Growth Rates of Ideal Small-Scale Modes

2017 ◽  
pp. 161-171
Author(s):  
A. B. Mikhailovskii
Keyword(s):  
Growth Rates ◽  
Small Scale

Experimental study of the initial stages of wind waves' spatial evolution

2011 ◽  
Vol 681 ◽  
pp. 462-498 ◽  
Author(s):  
DAN LIBERZON ◽  
LEV SHEMER
Keyword(s):  
Energy Transfer ◽  
Growth Rates ◽  
Water Surface ◽  
Wind Waves ◽  
Pressure Fluctuations ◽  
Theoretical Models ◽  
Small Scale ◽  
Wave Flume ◽  
Spatial Growth ◽  
The Mean

Despite a significant progress and numerous publications over the last few decades a comprehensive understanding of the process of waves' excitation by wind still has not been achieved. The main goal of the present work was to provide as comprehensive as possible set of experimental data that can be quantitatively compared with theoretical models. Measurements at various air flow rates and at numerous fetches were carried out in a small scale, closed-loop, 5 m long wind wave flume. Mean airflow velocity and fluctuations of the static pressure were measured at 38 vertical locations above the mean water surface simultaneously with determination of instantaneous water surface elevations by wave gauges. Instantaneous fluctuations of two velocity components were recorded for all vertical locations at a single fetch. The water surface drift velocity was determined by the particle tracking velocimetry (PTV) method. Evaluation of spatial growth rates of waves at various frequencies was performed using wave gauge records at various fetches. Phase relations between various signals were established by cross-spectral analysis. Waves' celerities and pressure fluctuation phase lags relative to the surface elevation were determined. Pressure values at the water surface were determined by extrapolating the measured vertical profile of pressure fluctuations to the mean water level and used to calculate the form drag and consequently the energy transfer rates from wind to waves. Directly obtained spatial growth rates were compared with those obtained from energy transfer calculations, as well as with previously available data.

scholarly journals Growth rates and life histories in twenty-two small-scale societies

2006 ◽  
Vol 18 (3) ◽  
pp. 295-311 ◽  
Author(s):  
Robert Walker ◽  
Michael Gurven ◽  
Kim Hill ◽  
Andrea Migliano ◽  
Napoleon Chagnon ◽  
...  
Keyword(s):  
Growth Rates ◽  
Life Histories ◽  
Small Scale

scholarly journals Application of a Cohesive Zone Model for Simulating Fatigue Crack Growth from Moderate to High ΔK Levels of Inconel 718

2018 ◽  
Vol 2018 ◽  
pp. 1-13
Author(s):  
Huan Li ◽  
Jinshan Li ◽  
Huang Yuan
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Growth Rates ◽  
Cohesive Zone ◽  
Cohesive Zone Model ◽  
Small Scale ◽  
Model Parameters ◽  
Zone Model ◽  
Crack Growth Rates

A cyclic cohesive zone model is applied to characterize the fatigue crack growth behavior of a IN718 superalloy which is frequently used in aerospace components. In order to improve the limitation of fracture mechanics-based models, besides the predictions of the moderate fatigue crack growth rates at the Paris’ regime and the high fatigue crack growth rates at the high stress intensity factor ΔK levels, the present work is also aimed at simulating the material damage uniformly and examining the influence of the cohesive model parameters on fatigue crack growth systematically. The gradual loss of the stress-bearing ability of the material is considered through the degradation of a novel cohesive envelope. The experimental data of cracked specimens are used to validate the simulation result. Based on the reasonable estimation for the model parameters, the fatigue crack growth from moderate to high ΔK levels can be reproduced under the small-scale yielding condition, which is in fair agreement with the experimental results.

Secondary instability of a temporally growing mixing layer

1987 ◽  
Vol 184 ◽  
pp. 207-243 ◽  
Author(s):  
Ralph W. Metcalfe ◽  
Steven A. Orszag ◽  
Marc E. Brachet ◽  
Suresh Menon ◽  
James J. Riley
Keyword(s):  
Growth Rates ◽  
Stokes Equations ◽  
Mixing Layer ◽  
Three Dimensional ◽  
Mixing Layers ◽  
Navier Stokes ◽  
Small Scale ◽  
Two Dimensional ◽  
Mean Flow ◽  
Direct Numerical Integration

The three-dimensional stability of two-dimensional vortical states of planar mixing layers is studied by direct numerical integration of the Navier-Stokes equations. Small-scale instabilities are shown to exist for spanwise scales at which classical linear modes are stable. These modes grow on convective timescales, extract their energy from the mean flow and exist at moderately low Reynolds numbers. Their growth rates are comparable with the most rapidly growing inviscid instability and with the growth rates of two-dimensional subharmonic (pairing) modes. At high amplitudes, they can evolve into pairs of counter-rotating, streamwise vortices, connecting the primary spanwise vortices, which are very similar to the structures observed in laboratory experiments. The three-dimensional modes do not appear to saturate in quasi-steady states as do the purely two-dimensional fundamental and subharmonic modes in the absence of pairing. The subsequent evolution of the flow depends on the relative amplitudes of the pairing modes. Persistent pairings can inhibit three-dimensional instability and, hence, keep the flow predominantly two-dimensional. Conversely, suppression of the pairing process can drive the three-dimensional modes to more chaotic, turbulent-like states. An analysis of high-resolution simulations of fully turbulent mixing layers confirms the existence of rib-like structures and that their coherence depends strongly on the presence of the two-dimensional pairing modes.

Crack Growth in Pipes Under Service Contortions

2009 ◽  
Author(s):  
Oddvin O¨rjasaeter ◽  
Richard Verley ◽  
Per Egil Kvaale ◽  
Tor Gunnar Eggen
Keyword(s):  
Crack Growth ◽  
Cathodic Protection ◽  
Growth Rates ◽  
Fatigue Cracks ◽  
High Growth ◽  
Potential Drop ◽  
Fatigue Tests ◽  
Full Scale ◽  
Small Scale ◽  
Loading Frequency

At the A˚sgard field a leak on a 10″, 13Cr production pipeline was discovered in December 2000 during pressure testing. The cause was a crack at an anode pad fillet weld (pads are connectors for the cathodic protection system). Later, a similar leak occurred on another A˚sgard flowline. During pigging inspection (AUT) several smaller crack indications were found at similar locations. Propagation of such cracks will depend on loading and environmental conditions. To investigate this further, a test programme was carried out using 13Cr pipe materials. Both small scale tests and full scale pipes were used. Specimens were prepared with small initial fatigue cracks at the pad weld. The propagation of the cracks was then recorded under various environmental and loading conditions. The loading was selected to cover a crack growth rate range of ∼10−6 to 10−3 mm/cycle for various crack depths and for two loading frequencies. Tests were conducted under cathodic protection (hydrogen in the material measured) and for temperatures up to 140°C and pressures up to 30bar. The crack growth was recorded by the potential drop method (ACPD). For the full scale pipe tests, specially developed equipment was used for simultaneous measuring at up to 24 individual locations. The results showed that low loading frequency (0.1 Hz) enhances the growth rates; elevated temperature gave equal or lower propagation rates than at 25°C and a pressure of 30bar did not influence the results. A few cracks were also initiated during the corrosion fatigue tests and exhibited high growth rates; possibly due to the so-called “small crack” effect and possibly in synergy with the influence of hydrogen.

Small Scale Sour Fatigue Testing With Dense Phase Gases

2012 ◽  
Author(s):  
Weiwei Yu ◽  
Pedro M. Vargas ◽  
Ben Crowder ◽  
Sam Mishael ◽  
Ramgopal Thodla
Keyword(s):  
Growth Rate ◽  
High Pressure ◽  
Water Content ◽  
Crack Growth ◽  
Growth Rates ◽  
Fatigue Performance ◽  
Small Scale ◽  
Dense Phase ◽  
High Crack ◽  
Crack Growth Rates

One way generally accepted by industry to evaluate the effect of sour environment on fatigue performance of girth welds is by small scale testing in sour brines. These tests are commonly done at room temperature and pressure and therefore can only contain a maximum of 14.7psia of H2S in a gaseous phase. In comparison, very little has been published about fatigue performance in sour environments where negligible amounts or no water is present. Such condition can be found for pipelines serving in a “dry” sour environment (H2S and other gases in dense phase) with high H2S concentration. This paper documents both small scale fatigue crack growth rate (FCGR) tests and S-N fatigue tests in a dense phase sour environment with ultra-low water content and high H2S concentration under high pressure. Fatigue life reduction factors were calculated from FCGR approach (with the name crack growth acceleration factor, CGAF) and S-N approach (with the name knockdown factor), respectively. Industry understanding today is that water is necessary for accelerating fatigue crack growth. Quite opposite to the expected effect of water content on crack growth, even ultra-low water content (<450ppm) resulted in high crack growth rates. Crack growth rates were comparable among tests with various water contents, all ultra low. Through limited testing, no temperature dependency on crack growth rate was identified. It is postulated that hydrogen dissociation due to high pressure and high concentration may be the cause for high crack growth rates on the absence of water. Small scale S-N tests on smooth specimens reveal that fatigue performance in ultra-low-water sour environments is the same as in air. We find that the dry gas environment dose not attack the metal surface preserving the fatigue performance.

scholarly journals Growth rates and thallus loss in hair lichens along small-scale Picea abies-canopy gradients

2020 ◽  
Vol 47 ◽  
pp. 100947 ◽  
Author(s):  
Yngvar Gauslaa ◽  
Knut Asbjørn Solhaug ◽  
Nathan H. Phinney
Keyword(s):  
Picea Abies ◽  
Growth Rates ◽  
Small Scale

PSI in the case of internal wave beam reflection at a uniform slope

2016 ◽  
Vol 789 ◽  
pp. 347-367 ◽  
Author(s):  
Vamsi K. Chalamalla ◽  
Sutanu Sarkar
Keyword(s):  
Internal Wave ◽  
Froude Number ◽  
Growth Rates ◽  
Wave Amplitude ◽  
Wave Beam ◽  
Small Scale ◽  
Finite Width ◽  
Incoming Wave ◽  
Weakly Nonlinear ◽  
Reflected Wave

Two-dimensional numerical simulations are performed to examine internal wave reflection at a sloping boundary. Owing to reflection, the reflected wave amplitude and wavenumber increase. At low values of the incoming wave amplitude, the reflected wave beam is linear and its properties agree well with linear inviscid theory. Linear theory overestimates the reflected wave Froude number, $Fr_{r}$, for higher values of incoming wave amplitude. Nonlinearity sets in with increasing value of incoming wave Froude number, $Fr_{i}$, leading to parametric subharmonic instability (PSI) of the reflected wave beam: two subharmonics emerge from the reflection region with frequencies $0.33{\it\Omega}$ and $0.67{\it\Omega}$ and wavenumbers that add up to those of the reflected wave. The amplification of Froude number due to reflection must be sufficiently large for PSI to occur implying that the off-criticality in wave angle cannot be too large. The simulations also show that, all other parameters being fixed, a threshold in beam amplitude is required for the onset of PSI in the reflected beam, consistent with results from a previous weakly-nonlinear asymptotic theory for a freely propagating finite-width beam. Growth rates of subharmonic modes at moderate reflected wave amplitude are in reasonable agreement with that theory. However, for $Fr_{r}>0.5$, small scale fluctuations becomes prominent and the subharmonic energy growth rates saturate in the simulations in contrast to the theoretical prediction. Increasing the incoming beam thickness (number of carrier wavelengths) increases the strength of PSI. Keeping the incoming Froude number constant and increasing the incoming Reynolds number by a factor of 50 does not have an effect on the unequal division of frequencies among the subharmonic modes that is found in the simulations.

scholarly journals Influence of Moist Physics and Norms on Singular Vectors for a Tropical Cyclone

2009 ◽  
Vol 137 (2) ◽  
pp. 525-543 ◽  
Author(s):  
Hyun Mee Kim ◽  
Byoung-Joo Jung
Keyword(s):  
Growth Rates ◽  
Large Scale ◽  
Mesoscale Model ◽  
Lower Boundary ◽  
Initial Time ◽  
Small Scale ◽  
Lanczos Algorithm ◽  
Energy Distributions ◽  
Singular Vectors ◽  
Vertical Distributions

Abstract In this study, the structures and growth rates of singular vectors (SVs) for Typhoon Usagi were investigated using different moist physics and norms. The fifth-generation Pennsylvania State University–National Center for Atmospheric Research Mesoscale Model (MM5) and its tangent linear and adjoint models with a Lanczos algorithm were used to calculate SVs over a 36-h period. The moist physics used for linear (i.e., tangent linear and adjoint model) integrations is large-scale precipitation, and the norms used are dry and moist total energy (TE) norms. Overall, moist physics in linear integrations and a moist TE norm increase the growth rates of SVs and cause smaller horizontal structures and vertical distributions closer to the lower boundary. With a dry TE norm, the SV energy distributions show similar (dissimilar) large- (small-) scale horizontal SV structures for experiments, regardless of physics. The SVs with moist linear physics and a moist TE norm have maximum horizontal energy structures near the typhoon center. With a small weighting on the moisture term in the moist TE norm, both the remote and nearby influences on the TC are indicated by the horizontal SV energy distributions. The kinetic energy shows the largest contributions to the vertical SV TE distributions in most of the experiments, except for the largest moisture (potential energy) contributions to the SV TE at the final (initial) time in the moist TE norm (dry and weighted moist TE norms at uppermost levels). In contrast, the SV vorticity distributions show more consistent structures among experiments with different linear physics and norms, implying that, in terms of the rotational component of the wind field, the SVs are not sensitive to the choice of moist physics and norms. Given large-scale precipitation as the linear moist physics, the SV energy structures and growth rate with a moist TE norm show the largest difference when compared with those with other norms.

Nursery grounds, movement patterns and growth rates of dusky sharks, Carcharhinus obscurus: a long-term tag and release study in South African waters

2009 ◽  
Vol 60 (6) ◽  
pp. 571 ◽  
Author(s):  
Nigel E. Hussey ◽  
Ian D. McCarthy ◽  
Sheldon F. J. Dudley ◽  
Bruce Q. Mann
Keyword(s):  
South African ◽  
Growth Rates ◽  
Movement Patterns ◽  
Small Scale ◽  
Shark Species ◽  
Early Life Stages ◽  
Kwazulu Natal ◽  
Management Plans ◽  
Carcharhinus Obscurus

Knowledge of movement patterns of sharks in coastal waters is critical for the structuring of regional management plans. Through a long-term tag–recapture program, 9716 dusky sharks (Carcharhinus obscurus) were tagged and released along the east coast of South Africa. A total of 648 C. obscurus, principally small sharks (<100 cm PCL), were recaptured. Most recaptures were within 100 km of the tagging location in the nursery habitat in KwaZulu-Natal (KZN) with small scale movements occurring throughout the year. Forty-eight C. obscurus undertook movements >200 km that indicated a southerly migration between KZN and Eastern/Southern Cape (E/SC) between June and November. Seasonal northerly migrations were less well defined. The largest southerly and northerly movements were 1323 km and 1374 km, respectively. For sharks moving 1–100 km south from their tagging locality in KZN, an increase in displacement occurred between June and September identifying animals beginning their migration to the E/SC. With increasing displacement, there was also an increase in minimum swimming speed. Calculated growth rates of small sharks of 10.3–11.5 cm year–1 were in agreement with current literature values. Established tag–recapture programs provide an important tool in understanding the ecology of early life-stages of coastal shark species.

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