Transition Radius Research Articles

Cloud droplet size distributions governed by condensation, collision–coalescence, and sedimentation. Part 2: Analytical expressions for size distribution shape and asymptotic behavior for large-droplet tails

Abstract Droplet growth via condensation and collision-coalescence has been investigated in the limit of very weak coalescence growth: a collector-mode approximation emerges for coalescence growth that consists solely of droplets in the tail collecting droplets near the main mode of the cloud droplet size distribution, and that does not deplete the mode. In this second part, the approximation is formalized, leading to a simplified form of the collision-coalescence term in the equation governing the evolution of the droplet size distribution. This form allows for analytical solutions for transient growth and for steady-state distributions representing a balance between condensation, collision-coalescence growth, and removal by sedimentation. The solutions lead to an expression for the drizzle growth time, formally, the finite time in which a droplet approaches infinite size. The drizzle growth time is related to a transition radius at which droplet growth switches from condensation-dominated to coalescence-dominated. The solutions also provide a dimensionless group that governs the steady-state distribution shape, which is referred to as the drizzle number. The solutions are checked by comparing to a Monte Carlo model developed in Part 1, and it is found that the analytical solution is excellent when the drizzle number is much greater than unity, which is the typical situation for the microphysical conditions achievable in a convection-cloud chamber. The steady-state size distribution has the form of a modified gamma distribution, with a transition to power-law tail at sufficiently large radius. The solutions are formally valid for a convection-cloud chamber, but can also be extended to shallow, mixed-layer clouds such as mixing fogs.

Hadron-quark phase transition in the neutron star with vector MIT bag model and Korea-IBS-Daegu-SKKU functional

Employing the Korea-IBS-Daegu-SKKU (KIDS) density functional for the hadron phase and the MIT bag model with vector (vBag) model for the quark phase, we obtain hadron-quark phase transition in neutron stars considering Maxwell construction. The structural properties of the resultant hybrid stars are computed for three different values of bag constant (B) in the range B1/4=145−160 MeV). We study the effects of symmetry energy (J) on the hybrid star properties with the different KIDS model and found that J has important influence not only on the transition properties like the transition mass, transition radius and jump in density due to phase transition, but also on the stability of the hybrid stars. The vector repulsion of the quark phase via the parameter GV has profound influence in obtaining reasonable hybrid star configurations, consistent with the recent astrophysical constraints on the structural properties of compact stars. Within the aforesaid range of B, the value of GV is constrained to be 0.3 ≲GV≲ 0.4 in order to obtain reasonable hybrid star configurations.

The relationship between threshold power of wave mode transition and tube radius in argon helicon discharge

We report in this Letter a geometric similarity of threshold radio frequency (RF) power absorbed by the helicon wave coupled mode in argon helicon discharge. Helicon plasma was excited by a half-helical antenna in tubes of different radii at a pressure of 0.3 Pa. Plasma density was measured by using a Langmuir probe, and wave structure was measured by a B-dot probe. The results show that the threshold powers for triggering helicon wave mode are proportional to the tube cross sections, and the plasma densities at the transition point are the same, indicating a geometric scaling law between the RF power and the tube size. This similarity of threshold power might provide a comparison of results in different systems.

Laser Weld Seam Curved Path Effect on 6063 Aluminum Alloy Strength and Temperature Distributions: COMSOL Numerical Simulation

To improve the welding performance of aluminum alloys, a thermal source model of an irregular weld seam was established. COMSOL software was used for numerical simulation of the weld seam geometry effect on the temperature and stress fields in laser welding, which results were experimentally validated. The results show that the ellipsoidal laser welding melted micropool exhibited quasi-steady-state temperature field characteristics. The temperature gradient and thermal stress showed an increase followed by a decline. The temperature fluctuation amplitude of the square-tooth-shaped weld seam exceeded that of the arc-toothshaped one. The temperature evolution of the broken line tooth-shaped weld seam showed a slightly increasing trend, except for the inflection point. The experimental average tensile strength of the weld seam was the highest, reaching about 210 MPa, i.e., roughly 85% of the base material (245 MPa), which coincided with the COMSOL-based temperature field simulation results. With increasing deformation amplitude and transition radius, the maximum tensile force, tensile strength, and elongation at fracture showed an increasing trend. However, the deformation amplitude should be below a certain limit because its increase elongates the welding path and reduces the distance between weld seams, resulting in serious heat accumulation. The tensile fracture morphology of the 6063-T6 base material was curved shear, with shallow toughness pits, small tearing edges at the edges, and small granular objects, indicating small plastic deformation during the fracture process. The tensile fracture of the welded part spanned the weld seam and the base material, and the fracture occurred along the tangent direction of the weld seam. The fracture surface was smooth, the tearing edges at the edge of the toughness pit shifted along the weld seam direction, forming many co-directional slip bands, with highly pronounced plastic deformation.

Fatigue crack growth simulation by extended finite element method: A review of case studies

AbstractNumerical simulation of fatigue crack growth (FCG) is presented, based on the application of the extended finite element method (XFEM). Couple of case studies are presented, as a review of recent experience of the Belgrade school of XFEM simulations, established at the Faculty of Mechanical Engineering. Case studies comprised Charpy specimen with initial crack at the notch tip, oil rig pipe with an axial surface crack, pressure vessels with a crack at the welded joint with connecting pipe, turbine shaft with a crack at the transition radius, optimization of a wing spar in respect to FCG, the effect of mesh size on fatigue life estimation of a stringer panel, fatigue life estimation of wing‐to‐fuselage connecting lug, geometry effect on fatigue life of orthopedic plates and fatigue life of hip implant. Based on these case studies, XFEM is discussed in respect to its accuracy and efficiency. It is concluded that XFEM is a versatile tool for simulation of FCG, providing an excellent option for precise and reliable fatigue life of a cracked component.

The Initial Conditions of Clustered Core Collapse: Multiwavelength Analysis of Oph A SM1N and N6 at 100 au Resolution

We present new Atacama Large Millimeter/submillimeter Array (ALMA) continuum and NH2D, N2D+, and H2D+ line emission at matched, ∼100 au resolution toward the dense star-forming cores SM1N and N6 within the Ophiuchus molecular cloud. We determine the density and temperature structure of SM1N based on radiative transfer modeling and simulated observations of the multiwavelength continuum emission at 0.8, 2, and 3 mm. We show that SM1N is best fit by either a broken power-law or Plummer-like density profile with high central densities (n ∼ 108 cm−3), and an inner transition radius of only ∼80–300 au. The free-fall time of the inner region is only a few ×103 yr. The continuum modeling rules out the presence of an embedded first hydrostatic core (FHSC) or protostar. SM1N is therefore a dynamically unstable but still starless core. We find that NH2D is likely depleted at high densities within SM1N. The nonthermal velocity dispersions increase from NH2D to N2H+ and H2D+, possibly tracing increasing (but still subsonic) infall speeds at higher densities as predicted by some models of starless core contraction. Toward N6, we confirm the previous ALMA detection of a faint, embedded point source (N6-mm) in 0.8 mm continuum emission. NH2D and N2D+ avoid N6-mm within ∼100 au, while H2D+ is not strongly detected toward N6. The distribution of these tracers is consistent with heating by a young, warm object. N6-mm thus remains one of the best candidate FHSCs detected so far, although its observed (sub)millimeter luminosity remains below predictions for FHSCs.

Pemodelan Kondisi Geometrik Jalan Terhadap Potensi Kecelakaan Lalu Lintas

Road infrastructure has an impact on the occurrence of road traffic accidents. The geometry of a road is a variable that influences the occurrence of road traffic accidents. Interpreting the observed crashes into an equation that can describe the crashes is one of the most difficult problems faced by scientists and engineers in any research. The traffic accident research conducted is still limited to analyzing the causes of accidents and jumping to handling strategies that do not reveal how much geometric influence on accidents at the location. This research was developed using a comprehensive modeling approach to illustrate how highway geometric design, in this case the alignment, influences crash rates. This study aims to analyze the influence of road geometrics on the incidence of accidents. The method used is multiple liner regression measurement model using R-Studio. The variables to be studied include road geometry planning parameters, especially horizontal alignments which include stopping sight distance (X1), radius of horizontal curve (X2), shoulder width X3, and transition curve length (X4). The results of the study obtained a relationship in the mathematical equation Y = 99.55508-0.02634X1+1.17647X2-0.06999X3-0.03906X4 with the most significant correlation value produced is the transition curve length and radius of horizontal curve. Based on the multiple R-squareed value of 0.8775 this model has a very strong correlation category. Where the ability of X1 to X4 is able to explain Y by 80%.

Truncated, tilted discs as a possible source of Quasi-Periodic Oscillations

ABSTRACT Many accreting black holes and neutron stars exhibit rapid variability in their X-ray light curves, termed quasi-periodic oscillations (QPOs). The most commonly observed type is the low-frequency (≲10 Hz), type-C QPO, while only a handful of sources exhibit high-frequency QPOs (≳60 Hz). The leading model for the type-C QPO is Lense-Thirring precession of a hot, geometrically thick accretion flow that is misaligned with the black hole’s spin axis. However, existing versions of this model have not taken into account the effects of a surrounding, geometrically thin disc on the precessing, inner, geometrically thick flow. In Bollimpalli et. al 2023, using a set of GRMHD simulations of tilted, truncated accretion discs, we confirmed that the outer thin disc slows down the precession rate of the precessing torus, which has direct observational implications for type-C QPOs. In this paper, we provide a detailed analysis of those simulations and compare them with an aligned truncated disc simulation. We find that the misalignment of the disc excites additional variability in the inner hot flow, which is absent in the comparable aligned-disc simulations. This suggests that the misalignment may be a crucial requirement for producing QPOs. We attribute this variability to global vertical oscillations of the inner torus at epicyclic frequencies corresponding to the transition radius. This explanation is consistent with current observations of higher frequency QPOs in black hole X-ray binary systems.

Thermodynamics of deformed AdS-Schwarzschild black hole

By implementing the gravitational decoupling method, we find the deformed AdS-Schwarzschild black hole solution when there is also an additional gravitational source, which obeys the weak energy condition. We also deliberately choose its energy density to be a certain monotonic function consistent with the constraints. In the method, there is a positive parameter that can adjust the strength of the effects of the geometric deformations on the background geometry, which we refer to as a deformation parameter. The condition of having an event horizon limits the value of the deformation parameter to an upper bound. After deriving various thermodynamic quantities as a function of the event horizon radius, we mostly focus on the effects of the deformation parameter on the horizon structure, the thermodynamics of the solution and the temperature of the Hawking–Page phase transition. The results show that with the increase of the deformation parameter: the minimum horizon radius required for a black hole to have local thermodynamic equilibrium and the minimum temperature below which there is no black hole decrease, and the horizon radius of the phase transition and the temperature of the first-order Hawking–Page phase transition increase. Furthermore, when the deformation parameter vanishes, the obtained thermodynamic behavior of the black hole is consistent with that stated in the literature.

Identifying the discs, bulges, and intra-halo light of simulated galaxies through structural decomposition

ABSTRACT We perform a structural decomposition of galaxies identified in three cosmological hydrodynamical simulations by applying Gaussian mixture models (GMMs) to the kinematics of their stellar particles. We study the resulting disc, bulge, and intra-halo light (IHL) components of galaxies whose host dark matter haloes have virial masses in the range M200 = 1011–$10^{15}\, {\rm M_\odot }$. Our decomposition technique isolates galactic discs whose mass fractions, fdisc, correlate strongly with common alternative morphology indicators; for example, fdisc is approximately equal to κco, the fraction of stellar kinetic energy in corotation. The primary aim of our study, however, is to characterize the IHL of galaxies in a consistent manner and over a broad mass range, and to analyse its properties from the scale of galactic stellar haloes up to the intra-cluster light. Our results imply that the IHL fraction, fIHL, has appreciable scatter and is strongly correlated with galaxy morphology: at fixed stellar mass, the IHL of disc galaxies is typically older and less massive than that of spheroids. Above $M_{200}\approx 10^{13}\, {\rm M_\odot }$, we find, on average, fIHL ≈ 0.37, albeit with considerable scatter. The transition radius beyond which the IHL dominates the stellar mass of a galaxy is roughly $30\, {\rm kpc}$ for disc galaxies, but depends strongly on halo mass for spheroids. However, we find that no alternative IHL definitions – whether based on the ex situ stellar mass, or the stellar mass outside a spherical aperture – reproduce our dynamically defined IHL masses.

Fatigue strength of the joint of steel cantilevers in composite bridges

AbstractBox girders with steel cantilevers underneath the deck are frequently used in the design of composite steel bridges. Hereby, the welded joints between the main girder and the transverse system have to endure fatigue loads. Current design specifications for this joint, e.g., a tapering in thickness of the top flanges at the same position of a transition radius, are complex to manufacture and provide a higher fatigue resistance than necessary. This article addresses the optimization of this structural detail, which is realized hundreds of times per structure. Several laboratory tests and numerical simulations were carried out regarding the load‐bearing behavior and the fatigue safety of the cantilevers as double‐T‐sections and as box girders. Additionally, 60 fatigue tests were conducted on small‐scale specimen to classify the resulting simplified design variants in detail categories of the nominal stress concept. As a result, two design recommendations are proposed for the joint at the intersecting top flanges. Moreover, the effect of an unplanned axial misalignment on the fatigue strength of the joint at the bottom flange is quantified.

Influence of the geometry of butt welds and longitudinal attachments on their fatigue resistance

AbstractMany constructions, such as wind turbines, bridges and crane runways, are cyclic loaded so that fatigue failure may occur. Therefore, in the course of the revision of Eurocode 3, two research projects funded by AiF‐DASt re‐investigate the classification of constructional details of EN 1993‐1‐9. This paper focuses on the geometrical influence on the fatigue resistance of butt welds and longitudinal attachments. First, the influence of the plate thickness on butt welds was investigated. Both a meta‐study based on test results of various research projects and our own test series on butt welds up to 80 mm thickness led to interesting conclusions.Furthermore, the influence of the length and radius of longitudinal attachments on the fatigue resistance was investigated. By experiments and numerical analysis, clarification has been sought whether the transition radius larger than 150 mm or the ground weld toe is decisive for the improvement of the fatigue resistance. Since previous meta‐studies could not provide a clear result on the influence of the longitudinal attachment length, this was also investigated.A database established in the projects allows to integrate and assess the specified details of butt welds and longitudinal attachments in the context of the overall approach in EN 1993‐1‐9.

The scale of homogeneity in the Rh = ct universe

ABSTRACT Studies of the Universe’s transition to smoothness in the context of Lambda cold dark matter (ΛCDM) have all pointed to a transition radius no larger than ∼300 Mpc. These are based on a broad array of tracers for the matter power spectrum, including galaxies, clusters, quasars, the Ly-α forest, and anisotropies in the cosmic microwave background. It is therefore surprising, if not anomalous, to find many structures extending out over scales as large as ∼2 Gpc, roughly an order of magnitude greater than expected. Such a disparity suggests that new physics may be contributing to the formation of large-scale structure, warranting a consideration of the alternative Friedmann–Lemaître–Robertson–Walker cosmology known as the Rh = ct universe. This model has successfully eliminated many other problems in ΛCDM. In this paper, we calculate the fractal (or Hausdorff) dimension in this cosmology as a function of distance, showing a transition to smoothness at ∼2.2 Gpc, fully accommodating all of the giant structures seen thus far. This outcome adds further observational support for Rh = ct over the standard model.

Presence of crack due the constant exploitation of turbine shaft

Designing, constructing and putting into operation a hydroelectric power plant includes complex tasks. Stresses of turbine and hydromechanical equipment of hydro power plants arise during the production of parts and assembly of equipment (residual stresses), in the process of performing functional requirements in exploitation and in the disturbed process of exploitation. After several decades of constant exploitation of the horizontal bulb turbine, which is an integral part of the hydroelectric power unit, empirically, the formation of a crack occurs in the turbine shaft due to the influence of corrosion, erosion and cavitation. Through experimental tests and calculations it has been determined that values of bending stresses of the turbine, which occur due to the action of fatigue and corrosion, as well as stress concentration, are bigger than 25 MPa for flanges exposed to water, and in other case bigger than 40 MPa for flanges exposed to `corrosive water` and can cause the occurrence of surface cracks on the transition radius between the cylindrical part of the shaft and the flange. It has been determined that stress values in the zone under the influence of bending stresses were bigger than allowable values, which led to the occurrence of many cracks due to fatigue corrosion. One of those cracks caused the failure of the shaft and of the whole turbine. Key words: crack, turbine shaft, fatigue, stress concentration

Evolution of the truncation radius in GX 339−4 from XMM–Newton spectral timing

ABSTRACT We investigate the changing geometry of the accretion disc in the X-ray binary GX 339−4 using a combination of spectral and timing models to fit six XMM–Newton observations taken during the end of the 2015 X-ray outburst. We use progressively more complex models of the X-ray reflection spectra, from simple disc lines to full relativistic reflection models. For the timing analysis, the Power Spectral Densities (PSDs) are generated from the light curves in the 0.3–0.7 and 0.7–1.5 keV energy bands. We fit PSD models that assume the standard accretion disc truncates at a specific radius, inside of which are two hot-flow zones, one spectrally soft and one spectrally hard, separated by a transition radius. Finally, we combine and jointly fit the full reflection spectral models and the truncated disc PSD models. Our final model is consistent with the spectroscopic and timing data. It suggests that the truncation radius of the disc increases towards the end of the outburst, which is self-consistent with the obtained reflection fraction that is smaller. During this, the source spectrum becomes harder and the soft excess becomes more prominent. The disc truncation radius that increases as the source flux decreases is intermediate between the results of previous studies. However, our analysis of the model performance leads us to believe that higher quality data and better models are required to fully understand the GX 339-4 system and reduce the effect of systematic uncertainties.

Numerical study on convective heat transfer and flow characteristics in twisted tri-lobed tubes

ABSTRACT The convective heat transfer and flow resistance properties of water flowing through a twisted trilobed tube (TTT) with Reynolds numbers that ranged from 10,000 to 40,000 were examined in this work. Specifically, we examined how the tip circle radius (r), straight length (l), transition radius (R), and twist pitch (S) influenced the heat transfer and flow resistance in the tube. Our results showed that the TTT had an average Nusselt number (Nu) that was 30% higher than that of a plain tube, while the friction coefficient (f) increased by 39%. We also presented temperature and velocity field distributions and explained the enhanced heat transfer process using the field synergy principle. Furthermore, we found that a larger tip circle radius (r) and straight length (l), as well as a smaller transition radius (R) and twist pitch (S), led to better overall heat transfer performance of the TTT. Among the different cases evaluated, Case 7 had the highest overall heat transfer performance with a PEC of 1.37. The unusual structure of the TTT caused a rotating motion, which resulted in secondary and spiral flows that increased the synergy through the velocity and temperature fields. Finally, our research found a correlation with the Nusselt number (Nu) as well as the friction coefficient (f).

An investigation on microscopic and mechanical properties of polyethylene/boron nitride graphene nanocomposites by DFT calculations

In this paper, the molecular dynamics (MD) simulation is used to explore the mechanical properties of polyethylene (PE) /boron nitride (BN) graphene nanocomposite in the pressure range of 0–20 GPa and temperature range of 100–600 K. Parameters of the adsorption energy, Young's modulus, glass transition temperature and radius of gyration are analyzed. For the interaction between PE and BN-graphene, the constant adsorption energy is reached with the eight degree of polymerization. Meanwhile, the Young's modulus, bulk modulus, shear modulus and Poisson's ratio of PE/BN-graphene nanocomposite are all improved, where the PE/BN-graphene nanocomposite performs well in resisting the changes in volume and shape to reflect the enhanced mechanical effect of BN-graphene on polyethylene. The mechanical properties of the PE/BN-graphene nanocomposite during the pressurization process are strong enough without fracture, and the best performance is achieved at 18 GPa. BN-graphene heightens the glass transition temperature of the nanocomposite with the enhanced structural and thermal stability. Besides, friction and wear properties of the PE/BN-graphene are guaranteed according to the gyration radius diagram.

Investigating the influence of geometric parameters on the deformation of laser powder bed fused stents using low-fidelity thermo-mechanical analysis

Maintaining dimensional accuracy is a major challenge of laser powder bed fusion (L-PBF) preventing its application for more complex and filigree L-PBF structures in industrial practice. Previous studies have shown that residual stresses and distortion of benchmark L-PBF components may be predicted by sequential thermo-mechanical analyses. However, the reliability of these analyses for more complex structures must be critically questioned, as comprehensive validation and sensitivity analyses are scarce. In this paper, we present a calibrated and validated low-fidelity sequential thermo-mechanical finite element analysis (FEA) of a tubular L-PBF lattice structure, i.e., an aortic stent, where pronounced local deformation is expected. As a first step, the finite element model was extensively calibrated using experimental data to ensure reproducibility of the simulation results. Thereupon, geometric features critical to the distortion of L-PBF lattice structures and measures to compensate for the distortion, such as inversion of the distorted L-PBF structure, were investigated. It was found that the distortion of the L-PBF lattice structures can be reduced, but not completely prevented, by increasing the strut angles, increasing the strut thickness, and decreasing the transition radius in the area of merging struts. FEA-based inversion of the numerically predicted deformed structure minimized distortion, resulting in the L-PBF aortic stent approximating the intended CAD geometry even with a small strut thickness. This work shows that low-fidelity sequential thermo-mechanical FEA can be used not only for the analysis and deformation compensation of reference structures, but also for the analysis of more complex filigree structures with pronounced local deformation.

A Novel 2D Micromilling FEM simulation strategy to optimize the flow stress law of IN625

The products miniaturization tendency of the last years led to an acceleration of micromilling process development. Considering the high-quality requirements, a deep knowledge of this operation, concerning ploughing-shearing transition, tool run-out, and tool edge radius effects, is mandatory, especially when machining difficult-to-cut materials. For this reason, this paper introduces a novel 2D micromachining Finite Element Method simulation strategy for micromilling forces evaluation, when cutting IN625. The major output of this technique consists in the computation of an optimized flow stress law, suitable for the simulation of high-speed machining. Particle Swarm Optimization method was employed for optimizing the flow stress parameters by comparing the cutting force predicted by an analytical model previously calibrated on experimental data, providing good agreement. This strategy permits the micromilling process predictive analysis, avoiding costly optimization experimental tests.

Research on root appearance and fatigue life of steel catenary riser (SCR) using GMAW/GTAW-P double-sided root welding process

A steel catenary riser (SCR) is a flexible stand-up pipe that connects a subsea wellhead in the seabed (normally at a depth of more than 1500 m) to a floating platform. Waves, ocean currents, and winds apply substantial loads to SCRs that produce fatigue damage. Hence, the requirements for the appearance of SCR weld joints, particularly the weld root, are extremely strict. This paper proposes a new gas metal arc welding/pulse gas tungsten arc welding (GMAW/GTAW-P) double-sided root welding process for SCRs to obtain a nearly smooth root geometry. Test results show that the average values of root reinforcement, root transition angle, and transition radius achieved with this root welding process are only 169 μm, 6.4°, and 4055 μm, respectively. These values are dramatically lower than those achievable with the best technologies available, such as the surface tension transfer (STT) root welding process and cold metal transfer (CMT) root welding process. The fatigue strength of the double-sided welding joints is improved by at least 45.8% because the root stress concentration is significantly reduced. However, incomplete penetration defects were found when the molten pool position was not appropriate. Solutions for this problem are discussed. The proposed process is believed to be a potential strategy for welding high fatigue life SCRs.