Errors in Acoustic Doppler Profiler Velocity Measurements Caused by Flow Disturbance

Acoustic Doppler current profilers (ADCPs) are commonly used to measure streamflow and water velocities in rivers and streams. This paper presents laboratory, field, and numerical model evidence of errors in ADCP measurements caused by flow disturbance. A state-of-the-art three-dimensional computational fluid dynamic model is validated with and used to complement field and laboratory observations of flow disturbance and its effect on measured velocities. Results show that near the instrument, flow velocities measured by the ADCP are neither the undisturbed stream velocity nor the velocity of the flow field around the ADCP. The velocities measured by the ADCP are biased low due to the downward flow near the upstream face of the ADCP and upward recovering flow in the path of downstream transducer, which violate the flow homogeneity assumption used to transform beam velocities into Cartesian velocity components. The magnitude of the bias is dependent on the deployment configuration, the diameter of the instrument, and the approach velocity, and was observed to range from more than 25% at 5?cm from the transducers to less than 1% at about 50?cm from the transducers for the scenarios simulated.     

Reduced scale PWR passive safety system designing by genetic algorithms

This paper presents the concept of “Design by Genetic Algorithms (DbyGA)”, applied to a new reduced scale system problem. The design problem of a passive thermal-hydraulic safety system, considering dimensional and operational constraints, has been solved. Taking into account the passive safety characteristics of the last nuclear reactor generation, a PWR core under natural circulation is used in order to demonstrate the methodology applicability. The results revealed that some solutions (reduced scale system DbyGA) are capable of reproducing, both accurately and simultaneously, much of the physical phenomena that occur in real scale and operating conditions. However, some aspects, revealed by studies of cases, pointed important possibilities to DbyGA methodological performance improvement.     

The electron heat capacity of high-purity alpha and stabilized-delta plutonium

The authors measured the low-temperature heat capacities of α (monoclinic) and δ (face-centered cubic) plutonium from T≈2 K to T≈300 K. Heat capacity measurements were made via thermal relaxation calorimetry on high-purity plutonium metal prepared by a combination of levitation zone refining and distillation. The purification procedures show that 19 elements were reduced to quantities below the minimum detectable limits by zone refining, while phosphorous, potassium, and tungsten were significantly reduced. To date, these purified metal and alloys have been the focus of condensed matter physics and nuclear physics experiments including nuclear cross-section measurements, photoemission spectroscopy, optical properties in the liquid state, x-ray absorption fine structure spectroscopy, elastic moduli measurements, grain growth methods for phonon dispersion measurements and calculations, and feed material for the preparation of single crystals of δ-Pu. For more information, contact J.C. Lashley, e-mail jlash@lanl.gov.     

Blood-flow models of the circle of Willis from magnetic resonance data

Detailed knowledge of the cerebral hemodynamics is important for a variety of clinical applications. Cerebral perfusion depends not only on the status of the diseased vessels but also on the patency of collateral pathways provided by the circle of Willis. Due to the large anatomical and physiologic variability among individuals, realistic patient-specific models can provide new insights into the cerebral hemodynamics. This paper presents an image-based methodology for constructing patient-specific models of the cerebral circulation. This methodology combines anatomical and physiologic imaging techniques with computer simulation technology. The methodology is illustrated with a finite element model constructed from magnetic resonance image data of a normal volunteer. Several of the remaining challenging problems are identified. This work represents a starting point in the development of realistic models that can be applied to the study of cerebrovascular diseases and their treatment.     

Influence of extender type of performance of modified lamellar zinc primers

The objective of this work was to gain a deeper insight into the behavior of zinc primer, containing either lamellar zinc alone or lamellar zinc mixed with an extender by means of accelerated tests in salt spray (fog) chamber and a 100% relative humidity cabinet. Mica, kaolin, and synthetic calcium silicate were used as extenders. Several series of coatings were designed and manufactured employing the following binders: 20 cP chlorinated rubber, a vinyl copolymer, an unsaturated polymer, or an epoxy resin. A simultaneous analysis of the experimental data was performed taking into account that the best performance is attained at pigment volume concentration (PVC) values equal to or slightly lower than the critical one (CPVC). Results indicate that for every lamellar zinc primer, it is possible to select an extender of high oil absorption as the spacer of the zinc particles attaining both very good blistering resistance and anticorrosive performance.     

A Statistical Sampler for a New On-Line Analog Test Method

This work shows a new strategy to the on-line test of analog circuits. The technique presents a very low analog overhead and it is completely digital. In the System-on-Chip (SoC) environment the on-line test can be developed by using processing power already available in the system. As all the signal processing is done in the digital domain, it allows use of a purely digital tester or a digital BIST technique. The main principle of operation is based on the observation of statistical properties of the circuit under test. Since it has low analog power and performance overhead, the proposed technique can be used to analyze the output of several stages of complex analog systems without the use of switches or analog multiplexors for reconfiguration, and no additional AD converter is needed. This paper presents the fundamentals of the proposed test method and some experimental results illustrating the operation of the Statistical Sampler concerning linear analog systems.     

k–ε Turbulence Modeling of Density Currents Developing Two Dimensionally on a Slope

Dense underflows developing two dimensionally on a slope are simulated numerically. The k–ε model is used for the turbulence closure. The boundary-layer approximation renders the governing equations in the form of parabolic partial differential equations, which are easier to solve numerically than elliptic equations. Evolution of vertical structures of dense underflows is computed along the streamwise direction. Excellent similarity collapses of the computed vertical structures are obtained. The computed profiles of velocity and concentration are compared with measured data, resulting in good agreement. The impact of a parameter representing the stratification level in the k–ε model is investigated. Appropriate values of this parameter, yielding results that are nearly identical to the integral model, are proposed. Water entrainment coefficients are estimated from computed solutions, and are observed to fall within the range of previous measurements. Finally, by using the collapsed vertical structures, profile constants defined in the integral model are calculated, which assures that the top-hat assumption necessary for deriving the integral model is valid.     

Technical potential for developing natural gas use in the Brazilian red ceramic industry

The red ceramic industry in Brazil, consisting of over 7000 companies, requires large amounts of thermal energy, currently being met mainly by native fuelwood, which causes serious deforestation and soil erosion problems. The use of firewood does not allow achieving good energy performance in industrial ceramic kilns, causing high energy losses, low productivity and low quality products (bricks and roof tiles). Thus, to implement higher added value products, besides mitigate environmental problems caused by deforestation, the use of natural gas by the sector seems to be a promising alternative. Brazil’s natural gas market has grown at a fast pace in recent years. Its share in the country’s primary energy consumption increased from 3.7% to 9.3% between 1998 and 2007, compared to almost 21% in the world. The development of the Brazilian natural gas industry was grounded on stepping up supplies through integration with Bolivia from where natural gas is imported, together with fiscal incentives for promoting the demand. This paper estimates that the natural gas market that could be developed in the Brazilian red ceramic industry corresponds to less than 5% of the total industrial natural gas consumption, meaning that a major technological transformation of the country’s red ceramic industry will not severely affect the natural gas market equilibrium, contributing to reduce the country’s high rates of deforestation.