Rodrigo Soares

Numerical model of electromagnetic stirring for continuous casting billets

This paper introduces a numerical model of an electromagnetic rotary stirrer based on the finite-element model. Such stirrers are used to improve the quality of continuously cast steel, particularly billets and blooms. The method determines the magnetic flux density profile and compares it to experimental measurements. In addition, it calculates the Lorentz force field as a function of the stirrer position, the current applied, and the frequency. The stirrer position at the end of the mold affects the profile symmetry of the force, creating a z component of the force. With this model, it will be possible to simulate the fluid dynamics effects in the molten steel.

Taxa de soerguimento atual do arquipélago de São Pedro e São Paulo, Oceano Atlântico Equatorial

The Saint Peter and Saint Paul Islets are situated in the Equatorial Atlantic Ocean at the top of a submarine ridge made up of mantle peridotite. It is 90 km long, 25 km wide, and 3,800 m high, and is called the Saint Peter Saint Paul Peridotite Ridge. The submarine morphology is highly rugged with hundreds-of-meters-high scarps, suggesting the occurrence of probably recent active tectonism. The summit level map shows two surfaces of wave-cut benches with respective altitudes of 4~5 m and 7~9 m. The wave-cut benches are observed on three major islets in the same altitude ranges, indicating that no tilting or differential uplifting between the islets has occurred. Considering the upper platform to be formed during the Flandrian Transgression and the lower one developed by a recent erosive process, the mean uplift rate in the last 6.000 years is calculated to be 1.2~1.5 mm/year. The 14C datings for the coral fossils collected from the Belmont Island indicate the uplift rate in the last 6600 years to be 1.5~1.8 mm/year. Therefore, a rate of 1.5 mm/year should be reasonable for the present-day uplifting. Interpreting the peridotite ridge as a tectonically deformed megamullion, the total uplift would be 1500~3000 m and the tectonism should have started at 1~2 Ma. If the Peridotite Ridge is originated from the subcrustal oceanic mantle, the total uplift would be approximately 9000 m and the tectonism would have started close to 6 Ma.

Reavaliação genética do modelo do Vulcão de Nova Iguaçu, RJ: origem eruptiva ou intrusão subvulcânica?

This paper re-examines the geologic structures that were considered to be of eruptive origin of the Mendanha Alkaline Complex, State of Rio de Janeiro, Brazil. The valley interpreted to be a crater is not underlain by pyroclastic agglomerate, but by massive trachyte. The alluvial deposit on this valley is a few meters thick and composed of regolitic materials. The talus deposit of large boulders suggestive of crater wall collapse is not observed. No morphologic elevation indicative of volcanic cone is found. The outcrops around the supposed crater show no volcanic stratification. The valley is not considered to be a volcanic crater but a landform resulted from erosion. The most abundant trachyte of this area is cut by the alkali syenite, and therefore, cannot be the lava flow that covers the syenite. The trachyte takes place up to the top of the massif, 600 m above the supposed crater. The columnar joints are originated from dikes, and the bread crust-like structure is attributed to weathering. These observations indicate that the trachyte is not constituent of lava flows, but of subvolcanic bodies. The authors conclude that the volcanic rocks in question are not constituent of volcanic edifice, but of subvolcanic vent-filling tuff breccia, and the hypothesis of the Nova Iguacu Volcano is implausible.

Subvolcanic vent-filling welded tuff breccia of Cabo Frio Island, State of Rio de Janeiro, Brazil

At the southwestern corner of Cabo Frio Island, State of Rio de Janeiro, Brazil, a pyroclastic body is present in an area of 500 x 600 m, intruding into the host orthogneiss with subvertical contact. Between the orthogneiss and pyroclastic body, there is a trachyte intercalation, 5 to 10 m wide. The pyroclastic rocks have a clast-matrix supported structure and the clast size ranges from 1 mm to 40 cm. Larger than 10 cm clasts are semi-rounded and those that are less than 5 cm are angular. They are composed mainly of trachyte, subordinately of orthogneiss, and eventually of welded tuff. The texture is heterogeneous and no grain-size sorting or volcanic layering of the clasts was observed. Microscopic observations have revealed hydrothermal alteration featured by calcite dissemination, alkaline feldspar sericitization, and mafic mineral decomposition. The matrix is filled by angular fragments of alkaline feldspar, quartz, plagioclase, and opaque minerals, smaller than 0.6 mm. The existence of the welded tuff clasts indicates that explosive eruptions took place repeatedly. The subvertical intrusive contact, small exposure area, rounded clasts, heterogeneous clast size, and absence of volcanic layering indicate that the pyroclastic rock is subvolcanic vent-filling welded tuff breccia, and not a constituent of a subaerial eruptive deposit.

New method of semi-automatic modal analyses for phenocrysts of porphyritic rocks based on quantitative digital colour specification technique

This paper proposes a new method for modal analyses of centimetric phenocrysts and porphyroblasts using a digital rock image. The dot matrix image of the rock is imported into vectorial draw software as background. The outline of all of the phenocrysts is marked on the overlay by closed vectorial curves and their internal area is painted in black. After this operation, the rock image on the background is deleted and the background is painted in white. The vectorial objects composed of the background and the overlay are exported as a matrix image of BMP format. The percentage of the areas painted in black corresponds to modal abundance of the phenocrysts, and it is calculated by the Wilber colour specification software. This method has high precision in graphic processing. However the translucency of the groundmass causes uncertainness in vectorial phenocryst marking. Therefore, it is recommended for rocks with phenocrysts larger than 5 mm.

Efeitos térmicos e fluido-dinâmicos devidos a um agitador eletromagnético para tarugos

The electromagnetic stirring during the continuous casting became indispensable to obtain steel with high quality. Despite the fact that the stirring effects during the solidifying process are not very well known from the theoretical point of view, these effects can be studied on the steel flow. The aim of this work is to study the magnetic and the fluid dynamic effects due to a rotatory stirrer for billets. A model solved by the finite element method was developed using the Ansys commercial package to solve the coupled magnetic-fluid dynamic problem. To make a comparison simulations with two current values were carried out and the main differences concerning the fluid flow and the thermal profile were analyzed.