Bending Curvature Radius Research Articles

Three-dimensional finite element analysis of turbulent crude oil flow and solid particle deposition patterns in circular curved pipelines

This study presents a numerical investigation of turbulent crude oil flows in circular curved pipelines, with a focus on the deposition patterns of solid particles within the fluid. Simulations were conducted using the Reynolds–Averaged Navier–Stokes equations coupled with the k–ε turbulence model to examine the influence of structural characteristics, such as bend curvature angle and bend curvature radius, on flow dynamics and particle deposition. The results reveal that the complex flow patterns generated by these geometric features significantly affect pressure gradients and particle trajectories. Specifically, the study shows that turbulent flows within bends exhibit intricate behaviors, with deposition patterns being strongly influenced by the pipeline’s geometric parameters. Sand particles, commonly present in petroleum flows, are found to be more effectively transported in pipes with larger curvature angles, while they exhibit a higher propensity to settle at smaller curvature angles and larger bend curvature radii. Furthermore, the simulations indicate that the majority of deposited particles accumulate on the inner wall immediately downstream of the elbow entrance.

Analysis via 3D FEM of the Passing Capacity of Pipeline Inspection Gauges in Bends with Different Curvatures

Pipeline inspection gauges easily become wedged in offshore and onshore small-diameter pipelines (where the outer diameter, D, of the pipe is less than 150 mm), particularly at the bends. To reveal the relationship between PIG capacity and bend curvature radius, a quantitative study on the passing capacity of PIG was conducted in this paper from three key perspectives of performance: safe application, sealing, and driving. The results demonstrate that the pipeline inspection gauge exhibits better passing capacity as the curvature radius of the bend increases. To improve the poorest passing capacity, in the case of R = 3D, different numbers of grooves are opened in the cup. The results demonstrate that the cup with 24 square grooves has a substantial impact on optimizing the passing capacity of the pipeline inspection gauge. This enhancement results in improvements in safe application performance (40.8%), sealing performance (12.22%), and driving performance (17%). This research aims to expand our understanding of blockages in small-diameter pipelines and provide a basis for optimizing the structure of the pipeline inspection gauge for small-diameter pipelines.

Performance assessment of buried steel pipelines reinforced with carbon fibre-reinforced polymer under reverse fault movement

Buried oil and gas pipelines are often affected by the active zones across faults, and the failure of pipeline functions owing to relative fault movements has attracted widespread attention. Carbon fibre-reinforced polymer (CFRP) was proposed as a reinforcement measure for buried continuous pipelines crossing faults to mitigate the structural damage to pipelines subjected to large permanent ground deformations. In this study, the lamina model and Hashin failure criterion were used to simulate the CFRP material in a three-dimensional nonlinear finite element model of the pipeline-soil interaction. The peak strain and cross-sectional ovalization of the pipeline were used to quantify the nonlinear response of the steel pipeline subjected to reverse fault movement. Parametric studies in terms of the CFRP wrapping angle, thickness, length, as well as internal pressure were conducted to comprehensively assess overall performance of CFRP-wrapped steel pipelines. Results indicated that the CFRP wrapping in direction of 0°/90° with respect to the axial direction of the pipeline exhibit the optimum effects in improving the performance of pipelines. For steel pipelines subjected to reverse fault, increase of the CFRP wrapping thickness effectively reduces the development of compressive strain on the pipeline wall, thereby delay the local buckling failure of the pipeline. Besides, CFRP is effective in increasing the bending curvature radius and preventing the local buckling of the pipeline, but insufficient wrapping length of CFRP can lead to local buckling of steel pipelines under same fault displacement. For pipelines with internal pressures internal pressure can enhance the overall performance of CFRP wrapped pipelines against reverse fault movement.

The Exact Solution of the Bending Moment in the Folding Process of Negative Poisson’s Ratio Honeycomb Tape Spring and Multi-Objective Optimization Design

The tape spring is a crucial component used in the deployment mechanism of spacecraft, and the lightweight design of the deployment mechanism is currently one of the critical issues that need to be addressed. This paper explores the substitution effect of two different negative Poisson’s ratio honeycomb-corrugated spring structures for use in space-deployable structures. Theoretical and finite element methods demonstrated that the negative Poisson’s ratio honeycomb structure could be equivalent to an orthotropic structure. The cylindrical shell bending theory was adopted, taking into account the nonlinearity of the geometric equation, the influence of cross-sectional deformation and cross-sectional position on the internal force expression, and the influence of the geometric equation to derive expressions for the bending moment and curvature radius during the folding and bending process. Numerical methods were used for comparative analysis. The NSGA-II algorithm optimized the geometric parameters of the negative Poisson’s ratio honeycomb, resulting in the optimal solution under given constraints. The results showed that the Auxetic re-entrant honeycomb structure performed better in bending moment capacity than the Star-shaped honeycomb, and the bending moment capacity of the Auxetic re-entrant honeycomb structure per unit mass was superior to that of the traditional tape spring.

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.

General Theory of Nano Trilayer Film Bending

Multilayer sheets or films have many potential applications in micro-nanoelectromechanical systems. When surface and scale effects are not considered, the bending of multilayer film systems can theoretically be discussed by the classical Stoney formula or Timoshenko formula. When the system has anisotropic surface stress or mismatch strain, the four-parameter bending model proposed by Narsu et al. can be used. However, if the thickness of the film is several nanometers and the bending radius of curvature is less than 1micron, the existing theoretical model is no longer applicable. For this reason, a bending formulation for the nanomulti-layer film system is derived and the structure of the multilayer film is optimized in this paper.

Electrical Reliability of Flexible Low-Temperature Polycrystalline Oxide Thin-Film Transistors Under Mechanical Stress

Electronic devices based on flexible displays have been developed for use in various applications. Upon bending such devices, the applied mechanical force deteriorates the reliability of the devices. Therefore, a high bending reliability that is influenced by tensile and compressive forces that vary depending on the bending radius of curvature must be secured to ensure a reliable device operation. In this study, we investigated the electrical characteristics of flexible low-temperature polycrystalline silicon (LTPS) and amorphous indium–gallium–zinc–oxide (a-IGZO) thin-film transistors (TFTs) on polyimide (PI) substrate and subsequently conducted reliability evaluation of the devices under mechanical stress by applying negative bias temperature illumination stress (NBTIS). The degradations in the electrical properties, such as threshold voltage ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V}_{\text {th}}$ </tex-math></inline-formula> ) shift, OFF-state current ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${I}_{\text {off}}$ </tex-math></inline-formula> ), and subthreshold slope (SS), and reliability, increased, and the reliability worsened, as the tensile force increased under decreasing radius of curvature, whereas relatively low degradation occurred under compressive force. A tensile stress-induced increase in grain boundary state density in polycrystalline silicon (poly-Si) and oxygen vacancy in a-IGZO were verified by density of state (DOS) extraction; the cracks occurring due to tensile stress were optically analyzed; the external moisture penetration along the cracks further degrades the device characteristics. This study provides an analysis of device design for ensuring reliability under the application of mechanical stress, thereby contributing to the development of reliable flexible technology.

Multiaxis printing method for bent tubular structured gels in support bath for achieving high dimension and shape accuracy

Gels are soft materials that have high potential for use as alternative artificial blood vessels. 3D gel printing has attracted attention because it can be used to create gels with arbitrary and complicated shapes. The conventional 3D gel printing process (triaxial printing) is as follows: ⅰ) a sol material is patterned to form a layer on the XY plane, ⅱ) a crosslinker is added to it, ⅲ) the Z stage is lowered by the stacking pitch, and ⅳ) a new sol material is patterned on the previous layer. However, irregular protrusions and stepped structures appear at the overhang parts as the height and scale increase. In addition, there are non-adhesion sections between adjacent layers. To solve these problems, we propose a “multiaxis printing method,” in which layers are seamlessly stacked by changing the extruding direction by following the neutral line of a structure. We evaluate the dimension and shape accuracy of the proposed method by printing bent hollow tubular structured gels. The proposed method significantly suppresses irregular protrusions on outer walls. Moreover, each layer is seamlessly joined. The structures printed using the proposed method show good dimension and shape accuracy. The minimum lumen area ratio is 75%, which is comparable to native common carotid arteries. In addition, the maximum errors in the bending angle and curvature radius are 1.7% and 5.1%, respectively. However, the average outer and inner diameters are smaller than the patterning diameter, suggesting that the crosslinked gels attract each other in the circumferential direction. This indicates that a model should be designed considering gel shrinkage to further improve the accuracy of printing.

Structure optimization of a three-dimensional coil oscillating heat pipe

The effects of the bend curvature radius and tube diameter on the heat transfer performance of the three-dimensional coil oscillating heat pipe (3DCOHP) were experimentally studied in asymmetric heating mode. Three types of copper 3DCOHPs using water as the working fluid were studied in vertical orientation. And the filling ratio of each 3DCOHP was set to 50%. It was found that reducing the top bend curvature radius and increasing the tube diameter can both strengthen the formation of unidirectional flow and significantly improve the heat transfer performance of the 3DCOHP. The heat transfer performance of the OHP with a tube diameter of 1.90 mm increased by up to 34.6% when the heating power was set to 40 W. At the same time, the reason of the unidirectional flow in asymmetric heating mode was theoretically analyzed. It was shown that the calculated pressure drops in liquid slug flowing from the evaporation section to both sides powered by vapor expansion are different, which develops the unidirectional flow. These findings provide a guideline to optimize the structure of OHP to enhance its heat transfer capacity.

Flow Characteristics of Air-Water Two-Phase Flows in a Serpentine Tube

Experiments on air-water two-phase flows in a serpentine tube consisting of vertical U-bends and circular straight pipes were carried out to discuss the flow characteristics based on the high-speed video images of the flows at various gas and liquid superficial velocities. The pipe diameter, D, and the bend radius of curvature, R, were 20 mm, i.e. the bend ratio, R/D, was unity, and the length of the straight pipe was 1500 mm. The void fraction in each section was measured by using a quick-closing valve method. As a result, the following conclusions were obtained: (1) the top and bottom U-bends cause coalescence of large bubbles and liquid slug formation, respectively, which results in enhancement of flow pattern transition between the slug and annular flows, (2) the void fraction in the downward flow is larger than that in the upward flow due to acceleration of the liquid phase and the buoyancy acting on bubbles in the downward flow, and (3) void correlations based on the drift-flux model for fully-developed flows are applicable to the void fractions in the straight pipe sections under the present experimental conditions.

Modeling of Mach-Zehnder modulator using ferroelectric materials at 1.55 µm optical transmission

• Mach-Zehnder modulator (MZM) based ferroelectric materials has studied theoretically and simulated by using finite element method. • Different parameters of MZM have experimented which are coupling length, bending radius and applied voltage. • The results showed that the lowest coupling length of MZM was 304 µm by using KNO 3 crystal. MZM is operate as a modulator at bend radius of curvature with 2.5 mm for all three ferroelectric crystals and MZM didn’t worked with lower than this radius. • The effect of utilized voltage showed that MZM is operate actively at 0.38 V by using SriTO 3 . Mach-Zehnder modulator (MZM) based ferroelectric materials has studied theoretically and simulated by using finite element method with COMSOL Multiphysics software. Different parameters of MZM have experimented which are coupling length, bending radius and applied voltage. The results showed that the lowest coupling length of MZM was 304 µm by using KNO 3 crystal. MZM is operate as a modulator at bend radius of curvature with 2.5 mm for all three ferroelectric crystals and MZM didn’t worked with lower than this radius. The effect of utilized voltage showed that MZM is operate actively at 0.38 V by using SriTO 3 . While for LiNbO 3 and KNO 3 the effective voltage was 0.45 V and 0.5 V, respectively. The power loss for all MZM samples was 2%.

Analysis of two-phase air-water annular flow in U-bends

This paper presents an experimental and numerical study of gas-liquid annular flow in horizontal 180 U-bends. The paper aims to study the effect of bend curvature radius and superficial gas velocity in the liquid film's behavior and annular flow characteristics. The study is divided into three sections. The first section corresponds to the experimental methodology and results. The second section compresses the validation of the computational fluid dynamic (CFD) model with the experimental results. Finally, the last section presents the CFD estimation of additional variables that cannot be acquired with the existing experimental setup. The experimental results provide an initial understanding of the multiphase mixture obtained using optical techniques (i.e., High-Speed Filming (HSF) analysis). The comparison between the experiments and the numerical simulations is presented, and a reasonable agreement is observed between both approaches. Finally, additional results such as film distribution and rotation before and after the bend are extracted from the CFD simulations.

Evolution process of different abnormal river bends in the braided reach of the Lower Yellow River

1980s中期以来，黄河下游游荡段经常出现畸形河湾，分析其演变过程及特点对游荡段治理具有重要意义.本研究采用黄河下游游荡段的遥感影像和实测断面地形资料，描述了不同畸形河湾的演变过程并分析其河湾形态参数和断面形态的变化.研究表明，黄河下游游荡段的畸形河湾具有演变周期短、扭曲程度较大和易发生自然裁弯等特点.游荡段不同位置畸形河湾的演变特点不同：游荡段上段的畸形河湾演变缓慢，裁弯历时长；中段的畸形河湾演变速率较高，河湾扭曲程度大；下段的畸形河湾演变速率高，容易发生自然裁弯.河湾形态参数可反映畸形河湾的演变过程，其变化特点与畸形河湾的形成和裁弯过程相对应.在畸形河湾形成过程中，曲率半径和河湾间距减小，弯曲度、水流夹角和河湾振幅增大.游荡段3个畸形河湾弯曲度的最大值分别为1.20、2.10和1.61，反映了不同畸形河湾的扭曲程度.“Ω”形畸形河湾裁弯后的曲率半径、水流夹角、河湾振幅和河湾间距约为其演变过程中最值的605%、59%、27%和133%.“M”形畸形河湾裁弯后水流夹角、河湾振幅和河湾间距约为其最值的37%、83%和152%.在畸形河湾形成时期，伊洛河口断面位于畸形河湾凹岸侧的滩地以94 m/a的速率崩塌.裁弯后，河槽冲刷，两岸滩地崩退，河槽展宽速率为148 m/a.河床底部的冲刷从深泓点逐渐向两边发展.;Since the mid-1980s, the braided channel reach of the Lower Yellow River has formed some abnormal river bends. Analysis of the evolution processes and characteristics of abnormal river bends are of great significance for the regulation of the braided reach. Based on the remote sensing imagery and the cross-sectional topography, this study describes the evolution processes of abnormal river bends and variation of morphological characteristic parameters. The result shows that the abnormal river bends in braided channel reach of the Lower Yellow River have the characteristics of short evolution duration, high distortion level and prone to natural cutoff and the bends in different location have different evolution characteristics. The first bend in the upper braided reach evolves slowly and the cut-off period is long. The second bend in the middle braided reach evolves rapidly and highly distorted. The third bend in the lower braided reach evolves rapidly and is prone to generate natural cutoff. Variation of river bend morphology reflects the evolution process of three abnormal river bends, which are corresponding to the bend formation and cutoff processes. The formation of the abnormal river bend is a process in which the curvature radius and river bend spacing decreases, and the bend curvature radius, angle of water flow and bend amplitude increase. The maximum curvature radius of the three bends in the braided reach are 1.20, 2.10 and 1.61, respectively, reflecting the distortion degree of different bends. After cut-off, the curvature radius, angle of water flow, bend amplitude and river bend spacing are about 605%, 59%, 27%, and 133% of the extreme value during the evolution of the “Ω” shape river bend. For “M” shape river bend, angle of water flow, bend amplitude and river bend spacing after cutting are about 37%, 83%, and 152% of their extreme values. The cross-sectional profile at the Yiluo River outlet reflected that the beach on the concave bank of the river bend continuously collapsed at a rate of about 94 m/a during the formation period of abnormal river banks. The cut-off has a great influence on the cross-sectional profile. After cut-off, the beaches on both bank collapsed, and the river channel widen at a rate of 148 m/a. The erosion at the riverbed developed from the deep point to its two sides.

Design of fascines for riverbank protection in alpine rivers: Insight from flume experiments

We present the results of flume experiments specifically designed to investigate the conditions required for successful bank protection using fascines, considered in the early and critical stage of their installation (no developed root system), in the alpine context. A total of 145 runs were performed with erodible banks, considering different combinations of protection design (no protection, rip-raps, twigs), bed mobility (with or without bedload), discharge (from low to exceptional floods), and bend curvature radius. None of the runs showed any direct fascine grabbing by the flow observed; all destruction was the consequence of bank scouring, erosion and collapse around the structure. In all cases, most destructive effects resulted from water recirculation inside the bank. Thus, we conclude that all measures aiming to reduce water circulations during the first stage of the fascine construction and development are recommended. This include large bend curvature radii (when possible), fining of the filling material, use of antiscouring twigs, optimisation of the programming of the works with consideration of the hydrology (shape of hydrographs) and regular survey of the structure. Our experiments show that anti-scouring twigs have a real protective effect by modifying the local hydraulics and promoting sediment deposition at the bank toe.

Ultraflexible Glassy Semiconductor Fibers for Thermal Sensing and Positioning.

Flexible, large-area, and low-cost thermal sensing networks with high spatial and temporal resolution are of profound importance in addressing the increasing needs for industrial processing, medical diagnosis, and military defense. Here, a thermoelectric (TE) fiber is fabricated by thermally codrawing a macroscopic preform containing a semiconducting glass core and a polymer cladding to deliver thermal sensor functionalities at fiber-optic length scales, flexibility, and uniformity. The resulting TE fiber sensor operates in a wide temperature range with high thermal detection sensitivity and accuracy, while offering ultraflexibility with the bending curvature radius below 2.5 mm. Additionally, a single TE fiber can either sense the spot temperature variation or locate the heat/cold spot on the fiber. As a proof of concept, a two-dimensional 3 × 3 fiber array is woven into a textile to simultaneously detect the temperature distribution and the position of heat/cold source with the spatial resolution of millimeter. Achieving this may lead to the realization of large-area, flexible, and wearable temperature sensing fabrics for wearable electronics and advanced artificial intelligence applications.

Hybrid Architectures of Heterogeneous Carbon Nanotube Composite Microstructures Enable Multiaxial Strain Perception with High Sensitivity and Ultrabroad Sensing Range.

Low-dimensional nanomaterials are widely adopted as active sensing elements for electronic skins. When the nanomaterials are integrated with microscale architectures, the performance of the electronic skin is significantly altered. Here, it is shown that a high-performance flexible and stretchable electronic skin can be produced by incorporating a piezoresistive carbon nanotube composite into a hierarchical topography of micropillar-wrinkle hybrid architectures that mimic wrinkles and folds in human skin. Owing to the unique hierarchical topography of the hybrid architectures, the hybrid electronic skin exhibits versatile and superior sensing performance, which includes multiaxial force detection (normal, bending, and tensile stresses), remarkable sensitivity (20.9 kPa-1 , 17.7 mm-1 , and gauge factor of 707 each for normal, bending, and tensile stresses), ultrabroad sensing range (normal stress = 0-270 kPa, bending radius of curvature = 1-6.5 mm, and tensile strain = 0-50%), sensing tunability, fast response time (24 ms), and high durability (>10 000 cycles). Measurements of spatial distributions of diverse mechanical stimuli are also demonstrated with the multipixel electronic skin. The stress-strain behavior of the hybrid structure is investigated by finite element analysis to elucidate the underlying principle of the superior sensing performance of the electronic skin.

Forming characteristics analysis and springback prediction of bi-directional trapezoidal sandwich panels in the multi-point bend-forming

Bend-forming is an efficient and economical method to manufacture curved sandwich panels, and the major concerns for fabricating precise products are forming characteristics and springback prediction. In this paper, numerical simulation, analytical approach, and forming experiments were conducted to assess the multi-point cylindrical bend-forming process of bi-directional trapezoidal sandwich panel. Analysis was performed on the deformation characteristics, regularity, and forming defects of sandwich panel in the early stage. And afterwards, equivalent elastic constants of the core layer were deduced by the semi-analytic approach combined with finite element method (FEM). On this basis, a theoretical model was established to calculate bending moments and predict springback within formable range. The results indicate that the stress of face sheet in the welded area was obviously lower than that in the suspended area. The core cell was primarily deformed by changing the angle between the inclined plane and the platform, and the deformation of the cell layer mainly occurred in the transition surface area. The dimple and straight plane effect are the most common forming defects during the bending process. The main factors that affect the forming defects are face sheet thickness and bending radius. The springback amount of the sandwich panel approximates the equivalent thickness plate. Thus, it is easy to control the forming precision for small springback, and the springback ratio increases with the increase of bending curvature radius. The springback in theoretical model and experiment has an error of less than 1.0 mm, verifying the accuracy of the theoretical prediction model.

11.4: The Fabrication of Flexible Electrofluidic Display Arrays Based on PEN Substrate

Flexible electrofluidic display (FLEFD), as one of the most promising reflective display technology, has drawn an increasing attention in recent years. In this study, we report the fabrication process for the FLEFD based on the flexible PEN film with ITO layer on the surface. The hyflon material was selected as the hydrophobic insulator layer to control the fabrication temperature below 170°C, and the photoresist was used to manufacture the pixel grids. After oil filing and packaging process, the electrical properties and optical properties of FLEFD were both taken into consideration. The results showed that FLEFD presented good display characteristics. The driving voltage of flexible device was 14V when the bending radius of curvature was 10cm. Furthermore, response time for the device was 18ms, and the aperture opening ratio was 42.5%.

A simple analytical thermo-mechanical model for liquid crystal elastomer bilayer structures

The bilayer structure consisting of thermal-responsive liquid crystal elastomers (LCEs) and other polymer materials with stretchable heaters has attracted much attention in applications of soft actuators and soft robots due to its ability to generate large deformations when subjected to heat stimuli. A simple analytical thermo-mechanical model, accounting for the non-uniform feature of the temperature/strain distribution along the thickness direction, is established for this type of bilayer structure. The analytical predictions of the temperature and bending curvature radius agree well with finite element analysis and experiments. The influences of the LCE thickness and the heat generation power on the bending deformation of the bilayer structure are fully investigated. It is shown that a thinner LCE layer and a higher heat generation power could yield more bending deformation. These results may help the design of soft actuators and soft robots involving thermal responsive LCEs.

Experimental study of a wearable aperture-coupled patch antenna for wireless body area network

A new type of the wearable aperture-coupled patch antenna for 2.4 GHz wireless body area network (WBAN) application is proposed. The H-shaped slot in middle ground plane and rectangular ring microstrip feed line are optimized, so that it realizes the efficient electromagnetic coupling with the radiating element. The substrate layers are 2 mm thickness felt layers with relative permittivity of 1.2, and the other layers are copper foil tape (CFT) to ensure the performance of the antenna. Furthermore, the return loss, radiation pattern and gain are investigated in detail for the antenna under different bending curvature radius. Experimental results show a good agreement with simulation results. (C) 2017 Wiley Periodicals, Inc.