bluuebunny/crossref_metadata_2025 huggingface dataset:
Pressure Gage Measurements in a Dry to Wet Environment
Authors: Fullerton Anne M. , Fu Thomas C.
Published: July 2010

Pressure gages are used in many fluid measurements applications. One such application is the measurement of wave impact pressures on structures. This application poses a unique problem of measuring pressures in a “wet to dry” environment. Often there is a thermal drift component in the pressure readings that makes it difficult to extract the actual pressure rise due to wave loading. These types of measurements also require high response rates to measure the detail of the short duration impacts, usually on the order of one to twenty kilohertz. Several bench tests were carried out in at the Naval Surface Warfare Center, Carderock Division, in 2008 to investigate various types of gages to find a robust gage that could withstand this type of application. Three different gages were used in this investigation. The first sensor (gage 1) is a dynamics general purpose ICP (integrated circuit piezoelectric) pressure sensor, capable of making very high frequency dynamic pressure measurements, rated to 200 psi. The second sensor (gage 2) is a voltage compensated, media isolated piezoresistive sensor, rated to 15 psi. This gage had a pressure port which was filled with water during testing to eliminate air compression effects. The third sensor (gage 3) is a semiconductor pressure gage rated to 25 psi (172.4 kPa). A water “drop” test setup was constructed of 2 inch (5.1 cm) PVC pipe. The pressure gages were mounted to the bottom of the setup facing up, and the pipe was filled from the top, with a quick acting gate valve located 2 feet (0.61 m) from the pressure sensors. Once the pipe was filled with the desired amount of water, the gate valve was opened as quickly as possible, and the impact force was measured. Vent pipes were mounted to a “cross” fitting in the vertical pipe which allowed for the air to escape. Several water “drop” tests were performed with this setup. From these tests, the thermal drift of gage 1 is evident. Gage 3 exhibits similar behavior. Gage 2 captures the water pressure impact, and then returns to a small positive static pressure as a result of the water that is sitting above it. Of the three sensors, gage 2 appears to be the most temperature stable.
Design Optimization of a Centrifugal Compressor Impeller by Multi-Objective Genetic Algorithm
Authors: Kim Jin-Hyuk , Choi Jae-Ho , Husain Afzal , Kim Kwang-Yong
Published: July 2010

This paper presents design optimization of a centrifugal compressor impeller with hybrid multi-objectives evolutionary algorithm (hybrid MOEA). Reynolds-averaged Navier-Stokes equations with shear stress transport turbulence model are discretized by finite volume approximations and solved on hexahedral grids for flow analyses. Latin hypercube sampling of design of experiments is used to generate design points within the selected design space. Two objectives, i.e., isentropic efficiency and total pressure ratio are selected with four design variables defining impeller hub and shroud contours in meridional contours to optimize the system. Non-dominated Sorting of Genetic Algorithm (NSGA-II) with ε-constraint strategy for local search coupled with surrogate model is used for multi-objective optimization. The surrogate model, Radial Basis Neural Network is trained on the numerical solutions by carrying out leave-one-out cross-validation for the data set. The trade-off between the two objectives has been found out and discussed in light of the Pareto-optimal solutions. The optimization results show that isentropic efficiencies and total pressure ratios of the cluster points at the Pareto-optimal solutions are enhanced by multi-objective optimization.
Efficiency Enhancement by Shape Optimization of Centrifugal Fan Installed in Refuse Collecting System
Authors: Jang Choon-Man , Lee Sang-Yoon , Yang Sang-Ho
Published: July 2010

Shape optimization in the design of turbomachinery based on the three-dimensional flow analysis has been developed remarkably in recent years with the rapid enhancement of computational power. In the present study, optimal design of a centrifugal fan installed in refuse collecting system has been performed using response surface method and three-dimensional Navier-Stokes analysis to increase fan efficiency. The centrifugal fan is used to increase suction pressure for the moving of a waste through the pipe line of the system. Two design variables, which are used to define the shape of an inlet guide, are introduced to increase the efficiency of the fan. In the shape optimization using the response surface method, data points for response evaluations are selected, and linear programming method is used for an optimization on a response surface. To analyze three-dimensional flow field in the centrifugal fan, general analysis code, CFX, is employed in the present work: SST turbulence model is employed to estimate the eddy viscosity. Unstructured grids are used to represent a composite grid system including blade, casing and inlet guide. Throughout the shape optimization of a centrifugal fan, the fan efficiency is successfully increased by decreasing local losses in the blade passage. The result of shape optimization shows that the efficiency of the optimized shape at the design flow condition is enhanced by 1.42% based on the reference fan. It is found that recirculation flow region of optimum one is relatively small compared to the reference one. The reduction of recirculation region can be decreased the shaft power of an impeller, thus it can be increased the efficiency of the fan.
Modeling Microfluidic Microbubble Generators
Authors: John T. J. , Hegab H.
Published: July 2010

In this paper, two microfluidic bubble generators are proposed and modeled using COMSOL®. The first device consists of two microchannels perpendicular to each other. This arrangement of channels has been successfully used for generating bubbles with diameters in the millimeter range previously. The feasibility of miniaturizing this structure has been investigated in this paper. The bubble diameter generated using this method is found to vary inversly with the liquid flow rate (i.e. flow velocity). This is disadvantageous in terms of pressure drop while trying to generate microbubbles in microchannels. Therefore a second device, an extension of the first, has been proposed for eliminating this drawback by introducing a solid structure in the liquid channel right in front of the gas channel. The suitability of this device as a microbubble generator is checked through COMSOL® simulation model. At low flow rates, the bubble diameter is not significantly affected by the presence of the solid structure in the microchannel. In both devices the bubble attached itself to the walls at low Reynolds number but this did not happen at high Reynolds number. Further investigations are done in this study for understanding the effect of different shaped structures on the diameter of the microbubble.
Drag Reduction of a Simple Bluff Body by Changing the Rear End and Use the Ground Effect
Authors: Marklund Jesper , Lofdahl Lennart
Published: July 2010

The flow field around bluff bodies constitutes a classic area within fluid dynamics and has been the topic for much research through the years. However, in the use for road vehicles with the effect of the ground, the behavior is changed very much from more classical aviation usage. In this paper we are investigating the drag force reduction on a vehicle like simplified model with rear open diffuser when stationary ground simulation is considered. The objective with this work was to study the rear end of a bluff body and optimize it for drag with ground vehicle like boundaries. Here the testing contains two common body variants, square back, boat tailed/fastback in generic forms. Scale model testing combined with simulations is used to explain behavior and flow field. The model testing is performed in the L2 scale model wind tunnel at Chalmers University of Technology in Gothenburg, Sweden. Simulations are done with the commercial CFD code Fluent. A diffuser on a car is normally used to create down force but here it is tested to see if the energy in the flow can be used to optimize reduction of drag. One part of the study is to show the potential in optimizing the rear end underbody for drag, by varying the diffuser angle. The results show a potential in drag reduction by using a diffuser and varying effect depending on other rear end geometries.
Aerodynamic Analysis of the Helicopter Rotor Using the Time-Domain Panel Method
Authors: Lee Seawook , Cho Leesang , Choi Hyunmin , Cho Jinsoo
Published: July 2010

Recently, aerodynamic analysis of the helicopter rotor using computational fluid dynamics (CFD) is widely carried out with high accuracy. But, it is very long time to calculate aerodynamic performances and it is difficult to simulate the wake shape of the helicopter rotor using CFD analysis. In this research the time-domain panel method, which uses a numerical technique based on the piecewise constant source and doublet singularities, is applied to the analysis and prediction of the unsteady aerodynamic characteristics of helicopter rotor in a potential flow. And the free wake model is used for wake simulation. The results of present method are compared with the results of experiment of a helicopter rotor in hover and in forward flight. Results show good agreement with the experimental results.
Dynamic Behaviors of Butterfly Wing and Their Application to Micro Flight Robot
Authors: Imura Tadatsugu , Fuchiwaki Masaki , Tanaka Kazuhiro
Published: July 2010

Micro-Air-Vehicle (MAV) and micro-flight robot using insect and bird flight mechanisms has been attracting significant attention in recent years since the micro-electromechanical systems (MEMS) have been developed actively. Many researchers have attempted to develop MAV and micro-flight robot with various actuators and devices so far however their studies have not led to practical applications yet. One of the reasons is that flying mechanism of birds and insects has not been clarified sufficiently. In this study, we evaluate dynamic behaviors of a wing observed from the butterfly’s viewpoint in its flight. The authors conduct a flight observation experiment of Cynthia cardui performing a free flight and fixed flight and an image analysis and calculate flapping angles, lead-lag angle and feathering angles of the butterfly performing flapping flight to clarify the relation between them. Furthermore, we aim at developing the micro flight robot like the butterfly using these results. The butterfly realizes its flapping motions by changing not only flapping angles but also lead-lag angles in free and fixed flights. In a free flight, a butterfly performs flapping by greatly changing feathering angles in the wing span direction. The micro flapping robot has two wings and does not have the tail plane. The micro flapping robot flied stably for 12 minutes, which was the battery’s duration. The elastic deformations of a wing are one of the important parameters to realize stable flight performance.
Investigation of the Cooling and Underbody Flow Field on a Detailed Model Scale Passenger Car: Part 1—Cooling Flows and Reynolds Number Effects
Authors: Christoffersen Lasse M. , Landstro¨m Christoffer , Lo¨fdahl Lennart
Published: July 2010

To decrease the lead time and hence cost for an aerodynamic development programme for a new car model, extended use of down scaled wind tunnel models is one possibility. This however, requires that the models carry many of the exterior, engine bay and underbody details that are present on the full scale counterpart. An important issue in scale testing is to understand the Reynolds number effects that will be present and with an increased detail level of the model it is believed that there will be other Reynolds number effects than on the simplified models that historically have been used. Therefore; the aim of this work is to explain some of the Reynolds number effects that are developed on a detailed model of a sedan type passenger car. The analysis is based on experimental data with both load and pressure measurements as the primary source carried out on a 30% model of a Volvo S60. In the experiment both moving ground and rotating wheels were utilized. With the Reynolds number ranging from 8.8e5 to 3.5e6 it was possible to notice interesting Reynolds number effects. The results show that there is a significant Reynolds number dependency of the scale model. However, it is also shown that the Reynolds number dependency is dependent on the detail level of the model.
Loss Coefficients in Microelbows
Authors: Handy Tim A. , Lemley Evan C. , Papavassiliou Dimitrios V. , Neeman Henry J.
Published: July 2010

The goal of this study was to determine laminar pressure loss coefficients for flow in microelbows with circular and trapezoidal cross-sections. Flow conditions and pressure losses in these elbows are of interest in microfluidic devices, in porous media, and in other types of microfluidic networks. The literature focuses almost exclusively on loss coefficients due to turbulent flow in macroelbows with very little data on laminar flow in macroelbows. The pressure loss coefficients determined in this study are intended to aid in realistic simulation of existing laminar flow networks or the design of these networks. This study focused on an elbow of constant cross-section with inlet and outlet tubes of sufficient length so as to allow fully developed laminar flow at the entrance to the elbow and at the outlet tube exit. For the circular elbow, both the ratio of elbow radius to inner diameter and inlet Reynolds number were allowed to vary over the ranges of 0.5—10.5 and 1—2500, respectively. The laminar pressure loss coefficients were determined by simulating incompressible flow over the range of geometries and Reynolds numbers in the commercial CFD software FLUENT. The pressure and velocity distributions in the inlet and outlet tubes were averaged at multiple upstream and downstream positions, and were then used to extrapolate the loss coefficient due to the elbow. The results showed that the loss coefficient for larger ratios tended to be higher, in some cases in excess of 100, at low Reynolds number flows, but as the flow approached the transitional regime, the loss coefficients leveled out to roughly their accepted turbulent values of between 0.4 and 1.0. These results show good qualitative and quantitative agreement with limited laminar elbow experimental data available for macroelbows. For the trapezoidal elbows the loss coefficient levels off to about two for Reynolds numbers greater than 100.
An Investigation of the Aerodynamic Drag Mechanisms Due to Ground Simulation in Yawed Flow Conditions for Heavy Trucks
Authors: So¨derblom David , Lo¨fdahl Lennart , Elofsson Per , Hjelm Linus
Published: July 2010

The drag from the underbody, including wheels and wheel housings, constitute a significant amount of the total aerodynamic drag of heavy trucks. A correct simulation of the underbody boundary conditions, including rotating wheels and moving ground, has turned out to be of great importance in the minimising of the aerodynamic drag. Earlier studies on passenger cars have described the drag mechanisms involved when implementing proper ground simulation. However, model scale wind tunnel tests of heavy trucks have shown an opposite trend on the drag coefficient with ground simulation compared to passenger cars. An important aspect of truck aerodynamics is the yaw dependency of the drag coefficient when the vehicle is exposed to crosswinds. Therefore it is of outmost importance to evaluate the performance of the vehicle in yawed flow conditions during the development process. In the current study the influence of ground simulation, including moving ground and rotating wheels, on the flow has been investigated at several yaw angles using Computational Fluid Dynamics. For the simulations a tractor trailer geometry corresponding to a standard European configuration was used, and the geometry included a fully detailed underbody and engine compartment. It was found that there was a difference in the wheel wake structure and this was mainly due to the implementation of wheel rotation. It was also shown that the drag coefficient increased due to the utilisation of ground simulation in yawed flow conditions.
Simulation-Based Analysis of the Micropropulsion With Rotating Corkscrew Motion of Flagella
Authors: Koz Mustafa , Yesilyurt Serhat
Published: July 2010

Microorganisms such as ecoli bacterium can propel themselves by means of a corkscrew motion in flow regimes where the Reynolds number is much smaller than one and inertial propulsion methods are ineffective. Micropropulsion with the rotating corkscrew motion of flagella can prove useful as a navigation mechanism for microswimming robots in medical applications. In this work, we present the motion of a microswimmer that consists of an ellipsoid of length two-microns and diameter one micron with a flagellum of length two microns and diameter of 40 nanometers. The microswimmer resembles to a typical ecoli bacterium. We present the effect of parameters such as angular velocity and amplitude of the corkscrew motion. In simulations, time-dependent three-dimensional Navier-Stokes equations are solved in deforming mesh using a commercial package COMSOL. Mesh deformation is specified based on the displacement and rotation of the microswimmer that springs from the net force and torque around the center of mass due to the rotation of the corkscrew-like flagellum. The net linear and angular accelerations of the microswimmer are calculated using ordinary-differential equations that represent the equation of motion, and coupled with the Navier-Stokes equations and the mesh deformation. For simplicity, microswimmer is placed in a cylindrical channel of diameter 20 microns and length 60 microns.
Nanowire-GMR Integrated Microfluidic Biosensor
Authors: Bellamkonda Ramya , John Tom , Mathew Bobby , Hegab Hisham , DeCoster Mark , Davis Despina
Published: July 2010

Nanowires based GMR is ideal to be integrated in microfluidic devices due to its efficient detection of sensitive magnetic fields. Nanowire based GMR microfluidic sensor is used to detect different fluids based on their magnetic behavior. This paper demonstrates the fabrication and testing of nanowire based GMR biosensors with four different control solutions: 1) DI-water, 2) Phosphate Buffered Saline (PBS), 3) polystyrene superparamagnetic beads, and 4) commercially available magnetic Dynabeads. The device is fabricated in PDMS by using a lithographically patterned silicon wafer as the mold. The nanowire based GMR material, 3 mm by 3 mm in size, is inserted inside the PDMS close to the channel during the fabrication. The channel in the PDMS substrate is sealed by bonding it to a glass plate using Reactive-Ion-Exchanger (RIE). GMR device is tested potentiostatically using a computer controlled function generator (Solatron, SI 1287). A highest resistance of 0.748 Ω. is recorded for the sensor, in the absence of magnetic field. A resistance change of 0.6% is obtained in the presence of a magnetic field (B = 0.035T) between water and polystyrene superparamagnetic beads when pumped through the microchannel. The sensor showed a resistance difference of 0.31% between 1X diluted PBS and 100X diluted dynabeads, in the presence of a constant magnetic field of 0.035T. This characterization would be useful in the development of a BioMEMS sensor using nanowire based GMR.
Lagrangian Statistics of Droplet Velocity and Acceleration in Isotropic Turbulence
Authors: Gopalan Balaji , Malkiel Edwin , Katz Joseph
Published: July 2010

The addition of dispersants, water and oil soluble surfactants that lower the interfacial tension of the crude oil, along with oceanic turbulence can breakdown oil spills into droplets. Knowledge of the dispersion rate of these droplets by oceanic turbulence is essential for the development of better models to assess the environmental impact of spills. The objective of this research is to study, experimentally, the dispersion of oil droplets in turbulent flows. The measurements are performed in a specialized laboratory facility that enables generation of carefully controlled, isotropic, homogeneous turbulence at a wide range of fully characterized intensities and length scales. The oil dispersion is visualized using high-speed inline digital holographic cinematography. Holographic data has been analyzed and Lagrangian statistics of droplet velocity, dispersion and acceleration has been calculated. As the relative size of the droplet diameter to the Kolmogorov length scale and its Stokes number increases, the acceleration autocorrelation shifts from dropping to zero faster than the fluid particles to slower.
Characteristics of 3D Turbulent Wall Jets and Offset Jets With Small Offset Ratios
Authors: Agelinchaab M. , Tachie M. F.
Published: July 2010

This paper reports an experimental study of turbulent three-dimensional generic wall jets and offset jets. The jets were created from a long circular pipe. A particle image velocimetry technique was used to conduct velocity measurements in the symmetry plane of the jet. From these measurements, the salient features of the flows are reported in terms of the mean velocities, turbulence intensities and Reynolds shear stresses. The energy spectra and profiles of reconstructed turbulence intensities and Reynolds shear stresses from low order proper orthogonal decomposition modes are also reported.
Three-Dimensional Turbulent Wall Jets
Authors: Agelinchaab M. , Tachie M. F.
Published: July 2010

Particle image velocimetry (PIV) measurements were carried out on generic three-dimensional turbulent wall jets. The wall jets were created from a long circular pipe at Reynolds number based on the jet exit velocity (Uj) and inside diameter of pipe (d) of Rej = Ujd/v = 7680 to 19500. The profiles of the mean velocities, turbulence intensities and Reynolds shear stresses in the streamwise/wall-normal and streamwise/lateral planes are presented. Consistent with previous results, the profiles of the mean velocities and turbulent statistics are independent of Reynolds number. The mean velocity attained self-similarity before the turbulence quantities. The decay rate and spread rates obtained in the present study fall in between the values reported in previous studies. The contours of the two-point velocity correlations in the inner region of the 3D wall jet are qualitatively similar to those reported in boundary layer studies. The results from proper orthogonal analysis revealed that large scale structures are largely responsible for the distribution of the streamwise turbulence intensity and Reynolds shear stresses than the distribution of the wall-normal turbulence intensity.
CFD Simulation of Temperature Distribution in a Room With Various Under Floor Heating System Models
Authors: Izadi Mohammad Javad , Makaremi Kamyar
Published: July 2010

Limited resources of energy are the major challenges of the industrial and developing communities (countries), so engineers are increasingly encouraged for new ideas of producing energy from the today’s natural resources such as sun light and wind instead of fossil resources. In this study, flow of air in a 3D flow field surrounded by several walls and windows (a room) as laminar, and flow of water in a 3D flow filed (a pipe) placed on the bottom of the room as turbulent in an incompressible flow condition is modeled. The heat transfer through the pipe as the heat source placed under the floor in a sample room for several variables are studied numerically. The variables are two models of pipes arrangements, three types of pipes, and several pipe diameters. The wall conductivity and the air convection are considered constant for several outside room temperatures in this analysis. After analyzing all these parameters, the results obtained numerically are compared with each other and the best parameter values for the best room temperature as so called “comfort temperature” is selected. From the three variables considered here, it can be said that in an under floor heating system, the reciprocating model using the Pex-Al-Pex pipe type of 16mm pipe diameter are the best parameter values for a good and comfortable room temperatures for any outside temperature.
Investigation of the Formation of Microbubbly Liquid Fuel
Authors: Celik Emine , Katz Joseph , Van Wie David M.
Published: July 2010

There are several obstacles encountered during combustion in Supersonic Combustion Ramjet (SCRAMJET) engines such as mixing, ignition, and flame holding. In order to overcome these difficulties, a new type of fuel is generated with the use of combination of two methods namely an effervescent (barbotage) and thermal pyrolysis of the fuel. In the first step of the process, during effervescent method, small gas bubbles are introduced into liquid fuel to improve the spraying characteristics of the fuel. At the second stage, long-chain hydrocarbons are broken down into short-chain hydrocarbons that burn faster. An experimental facility has been designed and developed to study the underlying physics in each process.
A Modern Pump Design Process for Higher Efficiency and Product Accuracy
Authors: Cugal Michael , Bloomfield Stuart , Jensen Bo Mo̸ller , Jacobsen Christian Brix
Published: July 2010

This paper describes an innovative engineering process for the design of a new split-case, double-suction, and single-stage centrifugal pump. In order to achieve high pump efficiency and procure accurate and reliable castings, a process was developed utilizing a global network of engineering resources, Computational Fluid Dynamics (CFD) codes, 3-dimensional (3-D) solid modeling, Finite Element Analysis (FEA), and 3-D inspection tools. The hydraulic components of the pump are designed using in-house hydraulic design tools, empirical test data, and proven CFD technology. Once verified, these designs, in the form of 3-D surfaces, are directly exported to solid-modeling software, where the pump’s mechanical design can be completed. Finite Element Analysis (FEA) is used to analyze and help refine the final design before 3-D solid models of the pump casing and impeller are sent to the pattern maker. The pattern maker reviews the models before the final pattern equipment is generated. Once first-article castings are produced, a 3-D coordinate measuring machine is used—by generating the 3-D surfaces of the hydraulic passageways—to inspect the castings and compare them directly to the original solid model.
Experimental Investigation of Flow Instabilities and Rotating Stall in a High-Energy Centrifugal Pump Stage
Authors: Berten Stefan , Dupont Philippe , Fabre Laurent , Kayal Maher , Avellan Francois , Farhat Mohamed
Published: July 2010

In centrifugal pumps, the interaction between the rotating impeller and the stationary diffuser generates specific pressure fluctuation patterns. When the pump is operated at off design conditions, these pressure fluctuations increase. The resulting rise of mechanical vibration levels may negatively affect the operational performance and the life span of mechanical components. This paper presents detailed pressure fluctuation measurements performed in a high speed centrifugal pump stage at full scale at various operating conditions. The impeller and stationary part (diffuser, exit chamber) of the pump stage have been equipped with piezoresistive miniature pressure sensors. The measured data in the impeller have been acquired using a newly developed onboard data acquisition system, designed for rotational speeds up to 6000 rpm. The measurements have been performed synchronously in the rotating and stationary domains. The analysis of pressure fluctuations at the impeller blade trailing edge, which had significantly larger amplitudes as the pressure fluctuations in the stationary domain, allowed the detection and exploration of stalled channels in the vaned diffuser. This stall may be stationary or rotating with different rotational speeds and number of stalled channels, depending on the relative flow rate and the rotational speed of the pump. The stall yields pressure fluctuations at frequencies which are multiples of the rotational speed of the impeller and generates additional sources of mechanical excitation.
Simulation of Eccentric-Shaft Journal Microbearing by DSMC
Authors: Wang Sheng , Lei Kangbin , Luo Xilian , Kase Kiwamu , Merzari Elia , Ninokata Hisashi
Published: July 2010

Many micromachines use rotating shafts and other moving parts which carry a load and need fluid bearings for support. Most of them operate with air or water as the lubricating fluid. The present study analyzes air microbearing represented as an eccentric cylinder rotating in a stationary housing. The fluid mechanics and operating characteristics of microbearing are different from their larger cousins. The small length-scale may invalidate the continuum approximation in Navier-Stokes equations, and slip flow, rarefaction, compressibility and other unconventional effects may have to be taken into account. Surface effects dominate in small devices due to a high surface-volume ratio. In this study, two-dimensional eccentric-shaft journal microbearings with different eccentricities are simulated by direct simulation Monte Carlo (DSMC) code incorporated with a Volume-CAD software. The diffuse reflection model and Cercignani-Lampis-Lord (CLL) model are applied to model the molecule-surface interaction by considering the accommodation coefficients of shaft wall and housing wall separately. The distribution of mean free path in the flow field indicates that the continuum model may break down and it is necessary to carry our molecular modeling. Calculation results show that at high eccentricity and high accommodation coefficient on the housing wall (ACO) the flow may develop a recirculation region. However, the accommodation coefficient on shaft wall (ACI) does not have any effect on the occurrence of recirculation and the size of recirculation zone. There is antisymmetry of the pressure about a vertical axis, which produces a pressure force on the shaft wall. The influence of ACI to isobars is larger than that of ACO. The shear stress profile on shaft wall is big at low ACI. At the region of short clearance between the shaft wall and housing wall, it is also influenced by the surface condition of housing wall and may even change its direction at low ACO. The pressure profile is reduced in amplitude as the ACI increases, but it is enhanced a little with the increase of ACO. The ACO has great impact on the viscous force in the case of big eccentricity. With the increase of ACI, the viscous force decreases. The pressure force is high at large eccentricity. The influence of ACO to pressure force is insignificant, but the pressure force fall is enormous when ACI increases, especially for large eccentricity. The total force decreases markedly at high eccentricity when ACI increases. The ACO almost has no impact on the total force. The torque increases with ACO, but decreases with ACI. The eccentricity also has great impact on the torque, and the microbeaing may have large torque at high eccentricity. The method developed in this paper would be very useful for designing and evaluating journal microbearing.
In Situ Measurement Techniques for Characterizing Pulse Jet Mixing of Slurries
Authors: Bamberger Judith Ann , Greenwood Margaret S. , Morgan Gerald W. , Meyet Perry A. , Baer Ellen B. K. , Minette Michael J. , Scott Paul A.
Published: July 2010

Metrics to characterize mixing are the just suspended velocity (UJS) and the cloud height (HC). Two ultrasonic instruments to characterize pulse jet mixing of slurries were developed and deployed to measure related metrics: the thickness of the settled bed and the concentration within the cloud as a function of elevation [C(Z)]. Ultrasonic Doppler velocimetry was used to measure the thickness of the bed of nonmoving particles (the settled solids layer). During pulse jet mixing at the critical suspension velocity (UCS) the settled solids layer thickness approached zero at the end of the jet pulse. The UCS is related to the just suspended velocity (UJS) for steady mixing. Ultrasonic attenuation was used to measure the suspended solids concentration at locations in the vessel to determine the concentration profile as a function of radial position and elevation. The concentration profile provided data inside the particulate cloud and complemented the visual measurement of the cloud height (HC). The UDV and the ultrasonic concentration probe data are used to evaluate the desired metrics based on relative measurements. The relative measurements are correlated with results obtained from a series of working standards created for each slurry, and used to develop correlations specific to each slurry.
Instability and Breakdown of a Zero Net Mass-Flux Jet in a Blasius Boundary Layer
Authors: Watmuff Jonathan H.
Published: July 2010

Hot–wire measurements reveal the evolution of three-dimensional TS (Tollmien-Schlichting) waves and other nonlinear disturbances generated by a ZNMF (Zero Net Mass-Flux) jet. The base flow consists of a highly two-dimensional Blasius boundary layer with extremely small extraneous background disturbance levels (u/U1 < 0.08 %). The response is shown to be linear and symmetrical for sufficiently small actuator amplitudes and under these conditions the TS wave motions conform with the PSE (Parabolized Stability Equations) results of Mack & Herbert (1995). The observations suggest that a small-amplitude ZNMF jet would be a suitable device for active LFC (Laminar Flow Control) applications. For larger actuator amplitudes, other short–wavelength instabilities develop and grow with streamwise development and they ultimately breakdown to form a turbulent wedge. There is an actuator amplitude threshold below which these instabilities do not form, and a larger threshold below which the instabilities do not grow with streamwise development. The characteristics of the turbulent wedge are also considered in some detail.
Three‐dimensional microwave imaging of realistic numerical breast phantoms via a multiple‐frequency inverse scattering technique
Authors: Shea Jacob D. , Kosmas Panagiotis , Hagness Susan C. , Van Veen Barry D.
Published: July 2010

Purpose:

Breast density measurement has the potential to play an important role in individualized breast cancer risk assessment and prevention decisions. Routine evaluation of breast density will require the availability of a low‐cost, nonionizing, three‐dimensional (3‐D) tomographic imaging modality that exploits a strong properties contrast between dense fibroglandular tissue and less dense adipose tissue. The purpose of this computational study is to investigate the performance of 3‐D tomography using low‐power microwaves to reconstruct the spatial distribution of breast tissue dielectric properties and to evaluate the modality for application to breast density characterization.

Methods:

State‐of‐the‐art 3‐D numerical breast phantoms that are realistic in both structural and dielectric properties are employed. The test phantoms include one sample from each of four classes of mammographic breast density. Since the properties of these phantoms are known exactly, these testbeds serve as a rigorous benchmark for the imaging results. The distorted Born iterative imaging method is applied to simulated array measurements of the numerical phantoms. The forward solver in the imaging algorithm employs the finite‐difference time‐domain method of solving the time‐domain Maxwell's equations, and the dielectric profiles are estimated using an integral equation form of the Helmholtz wave equation. A multiple‐frequency, bound‐constrained, vector field inverse scattering solution is implemented that enables practical inversion of the large‐scale 3‐D problem. Knowledge of the frequency‐dependent characteristic of breast tissues at microwave frequencies is exploited to obtain a parametric reconstruction of the dispersive dielectric profile of the interior of the breast. Imaging is performed on a high‐resolution voxel basis and the solution is bounded by a known range of dielectric properties of the constituent breast tissues. The imaging method is validated using a breast phantom with a single, high‐contrast interior scattering target in an otherwise homogeneous interior. The method is then used to image a set of realistic numerical breast phantoms of varied fibroglandular tissue density.

Results:

Imaging results are presented for each numerical phantom and show robustness of the method relative to tissue density. In each case, the distribution of fibroglandular tissues is well represented in the resulting images. The resolution of the images at the frequencies employed is wider than the feature dimensions of the normal tissue structures, resulting in a smearing of their reconstruction.

Conclusions:

The results of this study support the utility of 3‐D microwave tomography for imaging the distribution of normal tissues in the breast, specifically, dense fibroglandular tissue versus less dense adipose tissue, and suggest that further investigation of its use for volumetric evaluation of breast density is warranted.
Recommended ethics curriculum for medical physics graduate and residency programs: Report of Task Group 159
Authors: Serago Christopher F. , Burmeister Jay W. , Dunscombe Peter B. , Gale Ashley A. , Hendee William R. , Kry Stephen F. , Wuu Cheng‐Shie
Published: July 2010

The AAPM Professional Council approved the formation of a task group in 2007, whose purpose is to develop recommendations for an ethics curriculum for medical physics graduate and residency programs. Existing program's ethics curricula range in scope and content considerably. It is desirable to have a more uniform baseline curriculum for all programs. Recommended subjects areas, suggested ethics references, and a sample curriculum are included. This report recommends a reasonable ethics course time to be 15–30 h while allowing each program the flexibility to design their course.
Monte Carlo simulator of realistic x‐ray beam for diagnostic applications
Authors: Bontempi Marco , Andreani Lucia , Rossi Pier Luca , Visani Andrea
Published: July 2010

Purpose:

Monte Carlo simulation is a very useful tool for radiotherapy and diagnostic radiology. Yet even with the latest PCs, simulation of photon spectra emitted by an x‐ray tube is a time‐consuming task, potentially reducing the possibility to obtain relevant data such as dose evaluations, simulation of geometric settings, or monitor detector efficiency. This study developed and validated a method to generate random numbers for realistic beams in terms of photon spectrum and intensity to simulate x‐ray tubes via Monte Carlo algorithms.

Methods:

Starting from literature data, the most common semiempirical models of bremsstrahlung are analyzed and implemented, adjusting their formulation to describe a large irradiation area (i.e., large field of view) and to take account of the heel effect as in common practice during patient examinations.

Results:

Simulation results show that Birch and Marshall's model is the fastest and most accurate for the aims of this work. Correction of the geometric size of the beam and validation of the intensity variation (heel effect) yielded excellent results with differences between experimental and simulated data of less than 6%.

Conclusions:

The results of validation and execution time showed that the tube simulator calculates the x‐ray photons quickly and efficiently and is perfectly capable of considering all the phenomena occurring in a real beam (total filtration, focal spot size, and heel effect), so it can be used in a wide range of applications such as industry, medical physics, or quality assurance.
Hybrid x‐ray/optical luminescence imaging: Characterization of experimental conditions
Authors: Carpenter C. M. , Sun C. , Pratx G. , Rao R. , Xing L.
Published: July 2010

Purpose:

The feasibility of x‐ray luminescence imaging is investigated using a dual‐modality imaging system that merges x‐ray and optical imaging. This modality utilizes x‐ray activated nanophosphors that luminesce when excited by ionizing photons. By doping phosphors with lanthanides, which emit light in the visible and near infrared range, the luminescence is suitable for biological applications. This study examines practical aspects of this new modality including phosphor concentration, light emission linearity, detector damage, and spectral emission characteristics. Finally, the contrast produced by these phosphors is compared to that of x‐ray fluoroscopy.

Methods:

Gadolinium and lanthanum oxysulfide phosphors doped with terbium (green emission) or europium (red emission) were studied. The light emission was imaged in a clinical x‐ray scanner with a cooled CCD camera and a spectrophotometer; dose measurements were determined with a calibrated dosimeter. Using these properties, in addition to luminescence efficiency values found in the literature for a similar phosphor, minimum concentration calculations are performed. Finally, a 2.5 cm agar phantom with a 1 cm diameter cylindrical phosphor‐filled inclusion (diluted at 10 mg/ml) is imaged to compare x‐ray luminescence contrast with x‐ray fluoroscopic contrast at a superficial location.

Results:

Dose to the CCD camera in the chosen imaging geometry was measured at less than 0.02 cGy/s. Emitted light was found to be linear with dose and concentration . Emission peaks for clinical x‐ray energies are less than 3 nm full width at half maximum, as expected from lanthanide dopants. The minimum practical concentration necessary to detect luminescent phosphors is dependent on dose; it is estimated that subpicomolar concentrations are detectable at the surface of the tissue with typical mammographic doses, with the minimum detectable concentration increasing with depth and decreasing with dose. In a reflection geometry, x‐ray luminescence had nearly a 430‐fold greater contrast to background than x‐ray fluoroscopy.

Conclusions:

X‐ray luminescence has the potential to be a promising new modality for enabling molecular imaging within x‐ray scanners. Although much work needs to be done to ensure biocompatibility of x‐ray exciting phosphors, the benefits of this modality, highlighted in this work, encourage further study.
Modulator design for x‐ray scatter correction using primary modulation: Material selection
Authors: Gao Hewei , Zhu Lei , Fahrig Rebecca
Published: July 2010

Purpose: An optimal material selection for primary modulator is proposed in order to minimize beam hardening of the modulator in x‐ray cone‐beam computed tomography (CBCT). Recently, a measurement‐based scatter correction method using primary modulation has been developed and experimentally verified. In the practical implementation, beam hardening of the modulator blocker is a limiting factor because it causes inconsistency in the primary signal and therefore degrades the accuracy of scatter correction.

Methods: This inconsistency can be purposely assigned to the effective transmission factor of the modulator whose variation as a function of object filtration represents the magnitude of beam hardening of the modulator. In this work, the authors show that the variation reaches a minimum when the ‐edge of the modulator material is near the mean energy of the system spectrum. Accordingly, an optimal material selection can be carried out in three steps. First, estimate and evaluate the polychromatic spectrum for a given x‐ray system including both source and detector; second, calculate the mean energy of the spectrum and decide the candidate materials whose ‐edge energies are near the mean energy; third, select the optimal material from the candidates after considering both the magnitude of beam hardening and the physical and chemical properties.

Results: A tabletop x‐ray CBCT system operated at 120 kVp is used to validate the material selection method in both simulations and experiments, from which the optimal material for this x‐ray system is then chosen. With the transmission factor initially being 0.905 and 0.818, simulations show that erbium provides the least amount of variation as a function of object filtrations (maximum variations are 2.2% and 4.3%, respectively, only one‐third of that for copper). With different combinations of aluminum and copper filtrations (simulating a range of object thicknesses), measured overall variations are 2.5%, 1.0%, and 8.6% for of copper, erbium, and tungsten, respectively. With and without of copper in the beam, the measured variations for of copper, erbium, and tungsten, 1 mm of aluminum, as well as of copper, are 1.8%, 0.2%, 5.5%, 1.9%, and 7.5%, respectively.

Conclusions: The spatial variation in the effective transmission factor of the modulator blocker due to beam hardening caused by the modulator itself reaches a minimum when the ‐edge of the modulator material is near the mean energy of the spectrum. An optimal modulator material selection using the ‐edge discontinuity is therefore proposed.
Effects of breast‐air and breast‐lung interfaces on the dose rate at the planning target volume of a MammoSite® catheter for Yb‐169 and Ir‐192 HDR sources
Authors: Cazeca Mario J. , Medich David C. , Munro John J.
Published: July 2010

Purpose:

To study the effects of the breast‐air and breast‐lung interfaces on the absorbed dose within the planning target volume (PTV) of a MammoSite® balloon dose delivery system as well as the effect of contrast material on the dose rate in the PTV.

Methods:

The Monte CarloMCNP5 code was used to simulate dose rate in the PTV of a 2 cm radius MammoSite® balloon dose delivery system. The simulations were carried out using an average female chest phantom (AFCP) and a semi‐infinite water phantom for both Yb‐169 and Ir‐192 high dose rate sources for brachytherapy application. Gastrografin was introduced at varying concentrations to study the effect of contrast material on the dose rate in the PTV.

Results:

The effect of the density of the materials surrounding the MammoSite® balloon containing 0% contrast material on the calculated dose rate at different radial distances in the PTV was demonstrated. Within the PTV, the ratio of the calculated dose rate for the AFCP and the semi‐infinite water phantom for the point closest to the breast‐air interface (90°) is less than that for the point closest to the breast‐lung interface (270°) by 11.4% and 4% for the HDR sources of Yb‐169 and Ir‐192, respectively. When contrast material was introduced into the 2 cm radius MammoSite® balloon at varying concentrations, (5%, 10%, 15%, and 20%), the dose rate in the AFCP at 3.0 cm radial distance at 90° was decreased by as much as 14.8% and 6.2% for Yb‐169 and Ir‐192, respectively, when compared to that of the semi‐infinite water phantom with contrast concentrations of 5%, 10%, 15%, and 20%, respectively.

Conclusions:

Commercially available software used to calculate dose rate in the PTV of a MammoSite® balloon needs to account for patient anatomy and density of surrounding materials in the dosimetry analyses in order to avoid patient underdose.