bluuebunny/crossref_metadata_2025 huggingface dataset:
High cystatin C levels predict undesirable outcome for diabetic foot ulcerations
Authors: Ai Ligen , Hu Yanyun , Zhang Xiaoyan , Zeng Hui , Zhao Jun , Zhao Jungong , Chai Yimin , Lu Junxi , Tang Junling , Bao Yuqian , Liu Fang , Jia Weiping
Published: February 2016

We investigated the relationship between serum cystatin C levels and the prognosis of diabetic foot ulcerations (DFU). A population‐based cohort study involving 1018 patients with type 2 diabetes was conducted. These patients recruited and divided into two groups: nondiabetic foot ulcer group (NDF, n = 865, 85.5%) and diabetic foot ulcer group (DFU, n = 147, 14.5%).After a 1‐year‐follow‐up, DFUs were grouped into healing (n = 110, 74.8%) and nonhealing (n = 37, 25.2%) group based on the clinical prognosis. Compared with the healing group, the nonhealing group were older, had long diabetic duration and had significantly increased serum cystatin C concentrations in DFU (p < 0.01). After adjustments for age, diabetes duration, renal function and infection control, multiple logistical regression analysis revealed that cystatin C remained associated increased risk of undesirable DFU outcome (OR = 7.279, 95% CI: 1.299–40.784, p < 0.05). When divided into quartiles according to cystatin C levels, the healing rate of Quartile 4 was significantly lower (57.9%) compared with other groups (p < 0.01). The odd is ratio (OR) analysis showed that the risk of undesirable DFU outcome in Quartile 4 was significantly higher (OR = 4.554, 95% CI: 3.14–5.12, p < 0.05) compared with that in Quartile 1. We concluded that there was a strong and independent association between serum cystatin C and diabetic foot ulceration prognosis, cystatin C > 1.35 mg/L predicts more than sixfold increased risk of incurable foot ulceration.
The use of brief post‐surgical low frequency electrical stimulation to enhance nerve regeneration in clinical practice
Authors: Chan K. M. , Curran M. W. T. , Gordon T.
Published: February 2016

Despite efforts to enhance peripheral nerve regeneration, there has been little progress in improving clinical outcomes. Recently, a method of brief post‐surgical low frequency electrical stimulation of surgically repaired nerves has been developed. It was shown to accelerate axon outgrowth across the repair site and it hastened target reinnervation. In this brief review, we describe the mechanistic insights and functional impacts of the post‐surgical electrical stimulation that have been gained through animal studies. Brain‐derived neurotrophic factor, cyclic AMP and regeneration‐associated genes play a vital role in expediting the outgrowth of axons across the injury site. The method of stimulation has also been shown to be effective in patients with severe compressive neuropathy as well as those with digital nerve laceration. Its clinical feasibility and positive impact open the door of further clinical translation in other peripheral nerve injuries.

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Defining a stem cell hierarchy in the intestine: markers, caveats and controversies
Authors: Smith Nicholas R. , Gallagher Alexandra C. , Wong Melissa H.
Published: February 2016

The past decade has appreciated rapid advance in identifying the once elusive intestinal stem cell (ISC) populations that fuel the continual renewal of the epithelial layer. This advance was largely driven by identification of novel stem cell marker genes, revealing the existence of quiescent, slowly‐ and active‐cycling ISC populations. However, a critical barrier for translating this knowledge to human health and disease remains elucidating the functional interplay between diverse stem cell populations. Currently, the precise hierarchical and regulatory relationships between these ISC populations are under intense scrutiny. The classical theory of a linear hierarchy, where quiescent and slowly‐cycling stem cells self‐renew but replenish an active‐cycling population, is well established in other rapidly renewing tissues such as the haematopoietic system. Efforts to definitively establish a similar stem cell hierarchy within the intestinal epithelium have yielded conflicting results, been difficult to interpret, and suggest non‐conventional alternatives to a linear hierarchy. While these new and potentially paradigm‐shifting discoveries are intriguing, the field will require development of a number of critical tools, including highly specific stem cell marker genes along with more rigorous experimental methodologies, to delineate the complex cellular relationships within this dynamic organ system.

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European Project “Supercritical Water Reactor–Fuel Qualification Test”: Results of Fuel Pin Mock-up Tests
Authors: Novotný Radek , Visser Dirk , Timke Theo , Vojáček Aleš , Frýbort Otakar , Siegl Jan , Haušild Petr , Macák Jan
Published: February 2016

The main target of the EURATOM FP7 project “fuel qualification test for supercritical water-cooled reactor” was to make significant progress toward the design, analysis, and licensing of a fuel assembly cooled with supercritical water (SCW) in a research reactor. Within the project, fuel pin mock-ups of a future fuel qualification test facility were designed and manufactured by Centrum Výzkumu Řež (CVR). Following that, it was decided to conduct three different types of tests considering two possible accident scenarios. Simulation of loss of external pressure was the target of Test 1. The autoclave was depressurized as fast as possible from 20 to 1 MPa by opening the close valve located behind the cooling part of the high-pressure part of the loop. Pressure inside the pin was held at a constant value of 20 MPa by pumping high-pressure water via the pin and in parallel via a separate relief valve that was connected directly to the pin using the filling pressure tube. A similar approach was chosen when the opposite case, i.e., loss of internal pressure in the pin, was simulated in Test 2A. Eventually, Test 2A was repeated with modified setup to determine the lower limit of the internal pin pressure (i.e., collapse/buckling of the pin due to external overpressure) more accurately. The presented paper summarizes the results of all three performed tests.
Robust Estimation of Balanced Simplicity-Accuracy Neural Networks-Based Models
Authors: Romero Ugalde Hector M. , Corbier Christophe
Published: February 2016

Neural networks are powerful tools for black box system identification. However, their main drawback is the large number of parameters usually required to deal with complex systems. Classically, the model's parameters minimize a L2-norm-based criterion. However, when using strongly corrupted data, namely, outliers, the L2-norm-based estimation algorithms become ineffective. In order to deal with outliers and the model's complexity, the main contribution of this paper is to propose a robust system identification methodology providing neuromodels with a convenient balance between simplicity and accuracy. The estimation robustness is ensured by means of the Huberian function. Simplicity and accuracy are achieved by a dedicated neural network design based on a recurrent three-layer architecture and an efficient model order reduction procedure proposed in a previous work (Romero-Ugalde et al., 2013, “Neural Network Design and Model Reduction Approach for Black Box Nonlinear System Identification With Reduced Number of Parameters,” Neurocomputing, 101, pp. 170–180). Validation is done using real data, measured on a piezoelectric actuator, containing strong natural outliers in the output data due to its microdisplacements. Comparisons with others black box system identification methods, including a previous work (Corbier and Carmona, 2015, “Extension of the Tuning Constant in the Huber's Function for Robust Modeling of Piezoelectric Systems,” Int. J. Adapt. Control Signal Process., 29(8), pp. 1008–1023) where a pseudolinear model was used to identify the same piezoelectric system, show the relevance of the proposed robust estimation method leading balanced simplicity-accuracy neuromodels.
Numerical Analysis of Dental Caries Effect on the Biomechanical Behavior of the Periodontal System
Authors: Merdji Ali , Della Noureddine , Benaissa Ali , Bouiadjra Bel-Abbes Bachir , Serier Boualem , Mootanah Rajshree , Muslih Iyad , Mukdadi Osama M.
Published: February 2016

The aim of this study was to investigate the effect of dental caries on the stability of the periodontal system. This study presents a numerical analysis performed with three-dimensional (3D) finite element (FE) method to evaluate stresses in the bone surrounding the tooth with dynamic mastication combined loadings. In this work, we present a comparative study on infected and healthy periodontal systems. The infected tooth was modeled and a caries defect was introduced to the tooth coronal part. The infected tooth was evaluated and equivalent von Mises interface stress values were obtained for comparison with the ones exhibited by the healthy tooth. Our results by 3D FE analysis indicated that maximum stresses occurred primarily at the cervical level of root and alveolar bone. In the cortical bone, the stress value was greater in infected system (21.641 MPa) than in healthy system (15.752 MPa), i.e., a 37.4% increase. However, in the trabecular bone we observed only 1.6% increase in the equivalent stress values for the infected tooth model. Stress concentration at the cervical level may cause abnormal bone remodeling or bone loss, resulting loss of tooth attachment or bone damage. Our findings showed that decayed single-rooted teeth are more vulnerable to apical root resorption than healthy teeth. The numerical method presented in this study not only can aid the elucidation of the biomechanics of teeth infected by caries but also can be implemented to investigate the effectiveness of new advanced restorative materials and protocols.
A Numerical Method for Solving Fractional Optimal Control Problems Using Ritz Method
Authors: Nemati Ali , Yousefi Sohrab Ali
Published: February 2016

Our paper presents a new method to solve a class of fractional optimal control problems (FOCPs) based on the numerical polynomial approximation. In the proposed method, the fractional derivative in the dynamical system is considered in the Caputo sense. The approach used here is to approximate the state function by the Legendre orthonormal basis by using the Ritz method. Next, we apply a new constructed operational matrix to approximate fractional derivative of the basis. After transforming the problem into a system of algebraic equations, the problem is solved via the Newton's iterative method. Finally, the convergence of the new method is investigated and some examples are included to illustrate the effectiveness and applicability of the proposed methodology.
Initial Conditions and Initialization of Fractional Systems
Authors: Tari Massinissa , Maamri Nezha , Trigeassou Jean-Claude
Published: February 2016

In this paper, the initialization of fractional order systems is analyzed. The objective is to prove that the usual pseudostate variable x(t) is unable to predict the future behavior of the system, whereas the infinite dimensional variable z(ω, t) fulfills the requirements of a true state variable. Two fractional systems, a fractional integrator and a one-derivative fractional system, are analyzed with the help of elementary tests and numerical simulations. It is proved that the dynamic behaviors of these two fractional systems differ completely from that of their integer order counterparts. More specifically, initialization of these systems requires knowledge of z(ω,t0) initial condition.
Haptic Assembly Using Skeletal Densities and Fourier Transforms1
Authors: Behandish Morad , Ilieş Horea T.
Published: February 2016

Haptic-assisted virtual assembly and prototyping has seen significant attention over the past two decades. However, in spite of the appealing prospects, its adoption has been slower than expected. We identify the main roadblocks as the inherent geometric complexities faced when assembling objects of arbitrary shape, and the computation time limitation imposed by the notorious 1 kHz haptic refresh rate. We addressed the first problem in a recent work by introducing a generic energy model for geometric guidance and constraints between features of arbitrary shape. In the present work, we address the second challenge by leveraging Fourier transforms to compute the constraint forces and torques. Our new concept of “geometric energy” field is computed automatically from a cross-correlation of “skeletal densities” in the frequency domain, and serves as a generalization of the manually specified virtual fixtures or heuristically identified mating constraints proposed in the literature. The formulation of the energy field as a convolution enables efficient computation using fast Fourier transforms (FFTs) on the graphics processing unit (GPU). We show that our method is effective for low-clearance assembly of objects of arbitrary geometric and syntactic complexity.
Testing the Digital Thread in Support of Model-Based Manufacturing and Inspection
Authors: Hedberg Thomas , Lubell Joshua , Fischer Lyle , Maggiano Larry , Barnard Feeney Allison
Published: February 2016

A number of manufacturing companies have reported anecdotal evidence describing the benefits of model-based enterprise (MBE). Based on this evidence, major players in industry have embraced a vision to deploy MBE. In our view, the best chance of realizing this vision is the creation of a single “digital thread.” Under MBE, there exists a model-based definition (MBD), created by the Engineering function, which downstream functions reuse to complete model-based manufacturing and model-based inspection activities. The ensemble of data that enables the combination of MBD, manufacturing, and inspection defines this digital thread. Such a digital thread would enable real-time design and analysis, collaborative process-flow development, automated artifact creation, and full-process traceability in a seamless real-time collaborative development among project participants. This paper documents the strengths and weaknesses in the current, industry strategies for implementing MBE. It also identifies gaps in the transition and/or exchange of data between various manufacturing processes. Finally, this paper presents measured results from a study of model-based processes compared to drawing-based processes and provides evidence to support the anecdotal evidence and vision made by industry.
A New Compact Stair-Cleaning Robot
Authors: Zhang Lei , Yang Yuan , Gu Yugang , Sun Xiaogang , Yao Xingtian , Shuai Liguo
Published: February 2016

Various stair-climbing or cleaning mechanisms have been proposed or developed in the past decades. Most of them are big-sized, complex, and/or expensive, which hinder their practical application. In this study, a new stair-cleaning robot is proposed and developed. In the new robot, a pair of legs is used for stair climbing. Rotating around the main body, the legs of the robot drive the feet to execute revolving but translational motions, thereby allowing the robot to climb. The new robot is highly compact compared with most traditional stair-cleaning or climbing robots, because only one motor is utilized to drive the climbing mechanism and the legs can be retracted at both sides of the robot when it is not climbing. Its compact structure enables the new robot to move along the riser to do cleaning on the stairs, which is a prominent advantage over most similar robots. The cleaning device is designed similar to that of current ground cleaning robots. The sensing and control system is designed for successful stair climbing and avoidance of falls and collisions. Experiments show that the new robot has high success rates in climbing up or down common types of stairs, and thus can do cleaning on the related stairs.
A Unified Formulation for Dimensional Synthesis of Stephenson Linkages
Authors: Bai Shaoping , Wang Delun , Dong Huimin
Published: February 2016

The unified formulation of dimensional synthesis of Stephenson linkages for motion generation is the subject of this paper. Burmester theory is applied to the six-bar linkage, which leads to a unified formulation applicable for all three types of Stephenson linkages. This is made possible by virtue of parameterized position vectors, which simplify the formulation of synthesis equations. A design example is included to demonstrate the application of the method developed.
Risk-Based Cost-Effectiveness Analysis of Waste Handling Practices in the Arctic Drilling Operation
Authors: Ayele Y. Z. , Barabadi A. , Droguett E. L.
Published: February 2016

As oil and gas companies in the Arctic attempt to maximize the value of each project and optimize their portfolio of investment opportunities, it has become vital to evaluate drilling waste handling practices for their cost-effectiveness in order to support strategic decisions. Identifying cost-effective waste handling practices, which have a minimal environmental footprint, however, is one of the biggest challenges for Arctic offshore industries. The cost and potential risks of drilling waste handling practices in the Arctic offshore operation will differ vastly, depending on the operating environment such as the ice conditions and negative sea temperature. However, in the majority of the available cost-effectiveness and risk analysis literature, the influence of the operating environment on the cost and risk profile has received less attention. Hence, the aim of this paper is to propose a methodology for risk-based cost-effectiveness analysis (RB–CEA) of drilling waste handling practices by considering the complex and fast-changing nature of the Arctic. The central thrust of this paper is to highlight the fact that comparing different alternatives based on the cost elements alone is misleading. The proposed methodology uses risk assessment as a key component for the cost-effectiveness analysis (CEA). The application of the proposed methodology is demonstrated by a case study of the drilling waste handling practices of an oil field in the Barents Sea. The case study results demonstrate that the operating environment causes costs to be between 1.18 and 1.52 times greater, depending on the type of practices and operating season, in the Arctic offshore compared with the North Sea. Further, the risk of undesirable events is between 1.48 and 2.60 times greater during waste handling activities under Arctic operational conditions.
An Approach to Heat Transfer Analysis of Wire Loops Over the Stelmor Conveyor to Predict the Microstructural and Mechanical Attributes of Steel Rods
Authors: Jain Ishant , Lenka Shaumik , Ajmani Satish Kumar , Kundu Saurabh
Published: February 2016

To understand and predict the microstructure evolution in various grades of steel, a heat transfer coupled with phase transformation model has been formulated with an enhanced stelmor cooling module. This module is capable of handling both blower assisted high cooling and retarded cooling using hoods. The stelmor module incorporates the change in ring spacing of the wire loops on the stelmor due to a change in mill speed and conveyor speed of the wire rod mill. A geometrical approach to convective and radiative losses taking into account the void fraction and shape factor of wire loop is reported. This makes the model robust by strengthening the heat transfer formulation. This paper deals with the correlation of wire rod mill process parameters on the cooling curve of wire rods. The cooling of wire rods is dependent on the stelmor operating parameters. Commercial high carbon grades require high capacity blowers for efficient cooling to refine the pearlite microstructure and impart greater strength. Welding grade wire rods (low carbon grades) on the other hand require retarded cooling to increase the ferrite grain size and decrease the ultimate tensile strength.
Studies on Characteristic Frequency and Length Scale of Shock Induced Motion in Transonic Diffuser Using a High Order LES Approach
Authors: Biswas Debasish , Jimbo Tomohiko
Published: February 2016

Unsteady transonic flows in diffuser have become increasingly important, because of its application in new propulsion systems. In the development of supersonic inlet, air breathing propulsion systems of aircraft and missiles, detail investigations of these types of flow behavior are very much essential. In these propulsion systems, naturally present self-sustaining oscillations, believed to be equivalent to dynamically distorted flow fields in operational inlets, were found under all operating conditions. The investigations are also relevant to pressure oscillations known to occur in ramjet inlets in response to combustor instabilities. The unsteady aspects of these flows are important because the appearance of undesirable fluctuations generally impose limitation on the inlet performance. Test results of ramjet propulsion systems have shown undesirable high amplitude pressure fluctuations caused by the combustion instability. The pressure fluctuations originated from the combustor extend forward into the inlet and interact with the diffuser flow-field. Depending on different parameters such as the diffuser geometry, the inlet/exit pressure ratio, the flow Mach number, different complicated phenomena may occur. The most important characteristics are the occurrence of shock induced separation, the length of separation region downstream of the shock location, and the oscillation of shock location as well as the oscillation of the whole downstream flow. Sajben experimentally investigated in detail the time mean and unsteady flow characteristics of supercritical transonic diffuser as a function of flow Mach number upstream the shock location and diffuser length. The flows exhibited features similar to those in supersonic inlets of air-breathing propulsion systems of aircraft. A High-order LES turbulence model developed by the author is assessed with experimental data of Sajben on the self-excited shock oscillation phenomena. The whole diffuser model configuration including the suction slot located at certain axial location around the bottom and side walls to remove boundary layer, are included in the present computation model. The time-mean and unsteady flow characteristics in this transonic diffuser as a function of flow Mach number and diffuser length are investigated in detail. The results of study showed that in the case of shock-induced separation flow, the length and thickness of the reverse flow region of the separation-bubble change, as the shock passed through its cycle. The instabilities in the separated layer, the shock /boundary layer interaction, the dynamics of entrainment in the separation bubble, and the interaction of the travelling pressure wave with the pressure fluctuation region caused by the step-like structure of the suction slot play very important role in the shock-oscillation frequency.
Comparison of Unsteady Heat Release Rate by Measurements From Chemiluminescence and Two Microphone Techniques
Authors: Verma Rajbir , Mariappan Sathesh
Published: February 2016

In the reaction zone of flame, electronically excited species are formed such as CH*, OH* etc. During de-excitation these radicals emit electromagnetic radiation of certain wavelength. This process is called chemiluminescence. The intensity of chemiluminescence, is in general captured using a photo multiplier tube (PMT), which is used to measure unsteady heat release rate from premixed flames. This technique is well established and is now a standard for unsteady heat release rate measurements in the parlance of combustion instability, however has certain limitations. In fuel rich mixtures, unreacted heated carbon emits broad band black body radiation, which in some cases large enough to mask the chemiluminescence signal. Hence, this technique is not valid for fuel rich conditions. Moreover, it cannot be applied, when the heat source is diffusion/partially premixed flames or electrically heated wires. We propose an alternative in this regard: two microphone technique. In this technique, we relate the acoustic velocity jump across the heat source to measure the unsteady heat release rate. The up and downstream acoustic velocity, in turn is obtained by two microphone technique. Experiments are performed in a premixed multiple flame burner at fuel lean conditions. This burner is enclosed in a duct, which acts as an acoustic resonator. Results indicate that the magnitude of the unsteady heat release rate obtained from both the techniques is found to agree within 18 %. Experiments are conducted for various lengths of the duct, thereby changing the oscillating frequency. This method is valid as long as the heat source is compact in comparison to the duct, which is true in most of the combustors during combustion instability and is irrespective of its type.
Minimum Weight Design of Aero Engine Turbine Disks
Authors: Kasina Lakshman , Kotur Raghavan , Gnanasundaram Govindaraji
Published: February 2016

The aero engine rotating parts are always fracture critical components and their failure in service affects the aircraft safety. Rotors / disks will burst at a certain speed if they operate at ever-increasing speed. Rotor burst is one of important failure mode in aero engine and resulting in disk disintegration into multiple fragments with high speed resulting in containment breach. Disks are subjected to fatigue loading and it limits the service life. Fatigue loading on disk includes high temperature environment, tremendous centrifugal and aerodynamic forces caused by blades.

The main aspect of turbine disk design is to safe guard against LCF failure. Design of disk should ensure that stresses due to thermal, centrifugal and aerodynamics loads during operating conditions should be within the limits. Turbine disks are also designed to operate at speed above 20% of maximum operating speed for maximum power and referred as over speed capability or burst margin. This over speed capability may require for the aircraft during emergency conditions.

The objective of this study is to design a turbine disk for minimum weight. A numerical investigation is performed to predict stresses and burst margins of turbine disk. A parametric disk model is developed with bore width, bore height, web width and web height parameters. Optimization of turbine disk design is carried out to achieve minimum weight. Sensitivity studies are carried out to understand the geometry parameters influence on the stress and burst margins.
Design Considerations for Syngas Turbine Power Plants
Authors: Ganjikunta Jaya
Published: February 2016

Market demands such as generating power at lower cost, increasing reliability, providing fuel flexibility, increasing efficiency and reducing emissions have renewed the interest in Integrated Gasification Combined Cycle (IGCC) plants in the Indian refinery segment. This technology typically uses coal or petroleum coke (petcoke) gasification and gas turbine based combined cycle systems as it offers potential advantages in reducing emissions and producing low cost electricity. Gasification of coal typically produces syngas which is a mixture of Hydrogen (H) and Carbon Monoxide (CO). Present state of gas turbine technology facilitates burning of low calorific fuels such as syngas and gas turbine is the heart of power block in IGCC. Selecting a suitable gas turbine for syngas fired power plant application and optimization in integration can offer the purchaser savings in initial cost by avoiding oversizing as well as reduction in operating cost through better efficiency.

This paper discusses the following aspects of syngas turbine IGCC power plant:

• Considerations in design and engineering approach

• Review of technologies in syngas fired gas turbines

• Design differences of syngas turbines with respect to natural gas fired turbines

• Gas turbine integration with gasifier, associated syngas system design and materials

• Syngas safety, HAZOP and Hazardous area classification

• Retrofitting of existing gas turbines suitable for syngas firing

• Project execution and coordination at various phases of a project

This paper is based on the experience gained in the recently executed syngas fired gas turbine based captive power plant and IGCC plant. This experience would be useful for gas turbine technology selection, integration of gas turbine in to IGCC, estimating engineering efforts, cost savings, cycle time reduction, retrofits and lowering future syngas based power plant project risks.
Gas Dynamic Designing of Pneumatic Braking System for Gas Turbine Engine Test Bench
Authors: Popov Grigorii M. , Novikova Yulia D. , Goriachkin Evgenii S.
Published: February 2016

The purpose of this research was the gas-dynamic design of the pneumatic brake system on the basis of the existing geometry of the three stage axial flow low-pressure compressor for application in the GTE test benches.

The pneumatic brake system has been obtained by adding of the add stage to the low-pressure compressor, the geometry of which repeats the geometry of the stages of the base compressor. In this work, two options were considered. First, the second stage of the base compressor was used as the add stage. Second, the third stage of the base compressor was used as the add stage.
Methods of Improving the Axial Compressor Flow Passage to Reduce the Flow Circumferential Nonuniformity
Authors: Kolmakova Daria , Popov Grigorii
Published: February 2016

Circumferential nonuniformity of gas flow is one of the main problems that can occur in the gas turbine engine. Usually, the flow circumferential nonuniformity appears near the support, located in the flow passage of the engine. The presence of circumferential nonuniformity leads to the increased dynamic stresses in the blade rows and the blade damage. The goal of this research was to find the ways of the flow non-uniformity reduction, which would not require a fundamental changing of engine design. A new method for reducing the circumferential nonuniformity of gas flow was proposed. It has been suggested to increase the gap of the leading edges of support racks from the trailing edge of the upstream guide vane blades which will result in achieving the desired results. An important advantage of this method is that the internal cavities of racks remain unchanged for the placement of engine systems. Moreover, the proposed method allows the prediction of the pressure peak values after the rotor blades without .
Thermal Analysis of a Turbine Blade: Effect of Film Cooling and Internal Convective Cooling
Authors: Sarkar S. , Gupta P.
Published: February 2016

Advanced gas turbines are designed to operate at increasingly higher inlet temperature that poses a greater challenge to the designer for more effective blade cooling strategies. In this paper, a generic high-pressure turbine (HPT) blade of a gas turbine, which is cooled by film cooling in conjunction with internal convective cooling, has been analysed by solving Navier-Stokes and energy equations. The intricate internal cooling passages and a series of holes on the suction surface are considered for the simulations. Large numbers of cell in different zones are used to truly replace the blade with cooling holes and the internal cooling passage. The CFD analysis with conjugate heat transfer condition is accomplished by Fluent, version 6.3. A detailed discussion has been made regarding the aerodynamics and heat transfer. In brief, the suction surface is well protected by film cooling, whereas, the pressure surface demands some additional protection for a longer life. The leading edge is under the metallurgical limit because of internal cooling for the present configuration.
Coupled Thermo-Mechanical Transient Stress Analysis of Functionally Graded Gas Turbine Rotor
Authors: Patil Dinesh , Rao D. Koteswara , Roy Tarapada
Published: February 2016

This paper is concerned with the coupled thermo-mechanical stress analysis of functionally graded (FG) gas turbine rotor shaft system. Gas turbine shaft may expose in high temperature environments which demands to use functionally graded materials (FGMs). The aim of the present work is to study the stresses developed in the FG turbine shaft due to temperature variations and mechanical loading due to unbalance masses. For the present analysis aluminum oxide (Al2O3) and stainless steel (SUS304) are taken as shaft materials, power law gradation is used for the determination of FG material properties of the turbine shaft. Three nodded Timoshenko beam element with six degree of freedom (DOF) per node is considered for the finite element modelling of FG shaft. First order shear deformation theory (FSDT) is used with rotary inertia, strain and kinetic energy. Solution for governing equation of motion is obtained by the Hamilton principle. Complete MATLAB code has been developed for thermosmechanical stress analysis. Comparative study between steel shaft and FG shaft have been carried out. Normal stress (σxx) on plane perpendicular to axial direction, shear stress (τxr) on plane perpendicular to axial direction in radial direction and shear stress (τxθ) on plane perpendicular to axial direction in circumferential direction are obtained against time and along radius of shaft. Also these stresses are obtained for different parameters like power law indexes and speed of rotation of shaft.
Numerical Analysis of Impingement/Effusion Cooling Effectiveness on Flat Plates
Authors: Ignatious Ivin , Janardanan Sarasamma Jayakumar
Published: February 2016

The impingement/effusion cooling is a method of using cooling air to protect the hot combustor liner surfaces from high temperature effectively. This paper investigates the impingement/effusion cooling over two perforated flat plates and proposes a better cooling scheme for high temperature combustion liners in aircrafts and electrical power generation application. The adiabatic cooling effectiveness distribution over the liner surface is numerically studied by control volume technique in CFD. In this hybrid scheme the hydraulic diameter (d) of the hole is 1mm and impingement plate is provided with holes normal to the plate over its whole length of 250d. While effusion plate has only 20 rows of holes inclined at 30° to its surface. The effect of blowing ratio (BR) over this hybrid scheme of cooling is studied for different BR of 0.5, 1.0, 1.5 and 2.0. It has been found that the area averaged effectiveness increases steeply for BR 0.5 to 1.0 but further increase in BR results only in a small increase. The results also show that increasing the hole diameter increases averaged effectiveness while increasing the center-to-center spacing decreases averaged effectiveness.
Design and Performance Evaluation of an Aero Engine Booster Pump
Authors: Mohammed Ashfaq C. , Ulaganathan Shivakumar , Kannan Lingamoorthy , Singaravelu Anbuchezhian , Degaonkar Girish K.
Published: February 2016

The primary function of an aero engine fuel system is to supply metered fuel to the combustion chamber at all operating conditions based on the flow demand set by the engine controller. Centrifugal pump is one of the components in fuel system that feeds fuel to the HP pump. Impeller design is a critical one which dictates the overall performance of centrifugal pump. This paper discusses about design and performance evaluation of impeller with twisted blade configuration. Impeller design is performed based on Euler’s one dimensional theory.

Steady state performance of the impeller at design and off-design operating conditions is analyzed by using commercial CFD code ANSYS-CFX with a standard SST turbulence model. The governing mathematical model for flow analysis is a three dimensional incompressible Reynolds Averaged Navier-Stokes (RANS) equation. Cavitation phenomenon is simulated in the CFD multiphase analysis to assess the pump impeller performance under cavitation at different NPSH values. Rayleigh-Plesset cavitation model is used along with RANS equation to perform cavitation analysis.

From this study, the simulation method and technique adapted is appropriate for predicting the performance of impeller of centrifugal pump with or without cavitation. Performance of the impeller reduces drastically as there is decrease in NPSH. The prediction of critical NPSH is vital for safer operation of the pump, specifically at high altitude the pump inlet pressure falls which may result in cavitation during operation.
In-House Development of Gerotor Pump for Lubrication System of a Gas Turbine Engine
Authors: Hussain Tarique , Sivaramakrishna M. , Kumar S. P. Suresh
Published: February 2016

In house development of lubrication oil pump of gerotor type used in gas turbine engine is described in this paper. A host of geometrical parameters determine the inner and outer rotor profiles which in turn define the flow characteristics of the pump. In this paper, a simulation model has been developed based on AMESim and MatLab which used to predict the flow characteristics of a pump. This model incorporates both the methodologies of design and parametric analysis of the pump which aids to design the pump in accordance with designer needs by varying the parameters. A gerotor pump is designed having fixed geometrical parameters using this model. The prototype pump has been tested for its flow characteristics and compared with estimated result. The comparison indicates that simulation results agree well with the measured data. Thus, this simulation model will be useful in designing and analyzing the lubrication pump of a gas turbine engine.
Experimental Analysis of Simplex Atomizer Spray and Swirling Flow Interactions in Unconfined Conditions
Authors: Selvan Muthu , Suryanarayana Rao Muralidhara , Kharb Indu , Thirumalachari Sundararajan , Vyas Vinod Kumar , Neelakandan Sivakumar
Published: February 2016

An experimental study has been conducted to investigate the interaction between the conical spray produced by simplex atomizer and the swirling flow from an axial swirler. This work has been carried out in an unconfined ambience at isothermal conditions, using water. Malvern spray analyzer with a three dimensional traverse is used to characterize the swirling flow and spray interactions at various axial and radial locations. Images of spray at different conditions of air and water mass flow rates have been analyzed. Increasing the air mass flow through swirler at constant water flow rate, changes the spray structure significantly. These structural changes are sudden and highly dependent on the initial conditions of the spray. At smaller air flow rates, single-mode droplet size distribution at mid-plane changes into a bi-modal distribution at an air flow rate of about 35 kg/hr, with higher contribution of larger droplets. With further increase in air flow rate (90, 110 and 130 kg/hr), the bi-modal size distribution is maintained but with a larger volumetric fraction of small droplets. At different axial distances, the droplet size distributions are similar (single mode and bimodal distributions depending on air flow rate). But volume percentage of larger droplets is less compared to those of smaller droplets, at larger axial distance. At outer radial locations of the spray, volume percentage of larger droplets reduces and that of smaller droplets increases significantly, due to secondary droplet breakup. The interaction between the swirl and spray causes droplets to move radially outwards, resulting in droplet break-up by impact on the dome. Cases with higher air to water flow ratios exhibit significant changes in drop size distribution due to such swirl-spray interactions.
Numerical Study of Variable Camber Inlet Guide Vane on Low Speed Axial Compressor
Authors: Rajesh Emandi , Roy Bhaskar
Published: February 2016

The modern engine has the requirement of high pressure ratio compressors. High diffusion blades are used to cater to this requirement. The high diffusion blades suffer from the low incidence range. A variable geometry inlet guide vane is used to improve the incidence range and to have an increased stable operating range.

In this paper a variable camber inlet guide is proposed in place of an existing inlet guide vane (IGV) to operate the compressor at increased stable operating range or to operate at improved efficiency at off design point. Numerical analysis is carried out in ANSYS CFX©. The existing compressor consists of IGV (20 blades) , rotor (43 blades) and stator (52 blades). The rotor rotates at 2400 rpm in clockwise direction.

The IGV blade is split two part forward blade and aft blade. Numerical studies are conducted to study the effect of varying the stagger angle on the performance of the compressor. The aft blade is given rotation in clockwise direction for +5° and +10°. The numerical results obtained are compared to the same stagger angle with full blades. It is observed that marginal improvement in the pressure ratio and efficiency. 7% stall margin improvement is achieved with slotted blade in place a fixed IGV at 0° setting angle. A new compressor characteristics is estimated which shows that the compressor can be operated to the left of the fixed-IGV-stage peak pressure with high efficiency.
Numerical Computation of a Turbulent Lifted Flame Using Flamelet Generated Manifold With Different Progress Variable Definitions
Authors: Yadav Rakesh , Nakod Pravin
Published: February 2016

Dimension reduction is a popular and attractive approach for modeling turbulent reacting flow incorporating finite rate chemistry effects. One of the earliest and most popular approaches in this category is the Laminar Flamelet Model (LFM), which represents the turbulent flame brush using statistical averaging of laminar flamelets whose structure is not affected by turbulence. The other common reduction approach is the intrinsic low dimensional manifold (ILDM). While, the LFM has limitations in predicting the non-equilibrium effects, the ILDM model suffers in the prediction of the low temperature kinetics. A combination of the two approaches where flamelet based manifold are generated called, Flamelet Generated Manifold (FGM) model considers that the scalar evolution in a turbulent flame can be approximated by the scalar evolution similar to that in a laminar flame. This model does not involve any assumption on flame structure. Therefore, it can be successfully used to model ignition, slow chemistry and quenching effects, which are far away from equilibrium. In the FGM, the manifold can be created using different flame configurations. For premixed flames, 1D unstrained flamelets are solved in reaction-progress space. In the case of diffusion flames, a counter flow configuration is used to generate a series of steady flamelets with increasing scalar dissipation and also an unsteady laminar flamelet is generated to create the diffusion FGM manifold. In the present work, a diffusion flamelet based FGM model is compared with the FGM model using premixed unstrained flamelet configurations. The performance and predictive capabilities of the two approaches are compared for a turbulent lifted methane flame in a diluted hot co-flow environment, where the reacting flow associated with the central jet exhibits similar chemical kinetics, heat transfer and molecular transport as recirculation burners without the complex recirculating fluid structures. It is observed that though the diffusion flamelet based FGM predicts a lifted flame, but the lift off height is lower compared to the premixed configuration. A parametric study with different normalization for the progress variable is done to study its impact on the flame characteristics and the manifold created. Finally, the computations are performed for different definitions of the progress variable from previously published works. It is seen that the results are sensitive to the various progress variable definitions, particularly when the number of species are higher and involve different time scales.
Quantifying masking in clinical mammograms via local detectability of simulated lesions
Authors: Mainprize James G. , Alonzo‐Proulx Olivier , Jong Roberta A. , Yaffe Martin J.
Published: February 2016

Purpose:

High mammographic density is known to be associated with decreased sensitivity of mammography. Recent changes in the BI‐RADS® density assessment address the effect of masking by densities, but the BI‐RADS® assessment remains qualitative and achieves only moderate agreement between radiologists. An automated, quantitative algorithm that estimates the likelihood of masking of simulated masses in a mammogram by dense tissue has been developed. The algorithm considers both the effects of loss of contrast due to density and the distracting texture or appearance of dense tissue.

Methods:

A local detectability (dL) map is created by tessellating the mammograms into overlapping regions of interest (ROIs), for which the detectability by a non‐prewhitening observer is computed using local estimates of the noise power spectrum and volumetric breast density (VBD). The dL calculation was validated in a 4‐alternative forced‐choice observer study on the ROIs of 150 craniocaudal digital mammograms. The dL metric was compared against the inverse threshold contrast, (ΔμT)−1 from the observer study, the anatomic noise parameter β, the radiologist's BI‐RADS® density category, and a validated measure of VBD (Cumulus).

Results:

The mean dL had a high correlation of r = 0.915 and r = 0.699 with (ΔμT)−1 in the computerized and human observer study, respectively. In comparison, the local VBD estimate had a low correlation of 0.538 with (ΔμT)−1. The mean dL had a correlation of 0.663, 0.835, and 0.696 with BI‐RADS density, β, and Cumulus VBD, respectively.

Conclusions:

The proposed dL metric may be useful in characterizing the potential for lesion masking by dense tissue. Because it uses information about the anatomic noise or tissue appearance, it is more closely linked to lesion detectability than VBD metrics.
Technical Note: Compact three‐tesla magnetic resonance imager with high‐performance gradients passes ACR image quality and acoustic noise tests
Authors: Weavers Paul T. , Shu Yunhong , Tao Shengzhen , Huston John , Lee Seung‐Kyun , Graziani Dominic , Mathieu Jean‐Baptiste , Trzasko Joshua D. , Foo Thomas K.‐F. , Bernstein Matt A.
Published: February 2016

Purpose:

A compact, three‐tesla magnetic resonance imaging (MRI) system has been developed. It features a 37 cm patient aperture, allowing the use of commercial receiver coils. Its design allows simultaneously for gradient amplitudes of 85 millitesla per meter (mT/m) sustained and 700 tesla per meter per second (T/m/s) slew rates. The size of the gradient system allows for these simultaneous performance targets to be achieved with little or no peripheral nerve stimulation, but also raises a concern about the geometric distortion as much of the imaging will be done near the system's maximum 26 cm field‐of‐view. Additionally, the fast switching capability raises acoustic noise concerns. This work evaluates the system for both the American College of Radiology's (ACR) MRI image quality protocol and the Food and Drug Administration's (FDA) nonsignificant risk (NSR) acoustic noise limits for MR. Passing these two tests is critical for clinical acceptance.

Methods:

In this work, the gradient system was operated at the maximum amplitude and slew rate of 80 mT/m and 500 T/m/s, respectively. The geometric distortion correction was accomplished by iteratively determining up to the tenth order spherical harmonic coefficients using a fiducial phantom and position‐tracking software, with seventh order correction utilized in the ACR test. Acoustic noise was measured with several standard clinical pulse sequences.

Results:

The system passes all the ACR image quality tests. The acoustic noise as measured when the gradient coil was inserted into a whole‐body MRI system conforms to the FDA NSR limits.

Conclusions:

The compact system simultaneously allows for high gradient amplitude and high slew rate. Geometric distortion concerns have been mitigated by extending the spherical harmonic correction to higher orders. Acoustic noise is within the FDA limits.