Simulation of Mould Level Velocities During Continuous Casting of Round Bloom Strands With Mould-Electromagnetic Stirring

In modern continuous casting of round steel blooms rotating electromagnetic fields are commonly employed to improve the product quality.Mould-electromagnetic stirrers(M-EMS)are used to excite a rotary motion along the solidification front in the liquid core.These velocities lead to a better strand surface quality as well as enhancing the transition from columnar to equiaxed solidification.Although the usage of electromagnetic stirrers is widespread,not all effects are fully known or understood.Due to harsh conditions at the plant,measurements are scarce and limited.Water model experiments-an established alternative for investigating continuous casting of steel-cannot be used due to the low electrical conductivity of water.Experiments with liquid metals like mercury,Galinstan or Wood’s metal are either expensive or difficult to perform.Thus numeric simulations are essential to gain a better understanding of the processes involved in continuous casting with electromagnetic stirring.However numeric simulations should always be validated with experiments and/or measurements.While the velocity field inside the liquid core of the bloom cannot be measured at the caster,the velocity at the mould level can be measured by dipping a nail into it.The skull forming at the tip of the nail is directly linked to the occurring surface velocity.These measurements can then be compared with numeric simulations of the nail dipping process.The numeric model is restricted to the upper part of the strand.The lower part of the strand is also taken into account through adjusted boundary conditions(velocity field etc.taken from a simulation of the whole strand).In this work the influence of the stirring field strength on the simulation results will be investigated.In the future these nail dipping simulations will be validated with plant measurements.This can then to a certain extentvalidate the simulation of the strand with M-EMS too,as it serves as the basis for the nail dipping model.     

生产微合金化钢的几点考虑

在20世纪60～80年代,连续浇铸是钢铁工业的一项重要的工艺变革。这项技术无论对提高炼钢生产效率还是改善产品质量都产生了深刻的影响。然而,为保持产品竞争力和成本效益,需要一个统筹的炼钢方法。从铁水生产开始或者从冶炼开始,经过精炼到连铸,再到轧钢和后续工序,钢产品的整条生产路线应该整体可控。关于连铸,有2个实例可以说明这种发展趋势:改进中间包设计和冶金技术,优化浸入式水口和高水平的结晶器液面控制。无止境的洁净钢研究已经从连铸机本身转到钢包冶金。同样,无缺陷表面质量研究不再简单地专注于连铸技术,同时也将炼钢考虑进去。随着结构钢品种的合金设计转变,从普通的中碳锰钢到裂纹敏感的现代低碳微合金化HSLA钢,连铸机的设计和技术发展并驾齐驱。     

Perceptual Evaluation of Ghosted View Techniques for the Exploration of Vascular Structures and Embedded Flow

This paper presents three controlled perceptual studies investigating the visualization of the cerebral aneurysm anatomy with embedded flow visualization. We evaluate and compare the common semitransparent visualization technique with a ghosted view and a ghosted view with depth enhancement technique. We analyze the techniques’ ability to facilitate and support the shape and spatial representation of the aneurysm models as well as evaluating the smart visibility characteristics. The techniques are evaluated with respect to the participants accuracy, response time and their personal preferences. We used as stimuli 3D aneurysm models of five clinical datasets. There was overwhelming preference for the two ghosted view techniques over the semitransparent technique. Since smart visibility techniques are rarely evaluated, this paper may serve as orientation for further studies.     

Anatomy‐Guided Multi‐Level Exploration of Blood Flow in Cerebral Aneurysms

For cerebral aneurysms, the ostium, the area of inflow, is an important anatomic landmark, since it separates the pathological vessel deformation from the healthy parent vessel. A better understanding of the inflow characteristics, the flow inside the aneurysm and the overall change of pre‐ and post‐aneurysm flow in the parent vessel provide insights for medical research and the development of new risk‐reduced treatment options. We present an approach for a qualitative, visual flow exploration that incorporates the ostium and derived anatomical landmarks. It is divided into three scopes: a global scope for exploration of the in‐ and outflow, an ostium scope that provides characteristics of the flow profile close to the ostium and a local scope for a detailed exploration of the flow in the parent vessel and the aneurysm. The approach was applied to five representative datasets, including measured and simulated blood flow. Informal interviews with two board‐certified radiologists confirmed the usefulness of the provided exploration tools and delivered input for the integration of the ostium‐based flow analysis into the overall exploration workflow.     

DSNotify – A solution for event detection and link maintenance in dynamic datasets

The dynamics of linked datasets may lead to broken links if data providers do not react to changes appropriately. Such broken links denote interrupted navigational paths between resources and may lead to unavailability of data. As a possible solution, we developed DSNotify, an event-detection framework that informs actors about various types of changes and allows them to maintain links to resources in distributed linked data sets. For representing changes we developed the DSNotify Eventset Vocabulary. Different from other vocabularies it applies a resource-centric perspective and preserves the timely order of changes. We further describe our reusable evaluation infrastructure, which can be extended for extracting change sets from arbitrary linked datasets.     

Failure of a bus hoisting platform due to unexpected system behaviour

A bus hoisting platform showed an unexpected behaviour under asymmetric loading. In order to assess the internal restraints and joint forces which had not been considered properly in initial design, a numerical approach was chosen. With a multi-body simulation tool, the loads were calculated for different system configurations and loading situations. The identified loads were used for the stress analysis of individual components (analytical and numerical with FEM). The results revealed joint forces of a higher order than the total external load, which was a consequence of first the underestimated internal loads due to unapparent horizontal force components in the statically indeterminate system, and second, the implemented force control of the hydraulic actuators working in parallel. The correctly identified high internal loads explained the peculiar observations and lead to an insufficient fatigue strength of the welded structure.     

Long-term stream invertebrate community alterations induced by the insecticide thiacloprid: effect concentrations and recovery dynamics

In pesticide risk assessment, effect concentrations and dynamics of long-term community-level effects caused by pulse exposures remain to be investigated. This is because long-term experiments are exceptionally rare, and most of the previously investigated communities had low proportions of sensitive long-living species. The aim of the present study was to investigate the effect of a single pulse contamination with the insecticide thiacloprid on invertebrates. We employed mesocosms designed to realistically mimic communities in small streams within the agricultural landscape. Specifically, the objectives were to (i) compare the community Lowest-Observed-Effect Concentration (LOEC) with organism-level median lethal concentrations (LC50), and (ii) to assess recovery dynamics with special focus on short- and long-living taxa. The contamination resulted in long-term alteration of the overall invertebrate community structure (7 months, until the end of the experiment). Long-term community LOEC was 3.2 microg/L (Redundancy Analysis), slightly below the acute LC50s known for sensitive invertebrates relevant to the mesocosm community. However, one species (stonefly Nemoura cinerea) was affected at the lowest tested concentration, 70 times below the lowest known LC50. Concerning time to recovery from the effect, we found that the duration depends on the life-cycle characteristics of species, but not on the toxicant concentration: short-living (mulivoltine) species recovered after 10 weeks following contamination, whereas long-living (uni- and semivoltine) species did not recover until the end of the experiment (7 months). The present example shows that concentrations of pesticides at which majority of the species is affected can be predicted by acute organism-level toxicity tests with sensitive species. However, tests with longer observation periods, as well as consideration of environmental factors and inter-taxon variability in sensitivity are required to predict effects on all species comprising a community. Realistic prediction of community recovery dynamics requires consideration of the species' life-cycle traits.