bluuebunny/crossref_metadata_2025 huggingface dataset:
Factors Influencing School Closure and Dismissal Decisions: Influenza A (H1N1), Michigan 2009
Authors: Dooyema Carrie A. , Copeland Daphne , Sinclair Julie R. , Shi Jianrong , Wilkins Melinda , Wells Eden , Collins Jim
Published: December 2013

BACKGROUND

In fall 2009, many US communities experienced school closures during the influenza A H1N1 pandemic (pH1N1) and the state of Michigan reported 567 closures. We conducted an investigation in Michigan to describe pH1N1‐related school policies, practices, and identify factors related to school closures.

METHODS

We distributed an online survey to all Michigan K‐12 school principals. Descriptive statistics and chi‐square tests summarize school policies, practices, adherence to government guidelines, and differences between schools that closed and those that remained open during the pandemic.

RESULTS

Of 4441 traditional K‐12 Michigan schools, 937 (21%) principals responded to our survey representing approximately 374,000 students and 17,700 teachers. The majority (88%) of schools had influenza preparedness plans and followed government school influenza guidelines. Among respondents, 15% (137/937) of schools closed in fall 2009 with high absenteeism as the primary reason for closure. Schools that closed reported significant illness in their school, had <300 students, and had invested substantial resources preparing and responding to influenza.

CONCLUSIONS

Adherence to government guidelines for schools appears high in Michigan. Closures occurred in schools that reported significant illness and were likely motivated by excessive absenteeism. Understanding factors related to closures during pH1N1 may inform future pandemic preparedness efforts.
Survey of New Mexico School Health Professionals Regarding Preparedness to Support Sexual Minority Students
Authors: Mahdi Inas , Jevertson Jenn , Schrader Ronald , Nelson Anna , Ramos Mary M.
Published: December 2013

BACKGROUND

For schools to be safe and supportive for students, school health professionals should be aware of the particular challenges lesbian, gay, bisexual, transgender, or questioning (LGBTQ) students face, especially the risk for discrimination, violent victimization, and depression in the school setting. We assessed school health professionals' preparedness to address needs of LGBTQ students.

METHODS

We conducted a secondary analysis of data collected during a New Mexico school health conference. This analysis focused on the preparedness of 183 school nurses, counselors, and social workers to address needs of LGBTQ students. Data were analyzed by using chi‐square tests, other non‐parametric tests, and logistic regression.

RESULTS

Social workers (84.6%) and counselors (81.5%) were more likely than school nurses (55.8%) to report moderate or high knowledge of LGBTQ youth health risks, including suicide and depression (p < .001). Approximately half of school counselors and social workers reported no or low knowledge of LGBTQ community‐based organizations or knowledge of counselors experienced with LGBTQ concerns.

CONCLUSION

School health professionals in New Mexico do not appear prepared to address needs of LGBTQ students. Schools should consider integrating specific content about LGBTQ health risks and health disparities in trainings regarding bullying, violence, cultural competency, and suicide prevention.
Hand Grip Strength is Associated With Body Sway Rate Among Older Adults With Intellectual Disability
Authors: Carmeli Eli , Imam Bita , Levi Ran , Merrick Joav
Published: December 2013

The authors undertook a study to determine whether hand grip strength is associated with body sway rate among older adults with intellectual disability. They employed cross‐sectional data from a nonrandomized controlled trial. Subjects were 16 older adults (8 females and 8 males; mean age 51.3 year) with mild‐to‐moderate intellectual disability residing in a supported living facility in Israel. Voluntary hand grip strength was measured isometrically using Jamar® hydraulic dynamometer, and body sway was assessed by Posture Scale Analyzer. Multivariate adjusted logistic regression model was used. Findings showed that hand grip strength in both arm flexed and extended was associated with body sway (−.608 to −.879), particularly among males. In females, the association was found only in eyes open condition, whereas in males it was found with both eyes closed and open. The authors concluded that hand grip strength was found to be negatively correlated with body sway rate and that low grip strength was associated with greater body sway. Low grip strength may be a rehabilitative impairment worthy of further investigation as a modifiable factor linked to sway rate among older adults with intellectual and developmental disability.
Functional hepatocellular regeneration in elderly patients undergoing hepatectomy
Authors: Fernandes Alexandra I. , Tralhão José G. , Abrantes Ana , Hoti Emir , Alexandrino Henrique , Oliveiros Bárbara , Ferreira Margarida , Botelho Maria F. , Sousa Francisco C.
Published: December 2013

Background & Aims

More than 50% of liver tumours occur in patients aged 65 years or more. Assessment of functional liver regeneration capacity is crucial to minimize postoperative liver failure. We aimed to study functional hepatocellular regeneration, through scintigraphic quantification of Mebrofenin hepatic extraction fraction (HEF), after partial hepatectomy, comparing elderly patients with younger ones.

Methods

One hundred and two patients undergoing partial hepatectomy for primary or secondary hepatic lesions were prospectively included and divided in two groups: Group A – 58 patients aged <65 years (33 men, 53.9 ± 8.7 years), Group B – 44 patients aged ≥65 years (32 men, 71 ± 5 years). Groups were comparable in several aspects except for the presence of cirrhosis (more common in Group B, all patients Child–Pugh score A) and the initial diagnosis (Group B – primary lesions, Group A – metastases). The scintigraphic evaluation of Mebrofenin‐HEF was performed before surgery, on the 5th and 30th day post‐hepatectomy.

Results

Mortality and morbidity were 3.4 and 12.1%, respectively, in Group A and 2.3 and 11.4% in Group B (n.s.). HEF values (%), T1/2 (min) and Tmax (min) showed no significant differences between the two groups: Group A (preoperative: HEF = 99.2 ± 1.5%, T1/2 = 36.7 ± 21.3, Tmax = 15 ± 6. Day 5: HEF = 96.3 ± 10.8%, T1/2 = 76.4 ± 75.9; Tmax = 13.3 ± 4.9. Day 30: HEF = 98.4 ± 5.5%, T1/2 = 38.6 ± 7.7, Tmax = 12.8 ± 3.6) and Group B (preoperative: HEF = 95.3 ± 13%, T1/2 = 38.1 ± 24.1; Tmax = 15.9 ± 9.4. Day 5: HEF = 98.4 ± 2.6%, T1/2 = 106.6 ± 131.7; Tmax = 15.1 ± 6.2. Day 30: HEF = 99 ± 2.1%, T1/2 = 40.5 ± 27; Tmax = 15.5 ± 6.7).

Conclusion

Our results suggest that functional hepatocellular regeneration is early, fast and similar between elderly and younger patients. Thus, age alone, does not appear to represent an absolute contraindication to hepatectomy.
Regulating Rates of Return Do Gravitate in US Manufacturing!
Authors: Tescari Stefania , Vaona Andrea
Published: December 2013

In this paper we test for the gravitation of regulating return rates, namely those return rates yielded by capital goods incorporating the best methods of production. We define them within a vintage capital model taking into consideration capacity utilization, capital depreciation and wages of workers using past capital vintages. We consider two data sets regarding US manufacturing activities and we find that gravitation does take place. Our results are contrasted with those of the previous literature. Research and policy implications are discussed.
South‐East Asia is the center of origin, diversity and dispersion of the rice blast fungus, Magnaporthe oryzae
Authors: Saleh Dounia , Milazzo Joëlle , Adreit Henri , Fournier Elisabeth , Tharreau Didier
Published: December 2013

Inferring invasion routes and identifying reservoirs of diversity of plant pathogens are essential in proposing new strategies for their control. Magnaporthe oryzae, the fungus responsible for rice blast disease, has invaded all rice growing areas. Virulent genotypes regularly (re)emerge, causing rapid resistance breakdowns. However, the world‐wide genetic subdivision of M. oryzae populations on rice and its past history of invasion have never been elucidated.

In order to investigate the centers of diversity, origin and migration of M. oryzae on rice, we analyzed the genetic diversity of 55 populations from 15 countries.

Three genetic clusters were identified world‐wide. Asia was the center of diversity and the origin of most migrations to other continents. In Asia, two centers of diversity were revealed in the Himalayan foothills: South China–Laos–North Thailand, and western Nepal. Sexual reproduction persisted only in the South China–Laos–North Thailand region, which was identified as the putative center of origin of all M. oryzae populations on rice.

Our results suggest a scenario of early evolution of M. oryzae on rice that matches the past history of rice domestication. This study confirms that crop domestication may have considerable influence on the pestification process of natural enemies.
Narcissism and Leadership: A Meta‐Analytic Review of Linear and Nonlinear Relationships
Authors: Grijalva Emily , Harms Peter D. , Newman Daniel A. , Gaddis Blaine H. , Fraley R. Chris
Published: December 2013

Past empirical studies relating narcissism to leadership have offered mixed results. This study integrates prior research findings via meta‐analysis to make 4 contributions to theory on narcissism and leadership, by (a) distinguishing between leadership emergence and leadership effectiveness, to reveal that narcissism displays a positive relationship with leadership emergence, but no relationship with leadership effectiveness; (b) showing narcissism's positive effect on leadership emergence can be explained by leader extraversion; (c) demonstrating that whereas observer‐reported leadership effectiveness ratings (e.g., supervisor‐report, subordinate‐report, and peer‐report) are not related to narcissism, self‐reported leadership effectiveness ratings are positively related to narcissism; and (d) illustrating that the nil linear relationship between narcissism and leadership effectiveness masks an underlying curvilinear trend, advancing the idea that there exists an optimal, midrange level of leader narcissism.
Digital Elevation Quality Derived from Medium‐Format Digital Cameras
Authors: Shih P. T. Y. , Wu J. Y. , Teo T. A. , Tsai J. C.
Published: December 2013

Medium‐format digital cameras are a useful tool in airborne lidar missions to produce digital ortho‐images. This study investigates the quality of digital elevation models (DEMs) and digital surface models (DSMs) derived from such cameras. An image‐matching strategy is used to produce height information from highly overlapping images and the quality of the derived height information is analysed using synchronous lidar point clouds as the reference data. The evaluation focused on various types of land cover and DEM generation methods. The RMSE between lidar and image‐derived height information for two datasets was 0·054% and 0·027% of the flying height in flat, bare‐earth areas, but studies with manually edited vegetated areas using stereo photogrammetry revealed high uncertainties, especially in steep terrain.
Automatic Segmentation of Urban Point Clouds Based on the Gaussian Map
Authors: Wang Yinghui , Hao Wen , Ning Xiaojuan , Zhao Minghua , Zhang Jiulong , Shi Zhenghao , Zhang Xiaopeng
Published: December 2013

A comprehensive method to segment urban point clouds based on the Gaussian map is presented. The normals of point clouds are firstly mapped to the Gaussian sphere and then partitioned into groups using a mean shift clustering algorithm. Next, a distance‐based clustering method is presented to tackle overlapping surfaces which avoids under‐segmentation. Based on the properties of the Gaussian map and the geometric information of the points, primitive shapes such as planes, cylinders, cones and spheres are recognised. Trees, cars, street lights and other objects are then segmented by using the distance‐based clustering method after removing the planes, cylinders, cones and spheres from the large urban scenes. Finally, a refinement process based on primitive shapes is implemented to improve the segmentation results which effectively avoids over‐segmentation. Experimental results demonstrate that the proposed method can be used as a robust way to segment urban point clouds based on the Gaussian map.
The Association between Parity and Birthweight in a Longitudinal Consecutive Pregnancy Cohort
Authors: Hinkle Stefanie N. , Albert Paul S. , Mendola Pauline , Sjaarda Lindsey A. , Yeung Edwina , Boghossian Nansi S. , Laughon S. Katherine
Published: December 2013

Background

Nulliparity is associated with lower birthweight, but few studies have examined how within‐mother changes in risk factors impact this association.

Methods

We used longitudinal electronic medical record data from a hospital‐based cohort of consecutive singleton live births from 2002–2010 in Utah. To reduce bias from unobserved pregnancies, primary analyses were limited to 9484 women who entered nulliparous from 2002–2004, with 23 380 pregnancies up to parity 3. Unrestricted secondary analyses used 101 225 pregnancies from 45 212 women with pregnancies up to parity 7. We calculated gestational age and sex‐specific birthweight z‐scores with nulliparas as the reference. Using linear mixed models, we estimated birthweight z‐score by parity adjusting for pregnancy‐specific sociodemographics, smoking, alcohol, prepregnancy body mass index, gestational weight gain, and medical conditions.

Results

Compared with nulliparas’, infants of primiparas were larger by 0.20 unadjusted z‐score units [95% confidence interval (CI) 0.18, 0.22]; the adjusted increase was similar at 0.18 z‐score units [95% CI 0.15, 0.20]. Birthweight continued to increase up to parity 3, but with a smaller difference (parity 3 vs. 0 β = 0.27 [95% CI 0.20, 0.34]). In the unrestricted secondary sample, there was significant departure in linearity from parity 1 to 7 (P < 0.001); birthweight increased only up to parity 4 (parity 4 vs. 0 β = 0.34 [95% CI 0.31, 0.37]).

Conclusions

The association between parity and birthweight was non‐linear with the greatest increase observed between first‐ and second‐born infants of the same mother. Adjustment for changes in weight or chronic diseases did not change the relationship between parity and birthweight.
Nutrigenomics: the role of nutrients in gene expression
Authors: Dang Tarana Singh , Walker Mark , Ford Dianne , Valentine Ruth A.
Published: December 2013

Improved understanding of the mechanism behind periodontal tissue destruction, the potential protective role of nutrients and the advent of modern genomic measurement tools has led to an increased interest in the association between nutrition and periodontal disease. To date, evidence for a direct link between periodontal disease and nutrition has come mainly from large observational cross‐sectional studies or very small double‐blind randomized supplementation trials, with a large proportion finding no significant association between the nutrient being analyzed and markers of periodontal disease status. The advent of the ‘genomic era’ has introduced the concept of nutrigenomic studies, which aim to reveal the relationship between nutrition and the genome to provide a scientific basis for improved public health through dietary means. Used alongside relatively inexpensive high‐throughput technology, this will allow the effect of diet on the etiology of periodontal disease to be studied in greater detail. As it is extremely likely that interactions between genotype and diet are important in determining the risk of the most common complex diseases, it is highly probable that these interactions will be important in determining periodontal disease risk. Numerous nutritional genetic studies where the outcome measures have been markers of disease risk, most notably cardiovascular disease and cancer, provide proof of principle, highlight the importance of understanding these interactions and illustrate where the effect of dietary modification on periodontal disease progression may have been overlooked previously by observational studies.
Appiah's Cosmopolitanism
Authors: Jeffers Chike
Published: December 2013

This article critically evaluates the cosmopolitan writings of Kwame Anthony Appiah, investigating especially the extent to which he challenges or fails to challenge the problem of Eurocentrism in cosmopolitan discourse. I begin by discussing the way Appiah's construction of his cosmopolitan vision attempts to address criticisms of cosmopolitanism as unable to accommodate the partiality that is an inescapable aspect of human relationships. I relate this issue to Eurocentrism, arguing that the historical integration of the world through European imperialism gives people of color added reason to uphold certain forms of group partiality. I then consider promising points in Appiah's work, in which he can be seen as helping to construct an anti‐Eurocentric form of cosmopolitanism, as well as problematic points, in which he shows insufficient regard for the importance of cultural resistance.
The Role of Welfare in Eudaimonism
Authors: Baril Anne
Published: December 2013

Eudaimonists deny that eudaimonism is objectionably egoistic, but the way in which they do so commits them to eschewing an important insight that has been a central motivation for eudaimonism: the idea that an individual must, in the end, organize her life in such a way that it isgood for her. In this paper I argue that the egoism objection prods eudaimonists to make a choice between (what we might roughly call) welfare‐prior and excellence‐prior eudaimonism, and I make some preliminary remarks on behalf of welfare‐prior eudaimonism.
Trs20 is Required for TRAPP III Complex Assembly at the PAS and its Function in Autophagy
Authors: Taussig David , Lipatova Zhanna , Segev Nava
Published: December 2013

The modular TRAPP complex acts as a guanine‐nucleotide exchange factor (GEF) for Ypt/Rab GTPases. Whereas TRAPP I and TRAPP II regulate the exocytic pathway, TRAPP III functions in autophagy. The TRAPP subunit Trs20 is not required for assembly of core TRAPP or its Ypt1 GEF activity. Interestingly, mutations in the human functional ortholog of Trs20, Sedlin, cause spondyloepiphyseal dysplasia tarda (SEDT), a cartilage‐specific disorder. We have shown that Trs20 is required for TRAPP II assembly and identified a SEDT‐linked mutation, Trs20‐D46Y, which causes a defect in this process. Here we show that Trs20 is also required for assembly of TRAPP III at the pre‐autophagosomal structure (PAS). First, recombinant Trs85, a TRAPP III‐specific subunit, associates with TRAPP only in the presence of Trs20, but not Trs20‐D46Y mutant protein. Second, a TRAPP complex with Ypt1 GEF activity co‐precipitates with Trs85 from wild type, but not trs20ts mutant, cell lysates. Third, live‐cell colocalization analysis indicates that Trs85 recruits core TRAPP to the PAS via the linker protein Trs20. Finally, trs20ts mutant cells are defective in selective and non‐selective autophagy. Together, our results show that Trs20 plays a role as an adaptor in the assembly of TRAPP II and TRAPP III complexes, and the SEDT‐linked mutation causes a defect in both processes.
IMAGING DIAGNOSIS—PARAGANGLIOMA OF THE CAUDA EQUINA: MR FINDINGS
Authors: Duconseille Anne‐Carole , Louvet Arnaud
Published: December 2013

The magnetic resonance imaging features of a cauda equina paraganglioma in a 5‐year‐old dog are described. Imaging revealed a well‐defined, strongly contrast‐enhancing mass invading the adjacent vertebral body and infiltrating the intervertebral foramen bilaterally. Flow void, compatible with increased drainage veins around the mass, and macroscopically visible neovessels in contrast‐enhanced magnetic resonance angiography, as reported in numerous human studies, were not visible in this single case. The tumor recurred despite aggressive surgery and radiotherapy. This neoplasm should be considered in the differential diagnosis of cauda equina abnormalities in dogs.
Optimal Gas-Turbine Design for Hybrid Solar Power Plant Operation
Authors: Spelling James , Laumert Björn , Fransson Torsten
Published: December 2013

A dynamic simulation model of a hybrid solar gas-turbine power plant has been developed, allowing determination of its thermodynamic and economic performance. In order to examine optimum gas-turbine designs for hybrid solar power plants, multi-objective thermoeconomic analysis has been performed, with two conflicting objectives: minimum levelized electricity costs and minimum specific CO2 emissions. Optimum cycle conditions: pressure-ratio, receiver temperature, turbine inlet temperature and flow rate, have been identified for a 15 MWe gas-turbine under different degrees of solarization. At moderate solar shares, the hybrid solar gas-turbine concept was shown to provide significant water and CO2 savings with only a minor increase in the levelized electricity cost.
Ship Gas Turbine Engine With the Intermediate Gas Reheating Before the Power Overexpansion Turbine
Authors: Andriets O. , Matviienko V. , Ocheretianyi V.
Published: December 2013

Gas-turbine engines (GTE) posses a number of technical merits and they are widely used in the structure of ship propulsion complexes. However, if GTE is used as a ship cruise engine it is necessary to increase efficiency with the goal to be competitive to diesels. Increasing of the simple cycle GTE efficiency is possible due to the overexpansion turbine employment, where the internal energy of exhaust gases is used. That allows to obtain, deducting energy expenses on exhaust gases pressing, the additional useful work without the additional fuel expenses.

Power overexpansion turbine employment leads to raising of power plant heaviness, that’s why it is desirable to increase engine power when its weight is constant. Insertion of the intermediate gas reheating before power turbine in the thermal scheme of GTE with the power overexpansion turbine considerably increases GTE’s specific power. GTE with the intermediate gas reheating before the power overexpansion turbine have greater specific power and they are more economic than simple cycle’s GTE on a large spectrum of ship’s power plant operating regimes. GTE with intermediate gas reheating before the power overexpansion turbine have stable efficiency on operating regimes, that’s why it is preferable to employ them for hydrofoil ships.
Life Calculation of First Stage Compressor Blade of a Trainer Aircraft
Authors: Rao J. S. , Rangarajan Narayan , Ratnakar Rejin , Rzadkowski R. , Soliński M. , Vorobiev I.
Published: December 2013

This paper is concerned with life estimation of a compressor rotor blade of an engine at the Air Force Institute of Technology in Warsaw used in a trainer aircraft. A bird strike is simulated by two or three blade passage blocks in the incoming flow and the pressure field is obtained from a CFD code. For the blade the Campbell diagram is prepared and the critical speeds are identified. The alternating pressures corresponding to the critical speed are obtained from an FFT. A nonlinear damping model is estimated using Lazan’s hysteresis law; the equivalent viscous damping model is determined as a function of reference strain amplitude in the given mode of vibration at the rotational speed. An iterative solution is developed with the nonlinear damping model and the resonant stress and location is determined. The life at this critical speed is determined using a cumulative damage criterion.
Aerodynamic Performance of Preferred Wind Turbine Airfoils
Authors: Perez-Blanco Horacio , McCaffrey Maureen
Published: December 2013

To investigate possible increases of the capacity factor of wind turbines, six airfoils are chosen for evaluation, three based on high Cl, low Cd/Cl, and wide operational range, and three others simply based on low Cd. Aerodynamic performance of the chosen airfoils is projected for a 45 m radius turbine using Blade Element Theory (BET) as translated in an existing computer program. Even though the airfoils do not differ significantly in shape, their performance is projected to differ in turbine performance calculations, with some generating more power than others at the same wind speed and air density. The aerodynamic performance obtained with the numerically tested airfoils is compared to that of an actual wind turbine of equal dimensions. Wind speed and directional changes can be large, and assessing their effect is complicated. Using data from the literature, a simple evaluation of the effect of wind speed can be incorporated into the power curve, and shown to be dependent on the airfoil type. Directional changes could lead to reduced output power, but they are more significant for BEs close to the hub than to the tip. The optimal incidence angle calculated with the program shows little variability with wind speed for all airfoils.
Performance Evaluation of an Integrated Solar Combined Cycle
Authors: Ojo Collins O. , Pont Damien , Conte Enrico , Carroni Richard
Published: December 2013

The integration of steam from a central-receiver solar field into a combined cycle power plant (CCPP) provides an option to convert solar energy into electricity at the highest possible efficiency, because of the high pressure and temperature conditions of the solar steam, and at the lowest capital investment, because the water-steam cycle of the CCPP is in shared use with the solar field.

From the operational point of view, the plant operator has the option to compensate the variability of the solar energy with fossil fuel electricity production, to use the solar energy to save fuel and to boost the plant power output, while reducing the environmental footprint of the plant operation.

Alstom is able to integrate very large amounts of solar energy in its new combined-cycle power plants, in the range of the largest solar field ever built (Ivanpah Solar Power Facility, California, 3 units, total 392 MWel). The performance potential of such integration is analyzed both at base load and at part load operation of the plant.

Additionally, the potential for solar retrofit of existing combined-cycle power plants is assessed. In this case, other types of concentrating solar power technologies than central receiver (linear Fresnel and trough) may be best suited to the specific conditions. Alstom is able to integrate any of these technologies into existing combined-cycle power plants.
Validation of ATI 20-25+Nb™ Alloy at 50,000 Hours in the Recuperator of a Gas Turbine Engine
Authors: Bender M. D. , Rakowski J. M. , Lipschutz M. D.
Published: December 2013

A field test program to validate high temperature oxidation resistance of the ATI 20-25+Nb™ alloy in a Solar Turbines Incorporated Mercury™ 50 gas turbine engine has exceeded 50,000 operating hours. A primary goal of this program is to assess the effect of the actual recuperator operating environment on high temperature degradation of primary surface recuperator (PSR) materials. As PSRs are generally fabricated from thin foil materials, excessive degradation can cause perforation, leading to failure of components. To avoid such problems, PSRs are generally fabricated from nickel-base superalloys or highly-alloyed austenitic stainless steels. Previously, ATI 20-25+Nb (UNS S35140) stainless steel was developed and experimentally shown to have excellent creep resistance and good environmental resistance for a PSR application. This field test program evaluates the long-term performance of this alloy in situ in turbine exhaust and compares it with the more highly alloyed Ni-based 625 superalloy.

Sub-size air cell samples of alloy 625 and ATI 20-25+Nb alloy exposed for 50,000 hours (running time) in turbine exhaust were removed and tested for materials characterization. Analysis showed that both alloy 625 and ATI 20-25+Nb alloy exhibit excellent long-term resistance to environmental degradation, even after service exposure equivalent to over 5.5 years.
Development and Validation of a Three-Dimensional Multiphase Flow CFD Analysis for Journal Bearings in Steam and Heavy Duty Gas Turbines
Authors: Uhkoetter Stephan , aus der Wiesche Stefan , Kursch Michael , Beck Christian
Published: December 2013

The traditional method for hydrodynamic journal bearing analysis usually applies the lubrication theory based on the Reynolds equation and suitable empirical modifications to cover turbulence, heat transfer, and cavitation. In cases of complex bearing geometries for steam and heavy-duty gas turbines this approach has its obvious restrictions in regard to detail flow recirculation, mixing, mass balance, and filling level phenomena. These limitations could be circumvented by applying a computational fluid dynamics (CFD) approach resting closer to the fundamental physical laws. The present contribution reports about the state of the art of such a fully three-dimensional multiphase-flow CFD approach including cavitation and air entrainment for high-speed turbo-machinery journal bearings. It has been developed and validated using experimental data. Due to the high ambient shear rates in bearings, the multiphase-flow model for journal bearings requires substantial modifications in comparison to common two-phase flow simulations. Based on experimental data, it is found, that particular cavitation phenomena are essential for the understanding of steam and heavy-duty type gas turbine journal bearings.
Design, Testing and Performance of the Recently Developed 37 MW Siemens SGT-750
Authors: Hellberg Anders , Andersson Thomas , Häggmark Anders
Published: December 2013

The 37MW Siemens SGT-750 is a high-performance twin-shaft gas turbine with a free power turbine. It can be employed both for power generation and as a mechanical drive. This gas turbine attains a simple cycle efficiency level of 40% and excellent performance in cogeneration as well as in combined cycle.

Requirements from the oil & gas industry as well as industrial power generation have been heeded in the design. Since customer earnings are dependant upon turbine availability, uptime has been a major focus. Long service intervals, rapid gas generator exchange and easy access for borescope inspection all guarantee optimized availability. Maintenance work can be performed on site on the installed machine, alternatively the gas generator can be exchanged to minimize downtime. With this solution, maintenance downtime can be cut to a mere 17 days in 17 years. Furthermore, the hot-section blade temperatures can be monitored during operation as a “health check” to ensure availability.

The SGT-750 is a “low-emission engine” equipped with a dry low emission (DLE) combustion system minimizing NOx and CO emissions. The high efficiency leads to a reduction of greenhouse gases with the further possibility to reduce the relative CO2-emissions in cogeneration or combined cycle.

This paper will describe the development and testing of the SGT-750 gas turbine and the additional features which have been incorporated. A new development process has made it possible to increase uptime and serviceability; special attention has been brought to this aspect during the design phase, as will be highlighted in the paper.
Steam Turbine Exhaust Hood With Swirl Flow Separation Ducts
Authors: Mizumi Shunsuke , Ishibashi Kouji , Sawamura Yasuaki
Published: December 2013

The efficiency of a steam turbine is significantly influenced by pressure recovery performance of its low-pressure exhaust hood; hence it is important to specify the cause of loss generation and to devise improved structures. The performance of the exhaust hood is greatly influenced by many structural factors such as the size of its outer casing, design of the diffuser parts and arrangement of internal supports.

Previously we optimized an exhaust hood using CFD. However, even for this exhaust hood, large and strong swirl flow was still observed and it seemed to be one of the main causes of the mixing loss. The vortex structure of the exhaust hood flow was carefully examined for this reason, and swirls with a strong vorticity were all found to originate from the upper part of the exhaust hood for all models calculated.

In the present study, we propose a new structure with special ducts capable of effectively decreasing the swirl strength. Then, we experimentally verify the effectiveness of the improved structure and confirm the possibility of further performance enhancement.
An Impact of Self-Recirculation Casing Treatment (SRCT) Configurations on Impeller Stall Margin and the Flow Field
Authors: Ma Yan , Xi Guang , Wu Guangkuan
Published: December 2013

The present paper describes an investigation of stall margin enhancement and a detailed analysis of the impeller flow field due to self-recirculation casing treatment (SRCT) configuration of a high-speed small-size centrifugal impeller. The influence of different SRCT configurations on the impeller flow field at near-stall condition has been analyzed, highlighting the improvement in stall flow ability. This paper also discusses the influence of the SRCT configurations on the inlet flow angle, inlet swirl velocity and loss distribution in the impeller passage to understand the mechanism of the SRCT configurations in enhancing the stall margin of the impeller. The variation of the bleed flow rate at different operating conditions is also presented in this paper. Finally, the time-averaged unsteady simulation results at near-stall point are presented and compared with steady-state solutions.
CFD-Predicted Rotordynamic Coefficients for a 20-Teeth-on-Stator Labyrinth Seal at High Supply Pressure Conditions
Authors: Pugachev Alexander O. , Degen Heiko
Published: December 2013

A twenty-teeth-on-stator labyrinth seal with a tooth radial clearance of 0.1 mm is modeled using a CFD method to predict leakage performance, as well as stiffness and damping coefficients. The calculations are performed at a supply pressure of 70 bar for three shaft rotational speeds (10200 rpm, 15200 rpm, and 20200 rpm), three preswirl ratios (low, medium, and high), and three pressure ratios (0.1, 0.35, and 0.5). The predicted performance of the seal is compared to experimental data obtained by Picardo and Childs (Picardo, A. and Childs, D.W., 2005, “Rotor-dynamic Coefficients for a Tooth-on-Stator Labyrinth Seal at 70 Bar Supply Pressures: Measurements Versus Theory and Comparison to a Hole-Pattern Stator Seal,” ASME J. Eng. Gas Turbines Power, 127, pp. 843–855). The results from CFD simulations follow the experimental data. Leakage performance is underpredicted by up to 19.8%. Direct and cross-coupled stiffness coefficients are in reasonable agreement with the measurements. However, predicted cross-coupled stiffness increases slower with increasing preswirl ratio than the experimental cross-coupled stiffness. Direct damping is also in agreement with the measured values with the exception of the high preswirl ratio at 20200 rpm. Cross-coupled damping reveals the largest deviations between predictions and experiments. Additionally, the coefficient of determination is calculated for all experimental rotordynamic coefficients to estimate the goodness of fit for the raw test data.
Steady-State Control of Hybrid Foil-Magnetic Bearings
Authors: Tian Ye , Sun Yanhua , Yu Lie
Published: December 2013

A hybrid foil-magnetic bearing is combination of a foil bearing and a magnetic bearing, which takes advantages of both bearings while compensating each other the weaknesses. It is a solution of friction and wear of foil bearings at low speeds and limited load capacity of magnetic bearings. Furthermore, load sharing and control of dynamics can be achieved in a hybrid foil-magnetic bearing. However, in the hybrid foil-magnetic bearing, the journal should run at certain eccentricity and attitude angle in order to take part of the loads, but the magnetic bearing would attempt to force the journal to the reference position at all times while using a conventional PID controller. Therefore, it is necessary to design a new control algorithm to overcome the contradictions. In this paper, the steady-state characteristics of a hybrid foil-magnetic bearing were analyzed. Then a searching algorithm was presented and a steady-state controller was designed to determine the steady-state working position of the hybrid foil-magnetic bearings. Finally, simulations were done to verify performances of the searching algorithm and designed steady-state controller, and the results show its validity.
Development of Steam Turbines for State of the Art Combined Cycle Power Plants (CCPP)
Authors: Quinkertz Rainer , Hecker Simon
Published: December 2013

In order to reduce CO2 emissions, reduce capital costs and increase the percentage of renewable energy in the electricity grid, common drivers of fossil power plant evolution continue to be efficiency, increased electricity output and operating flexibility.

For CCPP, the efficiency level has reached more than 60%. Besides new and updated gas turbine frames, an improved bottoming cycle also contributes to this achievement. Without increasing steam temperatures above 565°C, improving steam turbine inner efficiency and enhancing the cold end, the overall efficiency of >60% would not be feasible.

Extensive thermodynamic optimization is required to determine steam temperatures and condenser pressures. In addition, from a design standpoint, an optimum product strategy has to be developed. In order to minimize risks with future designs, both the practical and theoretical experiences from both ultra super critical applications at coal-fired steam power plants as well as from the CCPP steam turbine fleet have to be incorporated. For advanced technologies and components appropriate validation programs have to be defined.

This paper presents the approach being taking to develop steam turbines for CCPP with modern gas turbines and it also displays the operating results of the first unit.

Operational validation included the thermal behaviour of the high and intermediate pressure parts, a new last stage blade for the low pressure turbine and a patented start-up procedure. In particular, the paper focuses on the validation of three dimensional CFD calculations of the high and intermediate pressure turbine.
Effect of Flow Inclination on Wind Turbine Performance
Authors: Tsalicoglou C. , Barber S. , Chokani N. , Abhari R. S.
Published: December 2013

This work examines the effect of flow inclination on the performance of a stand-alone wind turbine and of wind turbines operating in the wakes of upstream turbines. The experimental portion of this work, which includes performance and flow-field measurements, is conducted in the ETH dynamically-scaled wind turbine test facility, with a wind turbine model that can be inclined relative to the incoming flow. The performance of the wind turbine is measured with an in-line torque-meter and a 5-hole steady-state probe is used to detail the inflow and wake flow of the turbine. Measurements show that over a range of tip-speed ratios of 4–7.5, the power coefficient of a wind turbine with an incoming flow of 15-degrees inclination decreases on average by 7% relative to the power coefficient of a wind turbine with a non-inclined incoming flow. Flowfield measurements show that the wake of a turbine with an inclined incoming flow is deflected; the deflection angle is approximately 6-degrees for an incoming flow with 15-degrees inclination. The measured wake profiles are used as inflow profiles for a Blade Element Momentum code in order to quantify the impact of flow inclination on the performance of downstream wind turbines. In comparison to the case without inclination in the incoming flow, the combined power output of two aligned turbines with incoming inclined flow decreases by 1%, showing that flow inclination in complex terrain does not significantly reduce the energy production.
Effect of Humidity Level on the Creep Properties of Alloy 903 at 650°C
Authors: Dryepondt Sebastien , Mitchell Ryan D. , Pint Bruce A.
Published: December 2013

Alloy 903 (FeNiCo+Nb) is currently used for certain components in industrial gas turbines for low coefficient of thermal expansion applications. A variance in creep behavior for material quality control evaluations suggested a possible effect of moisture level on stress rupture properties. To investigate the role of water vapor on the creep properties of alloy 903, controlled laboratory experiments were conducted at 650°C with 0 to 100% relative humidity. The water content was controlled by flowing dry air through a water bath at a constant temperature. A significant decrease of lifetime was observed in the presence of water vapor, which is likely related to grain boundary embrittlement by the inward diffusion of hydrogen. The increase of the microstructure grain aspect ratio by different forging processes generally improved the rupture lifetime and elongation in air. However, all specimens had reduced lifetime in the presence of water vapor despite the microstructure grain aspect ratios.
Probabilistic Mistuning Assessment Using Nominal and Geometry Based Mistuning Methods
Authors: Beck Joseph A. , Brown Jeffrey M. , Cross Charles J. , Slater Joseph C.
Published: December 2013

Two deterministic mistuning models utilizing component mode synthesis methods are used in a Monte Carlo simulation to generate mistuned response distributions for a geometrically perturbed Integrally Bladed Rotor. The first method, a frequency-perturbation approach with a nominal mode approximation used widely in academia and industry, assumes airfoil geometric perturbations alter only the corresponding modal stiffnesses while its mode shapes remain unaffected. The mistuned response is then predicted by a summation of the nominal modes. The second method, a geometric method utilizing non-nominal modes, makes no simplifying assumptions of the dynamic response due to airfoil geometric perturbations, but requires recalculation of each airfoil eigen-problem. A comparison of the statistical moments of the mistuned response distributions and prediction error is given for three different frequency ranges and engine order excitations. Further, the response distributions are used for a variety of design and testing scenarios to highlight impacts of the frequency-based approach inaccuracy. Results indicate the frequency-based method typically provides conservative response levels.
One Explanation for 2N Response due to Misalignment in Rotors Connected by Flexible Couplings
Authors: Avendano Raul D. , Childs Dara W.
Published: December 2013

Misalignment in turbomachinery is commonly thought to produce two-times-running-speed (2N) response. The source of 2N vibration response was investigated, starting with the development of finite-element models for three flexible disc-pack couplings (4-bolt, 6-bolt, and 8-bolt couplings). Parallel and angular misalignments were analyzed. The resultant lateral stiffness terms had 1N, 2N, and 3N harmonic components versus the shaft rotation angle. The 4-bolt coupling had large 1N stiffness components under angular and parallel misalignment. The 6-bolt coupling had only a 1N reaction component under angular misalignment, while parallel misalignment showed a strong 2N reaction component, larger than either the 1N or 3N components. Under angular misalignment, the 8-bolt model produced large 1N reaction components. Under parallel misalignment, it produced 1N, 2N, and 3N components that were similar in magnitude. All the couplings behaved linearly in the range studied.

Some experts attribute observed 2N response to nonlinear bearing forces produced by bearings at high unit loads. Static tests for a 5-pad tilting-pad journal bearing with unit loads up to 34.5bars produced small 2N motion components that did not grow with increasing unit load.

A Jeffcott-rotor model with shaft stiffness orthotropy and a fixed-direction side load predicts that 2N response depends on three related factors: (1) the degree of orthotropy (the 1N stiffness variation magnitude), (2) the magnitude of the side load, and (3) the relative ratio of running speed to rotor 1st natural frequency, (ω/ωn). The 2N response magnitude is largest when ω is close to ωn/2. The side load is required to create 2N response due to shaft stiffness orthotropy. Misaligned couplings create precisely the same (very old) physical model as a two-pole turbogenerator rotor with a gravity side load (gravity critical speed).

The response of a 2-rotor/coupling system with parallel and angular misalignment was simulated using a time-transient code. When the frequency ratio was 0.5, the system response with the 4-bolt and 6-bolt coupling had a synchronous 1N component as well as a significant 2N component. Parallel misalignment at a coupling produces stiffness orthotropy and a fixed-direction side load. For ranges of running speed near ωn/2, these two elements can combine to produce 2N response.
Design Study of Dovetail Geometries of Turbine Blades Using Abaqus and Isight
Authors: Hahn Youngwon , Cofer John I.
Published: December 2013

Blades in gas and steam turbines continually face more challenging requirements for high reliability and efficiency. In order to meet these challenges in an increasingly competitive marketplace, blade design engineers are always looking for more efficient ways to design the blades in the shortest possible time and at the lowest possible cost while meeting multiple design objectives. In this paper, several design studies are performed using Abaqus and Isight to optimize the minimum contact pressure and stress around the dovetail of a typical turbine blade in order to achieved desired goals for stress levels.

First, nine design parameters describing the dimensions of the dovetail are set up in a Python script which can be executed in Abaqus/CAE. The Python script generates the entire finite element model including boundary and loading conditions in Abaqus/CAE. A nonlinear static analysis considering centrifugal loading is performed in this work. After setting up the workflow using the Python script and Abaqus/CAE, Isight is used to automate the process to achieve the optimized dimensions of the dovetail.

The optimization is performed in two steps. First, a surrogate model using the Optimal Latin Hypercube approximation method is created using tools in Isight. In this step, the surrogate model is used to determine the optimum values of the design variables, as well as the sensitivity of the design to the selected design variables. It also can be observed that the design is especially sensitive to five of the design variables. In the second step of the optimization, the five design variables to which the design is most sensitive are selected for further optimization by setting the other design variables to the optimized values obtained in the first step of the optimization. In this second step, several different optimization methods supported in Isight are used, including the NSGA-II non-dominated sorting genetic algorithm, Downhill Simplex, and an evolutionary optimization algorithm. Results from these methods are compared with those obtained using other common optimization methods in Isight.