Surface Measurements And Predictions Of Full-coverage Film Cooling

Full-coverage film cooling is investigated both experimentally and numerically. First, surface measurements local of adiabatic film cooling effectiveness and heat transfer augmentation for four different arrays are described. Reported next is a comparison between two very common turbulence models, Realizable k-ε and SST k-ω, and their ability to predict local film cooling effectiveness throughout a full-coverage array. The objective of the experimental study is the quantification of local heat transfer augmentation and adiabatic film cooling effectiveness for four surfaces cooled by large, both in hole count and in non-dimensional spacing, arrays of film cooling holes. The four arrays are of two different hole-to-hole spacings (P/D = X/D = 14.5, 19.8) and two different hole inclination angles (α = 30◦ , 45◦ ), with cylindrical holes compounded relative to the flow (β = 45◦ ) and arranged in a staggered configuration. Arrays of up to 30 rows are tested so that the superposition effect of the coolant film can be studied. In addition, shortened arrays of up to 20 rows of coolant holes are also tested so that the decay of the coolant film following injection can be studied. Levels of laterally averaged effectiveness reach values as high as ¯η = 0.5, and are not yet at the asymptotic limit even after 20 − 30 rows of injection for all cases studied. Levels of heat transfer augmentation asymptotically approach values of h/h0 ≈ 1.35 rather quickly, iii only after 10 rows. It is conjectured that the heat transfer augmentation levels off very quickly due to the boundary layer reaching an equilibrium in which the perturbation from additional film rows has reached a balance with the damping effect resulting from viscosity. The levels of laterally averaged adiabatic film cooling effectiveness far exceeding ¯η = 0.5 are much higher than expected. The heat transfer augmentation levels off quickly as opposed to the film effectiveness which continues to rise (although asymptotically) at large row numbers. This ensures that an increased row count represents coolant well spent. The numerical predictions are carried out in order to test the ability of the two most common turbulence models to properly predict full coverage film cooling. The two models chosen, Realizable k − ε (RKE) and Shear Stress T ransport k − ω (SSTKW), are both two-equation models coupled with Reynolds Averaged governing equations which make several gross physical assumptions and require several empirical values. Hence, the models are not expected to provide perfect results. However, very good average values are seen to be obtained through these simple models. Using RKE in order to model full-coverage film cooling will yield results with 30% less error than selecting SSTKW

Lightning Induced Overvoltages Caused by Non-Vertical Lightning and Earth Current Behavior

RÉSUMÉ Les surtensions induites par la foudre deviennent un sujet important dans le domaine des réseaux de distribution. Une évaluation précise des tensions induites est très essentielle pour la protection contre la foudre. Un problème des évaluations existantes est qu'un canal de foudre vertical et une terre parfaitement conductrice, qui ne sont pas réalistes, sont supposés dans la plupart des cas. Ces hypothèses nécessitent des recherches plus approfondies pour une évaluation précise de la tension induite. L'objectif principal de cette thèse est de révéler et résumer (1) les influences de la foudre non verticale sur les surtensions induites par la foudre dans les réseaux de distribution et (2) le comportement du courant de foudre dans une terre avec pertes, pour une évaluation précise des tensions induites. Pour (1), les circuits du modèle FDTD pour représenter la foudre non verticale sont construits et les influences de la foudre non verticale sur les tensions induites sont étudiées avec diverses conditions telles que la forme d'onde du courant de foudre, la géométrie du canal de foudre, l'état de la terre et la distribution ligne, etc. De plus, le mécanisme des changements est discuté en comparaison avec une formule analytique. Il est clair que l'inclinaison de la foudre vers la ligne augmente considérablement les tensions induites. Les tensions atteignent plus de deux fois plus que celles du boîtier vertical. L'inclinaison le long de la ligne ne montre que des différences mineures sur la tension de crête alors qu'elle rend le profil de tension le long de la ligne asymétrique. Des tendances similaires sont observées même lorsque l'on suppose une ligne triphasée réaliste avec mises à la terre et parafoudres. Les connaissances acquises dans cette thèse indiquent clairement que les influences de la foudre non verticale doivent être prises en compte pour une évaluation précise des surtensions induites par la foudre. Pour (2), les circuits du modèle FDTD sont validés par rapport aux résultats expérimentaux dans des articles publiés, et les influences de la distance de la foudre, de la position de la foudre sur la ligne, de la structure de mise à la terre, de la position du fil neutre, etc. sont étudiées par la FDTD. Il est confirmé que le couplage électromagnétique foudre-terre influence le courant de surface de la terre et l'augmentation du potentiel de terre (GPR) qui en résulte pendant une période transitoire, et donc l'inclinaison de la foudre rend le courant et le GPR différents du cas vertical.----------ABSTRACT Lightning induced overvoltages are becoming one of the most important topics in the field of distribution networks. An accurate evaluation of the induced voltages is essential for the design of lightning protection. One problem of existing evaluations is that a vertical lightning channel and a perfectly conducting earth, which are not realistic, are assumed in most cases. These assumptions require further careful investigations for an accurate induced-voltage evaluation. The main objective of this thesis is to reveal and summarize (1) the influences of non-vertical lightning on the lightning induced overvoltages in the distribution systems and (2) lightning current behavior in a lossy earth, for an accurate evaluation of the induced voltages. For (1), FDTD model circuits to represent the non-vertical lightning are built and influences of the non-vertical lightning on the induced voltages are investigated with various conditions such as lightning current waveform, lightning-channel geometry, earth condition, and distribution-line configuration etc. In addition, the mechanism of the changes is discussed in comparison with an analytical formula. It is made clear that lightning inclination toward the line significantly increases the induced voltages. The voltages reach values that are more than two times larger than those of the vertical case. The inclination along the line shows only minor differences on the peak voltage while it makes the voltage profile along the line asymmetric. Similar trends are observed even when a realistic three-phase line with groundings and arresters is assumed. The knowledge obtained in this thesis clearly indicates that the influences of non-vertical lightning should be considered for an accurate evaluation of lightning induced overvoltages. For (2), FDTD model circuits are validated in comparison with experimental results in published papers, and influences of lightning distance, lightning-struck position to the line, grounding structure, neutral wire position etc. are investigated by FDTD. It is confirmed that lightning-to-earth electromagnetic coupling influences the earth surface current and resulting ground potential rise (GPR) in a transient period, and thus the lightning inclination makes the current and GPR different from the vertical case. The coupling effect should be considered for accurate earth current and GPR studies. When there is a distribution line nearby, a large portion of lightning current flows into the nearby line via its groundings. Although the current itself does not make a large difference to the induced voltage, it would cause lightning surge problems in the line

Asymptotic behavior of the number of solutions for non-Archimedean Diophantine approximations with restricted denominators

AbstractWe consider metric results for the asymptotic behavior of the number of solutions of Diophantine approximation inequalities with restricted denominators for Laurent formal power series with coefficients in a finite field. We especially consider approximations by rational functions whose denominators are powers of irreducible polynomials, and study the strong law of large numbers for the number of solutions of the inequalities under consideration

The peroxisome counteracts oxidative stresses by suppressing catalase import via Pex14 phosphorylation

Most of peroxisomal matrix proteins including a hydrogen peroxide (H2O2)-decomposing enzyme, catalase, are imported in a peroxisome-targeting signal type-1 (PTS1)-dependent manner. However, little is known about regulation of the membrane-bound protein import machinery. Here, we report that Pex14, a central component of the protein translocation complex in peroxisomal membrane, is phosphorylated in response to oxidative stresses such as H2O2 in mammalian cells. The H2O2-induced phosphorylation of Pex14 at Ser232 suppresses peroxisomal import of catalase in vivo and selectively impairs in vitro the interaction of catalase with the Pex14-Pex5 complex. A phosphomimetic mutant Pex14-S232D elevates the level of cytosolic catalase, but not canonical PTS1-proteins, conferring higher cell resistance to H2O2. We thus suggest that the H2O2-induced phosphorylation of Pex14 spatiotemporally regulates peroxisomal import of catalase, functioning in counteracting action against oxidative stress by the increase of cytosolic catalase

Influence of Ultrasonic-Shot Peening on Bending Fatigue of TiNi Shape Memory Alloy

The fatigue property of shape memory alloy (SMA) is one of the most important subjects in view of evaluating functional characteristics of SMA elements. In the present study，ultrasonic shot peening (USP) was applied to induce compressive residual stress on the surface layer of TiNi SMA tape and the influence of USP on the bending fatigue life was investigated. The fatigue life of USP-treated tape is longer than that of the as-received tape. The fatigui life of the tape USP-treated with high coverage is longer than that with low coverage. The fatigue life of the USP-treated tape increases in proportion to the hardness on the surface of the tape

Minimum oxygen cost of human walking with geometrically similar leg movements

The mechanism by which the expenditure of oxygen to walk per unit distance at an intermediate speed is minimized, by definition optimal walking, was investigated to characterize optimal walking in humans with variations in individual walking speeds. Oxygen uptake and step rate（SR）were measured among 7 young male subjects walking at an increasing speed from 16.7 to 131.7 m min−1 with 5 m min−1 increments every 1 min on a level treadmill. Measurements of leg length（L）were also made and step length（SL）was calculated by dividing walking speed by SR. The hip joint angle（θ）was calculated as a function of both L and SL such that θ＝2sin−［1 SL（／ 2L）］ deduced from a mathematical geometrically similar model of pendulum−like legs. The minimum oxygen cost to walk per unit distance for each subject was observed over a wide range of speeds from 60 to 100 m min−1.However, the oxygen cost of walking for all the subjects was minimized during a step cycle through a hip−joint angle of about 46 deg in the astride position, regardless of L. The stifflegged model demonstrated that the pathway of the trunk during optimal walking with a swing leg angle of 46 deg was approximately maintained at an even level by the counteracting effects of the leg decline and the heel rise. These results suggest that the minimum oxygen cost of transport during optimal walking was achieved by the mechanism underlying the maximum interchange between the gravitational−potential and kinetic energy for the body with an even level of the trunk that reduces extra muscular work needed against internal and external resistance, as well as against gravit

Risk of female athlete triad development in Japanese collegiate athletes is related to sport type and competitive level

Introduction: Menstrual dysfunction, musculoskeletal injury, and poor nutrition combine to form the female athlete triad (FAT), which results in serious health consequences for affected athletes. To this point, the risk factors of this phenomenon have not been fully explored in Japanese female college athletes. Additionally, the effect of competitive level on FAT risk factors has also not been reported. Therefore, we aimed to examine FAT risk factors in Japanese female athletes of various sports as well as examine the impact of competitive level on FAT.Methods: A Japanese-language survey was completed by 531 athletes and 20 nonathletes at two Japanese universities and answers with regard to menstrual status, musculoskeletal injury, nutrition, and other variables were analyzed based on classification of the sports into nine distinct groups based on activity type. Sport intensity, training volume, and competitive levels were used to further classify each sport. One-way ANOVA and the Bonferroni post hoc test using SPSS were carried out to analyze significance for relationships between sport intensity and FAT risk factors. Additionally, the relationship between competitive level and FAT risk factors was analyzed by ANOVA and Bonferroni post hoc tests.Results: Sport intensity was positively correlated with a delay in menarche as well as dysmenorrhea and poor nutrition while musculoskeletal injury was correlated with repetitive, high-training volume sports. Lower competitive levels increased dysmenorrhea but did not impact injury status or nutrition.Conclusion: Sport intensity and training volume, but not competitive level, are the critical factors affecting FAT risk in Japanese female college athletes