就是理想的方法之一,现已被广泛应用。本文将PML吸收边界条件应用于全波场地震波的数值模拟,数值计算实验表明,对qP波,匹配层的厚度为5个网格间距即可达到要求,而对qSV波与qSH波,为达到理想的吸收效果,匹配层的厚度应当增大,当厚度为13个网格间距时达到了理想的吸收效果。     

Reaction kinetics study of asymmetric polymer-polymer interface

In this study, the reaction kinetics of asymmetric polymer-polymer interface was experimentally and theoretically studied. A new rheological method correlating the change of rheological property of reactive system with the conversion of the in situ formed copolymers was applied to study the reaction kinetics of PBT/epoxy reactive system. Then, the new method was proved to be useful by comparing its results with that obtained from the conventional endgroup determination method. Moreover, the conversion of PBT/epoxy reactive system from rheological method could be well fitted by the numerical analysis, from which the kinetic constant and the diffusion constant of epoxy in PBT could be determined simultaneously.     

SIMOP: Efficient reactive distillation optimization using stochastic optimizers

A methodology to improve the efficiency of stochastic methods applied to the optimization of chemical processes with a large number of equality constraints is presented. The methodology is based on two steps: (a) the optimization of the simulation step, which involves the optimum choice of design variables and subsystems to be simultaneously solved; (b) the optimization of the nonlinear programming (NLP) problem using stochastic methods. For the first step a flexible tool (SIMOP) is used, whereby different numerical procedures can be easily obtained, taking into account the problem formulation and specific characteristics, the need for specific initialization schemes and the efficient solution of systems of nonlinear equations. This methodology was applied to the optimization of a reactive distillation process for the production of ethylene glycol. Due to the complexity of the mathematical model, several different numerical procedures were generated, and their influence on the computational burden and on the reliability and accuracy of the optimization to reach the global optimum were studied. The results obtained suggest that in addition to the choice of design variables, the structure of subsystems associated to numerical procedures has a considerable impact on the performance of the optimizers.     

斜顶偏心旋风筒的数值模拟研究

使用Fluent软件，通过RSM湍流模型和离散相模型对斜顶偏心旋风筒进行了数值模拟研究，结论是：斜顶偏心旋风简与普通型旋风筒的流场基本相同，但选择合理的顶板倾斜角度和内简的偏心距离更有利于提高旋风筒的分离效率和降低压力损失。     

4D MRI Flow Coupled to Physics‐Based Fluid Simulation for Blood‐Flow Visualization

Modern MRI measurements deliver volumetric and time‐varying blood‐flow data of unprecedented quality. Visual analysis of these data potentially leads to a better diagnosis and risk assessment of various cardiovascular diseases. Recent advances have improved the speed and quality of the imaging data considerably. Nevertheless, the data remains compromised by noise and a lack of spatiotemporal resolution. Besides imaging data, also numerical simulations are employed. These are based on mathematical models of specific features of physical reality. However, these models require realistic parameters and boundary conditions based on measurements. We propose to use data assimilation to bring measured data and physically‐based simulation together, and to harness the mutual benefits. The accuracy and noise robustness of the coupled approach is validated using an analytic flow field. Furthermore, we present a comparative visualization that conveys the differences between using conventional interpolation and our coupled approach.     

Interactive Simulation of Rigid Body Dynamics in Computer Graphics

Interactive rigid body simulation is an important part of many modern computer tools, which no authoring tool nor game engine can do without. Such high‐performance computer tools open up new possibilities for changing how designers, engineers, modelers and animators work with their design problems. This paper is a self contained state‐of‐the‐art report on the physics, the models, the numerical methods and the algorithms used in interactive rigid body simulation all of which have evolved and matured over the past 20 years. Furthermore, the paper communicates the mathematical and theoretical details in a pedagogical manner. This paper is not only a stake in the sand on what has been done, it also seeks to give the reader deeper insights to help guide their future research.     

Early age microstructure of Portland cement mortar investigated by ultrasonic shear waves and numerical simulation

This paper investigates the ability of a shear wave reflection (WR) method to monitor microstructural changes of Portland cement mortar during hydration. The wave reflection method measures the reflection loss of shear waves at an interface between a steel plate and mortar. Mortars with water/cement ratios of 0.35, 0.5 and 0.6 were tested at isothermal curing conditions of 25 °C. The numerical model HYMOSTRUC3D was used to simulate the evolution of microstructural properties of the cement paste phase of the tested mortars. The parameters obtained from the simulations were the volume fraction of the total and connected solid phase and the specific contact area of the hydrated cement particles. The investigations have shown that the wave reflection measurements are governed primarily by the degree of the inter-particle bonding of the cement particles as calculated from the specific contact area of a simulated microstructure.     

Simultaneous measurement of gas and solid holdups in multiphase systems using ultrasonic technique

Ultrasonic technique has been recently developed to measure dispersed phase holdups in multiphase flows. The experimental results obtained in this work have shown that the fluctuations of the sound speed and attenuation of ultrasound are well-defined functions with solid and gas holdups in liquid-solid and gas-liquid two-phase flows. When both solid particles and gas bubbles are present in a liquid flow, gas bubbles appear to be a dominant factor for the instability of ultrasound signals. These findings lead to a new approach for simultaneous detection of gas and solid holdups in a gas-liquid-solid three-phase flow. In this work, canonical analysis and optimization methods are successfully applied to differentiate the contributions of gas bubbles and solid particles to the ultrasonic signals recorded from three-phase systems. The gas and solid holdups determined by the proposed approach are in a good agreement with the experimental results obtained using differential pressure transducers and conductivity probes.