Angle Spread Research Articles

Phase-resolved wave prediction in highly spread seas using optimised arrays of buoys

In many offshore operations, including the operation of wave energy converters, phase-resolved wave prediction is essential for safety and efficiency. However, for sea-states with large directional spreading angles, wave prediction becomes increasingly difficult. This study investigates the benefit of exploiting concurrent surface-displacement time histories measured by a buoy in three degrees of freedom (DoF) to facilitate prediction in such highly spread sea-states. A direct comparison is made with arrays of sensors measuring in a single DoF using the same formulation. The arrays considered are extensively optimised along with multiple sets of representative angles used to describe wave propagation, which is assumed to be normally distributed. The performance of the scheme is tested on a range of synthetically generated, realistic sea-states comprising single and crossing swells prevalent along the south coast of Australia. Additional tests involve wind-sea and swell waves described using Ewans models. Accurate predictions are obtained for times up to three wave periods into the future, in typical cases. With the multiple sets of optimal angles obtained for each optimal array, we further enhance the capability of the scheme by aggregating and averaging the different predictions from these sets. We observe a marked increase in both performance with large spreading and tolerance to possible variation in mean wave directions.

Birch plywood as gusset plates in glulam frame via mechanical connectors: A combined experimental and numerical study

Birch is a short-lived hardwood species widespread in the Northern Hemisphere. Plywood made from birch has superior mechanical properties compared with that made from most softwoods, which makes it suitable for structural application. In this study, the feasibility of using birch plywood as gusset plates in timber-timber connections is presented. Test frames consisting of birch plywood gussets and glulam beams connected by nails were built and tested. A 2D analytical model based on truss theory and a 3D finite element model were proposed and constructed. Both models showed satisfactory agreements with the test results in terms of stiffness and strength. Tensile failure on the birch plywood gussets along the outermost row of nail holes was observed in the experiment. The observed failure modes and the stress distributions in the 3D numerical model suggest that the spreading angle (Whitmore effective width) theory should be considered in the design phase of birch plywood gusset plates. Besides, a modified spreading angle theory is proposed to both approximate the stress distribution and predict the load-bearing capacity.

An Experimental Investigation of Supercritical Methane Injection Characteristics in a CO2 Environment

Abstract Clean energy generation is gaining significant attention from industries, academia, and governments across the globe. The Allam cycle is one such technology that has been under focus due to its efficiency, environmental friendliness, and economics. This is a direct-fired cycle operating at supercritical conditions using carbon dioxide as a working fluid. Fuel or oxidizer jet mixing with CO2 is a vital phenomenon that governs combustion efficiency, and it is not well understood for the Allam cycle conditions. This paper experimentally investigated the jet characteristics of a methane jet injected into a subcritical to supercritical carbon dioxide environment. A wide range of injection pressures and temperatures were targeted between subcritical to supercritical conditions. Unlike previous studies, the current work focused on injecting lower-density (methane) jets into higher-density (carbon dioxide) environments. Schlieren imaging and methane absorption measurements were simultaneously performed with a CMOS high-speed camera and a 3.39 μm infrared laser. Specifically, we looked at the classical injection parameter of jet spreading angle, which was classically established to be mainly a density ratio function. Here, the jet cone angle was obtained from the postprocessed schlieren imaging. The jet cone angle is a critical characteristic parameter that describes the entrainment rate in a jet; thus, it is a crucial parameter in understanding the nature of the jet. The laser measurements were only used as an additional check to confirm the entry time of methane into the chamber filled with carbon dioxide. Notably, this paper makes a detailed comparison between the jet cone angles of jets with a density ratio. The result showed that the classical correlations, such as Abramovich's theory applied to submerged turbulent gas jets developed for low-density ratio jets, were unsuitable for higher-density ratio jets. It was also observed that the divergence angles were dependent not only on density ratio but also on other parameters such as pressure ratios and reduced pressures.

Interplay of temperature and calcium content in beta-casein solutions: From controlled self-aggregation of micelles in bulk to the design of stable foams

We describe in this study the aggregation behaviour of β-casein micelles from milk in bulk aqueous solution as function of both temperature and calcium content, and its influence on the foaming properties, in order to test if the different aggregation states of β-casein makes possible the design of proteins-based thermoresponsive foams. First, we characterized the morphology of the self-assembled β-casein molecules in solution by coupling turbidity measurements, Dynamic Light Scattering and Small Angle Neutron Scattering. They self-organize into individual micelles at low temperature (20°C) whatever the calcium content, and transit in a reversible way into aggregates of micelles at large temperature in presence of calcium, with a threshold transition that depend both on temperature and calcium content. The micelles aggregation is driven by the calcium through association with serine phosphate groups localized on the hydrophilic part of the β-casein. In the micelles regime, we demonstrated that the addition of calcium tunes the aggregation number of unimers per micelle in the same way than an increase of temperature through a change of hydrophobic interactions. The hydrophilic chains of the corona are however in a good solvent and interact through excluded volume interactions, even when the β-casein micelles aggregates themselves. The internal molecular structure of the micelles is thus not modified by calcium bridges, which explains the complete reversibility of the aggregation process over temperature cycling. Second, we studied the foam stability versus time as a function of the temperature and calcium content by measuring the kinetic evolution of both the foam volume and the liquid fraction. Foams produced by solutions containing only β-casein micelles were stable in terms of foam volume on a timescale of 1 h at 20°C but drained quickly. However, foams become unstable when the temperature was increased above 20°C. In presence of calcium, the aggregation of β-casein micelles inside the foam liquid channels enabled to increase foam stability at larger temperature by acting as a cork, which slows down the drainage. The increase of foam stability by such aggregates is however not sufficient on the long term to allow the design of thermoresponsive foams.

Bioinspired Meta‐Reflection‐Splitter for Near‐Infrared Laser Stealth with Large Scattering Angle

AbstractMetasurface based phase manipulation has shown great capable of controlling anomalous reflection for low observability against laser active detection. However, current meta‐based designs for laser stealth in near‐infrared (NIR) range suffer from small scattering angles and complex fabrication process, and this hinders their mass productivity and flexible application in actual environments. Here, a bioinspired strategy is proposed to design a meta‐reflection‐splitter with a large scattering angle and strongly extinct specular reflection for NIR laser stealth, motivated by the color splitting effect on the green scale of butterfly Diaethria clymena. The biological reflection splitting is demonstrated to originate from the 180° phase difference of reflection created by the unsymmetrical laminae on densely arranged ridges. A simple etching‐free approach is further developed to generate large‐scale meta‐reflector‐splitter by self‐assembly of colloidal particles. This large‐area meta‐reflector‐splitter shows high‐efficient low observability (ultralow specular reflectance <1%) accompanied by a scattering angle of nearly 50° under the 1064 nm laser detection as well as a low mid‐infrared emissivity. This work sheds light on the phase manipulation of biophotonic structures and thus benefits the innovation in advanced optical materials and devices.

Dynamic Light Scattering Plus Scanning Electron Microscopy: Usefulness and Limitations of a Simplified Estimation of Nanocellulose Dimensions

Measurements of nanocellulose size usually demand very high-resolution techniques and tedious image processing, mainly in what pertains to the length of nanofibers. Aiming to ease the process, this work assesses a relatively simple method to estimate the dimensions of nanocellulose particles with an aspect ratio greater than 1. Nanocellulose suspensions, both as nanofibers and as nanocrystals, are subjected to dynamic light scattering (DLS) and to field-emission scanning electron microscopy (FE-SEM). The former provides the hydrodynamic diameter, as long as the scatter angle and the consistency are adequate. Assays with different angles and concentrations compel us to recommend forward scattering (12.8°) and concentrations around 0.05-0.10 wt %. Then, FE-SEM with magnifications of ×5000-×20,000 generally suffices to obtain an acceptable approximation for the actual diameter, at least for bundles. Finally, length can be estimated by a simple geometric relationship. Regardless of whether they are collected from FE-SEM or DLS, size distributions are generally skewed to lower diameters. Width distributions from FE-SEM, in particular, are well fitted to log-normal functions. Overall, while this method is not valid for the thinnest fibrils or for single, small nanocrystals, it can be useful in lieu of very high-resolution techniques.

Mantle Tomography of Central‐Eastern USA: Influence of Inversion Volume Size

AbstractTeleseismic tomography is a powerful tool to study the 3‐D structure of the upper mantle beneath a local seismic network, but the robustness of its images has been challenged by the increasing size of the study volume in recent studies. This is because teleseismic tomography uses relative travel‐time residuals (RTTRs) that are contaminated more by the whole‐mantle heterogeneity for a larger study region. In this work, we correct the RTTRs of teleseismic events for the mantle heterogeneities outside the study volume using two global tomographic models. Our results show that the whole‐mantle correction is necessary when a study region is wider than ∼10°, and the maximum outside residual reaches 1.2 s for a study region of ∼35° wide. After the whole‐mantle correction, those teleseismic events with a large ray spread angle are still useful for tomographic imaging. Applying this approach to teleseismic travel‐time data recorded by the USArray, we obtain a high‐resolution 3‐D P‐wave velocity (Vp) model beneath the central and eastern United States. It shows three low‐velocity anomalies beneath the New Madrid Seismic Zone, the East Tennessee Seismic Zone, and the South Carolina Seismic Zone, suggesting that lithospheric weakness induced by fluids may play an important role in reactivating the intraplate seismic zones. The passage of the Bermuda hotspot and remnants of the subducted Farallon slab in the lower mantle might be responsible for the fluid release and lithospheric weakening, which reactivated ancient rifts and suture zones in the crust and facilitated the formation of the intraplate seismic zones.

Effect of high temperature on nanopores in cokes

Small Angle Neutron Scattering and Ultra Small Angle Neutron Scattering were used to study the effect of annealing at temperatures of 1400 and 1600 °C, in an inert atmosphere, on the pore size distribution of three cokes prepared from Australian coals. The pore size range investigated was 1 nm to 2 µm. It was found that annealing substantially changed the size distribution of these pores in similar ways for all three cokes examined, despite the difference in rank and maceral composition of the starting coals. The pore sizes at which the greatest percentage changes in numbers occurred on heating was around 10 nm, with an increase in the number of both open and closed pores, by up to a factor of four after annealing at 1600 °C. For pores in the size range 100 nm to 2 µm, the number of closed pores decreased slightly and the number of open pores increased substantially; new open pores were created. The percentage increase in pore numbers introduced by annealing decreased with increasing pore size above 100 nm, but even at 2 µm pore radius, some samples showed a 50 % increase in total pore numbers. Annealing at greater temperature or longer time had a greater effect on pore numbers.

Quantifying structure and dynamics of bound and bulk polymer in tailor-made rubber-silica nanocomposites

The dynamics of long polymer chains in the presence of nanoparticles have been investigated. The nanocomposites of interest were inspired by tire industry-like rubber materials and consisted of entangled polyisoprene linear chains mixed with chemically pre-treated silica nanoparticles. Combining rheology, dielectric spectroscopy, and neutron spin echo measurements, we measured the modification of the polymer chain dynamics from bulk state to high filler concentration over a broad range of time and length scales. We show that the end-to-end relaxation does not seem to be impacted, whereas the polymer dynamics is significantly slowed down at a very local scale in the presence of nano-fillers. In addition to this length scale dependent different dynamics, additional Neutron Spin Echo spectroscopy experiments and Small Angle Scattering on labelled polymer chains, irreversibly bound to the filler surface and re-dispersed in a fully deuterated matrix, revealed a negligible dynamical behavior of this particular population of localized chains in the rubber layer. The conformational statistics of these chains is that of self-avoiding walk train within a shell that is thinner than the size of the chain. To the best of our knowledge, this work is the first of its kind which measures the single chain form factor in the bound layer of chemically multi-linked chains to the filler surface.

Investigation of Needle Motion Profile Effect on Diesel Spray in Near-Nozzle Field.

A variety of needle-motion profiles are used in diesel injectors. However, it is unclear what the underlying mechanism is to determine the needle-motion profiles and how they affect the spray dynamics. It has been of significant interest to examine how the spray dynamics will change if only altering the needle valve opening speed or closing speed while all other parameters are kept the same. The different needle-motion profiles were obtained using a piezo nozzle (Nozzle #P) and a solenoid nozzle (Nozzle #S), which have identical nozzle geometry. By utilizing the X-ray imaging technique, it was observed that the average needle valve speed of Nozzle #P was 51% higher at the opening stage but 17% lower at the closing stage than Nozzle #S. When the needle valve lift is low (approximately 200 μm), the needle valve opening speed has a crucial effect on spray dynamics. The faster needle valve opening of Nozzle #P results in a 42% larger spray spreading angle and 34% lower spray velocity at the downstream field. The spray dynamics may be controllable by properly designing the needle-motion profiles in the scenarios of the low needle lifts. However, when the needle valve is sufficiently open (approximately over 200 μm), almost identical spray characteristics were observed regardless of the needle-motion profiles.

Aspect ratio and combined installation in fluidic oscillator-crossflow interactions

This paper describes a computational study of fluidic oscillator-crossflow interactions. Fluidic oscillators are high potential active flow control devices, which offer promise for cooling and flow separation. Previous experimental studies have investigated the internal/external flow fields of fluidic oscillators. This improved the understanding of three-dimensional flow fields; however, this has been limited to single aspect ratio nozzles in single variable installations. Research has not analyzed the effects of varying both oscillator parameters and installation conditions. Therefore, the present aim is to enhance flow field understanding by examining three aspect ratio (AR) nozzles in default perpendicular condition and in a “skewed incline” configuration (β = 60°, α = 75°). An unsteady Reynolds averaged Navier Stokes model was validated with prior experimental data and then used to evaluate time-averaged and time-accurate flow fields at three different blowing ratios. Strouhal number analysis uncovers the effectiveness of parametric changes. Internal flow fields are presented, identifying key differences and similarities. External flow field analysis in regard to spreading angles 55°–65° observes greater wall-normal penetration for lower AR oscillators with improved spanwise penetration for larger AR's. The combined installation produces stronger primary vortices, improving penetration along the wall, while inclination keeps vortices close to the wall. Oscillator effectiveness is dependent on the application.

Investigating the effect of density variation on pitch angle scattering events of runaway electrons as observed through electron cyclotron emission diagnostic at Aditya-upgrade tokamak.

Nascent observations about the influence of kinetic instabilities on electron cyclotron emission (ECE) from runaway electrons (REs) have been detected and explored at the Aditya-Upgrade (Aditya-U) tokamak. The developed broadband ECE radiometer system offers wideband measurements by integrating several radio frequency units with a fixed intermediate frequency receiver with multiple channels, which is a novel approach to meet the needs of the localized measurements at various toroidal fields and extend the system dynamic range. The low density (ne ≤ 1 × 10-19m-3) plasma discharges at Aditya-U are consistently accompanied by a 20%-40% increase in the ECE radiometer signal amplitude within 100 µs and sporadic step-like modulations. The Pitch Angle Scattering (PAS) of REs induced by kinetic instabilities is a potential candidate for their occurrence. This steep jump in the radiometer signals was detected due to its high temporal resolution of 10 µs. A "PREDICT" code that employs the relativistic test particle model validates these experimental findings of the radiometer diagnostic for the first time for Aditya-U tokamak. Preliminary observations of the ECE radiometer signals also show that additional gas puffs can be used to vary the trigger timings of such PAS events or even lead to their complete avoidance.

The dispersion of carbon nanotubes in composite materials studied by computer simulation of Small Angle Scattering

Although numerous efforts have been made to reinforce ceramic materials by adding a nanostructured phase like carbon nanotubes (CNT), the appearance of aggregates during the manufacturing processes continues to be a problem. Given the size of the CNT (nm–μm), techniques such as Small Angle Scattering (SAS) can be a useful tool to study the formation of the aggregates and to quantify the degree of homogenization of the nanophase in the matrix. In this work, systems with different concentrations of CNT have been simulated in different states of aggregation, starting from a perfectly homogeneous dispersion of individualized CNT, and progressively aggregated. A Guinier regime appears in the scattering signal in the range of low values of the modulus of the scattering vector, q, as the aggregation occurs. Two parameters from the intensity curve are proposed to quantify the quality of the dispersion of the nanophase in the ceramic matrix.

Effects of asymmetric basal texture on the stretchability and the microstructure variations for the rolled ZK60 magnesium alloy sheet

In order to clarify the asymmetric basal texture effects on the stretchability and the microstructure variations of magnesium alloy sheet, two kinds of stretch forming samples were extracted along the rolling direction (RD) and the transverse direction (TD) from ZK60 magnesium alloy sheet with asymmetric basal texture. Their variations involving the microstructure and the stretch formability were investigated using a visco-plastic self-consistent model, along with the three-dimensional finite element method. The experimental and simulated results together showed that the plastic deformation during stretch forming was concentrated in the central region of the stretch sample. Such plastic deformation was more easily propagated into the surrounding area in the TD sample, making its stretch formability higher by nearly 50.7 % than the RD sample. This was attributed to the weak basal texture in the TD sample which activated more basal slip and tension twinning and consequently increased its hardenability. Additionally, with the variation of the stretch forming behavior, the activation of basal slip narrowed the spread angle of the basal pole for the TD sample, while only increased the basal texture intensity for the RD sample. Moreover, activation of the prismatic slip rotated the <10−10> crystal direction toward the major strain direction (LD), promoting the development of <10−10>//LD-type texture in both samples. These results indicated that the comprehensive stretchability improvement of magnesium alloy sheet required weakening the basal texture symmetrically instead of asymmetrically.

Channel modeling based on multilayer artificial neural network in metro tunnel environments

AbstractTraditional deterministic channel modeling is accurate in prediction, but due to its complexity, improving computational efficiency remains a challenge. In an alternative approach, we investigated a multilayer artificial neural network (ANN) to predict large‐scale and small‐scale channel characteristics in metro tunnels. Simulated high‐precision training datasets were obtained by combining measurement campaign with a ray tracing (RT) method in a metro tunnel. Performance on the training data was used to determine the number of hidden layers and neurons of the multilayer ANN. The proposed multilayer ANN performed efficiently (10 s for training; 0.19 ms for prediction), and accurately, with better approximation of the RT data than the single‐layer ANN. The root mean square errors (RMSE) of path loss (2.82 dB), root mean square delay spread (0.61 ns), azimuth angle spread (3.06°), and elevation angle spread (1.22°) were impressive. These results demonstrate the superior computing efficiency and model complexity of ANNs.

Algorithm for vertical distribution of boundary layer aerosol components in remote-sensing data

Abstract. The vertical distribution of atmospheric aerosol components is vital to the estimation of radiative forcing and the catalysis of atmospheric photochemical processes. Based on the synergy of ground-based lidar and sun-photometer in Generalized Aerosol Retrieval from Radiometer and Lidar Combined data (GARRLiC), this paper developed a new algorithm to get the vertical mass concentration profiles of fine-mode aerosol components for the first time. Retrieval of aerosol properties was achieved based on the sky radiance at multiple scatter angles, total optical depth (TOD) at 440, 675, 870, and 1020 nm, and lidar signals at 532 and 1064 nm. In addition, the internal mixing model and normalized volume size distribution (VSD) model were established according to the absorption and water solubility of the aerosol components, to separate the profiles of black carbon (BC), water-insoluble organic matter (WIOM), water-soluble organic matter (WSOM), ammonium nitrate-like (AN), and fine aerosol water (AW) content. Results showed a reasonable vertical distribution of aerosol components compared with in situ observations and reanalysis data. The estimated and observed BC concentrations matched well with a correlation coefficient up to 0.91, while there was an evident overestimation of organic matter (OM = WIOM + WSOM, NMB = 0.98). Moreover, the retrieved AN concentrations were closer to the simulated results (R = 0.85), especially in polluted conditions. The BC and OM correlations were relatively weaker, with a correlation coefficient of ∼ 0.5. Besides, the uncertainties caused by the input parameters (i.e., relative humidity (RH), volume concentration, and extinction coefficients) were assessed using the Monte Carlo method. The AN and AW had smaller uncertainties at higher RH. Herein, the proposed algorithm was also applied to remote-sensing measurements in Beijing with two typical cases. In the clean condition with low RH, there were comparable AN and WIOM, but peaking at different altitudes. On the other hand, in the polluted case, AN was dominant and the maximum mass concentration occurred near the surface. We expected that the algorithm could provide a new idea for lidar inversion and promote the development of aerosol component profiles.

Experimental study on behaviors of flame spread over aviation kerosene under forced airflow

In realistic industrial scenarios, the leakage of aviation kerosene (RP-5) under forced airflow easily leads to fire spread, which seriously threatens the safety of human life and causes enormous economic losses. Therefore, it is necessary to study the characteristic parameters of flame spread over RP-5 aviation kerosene under forced airflow, such as flame tilt angle (θ), flame height (H), and flame spread rate (V). In this paper, the RP-5 flame spread experiments were carried out by varying the speed (u = 0–6 m/s) and direction (concurrent, opposed, and perpendicular airflows) of the forced airflow. The results show that the flame tilt angle increases as the airflow speed increases and finally tends to be stable, while the flame height decreases monotonically with airflow speed. The special behaviors of flame bifurcation and fire spread rate induced by the critical airflow speed are observed. The phenomenon of "flame bifurcation" will occur due to the influence of differential pressure resistance under high concurrent airflow conditions (u > 1 m/s). When the airflow is relatively small (u ≤ 1 m/s), the mean flame spread rate varies slightly with increasing airflow speed. With further increasing the airflow speed (u > 1 m/s), the mean flame spread rate increases with an increase in the concurrent airflow speed while decreasing as the opposed airflow speed increases. By contrast, the mean flame spread rate remains essentially unchanged under all perpendicular airflows.

Effect of Scattering Angle in Electron Transport of AlGaN and InGaN

The scattering angle between electrons plays a very important role for the calculation of scattering probability. The probability of scattering is an essential parameter for the simulation of electron paths. In this work, we calculated the scattering probability with scattering angle in AlGaN and InGaN at 77 K and found that the lower angle scatterings only dominate.

An experimental study on the in-nozzle cavitating flow and near-field breakup of spirally grooved hole nozzles

To improve liquid atomization for pressure atomizer, a spirally grooved hole (SGH) nozzle was designed, which produces swirling flow inside the nozzle hole and thereby promotes the disturbance in liquid jets, enhancing breakup of liquid jets. In this paper, the optical visualization of the cavitating flow inside nozzles and primary breakup behaviors in the near-nozzle field for three scaled-up transparent nozzles, including two SGH nozzles with different spiral angles, and a non-spiral hole (NSH) nozzle, were performed to clarify the effects of the spirally grooved structures on in-nozzle cavitating flow and near-field fuel breakup. The results show that with an identical K-factor, the cavitation was largely restrained in the SGH nozzles, and the discharge coefficients of the SGH nozzles with spiral angles of 63° and 43° were approximately 13% and 25% lower than that of the NSH nozzle, respectively. Moreover, a liquid column was observed for each of the jets, surrounded with scattering droplets. And the SGH nozzle yields 9–10 times higher number density, 9%–10% smaller Sauter mean diameter of the droplets, and 4–7 times wider spreading angle than those of the NSH nozzle. These facts verified that the use of spirally grooved hole enhanced primary breakup of liquid jets.

Analysis of the use of variable angular parameter tools in cross-wedge rolling

This paper proposes novel tools for cross-wedge rolling (CWR). Previously used standard tools have a flat forming surface described by two angles, i.e. the forming angle α and the wedge spreading angle β. In this study, the authors investigated whether the use of tools with modified forming surface due to the use of variable angles α and β would have a positive effect on the CWR process. Numerical modelling was employed to determine the impact of the tools with variable angles β and α on CWR. The focus was put on assessing the effect of the changed forming surface of the wedge tools on the radial and forming loads, effective strains, and damage functions determined by fracture criteria developed by Argon et al., Oyane et al. and Pater et al. Numerical results were used to design a novel wedge tool shape that would ensure a reduction of rolling forces and energy consumption as well as a reduced risk of internal cracking in the axial zone of the workpiece. Experiments were conducted using both standard and novel tools of the same size. Experimental results confirmed that the use of the proposed novel tools had a positive effect on the CWR process.