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Abstract Various assumptions are often made to model turbomachinery bladed assemblies. In particular, the cyclic symmetry of single rotor stages, and dynamically independence of isolated rotor stages are frequently used. The first assumption enables a drastic reduction of the required computational resources by considering only one sector instead of the entire assembly to model and analyze the dynamic behavior of the complete structure. However, small random blade-to-blade structural variations, known as mistuning, exist due to manufacturing tolerances, etc. and significantly affect the dynamic behavior of bladed disks. The second assumption also reduces the needed computational resources and time. However, ignore inter-stage coupling does not always describe accurately the disk or drum flexibility especially at the inter-stage boundaries. In this work, the component mode mistuning method is used for multi-stage assemblies to create a mistuning identification approach. An experimental modal analysis is performed on a two-stage monobloc academic bladed drum. The frequency response function is measured using a base excitation with an electrodynamic shaker and one measurement point per blade of each stage is used. The approach is used to identify mistuning in a multi-stage rotor. Numerical and experimental results are presented. Results show that the proposed approach is effective even for modes which are multi-stage.

Abstract The development of predictive mathematical models for water management in polymer electrolyte membrane fuel cells requires detailed understanding of water distribution and water transport across the Nafion layer. The anisotropic microstructure of Nafion suggests the measurement of water content and mass transport should be along the fuel cell functional direction, i.e. across the membrane. Non-invasive, high resolution, microscopy measurements of this type are very challenging. We report here the calibration of a minimal mathematical model for diffusive water transport in Nafion against data from high-resolution water content maps determined with a new magnetic resonance imaging methodology developed for this purpose. A mock fuel cell was designed to permit well-controlled wetting and drying boundary conditions. With no chemical potential driving force involved, we assume the water transport behavior will be dominated by diffusion. Moreover we show that, in this context, our model is mathematically equivalent to the traditional permeation models based upon saturation dependent pressure gradients via a capillary pressure ansatz. The non-linear equilibrium water distribution across the Nafion membrane measured in this work suggests a bi-modal diffusivity. The model constructed associates distinct transport behaviors to water contents above and below a critical threshold, consistent with a rearrangement of a micro-structural pore network. The experimental observation and the model prediction agree with the primary features of Weber's model of Nafion, which predicts distinct modes of transport for hydration fronts traversing the through-plane direction of the membrane.

Abstract A record radiation efficiency of 37% is achieved using a two-layered porous (SiC foam, fine and course) burner using multiscale thermal nonequilibria and effective heat recirculation. The porous burner holds the flame and heats finned SiC rods effectively conducting heat to radiating disks downstream, while the flue gas is intercepted before leaving the disk spacing by a preheater carrying secondary air that mixes upstream with the fuel and primary air. These result in superadiabatic combustion in porous layers and fuel-gas preheating that causes exiting flue gas having a temperature lower than the radiating disks. These orchestrated heat recirculation and preheating extend the lean flammability to 0.24 equivalence ratio, and allow the flue gas temperature to be over 50 K below the radiating disks temperature. A three-dimensional model of the structures with a two-step combustion reaction allow to predict the combustion and emission and related convection, conduction and radiation heat transfer, with excellent agreement with the experiments over wide ranges of fuel flow rate and equivalence ratio.

About 50% of U.S. water pollution problems are caused by non-point source (NPS) pollution, primarily sediment and nutrients from agricultural areas, despite the widespread implementation of agricultural Best Management Practices (BMPs). However, the effectiveness of implementation strategies and type of BMPs at watershed scale are still not well understood. In this study, the Soil and Water Assessment Tool (SWAT) ecohydrological model was used to assess the effectiveness of pollutant mitigation strategies in the Raccoon River watershed (RRW) in west-central Iowa, USA. We analyzed fourteen management scenarios based on systematic combinations of five strategies: fertilizer/manure management, changing row-crop land to perennial grass, vegetative filter strips, cover crops and shallower tile drainage systems, specifically aimed at reducing nitrate and total suspended sediment yields from hotspot areas in the RRW. Moreover, we assessed implications of climate change on management practices, and the impacts of management practices on water availability, row crop yield, and total agricultural production. Our results indicate that sufficient reduction of nitrate load may require either implementation of multiple management practices (38.5% with current setup) or conversion of extensive areas into perennial grass (up to 49.7%) to meet and maintain the drinking water standard. However, climate change may undermine the effectiveness of management practices, especially late in the 21st century, cutting the reduction by up to 65% for nitrate and more for sediment loads. Further, though our approach is targeted, it resulted in a slight decrease (~5%) in watershed average crop yield and hence an overall reduction in total crop production, mainly due to the conversion of row-crop lands to perennial grass. Such yield reductions could be quite spatially heterogeneously distributed (0 to 40%).

Abstract Two prethinned spinel specimens containing either Y0.15Zr0.85O2 or Ce0.5Zr0.5O2 particles were implanted with 200–400 keV Xe ions at 873 K using the IVEM-Tandem Facility at Argonne National Laboratory. In situ transmission electron microscopy (TEM) was conducted during the implantation in order to follow the evolution of the microstructure. At an ion fluence between 2.4x1020 to 3x1020 m−2 (up to 50 dpa and 4.7 at %), large Xe bubbles of 50–100 nm developed at the boundaries of the small oxide particles, while a high density of dislocation loops (up to 8 nm in diameter) and much smaller bubbles (up to ∼4 nm in diameter) formed in the spinel matrix. No large bubbles were observed at the boundaries between the spinel grains. These results suggest that the boundaries between spinel and oxide particles are preferred sites for fission gas accumulation.

Abstract As the capacity of wind turbines has increased, the loads on crucial components such as a gearbox, a generator, and blades are significantly increasing. An intelligent online monitoring system is indispensable to protect the excessive load on core components and manage a wind farm efficiently. In order to verify new online monitoring and diagnostic methods for such a monitoring system in advance, a wind turbine simulator is essential. For this purpose, we developed a simulator that has similar dynamics to an actual 3 MW wind turbine, and is thereby able to acquire a state of operation that closely resembles that of the 3 MW wind turbine under a variety of wind conditions. This paper describes the implementation of a torque and a collective pitch controller, which is used for a new type of simulator with the intention of exploiting online monitoring and diagnostic methods. The torque and the collective pitch controllers were developed to facilitate variable speed-variable pitch control strategies in the wind turbine simulator. Experiments demonstrated that three control regions were successfully deployed on the simulator, and thereby the simulator was operated at all control regions in a stable and accurate manner. Moreover, the strain and vibration measured from the blade and the gearbox showed different trends at three control regions. Therefore, a new type of simulator is an effective means to develop diagnostic and prognostic algorithms as well as online monitoring methods reflecting the dependency of dynamic characteristics on the control regions.

Abstract A model elucidates two transport mechanisms associated with the volumes dissolved electrolytes occupy: the ‘excluded-volume effect’, which arises when concentration polarization induces solution-density gradients that drive volume redistribution; and ‘Faradaic convection’, which occurs when interfacial electrochemical reactions induce bulk flow. The excluded-volume effect can be accounted for in Newman's concentrated-solution theory by incorporating a thermodynamic state equation that describes the solution's local molar volume. Faradaic convection is introduced through boundary conditions that include volume-average velocity, which is distributed throughout a solution by a volume-balance governing equation. Two dimensionless parameters quantify the importances of these phenomena, which prove relevant when modeling nonaqueous electrolytes. Analytical formulas are derived to describe concentration polarization and diffusion potentials in parallel-electrode cells undergoing symmetric ion-deposition/stripping half-reactions. In moderately concentrated nonaqueous electrolytes, Faradaic convection elevates limiting currents by as much as ten percent above those predicted by a theory neglecting it. The excluded-volume effect similarly impacts diffusion potentials.

Abstract This research studies the low carbon transition of the electric power sector in China using a multi-level perspective (MLP) of niches, socio-technical regime, and landscape, as well as literature on innovation systems. Three lines of thought on transition process are integrated in the paper to probe the possible transition pathways in China. A MLP analysis is presented to understand the current niches, regime, and landscape of China’s power sector. A brief analysis on the future macroscopic socio-economic transition in the process of industrialization, urbanization, and modernization of Chinese society and its implication on power landscape are depicted to prove the urgency and magnitude of transition in China and why systematic transition management is needed. Five transition pathways, namely reproduction, transformation, substitution, reconfiguration, de-alignment/re-alignment, and reconfiguration, with their possible technology options are presented. The paper goes further to propose an interactive framework for managing the transition to a low carbon energy system in China. Representative technology options are appraised by employing innovation theory to indicate the logic of policymaking within the framework. Institutional gaps in realizing the transition are also addressed. The work presented in the paper will be useful in informing policy-makers and other stakeholders and may provide references for power sector transition management in other countries.