Inclination Research Articles

Design of composite stealth cloak based on anomalous reflections and vortex singularities

In this paper, an ultra-thin (0.072λ) composite stealth cloak is proposed to cover a cloak with a center height of 98.88 mm and an inclination angle of 25° to achieve the dual stealth effect of scattering and gain. Firstly, based on the Generalized Snell theorem, the designed anomalous reflective metasurface has been shown to have a good invisibility in the 14–30 GHz region in simulations as well as in experiments. Secondly, the 3-bit metasurface unit is utilized to generate vortex beams with different number of modes, whose electric field strength at the vortex singularity is 0, which achieves energetically stealth. Finally, the phases of the above two metasurfaces are superimposed using the convolution theorem, and the designed composite stealth cloak significantly reduces the scattering amplitude and reconstructs the wavefront over a wide frequency range when a circularly polarized wave is incident vertically. Based on the above study, the stealth cloak provides a feasible solution for application to radar and microwave antenna stealth systems.

Experimental and meshless numerical simulation on the crack propagation processes of marble SCB specimens

In order to correctly understand the rock multi-fissure interactions and crack propagation laws, three-point bending fracture tests of the marble semi-circular bend samples (SCB samples) are carried out, and the crack propagation processes are simulated by the Smoothed Particle Hydrodynamics (SPH) method. Results show that: Cracks initiate from the guide fissure tip and propagate vertically in the SCB sample with no obstacle fissures; The overlap positions of crack1 and the obstacle fissure are biased towards the lower left end of the obstacle fissure with the increase of the inclination angle α; With the increase of the eccentric distance d, the overlap positions of crack1 and the obstacle fissure are biased towards the upper right end of the obstacle fissure; The peak load of the samples decreases with the increase of inclination angle α, while increases with the increase of eccentric distance d. The “failure coefficient” η is introduced into the conventional SPH momentum equations, which can simulate the multi-fissure propagations of the SCB samples. The simulation results are consistent with the experimental results, and the mechanisms of the crack propagation morphologies between the guide fissure and the obstacle fissure are discussed. The research results can provide some references for correctly understanding the crack propagation mechanisms of multi-fissure rock masses and the applications of the SPH method into simulating rock multi-fissure interactions.

Crack coalescence prediction and load-bearing mechanism of defective specimen based on computer vision recognition model

The coalescence of cracks in rock, triggered by external stress or geological activities, plays a pivotal role in determining the mechanical properties and stability of rock structures. Consequently, the prediction method of crack coalescence become critical tools in ensuring the safety and stability of geotechnical engineering facilities. In this paper, based on the strain field data obtained by digital image correlation (DIC), a set of programs was developed to automatically identify the values and percentage changes of different strain intervals in the strain field of the specimen. Then, a computer vision recognition (CVR) model is established to study the process and prediction of crack coalescence in sandstone specimens with open flaws. This method overcomes the limitations, subjectivity and unpredictability of the traditional method of identifying cracks through artificial vision. The results show that the increase of the flaw width causes the displacement trend to be squeezed and deflected along the width direction, thereby changing the angle of crack initiation and exhibiting different forms of crack coalescence. The increase in the inclination angle of the flaw leads to an increase in the effective compressive area (ECA) of sandstone, and the magnitude of ECA is positively correlated with the uniaxial compressive strength (UCS) of the sandstone. Additionally, the CVR model identifies two types of numerical fluctuation signals before crack coalescence, namely the plastic characteristic signal (PCS) in the early stage of the experiment and the early-warning signal (EWS) near the period of crack coalescence, where EWS can be used as a predictive signal for crack coalescence. The research results provide a new algorithm technical support for the process analysis and prediction of crack coalescence, and provide a basis for early warning of rock mass engineering disasters.

Research on Monitoring Technology for Frame Piers of Continuous Box-Girder Bridges Constructed by the Cantilever Method

This paper focuses on the analysis of the stress state of a large-span frame pier-continuous box girder bridge with pier crossbeams anchored by pier crossbeams on the main pier of the Guangfo-Zhao Expressway. The bridge is constructed by the cantilever method, and a refined finite element model of the entire bridge is established using the finite element software Midas/FEA to analyze the stress state of the frame pier during the cantilever construction process. It is found that under the possible combined action of an unbalanced load during construction, the torsional resistance of the frame pier crossbeam does not meet the requirements of the design code. In order to eliminate the torsion of the frame piers, counterweights were used to monitor the frame piers during the construction of the box girders. In this paper, the theoretical calculation formula of the inclination angle of the end section of the frame pier crossbeam with the change of unbalanced bending moment, the calculation formula of the relationship between the horizontal displacement of the frame pier and the unbalanced bending moment, and the calculation formula corresponding to the relationship with the water tank counterweight are derived using the structural mechanics method. Two monitoring methods for the frame pier are proposed. In the construction monitoring of the bridge, the numerical fitting formula obtained by finite element numerical analysis calculation is compared with the calculated formula obtained by substituting the design parameters of the frame pier into the theoretical formula. The basic constants in both formulas are basically equal, verifying the correctness of the monitoring calculation formula proposed in this paper for the torsional resistance of the frame pier crossbeam. The applicability of the two monitoring methods is also compared and analyzed. This paper takes the main pier of Chaoyang overpass’s mainline bridge as the engineering background, which adopts the framework pier with a large-span prestressed concrete continuous box girder bridge. It analyzes the torsional state of the beam of the framework pier during the bridge construction process and conducts research on the construction monitoring of the framework pier crossbeam, providing valuable references for the construction monitoring of framework pier crossbeams in the construction of large-span framework pier continuous bridges in the future. The research results of this paper can provide assistance for the construction monitoring of similar projects. This paper’s innovation primarily resides in employing structural mechanics methods to compute the torsion of frame piers. On this basis, a simplified beam torsion calculation formula is proposed to strengthen its practical application in construction monitoring. The findings of this paper can help in the construction monitoring of similar projects.

The effect of inclination on flow and heat transfer in a 3×3 rod bundle channel in a natural circulation system

Unlike ordinary nuclear power reactors, the floating nuclear power plants are constantly affected by sea waves and are often under inclined condition. The flow and heat transfer characteristics in the rod bundle channel for inclined condition is crucial for the design and operation of floating nuclear power plants. This paper experimentally investigates the flow resistance and heat transfer in an inclined 3 × 3 rod bundle channel at 10∼15 MPa in a natural circulation system and the inclination angle is 10°–30°. The mass flux becomes smaller as the experimental loop is inclined due to the decrease of the natural circulation driving force. As the system inclination angle becomes larger, the mass flux decreases more. Re and the outlet mass quality also affect the mass flux decreasing amplitude for inclined condition. For single phase flow, the friction coefficient correlation in a rod bundle channel is developed and the MAE (mean absolute error) is 2.82 %. The friction coefficients when the channel is inclined are larger than the friction coefficients when the channel is vertical. Correlations for Nu in the static vertical rod bundle channel are also developed and the MAE is less than 2 %. The heat transfer coefficient is enhanced for inclined condition if the effect of mass flux change is eliminated. For flow boiling, inclination has little effect on the number and size of the bubbles for highly subcooled boiling, while inclination has large influence on the flow pattern for saturated boiling. When the inclination angle becomes larger, the two phase multiplier increases. As the outlet mass quality increases, the increasing amplitude of two phase multiplier will become even larger when the inclination angle is larger. The heat transfer coefficient of flow boiling increases when the channel is inclined, and the enhancement is larger when the mass flux is smaller. When the inclination angle is 30°, the boiling heat transfer coefficient could increase by 25.7 % at a low mass flux. The paper reveals the quantitive influence of inclination on both single phase flow and flow boiling in the rod bundle channel. The working pressure and temperature have reached the operating conditions of the floating nuclear power plants, and the results can be applied to the design of nuclear power floating plants and pressurized water reactor using rod bundle fuel assembly.

Determining of the thermo-hydraulic characteristics and exergy analysis of a triple helical tube with inner twisted tube

An innovative technique to enhance heat transfer as a passive method was investigated. The combination of the twisted tube and helical coil to increase the swirl intensity is presented. The current investigation showed experimentally and numerically the exergy and thermal performance analysis of a new design of a triple tube design called a triple helical tube with inner twisted tube, THTITT. The new design is a modified design of a double helical tube with inner twisted tube, DHTITT which is created by twisting the inner tube. Besides the benefits of adding the third fluid to DHTITT that achieve extra contact surface area per unit length between the intermediate tube and the new passage in the outer tube. In which expected to enhance the temperature gradient between the three fluids and consequently, the thermal characteristics augment occurred. The twisted tube increased the intensity of the swirl flow and more intense disturbance of the fluid in the tube occurred. A 3d CFD model was established to get more insight at a level of detail not always available in the experiment. The effects of twisted pitch ratio, ξ hydraulic diameter, ω, helical coil torsion, α, helical coil inclination angle, φ, as well as Dean number, NDn, h were explored. Four groups of test specimens include various ξ of 5.32, 7.97, and ∞, various ω of 3.8, 6.8, and 9.9 mm, various α of 0.068, 0.095, and 0.121, and various φ of 0°, 45°, and 90° were established, manufactured and examined in this investigation. The investigation covered Reynolds number, NRe,h, for a range of 2450:29300 corresponding to Dean number, NDn, h, for a range of 570:4800. The results showed a higher Nusselt number, NNu, h, of THTITT compared to DHTITT by 61.8 %%, while the increase in fh is approximately negligible. Also, by decreasing ξ from ∞ to 5.32 increases NNu, h by 33.4 %, with an increase in friction factor, fh by 57.6 %. Furthermore, with a decreasing ω from 9.9 mm to 3.8 mm, a significant increase in NNu, h occurs by 20.6 %, at the expense of increasing fh by 36.4 %. In addition, with decreasing α from 0.121 to 0.068, a significant increase in NNu, h occurs by 27.6 %, at the expense of increasing fh by 17.1 %. Finally, the THTITT decreases the heat loss (exergy destruction) between the hot and cold fluids. New correlations to predict NNu,h, and fh are presented.

Pullout behavior of polyethylene fiber from cement matrix: Effect of embedment length, matrix strength, and inclination angle

Engineered cementitious composites reinforced with polyethylene fibers (PE-ECC) exhibit the potential for high strength and toughness. To optimize the performance and tailor the properties of PE-ECC, this study focuses on analyzing the pullout behavior of polyethylene (PE) fibers from matrices through single fiber pullout tests and scanning electron microscopy analysis. One fiber type was used throughout the experiment, while three embedment lengths and three inclination angles were considered to investigate the pullout behavior from high-strength matrices. Furthermore, the pullout response from matrices with middle and low strength was examined, considering two embedment lengths. The results indicate that fibers with shorter embedment lengths exhibit lower pullout loads but higher energy absorption capacities. High matrix strength enhances adhesion and friction at the fiber-matrix interface, resulting in plumper pullout load versus slip curves. Owing to snubbing and matrix spalling effects, as the inclination angle increases, both the peak load and slip at the peak load of the inclined fibers exhibit an exponential increasing trend. Additionally, following the peak load, the pullout load of inclined fibers decreases more gradually than that of aligned fibers, and the energy absorption capacity of inclined fibers is significantly improved. Ultimately, general equations are derived for the calculation of pullout work and equivalent bond strength.

Terminal velocity and drag coefficient of a smooth steel sphere moving in the water-filled vertical and inclined glass pipe (Newton regime)

This paper aimed to determine new data on terminal velocities and drag coefficients of single spheres moving inside a vertical and inclined glass pipe filled with water using the Particle Image Shadowgraph technique in the range of Reynolds numbers from 1420 to 12,740. The inclination angle α of the pipe varied from 0° to 30° relative to the vertical position. In the experiment, smooth steel spheres with diameters ranging from 3 to 9.5 mm were used, and the pipe had a fixed inner diameter of 40 mm. For verification, the experimental results of the drag coefficients were compared with known data from other authors for a free-settling sphere and a sphere rolling down a pipe wall or plane. Finally, the paper presents a new regression model describing the relationship between the sphere drag coefficient and Reynolds number when the cosine of the pipe inclination angle is varied.

Tool inclination angle designing for low-deformation and high-efficiency machining of thin-wall blade based on edge-workpiece-engagement

The maximum flexibility direction(MFD) is solved for establishing the deformation estimation criterion of the blade during machining process, and the larger the milling force in MFD, the bigger the deformation of the blade during machining process. A new milling force calculation algorithm based on edge-workpiece-engagement(EWE) is proposed by analyzing the contact process between the ball-end milling tool and the chip. The chip thickness of each tool element of each edge curve at any rotation angle is calculated, the milling force of MFD and SLDs under different inclination angles are calculated. The average absolute milling force in MFD reaches the minimum value of 0.65126N when the lead/tilt angle is 30°/-45°, and the maximum machining efficiency is reached when the lead/tilt angle is 45°/-45°.The optimized tool inclination angle, which is 30°/-45° for lead/tilt angle, is obtained by solving the multi-objective optimization problem of machining deformation represented by relative deformation and machining efficiency represented by relative stable machining area. The effectiveness of the proposed scheme is verified by comparison of simulation and experiment for blade machining error under two kinds of tool orientations.

Flame transfer functions of asymmetric conical and V-shaped flames

Transfer functions of asymmetric flames subjected to incident flow perturbations are explored using the classical kinematic model, the G-equation, parameterized by flame tip angle α, flame-base incline angle β, and eccentricity e. With perturbations of various frequencies, we analyze perturbed asymmetric flames and derive analytical formulations of Flame Transfer Functions (FTF) for various flame conditions. It is observed that the gain of the asymmetric conical flame is increased compared to the symmetric case. Meanwhile, the amplification effect of the V-shaped flame is considerably suppressed as the flame becomes asymmetric. That means with a proper asymmetric geometry setting, the V-shaped flame no longer tends to amplify the perturbation and in other words becomes less susceptible to combustion instability. These findings have significant value for the future design and optimization of propulsion systems, where improving flame stability and reducing thermoacoustic instabilities are critical. Subsequently, a numerical study is conducted to verify the FTF results and examine the response of asymmetric flames under various perturbation levels. It has been demonstrated that the asymmetric conical flame is minimally affected by the amplitude of these perturbations, and the asymmetric V-shaped flame is highly sensitive to the convective amplitudes.

Investigation of Taylor bubble behavior in upward and downward vertical and inclined pipe flows

The Taylor bubble behavior in two-phase flow is critical for various engineering applications, including momentum, heat, and mass transfer efficiencies. Therefore, understanding the dynamics of Taylor bubbles is crucial for the optimal design, operation, and safety of reactors and pipelines. In slug flow in pipes, the successive translation of liquid slugs and Taylor bubbles is characterized by the Taylor bubble velocity, which is a function of the flow distribution coefficient (C0). This study aims to compile a large database of Taylor bubble velocity and flow distribution coefficient in upward, horizontal, and downward flows, evaluate existing models, and propose a unified C0 model. As a result, it is found that the physics governing the flow distribution coefficient in downward flow is drastically different from that in upward flow, and it goes through two flow transitions, which are governed by the pipe inclination angle. This behavior is modeled by the proposed model, which predicts the Taylor bubble flow distribution coefficient through both transitions and captures its physical behavior in the downward flow. A validation study of the proposed model revealed that the proposed model outperforms the existing models as it has an average absolute percent error and standard deviation of 4.2% and 6.2%, respectively.

Investigation of flow over an inclination pile under a Reynolds number of 3900 by numerical simulation

Flow over an inclination pile was studied numerically by solving the Navier–Stokes equations with large eddy simulation closure under a Reynolds number of 3900, and the inclination angles were in the range of −45° ≤ θ ≤ 45°. First, flow over a finite-length vertical pile with symmetric boundary conditions at both the upper and lower boundaries is used for verification, and the results are in good agreement with the previous results. Then, the lower boundary is set as a no-slip wall to simulate a rigid seabed, and 19 different inclination angles are numerically simulated to investigate the effects of the rigid seabed on the hydrodynamic characteristics and the wake structure of the cylindrical wake with different inclination angles. It is found that there is a significant difference between the forces on the piles, which were inclined forward and backward due to the end boundary conditions. When the pile is inclined forward, the force on the pile and the frequency of vortex shedding are lower than that of a vertical pile, which is more conducive to the stability of the structure. When the pile is inclined backward, the lower sidewall induces a strong spiral upward flow of the fluid at the lower end around the pile, which leads to the shedding of the wake vortex at a very close position to the pile. The return zone tightening phenomenon occurs at inclination angles greater than 25° backward, and this phenomenon leads to a sharp increase in the forces on the pile. Backward inclination angles greater than 30° are extremely unfavorable for structural forces.

Condensation dynamics on inclined heterogeneous substrates

This study presents numerical simulations of dropwise condensation on inclined chemically heterogeneous substrates in pure vapor atmosphere. To capture the dynamics of this process, a one-sided condensation model with a disjoining pressure is employed that incorporates the effects of gravity and chemical heterogeneities. We consider surfaces decorated with an array of square patches which are more hydrophilic compared to the rest of the surface, which act as nucleation, inception regions over which droplets form and grow and ultimately depin once their size becomes sufficiently large. The impact of the size and of the inception regions and the angle of inclination on the dynamics is considered, revealing significant qualitative and quantitative differences between the cases. For cases with purely structured substrates, it is observed that, as the number of inception regions increases, the condensation process transitions from steady to unsteady, with the critical number of inception regions increasing with the inclination angle increases. Further insight is provided by analyzing the snapshots of the liquid phase on the substrate, revealing the formation of liquid streaks or films, which influence both the dynamics of the flow and the total liquid volume on the substrate. The inclusion of random impurities on the structured substrate dramatically impacts the condensation dynamics, which is found to hinder the formation of liquid film, leading to a decrease in the total liquid volume generated on the substrate.

Experimental study on the influence of non-penetrating crack spatial distribution on brittle fracture process

To gain insights into the spatial distribution of non-penetrating cracks during the rock fracture process, a comprehensive uniaxial compression test is conducted on cubic gypsum specimens (100 mm × 100 mm × 100 mm) containing two non-penetrating cracks. The two pre-formed cracks are rectangular, with dimensions of 25 mm length, 2 mm width, and depths of 80 mm and 35 mm on adjacent sides of the specimen. The depth of the 80 mm crack can be adjusted from 0° to 150° in increments of 30°, while the other is fixed at a 45° angle. The results show that the spatial distribution of non-penetrating cracks can significantly influence the strength of the specimen. Initially, the strength of the specimen exhibits an upward trend and subsequently declines as the pre-crack inclination angle of the main rupture plane increases, ultimately reaching its pinnacle at 90°. The total percentage of tensile cracks in specimens with different inclinations are found to be 57%, 57%, 63%, 77%, 68%, and 61%, respectively. This change aligns seamlessly with the fluctuation in specimen strength as influenced by the angle of inclination. Non-penetrating cracks can also induce spalling on the specimen surface and give rise to anti-wing cracks, thereby exacerbating the spalling on the specimen surface. The inclinations of non-penetrating cracks can inevitably exert a certain influence on the propagation of neighboring non-penetrating cracks. Additionally, the macro-scale shear fracture of the specimen often occurs on the side of the non-penetrating crack that is deeper. The curved tensile fracture surface formed by the extension of the non-penetrating crack bears resemblance to the non-penetrating region in its ability to somewhat restrain the propagation of new cracks. Even under uniaxial compression, the spalling surface of the specimen containing spatial non-penetrating cracks frequently exhibits fracture characteristics belonging to I-III mode fracture, while its interior may display characteristics belonging to I-II-III mode fracture. These findings hold significant implications for comprehending and elucidating the genuine fracture process and three-dimensional fracture theory of rocks.

Orbit design for a future geodetic satellite and gravity field recovery

Spherical geodetic satellites tracked by satellite laser ranging (SLR) stations provide indispensable scientific products that cannot be replaced by other sources. For studying the time-variable gravity field, two low-degree coefficients C20 and C30 derived from GRACE and GRACE Follow-On missions are replaced by the values derived from SLR tracking of geodetic satellites, such as LAGEOS-1/2, LARES-1/2, Starlette, Stella, and Ajisai. The subset of these satellites is used to derive the geocenter motion which is fundamental in the realization of the origin of the terrestrial reference frames. LAGEOS satellites provide the most accurate standard gravitational product GM of the Earth. In this study, we use the Kaula theorem of gravitational perturbations to find the best possible satellite height, inclination, and eccentricity for a future geodetic satellite to maximize orbit sensitivity in terms of the recovery of low-degree gravity field coefficients, geocenter, and GM. We also derive the common station-satellite visibility-coverability coefficient as a function of the inclination angle and satellite height. We found that the best inclination for a future geodetic satellite is 35°–45° or 135°–145° with a height of about 1500–1700 km to support future GRACE/MAGIC missions with C20 and C30. For a better geocenter recovery and derivation of the standard gravitational product, the preferable height is 2300–3500 km. Unfortunately, none of the existing geodetic satellites has the optimum height and inclination angle for deriving GM, geocenter, and C20 because there are no spherical geodetic satellites at the heights between 1500 (Ajisai and LARES-1) and 5800 km (LAGEOS-1/2, LARES-2).

Study on crack propagation characteristics of rocks with different lateral pressure based on joint monitoring of DIC and AE

During the process of rock failure, the characteristics of crack propagation affect the fracture characteristics and macroscopic mechanical behavior of rocks, indirectly affecting the safety and stability of rock engineering. In order to study the evolution characteristics of cracks during rock failure under different lateral pressure, based on an improved digital image correlation (DIC) and acoustic emission (AE) signal recognition method, a visual biaxial servo loading device was developed to conduct biaxial compression tests on mudstone with prefabricated cracks of the same inclination angle. The research results indicate that the stages of crack propagation include microcracks propagation, crack tip formation, stable macroscopic cracks propagation, and unstable macroscopic cracks propagation. As the lateral pressure increased, the initiation frequency of cracks decreased, the quantity of propagation decreased, and the propagation path shortened, indirectly increasing the bearing strength of rocks. The initiation stress, peak stress, and elastic modulus of pre-cracked rocks with lateral pressure ≤ 2 MPa were lower than those of pre-cracked rocks with lateral pressure > 3 MPa, with the minimum reduction amplitude of 14.1%, 21.2%, and 12.6%, respectively. As the lateral pressure decreased, the dispersion of the AE main frequency distribution increased and accelerated its downward expansion. The surface temperature curves of rocks were prone to fluctuations and rapid upward evolution characteristics corresponding to crack tip formation and crack propagation, respectively. The research results provide theoretical and engineering references for the mining of weak coal seams.

Effects of low clay content on the anisotropic behavior of sand-clay mixtures: laboratory investigation using TSHCA

Undrained behavior of sandy soil with fines content is a challenge in geotechnical research. In this article, the effect of low clay content (plastic Kaolin) on the anisotropic behavior of sand is studied. In the technical literature, there are different data about the effect of fine particles (generally high percentage), but there are not enough studies on low fines content (especially plastic fines) and anisotropic conditions. For this purpose, 30 undrained tests are performed using a torsional shear hollow cylindrical apparatus (TSHCA) with constant (αo) and (b) values on Firoozkuh sand. The specimens had Kaolin contents of 0, 3, 5, 7 and 10%, and the inclination angle (αo) is varied from 15o to 60o. The specimens are prepared by dry deposition method and are consolidated under P'c= 100 and 200 kPa. The results of the experiments show that increasing the (αo) leads to more contractive behavior in sand. By adding clay particles to the host sand up to 3%, the peak strength of the specimen is increased (7% and 6% for α=15°and 30°, respectively), and then with the increase of clay content up to 10%, the strength of the specimen is decreased (33% and 22% for α=15°and 30°, respectively). But at α = 60o, with the addition of 5% clay, decrease in the peak strength is observed (about 15%) and with a further increase in the clay content, unlike the angles of 15o and 30o, increase in the peak strength of the specimen is observed, so that at 10% clay, the strength of the specimen is higher than the host sand (about 7%), which can be attributed to the cohesion nature of the clay particles. With the increase of clay content, anisotropy degree is decreased. In other words, with the increase of fines content, the anisotropic behavior is decreased.

On the use of perforated disk inserts in a round pipe to form a gas flow of the required structure in front of an ultrasonic flow meter

Unlike conventional gas meters, ultrasonic flow meters have such advantages as contactless operation, minimal pressure loss and high accuracy. When developing ultrasonic flow meters, like any other devices, assumptions and simplifications related to the theory of ultrasonic flow meters are used. When developing such devices, researchers do not always have the necessary space to deploy such structures. Therefore, the question arises of developing devices that can replace large sections of pipelines with various turns in the role of local resistances. The paper presents some studies conducted during the development of a perforated disk capable of forming a flow profile similar to the profile after a double bend. The presented results of a study of the influence of the perforated disk geometry on the gas dynamics and flow structure. The calculations were carried out using three-dimensional computer modeling. The analysis of the influence of the hole location, their sizes and the angles of inclination of the holes relative to the disk axis on the velocity distribution and the formation of the velocity profile downstream of the disk is the purpose of this study. Scalar and vector fields of velocities downstream of the perforated disk are obtained. Velocity profiles in sections behind the disk are constructed. A comparative analysis of different designs of perforated disks is carried out. The design principles of such flow formers are indicated. The geometric factors influencing the flow structure after the former are revealed. The revealed subtleties and described design principles made it possible to develop straighteners and flow formers based on perforated disks. The final samples of disks and the results of their operation are shown

VVV catalog of ab-type RR Lyrae in the inner Galactic bulge

Observational evidence has accumulated in recent years, showing that the Galactic bulge includes two populations, a metal-poor one and a metal-rich one, which in addition to having different metallicities show different alpha over iron abundances, spatial distribution, and kinematics. While the metal-rich, barred component has been fairly well characterized, the metal-poor, spheroidal component has been more elusive and harder to describe. RR Lyrae variables are clean tracers of the old bulge component, and they are, on average, more metal-poor than red clump stars. In the present paper, we provide a new catalog of 16488 ab-type RR Lyrae variables in the bulge region within |l|$ and |b|$ extracted from multi-epoch Point Spread Function photometry performed on VISTA Variable in the V\' a L\'actea survey data. We used the catalog to constrain the shape of the old, metal-poor, bulge stellar population. The identification of ab-type RR Lyrae among a large sample of candidate variables of different types has been performed via a combination of a Random Forest classifier and visual inspection. We optimized this process in such a way to extract a clean catalog with high purity, although for this reason its completeness, close to the midplane, is lower compared to a few other near-infrared catalogs covering the same region of the sky. We used the present catalog to derive the shape of their distribution around the Galactic center, resulting in an elongated spheroid with projected axis ratio of b/asim 0.7 and an inclination angle of phi sim 20 degrees. We discuss how observational biases, such as errors on the distances and a nonuniform sampling in longitude, affect both the present measurements and previous ones, especially those based on red clump stars. Because the latter have not been taken into account before, we refrain from a quantitative comparison between these shape parameters and those derived for the main Galactic bar. Nonetheless, qualitatively, taking into account observational biases would lower the estimated ellipticity of the bar derived from red clump stars, and hence reduce the difference with the present results. We publish a high-purity RRab sample for future studies of the oldest Galactic bulge population, close to the midplane. We explore different choices for the period-luminosity-metallicity relation, highlighting how some of them introduce spurious trends of distance with either the period or the metallicity, or both. We provide evidence that they trace a structure that is less elongated than the main bar, though we also highlight some biases of these kind of studies not discussed before.

The Neutron Star Mass, Distance, and Inclination from Precision Timing of the Brilliant Millisecond Pulsar J0437-4715

The observation of neutron stars enables the otherwise impossible study of fundamental physical processes. The timing of binary radio pulsars is particularly powerful, as it enables precise characterization of their (three-dimensional) positions and orbits. PSR J0437–4715 is an important millisecond pulsar for timing array experiments and is also a primary target for the Neutron Star Interior Composition Explorer (NICER). The main aim of the NICER mission is to constrain the neutron star equation of state by inferring the compactness (M p /R) of the star. Direct measurements of the mass M p from pulsar timing therefore substantially improve constraints on the radius R and the equation of state. Here we use observations spanning 26 yr from Murriyang, the 64 m Parkes radio telescope, to improve the timing model for this pulsar. Among the new precise measurements are the pulsar mass M p = 1.418 ± 0.044 M ⊙, distance D = 156.96 ± 0.11 pc, and orbital inclination angle i = 137.°506 ± 0.°016, which can be used to inform the X-ray pulse profile models inferred from NICER observations. We demonstrate that these results are consistent between multiple data sets from the Parkes Pulsar Timing Array (PPTA), each modeled with different noise assumptions. Using the longest available PPTA data set, we measure an apparent second derivative of the pulsar spin frequency and discuss how this can be explained either by kinematic effects due to the proper motion and radial velocity of the pulsar or excess low-frequency noise such as a gravitational-wave background.