Hydrogen fuel-cell forklift vehicle releases in enclosed spaces

Sandia National Laboratories has worked with stakeholders and original equipment manufacturers (OEMs) to develop scientific data that can be used to create risk-informed hydrogen codes and standards for the safe operation of indoor hydrogen fuel-cell forklifts. An important issue is the possibility of an accident inside a warehouse or other enclosed space, where a release of hydrogen from the high-pressure gaseous storage tank could occur. For such scenarios, computational fluid dynamics (CFD) simulations have been used to model the release and dispersion of gaseous hydrogen from the vehicle and to study the behavior of the ignitable hydrogen cloud inside the warehouse or enclosure. The overpressure arising as a result of ignition and subsequent deflagration of the hydrogen cloud within the warehouse has been studied for different ignition delay times and ignition locations. Both ventilated and unventilated warehouses have been considered in the analysis. Experiments have been performed in a scaled warehouse test facility and compared with simulations to validate the results of the computational analysis.     

雷达天线车液压升降系统同步控制仿真研究

雷达天线车自动调平系统是雷达的一个重要组成部分,对提高雷达的测量性能和机动能力起着决定性作用.为了解雷达车电液升降系统的同步协调特性,采用MATLAB和Simulink软件建立了系统调平模型并进行了仿真研究.为消除电液调平系统液压缸参数制造误差、各通道负载不均衡等对同步控制精度的影响,设计了定量反馈控制( QFT)同步调平控制器来提高倾角调平精度.仿真结果表明:设计的调平控制器具有良好的同步精度和快捷的响应速度,能驱动调平仿真台快速、稳定地运动.     

Fe-1.95％Cu-1.95％Ni合金时效过程的分子动力学模拟

采用分子动力学模拟了Fe-1.95％ Cu-1.95％ Ni合金在823 K下的时效过程.结果表明:在Fe-Cu-Ni合金中,Cu和Ni之间存在一种相互促进扩散相互促进析出的协同作用;Cu、Ni的扩散过程都存在三个扩散速率不同的阶段,分别为自由迁移形成团簇的过程,溶质团簇的不断形成过程和团簇的长大过程.     

ATS 2007

Abstract

The 28th Journées Sideusgiques Internationales, organised by ATS, was held in Paris on 13–14 December 2007. Over 500 delegates participated in 20 technical sessions over two days, covering ironmaking through to product development. I&S Executive Editor, Dr David Price, reviews a selection of interesting presentations.     

Simulating the drawing of spunbonding nonwoven process using an artificial neural network technique

The statistical and artificial neural network (ANN) models are established for predicting the fiber diameter of spunbonded nonwovens from the processing parameters. The ANN of Bayesian frameworks produces smaller prediction errors and thus is determined to be the preferred network. Results show that the ANN model yields more accurate and stable prediction than the statistical model, and a reasonably good ANN model can be established with relatively few data points. Four methods are used to reveal the relative importance of the processing parameters in terms of their effect on the fiber diameter. It is found that the initial polymer temperature plays an most important role in reducing the fiber diameter, while the effect of the initial air temperature is not significant. Using an established ANN model, computer simulations of the effects of the processing parameter on the fiber diameter are carried out. It is found that higher polymer melt index, smaller polymer flow rate, higher initial polymer temperature, higher initial air temperature, and higher initial air velocity can all produce finer fibers. This area of research has great potential in the field of computer-assisted design in spunbonding technology.     

DCworms – A tool for simulation of energy efficiency in distributed computing infrastructures

In the recent years, energy-efficiency of computing infrastructures has gained a great attention. For this reason, proper estimation and evaluation of energy that is required to execute data center workloads became an important research problem. In this paper we present a Data Center Workload and Resource Management Simulator (DCworms) which enables modeling and simulation of computing infrastructures to estimate their performance, energy consumption, and energy-efficiency metrics for diverse workloads and management policies. We discuss methods of power usage modeling available in the simulator. To this end, we compare results of simulations to measurements of real servers. To demonstrate DCworms capabilities we evaluate impact of several resource management policies on overall energy-efficiency of specific workloads executed on heterogeneous resources.     

Electron microscopy: probing the atomic structure and chemistry of grain boundaries, interfaces and defects

At the heart of ‘ dynamic embrittlement’ phenomena is the stress-induced segregation of microscopic quantities of embrittling impurities to fracture surfaces. Grain boundaries and interfaces are often the natural weak links in a material. The structural and chemical information of such internal interfaces can be probed on an atomic scale using transmission electron microscopy. High-resolution electron microscopy can be used to determine the atomic coordinates of crystalline interfaces. Electron-energy-loss spectroscopy (EELS) and energy-dispersive X-ray spectroscopy can be performed on any boundary or defect and can provide chemical information such as composition and bonding. The spatial resolution of EDS is limited by low collection efficiency to around 10 Å. The more efficient signal collection for EELS allows almost atomic resolution for light elements. EELS fine structure offers a fingerprint of the local boundary arrangements, and also insight into the bonding (and possible reactivity) of boundaries and other defects. Overall, electron microscopy can be used to identify the atomistic characteristics of those interfaces susceptible to dynamic embrittlement. The structural and electronic information obtained can be used as a starting point for semi-empirical and ab initio simulations.     

A video lecture and lab-based approach for learning of image processing concepts

The current practice of traditional in-class lecture for learning computer science (CS) in the high schools of Taiwan is in need of revamping. Teachers instruct on the use of commercial software instead of teaching CS concepts to students. The lack of more suitable teaching materials and limited classroom time are the main reasons for the software-based teaching practices. This study proposes a pre-class video viewing of the lecture content plus in-class supervised laboratory work as a model that can overcome the above problems. Experiments on teaching image processing concepts at two local high schools have been conducted. The experimental results show that the proposed model is a feasible and effective way for the teaching and learning of image processing. The new approach also facilitates student–student and student–teacher interactions in the classroom. Finally, an improvement in the understanding of the subject by the students and an increased interest toward learning CS are also evident.     

Monte Carlo simulation of steps behavior on Si(111) surface during sublimation

Investigation of steps behavior on vicinal (111) surface during sublimation was carried out using 3D-model of diamond-like crystal. Step width periodic variations predicted by Schwoebel were found by modeling. Diamond-like crystal structure results in the asymmetry in atom fluxes to the upper or lower terraces, with the sign of asymmetry depending on the step structure. The essential effect of vacancies created on terraces on migration length of atoms was revealed.     

Characteristic value determination from small samples

The paper deals with the characteristic value determination from relatively small samples. When the distribution and its parameters of a random variable are known, the characteristic value is deterministic quantity. However, in practical problems the parameters of distribution are unknown and can only be estimated from random samples. Therefore the characteristic value is by itself a random variable. The estimates of characteristic values are strongly dependant on the distribution of random variable. In the paper we show the analytical solution for characteristic value determination from random samples of normal and lognormal random variables. The confirmation of analytical results is accomplished by the use of computer simulations. For Gumbel, and Weibull distribution the characteristic value estimates are obtained numerically by combination of simulations and bisection method. In the paper the numerical results are presented for 5% characteristic values with 75% confidence interval, which is in accord with the majority of European building standards. The proposed approach is demonstrated on the data of experimentally obtained bending strengths of finger jointed wooden beams.