Pipe Bend Research Articles

A local resistance coefficient model of aircraft hydraulics bent pipe using laser powder bed fusion additive manufacturing

Laser powder bed fusion (L-PBF) technology has remarkable advantages in achieving lightweight and miniaturized products, and a short manufacturing cycle. However, for the inner suface of L-PBF bent pipe, the distribution of surface roughness is not uniform. The surface roughness at the top of the bent pipe is much greater than that of other positions, which results that the local resistance coefficient of the bent pipe manufactured by L-PBF cannot be estimated accurately through the existing theory dedicated for conventional pipelines. Aiming at resolving this shortcoming, a new model is proposed to predict the local resistance coefficient of aircraft hydraulic bent pipes. In this regard, numerous 90°-bend Ti6Al4V (TC4) pipelines with different diameter-bend ratios (D/R) are fabricated using the L-PBF technique, and the geometry and surface roughness of the machined samples are measured experimentally and calculated numerically. Based on the obtained results from the finite element simulation and measurements from the experiment for local resistance coefficients of various bent pipes, a model is established to predict local resistance coefficients. The obtained results indicate that the surface roughness, Reynolds number, and diameter-bend ratios affect the local resistance coefficient of the bent pipe. Transition between flow regimes is observed in L-PBF bent pipes. The Reynolds number range in the transition region increases with the decrease of surface roughness, and the critical value of the transition region is modeled. Compared with the experimental data, the predicted values have an average error of less than 10%, indicating that the prediction accuracy is greatly improved.

Проблема изготовления труб по проектной информации

The article considers the problem of increasing the efficiency of shipbuilding production on the basis 
 of pipe manufacturing technologies by design information. The reasons that prevent the manufacture of pipes by design information and possible ways to eliminate them are analyzed. Great attention to the manufacture of pipelines is explained by the significant amount of pipeline work, which makes 10-12% of the total labor intensity of building 
 a ship, and on some projects - up to 14-17%. At the same time, the share of pipes manufactured in advance does not exceed 40%. The solution of the problem is considered in a historical retrospective taking into account modern realities, because the development and improvement of the technology of pipe production is one of the main important directions in the development of shipbuilding not only in Russia, but also in the world. Significant changes in the technology are associated with the widespread use of computing devices to improve the computer-aided design, technological preparation of production and the manufacture of pipelines according to design information. There has been carried out comparative analysis of pipe production efficiency using pipe bending machines, bent segments and straight sections. To form the pipe configuration, it is proposed to retain the traditional technology of pipe bending using pipe bending machines. Directions for further research in this area are identified and solutions are proposed, the implementation of which will help reduce construction time, reduce labor intensity and increase the productivity of pipeline work when fulfilling shipbuilding orders. Ensuring the reliability of design information is aimed at increasing the proportion of pipes manufactured in advance, regardless of the functional purpose of pipelines.

Hybrid LES/RANS simulations of a 90° pipe bend using different CFD solvers

In this study, the performance of several RANS and hybrid LES/RANS turbulence models along with different CFD solvers (ANSYS Fluent, OpenFOAM and RapidCFD) is tested in terms of their ability to reproduce the flow downstream of a 90° pipe bend. The focus is on the temporal mean profiles downstream of the bend up to approximately 31 times the pipe's diameter D. The turbulence models' accuracy is evaluated by means of performance indicators and flow profiles in comparison to LDA measurements. The results demonstrate that the use of RANS models is suitable as long as the location of interest is in the vicinity of the bend up to approximately 10 D downstream of the bend. With increasing distance, the accuracy of the RANS models decreases, and the use of hybrid LES/RANS models is recommended.Three hybrid LES/RANS models are tested: the stress-blended eddy simulation (SBES) model as well as the Spalart-Allmaras-based and the k-omega SST-based improved delayed detached eddy simulation (IDDES) models. All three models show enhanced results for a distance to the bend >10 D. Additionally, it is found that in this geometry configuration, the IDDES models require a transient inlet. The flow separation due to the redirection inside the bend is too weak to generate turbulent fluctuations and a fast transition to full LES mode in the separation region. Due to the turbulent excitation at the inlet, the RANS region downstream of the bend is distinctly reduced, resulting in an enhanced performance of the hybrid IDDES models.

Mechanical deformation of elastomer medical devices can enable microbial surface colonization

Elastomers such as silicone are common in medical devices (catheters, prosthetic implants, endoscopes), but they remain prone to microbial colonization and biofilm infections. For the first time, our work shows that rates of microbial surface attachment to polydimethylsiloxane (PDMS) silicone can be significantly affected by mechanical deformation. For a section of bent commercial catheter tubing, bacteria (P. aeruginosa) show a strong preference for the ‘convex’ side compared to the ‘concave’ side, by a factor of 4.2. Further testing of cast PDMS materials in bending only showed a significant difference for samples that were manually wiped (damaged) beforehand (1.75 × 104 and 6.02 × 103 cells/mm2 on the convex and concave sides, respectively). We demonstrate that surface microcracks in elastomers are opened under tensile stress (convex bending) to become ‘activated’ as sites for microbial colonization. This work demonstrates that the high elastic limit of elastomers enables these microcracks to reversibly open and close, as ‘dynamic defects’. Commercial catheters have relatively high surface roughness inherent to manufacturing, but we show that even manual wiping of newly-cast PDMS is sufficient to generate surface microcracks. We consider the implication for medical devices that feature sustained, surgical, or cyclic deformation, in which localized tensile conditions may expose these surface defects to opportunistic microbes. As a result, our work showcases serious potential problems in the widespread usage and development of elastomers in medical devices.

Design and Experiment on a Distributed Seed Delivery System with a Pneumatic Central-Cylinder Seeder

A distributed seed delivery system is the most important component of a pneumatic central-cylinder seeder. We performed a fluent simulation analysis for seed-drop tubes at different parameters and airflow velocities, and with an increase in air velocity, the larger the angle is, the easier it is to produce a vortex, which considerably changes the angle, with the little bend tube improving the uniformity of seeding performance. The distribution of rice seeds in the seeding furrow using seed-drop tubes of different angles was also analyzed, and with an increase in delivery airflow velocity, the rice-sowing belts aggregated toward the seeding furrow central line, and with an increase in the forward speed, the seed distribution in the forward-speed direction presented an aggregation and then dispersion trend. The field experiment and physiological indices show that the yield of germination acceleration by seed pelleting can reach 7.92 t. ha−1, which was significantly higher than the yields with other treatments.

Numerical study of wall erosion using energy approach for the flow of dense slurry in 90o horizontal pipe bend

Erosion of bends is common in pipelines transporting slurry. The present study implements erosion models based on the energy approach in predicting erosion of bends subject to moderate-to-high solids concentration. Eulerian-Eulerian numerical modeling of the flow of settling slurries in 90o horizontal pipe bend is performed to examine erosion wear characteristics for various flow/geometry conditions. The solid-liquid flow field is validated with experimental results of bend pressure drop and solids distribution. The erosion model could predict erosion at the bend walls in good agreement with experimental data and qualitatively reasonably with the CFD-DEM data. Interesting results are revealed in the parametric studies with maximum erosion rate and its location near/at the bend exit for the range of operating conditions in this study. It is further observed that erosion wear is reduced when the slurry is transported at higher solids efflux concentration with velocities close to the deposition (or critical) velocity.

Preparation and characterization of a mussel-inspired and programmable PDA@MXene/PNIPAM hydrogel actuator with ultrafast temperature and NIR responsiveness

In recent years, smart hydrogels have been widely applied to various types of hydrogel actuators due to their unique stimulus responsibility, such as temperature responsiveness, near-infrared (NIR) light responsiveness, pH responsiveness, etc. Herein, segmented poly (N-isopropyl acrylamide) (PNIPAM) based hydrogel actuators with both temperature and NIR light actuation behaviors were constructed. Polydopamine (PDA) was firstly used to modify MXene nanosheets to fabricate an efficient photothermal conversion material. Then they were added into PNIPAM matrix to prepare PDA@MXene/PNIPAM hydrogels. The prepared PDA@MXene/PNIPAM hydrogels exhibited three-dimensional network structure with the tensile strength of 26.84 kPa, and they were successfully assembled into segmented hydrogel actuators. The assembled segmented hydrogel actuator exhibited high bending angle of 470° in 1.75 s in 55 °C hot water and bending angle of 203° in 15 s when irradiated by 6 W/cm2 NIR light. The segmented hydrogel actuators displayed good programmable actuation performance. Finally, they were applied as smart devices, such as hydrogel hook for grasping object, switch for controlling circuit and valve for governing fluid flow. This work provides a novel strategy for fabricating programmable hydrogel actuators and will inspire new ideas and constructions for smart soft hydrogel actuators.

Numerical Simulation on the Influence of Inlet Flow Characteristics on the Performance of a Centrifugal Compressor

Although inlet bent pipes are usually adopted due to limited installation space, the influences of different bend pipes on the inlet flow characteristics and performance of centrifugal compressors are still unclear. The numerical simulation of a centrifugal compressor is established and validated by experimental results with the case of a straight inlet pipe. Then, the internal flow characteristics of the centrifugal compressor with a 90-degree bent pipe (p90) and Z-shaped bent pipe (pz) are simulated and discussed. The results show that the adoption of two inlet bent pipes reduces the performance of the centrifugal compressor to a certain extent, which reduces more greatly with pz, with a maximum reduction of 6.82% in pressure ratio and 14.83% in efficiency, respectively. The pressure ratio and efficiency reduction of the centrifugal compressor both increase with the increment of distortion degree, which maintains the increasing trend as the flow rate increases, and the maximum distortion degree of p90 and pz reaches 0.0351 and 0.0479, respectively. The reduction degree of the pressure ratio shows a power–law relationship with the distortion degree, while the reduction degree of efficiency shows an exponential relationship with it. The flow characteristics at the outlet section of the inlet pipe affect the flow field distribution at the inlet of the impeller, and the distortion area ranges of the total pressure and axial velocity at the inlet of the impeller are near 72°–144° in the circumferential direction for p90, while those of pz are close to 108°–180° and 288°–360°. When the flow with a high distortion degree enters the impeller, a large area with high turbulent kinetic energy is formed in the downstream flow channel, resulting in an increase in the flow loss.

Analyzing the Possible Causes of Inadmissible Axial Bending of Reaction Tubes of a Pyrolysis Plant that are Made of Alloy of Base Composition 45Cr25Ni35SiNb

Analyzing the Possible Causes of Inadmissible Axial Bending of Reaction Tubes of a Pyrolysis Plant that are Made of Alloy of Base Composition 45Cr25Ni35SiNb

Improved Thrust Restraint Design Considering Displacement of Pipe Bend and Joint Separation

Improved Thrust Restraint Design Considering Displacement of Pipe Bend and Joint Separation

Case study: Analysis and research on pipeline vibration of liquid oxygen kerosene of rocket engine and vibration reduction measures Measures

Abnormal vibration often occurs in the liquid oxygen kerosene transmission pipe- line of rocket engines, seriously threatening the safety of rocket engines. Improper handling will result in rocket launch failure and enormous economic losses. Therefore, the vibration of the transmission pipeline must be studied. In this paper, a three-dimensional high-pressure transmission pipeline model comprising a corrugated pipe, a multi-section bending pipe, and other auxiliary structures is established. Using the two-way fluid–solid coupling method, vibration analysis is performed on the pipeline under external pressure pulse excitation. The accuracy of the computation results is verified by a thermal test. Two vibration reduction strategies are presented and validated by simulation in accordance with the findings of the vibration study. The main conclusions are as follows: (1) At the same frequency, the amplitude distribution of vibration acceleration significantly correlates with the flow field pressure, indicating that fluid pressure fluctuation is the root cause of the abnormal vibration of the pipeline, and the vibration of the pipeline increases with the average pressure. (2) The time-average value and fluctuation amplitude of the larger stress and strain are mainly concentrated in the two supports, namely, the inside of the elbow and the bellows, which is different from the distribution of vibration acceleration. Such places are prone to structural failure and should be given attention. (3) The guide plate and the support enhancement method can reduce the vibration, but the support enhancement method has a better effect, reducing the vibration velocity and acceleration by 86.4% and 93%, respectively.

Computational Analysis of Erosion Wear Rate by Multiphase Flow in Optimum Bend Ratio of Pipeline

Abstract: Pipe bends are an integral part of transportation system as they help by providing flexibility in the path. In this paper, flow of mono-dispersed particles with carrier flow is simulated using Computational Fluid Dynamics by implementing Eulerian two-phase model in FLUENT. This paper is a forward stepping stone as it depicts the effect of pipeline bend on flow characteristic such as erosion rate, concentration profile, wall shear stress, etc. after numerous researches on pressure drop and velocity profiles. In this paper, a two-phase fluid of silica sand, having mean diameter of 450 µm (density = 2650 kg/m3 ), and water are mixed at the ratio of 8.82% solid concentration by weight and flown through a pipeline with diameter 53.0 mm and the optimum pipe bend ratio of 5.60 for minimum pressure loss.

Reinforced quantum-behaved particle swarm-optimized neural network for cross-sectional distortion prediction of novel variable-diameter-die-formed metal bent tubes

Abstract With light weight, high strength, and high performance, metal bent tubes have attracted increasing applications in aeronautics. However, the growing demand for customized tubular parts has led to a significant increase in the cost of conventional tube-bending processes, as they can only process tubes of a specific diameter. To this end, this paper proposes a variable diameter die (VDD) scheme which can bend tubes with a specific range of diameters. To investigate the formability of VDD-processed tubes for practical VDD applications, an accurate and reliable prediction method of cross-sectional distortion is imperative. Hence, we pioneer a novel intelligent model based on quantum-behaved particle swarm optimization (QPSO)-optimized back-propagation neural network (BPNN) to predict a rational cross-sectional distortion characterization index: average distortion rate. The adaptive adjustment of coefficients and the Gaussian distributed random vector are introduced to QPSO, which balance the search and enhance the diversity of the population, respectively. For further improvement in optimization performance, the informed initialization strategy is applied to QPSO. The efficiency of the proposed reinforced QPSO (RQPSO)-optimized BPNN model is evaluated by comparing the results with those of the BPNN, BPNN with Xavier initialization, several different particle swarm optimization variants-optimized BPNN models, and variants of popular machine learning models. The results indicated the superiority of RQPSO over other methods in terms of the coefficient of determination (${R}^2$), variance account for, root mean square error (MSE), mean absolute error, and standard deviation of MSE. Thus, the proposed novel algorithm could be employed as a reliable and accurate technique to predict the cross-sectional distortion of VDD-processed tubes.

Developing a Support Vector Regression (SVR) Model for Prediction of Main and Lateral Bending Angles in Laser Tube Bending Process.

The laser tube bending process (LTBP) is a new and powerful manufacturing method for bending tubes more accurately and economically by eliminating the bending die. The irradiated laser beam creates a local plastic deformation area, and the bending of the tube occurs depending on the magnitude of the heat absorbed by the tube and its material characteristics. The main bending angle and lateral bending angle are the output variables of the LTBP. In this study, the output variables are predicted by support vector regression (SVR) modeling, which is an effective methodology in machine learning. The SVR input data is provided by performing 92 experimental tests determined by the design of the experimental techniques. The measurement results are divided into two sub-datasets: 70% for the training dataset, and 30% for the testing dataset. The inputs of the SVR model are process parameters, which can be listed as the laser power, laser beam diameter, scanning speed, irradiation length, irradiation scheme, and the number of irradiations. Two SVR models are developed for the prediction of the output variables separately. The SVR predictor achieved a mean absolute error of 0.021/0.003, a mean absolute percentage error of 1.485/1.849, a root mean square error of 0.039/0.005, and a determination factor of 93.5/90.8% for the main/lateral bending angle. Accordingly, the SVR models prove the possibility of applying SVR to the prediction of the main bending angle and lateral bending angle in LTBP with quite an acceptable accuracy.

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.

Design and optimization study of discrete inclined ribs enhanced bend tube based on “Diamond” active cooling thermal protection systems of hypersonic aircraft

When the hypersonic aircraft cruises, the surface will generate huge aerodynamic heating. Aiming at the thermal protection of hypersonic aircraft, this paper presented a study on the thermal–hydraulic and thermodynamic performance of discrete inclined ribs enhanced bend tube based on the designed “Diamond” channel. Meanwhile, a comprehensive numerical investigation was carried out for different models. The fluid velocity was found to vary in the range of 0.1–3.5 m·s−1, with the corresponding Reynolds number ranging from 3600 to 127000. The inlet temperature of heat transfer fluid was set to 253 K. It was visible that double–symmetrical longitudinal swirl was generated under a single upper and lower arrangement (Model D), which led to the best cooling performance on the inner wall. The performance evaluation criteria (PEC) and efficiency evaluation criterion (EEC) reached 0.99–1.18 and 0.66–1.00, respectively. The effect of four geometrical parameters (height–width ratio(H/d), length–width ratio (L/d), group number of ribs (n), and tilt angle (α)) of which the ranges are 0.5–2.5, 1.0–4.0,6–15 and 0°–90°, separately, was explored. The results showed that the inner wall temperature decreased up to 4.4 K when the Reynolds number was 72000. The Nusselt number and friction factor increased about 9.9 %–28.8 % and 16.5 %–111.5 %. Efficiency evaluation criterion reached 0.43–0.96. It was found that the combination of parameters would significantly affect the distribution of longitudinal swirls under the influence of secondary circulation in the bend tube. Moreover, many pairs of small vortices near the wall could improve active thermal protection performance. After obtaining the fitting function through the artificial neural network (ANN), the genetic algorithm (GA) was applied to obtain the Pareto front. The design variable for the L/d = 3.19, n = 11, and α = 14.3° was selected as the optimal solution by the TOPSIS method. When Reynolds number is 72000, the corresponding Tin and ΔP were 261.86 K and 2471.2 Pa. The performance evaluation criteria and efficiency evaluation criterion reached 1.02 and 1.09, respectively. Furthermore, a design variable for the L/d = 3.0, n = 11, and α = 15° was given for ease of engineering. The present work verified the feasibility of realizing heat transfer enhancement by combining the secondary circulation with longitudinal swirls formed by bend tube and discrete inclined ribs and proposed a new design scheme of active cooling thermal protection systems (ACTPS).

Coolant leak rate through fatigue cracked pipe bend: An experimental and design standard based investigation

Leak-Before-Break (LBB) requirement plays a vital role in demonstrating the structural integrity of sodium-cooled Fast Breeder Reactor (FBR) piping system. Crack size at penetration (2CS), crack size that corresponds to detectable coolant leak rate (2CL), and unstable crack size (2CG) are the primary crack parameters associated with the LBB design of FBR piping system. The detectable leak rate through a piping system is directly related to the differential pressure (ΔP) and crack size. The design pressure of FBR piping systems is relatively low, resulting in a high value of CL. Considering the need for an optimum LBB design of the FBR piping system, an experimental approach is adopted to arrive at a realistic estimate of CL. Based on the experiments, a power-law type correlation can be derived to predict the value of CL as a function of ΔP. The evidence from this study points towards the conservatism present in the current FBR LBB design philosophy as per RCC-MRx A16. These observations have several implications for achieving an optimum LBB design criterion for an FBR piping system.

Bending Deformation and Ultimate Moment Calculation of Screen Pipes in Offshore Sand Control Completion

Horizontal wells, extended-reach wells, and multi-branch wells were often used to exploit subsea oil and gas efficiently. However, during the sand control screen completion of those wells, the sand control screen pipe was easily deformed. Failure occurred when passing through the bending section due to the large bending section in the wellbore trajectory. A parametric analysis model of the screen pipe was established based on ABAQUS and Python software under pure bending load first. Then, deformation patterns and mechanisms were identified and discussed. The effects of parameters on the screen pipe bending deformation patterns and the ultimate moment were analyzed. Finally, an empirical formula for calculating the ultimate moment of the screen pipe was established. The results showed that the deformation of the screen pipe was complex, and three deformation patterns were related to the hole parameters. Due to an increase in the diameter and number of circumferential and axial holes, the ultimate moment of the screen pipe gradually decreased, and the circumferential holes had a more significant effect on the ultimate moment than the axial holes. The established empirical formula could accurately calculate the ultimate moment of the screen pipe, and the average difference between the formula and numerical simulation results was 3.25%.

Uniaxial Eccentric Load Behavior of L-CFSST Composite Column

This study presents the mechanical behavior of L-shaped concrete-filled square steel tube (L-CFSST) composite columns under uniaxial eccentric compression. Nine specimens were tested and the effects of eccentricity, steel tube thickness, steel yield strength, and slenderness ratio were investigated regarding failure modes, ultimate load, load-lateral displacement curves, and load-strain curves. Test results showed that, under uniaxial eccentric load, these columns showed favorable mechanical properties and steel tubes showed strong cooperative working performance. There were two types of failure modes for these columns: local buckling of the steel tube or overall bending of the specimen. ABAQUS was used to simulate the loading process and the accuracy of the numerical simulation results was verified by comparing failure characteristics, load-displacement curves, and ultimate bearing capacity with the test results. The N/Nu-M/Mu curves of the columns under uniaxial eccentric load with different parameters were simulated by the finite element method. A simplified formula for predicting the N/Nu-M/Mu relationship was established based on the finite element analysis results, which might be a workable approach for designing L-CFSST composite columns in engineering practice.

Void Fraction of Air-Water Two-Phase Flows in a Vertically Placed Horizontal U-Bend

Experiments on air-water two-phase flows in a horizontal U-bend placed in the vertical plane were carried out to investigate effects of pipe bending on the void fraction. The inner diameter and the bend radius of curvature were 8 and 24.3 mm, respectively, so that the dimensionless bend diameter was 6. The flow patterns dealt with were plug, slug and annular flows. The void fractions in the bend and the straight section were measured by using quick-closing valves and the void fraction distribution was evaluated with an image processing method. The applicability of available correlations for the void fraction in the straight pipe was also discussed. For the straight pipe, the void fractions of the plug and slug flows can be accurately evaluated using the Smith correlation, whereas in the annular flow regime the Cioncolini and Thome correlation and the Mauro et al. liquid film thickness model give better agreement with the data. The bend void fractions in the downward and upward flows agree well with those for the pipe diameter of 26 mm given in literature, implying that the diameter effect on the void fraction is weak. The Usui et al. void fraction correlation gives reasonable evaluation for downward flows.