Local Peak Value Research Articles

Thermo-mechanical shock fracture analysis by meshless method

Different types of mechanical and thermal shock loads are considered to investigate transient stress intensity factors of two/three dimensional cracked specimens via meshless method with linear test function. Steady state and transient analyses show that the method is reliable. The effect of crack length, density and Lord-Shulman relaxation time on stress intensity factors are studied. Results represent the different effect of crack length on mechanical and thermal stress intensity factors. Various theoretical and real values of relaxation time are used to show how thermal stress intensity factor curves change when modified Fourier heat conduction law is employed compared with classical Fourier law. Additionally, the effect of specimen size on non-Fourier thermal stress intensity factor curves is investigated. We observed that using a functionally graded material instead of a composite coated substrate reduces local mean and peak values of transient thermal stress intensity factors.

Dynamic analysis on fluid-structure interaction of an elastically mounted square cylinder at low Reynolds numbers

Fluid-structure interaction of an elastically mounted rigid square cylinder of low non-dimensional mass immersed in fluid flow is investigated numerically in the Reynolds numbers range of 60≤Re≤250. The square cylinder is allowed to freely vibrate only in the transverse direction perpendicular to the incoming flow. The two-dimensional incompressible Reynolds-averaged Navier-Stokes equations are solved by the finite volume method for the fluid flow. The equation of motion is solved for the vibration of the square cylinder. The results show that abrupt both the frequency and amplitude ratios curves experience sudden change at Re=90 and 168, which marks the onset of the lock-in and galloping regime, respectively. Thus, four regimes can be divided in the present study and which are the initial regime, the lock-in regime, the lower branch and galloping regime. A local peak value is observed in the force coefficients curve and the maximum value is reached at Re=231. It is found that the peak oscillating amplitude of the lock-in regime is reached at 0.22D and the width of lock-in region with sharp corner is very narrow. In the galloping regime, the peak amplitude of the oscillating square cylinder is close to 0.70D at Re=231. Typical 2S vortex structure is observed in the initial regime, the lock-in regime, and the lower branch. While in the galloping regime, 2P, 2P+2S and more complicated vortex patterns are observed as Re increases.

Some Remarks on the Estimation of Informal Economy in the Republic of Macedonia

In this paper we discuss some findings on the estimation of the informal economy in a particular economical system, the Republic of Macedonia. We observed that undeviating application of standard models could produce different results and therefore some preliminary precaution has been taken. Therefore, by performing step by step analysis we conclude in acceptable values and in the evidencing of dominant factors that simulate informal economy. The work reveals the importance of model’s assumption fulfilling in the case of economic systems where observables are non-stationary and the economy itself is typically in dynamical evolution. As result of such improvement of the procedure we obtained that the country’s informal economy is going slight down starting from a local peak value touched in 2010-2011. By now it is stabilized around the values 33%-35% of GDP. We obtained herein that the majority of economic and political measures undertaken recently in the framework of informality reduction have worked in the aimed direction. From the factors point of view we obtained that contribution of some variables in the informal economy growth in the period analyzed

Analysis of vortex breakdown in an enclosed cylinder based on the energy gradient theory

Numerical simulation is carried out to study the phenomenon of vortex breakdown in an enclosed cylinder. The energy gradient theory is used to explain the vortex breakdown in the cylinder with consideration of centrifugal force, Coriolis force, angular momentum and azimuthal vorticity. The research results show that the large value of energy gradient function K is mainly located at the centerline and the region between the circulation vortices on both sides of the cylinder and the vortex breakdown bubbles at the centerline. It is found that the position of the local peak value of the energy gradient function K at the centerline corresponds to the location of vortex breakdown first occurrence. The position of the local peak value of K function in horizontal direction corresponds to the velocity inflection points except for the centerline. The vortex breakdown is mainly determined by the high K value at the centerline for low aspect ratio. The influence of the region of high K value between the circulation vortices on both sides of the cylinder and the vortex breakdown bubbles at the centerline becomes larger with the increase of the aspect ratio. The occurrence and development of the vortex breakdown bubble may be affected by the region of high K value between the circulation vortices on both sides of the cylinder and the vortex breakdown bubbles at the centerline for high aspect ratio.

Numerical Investigation on the Water Entry of Convex Objects Using a Multiphase Smoothed Particle Hydrodynamics Model

In this paper, the hydrodynamic behaviors of a typical convex object during water entry are numerically investigated using a meshfree particle method, smoothed particle hydrodynamics (SPH). In order to consider the practical air-cushion effects during water–entry process, a multiphase model with interface force is incorporated to the SPH method to maintain sharp water–air interface. Three numerical examples including bubble rising, water impact on a flate plate and water entry of a wedge are firstly simulated to validate the effectiveness of the multiphase SPH method in predicting the slamming forces and trajectories of falling objects. Water entry of free falling convex objects with different shapes and sizes is then simulated using the validated numerical method for comparative studies. Two slamming processes, including the convex slamming and the structure slamming, are observed in simulations, with double-jetting pattern occurring after the structure slamming. The air-cushion effects are well captured with slamming-induced vortexes clearly shown in the simulation snapshots. Quantitatively, significant drop in pressure peak value is observed when the dimensionless width of the convex is larger than 0.2. Among various shapes of convexes, the square shaped convex experiences the minimal local pressure peak value.

Reduction of ion thermal transport due to non-uniformity effects of the radial electric field at the edge of the JT-60U tokamak

Non-uniformity effects of the edge radial electric field, Er, on edge transport barrier (ETB) formation have been identified with high-spatiotemporal resolution spectroscopic measurement. We identified the decisive importance of Er-curvature (i.e. 2nd derivative of Er) on ETB formation corresponding to a local peak value in the pedestal region of the normalized ion temperature gradient, . On the other hand, the Er-shear (i.e. 1st derivative of Er) was discovered to promote the expansion of pedestal width, compensating an unfavorable effect of the Er-curvature having its sign dependence on the transport reduction/enhancement—predicted by a theoretical model as . A significant reduction of the inferred ion thermal transport coefficient in the pedestal region, , due to the non-uniformity effects of Er was also confirmed quantitatively in the H-mode plasma at the initial ELM-free phase. When the inhomogeneity of radial electric field became strong enough, the inferred value was close to its neoclassical one at the later ELM-free H-phase until 1st type-I ELM onset. Nevertheless, we observed the further reduction of electron density fluctuations (in the range up to 300 kHz) and signals in association with the increment of electric field inhomogeneity. These suggest that the electron turbulent transport is suppressed further.

The 27-day rotational variations in total solar irradiance observations: From SORCE/TIM, ACRIMSAT/ACRIM III, and SOHO/VIRGO

During the last decade, observations from SORCE (Solar Radiation and Climate Experiment)/TIM (Total Irradiance Monitor), ACRIMSAT (Active Cavity Radiometer Irradiance Monitor Satellite)/ACRIM III, and SOHO (Solar and Heliospheric Observatory)/VIRGO (Variability of IRradiance and Gravity Oscillations Sun PhotoMeter) provided Total Solar Irradiance (TSI) measurements with unprecedented accuracy and stability to determine the amount of solar irradiance reaching the top of the atmosphere and how solar irradiance varies on different time scales. These three independent measurements are analyzed using the EEMD (Ensemble Empirical Mode Decomposition) method to characterize the phase and amplitude of the 27-day solar rotational variation in TSI. The mode decomposition clearly identifies a 27-day solar rotational signature on TSI measurements. The rotational variations of TSI from the three independent observations are generally consistent with each other, despite different mean TSI values. During the declining phase of solar cycle 23, the amplitude of TSI 27-day variations is as high as 0.8W/m2 (~0.05%), while during the rising phase of solar cycle 24, the amplitude is up to 0.4W/m2 (~0.04%). During the minimum phase (2008–2009), the amplitude of the rotational mode is only ~0.1W/m2. The correlation of this rotational mode between TIM and ACRIM III is ~0.92 and the slope of the local peak values is ~0.98. The correlation between TIM and VIRGO is ~0.96 and the slope of the local peak values is ~0.98, very similar to the slope with ACRIM III.

Questioning a widespread euxinia for the Furongian (Late Cambrian) SPICE event: indications from δ13C, δ18O, δ34S and biostratigraphic constraints

AbstractResults from a high-resolution study of δ13Ccarb, δ18Ocarb, δ34SCAS, δ34SCRSand elemental concentrations (Ca, Fe, Mg, Mn and Sr) in the Furongian Kyrshabakty section, southern Kazakhstan, are reported here. The investigated interval covers the Drumian to Jiangshanian stages of the Cambrian Period, respectively the regionalPtychagnostus atavustoIvshinagnostus ivshini-Irvingella majortrilobite zones. δ13Ccarbdata include the Steptoean positive carbon isotope excursion (SPICE) with a local peak value of +5‰. The onset of SPICE corresponds to theKormagnostus simplex–Glyptagnostus stolidotuszones and pre-dates the base of the Paibian Stage/Furongian Series. δ34SCASdata already increase during theLejopyge armatabiozone culminating in three positive excursions prior and after the SPICE maximum. Differences in onset, peak values and shape of the δ13Ccarband/or δ34SCASexcursions at Kyrshabakty, but also in almost all sections characterized by the SPICE, are pointing towards Furongian seawater that was low in sulphate concentration and heterogeneous in its carbonate carbon and sulphate sulphur isotopic composition. The occurrence of benthic faunal elements in almost all SPICE-related sections strongly supports oxygenated conditions at the seafloor, therefore excluding widespread anoxia or euxinia. Regional anoxic conditions are most probable. A positive δ18Ocarbexcursion parallel to the SPICE could probably be explained by a decline in seawater pH associated with a sea-level rise. Again, no euxinic conditions would be mandatory for explaining the SPICE event.

Experimental study of heat transfer characteristics in a 180-deg round turned channel with discrete aluminum-foam blocks

This work experimentally investigated the local and average heat transfer characteristics in a 180-deg round turned channel with discrete aluminum-foam blocks. The air was used as coolant. Several aluminum-foam blocks (0.90 porosity and 10PPI pore density) were installed discretely in the 180-deg round turned channel with the square cross section. Total four kinds of test section, with various arrangements of aluminum-foam blocks, were employed. The results indicate that the local peak values of the Nusselt numbers would appear at the positions of the aluminum-foam blocks. The local Nusselt numbers of the upper and bottom walls were higher than those of the side walls in the straight ducts; while the local Nusselt numbers of the outer side wall were higher than those of others walls in the turn. The local Nusselt numbers of the inner side wall generally were the lowest values. Besides, the average Nusselt numbers of the present porous channels were 74–140% higher than that of the empty channel, suggesting the significant heat transfer enhancement of the aluminum-foam blocks. Furthermore, in the straight duct, the staggered aluminum-foam blocks could promote heat transfer more efficiently than the symmetric aluminum-foam blocks did. The average Nusselt numbers of Model 3 and Model 4 (the whole channel filled with aluminum-foam blocks) were 20–30% higher than those of Model 1 and Model 2 (only straight ducts filled with aluminum-foam blocks). It is noteworthy that the pressure drops of Model 1 and Model 3 test sections (vertically symmetric configuration) are much higher than those of Model 2 and Model 4 test sections (vertically staggered configuration) by 180–280%.

Sand Transport and Sedimentary Features Based on Feldspar Thermoluminescence: A Synthesis of the Tenryu–Enshunada Fluvial System, Japan

Liu, H.; Takagawa, T., and Sato, S., 2014. Sand transport and sedimentary features based on feldspar thermoluminescence: a synthesis of the Tenryu–Enshunada fluvial system, Japan. On the basis of the feldspar thermoluminescence (TL) measurement, sediment transport features were investigated in the entire Tenryu River watershed and the corresponding littoral sediment zone of the Enshunada coast. Subsequently, the sedimentary configuration and sand provenance in the river mouth area were studied using subsurface samples. In the Tenryu River watershed, TL intensities of the riverine samples fluctuated with respect to the local geological characteristics. Comparing with samples collected from the main river route, branch samples generally present larger TL intensities. Nevertheless, sediment supply from branches is considered to be rather limited in terms of their small discharges. Increase in the riverine TL property can be detected in the immediate dam downstream area, as well as the region with mass sand movements. Taking into account the Enshunada coastal samples, measured sediment TL intensities present a local peak value around the river mouth and a decreasing trend with the increasing distance away from the river mouth. This is attributed to the river sand supply and the gradual sunlight exposure during the longshore sediment transport. In general, riverine samples present much larger TL intensities than coastal samples, and a criterion on the basis of a TL intensity value of 5 was recognized to distinguish these two types of sands in the study area. Applying this criterion to the subsurface samples collected in the river mouth sand spit, a sedimentary interface at Tokyo Peil −1 m was confirmed with coastal sands (small TL intensity with wave experience) located on the top and riverine sands (large TL intensity without wave experience) deposited at the bottom, which is in agreement with estimations from other physical and geomorphological approaches.

A Survey of External Feature of Solar Cells in Partially Shading

Existing model of solar cells is not suitable for partial shading condition, which makes output current-voltage (I-V) curve of photovoltaic (PV) array staid-stepping. Furthermore, Power-Voltage (P-V) characteristics may exist more than two local peak value in partially shading which bring interferences to maximum power point tracking (MPPT). Based on modified engineering model of solar cells, an accurate model of array was proposed considering variation of shadows. And the I-V characteristic, P-V characteristic and yield of PV modules were analyzed. At last, the optimum output power with different shadows arrangement was discussed.

Secondary electromagnetic polarimetric scattering from dune surface

Secondary electromagnetic polarimetric scattering from a barchan dune is studied. The secondary polarimetric scattering field from the secondary scattering facet is deduced in the Kirchhoff approximation with the waves reflecting from the first scattering facet based on the Ray-tracing theory. The results show that secondary scattering plays an important role in specific range of angle. The co-polarized backscattering coefficients of the lee slope have a local peak value when the incident angle equals the repose angle. Cross-polarized bistatic coefficient of the lee slope near the backscattering region is enhanced when the incident angle is close to the repose angle. The secondary polarimetric scattering between two dunes in line is especially noticeable. The information about wind field in desert region can be retrieved and analyzed by the results in this paper.

Prediction of Plantar Shear Stress Distribution by Artificial Intelligence Methods

Shear forces under the human foot are thought to be responsible for various foot pathologies such as diabetic plantar ulcers and athletic blisters. Frictional shear forces might also play a role in the metatarsalgia observed among hallux valgus (HaV) and rheumatoid arthritis (RA) patients. Due to the absence of commercial devices capable of measuring shear stress distribution, a number of linear models were developed. All of these have met with limited success. This study used nonlinear methods, specifically neural network and fuzzy logic schemes, to predict the distribution of plantar shear forces based on vertical loading parameters. In total, 73 subjects were recruited; 17 had diabetic neuropathy, 14 had HaV, 9 had RA, 11 had frequent foot blisters, and 22 were healthy. A feed-forward neural network (NN) and adaptive neurofuzzy inference system (NFIS) were built. These systems were then applied to a custom-built platform, which collected plantar pressure and shear stress data as subjects walked over the device. The inputs to both models were peak pressure, peak pressure-time integral, and time to peak pressure, and the output was peak resultant shear. Root-mean-square error (RMSE) values were calculated to test the models' accuracy. RMSE/actual shear ratio varied between 0.27 and 0.40 for NN predictions. Similarly, NFIS estimations resulted in a 0.28-0.37 ratio for local peak values in all subject groups. On the other hand, error percentages for global peak shear values were found to be in the range 11.4-44.1. These results indicate that there is no direct relationship between pressure and shear magnitudes. Future research should aim to decrease error levels by introducing shear stress dependent variables into the models.

Specific absorption rate and electric field measurements in the near field of six mobile phone base station antennas

In this article, the exposure to radio frequency electromagnetic fields was studied in close proximity (distances of 10, 100, 300, and 600 mm) to six base station antennas. The specific absorption rate (SAR) in 800 mm x 500 mm x 200 mm box phantom as well as unperturbed electric field (E) in air was measured. The results were used to determine whether the measurement of local maximum of unperturbed electric field can be used as a compliance check for local exposure. Also, the conservativeness of this assessment method compared to the ICNIRP basic restriction was studied. Moreover, the assessment of whole-body exposure was discussed and the distance ranges presented in which the ICNIRP limit for local exposure could be exceeded before the limit for whole-body SAR. These results show that the electric field measurement alone can be used for easy compliance check for the local exposure at all distances and for all antenna types studied. However, in some cases when the local peak value of E was compared directly to the ICNIRP reference level for unperturbed E, the exposure was overestimated only very slightly (by factor 1.1) compared to the basic restriction for localized SAR in a human, and hence these results can not be generalized to all antenna types. Moreover, it was shown that the limit for localized exposure could be exceeded before the limit for the whole-body average SAR, if the distance to the antenna was less than 240 mm.

Exposure of the general public due to wireless LAN applications in public places

The typical exposure caused by wireless LAN applications in public areas has been investigated in a variety of scenarios. Small-sized (internet café) and large-scale (airport) indoor scenarios as well as outdoor scenarios in the environment of access points (AP) supplying for residential areas and public places were considered. The exposure assessment was carried out by numerical GTD/UTD computations based on optical wave propagation, as well as by verifying frequency selective measurements in the considered scenarios under real life conditions. In the small-sized indoor scenario the maximum temporal peak values of power density, spatially averaged over body dimensions, were found to be lower than 20 mW/m(2), corresponding to 0.2% of the reference level according to the European Council Recommendation 1999/519/EC. Local peak values of power density might be 1-2 orders of magnitude higher, spatial and time-averaged values for usual data traffic conditions might be 2-3 orders of magnitude lower, depending on the actual data traffic. In the considered outdoor scenarios, exposure was several orders of magnitude lower than in indoor scenarios due to the usually larger distances to the AP antennas.

Signature of patchy reionization in the polarization anisotropy of the CMB

The inhomogeneous ionization state of the universe when the first sources of ionizing radiation appeared should lead to anisotropies in the polarization of the cosmic microwave background. We use cosmological simulations of the process by which the first sources ionized the intergalactic medium to study the induced polarization anisotropies. We find that the polarization anisotropies have rms of order {approx} 0.01 {mu}K, and local peak values of {approx} 0.1 {mu}K, smaller than those due to gravitational lensing on small scales. The polarization direction is highly coherent over degree scales. This directional coherence is not expected from either primary anisotropy or gravitational lensing effects, making the largest signals due to inhomogeneous ionization relatively easy to isolate, should experiments achieve the necessary very low noise levels.

ASSESSMENT OF COMPLEX EMF EXPOSURE SITUATIONS INCLUDING INHOMOGENEOUS FIELD DISTRIBUTION

Assessment of exposure to time varying electric and magnetic fields is difficult when the fields are non-uniform or very localized. Restriction of the local spatial peak value below the reference level may be too restrictive. Additional problems arise when the fields are not sinusoidal. The objective of this review is to present practical measurement procedures for realistic and not too conservative exposure assessment for verification of compliance with the exposure guidelines of ICNIRP. In most exposure situations above 10 MHz the electric field (E) is more important than the magnetic field (B). At frequencies above 500 MHz the equivalent electric field power density averaged over the body is the most relevant indicator of exposure. Assessment of specific absorption rate (SAR) is not needed when the spatial peak value does not exceed by 6 dB the average value. Below 50 MHz down to 50 Hz, the electric field induces currents flowing along the limbs and torso. The current is roughly directly proportional to the electric field strength averaged over the body. A convenient way to restrict current concentration and hot spots in the neck, ankle and wrist, is to measure the current induced in the body. This is not possible for magnetic fields. Instead, for a non-uniform magnetic field below 100 kHz the average magnetic flux density over the whole body and head are valid exposure indicators to protect the central nervous system. The first alternative to analyze exposure to non-sinusoidal magnetic fields below 100 kHz is based on the spectral comparison of each component to the corresponding reference level. In the second alternative the waveform of B or dB/dt is filtered in the time domain with a simple filter, where the attenuation varies proportionally to the reference level as a function of frequency, and the filtered peak value is compared to the peak reference level derived from the ICNIRP reference levels.

Experimental study on the gas–solid suspension flow in a square cyclone separator

Abstract A three-dimensional particle dynamic analyzer (3D-PDA) was employed to measure the gas–solid two-phase flow in a lab-scale square cyclone separator with downward gas-exit. Several cases of different inlet velocity and particle concentration were studied. The particle used in the test was glass bead of mean diameter 30–40 μm. Discussion was given on the distribution of flow vector, mean velocity, turbulent intensity and kinetic energy of both gas and particles of different diameter at different position in the separator. It was found that the center of the flow field deviated from the geometric center of the cyclone. The flow fields had the feature of Rankine eddy, i.e., strongly swirling region in the central part and pseudo-free eddy region of weak swirling intensity near the cyclone wall. Local vortex existed at the corners where the flow changed its direction sharply. When the cyclone wall was heated and the suspension temperature was elevated, the flow field became more uniform than that under room-temperature condition. The local vortexes at the corners were weakened and the swirling intensity became poorer which led to decreased total mean separation efficiency from about 81% to 76.5%. The right-side wall facing the suspension inlet gave the major contribution to the separation efficiency, where the largest downward velocity was measured. Back-flow (upward velocity) was found around the center of the separator above the gas-exit. The quasi-laminar motion of particles enhanced the turbulent motion at the corners due to particle–particle or particle-wall collision, which led to the local peak value of the turbulent kinetic energy and turbulent intensity. The corner was one of the major regions to cause pressure drop and was found to be beneficial to particle separation mainly because the strong fluctuating flow consumed much of the kinetic energy of both the particle and gas.

Modeling the Impact of Convective Entrainment on the Tropical Tropopause

Abstract Simulations with the Weather Research and Forecasting (WRF) cloud-resolving model of deep moist convective events reveal net cooling near the tropopause (∼15–18 km above ground), caused by a combination of large-scale ascent and small-scale cooling by the irreversible mixing of turbulent eddies overshooting their level of neutral buoyancy. The turbulent cooling occurred at all CAPE values investigated (local peak values ranging from 1900 to 3500 J kg−1) and was robust to grid resolution, subgrid-scale turbulence parameterization, horizontal domain size, model dimension, and treatment of ice microphysics. The ratio of the maximum downward heat flux in the tropopause to the maximum tropospheric upward heat flux was close to 0.1. This value was independent of CAPE but was affected by changes in microphysics or subgrid-scale turbulence parameterization. The convective cooling peaked roughly 1 km above the cold point in the background input sounding and the mean cloud- and (turbulent kinetic energy) TKE-top heights, which were all near 16.5 km above ground. It was associated with turbulent entrainment of stratospheric air from as high as 18.25 km into the troposphere. Typical cooling in the experiments was of order 1 K during convective events that produced order 10 mm of precipitation, which implied a significant contribution to the tropopause energy budget. Given the sharp concentration gradients and long residence times near the cold point, even such a small entrainment rate is likely consequential for the transport and ambient distribution of trace gases such as water vapor and ozone, and probably helps to explain the gradual increase of ozone typically observed below the tropical tropopause.

The turbulent characteristics of the gas–solid suspension in a square cyclone separator

Three-dimensional particle dynamics analyzer was employed to study the gas–solid flow in a square-shaped cyclone separator which was designed for large CFB application. Distribution of flow vector, fluctuating velocity, turbulent kinetic energy, turbulent intensity and particle concentration were discussed. The swirling flow inside the cyclone showed the Rankine vortex characteristics, i.e., strong swirling vortex at the central region of the cross-section and weak swirling quasi-free vortex near the wall. The quasi-laminar motion of particles enhanced the turbulent movement at the corners due to particle–particle/wall collision, which led to the local peak value of the turbulent kinetic energy and turbulent intensity. The corner is one of the major region to cause pressure drop because the suspension at the corners consumed more energy of the flow. The corners were found to be beneficial to particle separation mainly because the strong fluctuating flow consumed much of the kinetic energy of both the particle and the gas.