bluuebunny/crossref_metadata_2025 huggingface dataset:
Type Curves Analysis for Asymmetrically Fractured Wells
Authors: Wang Lei , Wang Xiaodong
Published: October 2013

In this paper, a new constant rate solution for asymmetrically fractured wells was proposed to analyze the effect of fracture asymmetry on type curves. Calculative results showed that for a small wellbore storage coefficient or for the low fracture conductivity, the effect of fracture asymmetry on early flow was very strong. The existence of the fracture asymmetry would cause bigger pressure depletion and make the starting time of linear flow occur earlier. Then, new type curves were established for different fracture asymmetry factor and different fracture conductivity. It was shown that a bigger fracture asymmetry factor and low fracture conductivity would prolong the time of wellbore storage effects. Therefore, to reduce wellbore storage effects, it was essential to keep higher fracture conductivity and fracture symmetry during the hydraulic fracturing design. Finally, a case example is performed to demonstrate the methodology of new type curves analysis and its validation for calculating important formation parameters.
An Experimental Study on Heat Transfer Enhancement of Non-Newtonian Fluid in a Rectangular Channel With Dimples/Protrusions
Authors: Zhang Di , Zheng Lu , Xie Gongnan , Xie Yonghui
Published: October 2013

Dimple and protrusion play important roles in the heat transfer enhancement and flow characteristic in cooling channels, which widely employed within electronic cooling systems. Non-Newtonian fluid has significant differences with Newtonian fluid, such as water, in fluid characteristic. In this study, an experiment on the viscosity of three different kinds of non-Newtonian fluids, i.e., xanthan gum solution, Carbopol 934 solution, polyacrylamide solution, was first accomplished to acquire the viscosity with different mass fractions. Then, experimental measurements on heat transfer and friction characteristics of non-Newtonian fluid in a rectangular channel with dimples and protrusions were conducted. The overall Nusselt numbers (Nu) and Fanning friction factors at different dimple/protrusion structures were obtained with various inlet flow rates and mass fractions. The results show that only xanthan gum solution has the significant shear thinning effect within the concentration range of this study, and the dimples/protrusions both have great effect on the heat transfer enhancement in the rectangular channel, and that the heat transfer of the case with the protrusions and crossing arrangement can be further enhanced with the higher Nu when compared to the case with the dimples and aligned arrangement. Moreover, an increase in Nu with the higher non-Newtonian fluid mass fraction is observed.
Assessment of a Power Plant With CO2 Capture Using an Advanced Exergoenvironmental Analysis
Authors: Petrakopoulou Fontina , Tsatsaronis George , Morosuk Tatiana
Published: October 2013

This paper presents an evaluation of the environmental performance of an advanced zero emission plant (AZEP) including CO2 capture. The evaluation is conducted with the aid of an advanced exergoenvironmental analysis. The results are compared with those of a reference combined-cycle power plant without CO2 capture. Advanced exergy-based methods are used to (a) quantify the potential for improving individual components or overall systems, and (b) reveal detailed interactions among components—two features not present in conventional analyses, but very useful, particularly when evaluating complex systems. In an advanced exergoenvironmental analysis, the environmental impacts calculated in a conventional exergoenvironmental analysis are split into avoidable/unavoidable (to evaluate the potential for component improvement) and endogenous/exogenous (to understand the interactions among components) parts. As in the reference plant, the potential for reducing the environmental impact of the AZEP has been found to be limited by the relatively low avoidable environmental impact associated with the thermodynamic inefficiencies of several of its components. However, although the environmental impacts for the majority of the components of the plant are related mainly to internal inefficiencies and component interactions are of secondary importance, there are strong interactions between the reactor and some other components.
A Novel Pattern for Energy Estimation Framework and Tools to Compute Energy Consumption in Product Life Cycle
Authors: Huang He , Ameta Gaurav
Published: October 2013

Excessive energy consumption has become a worldwide issue in today's design and manufacturing industry. An energy estimation framework that could later be used to integrate with CAD/CAM systems is in demand. This research develops a novel pattern to estimate energy consumptions. The pattern involves a software energy estimation framework and various software energy computational tools. Using this pattern, energy can be calculated by an energy estimation framework which can be attached with diverse energy computational tools. These computational tools can be designed for any purpose to calculate energy consumptions during a product life-cycle and for various manufacturing processes. The framework involved in this pattern features to be domain independent and flexible so that it will be expandable for different manufacturing domains and customizable for users. Details for developing such pattern are presented. Interaction between the framework and its computational tools is also discussed. With help of this pattern, energy estimation framework and energy computational tools can interact smoothly, and the development of computational tools can be extended or expanded for any purpose. Knowledge engineers who exert to integrate knowledge into computer systems can interpret domain-specific knowledge and share their expertise to improve the framework. The framework also assists users who have little knowledge about energy computations to estimate energy consumptions during the design stage, leading to products with reduced energy.
A Method to Approximate the Steady-State Creep Response of Three-Dimensional Pipe Bend Finite Element Models Under Internal Pressure Loading Using Two-Dimensional Axisymmetric Models
Authors: Rouse J. P. , Sun W. , Hyde T. H. , Morris A. , Montgomery W.
Published: October 2013

Pipe bends are regions of geometric discontinuities in the pipe systems used in power plants and most industry recorded failures have been located around similar regions. Understanding these potential locations of weakness is therefore of great interest for the safe and economic operation of piping components. Increased predictive accuracy would assist in component design, condition monitoring, and retirement strategy decisions. Modeling of piping components for finite element analysis (FEA) is complicated by the variation of the cross section dimensions (changes in wall thicknesses or cross section ovality) around the pipe bend due to the manufacturing procedure implemented. Quantities such as peak rupture stress and creep rupture life can be greatly affected by these geometric variation (Rouse, J. P., Leom, M. Z., Sun, W., Hyde, T. H., Morris, A., “Steady-state Creep Peak Rupture Stresses in 90 Pipe Bends with Manufacture Induced Cross Section Dimension Variations”International Journal of Pressure Vessels and Piping, Volumes 105–106, May–June 2013, pp. 1–11). Three dimensional (3D) models can be used to approximate to the realistic level of detail found in pipe bends. These simulations may however be computationally expensive and could take a considerable amount of time to complete. Two dimensional (2D) axisymmetric models are relatively straight forward to produce and quick to run, but of course cannot represent the full geometric complexity around the pipe bend. A method is proposed that utilises multiple 2D axisymmetric pipe bend models to approximate the result of a 3D analysis through interpolation, thus exploiting the greatly reduced computing time observed for the 2D models. The prediction of peak rupture stress (both magnitude and location) is assessed using a simple power law material model. Comments are made on the applicability of the proposed procedure to a range of bends angles (90 deg, 60 deg, and 30 deg), as well as the effect of the stress exponent (n) and tri-axial (α) material constants. Provided that peak stresses do not occur at the bend/straight interface, the magnitude and location of the peak rupture stress can be predicted by the 2D axisymmetric interpolation method with a typical percentage difference of less than 1%.
Interfacial Flaw Evolution of Coatings Under Severe Thermal and Pressure Transients
Authors: Harris J. T. , Segall A. E. , Robinson D. , Carter R.
Published: October 2013

The effects of severe thermal and pressure transients on coated substrates with indentation-induced, blister defects were analyzed by experimental and finite element methods. Cohesive zone properties evaluated in a previous study were first used in an implicit indentation simulation. Indentation simulation results then served as the initial conditions for explicit modeling of interfacial flaw evolution due to the already determined thermal and pressure transients that included interstitial pressure in the defect. The thermal structural model was used to assess the transient thermal- and stress-states and the propensity for fracture related damage and evolution while undergoing severe convective heating and pressure loading analogous to gun tube conditions. Results illustrated the overall benefits of the in-phase applied pressure in terms of suppressing crack growth except when delayed interstitial loading was considered. Thermal capacitance was also studied and it was found that crack growth decreased significantly with higher specific heat and demonstrates the potential importance of coating thermophysical properties.
Experimental Investigations on Diesel Engine Forced Induction and Exhaust Gas Recirculation (EGR) Using Exhaust Gas Assisted Jet Compressor
Authors: Kalaisselvane A. , Gunasegarane G. S. , Alagumurthy N. , Palaniradja K.
Published: October 2013

Even though the conventional method of supercharging and turbocharging of an internal combustion engine increases the engine specific power output, part of the shaft power developed by the engine is consumed by the superchargers. The control system that is present in both the chargers further complicates the system. This study proposes a novel method of forced induction in a diesel engine by using a jet compressor run by exhaust gas recirculation (EGR). This method apart from increasing the specific power output reduces the NOx formation by the engine due to forced induction. Performance analysis of the jet compressor using exhaust gas as the motive stream and atmospheric air as the propelled stream was carried out. Using the standard available code, the governing equations were solved numerically to get the optimum operating conditions such as exhaust gas pressure, temperature, and flow rate for a three cylinder diesel engine. The dimensions of the jet compressor were determined by solving the energy balance equations obtained from the constant rate momentum change method. Using the commercial software fluent, the performance optimization of jet compressor used for forced induction in a diesel engine was made for different percentage of EGR input and estimated the power output. From the results obtained, a performance map was drawn for the three cylinder diesel engine to get the optimum boost pressure and maximum entrainment ratio for a given percentage of exhaust gas recirculation and power output. Experiments were conducted on a three cylinder diesel engine fitted with a fabricated jet compressor with EGR used for forced induction application. Results obtained from the experiments were in good agreement with the numerical results obtained from fluent analysis.
Comparative Study of Diesel Oil and Biodiesel Spray Combustion Based on Detailed Chemical Mechanisms
Authors: Yang Junfeng , Golovithcev Valeri I. , Naik Chitralkumar V. , Meeks Ellen
Published: October 2013

In the present work, a semidetailed combustion mechanism for biodiesel fuel was validated against the measured autoignition delay times and subsequently implemented in the fortÉ cfd engine simulation package (Reaction Design Inc., 2010, “fortÉ, FOR-UG-40102-1009-UG-1b,” Reaction Design Inc., San Diego, CA) to investigate the spray characteristics (e.g., the liquid penetration and flame lift-off distances of rapeseed oil methyl ester (RME) fuel in a constant-volume combustion chamber). The modeling results were compared with the experimental data. Engine simulations were performed for a Volvo D12C heavy-duty diesel engine fueled by RME on a 72 deg sector mesh. Predictions were validated against measured in-cylinder parameters and exhaust emission concentrations. The semidetailed mechanism was shown to be an efficient and accurate representation of actual biodiesel combustion phases. Meanwhile, as a comparative study, the simulations based on a detailed diesel oil surrogate mechanism were performed for diesel oil under the same conditions.
Experimental Study of Adiabatic Two-Phase Flow in an Annular Channel Under Low-Frequency Vibration
Authors: Chen Shao-Wen , Hibiki Takashi , Ishii Mamoru , Mori Michitsugu , Watanabe Fumitoshi
Published: October 2013

In order to investigate the possible effect of seismic vibration on two-phase flow dynamics and thermal-hydraulics of a nuclear reactor, experimental tests of adiabatic air-water two-phase flow under low-frequency vibration were carried out in this study. An eccentric cam vibration module operated at low motor speed (up to 390 rpm) was attached to an annulus test section which was scaled down from a prototypic boiling water reactor (BWR) fuel assembly subchannel. The inner and outer diameters of the annulus are 19.1 mm and 38.1 mm, respectively. The two-phase flow operating conditions cover the ranges of 0.03 m/s ≤ 〈jg〉 ≤ 1.46 m/s and 0.25 m/s ≤ 〈jf〉 ≤ 1.00 m/s and the vibration displacement ranges from ±0.8 mm to ±22.2 mm. Steady-state area-averaged instantaneous and time-averaged void fraction were recorded and analyzed in stationary and vibration experiments. A neural network flow regime identification technique and fast Fourier transformation (FFT) analysis were introduced to analyze the flow regimes and void signals under stationary and vibration conditions. Experimental results reveal possible changes in flow regimes under specific flow and vibration conditions. In addition, the instantaneous void fraction signals were affected and shown by FFT analysis. Possible reasons for the changes include the applied high acceleration and induced void/flow structure changes at certain ports under the specific flow and vibration conditions.
On the Influence of Fuel Distribution on the Flame Structure of Bluff-Body Stabilized Flames
Authors: Lovett Jeffery A. , Ahmed Kareem , Bibik Oleksandr , Smith Andrew G. , Lubarsky Eugene , Menon Suresh , Zinn Ben T.
Published: October 2013

This paper describes recent learning on the flame structure associated with bluff-body stabilized flames and the influence of the fuel distribution with nonpremixed, jet-in-crossflow fuel injection. Recent experimental and analytical results disclosing the flame structure are discussed in relation to classical combustion reaction zone regimes. Chemiluminescence and planar fluorescence imaging of OH* radicals as an indicator of the flame zone are analyzed from various tests conducted at Georgia Tech using a two-dimensional vane-type bluff-body with simple wall-orifice fuel injectors. The results described in this paper support the view that combustion occurs in separated flame zones aligned with the nonpremixed fuel distribution associated with the fuel jets that are very stable and contribute to flame stability at low fuel flow rates. The experimental data is also compared with computational reacting flow large-eddy simulations and interpreted in terms of the fundamental reaction zone regimes for premixed flames. For the conditions of the present experiment, the results indicate combustion occurs over a wide range of flame regimes including the broken reaction zone or separated flamelet regimes.
Development and Application of a Transported Probability Density Function Method on Unstructured Three-Dimensional Grids for the Prediction of Nitric Oxides
Authors: Fiolitakis Andreas , Ess Peter , Gerlinger Peter , Aigner Manfred
Published: October 2013

The present work explores the capability of the transported probability density function (PDF) method to predict nitric oxide (NO) formation in turbulent combustion. To this end a hybrid finite-volume/Lagrangian Monte Carlo method is implemented into the THETA code of the German Aerospace Center (DLR). In this hybrid approach the transported PDF method governs the evolution of the thermochemical variables, whereas the flow field evolution is computed with a Reynolds-averaged Navier–Stokes (RANS) method. The method is used to compute a turbulent hydrogen-air flame and a methane-air flame and computational results are compared to experimental data. In order to assess the advantages of the transported PDF method, the flame computations are repeated with the “laminar chemistry” approach as well as with an “assumed PDF” method, which are both computationally less expensive. The present study reveals that the transported PDF method provides the highest accuracy in predicting the overall flame structure and nitric oxide formation.
Combined Experimental/Numerical Method Using Infrared Thermography and Finite Element Analysis for Estimation of Local Heat Transfer Distribution in an Internal Cooling System
Authors: Egger Christian , von Wolfersdorf Jens , Schnieder Martin
Published: October 2013

In the present study a method for estimating local heat transfer distributions of internal cooling systems is described. Experimental data and finite element analysis are applied for this method. The investigations considered in this paper are based on experiments performed on a two-pass cooling channel connected by a 180 deg bend with internal rib arrangements. The solid walls of the cooling channels are made of a metallic material. During the experiment the temperature response of the outer surface induced by heated internal flow is recorded by infrared thermography. The internal heat transfer distribution is obtained using an optimization routine. For each loop of the optimization a transient thermal simulation of the solid body is performed applying the boundary and inlet conditions of the experiment. The temperature of the outer surface calculated by the finite element simulation is compared to the measured temperature recorded by infrared thermography. The difference of these temperature distributions is minimized by adapting the distribution of the internal heat transfer coefficients. The adaptation is conducted on single elements of the inner surface and will be presented in detail in the paper. This approach allows us to achieve a high resolution in heat transfer while minimizing the required iterations. The combination of experimental data and finite element analysis allows us to consider three-dimensional conduction effects in the solid and the streamwise fluid temperature development. Results are compared to literature data.
Heat Transfer Enhancement Using Angled Grooves as Turbulence Promoters
Authors: Saha Krishnendu , Acharya Sumanta
Published: October 2013

An experimental study is conducted on a simulated internal cooling channel of a turbine airfoil using angled grooves and combination of grooves-ribs to enhance the heat transfer from the wall. The grooves are angled at 45 deg to the mainstream flow direction and combinations of four different geometries are studied that include (1) angled grooves with a pitch, p/δ = 10, (2) angled groove with a larger pitch, p/δ = 15, (3) combination of angled groove and 45 deg angled rib, and (4) combination of angled groove with transverse rib. Transient liquid crystal experiments are conducted for a Reynolds number range of 13,000–55,000, and local and averaged heat transfer coefficient values are presented for all the geometries. Pressure drops are measured between the inlet and the exit of the grooved channel and friction factors are calculated. The combination of the angled groove and 45 deg angled rib provided the highest performance factor of the four cases considered, and these values were higher or comparable to among the best-performing rib geometries (45 deg broken ribs) commonly used in gas turbine airfoils.
Rotating Instability in an Annular Cascade: Detailed Analysis of the Instationary Flow Phenomena
Authors: Pardowitz Benjamin , Tapken Ulf , Sorge Robert , Thamsen Paul Uwe , Enghardt Lars
Published: October 2013

Rotating instability (RI) occurs at off-design conditions in compressors, predominantly in configurations with large tip or hub clearance ratios of s* ≥3%. RI is the source of the blade tip vortex noise and a potential indicator for critical operating conditions like rotating stall and surge. The objective of this paper is to give more physical insight into the RI phenomenon using the analysis results of combined near-field measurements with high-speed particle image velocimetry (PIV) and unsteady pressure sensors. The investigation was pursued on an annular cascade with hub clearance. Both the unsteady flow field next to the leading edge as well as the associated rotating pressure waves were captured. A special analysis method illustrates the characteristic pressure wave amplitude distribution, denoted as “modal events” of the RI. Moreover, the slightly adapted method reveals the unsteady flow structures corresponding to the RI. Correlations between the flow profile, the dominant vortex structures, and the rotating pressure waves were found. Results provide evidence to a new hypothesis, implying that shear layer instabilities constitute the basic mechanism of the RI.
Modeling Vortex Generating Jet-Induced Transition in Low-Pressure Turbines
Authors: Herbst Florian , Fiala Andreas , Seume Joerg R.
Published: October 2013

The current design of low-pressure turbines (LPTs) with steady-blowing vortex generating jets (VGJs) uses steady computational fluid dynamics (CFD). The present work aims to support this design approach by proposing a new semiempirical transition model for injection-induced laminar-turbulent boundary layer transition. It is based on the detection of cross-flow vortices in the boundary layer which cause inflectional cross-flow velocity profiles. The model is implemented in the CFD code TRACE within the framework of the γ-Reθ transition model and is a reformulated, recalibrated, and extended version of a previously presented model. It is extensively validated by means of VGJ as well as non-VGJ test cases capturing the local transition process in a physically reasonable way. Quantitative aerodynamic design parameters of several VGJ configurations including steady and periodic-unsteady inflow conditions are predicted in good accordance with experimental values. Furthermore, the quantitative prediction of end-wall flows of LPTs is improved by detecting typical secondary flow structures. For the first time, the newly derived model allows the quantitative design and optimization of LPTs with VGJs.
Characterizing the Effect of Laser Power Density on Microstructure, Microhardness, and Surface Finish of Laser Deposited Titanium Alloy
Authors: Mahamood Rasheedat M. , Akinlabi Esther T. , Shukla Mukul , Pityana Sisa
Published: October 2013

This paper reports the effect of laser power density on the evolving properties of laser metal deposited titanium alloy. A total of sixteen experiments were performed, and the microstructure, microhardness and surface roughness of the samples were studied using the optical microscope (OP), microhardness indenter and stylus surface analyzer, respectively. The microstructure changed from finer martensitic alpha grain to coarser Widmastätten alpha grain structure as the laser power density was increased. The results show that the higher the laser power density employed, the smoother the obtained surface. The microhardness initially increased as the laser power density was increased and then decreased as the power density was further increased. The result obtained in this study is important for the selection of proper laser power density for the desired microstructure, microhardness and surface finish of part made from Ti6Al4V.
An Experimental Study of Mist/Air Film Cooling On a Flat Plate With Application to Gas Turbine Airfoils—Part II: Two-Phase Flow Measurements and Droplet Dynamics
Authors: Zhao Lei , Wang Ting
Published: October 2013

A phase Doppler particle analyzer (PDPA) system is employed to measure the two-phase mist flow behavior including flow velocity field, droplet size distribution, droplet dynamics, and turbulence characteristics. Based on the droplet measurements made through PDPA, a projected profile describing how the air-mist coolant jet flow spreads and eventually blends into the hot main flow is proposed. This proposed profile is found to be well supported by the measurement results of the turbulent Reynolds stresses. The coolant film envelope is identified with shear layers characterized by higher magnitudes of turbulent Reynolds stresses. In addition, the separation between the mist droplet layer and the coolant air film is identified through the droplet measurements—large droplets penetrate through the air coolant film layer and travel further into the main flow. With the proposed air-mist film profile, the heat transfer results on the wall presented in Part I are re-examined and more in-depth physics is revealed. It is found that the location of the optimum cooling effectiveness coincides with the point where the air-mist coolant stream starts to bend back towards the surface. Thus, the data suggests that the “bending back” film pattern is critical in keeping the mist droplets close to the surface, which improves the cooling effectiveness for mist cooling.
An Innovative Method to Measure the Cutting Temperature in Process by Using an Internally Cooled Smart Cutting Tool
Authors: Shu Shengrong , Cheng Kai , Ding Hui , Chen Shijin
Published: October 2013

This paper presents a novel approach to measure the cutting temperature in process and control it to some extent by using an internally cooled smart cutting tool with a closed internal cooling circuitry. Numerical modeling based on the finite element analysis-computational fluid dynamics (CFD) method is carried out by using ansys and fluent, then the surface temperature distribution of the tool is fitted and the equivalent heat transfer coefficient of the tool surface contacting with cooling fluid is computed. Analytical thermal model of the tool is established based on the lumped parameter method. Theoretical analysis and numerical simulation results are in good agreement, which demonstrate that the innovative smart tooling design concept can effectively sense the cutting temperature at the cutting tool tip in process and also be used to reduce and control the critical cutting temperature in cutting zone for adaptive machining of difficult-to-machine materials, such as titanium and Inconel alloys. Experimental cutting trials are carried out to further examine and validate the method and concept of applying the smart cutting tool system.
Magnetic Field Effects on Laser Drilling
Authors: Ye Chang , Cheng Gary J. , Tao Sha , Wu Benxin
Published: October 2013

A magnetic field-assisted laser drilling process has been studied, where nanosecond laser ablation is performed under an external magnetic field. The study shows that the magnetic field-assisted laser drilling process produces deeper drilling depth and generates more confined plasma plume and relative less residual, as compared with laser drilling without magnetic field. This phenomenon has been rarely reported in the literature. The magnetic field effects on laser ablation have been analyzed analytically and a hypothesized explanation has been proposed based on the effect of the magnetic field on the plasma produced during laser ablation.
Design and Modeling of a New Drive System and Exaggerated Rectilinear-Gait for a Snake-Inspired Robot
Authors: Hopkins James K. , Gupta Satyandra K.
Published: October 2013

In recent years, snake-inspired locomotion has garnered increasing interest in the bio-inspired robotics community. This positive trend is largely due to the unique and highly effective gaits utilized by snakes to traverse various terrains and obstacles. These gaits make use of a snake's hyper-redundant body structure to adapt to the terrain and maneuver through tight spaces. Snake-inspired robots utilizing rectilinear motion, one of the primary gaits observed in natural snakes, have demonstrated favorable results on various terrains. However, previous robot designs utilizing rectilinear gaits were slow in speed. This paper presents a design and an exaggerated rectilinear gait concept for a snake-inspired robot which overcomes this limitation. The robot concept incorporates high speed linear motion and a new multimaterial, variable friction force anchoring concept. A series of traction experiments are conducted to determine appropriate materials to be used in the friction anchor (FA) design. The gait concept includes four unique gaits: a forward and a turning gait, which both emphasize speed for the robot; and a forward and turning gait which emphasize traction. We also report a comparative study of the performance of prototype robot designed using these concepts to other published snake-inspired robot designs.
Position Domain Synchronization Control of Multi-Degrees of Freedom Robotic Manipulator
Authors: Ouyang P. R. , Pano V.
Published: October 2013

In this paper, a new position domain synchronization control (PDSC) law is proposed for contour control of multi-DOF nonlinear robotic manipulators with the main goal of improving contour tracking performance. The robotic manipulator is treated as a master-slave motion system, where the position of the master motion is used as an independent reference via equidistant sampling, and the slave motions are described as functions of the master motion. To build this relationship, the dynamics of the original system is transformed from time domain to position domain. The new control introduces synchronization and coupled errors in the control law to further coordinate the master and slave motions. Stability analysis is performed based on the Lyapunov method for the proposed PDSC, and simulations are conducted to verify the effectiveness of the developed control system.
Simulation of Wake Interactions in Wind Farms Using an Immersed Wind Turbine Model
Authors: Jafari S. , Chokani N. , Abhari R. S.
Published: October 2013

The accurate modeling of the wind turbine wakes in complex terrain is required to accurately predict wake losses. In order to facilitate the routine use of computational fluid dynamics in the optimized micrositing of wind turbines within wind farms, an immersed wind turbine model is developed. This model is formulated to require grid resolutions that are comparable to that in microscale wind simulations. The model in connection with the k-ω turbulence model is embedded in a Reynolds-averaged Navier–Stokes solver. The predictions of the model are compared to available wind tunnel experiments and to measurements at the full-scale Sexbierum wind farm. The good agreement between the predictions and measurements demonstrates that the novel immersed turbine model is suited for the optimized micrositing of wind turbines in complex terrain.
A Method of Map Extrapolation for Unequal and Partial Admission in a Double Entry Turbine
Authors: Newton Peter , Romagnoli Alessandro , Martinez-Botas Ricardo , Copeland Colin , Seiler Martin
Published: October 2013

This paper presents a method for prediction of the unequal admission performance of a double entry turbine based on the full admission turbine maps and a minimal number of unequal admission points. The double entry turbine has two separate inlet ports which feed a single turbine wheel: this arrangement can be beneficial in a turbocharger application; however the additional entry does add complexity in producing a complete turbine map which includes unequal admission behavior. When a double entry turbine is operated under full admission conditions, with both entries feeding the turbine equally, this will act effectively as a single entry device and the turbine performance can be represented by a standard turbine map. In reality a multiple entry turbine will spend the majority of time operating under varying degrees of unequal admission, with each entry feeding the turbine different amounts; the extent of this inequality can have a considerable impact on turbine performance. In order to produce a full map which extends from full admission through to the partial admission case (where one inlet has no flow) a large number of unequal admission data points are required. The paper starts by discussing previous attempts to describe the partial and unequal admission performance of a double entry turbine. The full unequal admission performance is then presented for a nozzled, double entry turbine. The impact of unequal admission on turbine performance is demonstrated. Under some conditions of operation, the turbine efficiency may be less than half that of the equivalent full admission case based on the average turbine velocity ratio. A method of using the steady, equal admission maps, with a limited number of unequal admission data points, to predict the full unequal admission behavior is presented. A good agreement is found when the map extension method is validated against the full unequal admission turbine performance measured on a test stand. In the prediction of efficiency a mean error of approximately 0.39% is found between the test stand data and the proposed extrapolation method, with a standard deviation of 2.79%. A better agreement is generally found at conditions of higher power.
Uncertainty Analysis of Heat Transfer Predictions Using Statistically Modeled Data From a Cooled 1-1/2 Stage High-Pressure Transonic Turbine
Authors: Kahveci Harika S. , Kirtley Kevin R.
Published: October 2013

This paper compares predictions from a 3D Reynolds-averaged Navier–Stokes code and a statistical representation of measurements from a cooled 1-1/2 stage high-pressure transonic turbine to quantify predictive process sensitivity. A multivariable regression technique was applied to both the inlet temperature measurements obtained at the inlet rake, the wall temperature, and heat transfer measurements obtained via heat-flux gauges on the blade airfoil surfaces. By using the statistically modeled temperature profiles to generate the inlet boundary conditions for the computational fluid dynamics analysis, the sensitivity of blade heat transfer predictions due to the variation in the inlet temperature profile and uncertainty in wall temperature measurements and surface roughness is calculated. All predictions are performed with and without cooling. Heat transfer predictions match reasonably well with the statistical representation of the data, both with and without cooling. Predictive precision for this study is driven primarily by inlet profile uncertainty followed by surface roughness and gauge position uncertainty.
An In Vitro Assessment of the Cerebral Hemodynamics Through Three Patient Specific Circle of Willis Geometries
Authors: Fahy Paul , Delassus Patrick , McCarthy Peter , Sultan Sheriff , Hynes Niamh , Morris Liam
Published: October 2013

The Circle of Willis (CoW) is a complex pentagonal network comprised of fourteen cerebral vessels located at the base of the brain. The collateral flow feature within the circle of Willis allows the ability to maintain cerebral perfusion of the brain. Unfortunately, this collateral flow feature can create undesirable flow impact locations due to anatomical variations within the CoW. The interaction between hemodynamic forces and the arterial wall are believed to be involved in the formation of cerebral aneurysms, especially at irregular geometries such as tortuous segments, bends, and bifurcations. The highest propensity of aneurysm formation is known to form at the anterior communicating artery (AcoA) and at the junctions of the internal carotid and posterior communicating arteries (PcoAs). Controversy still remains as to the existence of blood flow paths through the communicating arteries for a normal CoW. This paper experimentally describes the hemodynamic conditions through three thin walled patient specific models of a complete CoW based on medical images. These models were manufactured by a horizontal dip spin coating method and positioned within a custom made cerebral testing system that simulated symmetrical physiological afferent flow conditions through the internal carotid and vertebral arteries. The dip spin coating procedure produced excellent dimensional accuracy. There was an average of less than 4% variation in diameters and wall thicknesses throughout all manufactured CoW models. Our cerebral test facility demonstrated excellent cycle to cycle repeatability, with variations of less than 2% and 1% for the time and cycle averaged flow rates, respectively. The peak systolic flow rates had less than a 4% variation. Our flow visualizations showed four independent flow sources originating from all four inlet arteries impacting at and crossing the AcoA with bidirectional cross flows. The flow paths entering the left and right vertebral arteries dissipated throughout the CoW vasculature from the posterior to anterior sides, exiting through all efferent vessels. Two of the models had five flow impact locations, while the third model had an additional two impact locations within the posterior circulation caused by an additional bidirectional cross flows along the PcoAs during the accelerating and part of the decelerating phases. For a complete CoW, bidirectional cross flows exist within the AcoA and geometrical variations within the CoW geometry can either promote uni- or bidirectional cross flows along the PcoAs.
CONRAD—A software framework for cone‐beam imaging in radiology
Authors: Maier Andreas , Hofmann Hannes G. , Berger Martin , Fischer Peter , Schwemmer Chris , Wu Haibo , Müller Kerstin , Hornegger Joachim , Choi Jang‐Hwan , Riess Christian , Keil Andreas , Fahrig Rebecca
Published: October 2013

Purpose:

In the community of x‐ray imaging, there is a multitude of tools and applications that are used in scientific practice. Many of these tools are proprietary and can only be used within a certain lab. Often the same algorithm is implemented multiple times by different groups in order to enable comparison. In an effort to tackle this problem, the authors created CONRAD, a software framework that provides many of the tools that are required to simulate basic processes in x‐ray imaging and perform image reconstruction with consideration of nonlinear physical effects.

Methods:

CONRAD is a Java‐based state‐of‐the‐art software platform with extensive documentation. It is based on platform‐independent technologies. Special libraries offer access to hardware acceleration such as OpenCL. There is an easy‐to‐use interface for parallel processing. The software package includes different simulation tools that are able to generate up to 4D projection and volume data and respective vector motion fields. Well known reconstruction algorithms such as FBP, DBP, and ART are included. All algorithms in the package are referenced to a scientific source.

Results:

A total of 13 different phantoms and 30 processing steps have already been integrated into the platform at the time of writing. The platform comprises 74.000 nonblank lines of code out of which 19% are used for documentation. The software package is available for download athttp://conrad.stanford.edu. To demonstrate the use of the package, the authors reconstructed images from two different scanners, a table top system and a clinical C‐arm system. Runtimes were evaluated using the RabbitCT platform and demonstrate state‐of‐the‐art runtimes with 2.5 s for the 256 problem size and 12.4 s for the 512 problem size.

Conclusions:

As a common software framework, CONRAD enables the medical physics community to share algorithms and develop new ideas. In particular this offers new opportunities for scientific collaboration and quantitative performance comparison between the methods of different groups.
Radiation pressure of standing waves on liquid columns and small diffusion flames
Authors: Thiessen David B. , Marr-Lyon Mark J. , Wei Wei , Marston Philip L.
Published: October 2013

The radiation pressure of standing ultrasonic waves in air is demonstrated in this investigation to influence the dynamics of liquid columns and small flames. With the appropriate choice of the acoustic amplitude and wavelength, the natural tendency of long columns to break because of surface tension was suppressed in reduced gravity [M. J. Marr-Lyon, D. B. Thiessen, and P. L. Marston, Phys. Rev. Lett. 86, 2293–2296 (2001); 87(20), 9001(E) (2001)]. Evaluation of the radiation force shows that narrow liquid columns are attracted to velocity antinodes. The response of a small vertical diffusion flame to ultrasonic radiation pressure in a horizontal standing wave was observed in normal gravity. In agreement with our predictions of the distribution of ultrasonic radiation stress on the flame, the flame is attracted to a pressure antinode and becomes slightly elliptical with the major axis in the plane of the antinode. The radiation pressure distribution and the direction of the radiation force follow from the dominance of the dipole scattering for small flames. Understanding radiation stress on flames is relevant to the control of hot fluid objects. [Work supported by NASA.]
Theoretical and experimental study of vibration, generated by monorail trains
Authors: Rybak Samuil A. , Makhortykh Sergey A. , Kostarev Stanislav A.
Published: October 2013

Monorail transport as all other city transport vehicles is the source of high noise and vibration levels. It is less widespread than cars or underground transport but its influence in modern cities enhances. Now in Moscow the first monorail road with trains on tires is designed, therefore the problem of vibration and noise assessments and prediction of its impact on the residential region appears. To assess the levels of generated vibration a physical model of interaction in the system wagon-tire-road coating-viaduct-soil has been proposed and then numerically analyzed. The model is based on the known from publications facts of automobile transport vibration and our own practice concerning underground trains vibration generation. To verify computer simulation results and adjust model parameters the series of measurements of noise and vibration near experimental monorail road was carried out. In the report the results of calculations and measurements will be presented and some outcomes of possible acoustical ecologic situation near monorail roads will be proposed.
Psychoacoustic influences of the echoing environments of prehistoric art
Authors: Waller Steven J.
Published: October 2013

Cave paintings and ancient petroglyphs around the world are typically found in echo rich locations such as caves, canyons, and rocky cliff faces. Analysis of field data shows that echo decibel levels at a large number of prehistoric art sites are higher than those at nondecorated locations. The selection of these echoing environments by the artists appears not to be a mere coincidence. This paper considers the perception of an echoed sound as a psychoacoustic event that would have been inexplicable to ancient humans. A variety of ancient legends from cultures on several continents attribute the phenomenon of echoes to supernatural beings. These legends, together with the quantitative data, strongly implicate echoing as relevant to the artists of the past. The notion that the echoes were caused by spirits within the rock would explain not only the unusual locations of prehistoric art, but also the perplexing subject matter. For example, the common theme of hoofed animal imagery could have been inspired by echoes of percussion noises perceived as hoof beats. Further systematic acoustical studies of prehistoric art sites is warranted. Conservation of the natural acoustic properties of rock art environments—a previously unrecognized need—is urged.
Wavelet denoising of underwater acoustic data
Authors: Ioup Juliette W. , Ioup George E.
Published: October 2013

The Littoral Acoustic Demonstration Center (LADC) deployed three Environmental Acoustic Recording System (EARS) buoys in the northern Gulf of Mexico during the summer of 2001. The buoys recorded frequencies up to 5859 Hz continuously for 36 days. The acoustic signals measured include sperm whale vocalizations and seismic airguns. The data are analyzed using time series, Fourier transforms, and spectrograms. Noise removal or denoising of these data at selected times using wavelets is investigated. The effectiveness of the technique is influenced by the choice of wavelet, the decomposition level, and the threshold amplitude. Results will be presented of wavelet denoising of the LADC Summer 01 data and compared with Fourier noise removal methods including bandpass filtering and thresholding. [Research supported by ONR.]
Microphone interlaboratory comparison in the Americas
Authors: Wong George S. K. , Wu Lixue
Published: October 2013

The final results of a Sistema Interamericano de Metrologia (SIM) interlaboratory comparison on microphone calibration are presented. Initially the comparison involved NORAMET countries: USA, Canada, and Mexico. Later, the comparison was extended to include Argentina and Brazil, resulting in a SIM AUV.A-K1 microphone interlaboratory comparison. The National Metrology Institutes (NMIs) of the five American countries that participated were the Institute for National Measurement Standards (INMS—Canada), National Institute of Standards and Technology (NIST—USA), Centro Nacional de Metrología (CENAM—Mexico), Instituto Nacional de Metrologia, Normalização e Qualidade Industrial (INMETRO—Brazil) and Unidad Técnica Acústica, (INTI—Argentina). INMS, Canada was the pilot laboratory that provided the data for the final report. The maximum rms deviation for the two LS1P laboratory standard microphones measured by the above participants is 0.037 dB that may be considered as the key comparison reference value.
Thrombolytic effects of 120-kHz and 1-MHz ultrasound and tissue plasminogen activator on porcine whole blood clots
Authors: Holland Christy K. , Vaidya Sampada S. , Coussios Constantin-C. , Shaw George J.
Published: October 2013

Stroke is the third leading cause of death and the leading cause of disability in the United States. For patients with ischemic stroke, the thrombolytic drug tissue plasminogen activator (tPA) is the only FDA-approved treatment. To aid in the development of a stroke therapy, the synergistic thrombolytic effect of tissue plasminogen activator (t-PA) and ultrasound was assessed in vitro in a porcine clot model. Whole blood clots were prepared from fresh porcine blood by aliquoting 1.5 ml into 8-mm-i.d. glass tubes, immersing the tubes in a 37°C water bath for 3 h and storing the clots at 5°C for at least 3 days prior to use in comparative ultrasound and t-PA studies, which ensured complete clot retraction. The 120-kHz or 1-MHz ultrasound peak-to-peak pressure amplitude used for exposures was 0.35, 0.70, or 1.00 MPa. The range of duty cycles varied from 10% to 100% (continuous wave) and the pulse repetition frequency was 1.7 kHz. Clot mass loss was measured as a function of t-PA concentration (without ultrasound) from 0.25 to 8.5 times the human clinical dose. The mass loss increased monotonically as a function of [t-PA] and saturated at 4 times the clinical dose. The degree of the ultrasound enhancement of t-PA was also explored at 120 kHz and 1 MHz. With ultrasound exposure, clot mass loss increased by as much as 250% over sham (t-PA alone). A weak dependence of clot mass loss on duty cycle was noted. We conclude that 120-kHz and 1-MHz ultrasound enhances thrombolysis. [Work supported by Senmed Medical Ventures.]