bluuebunny/crossref_metadata_2025 huggingface dataset:
A More Realistic Scheme of Deviation Error Representation for Gas Turbine Diagnostics
Authors: Loboda Igor , Yepifanov Sergiy , Feldshteyn Yakov
Published: July 2013

Gas turbine diagnostic algorithms widely use fault simulation schemes, in which measurement errors are usually given by theoretical random number distributions, like the Gaussian probability density function. The scatter of simulated noise is determined on the basis of known information on maximum errors for every sensor type. Such simulation differs from real diagnosis because instead of measurements themselves the diagnostic algorithms work with their deviations from an engine baseline. In addition to simulated measurement inaccuracy, the deviations computed for real data have other error components. In this way, simulated and real deviation errors differ by amplitude and distribution. As a result, simulation-based investigations might result in too optimistic conclusions on gas turbine diagnosis reliability.

To understand error features, deviations of real measurements are analyzed in the present paper. To make error presentation more realistic, it is proposed to extract an error component from real deviations and to integrate it in fault description. Finally, the effect of the new noise representation mode on diagnostic reliability is estimated. It is shown that the reliability change due to inexact error simulation can be significant.
Experimental Measurements and Numerical Simulations in Isothermal Turbulent Flows
Authors: Florean Florin G. , Popescu Jeni A. , Porumbel Ionut , Carlanescu Cristian , Dumitrascu Gheorghe
Published: July 2013

The paper presents Particle Image Velocimetry experimental measurements and an ANSYS CFX numerical simulation of the mean and fluctuating velocity field in a turbulent, isothermal flow downstream of a V-shaped bluff body flame stabilizer equipping a post-combustion system installed downstream of a Garrett 30-67 gas turbine engine.

The post-combustion system used as experimental model is described in detail, and the main characteristics of the Garrett 30-67 gas generator are included in the paper. Also, the instrumentation used on the experimental rig, including the Particle Image Velocimetry equipment, is briefly described.

The presence of a bluff body inside the high speed flow creates a re-circulating wake structure, clearly seen in the experimental data. In the near field, the re-circulating region’s length and width of are captured reasonably well by the numerical simulation, but the momentum rate transfer further downstream is over-predicted, as the grid resolution worsens.

An overall over prediction of the axial velocity by the numerical simulation is noted by comparing the numerical simulation results to the experimental data, explained by an over estimated inlet velocity in the numerical simulation, provided by Particle Image Velocimetry experimental measurements in the free exhaust jet behind the gas generator, without the installation of the post-combustion system, thus neglecting the effect of the latter on the operating regime of the gas turbine engine.
Monitoring of Blade Vibrations and Tip Clearance at Non-Metallic Rotors in Turbo Machines
Authors: Dreier Florian , Pfister Thorsten , Czarske Jürgen
Published: July 2013

In order to improve the safety, the lifetime and the energy efficiency of turbo machines, the dynamic behaviour of the rotor has to be analysed and optimized. Thus, rotor unbalances, dynamic deformations and blade vibrations as well as blade tip clearance changes have to be monitored during operation to optimize the rotor design and to validate numerical models. However, these are great challenges for metrology, since small, robust and non-contact measurement techniques are required offering both micrometer accuracy and microsecond temporal resolution which is not fulfilled with currently available measurement techniques. To solve this problem, we present in this contribution a miniaturized fiberoptic laser Doppler probe that measures simultaneously the in-plane velocity and the out-of-plane position of laterally moving objects. Experiments have been carried out demonstrating the capability of this sensor to measure engine order blade vibrations instantaneously. Assuming a single engine order and a known vibration frequency, only one laser Doppler probe is necessary to measure the vibration amplitude. Thus, in contrast to blade tip timing, only one optical access to the blade tip is sufficient to measure the vibration amplitude. Furthermore, the novel sensor performs even at composite materials such as strongly absorbing carbon-fiber-reinforced plastic (CFRP) which became more popular in rotors of turbo machines.
Crackle Noise in Heated Supersonic Jets
Authors: Nichols Joseph W. , Lele Sanjiva K. , Ham Frank E. , Martens Steve , Spyropoulos John T.
Published: July 2013

Crackle noise from heated supersonic jets is characterized by the presence of strong positive pressure impulses resulting in a strongly skewed far-field pressure signal. These strong positive pressure impulses are associated with “N-shaped” waveforms involving a shock-like compression, and thus is very annoying to observers when it occurs. Unlike broadband shock-associated noise which dominates at upstream angles, crackle reaches a maximum at downstream angles associated with the peak jet noise directivity. Recent experiments [1] have shown that the addition of chevrons to the nozzle lip can significantly reduce crackle, especially in full-scale high-power tests. Because of these observations, it was conjectured that crackle is associated with coherent large scale flow structures produced by the baseline nozzle, and that the formation of these structures are interrupted by the presence of the chevrons, which leads to noise reduction. In particular, shocklets attached to large eddies are postulated as a possible aerodynamic mechanism for the formation of crackle. In this paper, we test this hypothesis through high-fidelity Large-Eddy Simulation (LES) of a hot supersonic jet of Mach number 1.56 and total temperature temperature ratio of 3.65. We use the LES solver “CharLES,” developed by Cascade Technologies, Inc., to capture the turbulent jet plume on fully-unstructured meshes.
Component Map Tuning Procedure Using Adaptive Modeling
Authors: Verbist Michel L. , Visser Wilfried P. J. , Pecnik Rene , van Buijtenen Jos P.
Published: July 2013

Performance models are effective tools for analysis of engine condition throughout the life cycle of a gas turbine engine. Component maps necessary for accurate performance modeling are typically not provided by the original equipment manufacturers. To compensate for the missing information, available maps of similar components are scaled to match component performance at one or more reference points. Although scaled maps can provide sufficiently accurate results close to the reference points, modeling errors tend to increase further away from these reference points. For applications such as gas path analysis, the resulting modeling errors can be of the same order of magnitude as the deterioration to be detected. This severely limits the application of such techniques.

This article presents a component map tuning procedure that tunes maps with more detail than just scaling. The tuned maps are a closer match to real component performance. The tuning procedure combines the adaptive modeling capability of the Gas turbine Simulation Program (GSP) and on-wing measured engine performance data. On-wing measured engine performance data allows map tuning over a wider range of power settings compared to engine performance data measured in a test cell. Effects of measurement uncertainty and scatter, and effects of compressor bleed flows on the map tuning procedure are analyzed and discussed. The tuned component maps enabled more accurate component condition estimations, mainly characterized by less scatter. By improving the accuracy of gas path analysis with on-wing measured performance data, this work has enabled more effective use of performance diagnostic techniques in the aero-engine maintenance industry.
Jet-Surface Interaction Test: Phased Array Noise Source Localization Results
Authors: Podboy Gary G.
Published: July 2013

An experiment was conducted to investigate the effect that a planar surface located near a jet flow has on the noise radiated to the far-field. Two different configurations were tested: 1) a shielding configuration in which the surface was located between the jet and the far-field microphones, and 2) a reflecting configuration in which the surface was mounted on the opposite side of the jet, and thus the jet noise was free to reflect off the surface toward the microphones. Both conventional far-field microphone and phased array noise source localization measurements were obtained. This paper discusses phased array results, while a companion paper discusses far-field results. The phased array data show that the axial distribution of noise sources in a jet can vary greatly depending on the jet operating condition and suggests that it would first be necessary to know or be able to predict this distribution in order to be able to predict the amount of noise reduction to expect from a given shielding configuration. The data obtained on both subsonic and supersonic jets show that the noise sources associated with a given frequency of noise tend to move downstream, and therefore, would become more difficult to shield, as jet Mach number increases. The noise source localization data obtained on cold, shock-containing jets suggests that the constructive interference of sound waves that produces noise at a given frequency within a broadband shock noise hump comes primarily from a small number of shocks, rather than from all the shocks at the same time. The reflecting configuration data illustrates that the law of reflection must be satisfied in order for jet noise to reflect off of a surface to an observer, and depending on the relative locations of the jet, the surface, and the observer, only some of the jet noise sources may satisfy this requirement.
Towards the Development of a Multi-Disciplinary Flight Trajectory Optimization Tool: GATAC
Authors: Gu Weiqun , Navaratne Rukshan , Quaglia Daniele , Yu Yang , Madani Irfan , Sethi Vishal , Jia Huamin , Chircop Kenneth , Sabatini Roberto , Zammit-Mangion David
Published: July 2013

Reducing the impact on the environment and the associated commercial implications are two major challenges that the global commercial aviation industry is addressing with significant commitment today. In this respect, Clean Sky, which is a €1.6 billion Joint Technology Initiative part funded by the European Commission is the largest ever programme addressing the greening of air transportation in response to the Advisory Council for Aeronautics Research in Europe (ACARE) goals of reducing CO2 and perceived noise emissions by 50% and NOx by 80% by 2020 compared to 2000 condition.

This paper presents research work carried out within the Systems for Green Operations Integrated Technology Demonstrator (ITD) of Clean Sky that is associated with GATAC, a trajectory and route planning tool to enable the multi-objective optimization of flight trajectories and missions. The design and operational methodology of the tool, the optimization algorithms and models are discussed and the results of a preliminary application for a long-range commercial flight are presented.
An Integrated Approach for Aircraft Engine Performance Estimation and Fault Diagnostics
Authors: Simon Donald L. , Armstrong Jeffrey B.
Published: July 2013

A Kalman filter-based approach for integrated on-line aircraft engine performance estimation and gas path fault diagnostics is presented. This technique is specifically designed for underdetermined estimation problems where there are more unknown system parameters representing deterioration and faults than available sensor measurements. A previously developed methodology is applied to optimally design a Kalman filter to estimate a vector of tuning parameters, appropriately sized to enable estimation. The estimated tuning parameters can then be transformed into a larger vector of health parameters representing system performance deterioration and fault effects. The results of this study show that basing fault isolation decisions solely on the estimated health parameter vector does not provide ideal results. Furthermore, expanding the number of the health parameters to address additional gas path faults causes a decrease in the estimation accuracy of those health parameters representative of turbomachinery performance deterioration. However, improved fault isolation performance is demonstrated through direct analysis of the estimated tuning parameters produced by the Kalman filter. This was found to provide equivalent or superior accuracy compared to the conventional fault isolation approach based on the analysis of sensed engine outputs, while simplifying online implementation requirements. Results from the application of these techniques to an aircraft engine simulation are presented and discussed.
Flow Control Over a Circular Cylinder Using Pulsed DBD Actuators
Authors: Schneck William C. , O’Brien Walter F.
Published: July 2013

Immersed bodies such as struts, vanes, and instrumentation probes in gas turbine flow systems will, except at the lowest of flow velocities, shed separated wakes. These wakes can have both upstream and downstream effects on the surrounding flow. In most applications, surrounding components are designed to be in the presence of a quasi-steady or at least non-variant flow field. The presence of unsteady wakes has both aerodynamic and structural consequences. Active flow control of wake generation can therefore be very valuable. One means to implement active flow control is by the use of plasma actuation. Plasma actuation is the use of strong electric fields to generate ionized gas that can be actuated and controlled using the electric fields. The controlling device can be based on AC, DC, or pulsed-DC actuation. The present research was conducted using pulsed-DC from a capacitive discharge power supply.

The study demonstrates the applicability of, specifically, pulsed-DC plasma flow control of the flow on a circular cylinder at high Reynolds numbers. The circular cylinder was selected because its flow characteristics are related to gas turbine flowpath phenomena, and are well characterized. Further, the associated pressure gradients are some of the most severe encountered in fluid applications. The development of effective plasma actuators at high Reynolds numbers under the influence of severe pressure gradients is a necessary step toward developing useful actuators for gas turbine applications beyond laboratory use.

The reported experiments were run at Reynolds numbers varying from 50,000 to 97,000, and utilizing various pulse frequencies. Further, the observed performance differences with varying electric field strengths are discussed for these Reynolds numbers. The results show that flow behaviors at high Reynolds numbers can be influenced by these types of actuators. The actuators were able to demonstrate a reduction in both wake width and momentum deficit.
Effects of Scalloping on the Mixing Mechanisms of Forced Mixers With Highly Swirling Core Flow
Authors: Wright Alex , Lei Zhijun , Mahallati Ali , Cunningham Mark , Militzer Julio
Published: July 2013

This paper presents a detailed experimental and computational investigation of the effects of scalloping on the mixing mechanisms of a scaled 12-lobe turbofan mixer. Scalloping was achieved by eliminating approximately 70% of the lobe sidewall area. Measurements were made downstream of the mixer in a co-annular wind tunnel and the simulations were carried out using an unstructured RANS solver, Numeca FINE/Hexa, with k-ω SST model. In the core flow, the swirl angle was varied from 0° to 30°. At high swirl angles, a three-dimensional separation bubble was formed on the lobe’s suction surface penetration region and resulted in the generation of a vortex at the lobe valley. The valley vortex quickly dissipated downstream. Most of the swirl was removed by the lobes, but scalloping allowed residual swirl to persist downstream of the mixer. The interaction of the swirling flow and the vortices resulted in improved mixing rates for the scalloped mixer. Inlet swirl up to 10° provided improved mixing rates, reduced pressure loss and thrust loss for both mixers. High inlet swirl resulted in improved mixing but produced higher pressure and thrust losses as compared to the zero swirl case. At high swirl, the scalloped mixer resulted in better mixing and lower pressure losses than the unscalloped mixer, but at the expense of reduced thrust.
Large Eddy Simulations of Supersonic Impinging Jets
Authors: Erwin James P. , Sinha Neeraj , Rodebaugh Gregory P.
Published: July 2013

Supersonic impinging jet flowfields contain self-sustaining acoustic feedback features that create high levels of discrete frequency tonal noise. These types of flowfields are typically found with short takeoff and landing military aircraft as well as jet blast deflector operations on aircraft carrier decks. The US Navy has a goal to reduce the noise generated by these impinging jet configurations and is investing in computational aeroacoustics to aid in the development of noise reduction concepts. In this paper, implicit Large Eddy Simulation (LES) of impinging jet flow-fields are coupled with a far-field acoustic transformation using the Ffowcs Williams and Hawkings (FW-H) equation method. The LES solves the noise generating regions of the flow in the nearfield, and the FW-H transformation is used to predict the far-field noise. The noise prediction methodology is applied to a Mach 1.5 vertically impinging jet at a stand-off distance of five nozzle throat diameters. Both the LES and FW-H acoustic predictions compare favorably with experimental measurements. Time averaged and instantaneous flowfields are shown. A calculation performed previously at a stand-off distance of four nozzle throat diameters is revisited with adjustments to the methodology including a new grid, time integrator, and longer simulation runtime. The calculation exhibited various feedback loops which were not present before and can be attributed to an explicit time marching scheme. In addition, an instability analysis of two heated jets is performed. Tonal frequencies and instability modes are identified for the sample problems.
Transient 3D Simulation of the Turbulent Gas Solid Flow in Large Scale Risers Using a Density Based Solution Algorithm
Authors: Das Asit K. , Van Engelandt Gorik , Marin Guy B. , Heynderickx Geraldine J.
Published: July 2013

Transient 3D simulation of the gas-solid flow in large diameter (> 0.3 m) risers is performed using a new density based solution algorithm. Unlike the conventional pressure based algorithm used so far for riser simulation, the density based solution method uses the pre-conditioning of time derivatives, does not have the internal pressure and velocity correction loop and hence provides a much faster convergence speed. The two phase flow is highly oscillatory with many small scale high frequency (10Hz) fluctuations and a few dominating low frequency (0.02 Hz) oscillations. The transient simulation of a case belonging to a fast fluidized regime with Geldart B particles, demonstrated the density inversion phenomena, experimentally observed before. Cluster formation is simulated on a real time scale for a dilute phase riser having solid fraction < 0.0007, although the time averaged flow fields still resemble a core-annular flow structure.
Multiphase Flow Investigation of a Centrifugal Filter Using Computational Fluid Dynamics and Experiments
Authors: Megson Steven D. , Wilson Michael , MacGregor Stuart A.
Published: July 2013

Modern “high tech” lubricant oils have been developed to contain a high level of dispersant additive to the base oil. As contaminant loading has increased, designers are required to address the problem of controlling the contamination found in the oil. One method is the use of bypass centrifugal sedimentation. This paper describes a computational study of the basic flow characteristics in a centrifugal sedimenting rotor using the computational fluid dynamics (CFD) package STAR-CD. Simplified CFD models have indicated regions of flow which would be difficult to demonstrate by experimental methods alone. For example, backflow from the outlet channel is found to cause a disruptive secondary flow in some models, but this flow is contained by the inclusion of a more realistic geometry. Two–phase flow computations have also been carried out to investigate the behaviour of spherical particulates of different sizes. Flow and geometry factors affecting the centrifuge performance are discussed.
A Comparison of Several CFD Approaches for Predicting Gas-Liquid Contacting in a Cylindrical Tank Agitated With a Single Rushton Turbine
Authors: Gillis Paul A. , Hommersom Gerrit , Scha¨fer Matthias
Published: July 2013

The expansion of physical models integrated into Computational Fluid Dynamics (CFD) codes is broadening the range of problems being addressed. Multi-phase flow modeling techniques are becoming computationally stable and industrial applications are expanding. This paper focuses on modeling gas/liquid mixing in a stirred tank. This type of multi-phase reactor is widely used in the chemical and pharmaceutical industries. The performance of these reactors can be dependent upon the interfacial surface area. The objective of this work is to evaluate the current capabilities of various multiphase models for predicting the gas/liquid contacting. Accurate predictive models facilitate the screening of unconventional gas/liquid reactor designs, where full-scale trials can be cost prohibitive. Modeling results are compared against experimental data reported in 1977 by Smith and others. These experiments demonstrated the effect of impeller speed and gassing rate on the gas-liquid mass transfer rate, kLa. A standard baffled stirred tank configuration was used (H/T = 1, single Rushton impeller, D/T = 1/3). The data was compared to predictions for three different multiphase approaches. The first model evaluated was the steady Algebraic Slip Model (ASM) implemented in Fluent 5. The second model was a steady Euler/Euler formulation using CFX4. The third approach was a transient Euler/Euler method in Fluent 4. These algorithms employ a single bubble size in the dispersed-phase momentum equations. The effect of variation of the dispersed-phase bubble diameter is shown for the shear-dependent mean-size (SDMS) and the Multiple Size Group (MUSIG) models. The interphase interaction term for all models is commonly calculated using the assumption of rigid spherical bubbles. The effect of bubble distortion is illustrated by using an empirical correlation for bubble rise velocity. Both qualitative and quantitative comparisons are made between the experimental and numerical results. The qualitative comparisons examine the various flow regimes. The quantitative evaluations involve the prediction of interfacial area, overall gas hold-up, and the ratio of gassed impeller power to ungassed impeller power. These comparisons show the bubble size modeling have a significant positive impact on the prediction of gas-liquid contacting.
Numerical Investigations of a Turbulence Mixing Process Related to Thermal Striping Phenomena at a T-Junction of Liquid Metal Fast Reactor Piping Systems
Authors: Muramatsu Toshiharu
Published: July 2013

Fluid-structure thermal interaction phenomena characterized by stationary random temperature fluctuations, namely thermal striping are observed in the downstream region of a T-junction piping system of liquid metal fast reactor (LMFR). Therefore the piping walls located in the downstream region must be protected against the stationary random thermal process which might induced high-cycle fatigue. This paper describes the evaluation system based on numerical simulation methods for the thermal striping, and numerical results of the thermal striping at a T-junction piping system under the various parameters, i.e., velocity ratio and diameter ratio between both the pipes and Reynolds number. Then detailed turbulence mixing process at the T-junction piping region due to arched vortexes generating lower frequency fluctuations are evaluated through a separate numerical analysis of a fundamental water experiment.
Large-Eddy Simulations of Flow Induced Vibrations in a Vacuum Flasher Unit
Authors: Tafti D. K. , Menon R. G.
Published: July 2013

Large-eddy simulations of flow through a vacuum flasher are conducted to study unsteady flow dynamics and resulting flow-induced vibrations. The objective of this study is to isolate energetic vibrational modes encountered in the vessel, and also study the effect of a “Vibration Reducer” (VR), which is found to be highly effective in practice. An energetic mode at 3 Hz is found to exist in tile overhead lines coming out of the dome of the flasher vessel. These simulations show that by placing the VR, a perforated pipe, in tile dome region, the amplitude of the 3 Hz mode can be reduced by a factor of 5, provided that the effective open area of the VR is optimized. In addition, by stabilizing the flow, these simulations predict that the VR also decreases the overall pressure drop by 35%.
Interactive Simulation of Gas Decompression and Crack Propagation in Natural Gas Transmission Pipelines
Authors: Makino Hiroyuki , Kawaguchi Yoshiaki , Matsumoto Yoichiro , Takagi Shu , Yoshimura Shinobu
Published: July 2013

In this paper, the propagating shear fracture in natural gas transmission pipelines is simulated by an interactive method between gas decompression and crack propagation. A rich gas which contains heavier hydrocarbons than methane is highlighted and the relation between the crack velocity and the distance is simulated for varied condition of pipelines. The results of simulation are shown in the relation between the fracture arrest distance and the toughness of the pipes used, and the effects of the difference in gas compositions, increase of the operating pressure and the change of the initial gas temperature are discussed. The results of the simulation make it clear that the rich gas increases the risk for long running fracture, the simple increase of the operating pressure by increasing the design factor causes long crack propagation, increase of the operating pressure by using higher grade pipes not always invites long crack propagation and lower temperature increases the fracture arrest distance in relatively lower pressure but decreases the distance in relatively higher pressure. All the discussion in this study indicates that the analysis of the decompression behavior of the inner gas is essential for the interpretation of the phenomenon of the propagating shear fracture in pipelines. It is concluded that the fluid characteristics of the gas transmitted and material characteristics of the pipes used should be matched appropriately for the safety of the pipelines.
Investigation of Two-Equation Turbulence Models Applied to a Confined Axis-Symmetric Swirling Flow
Authors: Engdar Ulf , Klingmann Jens
Published: July 2013

The modeling of industrial combustion applications today is almost exclusively based on two-equation turbulence models. Despite its known limitations, the most the widely used model is still the standard k-ε model. The objective of this paper is to investigate the performance of two-equation turbulence models applied to a confined swirling flow. Numerical modeling of an axis-symmetric confined sudden expansion, followed by a contraction with the assumption of steady flow and an incompressible fluid, has been conducted. The flow field is what can be expected in simplified dump gas turbine combustor geometry. In this investigation, three different swirl cases were considered: no swirl, moderate swirl (no central re-circulation zone) and strong swirl (a central re-circulation zone occurring). The models investigated were: the standard k-ε model, a curvature-modified k-ε model, Chen’s k-ε model, a cubic non-linear k-ε model, the standard k-ω model and the Shear Stress Transport (SST) k-ω) model. The results show that almost all models were able to predict the major impact of the moderate swirl: reduced outer re-circulation lengths and retardation of the axial velocity on the center-line. However, the Chen k-ε model and the SST k-ω) model were found to better reproduce the mean velocity field and the turbulent kinetic energy field from the measurements. For a strong swirl, a large re-circulation zone is formed along the center-line, which the standard k-ε model and the modified k-ε model fail to predict. However, the shape and size of the re-circulation zone differ strongly between the models. At this swirl number, the performances of all models were, without exception, worse than for the lower swirl numbers. The SST k-ω model achieved the best agreement between computations and experimental data.
The Reconstructive Method for the Enhancement of Depth Resolution for Acoustic Image Using the Spatial Frequency Response in NPPs’ Material
Authors: Koo Kil-Mo , Kim Sang-Baik , Oh Dong-In , Park Chi-Seung , Hong Soon-Sin , Kim Sun-Jin
Published: July 2013

In this paper, we have studied the images which have been reconstructed by using combination of images acquired by the variation of operating frequency. When inner images have been reconstructed, they have been superposed by the surface state effect. In this case, the images of the phase object can be enhanced by the contrast of inner images. In this experiment, there are two kinds of specimens, one is a reference block having 1/4T, 1/2T, 3/4T side drilled holes as main run piping material of the steam generator in NPP’s and the another is a part of a hemisphere type specimen having about 1–2mm distance gap. It has been shown that the two results of defect shapes have better than before in this processing and phase contrast grow about twice. And we have constructed the acoustic microscope by using a quadrature detector that enables to acquire the amplitude and phase of the reflected signal simultaneously. Further more we have studied the reconstruction method of the amplitude and phase images and the enhancement method of the defect images contrast.
CFD Application to Construction of Hazard Maps of Volcanic Eruptions
Authors: Saito T. , Yamashita H. , Takayama K.
Published: July 2013

Shock wave propagation due to explosive-type volcano eruptions are numerically simulated in order to produce hazard maps. Different types of damages caused by pyroclastic-surge and ballistic fragments as well as positive and negative pressure loading are related to the maximum overpressure of the blast waves. Hazard maps produced by the present method is useful for establishing better safety countermeasures for volcanic eruptions. Simulations of blast wave propagation take the complex terrain of the interested area into account. Several eruption models for the energy release such as the reservoir-break model and the jet models are considered and discussed. The three-dimensional numerical code employs the finite volume method with WAF scheme for evaluating the numerical fluxes at the cell interface. The WAF scheme is one of the high-order Godunov schemes and HLLC approximate Riemann solution is used in the present work.
An Assessment of PDP Installed with Various Ribbed Heat Spreader for Cooling Enhancement
Authors: Kim Jaejung , Roh Hongkoo , Doh Deoghee , Chang Seogweon
Published: July 2013

An numerical investigation on the cooling of PDP (Plasma Display Panel) was performed in this study. Four shapes of the heat spreader, as the cooling enhancement devices in PDP, were tested: Flat shape, I-shaped rib, V-shaped rib, and Z-shaped rib. The heat spreader of flat shape was simple aluminum flat plate and three heat spreaders of I-shaped rib, V-shaped rib, and Z-shaped rib had a lot of ribs which were ribbed on an aluminum flat plate to increase the surface area and to interrupt the growth of the boundary layer. The results of three ribbed shapes were compared to those of the flat shape in this study. Cooling performance have evaluated with temperature uniformity and dimensionless temperature difference between surface temperature of heat spreader and ambient temperature. Additionally an PIV (Particle Image Velocimetry) experiment was made and some related results have been presented. As a final result, it has been found that the heat spreader of V-shaped rib had the best performance among the three ribbed shapes.
Flow Separation and Heat Transfer in Shear Flow Around a Wall-Mounted Obstacle
Authors: Mahapatra S. , Bhattacharyya S.
Published: July 2013

Flow structure and surface heat transfer around a single small obstacle of rectangular cross-section mounted on a smooth plane surface are investigated. The obstacle is considered to be submerged in the viscous layer so that the far field flow may be viewed as uniform shear. The obstacle is considered to be at a temperature higher than that of the surrounding fluid and the flat surface is insulated. The unsteady Navier-Stokes equations and heat transport equation are solved numerically through a finite volume method on a staggered grid system. Solutions are obtained over a range of Reynolds number Re, which is based on the obstacle height and the incident uniform shear and Grashof number Gr. An investigation of the influence of buoyancy on the upstream and downstream flow separation from the obstacle and the interaction of the separation with the thermal field is also made. Numerical results reveal that in absence of the buoyancy force, the recirculating eddy upstream of the obstacle elongates with increasing Re. It is found that the buoyancy effect reduces the size of the upstream eddy when Re ≤ 200 with Gr (which is a measure of buoyancy) equal to 100. At an increased value of buoyancy force, Gr = 104, the upstream separation zone shifts further close to the obstacle. It is also found that the downstream separation length (which increases with increasing Re) further increases with increasing Gr as long as Re ≤ 200. Buoyancy effects on the flow are not prominent when Re is above 200. The surface heat transfer is quite high at the protruding corners and it increases with increase in Re. Increase of Grashof number produces an increment on surface heat transfer.
Bone Properties Surrounding Hydroxyapatite-Coated Custom Osseous Integrated Dental Implants
Authors: Baker Maribel I. , Lemons Jack E. , Eberhardt Alan W.
Published: July 2013

Dental implants are widely used for replacement of teeth and correction of defects in maxillary and mandibular bone. Their effectiveness is largely dependent upon biostability and osteointegration between the bone and implant. One of the major causes of dental implant failure is aseptic loosening or resorption of bone at the interface [2]. In order to diminish such failures, coatings and surface roughening are used to enhance osteointegration and biostability between the bone and the implant [3].
Experimental and Computational Study of the Mechanics of Brain Folding
Authors: Xu Gang , Bayly Philip V. , Taber Larry A.
Published: July 2013

The human brain cortex undergoes substantial folding during development. Folding is essential to accommodate the expansion of the cortex in the skull. Abnormal cortical folding is associated with various genetic perturbations and neurological disorders.
Correlation of Biomechanics to Tissue Reaction in Aortic Aneurysm Assessed by Computational Finite Element Analysis and FDG-PET-CT
Authors: Reeps Christian , Gee Michael W. , Wall Wolfgang A. , Eckstein Hanns-Henning
Published: July 2013

The widely accepted hypothesis that mechanobiological transduction plays a central role in pathogenesis of abdominal aortic aneurysm (AAA) is plausible, but so far was never directly proven in vivo for methodical reasons. At present, stresses and strains acting in AAA wall can be assessed by computational finite element analyses (FEA) [1,2,3]. Independently, it has also been reported that glycolytic activity in AAA wall non-invasively assessed by [18F]flourodeoxyglucose positron emission tomography/CT (FDG-PET/CT) is associated with increased proteolytic activity, structure-protein-degradation, AAA progression and consequently AAA wall instability as well as rupture risk [4]. Both methods were studied by our research group in an individual AAA patient [5]. Here, the correlation of computational biomechanics with metabolic activity assessed by FDG-PET/CT is analyzed in a larger patient cohort (n=18) [8].
Using MicroCT Imaging to Quantify Heat Generation Distribution Induced by Magnetic Nanoparticles
Authors: Attaluri Anilchandra , Ma Ronghui , Zhu Liang
Published: July 2013

In the past decade, there have been renewed interests in using magnetic nanoparticles as heating agents when subjected to an alternating magnetic field in cancer treatments. Due to the technical advancement in manufacturing nano-sized magnetic particles, nanoparticle hyperthermia has emerged as an attractive alternative to costly and risky surgical procedures because of its few associated complications and targeted delivery of thermal energy to the tumor.
Finite Element Analysis of the Ulnar Tunnel in Ulnar Collateral Ligament Reconstruction
Authors: Cook Harold A. , Akhavan Sam , DeMeo Patrick J. , Miller Mark Carl
Published: July 2013

The ulnar collateral ligament (UCL) of the elbow originates on the medial epicondyle of the humerus and inserts on the sublime tubercle of the proximal ulna. This ligament is classically composed of three distinct structures: the anterior bundle, the posterior bundle, and the transverse bundle. Of these three, the anterior bundle has been shown to be the primary stabilizer to valgus load between 20° and 120° of flexion [1]. Injuries to the anterior bundle of the UCL are commonly seen in baseball pitchers, where the valgus load on the elbow during the throwing motion approaches the failure load of the ligament [2].
Design Optimization of a Polycarbonate-Urethane Meniscal Implant in the Sheep Knee: In-Vitro Study
Authors: Elsner Jonathan J. , Zur Gal , Guilak Farshid , Linder-Ganz Eran , Shterling Avi
Published: July 2013

Meniscus replacement still represents an unsolved problem in orthopedics. Allograft meniscus implantation has been suggested as a means to restore contact pressures following meniscectomy. However, issues such as graft availability, disease transmission, and size matching still limit the use of allograft menisci. Furthermore, the complexities of meniscal repairs may contribute to uneven distribution of load, instability and initiation of degenerative damage. A synthetic meniscal substitute could have significant advantages for meniscal replacement, as it could be available at the time of surgery in a substantial number of sizes and shapes to accommodate most patients. There is, however, a need to establish an optimal configuration of such an implant that would result in pressure distribution ability closest to that of the natural meniscus.
Chondroprotective Effects of a Polycarbonate-Urethane Meniscal Implant: Semi-Quantitative Results in a Sheep Model
Authors: Linder-Ganz Eran , Elsner Jonathan J. , Zur Gal , Shani Jonathan , Brenner Ori , Hershman Elliott , Shterling Avi , Guilak Farshid
Published: July 2013

The menisci play a critical role in load-bearing and stability of the knee joint [1]. Damage or removal of the meniscus leads to alterations in the magnitude and distribution of stresses in the knee, which have been associated with degenerative osteoarthritis [2]. Clearly, there remains a need to develop means of protecting the articular cartilage following meniscal injury by either repairing or replacing the menisci. While allograft meniscal replacements can improve joint stability and function, they often provide little benefit in preventing osteoarthritic changes [3]. The development of an artificial meniscus that is available at the time of surgery in several sizes that can accommodate most patients would provide important therapeutic potential for treatment meniscal injury.
Structural 3-D Constitutive Model for the Passive Arterial Media and Its Experimental Validation
Authors: Hollander Yaniv , Durban David , Lu Xiao , Kassab Ghassan S. , Lanir Yoram
Published: July 2013

The mechanical properties of arteries are of essential importance in hemodynamics and blood wave propagation along the arterial tree. They play a pivotal role in determining the local state of micro-stress imposed on the vessel cells and the cells’ consequent biological reaction. The wall is mechanically nonlinear, anisotropic and heterogeneous, and subjected in the unloaded state to residual stress and strain. Reliable model prediction of arterial response under physiological loads and pathological conditions could help clarify their function, and shed light on the processes leading to initiation and progression of diseases and their clinical treatment.
Quasi-Linear Viscoelastic Theory is Insufficient to Comprehensively Describe the Time-Dependent Behavior of Human Cervical Spine Ligaments
Authors: Troyer Kevin L. , Puttlitz Christian M.
Published: July 2013

Stress relaxation experiments were conducted on cervical spine ligaments at multiple strain magnitudes to determine the validity and applicability of the quasi-linear viscoelastic (QLV) theory to model their dynamic behavior. The results indicate that the shape of the stress relaxation curve is dependent upon the magnitude of the applied strain. Thus, a more general, nonlinear formulation is required to model these ligaments within the physiological strain range.
Dehydration and Rehydration Alter Elastic and Viscoelastic Nanomechanical Properties of Cortical and Trabecular Bone
Authors: Ferreri Suzanne , Hu Bing , Qin Yi-Xian
Published: July 2013

Evaluation of bone’s response to mechanical loading is of critical importance in studies addressing the overall efficacy of therapeutic interventions. Moreover, thorough characterization of bone’s response to applied loads should reflect the contributions of both bone mineral (elastic properties) and collagen (viscoelastic properties).
The Inertia of the Anterior Leaflet of the Heart’s Mitral Valve
Authors: Kendoush Abdullah A. , Padala Muralidhar , Icenogle David , Yoganathan Ajit P.
Published: July 2013

Virtual mass effects generate forces that act on any object accelerating in a fluid medium. While there have been computational models of bileaflet mechanical valves that include virtual mass effects [1], current computational models of fluid structure interaction of native mitral valves do not consider virtual mass effects, resulting in an incomplete measure of the forces acting on the valve. As far as the authors aware no closed-form relationship for the virtual mass coefficient, Cm, of the native mitral valve has been determined. Integrating the effects of virtual mass into computational models of the mitral valve would result in a more complete model, and could yield more accurate and relevant results from computational models of the mitral valve.
A Novel Approach to Quantify Alterations in Ventricular Principal Strain Vectors Secondary to Ischemic Injury
Authors: Xu Chun , Koomalsingh Kevin , Isaac Gamaliel , Gorman Robert C. , Gorman Joseph H. , Dougherty Lawrence , Pilla James J.
Published: July 2013

Accurate assessment of regional and global left ventricular (LV) function is critical for understanding ischemic heart disease. The orientation and the magnitude of the myocardial principal strains have been shown to be sensitive to ischemic development [1]. Combing MR tagging, cardiac mechanics, and computer visualization, this study presents a novel method to fully characterize the alterations in the magnitude and orientations of principal strains in the LV post-infarct.
Importance of Pre-Operative Hemodynamics in the Surgical Planning of Complex Single Ventricle Patients
Authors: Haggerty Christopher M. , de Zélicourt Diane A. , Sundareswaran Kartik S. , Fogel Mark A. , Yoganathan Ajit P.
Published: July 2013

Unbalanced distribution of hepatic blood flow to the lungs in single ventricle patients can result in the formation of harmful arterial-venous shunts. Careful planning of the hepatic baffle placement to optimize its distribution can help to minimize this risk. The combination of in vivo imaging, a computational fluids solver, and a state-of-the-art virtual surgery interface have successfully been demonstrated to assist in this planning step. In the present study, we analyze the effect of the patient-derived flow boundary conditions on the optimal solutions obtained from the simulations for a particular set of complex cases with interrupted inferior vena cava. By considering two patients with similar anatomical configurations but drastically different hemodynamics, we see that differences in the percentage of cardiac output carried by each of the inflow vessels can drastically alter the optimal surgical approach.
Elastic Network Modeling of Actin Filaments
Authors: Bidone Tamara C. , Deriu Marco A. , Mastrangelo Francesco , Di Benedetto Giacomo , Soncini Monica , Morbiducci Umberto
Published: July 2013

Cell mechanics depends on the mechanical properties of actin microfilaments (MFs), microtubules (MTs) and intermediate filaments (IFs), that build the cytoskeleton. Actin microfilaments are the most abundant components and play significant roles in various cellular processes [1]. Among them, the mechanical properties of MFs are essential for the functions of the cytoskeleton and are directly related to their molecular architecture.
Propagation of an Air Finger Into a Fluid Filled Bifurcation
Authors: Vaughan Benjamin L. , Grotberg James B.
Published: July 2013

The occlusion of pulmonary airways can be caused by many respiratory diseases such as respiratory distress syndrome. It is believed that these occluded airways are reopened by the propagation of an air finger. The mechanics of airway reopening have been studied in-depth for an individual airway [1,2] without considering the frequent branching of pulmonary airways. The presence of a bifurcation leads to the question of whether the propagating air finger will clear both branches of the airway or will propagate through a single branch, leaving the other branch occluded. The propagation of a finite length liquid plug through a fixed bifurcation has been studied experimentally [3, 4]. We wish to develop a numerical model for the propagation of an air finger through bifurcating channel filled with a viscous fluid. In this model, the air finger is driven by a pressure difference between the parent channel and the two daughter branches. The presence of an additional pressure difference between the two branches can cause unsymmetrical splitting of the air finger and, above a critical pressure difference, prevent the clearance of both branches.
Three Dimensional Fluoroscan is More Accurate and Repeatable Than Two Dimensional Fluoroscan for Measuring Central Scaphoid Screw Placement in a Cadaver Model
Authors: Han Hyun Kyu , Green W. Scott , Buckley Jenni M. , Lattanza Lisa L.
Published: July 2013

A commonly accepted treatment method for scaphoid fractures is dorsal percutaneous fixation [1, 2]. This has been shown to decrease the need for cast immobilization and allow faster recovery [3, 4]. For this approach a central screw placement is critical as it provides greater stiffness and load to failure, and allows a longer screw to be inserted which increases screw compression. All of these factors aid in fracture union [5]. However, the complex shape of the scaphoid bone makes central screw placement difficult, as the main axis cannot be easily visualized. Currently, scaphoid screws are placed using K wires guided under 2D fluoroscopy; however, intra-operative 3D fluoroscopy, which can create a CT reconstruction, is becoming more readily available. The goals of this study are to see if there is a significant difference between 2D and 3D fluoroscopic imaging in measuring screw malpositioning (distance off-center) and if there is a difference in repeatability.