A Multi Scale Method for Thermoelectric MHD in Dendritic Solidification

A fully coupled transient 3-dimensional multi-scale model has been developed to predict the evolution of dendritic growth in alloys.The motivation to use such a method is to both reduce computational costs and increase the size of the computational domain.The model consists of a mixture of finite volume and finite difference solvers integrated within a novel multi-scale method that solves the three sets of equations(electromagnetism,heat transfer/solidification and fluid dynamics)on appropriate length and time scales.A locus-based method,allows for mesh ref’mement in regions of interest localised around the interface,to improve accuracy without incurring significant computational overheads.This method has facilitated modelling the evolution of complex 3-dimensional structures on a single processor within a reasonable amount of time.As a demonstration,the model is applied to a super-cooled dendritic solidification problem,in the presence of a constant high magnetic field.     

Simulation of Dynamic Recrystallization Using Cellular Automaton Method

A new modeling approach that couples fundamental metallurgical principles of dynamical recrystallization with the cellular automaton method was developed to simulate the microstructural evolution linking with the plastic flow behavior during thermomechanieal processing. The driving force for the nucleation and growth of dynamically recrystallized grain is the volume free energy due to the stored dislocation density of a deformation matrix. The growth terminates the impingement. The model is capable of simulating kinetics, microstructure and texture evolution during recrystallization. The predictions of microstructural evolution agree with the experimental results.     

TB-EPUDC-015复合材料层压板的疲劳损伤模型

This paper develops a mathematical model for fatigue damage evolution in composite materials. The characteristics of damage growth in composite materials are studied and compared with those of damage growth in homogeneous materials. Continuum damage mechanics concepts are used to evaluate the degradation of composite materials under cyclic loading. A new damage accumulation model is proposed to capture the unique characteristics of composite materials. The proposed model is found to be more accurate than existing models, both in modelling the rapid damage growth at the early stages of life and near the end of fatigue life. The parameters of the proposed model are obtained from experimental data. A example is implemented to illustrate that the proposed model is able to accurately fit several different sets of experimental data.     

Hydrogen Evolution on Binary and Ternary Cobalt Alloys Deposited With Superimposed Magnetic Field

The article presents results of electrodeposition of Co-Mo Co-Mo-C alloys in a magnetic field characterized by low overvoltage of hydrogen evolution.Addition of molybdenum and carbon was to lower the values of overvoltage of hydrogen evolution on cobalt.The influence of bath pH,bath composite,current density and magnetic field with different orientation on the deposits composition,structure and overpotential for hydrogen evolution reaction(HER)was determined.Electrocatalytic properties of the obtained alloy coatings within the range of hydrogen evolution were tested in a concentrated NaOH solution.The comparison of electrocatalytic properties of Co-Mo alloys with properties of Co-Mo-C ones enabled determining the influence of carbon presence in cathodic deposits on the overpotential values for hydrogen evolution.     

Modeling of Electromagnetic,Temperature,and Velocity Fields During Solidification in an Electromagnetically Stirred Melt

This paper describes a comprehensive model for predicting the evolution of the velocity and temperature fields in electromagnetically-driven flows during solidification.The electromagnetic field was formulated using the mutual inductance method,which accounts for the metal,chill blocks,and magnetic shields.The model solves the heat transfer equation throughout the system,as well as the fluid flow equations in the liquid and mushy regions.A two-zone model for the mushy region that accounts for dampening of momentum by the turbulent field has been developed.The turbulence in the molten region was determined using the k-s model.Calculations were performed for unidirectional solidification in a bottom chill mold placed in a stationary magnetic field.Computed results show that the flow field at the beginning of solidification shows typical four recirculating loops,and later evolves to two recirculating loops as solidification progresses.The magnitude of the velocity in the bulk liquid was found to decrease as solidification progresses.     

Structure evolution and thermal stability of La2O3-doped mullite fibers via sol-gel method

The lanthana-doped mullite fibers were prepared via a sol-gel method from the aluminum isopropoxide-aluminum nitrate-tetraethyl orthosilicate system. The structure evolution and thermal stability of the mullite fibers were investigated by means of X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, differential scanning calorimetry (DSC), scanning electron microscopy (SEM) and trans-mission electron microscopy (TEM). The results showed that the fibers obtained after calcination at 1000℃ was in the form of Al2O3-rich mullite, which tended to transform to stoichiometric mullite with the lanthana content increasing. The lattice parameter a exhibited a decline trend with the lanthana content increasing, while b showed an upward tendency. Correspondingly, the redshift of Si-O-Si bond from 1255 to 1245 cm-1 was observed. The grain growth was inhibited for the doped fibers, among which the 5% La2O3-doped sample presented a mini-mum crystallite size (17.2 nm) after calcination at 1000 ℃ for 1 h.     

Microstructural evolution and superplastic deformation behavior of fine grain 5083Al

The microstructural evolution during superplastic deformation of a fine grain Al-4.7 pct Mg alloy (5083Al) has been studied quantitatively. Starting from an average grain size of 7 μm, grain growth was monitored in this alloy both under static annealing and with concurrent superplastic deformation at a high test temperature of 550°C. Grain size was averaged from measurements taken in longitudinal, transverse, and thickness directions and was found to grow faster during concurrent superplastic deformation than for static annealing. A grain growth law based on an additive nature between time-based and strain-based growth behavior was used to quantify the dynamics of concurrent grain growth. The extent of void formation during deformation was quantified as the area fraction of voids on L-S planes. This void fraction, referred to as the cavity area percent, was recorded at several levels of strain for specimens deformed at two different strain rates. A constitutive equation incorporating this grain growth data into the stress-strain rate data, determined during the early part of deformation, was generated and utilized to model the superplastic tensile behavior. This model was used in an effort to predict the stress-strain curves in uniaxial tension under constant and variable strain rate conditions. Particular attention was paid to the effects of a rapid prestrain rate on the overall superplastic response and hardening characteristics of this alloy.     

Prediction of Endpoint Phosphorus Content of Molten Steel in BOF Using Weighted K-Means and GMDH Neural Network

 The hybrid method composed of clustering and predicting stages is proposed to predict the endpoint phosphorus content of molten steel in BOF (Basic Oxygen Furnace). At the clustering stage, the weighted K-means is performed to generate some clusters with homogeneous data. The weights of factors influencing the target are calculated using EWM (Entropy Weight Method). At the predicting stage, one GMDH (Group Method of Data Handling) polynomial neural network is built for each cluster. And the predictive results from all the GMDH polynomial neural networks are integrated into a whole to be the result for the hybrid method. The hybrid method, GMDH polynomial neural network and BP neural network are employed for a comparison. The results show that the proposed hybrid method is effective in predicting the endpoint phosphorus content of molten steel in BOF. Furthermore, the hybrid method outperforms BP neural network and GMDH polynomial neural network.     

Precipitation Kinetics on a Nb-V Microalloyed Steel

The precipitation kinetics in a low carbon high strength low alloy (HSLA) steel,microalloyed with V+Nb has been studied by using the stress relaxation method.This technique was carried out in a dynamic dilatometer and allows to determine the onset and finishing precipitation times in hot deformed austenite.The evolution of the precipitates was also observed using field emission scanning electron microscopy (FESEM) on samples quenched at different times at given temperatures.Discussion is completed with the predictions by the thermodynamic software FactSage to identify stable precipitate phases under equilibrium conditions.Results confirm the feasibility of the stress relaxation technique as an efficient method for investigating precipitation kinetics.     

Study on grain refinement of interstitial-free steel during continuous frictional angular extrusion

To explore the application of severe plastic deformation for grain refinement in steel production,a new method called continuous frictional angular extrusion (CFAE) was applied to refine the grain of interstitial-free steel.The deformation was carried out at room temperature and individual sheet specimens were processed in different number of passes.An overall grain size of 200nm was achieved after 8 passes and the proportion of high-angle boundaries to the total boundaries was more than 60%.Through the characterization of high resolution EBSD,X-ray diffraction (XRD) and hardness testing,this paper discussed the evolution of microstructures and textures during deformation and explored the development direction of the method.     

Numerical calculation of energy deposition by high-energy electron beams: III-B. Improvements to the 6D phase space evolution model

The phase space evolution model of Huizenga and Storchi, Morawska-Kaczyńska and Huizenga and Janssen et al has been modified to (i) allow application on currently available computer equipment with limited memory (128 Megabytes) and (ii) allow 3D dose calculations based on 3D computer tomographic patient data. This is a further development aimed at the use of the phase space evolution model in radiotherapy electrons beam treatment planning. The first modification regards the application of depth evolution of the phase space state combined with an alternative method to transport back-scattered electrons. This depth evolution method requires of the order of 15 times less computer memory than the energy evolution method. Results of previous and new electron transport methods are compared and show that the new electron transport method for back-scattered electrons hardly affects the accuracy of the calculated dose distributions. The second modification regards the simulation of electron transport through tissues with varying densities by applying distributed electron transport through similarly composed media with a limited number of fixed densities. Results of non-distributed and distributed electron transport are compared and show that the distributed electron transport method hardly affects the accuracy of the calculated dose distributions. It is also shown that the results of the new dose distribution calculations are still in good agreement with and require significantly less computation time than results obtained with the EGS4 Monte Carlo method.     

板带热连轧过程氧化铁皮厚度变化的数值模拟

介绍了板带热连轧过程中表面氧化铁皮的结构和厚度演变规律,通过实验室氧化增重试验建立了氧化动力学模型,在此基础上结合热连轧过程钢板的温度变化趋势,对汽车大梁钢(510L)在热连轧过程中氧化铁皮的厚度变化进行了数值模拟,模拟结果与现场实际吻合较好。这为掌握热连轧过程中氧化铁皮厚度变化规律,调整生产工艺参数,抑制氧化铁皮生长提供了参考。     

基于改进差分进化算法的无人机在线低空突防航迹规划

为了解决无人机在部分未知敌对环境中的低空突防航迹规划问题,提出了一种改进的差分进化算法.该算法的进化模型采用冯.诺伊曼拓扑结构,并对其进行拓展,使种群在进化初期保持多样性,避免进化早期陷入局部最优,而进化后期加快收敛速度.该算法改进了差分进化算子中的变异操作,从而加快算法的收敛速度,快速找到多目标优化问题的最优解;同时,采用将绝对笛卡儿坐标和相对极坐标相结合的编码方式以提高搜索效率.将该算法用于无人机在线航迹规划仿真实验,并和未改进的算法结果作比较,验证了该算法的有效性.      

距离幂次反比法品位估计公式中参数确定的遗传算法

应用遗传算法提出了自动确定距离幂次反比法品位估计公式中最优幂次的方法。该方法根据生存竞争的自然进化法则，对众多随机生成的幂次进行类似于生物进化时发生的复制、交换、变异等若干个改良操作，淘汰极不合理的幂次，改良较合理的幂次，最后优选出具有很高品位估计精度的幂次。该方法完全不依赖人，具有很好的客观性和通用性。     

Detection of convergent and parallel evolution at the amino acid sequence level

Adaptive evolution at the molecular level can be studied by detecting convergent and parallel evolution at the amino acid sequence level. For a set of homologous protein sequences, the ancestral amino acids at all interior nodes of the phylogenetic tree of the proteins can be statistically inferred. The amino acid sites that have experienced convergent or parallel changes on independent evolutionary lineages can then be identified by comparing the amino acids at the beginning and end of each lineage. At present, the efficiency of the methods of ancestral sequence inference in identifying convergent and parallel changes is unknown. More seriously, when we identify convergent or parallel changes, it is unclear whether these changes are attributable to random chance. For these reasons, claims of convergent and parallel evolution at the amino acid sequence level have been disputed. We have conducted computer simulations to assess the efficiencies, of the parsimony and Bayesian methods of ancestral sequence inference in identifying convergent and parallel-change sites. Our results showed that the Bayesian method performs better than the parsimony method in identifying parallel changes, and both methods are inefficient in identifying convergent changes. However, the Bayesian method is recommended for estimating the number of convergent-change sites because it gives a conservative estimate. We have developed statistical tests for examining whether the observed numbers of convergent and parallel changes are due to random chance. As an example, we reanalyzed the stomach lysozyme sequences of foregut fermenters and found that parallel evolution is statistically significant, whereas convergent evolution is not well supported.     

Concurrent Engineering Approach to Reducing Design Delivery Time

A common method used to reduce project delivery time is to overlap sequential activities. Evolution and sensitivity characterizations of design activities provide a practical tool for identifying overlapping opportunities. The faster the evolution of information in an activity, the less risky it is to begin a downstream activity before the upstream activity is finalized. Also, the lower the sensitivity to changes in upstream information, the less risky it is to overlap activities. A methodology for determining the evolution and sensitivity of design activities has been developed through a series of expert interviews. The evolution of an activity can be determined by evaluating the levels of design optimization, constraint satisfaction, external information exchange, and standardization. The sensitivity of an activity can be determined by evaluating activity constraints, input variables, and the level of design integration. This framework for characterizing design activities in terms of evolution and sensitivity will lead to significant reductions in project delivery times.     

基于H型钢残余应力主动控制的矫直工艺设计

针对H型钢辊式矫直过程残余应力的主动控制,基于工程弹塑性理论建立一种矫直过程应力演变的分析模型;采用离散解析实现对模型的快速数值求解;继而基于该分析模型建立一套能够实现残余应力主动控制的工艺参数主动设计方法;运用该方法对典型规格H型钢矫直工艺参数进行工艺设计.建立的分析模型运算结果与有限元结果吻合且计算成本得到有效控制,模型能够实现有限时间内整个矫直工艺参数域内残余应力演变结果的分析;工艺设计方法能够得到一定目标参数和约束条件下的残余应力主动控制工艺参数.      

Estimating the rate of evolution of the rate of molecular evolution

A simple model for the evolution of the rate of molecular evolution is presented. With a Bayesian approach, this model can serve as the basis for estimating dates of important evolutionary events even in the absence of the assumption of constant rates among evolutionary lineages. The method can be used in conjunction with any of the widely used models for nucleotide substitution or amino acid replacement. It is illustrated by analyzing a data set of rbcL protein sequences.     

铝用石墨质阴极不同焙烧温度下孔隙结构演化

采用图像分析方法研究铝用石墨质阴极在不同焙烧温度下孔隙结构特征及其演变,考察孔隙率、孔径分布、形状因子、视孔隙比表面积、连通性等参数的变化规律和孔隙复杂度的分形特征.结果表明:随着焙烧温度增加,孔隙率逐渐增大,而视孔隙比表面积、形状因子和连通性呈先减小后增大趋势;石墨质阴极试样不同温度下焙烧生成孔隙均符合分形规律,借助图像分析孔隙结构参数和分形维数可界定不同典型焙烧温度下阴极孔隙结构的演变特征,并据此提出相应的孔隙特征演化模式.