The effect of intermittent leg-cuff inflation and intermittent exercise on the tilt table response after ten days bed recumbency
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Vogt, F. B.↗
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Predictions of Separated and Transitional Boundary Layers Under Low-Pressure Turbine Airfoil Conditions Using an Intermittency Transport Equation
A new transport equation for the intermittency factor was proposed to predict separated and transitional boundary layers under low-pressure turbine airfoil conditions. The intermittent behavior of the transitional flows is taken into account and incorporated into computations by modifying the eddy viscosity, mu(sub t), with the intermittency factor, gamma. Turbulent quantities are predicted by using Menter's two-equation turbulence model (SST). The intermittency factor is obtained from a transport equation model, which not only can reproduce the experimentally observed streamwise variation of the intermittency in the transition zone, but also can provide a realistic cross-stream variation of the intermittency profile. In this paper, the intermittency model is used to predict a recent separated and transitional boundary layer experiment under low pressure turbine airfoil conditions. The experiment provides detailed measurements of velocity, turbulent kinetic energy and intermittency profiles for a number of Reynolds numbers and freestream turbulent intensity conditions and is suitable for validation purposes. Detailed comparisons of computational results with experimental data are presented and good agreements between the experiments and predictions are obtained.
Suzen, Y. Bora↗
Predictions of Separated and Transitional Boundary Layers Under Low-Pressure Turbine Airfoil Conditions Using an Intermittency Transport Equation
A new transport equation for the intermittency factor was proposed to predict separated and transitional boundary layers under low-pressure turbine airfoil conditions. The intermittent behavior of the transitional flows is taken into account and incorporated into computations by modifying the eddy viscosity, t , with the intermittency factor, y. Turbulent quantities are predicted by using Menter s two-equation turbulence model (SST). The intermittency factor is obtained from a transport equation model, which not only can reproduce the experimentally observed streamwise variation of the intermittency in the transition zone, but also can provide a realistic cross-stream variation of the intermittency profile. In this paper, the intermittency model is used to predict a recent separated and transitional boundary layer experiment under low pressure turbine airfoil conditions. The experiment provides detailed measurements of velocity, turbulent kinetic energy and intermittency profiles for a number of Reynolds numbers and freestream turbulent intensity conditions and is suitable for validation purposes. Detailed comparisons of computational results with experimental data are presented and good agreements between the experiments and predictions are obtained.
Suzen, Y. B.↗
Magnetic Field Intermittency in the Solar Wind: Parker Solar Probe and SolO Observations Ranging from the Alfvén Region up to 1AU
Parker Solar Probe (PSP) and SolO data are utilized to investigate magnetic field intermittency in the solar wind (SW). Small-scale intermittency (20−100 di) is observed to radially strengthen when methods relying on higher-order moments are considered (SFq; SDK), but no clear trend is observed at larger scales. However, lower-order moment-based methods (e.g., partial variance of increments; PVI) are deemed more appropriate for examining the evolution of the bulk of coherent structures (CSs), PVI ≥ 3. Using PVI, we observe a scale-dependent evolution in the fraction of the data set occupied by CSs, fPVI≥3. Specifically, regardless of the SW speed, a subtle increase is found in fPVI≥3 for ℓ = 20 di, in contrast to a more pronounced radial increase in CSs observed at larger scales. Intermittency is investigated in relation to plasma parameters. Though, slower SW speed intervals exhibit higher fPVI≥6 and higher kurtosis maxima, no statistical differences are observed for fPVI≥3. Highly Alfvénic intervals display lower levels of intermittency. The anisotropy with respect to the angle between the magnetic field and SW flow, ΘVB is investigated. Intermittency is weaker at ΘVB ≈ 0° and is strengthened at larger angles. Considering the evolution at a constant alignment angle, a weakening of intermittency is observed with increasing advection time of the SW. Our results indicate that the strengthening of intermittency in the inner heliosphere is driven by the increase in comparatively highly intermittent perpendicular intervals sampled by the probes with increasing distance, an effect related directly to the evolution of the Parker spiral.
Nikos Sioulas↗
Comprehensive Validation of an Intermittency Transport Model for Transitional Low-Pressure Turbine Flows
A transport equation for the intermittency factor is employed to predict transitional flows under the effects of pressure gradients, freestream turbulence intensities, Reynolds number variations, flow separation and reattachment. and unsteady wake-blade interactions representing diverse operating conditions encountered in low-pressure turbines. The intermittent behaviour of the transitional flows is taken into account and incorporated into computations by modifying the eddy viscosity, Mu(sub t), with the intermittency factor, gamma. Turbulent quantities are predicted by using Menter's two-equation turbulence model (SST). The onset location of transition is obtained from correlations based on boundary-layer momentum thickness, acceleration parameter, and turbulence intensity. The intermittency factor is obtained from a transport model which can produce both the experimentally observed streamwise variation of intermittency and a realistic profile in the cross stream direction. The intermittency transport model is tested and validated against several well documented low pressure turbine experiments ranging from flat plate cases to unsteady wake-blade interaction experiments. Overall, good agreement between the experimental data and computational results is obtained illustrating the predicting capabilities of the model and the current intermittency transport modelling approach for transitional flow simulations.
Suzen, Y. B.↗
Modeling of Flow Transition Using an Intermittency Transport Equation
A new transport equation for intermittency factor is proposed to model transitional flows. The intermittent behavior of the transitional flows is incorporated into the computations by modifying the eddy viscosity, mu(sub t), obtainable from a turbulence model, with the intermittency factor, gamma: mu(sub t, sup *) = gamma.mu(sub t). In this paper, Menter's SST model (Menter, 1994) is employed to compute mu(sub t) and other turbulent quantities. The proposed intermittency transport equation can be considered as a blending of two models - Steelant and Dick (1996) and Cho and Chung (1992). The former was proposed for near-wall flows and was designed to reproduce the streamwise variation of the intermittency factor in the transition zone following Dhawan and Narasimha correlation (Dhawan and Narasimha, 1958) and the latter was proposed for free shear flows and was used to provide a realistic cross-stream variation of the intermittency profile. The new model was used to predict the T3 series experiments assembled by Savill (1993a, 1993b) including flows with different freestream turbulence intensities and two pressure-gradient cases. For all test cases good agreements between the computed results and the experimental data are observed.
Suzen, Y. B.↗
Intermittent turbulence in solar wind from the south polar hole
The magnetic fields measured by the Ulysses spacecraft are used to study solar wind turbulence in the fast solar wind from the south polar hole. The spacecraft was at about 46 deg south latitude and 3.9 AU. For a magnetic field with a Gaussian distribution the power spectrum (second-order structure function) is sufficient to completely characterize the turbulence. However, the actual distribution is non-Gaussian so that the effects of intermittency must be taken into account. The observed spectral exponents include effects of intermittency and cannot be directly compared with the standard second-order spectral theories such as the Kolmogorov and Kraichnan theories. To permit a better comparison of the observations with the theoretical models, we study the structure characteristics of the data. We find the exponents of the second-order structure functions (power spectra) and the higher-order normalized structure functions for the components of the magnetic fields. We show that these sets of exponents can be approximately described by two basic numbers: the spectral exponent and the intermittency exponent. The intermittency exponent characterizes correlation properties of the energy cascade from large to small scales. Before comparing the observations to the theoretically expected values, a reduction must be made to the observed spectral exponent. The amount of the reduction depends on both the intermittency exponent and the model of the energy cascade assumed in the turbulence theory. We reduce the measured spectral indices according to a simple model for Alfven turbulence that is described here. We then compare our reduced spectral indices with second-order spectral theory. The reduced spectral indices for the period range of 1 min to about a half hour are remarkably constant and in good agreement with the value of 3/2. Thus our treatment is self-consistent. Our tentative conclusion is that the high-frequency turbulence appears to agree with the model of random-phased Alfven waves. This tentative conclusion must be tested by further theoretical and observational work.
Ruzmaikin, A. A.↗
Dynamic resetting of the human circadian pacemaker by intermittent bright light
In humans, experimental studies of circadian resetting typically have been limited to lengthy episodes of exposure to continuous bright light. To evaluate the time course of the human endogenous circadian pacemaker's resetting response to brief episodes of intermittent bright light, we studied 16 subjects assigned to one of two intermittent lighting conditions in which the subjects were presented with intermittent episodes of bright-light exposure at 25- or 90-min intervals. The effective duration of bright-light exposure was 31% or 63% compared with a continuous 5-h bright-light stimulus. Exposure to intermittent bright light elicited almost as great a resetting response compared with 5 h of continuous bright light. We conclude that exposure to intermittent bright light produces robust phase shifts of the endogenous circadian pacemaker. Furthermore, these results demonstrate that humans, like other species, exhibit an enhanced sensitivity to the initial minutes of bright-light exposure.
Non-NASA Center↗
Diagnosable systems for intermittent faults
The fault diagnosis capabilities of systems composed of interconnected units capable of testing each other are studied for the case of systems with intermittent faults. A central role is played by the concept of t(i)-fault diagnosability. A system is said to be t(i)-fault diagnosable when it is such that if no more than t(i) units are intermittently faulty then a fault-free unit will never be diagnosed as faulty and the diagnosis at any time is at worst incomplete. Necessary and sufficient conditions for t(i)-fault diagnosability are proved, and bounds for t(i) are established. The conditions are in general more restrictive than those for permanent-fault diagnosability. For intermittent faults there is only one testing strategy (repetitive testing), and consequently only one type of intermittent-fault diagnosable system.
Mallela, S.↗
Study of intermittent field hardware failure data in digital electronics
The collection and analysis of data concerning intermittent dailures in digital devices was performed using data from a computer design for shipboard usage. The failure data consisted of actual field failures classified by failure mechanisms and their likelihood of having been intermittent, potentially intermittent, or hard. Each class was studies with respect to computer operation in the ranges of 0 to 2,000 hours, 0 to 5, hours, and 0 to 10,000 hours. The study was done at the computer level as well as the microcircuit level. Results indicate that as age increases, the quasi-intermittent failure rate increases and the mean time to failure descreases.
Oneill, E. J.↗
Experimental and numerical study of the intermittency exponent mu
After publication of the Kolmogorov refined similarity hypotheses, the small-scale intermittency of the energy dissipation field became a central problem in fully developed turbulence (FDT). This phenomenon has been studied in many different ways, e.g. by searching for corrections to scaling exponents in the inertial range velocity structure functions. A direct measure of this intermittency is, however, available by studying the local rate of energy dissipation, and it may be quantitatively characterized by the intermittency exponent mu. As far as we know, nobody has posed an obvious question: Is the intermittency exponent mu a unique constant, i.e., are the values mu(sub kappa), mu(sub epsilon), mu(sub r), mu(sub b), and mu(sub e) the same at high Reynolds numbers, or do they create a set of different (and perhaps independent) exponents? This paper addresses the above question using the high Reynolds number experiments.
Praskovsky, Alexander↗
Characterizing multiscale variability of zero intermittency in spatial rainfall
In this paper the authors study how zero intermittency in spatial rainfall, as described by the fraction of area covered by rainfall, changes with spatial scale of rainfall measurement or representation. A statistical measure of intermittency that describes the size distribution of 'voids' (nonrainy areas imbedded inside rainy areas) as a function of scale is also introduced. Morphological algorithms are proposed for reconstructing rainfall intermittency at fine scales given the intermittency at coarser scales. These algorithms are envisioned to be useful in hydroclimatological studies where the rainfall spatial variability at the subgrid scale needs to be reconstructed from the results of synoptic- or mesoscale meteorological numerical models. The developed methodologies are demsonstrated and tested using data from a severe springtime midlatitude squall line and a mild midlatitude winter storm monitored by a meteorological radar in Norman, Oklahoma.
Kumar, Praveen↗
Intermittent Behavior of the Separated Boundary Layer along the Suction Surface of a Low Pressure Turbine Blade under Periodic Unsteady Flow Conditions
The paper experimentally and theoretically studies the effects of periodic unsteady wake flow and aerodynamic characteristics on boundary layer development, separation and re-attachment along the suction surface of a low pressure turbine blade. The experiments were carried out at Reynolds number of 110,000 (based on suction surface length and exit velocity). For one steady and two different unsteady inlet flow conditions with the corresponding passing frequencies, intermittency behaviors were experimentally and theoretically investigated. The current investigation attempts to extend the intermittency unsteady boundary layer transition model developed in previously to the LPT cases, where separation occurs on the suction surface at a low Reynolds number. The results of the unsteady boundary layer measurements and the intermittency analysis were presented in the ensemble-averaged and contour plot forms. The analysis of the boundary layer experimental data with the flow separation, confirms the universal character of the relative intermittency function which is described by a Gausssian function.
Oeztuerk, B↗
Diagnosing Intermittent and Persistent Faults using Static Bayesian Networks
Both intermittent and persistent faults may occur in a wide range of systems. We present in this paper the introduction of intermittent fault handling techniques into ProDiagnose, an algorithm that previously only handled persistent faults. We discuss novel algorithmic techniques as well as how our static Bayesian networks help diagnose, in an integrated manner, a range of intermittent and persistent faults. Through experiments with data from the ADAPT electrical power system test bed, generated as part of the Second International Diagnostic Competition (DXC-10), we show that this novel variant of ProDiagnose diagnoses intermittent faults accurately and quickly, while maintaining strong performance on persistent faults.
Megshoel, Ole Jakob↗
Intermittent turbulence in the solar wind
This paper demonstrates the existence of intermittent turbulence in the solar wind at 8.5 AU. The pth-order velocity structure functions show scaling behavior in the range of periods from 0.85 hour to 13.6 hours for p of less than 20. The exponent of the scaling law s(p) is a quadratic function of p. These observations of s(p) for compressible MHD turbulence on a scale of the order of about 1 AU are consistent with laboratory measurements of s(p) for gasdynamic turbulence on a scale of the order of 1 m, indicating the universal character of intermittent turbulence. The observations are not described by the 'constant beta' model of intermittent turbulence. They are marginally consistent with the lognormal model. The observations are consistent with a random beta model prediction which assumes that the turbulence is a mixture of sheets and space-filling eddies.
Burlaga, L. F.↗
Effects of Intermittent Versus Continuous Heating upon the Tensile Properties of 2024-T4, 6061-T6 and 7075-T6 Alloys
In some applications, aluminum alloys are subjected to intermittent heating at elevated temperature. It is generally considered that the effects of such intermittent heating are cumulative, and therefore are the same as if the heating had been continuous for the same total length of time. The object of these tests was to determine the effects of intermittent and continuous heating at 300 and 400 F, for total periods of 100 and 200 hr, upon the tensile properties of 2024-T4 and 6061-T6 alloy rolled-and-drawn rod and 7075-T6 alloy extrusions, at room temperature and at the temperature of heating.
Stickley, G. W.↗
Complexity Induced Anisotropic Bimodal Intermittent Turbulence in Space Plasmas
The "physics of complexity" in space plasmas is the central theme of this exposition. It is demonstrated that the sporadic and localized interactions of magnetic coherent structures arising from the plasma resonances can be the source for the coexistence of nonpropagating spatiotemporal fluctuations and propagating modes. Non-Gaussian probability distribution functions of the intermittent fluctuations from direct numerical simulations are obtained and discussed. Power spectra and local intermittency measures using the wavelet analyses are presented to display the spottiness of the small-scale turbulent fluctuations and the non-uniformity of coarse-grained dissipation that can lead to magnetic topological reconfigurations. The technique of the dynamic renormalization group is applied to the study of the scaling properties of such type of multiscale fluctuations. Charged particle interactions with both the propagating and nonpropagating portions of the intermittent turbulence are also described.
Chang, Tom↗
Differential effects of intermittent and continuous administration of parathyroid hormone on bone histomorphometry and gene expression
A mechanism explaining the differential skeletal effects of intermittent and continuous elevation of serum parathyroid hormone (PTH) remains elusive. Intermittent PTH increases bone formation and bone mass and is being investigated as a therapy for osteoporosis. By contrast, chronic hyperparathyroidism results in the metabolic bone disease osteitis fibrosa characterized by osteomalacia, focal bone resorption, and peritrabecular bone marrow fibrosis. Intermittent and continuous PTH have similar effects on the number of osteoblasts and bone-forming activity. Many of the beneficial as well as detrimental effects of the hormone appear to be mediated by osteoblast-derived growth factors. This hypothesis was tested using cDNA microgene arrays to compare gene expression in tibia of rats treated with continuous and pulsatile administration of PTH. These treatments result in differential expression of many genes, including growth factors. One of the genes whose steady-state mRNA levels was increased by continuous but not pulsatile administration was platelet-derived growth factor-A (PDGF-A). Administration of a PDGF-A antagonist greatly reduced bone resorption, osteomalacia, and bone marrow fibrosis in a rat model for hyperparathyroidism, suggesting that PDGF-A is a causative agent for this disease. These findings suggest that profiling changes in gene expression can help identify the metabolic pathways responsible for the skeletal responses to the hormone.
Review↗