Higher Velocity Values Research Articles

DINÂMICA HÍDRICA DO SOLO DE FITOFISIONOMIA DE CERRADO RALO DO CHAPADÃO DO DIAMANTE - SERRA DA CANASTRA (MG)

The Cerrado is characterized as an important Brazilian biome, forming strategic hydrographic basins within its territory that are significant both nationally and internationally. Despite its importance, the biome has been increasingly impacted by anthropogenic activities. In this context, this study aims to analyze and understand the physical-hydraulic characteristics of the soil in a sparse Cerrado physiognomy located in the Chapadão do Diamante (Serra da Canastra-MG), providing the necessary foundation for the assessment and development of future management strategies for similar areas. For field data prospecting, a rain simulator and a concentric ring infiltrometer were used. The results demonstrated a high infiltration capacity in the study area, with no significant surface runoff even under high-intensity precipitation (57.35 mm), revealing high values of basic infiltration velocity (BIV) at 626.56 mm/h. Overall, these values are associated with the dynamics of landscape elements, emphasizing the importance of biological processes, such as the role of vegetation and soil fauna, in modulating the soil's ability to retain, infiltrate, and store water. Keywords: Water Infiltration; Rain Simulator; Concentric Ring Infiltrometer.

Impact of Various High Intensity Earthquake Characteristics on the Inelastic Seismic Response of Irregular Medium-Rise Buildings

In the twenty-first century, the seismic design of buildings seems to have become a fully recognized topic. There are guidelines and standards which should be taken into account by designers in seismic areas. Designers using modern international guidelines have ascertained that the behavior of structures is not as expected. New challenges in the construction industry result in the construction of structures with new, unusual shapes. These are structures that do not meet the assumptions of safe construction in seismic areas. Contemporary buildings are also characterized by their irregular distribution of structural elements. Such solutions are not beneficial from the point of view of seismic engineering and can lead to reduced dynamic resistance and damage in such structures. In this paper, a five-storey, irregular-shaped reinforced concrete (RC) building model was subjected to different earthquakes with varying magnitudes, PGA (peak ground acceleration) and PGV (peak ground velocity) values, and durations of the intense shock phase. Once the model was verified using previous in situ measurements, the building model was subjected to five earthquakes. A numerical nonlinear analysis of the building was performed using a verified FEA (finite element analysis) model in the time domain through non-linear time history analysis with the Broyden–Fletcher–Goldfarb–Shanno (BFGS) method. The building’s dynamic properties were measured using various methods of excitation. The model was influenced, among others, by two far-field representative events caused by the last earthquake in Turkey, which resulted in strong ground motion. The analysis results identified the locations of structural damage and allowed for the assessment of the structure’s dynamic resistance. The results of the calculations prove that the duration of the intensive phase of extortion is one of the reasons for building damage in earthquake-prone areas. Building damage occurs with earthquakes that are characterized by an intensive phase of excitation with a long duration and high values of velocity in the earthquake components. The article highlights the inadequate dynamic resistance of the building, leading to excessive displacements and unfavorable structural solutions. Damage to buildings at this earthquake intensity caused damage to the load-bearing structure, which was not designed for such intensities. This paper is a research report with a specific case study of medium-rise irregular RC buildings.

High sound pressure level sound absorption in acoustic resonant metamaterials: adapting a mass-spring model for nonlinear effects

In aerospace, conventional materials as micro-perforated panels backed by cavities are used to absorb sound at high sound pressure levels. These solutions are not optimal at low frequencies compared to resonant acoustic metamaterials, which present an acoustic absorption peak with a wavelength-to-thickness ratio greater than conventional materials, i.e., a ratio>>5. Acoustic resonant metamaterials are mainly studied at low sound pressure levels (<100dB). However, they are sensitive to increasing the amplitude of acoustic excitation. The studied metamaterial is composed of a compact array of thin single-perforation panels spaced by thin cylindrical air cavities. In a previous study, a mass-spring model was developed for low sound pressure levels. The perforations are modeled by equivalent masses, whereas cavities by equivalent springs. In the perforations, high values of the acoustic velocity lead to an increase in the acoustic resistance of the material. This effect is considered by the Forchheimer parameter in the mass-spring model. To determine this parameter and to study how it is impacted by the metamaterial geometry, the computational fluid dynamic method is used. The mass-spring model is adapted with a nonlinear term. The adapted model agrees well with simulations by finite element method at sound pressure levels up to 140dB.

Determination of “tribological performance working fields” for pure PEEK and PEEK composites under dry sliding conditions

Poly-ether-ether-ketone (PEEK) and PEEK composites are widely used polymers in many engineering applications where dry sliding is required. In this study, the influence of sliding velocity and applied load values on the friction and wear behavior of pure PEEK, 30 wt% glass fiber reinforced PEEK (PEEK-30GF), 30 wt% carbon fiber reinforced PEEK (PEEK-30CF) and 10 wt% carbon fiber+10 wt%graphite +10 wt%poly-tetra-fluoro-ethylene (PTFE) filled PEEK (ie. High (H) pressure (P) and velocity (V) resistant PEEK (PEEK-HPV)) composites rubbing against AISI 304 stainless steel disc was investigated. The experiments were carried out at room temperature under dry sliding conditions in a pin-on-disc wear rig. The applied loads ranged from 30 to 250 N, while the sliding velocities ranged from 1.0 to 4.0 m/s. At these load and velocity ranges, the friction coefficient-wear rate relationship of pure PEEK and composites was established and evaluated. In addition, the operating load-velocity limits of each material were determined and stated. The lowest coefficient of friction and wear rate were obtained in PEEK-HPV, PEEK-30CF, PEEK-30GF composites and pure PEEK polymer, respectively. In addition, it was observed that the coefficient of friction (CoF) decreased and the specific wear rate (SWR) increased with the increase in sliding velocity and applied load in all PEEK materials. The wear rate values of PEEK-HPV and PEEK-30%CF composites are in the range of 10−7 - 10−6 (mm3/Nm), while the wear rate values of pure PEEK and PEEK-30%GF are in the range of 10−6 - 10−5 (mm3/Nm). It was determined that carbon fiber, graphite and PTFE additives added to PEEK polymer as hybrid were very effective in reducing the wear rate of PEEK composite (PEEK-HPV). An adhesive wear mechanism was observed in PEEK-HPV and PEEK-30CF composites both at low load and velocity values and at high load and velocity values.

Influence Evaluation of Open Propellers with Boss Cap Fins: Case Studies on Types B4-70 and Ka4-70

Numerical analysis of fins effect on propeller performance was conducted, specifically using the B4-70 and Ka4-70 propellers. The study investigated different types of fins, including bare fins and PBCF (Propeller Boss Cap Fins) using computational fluid dynamics (CFD) simulations. The explicit algebraic stress model (EASM) based on Reynolds-Averaged Navier-Stokes (RANS) equations and turbulence modeling was employed to determine the optimal results. The main objective of this research was to enhance energy efficiency in ships by examining various open propeller configurations. The CFD simulation results for open propellers B4-70 and Ka4-70, with the addition of boss cap fins, revealed interesting phenomena. When the open propellers B4-70 and Ka4-70 were equipped with PBCF, they would experience an increase in efficiency (η0). This was because the performance of the fins functioned optimally when the advance ratio (J) is high, as evident from the high velocity values. Thus, with higher velocity and lower pressure in the boss cap region at high J values, there was an elevation in thrust force due to the reduction of hub vortex. In the case of open propeller B4-70 with added PBCF, there was an increase in the efficiency value (η0) ranging from 3% to 5% when J varied from 0 to 0.7. Similarly, for propeller Ka4-70 with the addition of PBCF, there was an increase in the efficiency value (η0) ranging from 1% to 3% when J varied from 0 to 0.7. Notably, the use of an Energy-Saving Device (ESD) in the form of PBCF can increase the efficiency of ship propeller, as reported in this paper. Consequently, these findings affirmed the reliability of the overall calculations using the CFD approach.

Physics-informed differentiable method for piano modeling

Numerical emulations of the piano have been a subject of study since the early days of sound synthesis. High-accuracy sound synthesis of acoustic instruments employs physical modeling techniques which aim to describe the system’s internal mechanism using mathematical formulations. Such physical approaches are system-specific and present significant challenges for tuning the system’s parameters. In addition, acoustic instruments such as the piano present nonlinear mechanisms that present significant computational challenges for solving associated partial differential equations required to generate synthetic sound. In a nonlinear context, the stability and efficiency of the numerical schemes when performing numerical simulations are not trivial, and models generally adopt simplifying assumptions and linearizations. Artificial neural networks can learn a complex system’s behaviors from data, and their application can be beneficial for modeling acoustic instruments. Artificial neural networks typically offer less flexibility regarding the variation of internal parameters for interactive applications, such as real-time sound synthesis. However, their integration with traditional signal processing frameworks can overcome this limitation. This article presents a method for piano sound synthesis informed by the physics of the instrument, combining deep learning with traditional digital signal processing techniques. The proposed model learns to synthesize the quasi-harmonic content of individual piano notes using physics-based formulas whose parameters are automatically estimated from real audio recordings. The model thus emulates the inharmonicity of the piano and the amplitude envelopes of the partials. It is capable of generalizing with good accuracy across different keys and velocities. Challenges persist in the high-frequency part of the spectrum, where the generation of partials is less accurate, especially at high-velocity values. The architecture of the proposed model permits low-latency implementation and has low computational complexity, paving the way for a novel approach to sound synthesis in interactive digital pianos that emulates specific acoustic instruments.

Petrophysical Analyses of Rock Construction Materials from a Roman Rural Settlement in Podšilo Bay on Rab Island (North-East Adriatic, Croatia).

This article presents the results of petrophysical analyses of limestones and sandstones used for the construction of the wall structures of a Roman rural settlement located in Podšilo Bay on Rab Island (Croatia). An on-site analysis of the walls indicated the use of different lithotypes, which is an uncommon case in the area. So far, no petrophysical properties of the applied materials have been tested, and their provenance has not been specified. The aim of this research was to determine their usability as construction materials in an attempt to determine the possible reasons behind the usage of multiple lithotypes and their suitability as building materials. The following procedure was used to address these issues: (1) determination of the petrographic characteristics of the rocks, (2) performance of tests to characterise the mechanical properties in a complex stress state of uniaxial tension followed by uniaxial and triaxial compression, and, finally, (3) determination of the internal structure of the rocks using methods based on X-ray imaging. Multi-proxy characteristics of the materials including numerous observations and methods were performed: optical microscopy used to characterise rock petrography and mineralogy, scanning electron microscopy (SEM) coupled with EDS, as well as grinding tests; furthermore, mechanical properties were determined on cylindrical samples in accordance with European standards. X-ray microtomography using the XμCT method enabled microscopic observations and determination of the orientation of discontinuities and the rock structure. The performed analyses allowed us to distinguish three lithological types of sandstone and two types of limestone among the examined stone blocks. Stone blocks of fine- and medium-grained sandstone with carbonate binders, as well as sparitic limestone and mudstone with calcite veins, were used to build the studied structures. The analysed blocks showed traces of partial edge processing. Despite the defects in the material structure identified using XμCT, all the types of rock were characterised by high or very high strength. High values of longitudinal wave velocity confirmed the good quality of the material. These results contribute to a better understanding of the construction process and the related technological choices, and they provide the first dataset which can be used for the reconstruction of the building's original appearance in the future.

Evaluation of the Primary Pipe Network at Banua Anyar Booster Pump as an Effort to Reduce Water Loss in the Service area of Northern Banjarmasin, South Kalimantan

Recorded as the best PDAM in South Kalimantan in Banjarmasin City. PT. Bandarmasih Perseroda Drinking Water (PAM Bandarmasih) is still facing the problem of high water loss rates of 29.07% in 2022, which is still far above the National Medium Term Development Plan (RPJMN) target with a minimum water loss value of 20%. One of the ways PDAM can reduce water loss is by evaluating the pipe network in a District Meter Area (DMA). This research focuses on evaluating the primary pipe network in the area served by the Banua Anyar booster which serves 18 DMAs. Network evaluation using EPANET 2.0 software. The evaluation results show that the diameter of the primary pipe from the booster pump to the Banua Anyar pipe bridge has quite high unit-head loss and flow velocity values due to flow friction with the pipe surface. It is necessary to change the diameter of the primary pipe used in the Banua Anyar booster network from a diameter of 400 mm to 600 mm which can reduce the rate of water loss by 6.3%. In the future, it is hoped that the value of water loss at PDAM Banjarmasin City can be reduced and the affordability of drinking water services for the people of Banjarmasin City can increase.

A cross-sectional study in type 2 diabetes patients reveals that elevated pulse wave velocity predicts asymptomatic peripheral arterial disease associated with age and diabetes duration

BackgroundPeripheral arterial disease (PAD) reduces functional capacity and raises cardiovascular risks, but underdiagnosis is common, resulting in less comprehensive care than other cardiovascular conditions. While diabetes has long been viewed as a key risk factor for PAD, recent studies indicate that its impact is influenced by the presence of concurrent cardiovascular risk factors. The aim of this study is to elucidate the intricate relationship between the prevalence of PAD, diabetic complications, and cardiovascular risk factors among asymptomatic patients with type 2 diabetes mellitus (T2DM). MethodsNinety-one patients with T2DM and no symptoms or previous diagnosis of PAD were recruited from the outpatient diabetic clinic. Clinical data were extracted from electronic medical records, and the screening for PAD was conducted using MESI mTABLET. ResultsScreening for PAD among asymptomatic individuals with T2DM revealed that 5.49 % of patients exhibit a low ankle-brachial index (ABI). Patients who had previously experienced major adverse cardiovascular events or exhibited albuminuria displayed lower ABI values. Furthermore, a striking 45.05 % of the participants displayed an abnormally high carotid-femoral pulse wave velocity (cfPWV) value, with elevated PWV values correlating with advanced age and longer diabetes duration. ConclusionsThe prevalence of elevated cfPWV is more pronounced than that of decreased ABI in T2DM patients with asymptomatic PAD and is associated with older age and longer diabetes duration, therefore measurement of both ABI and PWV is crucial for the cardiovascular risk assessment protocol for patients with T2DM and timely PAD diagnosis.

Syngas to FCC-like gasoline range hydrocarbons with upgraded light olefin selectivity catalyzed by readily synthesized Fe-MOF

The global trend toward sustainability is due to the growing demand for synthetic chemicals and fuels relying on fossil crude oil with the associated concerns of climate change. The Fischer-Tropsch synthesis (FTS) process is a key sustainable pathway for supplying light olefins, gasoline, and other petrochemicals using green hydrogen and energy. Here we report a simple, green, cost-effective synthesis strategy to prepare an iron-based metal–organic framework (Fe-BTC MOF) at room temperature with a remarkable porous structure analogous to the commercially available Basolite F300. The catalyst shows a 97% syngas conversion to gasoline-range hydrocarbons (C5-C12) at high temperatures, with a selectivity of 48.3%, yield of 28%, low methane selectivity (15.5%) and low C13+ selectivity (1%). In addition, the catalyst is 29% selective to light olefin (C2-C4=), yielding 17%, besides an olefin/paraffin ratio (O/P) of 4.3 with 81% olefin selectivity of the C2-C4 fraction. The resulting gasoline is equivalent to gasoline produced by Fluid Catalytic Cracking (FCC) of crude oil. The highest C5-C12 selectivity reached 63.6%, yielding 12% at 29% CO conversion. The Fe-BTC/C catalyst showed excellent stability for time on stream >100 h and a high gas hourly space velocity (GHSV) value of 20000 mL g-1cat h−1 with an Fe-time yield of 165 µmolCO g-1Fe s−1. The prepared Fe-BTC catalyst, with a 2-fold larger pore volume than the previously prepared Fe-MIL-88B catalyst, has a higher olefin production capability by 2-fold, 7-fold higher O/P for the light fraction and 2.3-fold higher C5+ selectivity. The sustainable synthesis of catalysts with improved porous structure may significantly foster FTS technology for being economically practical to be scaled up and commercialized for national fuel and olefin production projects.

Comparative Assessment of Wildland Fire Rate of Spread Models: Effects of Wind Velocity

Wildland fire rate of spread prediction models are important tools for the effective coordination of resident evacuation and fire suppression efforts. A comparative assessment of ten empirical and semi-empirical rate of spread prediction models is performed, using a selection of 203 laboratory experiments of surface spreading fires; special emphasis is given to the effects of external wind velocity. Five of the evaluated models have been developed using measurements obtained in laboratory-scale tests; these models are combined with two supplementary sub-models that account for the effects of wind. In addition, a selection of five empirical models that have been developed using large-scale field tests are also assessed. The performance of the ten prediction models is evaluated, both qualitatively and quantitatively, by employing a range of statistical error metrics. The laboratory-developed models are found to exhibit high sensitivity on low fuel load values, when no external wind is present, as well as on low packing ratios and high wind velocity values. The field-developed models exhibit significant discrepancies against the experimental data, due to the use of specific parameters regarding fuel type, scale and wind velocity.

Assessment of male reproductive traits in endangered leuciscids from the Iberian Peninsula: first attempts to store gametes both at short- and long-term

During the spring of 2022, several endangered leuciscid species (Anaecypris hispanica, Squalius aradensis, Anachondrostoma Occidentale, and Iberochondrostoma lusitanicum) were sampled both at the Vasco da Gama aquarium facilities and in some rivers of the Algarve region, Portugal. Sperm samples were extracted by gentle abdominal pressure and sperm motion parameters were assessed for the first time in four species, using a computerized analysis system. The results obtained showed that spermatozoa kinetic patterns were similar for all 4 species, with high motility and velocity values after the sperm activation time and with a marked decrease after 20. On the other hand, sperm longevity was highly variable between species, with short longevities (around 40s) for A. hispanica and S. aradensis, and longer longevities (100-120s) for A. occidentale and I. lusitanicum, which could indicate a latitudinal pattern in terms of sperm longevity. At the same time, morphometric analysis was carried out for the four target species, revealing that spermatozoa showed similar sizes and shapes to other external fertilizers belonging to Leuscididae, with small spherical heads, uniflagellate, and without acrosomes. In addition, a short-term gamete storage trail was performed by diluting sperm in 1:9 (sperm:extender) and storing them at 4ºC. Although the results obtained were uneven among the species studied, the dilution and extender used generated motilities above 40% up to day 4 of storage in S. aradensis and I. lusitanicum, and up to days 1-2 in A. hispanica and A. occidentale, respectively. Finally, gamete cryopreservation trials were also carried out on these threatened species. Although cryopreserved samples showed significantly lower motility than fresh samples, some protocols generate acceptable percentages of viability, DNA integrity, and sperm motility in some species such as I. lusitanicum and A. occidentale. The data revealed that the protocol based on 10% DMSO plus 7.5% egg yolk generated the best results.This study is the first to assess the reproductive traits of wild and captive populations of endangered leuciscids endemic from the Iberian Peninsula, describing the spermatozoa kinetics and developing protocols for managing male gametes both in short- and long-term storage. Outcomes will provide new and useful tools to complement the management and conservation of ex situ breeding programs that are being developed for these four endangered species.

Nonlinear dynamics of a nearly taut cable subjected to parametric aerodynamic excitation due to a typical pulsatile wind flow

In this study, the dynamic response of a nearly taut nonlinear cable that is actuated by a pulsatile wind flow is investigated for the sake of obtaining the regime of motion and bifurcations of the system. The aerodynamic model is a general modelling of wind excitation including nonlinear cubic terms. Since realistic wind blows frequently and is not invariant, the velocity of the time-variant flow is considered to be a typical combination of a constant and a small harmonic perturbation. The equation of motion of the system has a simple form and is discretized by single-mode Galerkin method and by employing the method of multiple scales (MMS) the parametric resonance of the system is obtained. The results of bifurcations of the system assuming solely its first mode, exhibit a complicated behavior, whose occurrence in a simple dynamical system is interesting from the nonlinear dynamic point of view. Moreover, we show that as the frequency of the wind flow is decreased, the amplitude of the cable is also decreased. Also, as both constant and harmonic wind velocities are increased, the maximum amplitude of the system is not significantly influenced. Furthermore, the numerical-based bifurcation analyses show that for high values of constant wind velocity, small values of harmonic wind velocity, and excitation frequency, the system undergoes less chaos and actually unpredictable motions. The presented model can be evaluated more precisely to extend the above results to more realistic ones.

An Analysis of The Material and Design of an Exhaust Manifold for A Single-Cylinder Internal Combustion Engine

This study aims to find the best material for the manifold and improve airflow in the UniMAP Automotive Racing Team (uniART) exhaust manifold. The exhaust manifold is a part of the exhaust system that collects and delivers exhaust gases from the cylinder head to the exhaust outlet. The exhaust manifold’s design is significant to the engine performance. The current design and new designs of the exhaust manifold were modelled using SOLIDWORKS software. Stainless steel, cast iron and mild steel were chosen as materials for manifold and were studied by conducting the Steady-State Thermal analysis. The flow of the air in the manifold is analysed and evaluated in terms of pressure and velocity. The fluid flow and thermal analysis are simulated in Computational Fluid Dynamics analysis software known as ANSYS. Results of thermal analysis prove that Stainless steel is better than other materials since it has a high temperature difference and low heat flux. The results of fluid flow analysis were compared between the current design and new designs of the exhaust manifold. The outcome indicated that validated Design 2 has a higher velocity value at the outlet and lower pressure at inlets which improves the airflow in the exhaust manifold.

Doping effects on minority carrier parameters in bulk GaAs

In this paper, we measured the experimental amplitude and phase of the Photothermal deflection signal for bulk GaAs “silicon” doped n + type, “chromium” doped n type and “carbon” doped p type in order to determine the nonradiative recombination parameters. The results obtained for non-radiative lifetime and the electronic diffusion agree with those appearing in the literature for similar samples. By comparison with values reported in literature, the increase of doping density favors auger recombination that produce an increase of non-radiative lifetime. We have found that electron mobility in p type C-doped GaAs is about 300 cm2/V·s. In fact, holes motilities are respectively 177 and 193 cm2/V·s for n + type Si-doped GaAs and n type Cr-GaAs doped. However, we obtained high values of the recombination velocity for non passivated surface.

Assessment of Maximum Velocity: A Case Study of Pogon Szczecin Football Players in Polish Ekstraklasa

The aim of this study was to assess the maximum velocity achieved by professional soccer players. The study involved 20 professional football players. The analysis of the achieved velocities during the season was based on individual maximum velocity values obtained in a preseason period test using the GPS monitoring device Catapult Vector S7. The study covered 20 match units and 77 training units. A velocity equal to or greater than 100% of the maximum velocity was achieved 24 times - 21 times (accounting for 88%) during a competitive match (MD 0), 1 time (accounting for 4%) two days before (MD-2), and two times (accounting for 8%) three days before (MD-3). A velocity in the range of 90-99% of the maximum velocity was achieved 207 times. The results confirm that football players can achieve values equal to or greater than 100% of their maximum velocities; however, this occurrence is rare. Due to the low probability of high maximum velocity values during a training microcycle, it is recommended to incorporate specific training methods that allow for achieving high maximum velocities to reduce the risk of hamstring muscle injuries among players, especially among reserve players (who rarely participate in competitive matches).

RESEARCH OF THE INDIUM ARSENIDE IMPULSE PROPERTIES

Indium arsenide is a promising material for creation of high-performance electronic and optoelectronic devices. A high level of knowledge of indium arsenide properties will make it possible to predict the potential possibilities of its application, as well as multicomponent semiconductors based on it. The problem of studying the properties of InAs in the regime of a strong electric field is relevant.
 In scientific and technical sources, data on the impulse properties of indium arsenide in the regime of a strong electric field are poorly presented. The purpose of the work is to study the field-velocity dependence in the pulsed mode of a strong electric field and to analyze the response to changes in its amplitude, pulse duration, and leading edge duration.
 The method of relaxation equations was used to analyze the field-velocity characteristic in the regime of a strong electric field. In the electric field static regime, the highest value of the drift velocity was 3·105 m/s (with a field amplitude of 2 kV/cm), in the saturation section it was 0.9·105 m/s.
 An analysis of the field-velocity dependence in the pulsed mode of a strong electric field showed that with an increase in the field amplitude, the maximum value of the drift velocity increases, and the duration of the "overshoot" shortens. Fields of 5–30 kV/cm correspond to an increase in the highest velocity value by a factor of 2.7–8. The spatial distribution of the drift velocity gave an estimate of the average velocity and distance traveled by charge carriers at different field values.
 An increase in the duration of the leading edge duration of the field pulse caused a delay in transient processes. At 12 kV/cm < E, the peak value of the drift velocity additionally decreases. The duration of a strong electric field pulse has a significant effect only at values less than the formation time of the drift velocity maximum. Such values of the pulse duration lead to a decrease in the rate of drift and relaxation processes.
 Comparison of the field-velocity dependences in the high-field pulsed mode showed that the maximum value of the drift velocity of InAs electrons exceeds the corresponding values: GaAs, InP – by several times; GaN - an order of magnitude. The duration of the “ overshoot ” of the drift velocity for InAs is somewhat longer than for GaAs, InP, GaN.

Effects of Upstream Wakes on the Boundary Layer Over a Low-Pressure Turbine Blade

Abstract In the present work, the evolution of the boundary layer over a low-pressure turbine blade is studied using direct numerical simulations, with the aim of investigating the unsteady flow field induced by the rotor-stator interaction. The freestream flow is characterized by the high level of freestream turbulence and periodically impinging wakes. As in the experiments, the wakes are shed by moving bars modeling the rotor blades and placed upstream of the turbine blades. To include the presence of the wake without employing an ad-hoc model, we simulate both the moving bars and the stationary blades in their respective frames of reference and the coupling of the two domains is done through appropriate boundary conditions. The presence of the wake mainly affects the development of the boundary layer on the suction side of the blade. In particular, the flow separation in the rear part of the blade is suppressed. Moreover, the presence of the wake introduces alternating regions in the streamwise direction of high- and low-velocity fluctuations inside the boundary layer. These fluctuations are responsible for significant variations of the shear stress. The analysis of the velocity fields allows the characterization of the streaky structures forced in the boundary layer by turbulence carried by upstream wakes. The breakdown events are observed once positive streamwise velocity fluctuations reach the end of the blade. Both the fluctuations induced by the migration of the wake in the blade passage and the presence of the streaks contribute to high values of the disturbance velocity inside the boundary layer with respect to a steady inflow case. The amplification of the boundary layer disturbances associated with different spanwise wavenumbers has been computed. It was found that the migration of the wake in the blade passage stands for the most part of the perturbations with zero spanwise wavenumber. The non-zero wavenumbers are found to be amplified in the rear part of the blade at the boundary between the low- and high-speed regions associated with the wakes.

The potential of shear wave velocity as an erosion risk index

Soil erosion is a captious environmental problem in regions of hot tropical climates, causing loss of land and natural disasters such as river sedimentation, flooding, and slope failures. Based on soil properties and their response to erosion agents, efforts have been made to develop simplified models and indices for the estimation of erosion. ROM scale is proven to be effective in forecasting risk levels for erosion assessment. However, the method requires soil sampling and laboratory experimentation, which is time-consuming and laborious, especially when analyzing huge areas. Therefore, this study aims to develop a relation between ROM scale and shear wave velocity estimated by the spectral-analysis-of-surface-waves (SASW) method. For this purpose, 36 soil samples were extracted, and twelve SASW tests were conducted at twelve sites identified along Sungai Langat. Soil particle distribution was carried out to calculate the ROM erosion index value for all the extracted soil samples. The fast Fourier Transform (FFT) algorithm was used to transform the time-recorded signals into the frequency domain, and the dispersion curves were generated after the masking process. The shear wave velocity erosion risk ranged from 10 m/s to 120 m/s, indicating critical risk and low risk, respectively. Low erosion risk levels were observed for high shear wave velocity values, representing a decaying pattern in exponential relation. The resulting correlation between ROM scale and shear wave velocity produced a coefficient of determination value of 0.71, indicating a strong relation. This study indicated the potential of shear wave velocity as an erosion risk index.

Heterogeneity evaluation of pore types based on dipole shear sonic imager logs by means of statistical parameters, the central Persian Gulf

AbstractHeterogeneity analysis in carbonate reservoirs is of great importance for the interpretation of their characteristics. This study focuses on the evaluation of pore‐type heterogeneity by means of the sonic wave velocities in the carbonate–evaporite series of Permian–Triassic sequences in the Persian Gulf. Thin section petrography and laboratory measured the porosity and permeability of 1576 samples, as well as routine wire‐line logs, were employed. To manage heterogeneity, six electrofacies (EF) were determined based on an integrated analysis of compressional, shear and Stoneley waves as well as three routine logs (gamma, neutron and density). The frequency of pore types in each electrofacies was calculated. Then, the heterogeneity of pore‐type distribution in each electrofacies was measured by standard error and coefficient of variation. Sonic velocity has been compared with the geological properties of electrofacies. Results indicated that velocity is affected by factors other than the amount of porosity, facies or lithology. The standard error values in all electrofacies were close to zero. The coefficient of variation values ranges from 1.08 to 4.60. The lowest amount of coefficient of variation was observed in EF6 in the Khuff (K) 4 zone for moldic porosity. This value for intercrystalline porosity distribution in EF1 in the K1 zone was low, too. These results indicate the lowest standard deviation and the highest homogeneity in the distribution of intercrystalline and moldic porosities in K1 and K4. Also, comparing the mean values of sonic logs in each electrofacies with the total mean value in the whole sequence indicated that there is a relationship between sonic velocity logs and the type of porosity. High values of sonic velocity correspond to intercrystalline porosity in K1 and low values of velocity correspond to moldic porosity in K4. Results show that integrated pore‐type studies should be carried out to understand the sonic velocities in carbonate reservoir rocks.