Degree Bend Research Articles

Experimental Assessment of the Turbulent Flow Field Due to Emergent Vegetation at a Sharply Curved Open Channel

Emergent vegetation in river corridors influences both the flow structure and subsequent fluvial processes. This investigation aimed to analyze the impact of the bending and vegetation components in a sharply curved open channel on the flow field. Experiments were undertaken in a meandering flume (0.9 m wide, wavelength of 3.2 m, and a sinuosity of 1.05) with a 90-degree bend at the end of it, with and without vegetation, to achieve this goal. The individual vegetation elements arranged across the 90-degree bend of the flow channel were physically modelled using rigid plastic stems (of 5 mm and 10 mm diameters). Analysis of the findings from the flow velocimetry, taken at five cross-sections oriented at angles of 0°, 30°, 45°, 60°, and 90°, along the 90-degree bend indicates that as the plant density increases, the effect of centrifugal force from the channel’s bend on the cross-sectional flow patterns decreases. At the same time, the restricting influence of vegetation on lateral momentum transfer becomes more pronounced. Specifically, for increasing vegetation density: (a) higher transverse and vertical velocities are observed (increased by 4.35% and 9.68% for 5 mm and 10 mm reed vegetation, respectively, compared to the non-vegetated case); (b) greater turbulence intensity is seen in the transverse flow direction, along with increased turbulent kinetic energy (TKE); and (c) reduced near-bed Reynolds stresses are found. The average transverse flow velocity for the non-vegetated case is 18.19% of the longitudinal flow velocity and the average vertical velocity for the non-vegetated case and 5 mm and 10 mm reed vegetation is 3.24%, 3.6%, and 5.44% of the longitudinal flow velocity, respectively.

Finite Element Simulation of Aerosol Particle Trajectories in a Cantilever-Enhanced Photoacoustic Spectrometer for Characterization of Inertial Deposition Loss

The cantilever-enhanced photoacoustic spectrometer is a sensitive instrument developed originally for trace gas measurements and has lately been successfully applied for measuring light-absorbing particles, such as aerosols. The finite inertia of aerosol particles can cause the particles to be deposited on the walls in the spectrometer’s flow channels, which creates a source of uncertainty for the measurement process. In this study, we characterized this inertial deposition in the spectrometer using finite element-based modeling. First, computational fluid dynamics was used to calculate the distribution of airflow within a 3D model of the spectrometer’s flow channels. Then, the trajectories of aerosol particles were computed to evaluate the inertial deposition losses. The modeling method was validated by computing inertial deposition for two known cases of laminar flow, namely particles flowing through a pipe with a 90-degree bend and a pipe with an abrupt contraction. The particle transmission of the photoacoustic spectrometer was experimentally measured. Differences and similarities between measured and modeled results are discussed. The modeled inertial deposition losses ranged from approximately 5% to 70% for particle diameters between 50 and 500 nm. This modeling approach provides valuable insight into the influence of particle size and flow rate on the inertial deposition and also pinpoints the physical location of the loss within the spectrometer, which is valuable for improving the measurement process.

Comparative evaluation of pediatric endodontic rotary file systems to bending and torsion tests: A finite element analysis

Background and objectiveThe introduction of Paediatric NiTi instruments has transformed the field of paediatric endodontics. However, no studies are available on the mechanical behaviour of these files, wherein Finite Element Analysis (FEA) was found to play a major role. The objective of this study is to evaluate the mechanical behavior of three commercially available pediatric endodontic rotary file systems to bending and torsion stress analysis test through Finite Element Analysis (FEA). MethodsA Finite Element Analysis study was performed on three commercially available pediatric endodontic rotary files (Pro AF baby, Kedo SG and Neoendo pedoflex) available for cleaning and shaping the narrow root canals of the deciduous teeth to bending and torsion tests with the boundary conditions according to ISO 3630-1 specifications. ResultsIn the bending analysis, Pro AF baby files were found to withstand the complete bending tests without yielding with a maximum von Mises stress of 1366 MPa, and Kedo SG, Neoendo Pedoflex file exhibited maximum von Mises stress of 2296 MPa, 1971 MPa. Under torsion tests Kedo SG exhibited maximum stress distribution, while Neoendo Pedoflex and Pro AF baby files exhibited similar stress distribution. ConclusionPro AF baby file effectively withstood the rigorous 45 -degree bending examination without experiencing yielding, while Kedo SG file exhibited higher flexibility. Under torsional resistance test, all the three instruments exhibited similar stress distribution under the yield limit. In summary, the mechanical behaviour (bending and torsion) of pediatric rotary file systems were influenced by design of the files.

Sensitivity of Post-TAVR Hemodynamics to the Distal Aortic Arch Anatomy: A High-Fidelity CFD Study.

Patient-specific simulations of transcatheter aortic valve (TAV) using computational fluid dynamics (CFD) often rely on assumptions regarding proximal and distal anatomy due to the limited availability of high-resolution imaging away from the TAV site and the primary research focus being near the TAV. However, the influence of these anatomical assumptions on computational efficiency and resulting flow characteristics remains uncertain. This study aimed to investigate the impact of different distal aortic arch anatomies-some of them commonly used in literature-on flow and hemodynamics in the vicinity of the TAV using large eddy simulations (LES). Three aortic root anatomical configurations with four representative distal aortic arch types were considered in this study. The arch types included a 90-degree bend, an idealized distal aortic arch anatomy, a clipped version of the idealized distal aortic arch, and an anatomy extruded along the normal of segmented anatomical boundary. Hemodynamic parameters both instantaneous and time-averaged such as Wall Shear Stress (WSS), and Oscillatory Shear Index (OSI) were derived and compared from high-fidelity CFD data. While there were minor differences in flow and hemodynamics across the configurations examined, they were generally not significant within our region of interest i.e., the aortic root. The choice of extension type had a modest impact on TAV hemodynamics, especially in the vicinity of the TAV with variations observed in local flow patterns and parameters near the TAV. However, these differences were not substantial enough to cause significant deviations in the overall flow and hemodynamic characteristics. The results suggest that under the given configuration and boundary conditions, the type of outflow extension had a modest impact on hemodynamics proximal to the TAV. The findings contribute to a better understanding of flow dynamics in TAV configurations, providing insights for future studies in TAV-related experiments as well as numerical simulations. Additionally, they help mitigate the uncertainties associated with patient-specific geometries, offering increased flexibility in computational modeling.

Large transmittance contrast via 90-degree sharp bends in square lattice glide-symmetric photonic crystal waveguides.

We demonstrate an intriguing transmittance contrast in a glide-symmetric square-lattice photonic crystal waveguide with a 90-degree sharp bend. The glide-symmetry gives rise to a degeneracy point in the band structure and separates a high-frequency and a low-frequency band. Previously, a similar large transmittance contrast between these two bands has been observed in glide-symmetric triangular- or honeycomb-lattice photonic crystals without inversion symmetry, and this phenomenon has been attributed to the valley-photonic effect. In this study, we demonstrate the first example of this phenomenon in square-lattice photonic crystals, which do not possess the valley effect. Our result sheds new light onto unexplored properties of glide-symmetric waveguides. We show that this phenomenon is related to the spatial distribution of circular polarization singularities in glide-symmetric waveguides. This work expands the possible designs of low-loss photonic circuits and provides a new understanding of light transmission via sharp bends in photonic crystal waveguides.

Numerical Investigations of Turbulent Flow Through A 90-Degree Pipe Bend And Honeycomb Straightener

Abstract Pipe bends are commonly used in piping systems in offshore and subsea installations. The present study explores the design considerations for the honeycomb straightener inserted downstream of a 90-degree pipe bend. The objective of the study is to evaluate the effectiveness of the honeycomb in suppressing the flow swirling for different distances from the bend outlet (Lb) and different values of the honeycomb thickness (t). The turbulent flow through the 90-degree circular pipe bend with the honeycomb straightener is investigated by carrying out numerical simulations using the Reynolds-Averaged Navier-Stokes (RANS) turbulence modeling approach. The Explicit Algebraic Reynolds Stress Model (EARSM) is adopted to resolve the Reynolds stresses. The honeycomb thickness to pipe diameter ratio (t/D) is varied between 0.1 and 1. The normalized distance from the bend outlet to the honeycomb straightener (Lb/D) is varied between 1 and 5. The disturbance in the velocity field is generated by the pipe bend with the curvature radius to pipe diameter ratio (Rc/D) of 2 and Reynolds number (Re) of 2×105. It is found that both the increase in Lb/D and t/D improves the performance of the device in removing the swirl behind the bend outlet. The best performance is observed for the honeycomb straightener with the distance Lb/D=5 and thickness t/D=0.5.

Magneto-responsive wettability-switchable surfaces for in-situ large distance droplets capturing-releasing-bouncing

In this paper, superhydrophobic magnetically responsive micro-plate arrays (SMMAs) with reverse switching wettability were studied for in-situ capturing, releasing, and directional bouncing of droplets over a large distance. A novel method for producing superhydrophobic pattern on one side surface of the micro-plates by laser texturing at 90 degree bending state, created water contact angle of 151°, a rolling angle of < 10°, and a maximum surface adhesion force of 35.5 μN. Reversible switching between droplets (volume 5–40 μL) capturing with high adhesion force (high surface energy) and droplet releasing with low adhesion force were achieved spontaneously. The instantaneous response of the SMMAs to magnetic field provided a guarantee for the directional bouncing of droplets in long distance. Droplets transportation up to 40 μL, directional bouncing of 5 μL droplets with a vertical bounce height of 4.5 mm and a horizontal bounce distance of 24.7 mm have been achieved. This work provides a novel approach for flexible droplets manipulation and multifunctional operation of droplets for non-contact, remote-driven and non-destructive reagent transfer applications.

Development of an effective two-equation turbulence modeling approach for simulating aerosol deposition across a range of turbulence levels

Pharmaceutical aerosol systems present a significant challenge to computational fluid dynamics (CFD) modeling based on the need to capture multiple levels of turbulence, frequent transition between laminar and turbulent flows, anisotropic turbulent particle dispersion, and near-wall particle transport phenomena often within geometrically complex systems over multiple time scales. Two-equation turbulence models, such as the k−ω family of approximations, offer a computationally efficient solution approach, but are known to require the use of near-wall (NW) corrections and eddy interaction model (EIM) modifications for accurate predictions of aerosol deposition. The objective of this study was to develop an efficient and effective two-equation turbulence modeling approach that enables accurate predictions of pharmaceutical aerosol deposition across a range of turbulence levels. Key systems considered were the traditional aerosol deposition benchmark cases of a 90-degree bend (Re=6,000) and a vertical straight section of pipe (Re=10,000), as well as a highly complex case of direct-to-infant (D2I) nose-to-lung pharmaceutical aerosol delivery from an air-jet dry powder inhaler (DPI) including a patient interface and infant nasal geometry through mid-trachea (500<Re<7,000). Of the k−ω family of models, the low Reynolds number (LRN) shear stress transport (SST) approach was determined to provide the best agreement with experimental aerosol deposition data in the D2I system, based on an improved simulation of turbulent jet flow that frequently occurs in DPIs. Considering NW corrections, a new correlation was developed to quantitatively predict best regional values of the y+limit, within which anisotropic NW turbulence is approximated. Considering EIM modifications, a previously described drift correction approach was implemented in pharmaceutical aerosol simulations for the first time. Considering all model corrections and modifications applied to the D2I system, regional relative errors in deposition fractions between CFD predictions and new experimental data were improved from 19–207% (no modifications) to 2–15% (all modifications) with a notable decrease in computational time (up to ∼15%). In conclusion, the highly efficient two-equation k−ω models with physically realistic corrections and modifications provided a viable, efficient and accurate approach to simulate the transport and deposition of pharmaceutical aerosols in complex airway systems that include laminar, turbulent and transitional flows.

The effect of the pipe angle and protective inclined apron on the scouring and sedimentation pattern around a semi-buried pipe in a 90° mild bend

In fluid transmission projects, buried and semi-buried pipes passing through river bends change the conventional scouring and sedimentation patterns. In this research, the influence of pipeline angle in relation to flow direction in a 90-degree mild bend, along with the use of a protective inclined apron were experimentally investigated. Experiments were carried out in three different Froude numbers, three different passages (normal, repeller and attracting) as well as in the most critical condition, with three different protective inclined apron lengths. The results showed that in a condition where the pipeline passage is normal to the flow direction, the scour hole after the pipe is deepest, and in the repeller position, the most scouring was observed under the pipe. Moreover, placing a protective inclined apron, where the ratio of the apron length to the pipe diameter (LˊD) equals 1, reduces the amount of scour under the pipe by 75%. Furthermore, in the case where the ratio of the apron length to the pipe diameter (LˊD) equals 3 and 5, scouring under the pipe doesn't occur.

A three-dimensional solver for simulating detonation on curvilinear adaptive meshes

A generic solver in a parallel Cartesian adaptive mesh refinement framework is extended to simulate detonations on three-dimensional structured curvilinear meshes. A second-order accurate finite volume method is used with grid-aligned Riemann solvers for thermally perfect gas mixtures. Detailed, multi-step chemical kinetic mechanisms are employed and numerically incorporated with a splitting approach. The adaptive mesh refinement technique is applied to a mapped mesh using modified prolongation and restriction operators. The flux along the coarse-fine interface is considered in a correction procedure to ensure the conservation of the solver. The numerical accuracy, conservation and robustness of the simulations are verified and validated with suitable benchmark tests. The new solver is then used to simulate detonation problems in non-Cartesian geometries. A simulation is conducted of the three-dimensional detonation propagation in a 90-degree pipe bend. A detonation in a round tube is also simulated in a Galilean frame of reference. Both a rectangular mode and a spinning mode are observed in the simulations. In addition, the fundamental problem of detonation wave/boundary layer interaction is studied. The results show that the new solver can simulate high-speed reactive flows efficiently by the combined use of a curvilinear mapping with mesh adaptation.

High-Performance 32-Channel Silicon Arrayed Waveguide Grating With 100 GHz Spacing

A high-performance 32-channel silicon arrayed waveguide grating (AWG) with 100 GHz spacing is designed and fabricated using 180-nm lithography platform for massive production. For the arrayed waveguides, a rectangular structure compositing of a straight waveguide and a 90-degree bend waveguide is designed. Moreover, the overall structure only needs to be etched once to reduce the error introduced in the fabricating process. The experiment results show that the AWG operates with high performance within short, central, and long wavelength bands (i.e., S+C+L bands). Taking the measured central wave band (C band) as an example, a channel uniformity of 2.05 dB, a crosstalk lower than -20 dB, and an insertion loss less than 4.85 dB are achieved across the wavelength range from 1544 nm to 1576 nm. As far as we know, this fabricated silicon AWG demonstrates the best comprehensive performance for <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$32\times 100$ </tex-math></inline-formula> -GHz channels achieved using lithography, which will be highly desirable for wavelength division multiplexing communication and microwave photonics systems.

A supercapacitive all-inorganic nano metal–oxide complex: a 180° super-bendable asymmetric energy storage device

A complementary redox-pair, WO3 and Co3O4, was used to study their charge storage abilities by making a solid-state flexible device. The device shows 100% retention of device parameters even after 180 degree bending.

Flow Pattern and Erosion in a 90-Degrees Sharp Bend around a W−Weir

Different flow-altering methods, such as W−Weirs, have been developed to reduce erosion. For this study, we performed two experiments: (1) installing a W−Weir in various positions to determine the best angle for placement, and (2) investigating the variation of flow patterns and bed shear stress distribution in a 90-degree sharp bend by measuring the 3D components of flow velocities, with and without W−Weirs, where the greatest scour depth occurs. The results from the three installation angles indicate that less scour depth and volume of sediment removal occur when the weir is located close to the end of a bend. In addition, the value of the secondary circular power without a weir was higher than the position with a weir; however, this value significantly increased at 70 degrees due to turbulence flow near the W−Weir. This secondary flow power reduction at 45 degrees with a W−Weir increased by 65.8 percent for a Froude number value of 0.17, and by 29.8 percent for a Froude number value of 0.28, compared to values without the W−Weir, respectively.

The vortex structures of the mean turbulent flow field in a 90-degree bend pipe

We analyse the vortex structures of the mean turbulent flow field in a 90-degree bend pipe at bulk Reynolds number 5300 and radius of curvature 2.5 times the pipe radius. The Reynolds averaged Navier–Stokes equations are solved for the mean turbulent flow field in the finite volume framework of ANSYS Fluent. The Reynolds stress model is adopted for closure of turbulence quantities. Notwithstanding any scale resolving simulation, we show that a detailed exploration of the flow, turbulence, and vortex structures in the mean turbulent flow field inside a pipe bend is possible, through the paradigm based on complex conjugate eigenvalues of the velocity gradient tensor. The convex contour of the inner side of the bend is found to be the key vortex-generating surface. We find that the vortices start to gain swirling strength just after entering the bend. The strength further decays, rather than getting enhanced, within the remaining part of the bend. The outer side of the bend, on the other hand, appears to maintain a straining flow regime. Fluid particles move between the vortex region and the straining region through the strain-dominated vortex regions, the structure of which is also unveiled through the eigenvalue-based vortex defining paradigm. Both the straining and the vortex zone inject turbulence. However, the vortex-induced turbulence suffers significant dissipation within the bend region. The vortices transported downstream of the bend help in generating turbulence to recover the loss of turbulence in the bend region.

Effect of walls with large scale roughness in deposition efficiency for 90-degree square bend configurations

This paper presents a numerical study of particle deposition in turbulent flow across bends with large scale roughness. The k-ε RNG model with Enhanced Wall Functions (EWF) for wall treatment and a Lagrangian point particle tracking method with a discrete random walk (DRW) model for turbulence dispersion were chosen in order to study the effect of cavities and ribs on the particle deposition efficiency in 90-degree square bends. The study is a complementary approach to previous ones performed for duct and channel flows. Results show that while cavity-type (c-type) and rib-type (r-type) large scale roughness elements in the external wall of the bend have a low effect on particle deposition, there is significant enhancement for cases in which large scale elements are located also at the inner side of the bend inducing high increments of secondary slow and turbulent kinetic energy. This, in addition to the increment of deposition area, generates a global shift of the particle deposition curve, especially for low and intermediate Stokes numbers and cases with high curvature ratio. Our study shows that bends of square cross section, similar to those used in Heating, Ventilation, and Air Conditioning (HVAC) applications but modified with large scale roughness elements in their walls, can be a potential alternative for filtering applications to be considered and studied more in depth in the future.

Modelling Studies of Retrofitted Anchorage System in Exterior Beam Column Joint by Supplementary Steel

A Nonlinear finite element based ABAQUS modeling studies were conducted to evaluate the performance of exterior Beam Column Joint (BCJ) under quasi-static test loads. Six integrated BCJ models representing different configurations of beam reinforcement anchored in joint are verified by using a novel retrofitting technique called "Post Installation of Supplementary Anchorage" (PISA) by using headed bar as supplementary steel. The configuration of beam reinforcement anchored in column are described by straight bar,90 degree bend ,180 degree hook (confirming to design code IS456:2000) and single head, double head bars (confirming to ACI 318-19, ACI 352R-02 ) and 90 degree long bend of ductile detailing (as per IS 13920-2016). Two series (A&amp;B) of integrated joint specimens representing conventional (series-A) and retrofitted anchorage (series-B) systems are modeled and tested by using ABAQUS software. The test parameters considered are configuration of anchorage system and presence of supplementary anchorage. The test variables representing nonlinear performance of retrofitted joint system are Von Mises stress conditions, Principal tensile stress, Moment-Rotation, Degraded stiffness, Crack mechanics and Damage index. The results shows good improvement of post failure conditions of exterior beam-column joint such as relocation of plastic hinge mechanism and failure mechanics of retrofitted joint system. Also the results validated with experimental program on typical specimens casted and tested. This study imparts useful information on implicit retrofitting methods applied by external means in exterior beam-column joint. It also promotes performance based design principles with viable construction practice.

Coupling Design of Combined Function Bending Magnet and High Current Electron Beam for 100 kW Irradiation Accelerator

RF system is one of the key components of a 2 GeV, 6 MW high power fixed field alternating gradient (FFAG) accelerator being designed at China Institute of Atomic Energy (CIAE). In order to verify the design principle and the engineering feasibility, a scaled-down RF cavity is under construction, which can also be used as the main accelerating cavity for a 100 kW electron irradiation accelerator. By the deflections of several 180 degrees bending magnets, the electrons emitted from the electron gun can pass the cavity for multiple times. Due to the limited length of the cavity, the deflection radius should be as small as possible to ensure more acceleration times and consequently higher beam power, which will make the fringe field effect of the bending magnet be a problem. In addition, the bending magnet should provide beam focusing in both the radial and axial directions of the beam and keep the beam envelope stable during the whole acceleration process. Based on the above reasons, the parameters of the combined function bending magnet, such as the pole face rotations (Liu, 1994), magnetic field gradient and shielding distance, have a great influence on the beam dynamics behavior in the accelerator, which bring great difficulty to the design of the combined function bending magnet. In this paper, the coupling design of the bending magnet with focusing function and the high intensity electron beam for this 100 kW irradiation accelerator will be illustrated in detail.

PPM EMAT for Defect Detection in 90-Degree Pipe Bend.

Aircraft pipelines are mainly used for the storage and transportation of fuel, hydraulic oil and water, which are mostly bent pipes of non-ferromagnetic materials. We used PPM (Periodic Permanent Magnet) EMAT (Electromagnetic Acoustic Transducer) to detect the defects at 90-degree bends. A simulation model was established by finite element software to study the propagation characteristics and defect detection capability of T (0, 1) mode-guided wave in aluminum pipe bend. In terms of propagation characteristics, the energy of the guided wave was focused in the extrados of the bend, and the guided waves in the intrados and extrados of the bend were separated due to the difference in propagation distance. Regarding defect detection capability, T (0, 1) mode-guided wave had the highest detection sensitivity for the defect in the extrados of the bend and the lowest detection sensitivity for the defect in the middle area of the bend. We designed a PPM EMAT for 320 kHz to verify the simulation results experimentally, and the experimental results are in good agreement with the simulation results.

Research on a rectangular microwave filter with rectangular groove

In this paper, a rectangular microwave filter with rectangular groove is designed. The filter adopts symmetrical three-stage structure. The first section is the slot line waveguide section to realize the input / output of microwave signal, the second section is the transition section, which adopts the impedance gradient structure, and the third section is the sspps section composed of periodic symmetrical rectangular groove and 90 degree bending structure. By adjusting the geometric size of the rectangular groove and its air gap, the passband width and stopband characteristics of the filter can be adjusted, and its microwave sub wavelength binding effect can be further improved, making the anti space electromagnetic interference ability of sspps filter more excellent. The filter can be applied to L ∼ s Band civil microwave communication system.

Analytical Studies on Retrofitted Anchorage System in Concrete using Strut and Tie Method

Analytical studies were conducted on force transfer mechanism of retrofitted anchorage system in structural concrete by Strut-and-Tie modeling (STM). Post Installation of Headed anchorage (PIHA) as supplementary system introduced for implicit strengthening of anchorage system. The boundaries of STM are considered under direct tension pull-out test. Five different configurations of conventional reinforcement anchorage in concrete with straight bar, 90-degree bend, 180-degree hook, single head and double head bars are retrofitted by using PIHA technique. The mechanics of force transfer in anchorage system was analyzed by STM and validated the results by experimental program. The study parameters considered are (i) location of nodal zone, (ii) strut angle, (iii) size of strut (concrete) contributed during failure. The study variables are (i) configuration of anchorage system (ii) characteristic node formation and (iii) presence of supplementary reinforcement. The result shows good agreement with experimental findings against failure mode, stress pattern, and location of critical zone in conventional and retrofitted anchorage system. Use of this study may further extended to assess theoretical evaluation of failure mode, formation of critical section and stressed regions of discrete RC elements such as corbel projection, bracket connections and beam-column joints.