Junction and Drop-Shaft Boundary Conditions for Modeling Free-Surface, Pressurized, and Mixed Free-Surface Pressurized Transient Flows

A junction and drop-shaft boundary conditions (BCs) for one-dimensional modeling of transient flows in single-phase conditions (pure liquid) are formulated, implemented and their accuracy are evaluated using two computational fluid dynamics (CFD) models. The BCs are formulated in the case when mixed flows are simulated using two sets of governing equations, the Saint-Venant equations for the free-surface regions and the compressible water hammer equations for the pressurized regions. The proposed BCs handle all possible flow regimes and their combinations. The flow in each pipe can range from free surface to pressurized flow and the water depth at the junction or drop shaft can take on all possible levels. The BCs are applied to the following three cases: (1) a three-way merging flow; (2) a three-way dividing flow; and (3) a drop shaft connected to a single-horizontal pipe subjected to a rapid variation of the water surface level in the drop shaft. The flow regime for the first two cases range from free surface to pressurized flows, while for the third case, the flow regime is pure pressurized flow. For the third case, laboratory results as well as CFD results were used for evaluating its accuracy. The results suggest that the junction and drop-shaft BCs can be used for modeling transient free-surface, pressurized, and mixed flow conditions with good accuracy.     

Forensic analysis of buildings affected by mining subsidence

This work presents a forensic analysis of ground subsidence occurred in Lo Tacón industrial area, which is located at the outskirts of La Unión (Murcia, SE Spain). Subsidence was triggered by the collapse of abandoned underground mining labours occurred in 1998. Coinciding in time with this event, it was detected a seismic movement, whose epicentre was located close to the study area.In the first part the affected area is analysed and delimited, as well as the spatial and temporal evolution of the damages attributed to the collapse of 1998. Then the causes of ground failure are also determined, as well as their possible temporal and spatial relationship with the seismic movement detected. Through this analysis it is presented a methodology to determine the effects of this phenomenon. It consists on extending field work radially to all existing buildings within the affected area, considering the centre around the zone where the greatest damage was produced. Finally it is analysed the temporal and spatial evolution of the cracks inventoried in buildings to determine active areas where certain subsidence persists. According to the results presented in this work, it may be concluded that damages are the consequence of buildings constructed in a potentially dangerous area where ground settlement occurs due to mining subsidence.     

Analysis of a diesel generator cylinder failure

This paper analyses a catastrophic cylinder failure of a four stroke 14 V diesel engine of an electrical power plant when running to nominal speed of 600 rpm. The rated power of the engine was 7.5 MW and before failure had accumulated 80,000 h in service operating mainly at full load. As a result, the piston and liner of cylinder 4 were broken; the crankcase and main crankshaft bearings next to this cylinder were also damaged. The mechanical properties of the liner (grey cast iron) and piston body (aluminium alloy) including tensile properties and Brinell hardness were evaluated. No signs of fatigue failure were identified in liner and piston. A finite element model of the liner has shown that the most heavily loaded areas match the fractured zones.     

Nanogeometry matters: unexpected decrease of capillary adhesion forces with increasing relative humidity

The sticking effect between hydrophilic surfaces occurring at increasing relative humidity (RH) is an everyday phenomenon with uncountable implications. Here experimental evidence is presented for a counterintuitive monotonous decrease of the capillary adhesion forces between hydrophilic surfaces with increasing RH for the whole humidity range. It is shown that this unexpected result is related to the actual shape of the asperity at the nanometer scale: a model based on macroscopic thermodynamics predicts this decrease in the adhesion force for a sharp object ending in an almost flat nanometer-sized apex, in full agreement with experiments. This anomalous decrease is due to the fact that a significant growth of the liquid meniscus formed at the contact region with increasing humidity is hindered for this geometry. These results are relevant in the analysis of the dynamical behavior of nanomenisci. They could also have an outstanding value in technological applications, since the undesirable sticking effect between surfaces occurring at increasing RH could be avoided by controlling the shape of the surface asperities at the nanometric scale.     

Self-organized Ce(1-x)Gd(x)O(2-y) nanowire networks with very fast coarsening driven by attractive elastic interactions

Assembling arrays of ordered nanowires is a key objective for many of their potential applications. However, a lack of understanding and control of the nanowires' growth mechanisms limits their thorough development. In this work, an appealing new path towards self-organized epitaxial nanowire networks produced by high-throughput solution methods is reported. Two requisites are identified to generate the nanowires: a thermodynamic driving force for an unrestricted elongated equilibrium island shape, and a very fast effective coarsening rate. These requirements are met in anisotropically strained Ce(1-x)Gd(x)O(2-y) nanowires with the (011) orientation grown on the (001) surface of LaAlO(3) substrates. Nanowires with aspect ratios above ≈100 oriented along two mutually orthogonal axes are obtained leading to labyrinthine networks. A very fast effective nanowire growth rate (≈60 nm min(-1)) for ex-situ thermally annealed nanostructures derives from simultaneous kinetic processes occurring in a branched network. Ostwald ripening and anisotropic dynamic coalescence, both promoted by strain-driven attractive nanowire interaction, and rapid recrystallization, enabled by fast atomic diffusion associated with a high concentration of oxygen vacancies, contribute to such an effective growth rate. This bottom-up approach to self-organized nanowire growth has a wide potential for many materials and functionalities.     

In-band optical signal-to-noise ratio monitoring method based on high-resolution polarization analysis and induced differential group delay

We report on an in-band optical signal-to-noise ratio monitoring technique for wavelength division multiplexed channels. Our proposal relies on the different degree of polarization between the signal (highly polarized) and the noise (not polarized). Using this principle, we divide the signal under test into two orthogonal polarization components and induce a differential group delay via a controlled birefringence apparatus that produces a wavelength-dependent shift of the polarization state of the signal. After a linear polarizing filter, high-resolution spectral analysis allows measurement of the amplified spontaneous emission noise level. The method is tested by experimental measurements of a 40 Gbit/s differential phase-shift keying channel showing very good performance.     

Flux-assisted spreading of an Al–7 wt%Si alloy on TiC

The effect of a K–Al–F-based flux was investigated on the wettability of TiC by an Al–7 wt%Si alloy in the interval of temperatures between 660 and 900 °C in Ar and in atmospheric air. Null spreading was observed without flux whereas perfect wetting was enabled by the flux in both atmospheres. The liquid flux, which provides a locally protective atmosphere by spreading on the surfaces of the substrate and eventually on the Al alloy, dissolves the aluminium oxide covering the molten alloy enabling thus direct contact between the liquid alloy and the TiC substrate. The low tensions for the solid/flux and liquid metal/flux interfaces facilitate spontaneous spreading and instantaneous wetting. Meanwhile, the flux is displaced to the lateral periphery of the substrate and to the surface of the liquid. Under the resolution of the scanning electron microscope, microstructural examination of the interfaces did not reveal reaction products. Rapid infiltration of the alloy into TiC/flux compacts, at low temperatures, correlated well with the flux-assisted spreading kinetics observed.     

Ultrafine Grained HSLA Steels for Cold Forming

 This research shows, through the analysis of three steels that comply with the EN 10149-2 Euronorm, examples of ultrafine grained (or ultrafine ferrite) ferrous alloys, with ASTM grain sizes close to 14 (2 3 m). These steels are microalloyed with Ti-Nb and have been produced by advanced hot rolling controlled techniques in the factories of ArcelorMittal de Avilés (Asturias, Spain) and are mostly used in automotive and construction applications. By comparison, other techniques to obtain ultrafine grained steels are mentioned, though they have not yet reached the industrial level and are produced in laboratories due to the fact that their mechanical properties (low strain hardening coefficient "n") don't allow cold working operations such as bending, stretching nor drawing.     

On the measurement of 10Be on the 1 MV compact AMS system at the Centro Nacional de Aceleradores (Spain)

In this work we present the most recent improvements performed by our group on ¹⁰Be measurements on the 1 MV AMS system recently set up at the CNA (Centro Nacional de Aceleradores), in Seville (Spain). Our efforts have been focused on the study of the viability of our system for BeO and BeF^? measurements. To achieve this, different standard materials have been measured to demonstrate the reliability of the system for BeO measurements in a wide ¹⁰Be/⁹Be atomic ratio range and several environmental samples have been studied both at the 1 MV AMS CNA facility and at the 6 MV AMS ETH-PSI facility of Zurich to validate our measurements. The results show a good agreement between laboratories. New experiments also have been carried out selecting 1+ and 2+ charge states at the exit of the accelerator and inserting Si₃N_3.1 foils with different thicknesses to separate ¹⁰Be from its isobar, ¹⁰B. The influence of each foil on the overall transmission (detected ¹⁰Be compared to BeO^? injected into the accelerator) and background level was also assessed. In addition some tests were also done to assess the viability of BeF₂ and BaBeF₄ measurements at our system. Several metal matrices and cathode preparation procedures for BeO samples were investigated to maximize current and cathode lifetime.     

Full speed range permanent magnet synchronous motor control without mechanical sensors

This study presents a control method for permanent magnet (PM) motors based on a combination of a non-linear full-order observer and a signal injection scheme. Stable mechanical-sensorless operating range down to zero speed at full load is obtained using only voltage and current sensors. The signal injection scheme uses the asymmetry of the motor?s d and q-axis inductances to estimate rotor position and speed. Such asymmetry is also taken into account in the motor model used to construct the observer to reduce current estimation error. The performance of the proposed scheme is validated through experimental results.