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Auswahl der wissenschaftlichen Literatur zum Thema „Equivalent temperature gradient“
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Zeitschriftenartikel zum Thema "Equivalent temperature gradient"
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Baumann, Hannes, und David O. Conover. „Adaptation to climate change: contrasting patterns of thermal-reaction-norm evolution in Pacific versus Atlantic silversides“. Proceedings of the Royal Society B: Biological Sciences 278, Nr. 1716 (05.01.2011): 2265–73. http://dx.doi.org/10.1098/rspb.2010.2479.
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How organisms may adapt to rising global temperatures is uncertain, but concepts can emerge from studying adaptive physiological trait variations across existing spatial climate gradients. Many ectotherms, particularly fish, have evolved increasing genetic growth capacities with latitude (i.e. countergradient variation (CnGV) in growth), which are thought to be an adaptation primarily to strong gradients in seasonality. In contrast, evolutionary responses to gradients in mean temperature are often assumed to involve an alternative mode, ‘thermal adaptation’. We measured thermal growth reaction norms in Pacific silverside populations ( Atherinops affinis ) occurring across a weak latitudinal temperature gradient with invariant seasonality along the North American Pacific coast. Instead of thermal adaptation, we found novel evidence for CnGV in growth, suggesting that CnGV is a ubiquitous mode of reaction-norm evolution in ectotherms even in response to weak spatial and, by inference, temporal climate gradients. A novel, large-scale comparison between ecologically equivalent Pacific versus Atlantic silversides ( Menidia menidia ) revealed how closely growth CnGV patterns reflect their respective climate gradients. While steep growth reaction norms and increasing growth plasticity with latitude in M. menidia mimicked the strong, highly seasonal Atlantic coastal gradient, shallow reaction norms and much smaller, latitude-independent growth plasticity in A. affinis resembled the weak Pacific latitudinal temperature gradient.
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Thomas, Carl M., und David M. Schultz. „What are the Best Thermodynamic Quantity and Function to Define a Front in Gridded Model Output?“ Bulletin of the American Meteorological Society 100, Nr. 5 (Mai 2019): 873–95. http://dx.doi.org/10.1175/bams-d-18-0137.1.
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AbstractFronts can be computed from gridded datasets such as numerical model output and reanalyses, resulting in automated surface frontal charts and climatologies. Defining automated fronts requires quantities (e.g., potential temperature, equivalent potential temperature, wind shifts) and kinematic functions (e.g., gradient, thermal front parameter, and frontogenesis). Which are the most appropriate to use in different applications remains an open question. This question is investigated using two quantities (potential temperature and equivalent potential temperature) and three functions (magnitude of the horizontal gradient, thermal front parameter, and frontogenesis) from both the context of real-time surface analysis and climatologies from 38 years of reanalyses. The strengths of potential temperature to identify fronts are that it represents the thermal gradients and its direct association with the kinematics and dynamics of fronts. Although climatologies using potential temperature show features associated with extratropical cyclones in the storm tracks, climatologies using equivalent potential temperature include moisture gradients within air masses, most notably at low latitudes that are unrelated to the traditional definition of a front, but may be representative of a broader definition of an airmass boundary. These results help to explain previously published frontal climatologies featuring maxima of fronts in the subtropics and tropics. The best function depends upon the purpose of the analysis, but Petterssen frontogenesis is attractive, both for real-time analysis and long-term climatologies, in part because of its link to the kinematics and dynamics of fronts. Finally, this study challenges the conventional definition of a front as an airmass boundary and suggests that a new, dynamically based definition would be useful for some applications.
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Mohamed, Ashraf R., und Will Hansen. „Effect of Nonlinear Temperature Gradient on Curling Stress in Concrete Pavements“. Transportation Research Record: Journal of the Transportation Research Board 1568, Nr. 1 (Januar 1997): 65–71. http://dx.doi.org/10.3141/1568-08.
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Temperature and moisture gradients can lead to significant tensile stresses at the slab top and bottom. Current techniques for assessing the internal stresses due to such gradients are based on the assumption that temperature and moisture distributions through the slab thickness are linear. However, the actual distributions of such gradients have been found to be highly nonlinear. A new closed form solution technique for calculating the stresses in a pavement slab due to nonlinear gradients is introduced. The analysis is separated into two parts. In the first, an expression is presented for calculating the self-equilibrated stresses within a cross section due to internal restraint (i.e., satisfying equilibrium conditions and continuity of the strain field within the cross section). These stresses are independent of slab dimensions and boundary conditions. In the second, the stresses due to external restraint (i.e., self-weight and subgrade reaction) are calculated using an equivalent linear temperature gradient obtained from the first part and existing closed form solutions by Westergaard or Bradbury. The solution to this step includes slab length and boundary conditions. Total internal stresses due to nonlinear gradients are obtained by using the superposition principle. The methodology has been applied to field data from two studies in which the temperature profiles were recorded throughout a 24-hr period. Linear gradient solution methods cannot accurately predict the curling stresses in concrete pavements. This is especially pronounced during nighttime and early morning hours, during which nonlinear analysis predicts tensile stress in both the slab bottom and top before the application of any traffic loading.
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Huang, Zi Qian, und Qing Lian Xie. „Study on Thermal Stresses of Cylinder Liner’s Fabrication Using FEM Analysis“. Advanced Materials Research 189-193 (Februar 2011): 2058–61. http://dx.doi.org/10.4028/www.scientific.net/amr.189-193.2058.
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In the process of casing casting, great temperature gradient leads to contraction deformation of cylinder liner, which influences the quality of products. The thermal stresses caused by temperature gradient were analyzed by finite element method. The numerical results show that high equivalent Von Mises stress(242MPa) occurs in the surface zone of the cylinder liner as Cooling down to room temperature within pipe die ,also there is plastic deformation in the internal and external surface zone. Reducing the cooling speed, decreasing the temperature gradient and aging can reduce the influence of thermal stresses.
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Gao, Xiang, Ya Wei und Wei Huang. „Strain-based equivalent temperature gradient in concrete pavement and comparison with other quantification methods“. Road Materials and Pavement Design 18, Nr. 6 (17.08.2016): 1460–72. http://dx.doi.org/10.1080/14680629.2016.1218788.
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Billon, Noelle, Jean Marc Haudin, Camille Vallot und Charles Babin. „Stretch Blow Moulding of Mineral Filled PET“. Key Engineering Materials 504-506 (Februar 2012): 1099–104. http://dx.doi.org/10.4028/www.scientific.net/kem.504-506.1099.
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Injection Stretch Blow mouldng is a two step processing that was designed and optimized mainly using unfilled PET resins. This study focuses on stretch blow moulding of a PET filled with a few percent of sub micronic mineral fillers. Based on DSC, DMA, tensile tests as well as blowing on prototype machine main effects of fillers are analysed. It is demonstrated that fillers increases crystallization kinetics resulting in a reduction of the processing range. Difference in strain hardening induced by fillers makes it necessary to adjust blowing temperature. However main effect occurs during heating phase. Temperature within the perform is much less homogeneous than in PET making thermal gradient totally different if heating protocole is kept unchanged. Once heating is controlled to reach to equivalent thermal gradients as for PET blowing is possible and rather equivalent to that of pure PET.
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Domine, F., S. Morin, E. Brun, M. Lafaysse und C. M. Carmagnola. „Seasonal evolution of snow permeability under equi-temperature and temperature-gradient conditions“. Cryosphere 7, Nr. 6 (18.12.2013): 1915–29. http://dx.doi.org/10.5194/tc-7-1915-2013.
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Abstract. The permeability (K) of snow to air flow affects the transfer of energy, water vapor and chemical species between the snow and the atmosphere. Yet today little is known about the temporal evolution of snow permeability as a function of metamorphic regime. Furthermore, our ability to simulate snow permeability over the seasonal evolution of a snowpack has not been tested. Here we have measured the evolution of snow permeability in a subarctic snowpack subject to high temperature-gradient (TG) metamorphism. We have also measured the evolution of the same snowpack deposited over tables so that it evolved in the equi-temperature (ET) regime. Permeability varies in the range 31 × 10−10 (ET regime) to 650 × 10−10 m2 (TG regime). Permeability increases over time in TG conditions and decreases under ET conditions. Using measurements of density ρ and of specific surface area (SSA), from which the equivalent sphere radius r is determined, we show that the equation linking SSA, density ρ and permeability, K = 3.0 r2 e(−0.013 ρ) (with K in m2, r in m and ρ in kg m−3) obtained in a previous study adequately predicts permeability values. The detailed snowpack model Crocus is used to simulate the physical properties of the TG and ET snowpacks. For the most part, all variables are well reproduced. Simulated permeabilities are up to a factor of two greater than measurements for depth hoar layers, which we attribute to snow microstructure and its aerodynamic properties. Finally, the large difference in permeabilities between ET and TG metamorphic regimes will impact atmosphere-snow energy and mass exchanges. These effects deserve consideration in predicting the effect of climate change on snow properties and snow–atmosphere interactions.
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Domine, F., S. Morin, E. Brun und M. Lafaysse. „Seasonal evolution of snow permeability under equi-temperature and temperature-gradient conditions“. Cryosphere Discussions 7, Nr. 3 (17.06.2013): 2725–59. http://dx.doi.org/10.5194/tcd-7-2725-2013.
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Abstract. The permeability K of snow to air flow affects the transfer of energy, water vapor and chemical species between the snow and the atmosphere. Yet today little is known of the temporal evolution of snow permeability as a function of metamorphic regime. Furthermore, our ability to simulate snow permeability over the seasonal evolution of a snowpack has not been tested. Here we have measured the evolution of snow permeability in a subarctic snowpack subject to high temperature-gradient (TG) metamorphism. We have also measured the evolution of the same snowpack deposited over tables so that it evolved in the equi-temperature (ET) regime. Permeability varies in the range 31 × 10–10 (ET regime) to 650 × 10–10 m2 (TG regime). Permeability increases over time in TG conditions and decreases under ET conditions. Using measurements of density ρ and of specific surface area (SSA), from which the equivalent sphere radius r is determined, we show that the equation linking SSA, density ρ and permeability, K = 3.0 r2 e(–0.013 ρ) (with K in m2, r in m and ρ in kg m−3) obtained in a previous study adequately predicts permeability values. The detailed snowpack model Crocus is used to simulate the physical properties of the TG and ET snowpacks. For the most part, all variables are well reproduced. Simulated permeabilities are up to a factor of two greater than measurements for depth hoar layers, which we attribute to snow microstructure, as the aerodynamic properties of hollow depth hoar crystals are different from those of spheres. Finally, the large difference in permeabilities between ET and TG metamorphic regimes will impact atmosphere-snow energy and mass exchanges and these effects deserve consideration in predicting the effect of climate change on snow properties and snow-atmosphere interactions.
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Riley, Jeffrey B., Scott B. Hardin, Brad A. Winn und Michael B. Hurdle. „In vitro comparison of cavoatrial (dual stage) cannulae for use during cardiopulmonary bypass“. Perfusion 1, Nr. 3 (Juli 1986): 197–204. http://dx.doi.org/10.1177/026765918600100308.
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An in vitro normothermic, human blood test circuit was constructed to test four cavoatrial (dual stage) cannulae, their right atrial baskets and IVC tips for venous return flow versus siphon drainage gradient. Simulated patient CVP and ECC oxygenator/venous reservoir inlet resistance were held constant at 10 mmHg and 15 mmHg respectively as siphon gradient was varied from 0 centimetres (cm) to -40 cm of blood. At the same siphon gradients between -10 and -40 cm, the Research Medical, Inc. (RMI) VV 3651 L, its right atrial (RA) basket, and IVC tip yielded significantly greater flows than the Sarns Inc. 12340, CR Bard, Inc. 1969, and the RMI VV 3651 B cannula, except the RMI VV 3651 B RA basket was equivalent to the VV 3651 L basket. The 12340 and 1969 baskets were equivalent. The 1969 IVC tip was superior to the 12340 tip. The mechanism for CPB venous collapse and flutter, its treatment, and the importance of monitoring myocardial temperature, as well as assuring great vein and cardiac decompression during cavoatrial cannulation and aortic cross clamping are outlined.
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Yu, Peng, Ruiqing Li, Dapeng Bie, Xiancai Liu, Xiaomin Yao und Yahui Duan. „Precise Simulation of Heat-Flow Coupling of Pipe Cooling in Mass Concrete“. Materials 14, Nr. 18 (08.09.2021): 5142. http://dx.doi.org/10.3390/ma14185142.
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For a long time, temperature control and crack prevention of mass concrete is a difficult job in engineering. For temperature control and crack prevention, the most effective and common-used method is to embed cooling pipe in mass concrete. At present, there still exists some challenges in the precise simulation of pipe cooling in mass concrete, which is a complex heat-flow coupling problem. Numerical simulation is faced with the problem of over-simplification and inaccuracy. In this study, precise simulation of heat-flow coupling of pipe cooling in mass concrete is carried out based on finite element software COMSOL Multiphysics 5.4. Simulation results are comprehensively verified with results from theoretical solutions and equivalent algorithms, which prove the correctness and feasibility of precise simulation. Compared with an equivalent algorithm, precise simulation of pipe cooling in mass concrete can characterize the sharp temperature gradient around cooling pipe and the temperature rise of cooling water along pipeline more realistically. In addition, the cooling effects and local temperature gradient under different water flow (0.60 m3/h, 1.20 m3/h, and 1.80 m3/h) and water temperature (5 °C, 10 °C, and 15 °C) are comprehensively studied and related engineering suggestions are given.
Dissertationen zum Thema "Equivalent temperature gradient"
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Kovaľová, Alžbeta. „Kvantifikace turbulence pomocí ekvivalentního teplotního gradientu“. Master's thesis, Vysoké učení technické v Brně. Fakulta elektrotechniky a komunikačních technologií, 2021. http://www.nusl.cz/ntk/nusl-442412.
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The diploma thesis is focused on the optical beam propagating in the atmosphere in a wireless communication optical link. The first part of the work explains the atmospheric transmission media with turbulence and its effects on reliability of the optical system. The second part introduces methods for turbulence determination based on a statistical approach to turbulence quantification are introduced. In the third part, method of equivalent temperature gradient is described with the advantage of immediate turbulence evaluation. The output of this thesis is the model of turbulent environment formed by the optical elements. Analysis of turbulent properties and non-reciprocal nature of turbulent channel is processed by a 2D simulator based on the mentioned model and method of equivalent temperature gradient.
Bücher zum Thema "Equivalent temperature gradient"
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Zeitlin, Vladimir. Rotating Shallow-Water model with Horizontal Density and/or Temperature Gradients. Oxford University Press, 2018. http://dx.doi.org/10.1093/oso/9780198804338.003.0014.
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The derivation of rotating shallow-water equations by vertical averaging and columnar motion hypothesis is repeated without supposing horizontal homogeneity of density/potential temperature. The so-called thermal rotating shallow-water model arises as the result. The model turns to be equivalent to gas dynamics with a specific equation of state. It is shown that it possesses Hamiltonian structure and can be derived from a variational principle. Its solution at low Rossby numbers should obey the thermo-geostrophic equilibrium, replacing the standard geostrophic equilibrium. The wave spectrum of the model is analysed, and the appearance of a whole new class of vortex instabilities of convective type, resembling asymmetric centrifugal instability and leading to a strong mixing at nonlinear stage, is demonstrated.
Buchteile zum Thema "Equivalent temperature gradient"
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Fedkin, Valentin V., Theodore D. Burlick, Mary L. Leech, Andrey A. Shchipansky, Peter M. Valizer und W. G. Ernst. „Petrotectonic origin of mafic eclogites from the Maksyutov subduction complex, south Ural Mountains, Russia“. In Plate Tectonics, Ophiolites, and Societal Significance of Geology: A Celebration of the Career of Eldridge Moores. Geological Society of America, 2021. http://dx.doi.org/10.1130/2021.2552(09).
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ABSTRACT The Maksyutov complex is a mid- to late-Paleozoic high- to ultrahigh-pressure (HP-UHP) eclogite-bearing subduction zone terrane in the south Ural Mountains. Previous reports of radial fractures emanating from quartz inclusions in garnet, omphacite, and glaucophane, cuboid graphite pseudomorphs after matrix diamond, and microdiamond aggregates preserved in garnet identified by Raman spectroscopy indicate that parts of the complex were subjected to physical conditions of ∼600 °C and >2.8 GPa for coesite-bearing rocks, and >3.2 GPa for diamond-bearing rocks. Peak UHP eclogite-facies metamorphism took place at ca. 385 Ma, and rocks were exhumed through retrograde blueschist-facies conditions by ca. 360 Ma. Bulk analyses of 18 rocks reflect the presence of mid-oceanic-ridge basalt (MORB), oceanic-island basalt (OIB), and island-arc tholeiite (IAT) basaltic and andesitic series plus their metasomatized equivalents. To more fully constrain the petrotectonic evolution of the complex, we computed isochemical phase equilibria models for representative metabasites in the system Na2O-CaO-K2O-FeO-MgO-Al2O3-SiO2-H2O-TiO2 based on our new bulk-rock X-ray fluorescence (XRF) data. Both conventional Fe-Mg exchange thermometry and phase equilibrium modeling result in higher peak equilibrium temperatures than were previously reported for the complex. Pseudosection analysis provides minimum P-T conditions of 650–675 °C and 2.4–2.6 GPa for peak assemblages of the least retrogressed Maksyutov eclogites, whereas Fe-Mg exchange thermometry yields temperatures of 750 ± 25 °C for a pressure of 2.5 GPa. We interpret our new P-T data to reflect a thermal maximum reached by the eclogites on their initial decompression-exhumation stage, that defines a metamorphic field gradient; the relict coesite and microdiamond aggregates previously reported testify to pressure maxima that define an earlier prograde subduction zone gradient. The eclogitic Maksyutov complex marks underflow of the paleo-Asian oceanic plate and does not represent subduction of the Siberian cratonal margin.
Konferenzberichte zum Thema "Equivalent temperature gradient"
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Chen, Qingyou. „Effect of temperature gradient on equivalent background input of image intensifier“. In SPIE's International Symposium on Optical Engineering and Photonics in Aerospace Sensing, herausgegeben von Walter A. Flood und Walter B. Miller. SPIE, 1994. http://dx.doi.org/10.1117/12.177954.
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Hudcova, Lucie, und Otakar Wilfert. „Possibilities of Using the Modified Equivalent Temperature Gradient for a Turbulent Atmosphere“. In 2019 Conference on Microwave Techniques (COMITE). IEEE, 2019. http://dx.doi.org/10.1109/comite.2019.8733453.
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Hudcova, Lucie, und Otakar Wilfert. „Quantification of the atmospheric turbulence by the method of the equivalent temperature gradient“. In 2018 28th International Conference Radioelektronika (RADIOELEKTRONIKA). IEEE, 2018. http://dx.doi.org/10.1109/radioelek.2018.8376401.
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Bae, Sungjin. „Calculation of Curvature Using Linear Thermal Gradient“. In 2012 20th International Conference on Nuclear Engineering and the ASME 2012 Power Conference. American Society of Mechanical Engineers, 2012. http://dx.doi.org/10.1115/icone20-power2012-54912.
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Reinforced concrete structures for nuclear power plants are designed for thermal effects. When a structure is subject to transient temperature rise, the temperature distribution in a member becomes nonlinear. Commentary of ACI 349 code provides a method of converting a nonlinear temperature distribution to an equivalent linear temperature distribution in order to facilitate calculating curvature due to temperature change. However, the accuracy of estimated thermal curvatures for concrete sections with a liner plate needs to be examined because the ACI 349 method is based on a pure concrete section. The objective of this paper is to investigate the accuracy of thermal curvatures calculated using the equivalent linear temperature distribution for concrete sections with a liner. Temperature distributions across concrete sections are obtained from heat transfer analyses. Free thermal curvatures are calculated by converting temperature distribution to the equivalent linear temperatures and compared with those from a finite element analysis. Based on the study, the modified expression for linear thermal gradient is proposed which includes the effect of liner on curvatures.
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Chen, Cao, und Xiaojun Yan. „Creep/Fatigue Tests on Full Scale Hollow Turbine Blades Considering Temperature Gradient“. In ASME Turbo Expo 2016: Turbomachinery Technical Conference and Exposition. American Society of Mechanical Engineers, 2016. http://dx.doi.org/10.1115/gt2016-56807.
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Working in a harsh environment with high temperature gas and high rotation speed, hollow turbine blades of gas turbine engine commonly endure both creep damage and low cycle fatigue damage at the same time. It is difficult to predict the life of hollow turbine blades accurately because of a strong coupling effect between creep and low cycle fatigue (creep/fatigue) damage. To address this difficulty, one effective way is to carry out creep/fatigue tests on full scale hollow turbine blades in a bench environment. The present creep/fatigue test methods on full scale hollow turbine blades usually do not consider the temperature gradient between the wall of cooling hole and blade surface. It does not matches the actual working circumstance of hollow turbine blades, under which the temperature gradient at the blade body can reached 150°C or even more higher. This investigation proposes a new experimental setup of creep/fatigue tests on full scale hollow turbine blades, in which real hollow turbine blades are heated by the eddy current induction heating furnace and cooled by cooling air which goes through the hollow blade’s cooling hole. During the tests, the temperature gradient between the wall of cooling holes and blade surfaces were controlled by adjusting the power of eddy current induction heating furnace and the flux of cool-air. Several thermocouples are employed to measure and validate the temperature gradient at the key/critical section, among them three are embed inside the wall of cooling hole by cutting the hollow turbine blade along cooling hole into three parts, and two are glued on the blade’s surface. Tests results show that, when the eddy current induction heating furnace is working stably with an output power of 6.4 Kw and meanwhile the flux of cooling air which goes through the hollow turbine blade’s cooling hole reaches 10 liter per minute, the temperature gradient of the hollow turbine blade at the key/critical section can be well simulated in a bench environment. Eight full scale hollow turbine blades have been tested at four different stress levels in this investigation. The test data are processed to obtain the field life based on equivalent damage principle. The field life data of the hollow turbine blades fits well with that of their flight experience.
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Laval, Philippe, Jean-Baptiste Salmon, Galder Cristobal und Mathieu Joanicot. „Investigating Kinetics of Temperature-Dependent Processes Using Microfluidics“. In ASME 4th International Conference on Nanochannels, Microchannels, and Minichannels. ASMEDC, 2006. http://dx.doi.org/10.1115/icnmm2006-96056.
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We have developed an original microfluidic system to study fast kinetics of temperature-dependent processes in an emulsion. Using flow focusing geometries, aqueous droplets are continuously formed in an oil flow. These droplets, acting as microreactors (100 nL), contain the solution to be investigated, and are formed at high temperature. They flow in a microchannel to a cooled area through a controlled temperature gradient (typically from 60 to 10°C in a few seconds). Along the microchannel, the distance being equivalent to the time thanks to the use of droplets, the kinetics of the process can be followed (from 10 to 300 s). In particular, the microdevice has been used to study the kinetics of crystal nucleation of a solute dispersed in water after a temperature quench.
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Josserand, E., und F. Billon. „Application of Mixed Equivalent Solid and Explicit Hole Models to Analysis of Thick Perforated Plates“. In ASME 2008 Pressure Vessels and Piping Conference. ASMEDC, 2008. http://dx.doi.org/10.1115/pvp2008-61885.
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Confronted with the problem of how to conduct a complete fatigue analysis of the Tube Plate (TP) of Tubular and Shell Heat Exchangers and particularly of the Steam Generators equipping nuclear power plants of the Pressurized Water Reactor type (PWR), analysts have developed a method to analyse stress in perforated flat and thick Tube Plates with square penetration (crate) patterns, and in particular to analyse several specific zones such as the Interface Zones and various Effects, such as the Secondary (or Shell) Thermal Gradient Effect (STG Effect), the Thermal Gradient in the No-Tube Lane Effect (TGL Effect) and their interactions. The benefit of the approach is that it enables to analyze mechanical and thermal stress calculated using a full 3D Finite Element model incorporating an equivalent solid and the different Interface Zones, and allowing simulating the specific Thermo-Mechanical Effects. The Interface Zones (IZs) are those between the perforated and non-perforated area, the STG Effect is due to the strong gradient near the Secondary (or Shell) Side surface, the TGL Effect is produced by a temperature gradient across the No-Tube Lane. The method used for the fatigue analysis is based on a “Partitioning Stress Method” by means of which the stress induced by the various load types — mechanical loads, global thermal loads, local thermal effects (STG and TGL Effects), and local geometrical effects (IZs) — are first treated separately and then recombined with their appropriate Stress Multiplier Functions.
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Yañez Gonzalez, A., C. C. Pilgrim, J. P. Feist, P. Y. Sollazzo, F. Beyrau und A. L. Heyes. „On-Line Temperature Measurement Inside a Thermal Barrier Sensor Coating During Engine Operation“. In ASME Turbo Expo 2014: Turbine Technical Conference and Exposition. American Society of Mechanical Engineers, 2014. http://dx.doi.org/10.1115/gt2014-25936.
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Existing thermal barrier coatings (TBC) can be adapted enhancing their functionalities such that they not only protect critical components from hot gases, but also can sense their own material temperature or other physical properties. The self-sensing capability is introduced by embedding optically active rare earth ions into the thermal barrier ceramic. When illuminated by light the material starts to phosphoresce and the phosphorescence can provide in-situ information on temperature, phase changes, corrosion or erosion of the coating subject to the coating design. The integration of an on-line temperature detection system enables the full potential of TBCs to be realised due to improved accuracy in temperature measurement and early warning of degradation. This in turn will increase fuel efficiency and will reduce CO2 emissions. This paper reviews the previous implementation of such a measurement system into a Rolls-Royce jet engine using dysprosium doped yttrium-stabilised-zirconia as a single layer and a dual layer sensor coating material. The temperature measurements were carried out on cooled and uncooled components on a combustion chamber liner and on nozzle guide vanes respectively. The paper investigates the interpretation of those results looking at coating thickness effects and temperature gradients across the TBC. For the study a specialised cyclic thermal gradient burner test rig was operated and instrumented using equivalent instrumentation to that used for the engine test. This unique rig enables the controlled heating of the coatings at different temperature regimes. A long-wavelength pyrometer was employed detecting the surface temperature of the coating in combination with the phosphorescence detector. A correction was applied to compensate for changes in emissivity using two methods. A thermocouple was used continuously measuring the substrate temperature of the sample. Typical gradients across the coating are less than 1K/μm. As the excitation laser penetrates the coating it generates phosphorescence from several locations throughout the coating and hence provides an integrated signal. The study successfully proved that the temperature indication from the phosphorescence coating remains between the surface and substrate temperature for all operating conditions. This demonstrates the possibility to measure inside the coating closer to the bond coat. The knowledge of the bond coat temperature is relevant to the growth of the thermally grown oxide which is linked to the delamination of the coating and hence determines its life. Further, the data is related to a one dimensional phosphorescence model determining the penetration depth of the laser and the emission. Note: a video of the measurement system can be watched under: [http://www.youtube.com/watch?v=T6uXN1__Z7I].
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Matev, Nayden, Robert A. Ainsworth, Meini Su, Mark Stevens und Alan Jappy. „The Influence of Multiaxial Stress Relaxation on Component Creep Damage Accumulation in Biaxial, Mixed Primary, and Secondary Loading on a Pipe“. In ASME 2020 Pressure Vessels & Piping Conference. American Society of Mechanical Engineers, 2020. http://dx.doi.org/10.1115/pvp2020-21211.
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Abstract Unless detailed inelastic analysis is followed, high temperature codes base creep relaxation during a dwell period within a cycle on the start-of-dwell equivalent stress. The relaxation of the equivalent stress is then taken to be governed by a uniaxial creep law for the material being considered. Elastic follow-up is also included in such calculations. With this approach, only equivalent values of stress and creep strain rate are obtained and the stress multiaxiality is therefore assumed to remain at its initial value as the stress relaxes. The stress drop is limited to a small fraction (typically 20%) of the initial equivalent stress to ensure that this assumption does not lead to significant inaccuracy. This paper reports creep relaxation results for a pipe subjected to a combination of both primary and secondary stresses. The primary stress is generated by an internal pressure and an axial load, which enable different primary biaxial loading conditions to be generated. The secondary stress is through-wall bending in nature, produced by a through-wall temperature gradient, which influences the initial biaxial stress ratio. Several parameters are varied in order to produce relaxation behaviour in the pipe with an associated elastic follow-up. The starting biaxial stress ratio, the creep law power exponent and the amount of secondary stress result in varying degrees of elastic follow-up being present. The biaxial stress ratio is generally found to change as relaxation occurs and a multiaxial ductility approach is used to evaluate the associated effect on creep damage accumulation. This is compared with the creep damage estimated by assuming relaxation is simply controlled by the equivalent stress with no change in multiaxial stress state during relaxation. It is found that significant equivalent stress drops (up to about 40% of the initial value) can be allowed without the simplified equivalent stress approach being inaccurate. The results have been compared with a number of creep damage models to ensure that the conclusions are not sensitive to the detail of the damage model.
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Ogata, Hideki. „Thermohydrodynamic Lubrication Analysis of Slider Bearings With Steps on Bearing Surface“. In ASME/STLE 2009 International Joint Tribology Conference. ASMEDC, 2009. http://dx.doi.org/10.1115/ijtc2009-15144.
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This study focuses on the thermohydrodynamic lubrication analysis of fluid film bearings with step on the surface such as a Rayleigh step bearing. In general, the Reynolds equation does not satisfy the continuity of the fluid velocity components at steps. This discontinuity results in the difficulty to solve the energy equation for the lubricants, because the energy equation needs the velocity components explicitly. The author has solved this problem by introducing the equivalent clearance height and the equivalent gradient of clearance height at steps. These parameters remove the discontinuity of velocity components and the energy equation as well, so that one can solve these equations on all of the bearing surfaces including the step region by finite differential method (FDM). The numerical results of pressure and temperature distributions by the proposed method for a Rayleigh step bearing were compared with the results obtained by a commercial CFD package. These results showed good agreement with each other. This method is extended to 2D unequal grid problems.