bluuebunny/crossref_metadata_2025 huggingface dataset:
EXPLORING OLD AND NEW PATHS IN THEODICY
Authors: Sollereder Bethany
Published: August 2018

Christopher Southgate's work raises questions about God, evolution, and suffering. In this article, I begin by contributing an alternative to Southgate's “only way” argument and by offering a third option in speculations about the nature of nonhuman animals in heaven. The second half of the article starts with Southgate's approach of evolutionary theodicy as “an adventure in theology” and proposes a new path branching off his work. “Compassionate theodicy” is a reworking of the method and audience of traditional theodicy in the hope that it might become something that could offer theological resources to those who suffer.
A Nurturing HQ Is Good for the MNC
Authors: Godiwalla Yezdi H.
Published: August 2018

Good parenting, nurturing, training and close networking within the organization by the headquarters are very vital for the overall MNC. An MNC’s HQ must pursue better nurturing and fostering developmental and networking approaches in its relationships with its foreign subsidiary units. A well supported and nurtured constellation of foreign subsidiaries will perform more cooperatively and harmoniously within the framework of the overall MNC organization. In turn, these approaches will generate more effective strategies for competitive performance because of the improved cross-fertilization of ideas. This is for younger and mature organizations because of the inherent hierarchical difference between the HQ and the foreign subsidiaries. The HQ must pursue a spirit of collaboration and partnership that would generate a feeling of near equality among the partners. HQ may give the final assent even so, only after good deliberations and factual and rational analyses. Good nurturing and close communications would likely align the values and views of the many disparate foreign units, given the diverse environments of operations. Learning in an MNC organization, which has these collaborative, closer internal and stakeholder networking, communicative attributes, is multi-directional: HQ learns as much from the foreign subsidiary units as the units learns from the HQ. Closer internal and external stakeholder networking in an MNC and good parenting and nurturing involve good, continuous expatriate training. These activities result in better organizational effectiveness and competitiveness.
Reviewer Acknowledgements
Authors: Smith Robert
Published: August 2018

Journal of Education and Training Studies (JETS) would like to acknowledge the following reviewers for their assistance with peer review of manuscripts for this issue. Many authors, regardless of whether JETS publishes their work, appreciate the helpful feedback provided by the reviewers. Their comments and suggestions were of great help to the authors in improving the quality of their papers. Each of the reviewers listed below returned at least one review for this issue. Reviewers for Volume 6, Number 9Ajda Şenol Sakin, Uludag Univesity, TurkeyAvni Yildiz, Bülent Ecevit University, TurkeyBünyamin Aydin, Alaaddin Keykubat Üniversity, TurkeyChosang Tendhar, Long Island University (LIU), USAEmel Funda Türkmen, Afyon Kocatepe Univesity, TurkeyEmel Funda Türkmen, Afyon Kocatepe Univesity, TurkeyEsin Sahin Pekmez, Agean University, TurkeyGözde Ersöz, Namık Kemal University, TurkeyGülsüm Yuca, Aksaray University, TurkeyIntakhab Khan, King Abdulaziz University, Saudi ArabiaIoannis Syrmpas, University of Thessaly, GreeceJeyavel Sundaramoorthy, Gulbarga University Campus, IndiaJohn Bosco Azigwe, Bolgatanga Polytechnic, GhanaJon S. Turner, Missouri State University, USAKatya De Giovanni, University of Malta, MaltaKerim Gündogdu, Adnan Menderes University, TurkeyKerim Sözbir, Abant İzzet Baysal University, TurkeyMassimiliano Barattucci, Ecampus University, ItalyMehmet Aydin, Dicle University, TurkeyMehmet Inan, Marmara University, TurkeyMichail Kalogiannakis, University of Crete, GreeceMurat Taş, Manisa Celalbayar University, TurkeyNevzat Dinçer, University of Batman, TurkeyÖnder Şemşek, Abant İzzet Baysal University, TurkeyOzgur Demirtas, Inonu University, TurkeyOzkan Kırmızı, Karabuk University, TurkeySenem Seda Şahenk Erkan, Marmara University, TurkeySerdal Baltaci, Ahi Evran University, TurkeyŞirin Akbulut Demirci, Uludag Univesity, TurkeyTorok Marianna, University of Massachusetts Boston, USAYerlan Seisenbekov, Kazakh National Pedagogical University, Kazakhstan                             Robert SmithEditorial AssistantOn behalf of,The Editorial Board of Journal of Education and Training StudiesRedfame Publishing9450 SW Gemini Dr. #99416Beaverton, OR 97008, USAURL: http://jets.redfame.com
Controlling Fluctuated Chaotic Power Systems With Compensation of Input Saturation: Application to Electric Direct Current Machines
Authors: Aghababa Mohammad Pourmahmood
Published: August 2018

It is shown that brushless direct current (DC) motors (BLDCMs), which have found many useful applications in motion control areas, display chaotic behaviors. To avoid undesirable inherent oscillations of such DC motors, a control strategy should be adopted in the applications. So, the control problem of applied chaotic power systems is taken into account in this paper. Some important aspects of the design and implementation are considered to reach a suitable controller for the applications. In this regard, it is assumed that the system is fluctuated by unknown uncertainties and environmental noises. Additionally, a part of the system dynamics is supposed to be unknown in advance and the effects of nonlinear input saturation are fully taken into account. Then, a one input nonsmooth adaptive sliding mode controller is realized to handle the aforementioned issues. The proposed controller does not require any knowledge about the bounds of the system uncertainties and external fluctuations as well as about the parameters of the input saturation. The finite time convergence and robustness of the driven control scheme are mathematically proved and numerically illustrated using matlab simulations for DC motors.
Research on Dynamic Characteristic of Marine Shafting-Oil Film-Stern Structure System
Authors: Dong Liang-Xiong , Wang Shao-Hua
Published: August 2018

The working conditions of the propulsion system of ships are affected by many factors and partially by hull deformations and lubricating oil film. In order to solve the problem of engineering application of reliability assessment and control of ship propulsion system on heavy sea, a mechanical model of ship shafting-oil film-stern structure coupled system is established. The hull and shafting are studied as a whole, and a test rig with the wave loads system is assembled. By carrying out the integrative analysis and physical experiment, the motion characteristics of the system are analyzed. According to the various types of wave loads which ship faces on ocean, the influence of the stern structure on the vibration characteristics of the shafting is obtained. It is concluded that the coupling degree of shafting and stern structure is correlated with the natural frequency of the coupled system, and the wave-induced loads response is correlated with wave encountering frequency. The characteristics of the shafting-oil film-stern structure system, such as the maximum amplitude of tail shaft and the minimum oil film thickness of bearing, are significantly modified under the influence of stern structure.
A Mathematical Model for Simulation of Flow Rate and Chamber Pressures in Spool Valves
Authors: Afatsun Ahmet C. , Tuna Balkan R.
Published: August 2018

In this paper, a mathematical model to simulate the pressure and flow rate characteristics of a spool valve is derived. To improve the simulation accuracy, the discharge coefficient through the spool valve ports is assumed to be a function of both the Reynolds number and the orifice geometry rather than treating it as a constant. Parameters of the model are determined using the data obtained by computational fluid dynamics (CFD) analyses conducted on two-dimensional axisymmetric domains using ANSYS Fluent 15® commercial software. For turbulence modeling, shear stress transport (SST) k–ω model is preferred after a comparison of performance with the other available turbulence model options. The resulting model provides consistent pressure and flow rate estimations with CFD analyses and a smooth transition between different geometrical conditions. The ultimate aim of this study is to fulfill the need for a model to precisely determine the geometrical tolerances of spool valve components for optimum performance. Estimations of the developed model is compared with the experimental data of a spool valve, and the model is proved to be able to accurately estimate the maximum leakage flow rate, the pressure sensitivity, and the shapes of leakage flow/load pressure curves.
Elastic Response of Acoustic Coating on Fluid-Loaded Rib-Stiffened Cylindrical Shells
Authors: Doherty Christopher Gilles , Southward Steve C. , Hull Andrew J.
Published: August 2018

Reinforced cylindrical shells are used in numerous industries; common examples include undersea vehicles, aircraft, and industrial piping. Current models typically incorporate approximation theories to determine shell behavior, which are limited by both thickness and frequency. In addition, many applications feature coatings on the shell interior or exterior that normally have thicknesses which must also be considered. To increase the fidelity of such systems, this work develops an analytic model of an elastic cylindrical shell featuring periodically spaced ring stiffeners with a coating applied to the outer surface. There is an external fluid environment. Beginning with the equations of elasticity for a solid, spatial-domain displacement field solutions are developed incorporating unknown wave propagation coefficients. These fields are used to determine stresses at the boundaries of the shell and coating, which are then coupled with stresses from the stiffeners and fluid. The stress boundary conditions contain double-index infinite summations, which are decoupled, truncated, and recombined into a global matrix equation. The solution to this global equation results in the displacement responses of the system as well as the exterior scattered pressure field. An incident acoustic wave excitation is considered. Thin-shell reference models are used for validation, and the predicted system response to an example simulation is examined. It is shown that the reinforcing ribs and coating add significant complexity to the overall cylindrical shell model; however, the proposed approach enables the study of structural and acoustic responses of the coupled system.
Simulation of a Combined Nozzled and Nozzleless Twin-Entry Turbine for Improved Efficiency
Authors: Fan Houchuan , Ni Jimin , Shi Xiuyong , Qu Dayong , Zheng Yi , Zheng Yinghong
Published: August 2018

This paper discusses the performance and the mass flow characteristics of a twin-entry turbocharger turbine with a fixed nozzle entry and a nozzleless entry for the automotive application. Because the configuration, which is based on a conventional twin-entry nozzleless turbine, has both a fixed nozzle entry and nozzleless entry simultaneously, and the fixed nozzle entry and the nozzleless entry have different rotor incidence angles, stratified flow is formed in the rotor inlet. The numerical simulation results show that the new turbine with double-rotor incidence angles has higher efficiency compared to the original twin-entry nozzleless turbine, especially in low-speed condition, which can greatly improve the low-speed torque of the engine. By investigating the installation locations of the fixed nozzle, it is more beneficial to improve the turbine efficiency when the fixed nozzle is set at the outer scroll near the turbine outlet. The influence of the vane installation angle on the turbine performances is studied in order to optimize the turbine structure and to find out the turbine performance characteristics. It shows that 60 deg is the optimal vane angle. This paper introduces the concept of the double-rotor incidence angles and the details of the configuration optimization.
Understanding the Effect of Oxygenated Additives on Combustion Characteristics of Gasoline
Authors: Roy Shrabanti , Zare Saeid , Askari Omid
Published: August 2018

Laminar burning speed and ignition delay time behavior of iso-octane at the presence of two different biofuels, ethanol and 2,5 dimethyl furan (DMF), was studied in this work. Biofuels are considered as a better alternative source of fossil fuels. There is a potentiality that combustion characteristics of iso-octane can be improved using biofuels as an oxygenated additive. In this study, three different blending ratios of 5%, 25%, and 50% of ethanol/iso-octane and DMF/iso-octane were investigated. For laminar burning speed calculation, equivalence ratio of 0.6–1.4 was considered. Ignition delay time was measured under temperature ranges from 650 K to 1100 K. Two different mechanisms were considered in numerical calculation. These mechanisms were validated by comparing the results of pure fuels with wide range of experimental and numerical data. The characteristic change of iso-octane with the presence of additives was observed by comparing the results with pure fuel. Significant change was observed on behavior of iso-octane at 50% blending ratio. A comparison was also done on the effect of two different additives. It has found that addition of DMF brings significant changes on iso-octane characteristics comparing to ethanol.
Supraspinatus Tendons Have Different Mechanical Properties Across Sex
Authors: Bonilla K. A. , Pardes A. M. , Freedman B. R. , Soslowsky L. J.
Published: August 2018

Sex differences in the mechanical properties of different musculoskeletal tissues and their impact on tendon function and disease are becoming increasingly recognized. Tendon mechanical properties are influenced by the presence or absence of sex hormones and these effects appear to be tendon- or ligament-specific. The objective of this study was to determine how sex and hormone differences in rats affect supraspinatus tendon and muscle properties. We hypothesized that male supraspinatus tendons would have increased cross-sectional area but no differences in tendon material properties or muscle composition when compared to supraspinatus tendons from female or ovariectomized (OVX) female rats. Uninjured supraspinatus tendons and muscles from male, female, and OVX female rats were collected and mechanical and histological properties were determined. Our analysis demonstrated decreased dynamic modulus and increased hysteresis and cross-sectional area in male tendons. We found that male tendons exhibited decreased dynamic modulus (during low strain frequency sweep and high strain fatigue loading), increased hysteresis, and increased cross-sectional area compared to female and OVX female tendons. Despite robust mechanical differences, tendon cell density and shape, and muscle composition remained unchanged between groups. Interestingly, these differences were unique compared to previously reported sex differences in rat Achilles tendons, which further supports the concept that the effect of sex on tendon varies anatomically. These differences may partially provide a mechanistic explanation for the increased rate of acute supraspinatus tendon ruptures seen in young males.
Forming Limits Under Stretch-Bending Through Distortionless and Distortional Anisotropic Hardening
Authors: He Ji , Gu Bin , Li Yongfeng , Li Shuhui
Published: August 2018

The necking behavior of sheet metals under stretch-bending process is a challenge for the forming limit prediction. State-of-the-art forming limit curves (FLCs) allow the prediction under the in-plane stretching but fall short in the case under out-of-plane loading condition. To account for the bending and straightening deformation when sheet metal enters a die cavity or slide along a radius, anisotropic hardening model is essential to reflect the nonproportional loading effect on stress evolution. This paper aims to revisit the M-K analysis under the stretch-bending condition and extend it to accommodate both distortionless and distortional anisotropic hardening behavior. Furthermore, hardening models are calibrated based on the same material response. Then the detailed comparison is proposed for providing better insight into the numerical prediction and necking behavior. Finally, the evolution of the yield surface and stress transition states is examined. It is found that the forming limit prediction under stretch-bending condition through the M-K analysis strongly depends on the employed anisotropic hardening model.
Control Optimization for Multiple Gas Turbine Driven Compressors
Authors: Zamotorin Roman , Kurz Rainer , Zhang Donghui , Lubomirsky Matt , Brun Klaus
Published: August 2018

Many gas compressor stations use multiple gas turbine driven centrifugal compressors. In many instances, the units are not identical. The challenge is to control the units such, that certain operational parameters, for example fuel consumption, are optimized. The control system has to rely on measurable parameters. The system has to be reliable even if parameters that are not directly measured change during operation.

For practical use, the two methods available are to control all compressors for the same turndown, or to control all gas turbines for the same load. This methodology can be derived and discussed for the case of identical machines, and will be expanded for the case where the compressors and their drivers are not identical.

The paper describes a variety of optimization methods, starting with a simple algorithm, then comparing equalization methods, and finally illustration the capability of methods that combine turbomachinery optimization and the optimization of pipeline hydraulics.
On Gas Turbine Safety in Offshore Operations
Authors: Kurz Rainer , Mendoza Robert , Burnes Dan , Saxena Priyank , Alexander Sean
Published: August 2018

In the recent past, concerns have been raised regarding Gas Turbines (GTs) causing safety issues in offshore applications. Specifically the argument raised encompass a possible explosion due to a combination of a presence of a gas leak and exposed GT hot surfaces and/or ingested combustible. The above argument is made despite the thousands of GTs in offshore operation. This document provides a high level assessment of the arguments made on the basis of today’s state-of-the-art installations, assuming proper maintenance and general adherence to established safety protocols. It is based on the experience of designing and supporting the operation of hundreds of offshore gas turbine installations.
Local and Global Stability Analysis of an Academic Rotor/Stator Cavity
Authors: Queguineur Matthieu , Bridel-Bertomeu Thibault , Gicquel Laurent , Staffelbach Gabriel
Published: August 2018

Self-sustained oscillations of rotor/stator cavity flows are well known to industry. This unsteady phenomenon can be very dangerous and jeopardize the structural integrity of aeronautical engines by damaging turbomachinery components or turbopumps in the context of space applications. Today, the origin of such flow instability and resulting limit-cycle is not well understood and still difficult to predict numerically. In order to have more insight of this phenomenon dynamic, an academic rotor/stator cavity is investigated in the present paper. The main motivation of this study is to highlight the benefit of conjunct numerical strategies relying on Large Eddy Simulations (LES) and flow stability analyses to understand driving instability mechanisms. More specifically, results of a local and global methods are devised and compared to a Dynamic Mode Decomposition (DMD) of LES predictions. Good agreements between the stability methods studied and the present features in the LES limitcycle are found. On this basis, a sensitivity and receptivity analysis of the flow is realized to point the origin of the two most unstable modes: i.e the position within the flow where the problem issues.
Variable Geometry Turbine Nozzle Design for High Expansion Ratios
Authors: Chen Hua , Huang Lei
Published: August 2018

In variable nozzle geometry turbines (VNT), the vanes that form the nozzle are opened to control turbine mass flow and expansion ratio (ER) in order to allow better engine matching and the generation of more turbine power. In application to turbocharged road vehicles, the vanes are closed to provide higher boost pressure for engine and vehicle acceleration, and may also be used for engine braking assistance. In both situations, high nozzle expansion ratios (ERs) are created, and shockwaves may be produced from the nozzles. These shocks reduce turbine efficiency and can cause high cycle fatigue (HCF) damage to the downstream rotor blades. Design of high ER radial nozzles is difficult for VNT because transonic flows are very sensitive to small changes to vane geometry, and there is a large semi-vaneless space after the nozzle throat. Shock minimised nozzle designs are therefore often accomplished by an auto-optimisation technique. While design targets may be achieved, this technique does not offer sufficient insight into how and why an optimal flow field has been derived, so the same optimisation procedure must be applied to every new design. In this paper, a new design method that overcomes this problem is proposed. The method first uses a conformal mapping to transfer a radial nozzle from the r-0 plane into the x-y plane. The mapped nozzle displays amplification of supersonic acceleration that is explained by the curvature changes brought about by the mapping. In addition, a link between shock strength and the flatness of the suction surface of the mapped nozzle was found. These features can be utilised to design nozzles with reduced shock loss. Nozzles for 6:1 ER were designed in this way and CFD results show significantly weaker nozzle shockwaves. Other performances of the nozzles are either improved or unaffected.
A Method and Apparatus for Direct Enthalpy Rise Measurement for Gas Compression
Authors: Brun Klaus , Simons Sarah , Katcher Kelsi , Cater Ryan , Ridens Brandon , Kurz Rainer
Published: August 2018

Gas property prediction is necessary for proper design of compressors. Equations of state are utilized to predict the thermo-physical gas properties needed for such calculations. These are semi-empirical models that allow the calculation of thermodynamic properties such as density, enthalpy, and speed of sound of gas mixtures for known pressures and temperature. Currently, there is limited or no data publically available to verify the results of these equation of state calculations for the range of pressures, temperatures and gas compositions relevant to many oil & gas applications. Especially for isentropic enthalpy head (i.e., the enthalpy rise along constant entropy lines), which is a critical parameter required to accurately design and performance test compressors, limited public domain data is available for equation of state validation. In this paper a method and test apparatus is described to measure compression enthalpy rise directly. In this apparatus a test gas is compressed using a fast acting piston inside an adiabatic autoclave. Test results are then corrected using calibration efficiencies from a known reference gas compression process at a similar Reynolds number. The paper describes the test apparatus, calibration, measurement methodology, and test results for one complex hydrocarbon gas composition at elevated temperatures and pressures. An uncertainty analysis of the new measurement method is also presented and results are compared to several equations of state. The results show that commonly used equations of state significantly under-predicted the compression enthalpy rise for the test gas case by more than 6%.
Effects of Phase Contents in Feedstock Powder and Methods of Thermal Shock Test on Lifetime of Thermal Barrier Coatings
Authors: Park Kwangyong , Yang Byungil , Kim Insoo , Jang Kyungic , Myoung Sangwon , Park Chanyoung , Scrivani Andrea
Published: August 2018

The thermal durability of thermal barrier coating systems (TBCs) obtained using feedstock powders with different purity and phase content was investigated by thermal shock testing with different cycle times, including the effects on the sintering and phase transformation behaviors. Three kinds of 8 wt.% yttria-stabilized zirconia, namely regular purity (8YSZ), high purity (HP1 and HP2), and no monoclinic phase (NMP), were employed to prepare top coats by atmospheric plasma spraying on a NiCoCrAlY bond coat using a high-velocity oxy-fuel system. Use of 8YSZ, HP1, HP2, and NMP for plasma spraying affected the microstructure and lifetime of the TBC in furnace cyclic testing (FCT) at 1100 °C with 24 hour and 1 hour cycle times. In 24h cycling time, the TBCs deposited using NMP powder showed the highest durability, while that formed from HP showed lifetime performance similar to that obtained with regular purity 8YSZ. The TBC obtained with nMP also exhibited the lowest monoclinic phase transition rate, followed by those obtained using HP and 8YSZ. However, the 1 hour cycle test had the opposite result. Therefore, the coating material should be selected depending on the usage environment.
Fatigue of Advanced SiC/SiC Ceramic Matrix Composites at Elevated Temperature in Air and in Steam
Authors: Ruggles-Wrenn M. B. , Boucher N. J. , Przybyla C. P.
Published: August 2018

High-temperature mechanical properties and tension-tension fatigue of three SiC/SiC ceramic composites are discussed. Effects of steam on high-temperature fatigue are evaluated. The three composites consist of a SiC matrix reinforced with SiC (Hi-Nicalon™) fibers. Composite 1 was processed by chemical vapor infiltration (CVI) of SiC into fiber preforms coated with BN. Composite 2 had an oxidation inhibited matrix consisting of alternating SiC and B4C layers and was processed by CVI. Fiber preforms were coated with pyrolytic carbon with B4C overlay. Composite 3 had a melt-infiltrated (MI) matrix consolidated by combining CVI-SiC with SiC particulate slurry and molten Si infiltration. Fiber preforms were coated with BN. Tension-tension fatigue was investigated at 1200°C in air and in steam. Steam significantly degraded the fatigue performance of composites 1 and 3, but had little influence on the fatigue performance of composite 2. Composite microstructure, as well as damage and failure mechanisms were investigated.
Shock Tube Simulation of the Transient Surge Phase Inside an Axial Compressor
Authors: Huang Paul Xiubao , Mazzawy Robert S.
Published: August 2018

This paper is a continuing work from one author on the same topic of the transient aerodynamics during compressor stall/surge using a shock tube analogy by Huang [1, 2]. As observed by Mazzawy [3] for the high-speed high-pressure (HSHP) ratio compressors of the modern aero-engines, surge is an event characterized with the stoppage and reversal of engine flow within a matter of milliseconds. This large flow transient is accomplished through a pair of internally generated shock waves and expansion waves of high strength. The final results are often dramatic with a loud bang followed by the spewing out of flames from both the engine intake and exhaust, potentially damaging to the engine structure [3].

It has been demonstrated in the previous investigations by Marshall [4] and Huang [2] that the transient flow reversal phase of a surge cycle can be approximated by the shock tube analogy in understanding its generation mechanism and correlating the shock wave strength as a function of the pre-surge compressor pressure ratio. Kurkov [5] and Evans [8] used a guillotine analogy to estimate the inlet overpressure associated with the sudden flow stoppage associated with surge. This paper will expand the progressive surge model established by the shock tube analogy in [2] by including the dynamic effect of airflow stoppage using an “integrated-flow” sequential guillotine/shock tube model. It further investigates the surge formation (characterized by flow reversal) and propagation patterns (characterized by surge shock and expansion waves) after its generation at different locations inside a compressor. Calculations are conducted for a 12-stage compressor using this model under various surge onset stages and compared with previous experimental data [3]. The results demonstrate that the “integrated-flow” model closely replicates the fast moving surge shock wave overpressure from the stall initiation site to the compressor inlet.
Practical Optimization of Mistuned Bladed Disk of Steam Turbine With Free-Standing Blade Structure for Forced and Self-Excited Vibration
Authors: Kaneko Yasutomo , Mori Kazushi , Ooyama Hiroharu
Published: August 2018

Although bladed disks are nominally designed to be cyclically symmetric (tuned system), the vibration characteristics of all the blades on a disk are slightly different due to the manufacturing tolerance, deviations in the material properties, and wear during operation. These small variations break the cyclic symmetry and split the eigenvalue pairs. Bladed disks with small variations are referred to as a mistuned system. Many researchers suggest that while mistuning has an undesirable effect on the forced response, it has a beneficial (stabilizing) effect on blade flutter (the self-excited vibration). Therefore, it is necessary to optimize a bladed disk for forced vibration and blade flutter. In this study, firstly, the stability analysis of a mistuned bladed disk of a steam turbine that experienced the blade flutter in the field is carried out by use of the reduced order model, the Fundamental Mistuning Model. It is reported that the bladed disk analyzed failed due to unstalled flutter of the 1st mode, and the problem was solved by alternating mistuning. By comparing the analysis results with these field experiences, the analysis method is validated. Secondly, a parametric study on the mistuning effect is carried out for typical mistuning patterns, such as periodic and random mistuning, for both forced and self-excited vibrations. Finally, based on the above-mentioned results, a practical optimization method considering both forced vibration and self-excited vibration with respect to the bladed disk of a steam turbine with a free-standing blade structure is proposed.
Evaluation of Solid-State Electrochemical Sensors for Real Time Monitoring of NO and O2 in the Exhaust of a Commercial 60kW Gas Turbine
Authors: Ehlig Ryan A. , Takahashi Motonobu , McDonell Vincent G.
Published: August 2018

This study examines the viability of electrochemical solid-state nitric oxide sensors as an alternative to CEM (Continuous Emission Monitoring) instruments for use in monitoring the emissions of a 60 kW gas turbine. While CEM equipment is used regularly at large scale centralized power plants, it is not cost effective for small generators used for distributed power generation. Yet in areas with poor air quality, assessment of the emissions generated by such generators is an important question. A commercial and inexpensive potential alternative to the complex CEM systems used in power plants comes from the automotive industry, which employs solid-state sensors to monitor and control emissions in diesel vehicles. In the present study, two models of commercial solid-state sensors (UniNOx® and NTK) were evaluated in the exhaust stream of the Capstone C-60 gas turbine engine. A referee instrument (Horiba PG-350) using the EPA approved NO measurement method, chemiluminescence, was used in the study as a reference point. Over 8 months of testing, it was found that both solid state sensors followed the general NO trends measured by Horiba PG-350 analyzer. Both solid-state sensors responded to small incremental changes in engine load with high-resolution changes in NO ppm. It was determined that the NTK sensor had more favorable performance over test period than the UniNOx® sensor with regards to Accuracy, Lower Detectable Limit (LDL), and Rise Time and Fall Time. The UniNOx® sensor was found to have higher precision than the NTK sensor.
Digitalization: Laser Metal Deposition — The Future of Spare Parts and Repairs for Industrial Steam Turbines
Authors: Wittig Norman
Published: August 2018

Laser metal deposition (LMD) — also referred to as laser deposition welding — has been a well-established process for years. One example of its use is for tip repair for gas turbine blades from Siemens. The decision to also implement laser welding technology for the service of industrial steam turbines was based primarily on the fact that repairs — especially conventional welds and coatings including heat treatment and testing — are very time consuming and are very difficult to reconcile with the overhaul periods planned by customers. The robot supported automation of the LMD process and the fact of its lower heat input, reduced layer thicknesses and the resulting lowered deformation of the part due to reduced coating areas makes it possible to optimize lead times. The high level of process automation and reliability of a laser welding process represents another important benefit. Similarly, process parameters are constantly monitored and tracked, to ensure that the required quality standards are maintained and even increased. Furthermore, laser metal deposition completely replaced the conventional processes such as tungsten inert gas method (TIG), plasma transferred arc (PTA) and detonation spraying. In addition the technology unleashes now the possibility to repair and refurbish parts instead of new manufacturing, and therefore delivery times can be tremendously reduced. Based on the decision to six-axis robots it becomes possible enhancing the LMD process for complex 3D surfaces. After modeling a digital twin in Siemens NX CAM it is possible to generate, optimize and simulate the whole motion-sequences offline before starting the LMD process in the robot cell. So already designed parts in 3D-CAD can be used to develop the final robot program. In addition already existing technologies like 3D surface scanning will be implemented in the chain to support the LMD process. Digitalization turns from a buzzword to an established technology for industrial steam turbine manufacturing and repair.
Centrifugal Compressor Design for Near-Critical Point Applications
Authors: Ameli Alireza , Afzalifar Ali , Turunen-Saaresti Teemu , Backman Jari
Published: August 2018

The supercritical CO2 (sCO2) Brayton cycle has been attracting much attention to produce the electricity power, chiefly due to its higher thermal efficiency with the relatively lower temperature at the turbine inlet compared to other common energy conversion cycles. Centrifugal compressor operating conditions in the supercritical Brayton cycle are commonly set in vicinity of the critical point, owing to smaller compressibility factor and eventually lower compressor work.

This paper investigates and compares different centrifugal compressor design methodologies in close proximity to the critical point and suggests the most accurate design procedure based on the findings. An in-house mean-line design code, which is based on the individual enthalpy loss models, is compared to stage efficiency correlation design methods. Moreover, modifications are introduced to the skin friction loss calculation to establish an accurate 1-D design methodology. Moreover, compressor performances are compared to the experimental measurements.
Aeroelastic Control on Compressor Blades With Virtual Control Surfaces: A Numerical Assessment
Authors: Motta Valentina , Malzacher Leonie , Bicalho Civinelli de Almeida Victor , Peitsch Dieter
Published: August 2018

Plasma actuators are numerically implemented as virtual control surfaces to reduce turbomachinery blades vibration and enlarge flutter-free ranges. Actuators are located at the trailing edge of the blades, both on pressure and suction side, and are triggered either independently or alternately. Upstream blowing — i.e. plasma operating in a way that the induced flow is against the freestream — has been assessed by the authors in a previous work, and is now compared with downstream blowing — i.e. plasma-induced flow in the direction of the freestream. Steady state and traveling-wave mode calculations are performed. Transient results indicate that both upstream and downstream actuation increase remarkably the stability of the cascade. This improvement in the aeroelastic response is observed for the entire interblade phase angle range. Furthermore, the effects of locally actuating the flow on lift, drag and moment coefficients are typified. A wide range of angles of attack and blowing forces is simulated. The obtained results demonstrate that also downstream plasma actuation can be a powerful tool to deal with aeroelastic instabilities on turbomachinery, and make worthwhile to assess further in-depth the capabilities of the two actuation approaches.
Aero-Thermal Coupled Predictive Model for Preliminary Gas Turbine Blade Cooling Analysis
Authors: Ba Wei , Liu Longgang , Liu Hong
Published: August 2018

The turbine inlet temperature has been increasing over the years to improve gas turbine efficiency and specific power. Blade cooling technology is essential to keep component temperatures below their critical value, and this makes the aero-thermal coupled phenomenon more significant. Blade life assessment is closely related to blade metal temperature distribution and gradients, and blade cooling analysis is always considered starting from the preliminary design stage. However, traditional blade cooling analysis for preliminary design is always based on external boundary conditions determined by experience, which affects the prediction accuracy as the interaction effect between the main flow and coolant is not considered. In this paper, an aero-thermal coupled blade cooling model is further developed by combining the improved streamline curvature method with a one-dimensional thermo-fluid network. This model is capable of predicting blade surface temperature distribution and internal coolant flow conditions in the preliminary phase of blade cooling design with a limited amount of input information. Experimental data for the NASA C3X profile with film cooling was selected for validation. In addition, a sensitivity analysis was performed on different film cooling mass flow rates to demonstrate the model flexibility for different boundary conditions.
A Simple Contact Model for Simulating Tie Bolt Rotor Butt Joints With and Without Pilot Fits
Authors: Rimpel Aaron M.
Published: August 2018

Turbomachinery rotors constructed from shaft components held together with a central tie bolt can be referred to as “tie bolt rotors”. At the interface between adjacent shaft sections, a contact stiffness behavior acts to reduce the effective bending stiffness compared to a solid shaft. Therefore, bending natural frequencies tend to be over-predicted, which is a design risk if critical speed margins are compromised. The current research analyzed the effect of contact stiffness in tie bolt rotor butt joints with and without pilot fits. Test articles were fabricated to represent different joint contact areas and pilot feature dimensions, and bending stiffness was indirectly observed by measurement of shaft natural frequencies. An empirical model was derived from a subset of the data, and the model was used to predict performance in all other test cases. The model proposed adding a small thickness layer of material with a reduced modulus of elasticity to simulate the reduction in stiffness by the axial face contact, which is a practical approach for simulation by finite element analysis (FEA) not previously proposed in the literature. The presence of the contact stiffness behavior was evident in all of the test data, which showed a stiffening effect with an increase in contact pressure. By contrast, the baseline FEA simulation predicted a softening behavior with increased compressive load. Implementing the empirically-derived contact stiffness model in simulations showed improved predictions for all experimental shaft configurations tested in this study.
Numerical Study on the Effects of V-Shaped Rib Angle on Film Cooling Performance for Turbine Blade Trailing Edge
Authors: Ye Lin , Liu Cun-liang , Liu Hai-yong , He Qi-jiao , Xie Gang
Published: August 2018

The trailing edge of the high-pressure turbine blade presents significant challenges to cooling structure design. To achieve better cooling performance at turbine blade trailing edge, a novel ribbed cutback structure is proposed for trailing edge cooling, which has rib structures on the cutback surface for heat transfer enhancement. In this study, numerical simulations have been performed on the effects of V-shaped rib angle on the film cooling characteristics and flow physics. Three V-shaped rib angles of 30°, 45° and 60° are studied. The distributions of adiabatic cooling effectiveness and heat transfer coefficient are obtained under blowing ratios with the value of 0.5, 1.0 and 1.5 respectively. Due to the relatively small rib height, the effect of V-shaped ribs on the film cooling effectiveness is not notable. The disadvantage of V-shaped ribs mainly exhibits at the downstream area of cutback surface. With the increase of V-shaped rib angle, the film cooling effectiveness becomes lower, but the values are still above 0.9. The V-shaped ribs obviously enhance the heat transfer on trailing edge cutback surface. The area-averaged heat transfer coefficient of the V-rib case is higher than that of the smooth case by 26.3–41.2%. The 45° V-rib case has higher heat transfer intensity than the other two V-shaped rib cases under all the three blowing ratios. However, the heat transfer coefficient distribution of the 60° V-rib case is more uniform. The heat transfer intensity of the 30° V-rib case is higher in the downstream region than the other two cases, but lower in the upstream region in which the difference becomes smaller with the increase of blowing ratio. The 45° V-rib case and the 60° V-rib case both reach the maximum value of area-averaged heat transfer intensity under blowing ratio is 1.0. Under higher blowing ratio, the 30° V-rib case and the 45° V-rib case outperform 2.1% and 6.7% higher value relative to the 60° V-rib case respectively due to the smaller velocity gradient in the 60° V-rib case in the downstream.
Off-Design Prediction of Transonic Axial Compressors: Part 2 — Generalized Mean-Line Loss Modelling Methodology
Authors: Kidikian John , Reggio Marcelo
Published: August 2018

In Part 1, of this two-part paper, an off-design mean-line code and a generalized methodology to obtain “tuning” factors were presented. It was shown that the modified factors were capable of predicting the off-design performance of four well documented NASA transonic axial compressors.

In this paper, Part 2, a generalized methodology to create correlations for the rotor and stator total pressure losses, deviation angles, and blade row inlet and exit blockage factors is presented.

The generalized mean-line loss modelling methodology will allow the compressor designer to decommission the use of the performance map scaling techniques. In its place, the generalized predictive methodology will accurately estimate the off-design performance of transonic axial compressors and can be used to fill the gaps of missing data.
Demonstration of ORC System Powered by Waste Heat From the Heuksando Island Internal Combustion Diesel Power Plant
Authors: Lee Sanghyup , Jung Hoon
Published: August 2018

Geographical characteristics give the island of Heuksando no choice but to use diesel power generation. This option is not economical, and more than half of the generated energy is released through exhaust gas, cooling water, and other sources of energy loss. In order to reduce these losses and improve power generation efficiency, this research studied Organic Rankine Cycle systems that use waste heat from diesel power plants as a heat source. Unlike previous Rankine cycles, electric power generation and operation are possible because of low heat source and capacity. Cycle design and demonstration-operation logic are required to set the range of waste heat temperature and capacity. In addition, as the overall efficiency may change substantially depending on the efficiency of each component, the operating conditions of various BOPs should be optimized. It is necessary to obtain the optimization and operating conditions of each element of the system through modeling and numerical study of the whole system. In this research, heat source analysis and BOP design were conducted in order to apply the 20kW/30kW ORC systems to the Heuksando Island 1MW diesel power plant. A heat-connecting technique that thermally connects the heat exhaust end piping and the evaporator of the ORC system was developed in this study. The demonstration experiment was conducted sharing the waste heat source with the 20kW and 30kW ORC systems. This paper presents the waste heat analysis and the demonstration operation results of the Heuksando island power plant.
Some Aspects of Transonic Compressor Tandem Design
Authors: Hergt A. , Grund S. , Klinner J. , Steinert W. , Beversdorff M. , Siller U.
Published: August 2018

The development of modern axial compressors has already reached a high level. Therefore an enlargement of the design space by means of new or advanced aerodynamic methods is necessary in order to achieve further enhancements of performance and efficiency. The tandem arrangement of profiles in a transonic compressor blade row is such a method. It is necessary to address the design aspects a bit more in detail in order to efficiently apply this blading concept to turbomachinery. Therefore, in the current study the known design aspects of tandem blading in compressors will be summed up under consideration of the aerodynamic effects and construction characteristics of a transonic compressor tandem. Based on this knowledge, a new transonic compressor tandem cascade (DLRTTC) with an inflow Mach number of 0.9 is designed using modern numerical methods and a multi objective optimization process. Three objective functions as well as three operating points are used in the optimization. Furthermore, both tandem blades and their arrangement are parameterized. From the resulting database of 1246 members a final best member is chosen as state-of-the-art design for further detailed investigation. The aim of the ensuing experimental and numerical investigation is to answer the question, whether the tandem cascade resulting from the modern design process fulfills the described design aspects and delivers the requested performance and efficiency criteria. The numerical simulations within the study are carried out with the DLR flow solver TRACE. The experiments are performed at the Transonic Cascade Wind Tunnel of DLR in Cologne. The inflow Mach number during the tests is 0.9 and the AVDR [1, 2] is adjusted to 1.3 (design value). Wake measurements with a 3-hole probe are carried out in order to determine the cascade performance. The experimental results show an increase in losses and a reduction of the cascade deflection by about 2 degrees compared to design concept. Nevertheless, the experimental and numerical results allow a good understanding of the aerodynamic effects. In addition, Planar PIV was applied in a single S1 plane located at midspan to capture the velocity field in the wake of blade 1 in order to analyze the wake flow in detail and describe its influence on the cascade deflection and loss behavior. Finally, an outlook will be given on what future tandem compressor research should be focused.