Channel Bend Research Articles

Optimization design of water-cooled mirror for low thermal deformation

A novel structure of mirror layer for water-cooled mirror is proposed in this paper. Numerical simulations are carried out to compare the performance between the novel and conventional structure by examining four types of flow passage configuration and inlet/outlet arrangement. The analyses are based on computations of fluid-solid conjugated heat transfer. Advantages and limitations of each design are evaluated by analyzing the temperature rise, temperature uniformity, thermal deformation and deformation uniformity of the mirror surface. It is concluded that the novel structure of mirror layer shows steady improvement in both magnitude and uniformity of the thermal deformation. An effective design for water-cooled mirror must provide effective heat dissipation and ensure enough stiffness for the mirror layer at the same time. The configuration locating bent channels in the center and keeping the inlet/outlet away from the center is beneficial to water-cooled mirror, as it enhances heat dissipation and ensures stiffness. The average Reynolds number around 1000 is figured out to be optimal hydraulic conditions for different designs of water-cooled mirrors.

Bending Method for Forming Curvature and Various Cross-Section Shapes

Previous studies on the bending process of extruded aluminum alloys have focused on a high-precision bending process that controls various undesirable phenomena. In contrast, this paper proposes a new bending method in which undesirable deformations are intentionally occurred and can be deformed into an arbitrary cross-sectional shape. By bending the extruded section, we sought to establish a novel bending process, in which a curvature and cross-sectional shape are produced in a single process. Undesirable deformations that occur by bending channel materials with a removed tensile flange include both the outward and inward deformations of the webs. Based on such deformations, this report proposes several types of cross-sectional shapes that can be formed through simulations and press bending experiments.

Numerical modeling of erosional and depositional bank processes in migrating river bends with self‐formed width: Morphodynamics of bar push and bank pull

AbstractMeandering rivers display active communication between bank erosion and bar deposition processes. How does this occur? How does the river select its width? To answer these questions, we implement a model for meander migration where both bank processes (erosion and deposition) are considered independently. Bank erosion is modeled as erosion of purely noncohesive bank material damped by natural slump block armoring; channel deposition is modeled via flow‐retarded vegetal encroachment. Both processes are tied to a slope‐dependent channel forming Shields number; banks with near‐bank Shields number below this value undergo deposition, and those above it undergo erosion. Channel‐forming Shields number must increase with slope, as dictated by available data and model performance. Straight channel modeling shows that a channel arrives at an equilibrium width from any initial condition. For the channel bend, the river always approaches an asymptotic state where width reduces slowly in time and where bank erosion and deposition occur at nearly equal rates. Before this state is reached, however, the river follows a phase‐plane trajectory with four possible regimes: (a) both banks erode, (b) both banks deposit, (c) both banks migrate outward, but with a faster depositing bank (bar push), and (d) both banks migrate outward, but with a faster eroding bank (bank pull). The trajectory of migration on the phase plane depends on initial conditions and input parameters controlling the rate of depositional and erosional migration. All input parameters have specific physical meaning, and the potential to be measured in the field.

Numerical Investigation of the Effect of Froude Number on Flow Pattern around a Single T-shaped Spur Dike in a Bend Channel

Numerical Investigation of the Effect of Froude Number on Flow Pattern around a Single T-shaped Spur Dike in a Bend Channel

Highly Sensitive Non‐Classical Strain Gauge Using Organic Heptazole Thin‐Film Transistor Circuit on a Flexible Substrate

A non‐classical organic strain gauge as a voltage signal sensor is reported, using an inverter‐type thin‐film transistor (TFT) circuit, which is able to sensitively measure a large quantity of elastic strain (up to ≈2.48%), which approaches an almost folding state. Novel heptazole‐based organic TFTs are chosen to be incorporated in this gauge circuit; organic solid heptazole has small domain size in general. While large crystal domain‐pentacene TFTs seldom show sufficient current variation upon mechanical bending for tensile strain, these heptazole TFTs demonstrate a significant variation for the same strain condition as applied to pentacene devices. In addition, the pentacene channel does not recover to its original electric state after bending but heptazole channels are very elastic and reversible, even after going through serious bending. More interesting is that the heptazole TFTs show only a little variation of signal current under horizontal direction strain, while they make a significant amount of current decrease under vertical direction strain. Utilizing the anisotropic response to the tensile bending strain, an ultrasensitive voltage output strain gauge composed of a horizontally and vertically oriented TFT couple is demonstrated.

MRT lattice Boltzmann method for 2D flows in curvilinear coordinates

Objective: The objective of the presented paper is establishing the multi-relaxation-time lattice Boltzmann method (MRT-LBM) for solving 2D flow equations transformed in a curvilinear coordinate system.Method: Using the complete transformation approach – which includes transformation of both dependent and independent variables between the physical and computational domain – corresponding forms of the equilibrium function and of the force term for the 2D Navier–Stokes equations and the shallow water equations have been derived. The physical flow domain of arbitrary geometry in the horizontal plane, is covered with adequate curvilinear mesh, while the calculation procedure is carried out in the D2Q9 square lattice, applying the basic form of the boundary condition method on water-solid and open boundaries as well.Test cases: The method is tested using four different examples: Couette flow in a straight inclined channel, Taylor–Couette flow between two cylinders, a non-prismatic channel in a 180° bend, and a segment of irrigation channel with a parabolic cross section in a 90° bend. In the cases of the bent channels, previously available velocity measurements have been used for validation of the model. In addition, the procedure employs a mathematical model based on traditional CFD procedures.Results: The remarkable agreement between the results obtained by the proposed model and the corresponding analytical values and measurements shows that the presented curvilinear form of the LBM is capable of solving very complex environmental problems, maintaining the order of accuracy, simplicity and efficiency of the basic LBM.

Flow simulation and topological rearrangements of ordered foams

Flow through a narrow bent channel may induce topological rearrangements in a two-dimensional monodispersed dry liquid foam. We use the Cellular Potts Model to simulate a foam under a variable driving force in order to investigate the strain-rate response from these rearrangements. We observe a set of foams' behaviors ranging from elastic, viscoelastic to fluid regime. Bubble's topological rearrangements are localized and their cumulative rearrangements change linearly with time, thus non avalanches critical behavior is found. The strain-rate affects the rate of topological rearrangements, its dependence on the drag force is nonlinear, obeying a Herschel-Bulkley like relationship below the foam's flow point.

Spatial variability in streambed hydraulic conductivity of contrasting stream morphologies: channel bend and straight channel

AbstractStreambed hydraulic conductivity is one of the main factors controlling variability in surface water‐groundwater interactions, but only few studies aim at quantifying its spatial and temporal variability in different stream morphologies. Streambed horizontal hydraulic conductivities (Kh) were therefore determined from in‐stream slug tests, vertical hydraulic conductivities (Kv) were calculated with in‐stream permeameter tests and hydraulic heads were measured to obtain vertical head gradients at eight transects, each comprising five test locations, in a groundwater‐dominated stream. Seasonal small‐scale measurements were taken in December 2011 and August 2012, both in a straight stream channel with homogeneous elevation and downstream of a channel meander with heterogeneous elevation. All streambed attributes showed large spatial variability. Kh values were the highest at the depositional inner bend of the stream, whereas high Kv values were observed at the erosional outer bend and near the middle of the channel. Calculated Kv values were related to the thickness of the organic streambed sediment layer and also showed higher temporal variability than Kh because of sedimentation and scouring processes affecting the upper layers of the streambed. Test locations at the channel bend showed a more heterogeneous distribution of streambed properties than test locations in the straight channel, whereas within the channel bend, higher spatial variability in streambed attributes was observed across the stream than along the stream channel. Copyright © 2014 John Wiley & Sons, Ltd.

Curvature-induced secondary flow in submarine channels

The curvature-driven secondary flow in sinuous submarine channels has been a subject of considerable interest and controversy. Here, results from numerical model studies involving saline flow in laboratory-scale channels are presented. A 3D finite volume model of density and turbidity currents is used and simulations are run with different inflow discharges and channel-axis slopes. The simulation results show strong influence of bend wave length, channel gradient, confinement and cross sectional shape on the structure of secondary flow in submarine channels. Major findings are: (i) reversal of secondary flow in submarine channels is strongly associated with a tight bend characterized by a smaller wave length to width ratio or larger wave number, (ii) for the same inflow condition and planform characteristics, a trapezoidal channel cross section is more favorable to secondary flow reversal than a rectangular cross section, (iii) lateral convection resulting from the interaction between in-channel and overbank flows leads to the reversal of secondary flow in an unconfined channel at a lower channel slope than in a confined channel with the same dimensions, (iv) flow discharge has only nominal effect on the secondary flow in submarine channels.

A Polynomial Model for Lateral Thickness Decay of Submarine Channel-Levees

Abstract Active and relic channels with extensive levees are common on the seafloor adjacent to the continental margin. Exponential, power-law, and logarithmic functions have been proposed by others to describe the lateral thickness decay of submarine levees. In the present study, experiments have been conducted to study submarine levee growth by flow stripping at a channel bend. Various functions have been fitted to the data. The results show that a third-order polynomial function best describes the levee thickness in the cross-stream direction near a submarine channel bend. Generalized model coefficients are derived as functions of deposit thickness adjacent to the channel bank. The model is applied to experimental data obtained by others as well as levee shapes derived from seismic data. In both cases, satisfactory agreements are found. The proposed model can be a useful tool for stratigraphic modeling of submarine channel–levee systems and fill gaps in field data.

Research on optimal radius ratio of impellers in an oxidation ditch by using numerical simulation

Impellers are the main power source for oxidation ditches. Impeller radius has an important influence on the velocity distribution and the flow field structure in oxidation ditch channels. In this paper, the relation between the size of impeller radius and the structure of flow field in an oxidation ditch was studied by using the two-phase gas–liquid model and the 3D Realizable k–ε turbulence model. The pressure implicit with splitting of operators algorithm was used for the solution of velocity and pressure. The volume of fluid method was used to simulate the free surface. The research results show that when the ratio of the impeller radius to the diameter of the oxidation ditch channel bend, r/d, is 0.218, the percentage of the fluid with velocity greater than 0.3 m/s to the entire fluid is the greatest, and the length of the backflow region in straight channels is relatively shorter. The ratio of impeller radius to the diameter of an oxidation ditch channel bend, r/d, with a value of 0.218, is called the optimal impeller radius ratio.

Radiation damage in urania crystals implanted with low-energy ions

Implantations with low-energy ions (470-keV Xe and 500-keV La with corresponding ion range Rp∼85nm and range straggling ΔRp∼40nm) have been performed to investigate both radiation and chemical effects due to the incorporation of different species in UO2 (urania) crystals. The presence of defects was monitored in situ after each implantation fluence step by the RBS/C technique. Channelling data were analysed afterwards by Monte-Carlo simulations with a model of defects involving (i) randomly displaced atoms (RDA) and (ii) distorted rows, i.e. bent channels (BC). While increasing the ion fluence, the accumulation of RDA leads to a steep increase of the defect fraction in the range from 4 to 7dpa regardless of the nature of bombarding ions followed by a saturation plateau over a large dpa range. A clear difference of 6% in the yield of saturation plateaus between irradiation with Xe and La ions was observed. Conversely, the evolutions of the fraction of BC showed a similar regular increase with increasing ion fluence for both ions. Moreover, this increase is shifted to a larger fluence in comparison to the sharp increase step of RDA. This phenomenon indicates a continuous structural modification of UO2 crystals under irradiation unseen by the measurement of RDA.

Deflection of a 100-MeV positron beam by repeated reflections in thin crystals

The phenomenon of the deflection of a charged particle beam due to channeling in a bent crystal is thoroughly investigated and successfully applied for the extraction of the beam in high-energy accelerators, at the energies of about 10 GeV and higher. However, a big practical interest lies in the task of bending and extracting charged particles with energies below 1 GeV, for example, for the production of ultrastable beams of low emittance for medical and biological applications. That is why a novel crystal technique, namely thin straight crystal targets, is investigated in this article, using crystals as elements for extraction and collimation of the circulating beam in a ring accelerator. The advantages of reflection in straight crystals in comparison with bent crystal channeling consist in the small length of straight crystals along the beam that reduces the amount of nuclear interactions and improves the background. Experimental results were obtained for the bending of a 100 MeV positron beam with using five sequential straight crystals.

Experimental and Numerical Study on Velocity Fields and Water Surface Profile in a Strongly-Curved 90° Open Channel Bend

The flow pattern changes at open channel bend as the result of the presence of centrifugal force. Parameters such as water surface level, the transverse and depth velocity distribution, secondary flow and separation zones deeply depend on bend angel and radius, while many researchers are interested in flow patterns at bends. This paper presents an experimental and numerical study of the flow patterns in a strongly-curved 90° open channel bend. The numerical modelling was carried out using the finite volume method. In this numerical study, the k – ε (RNG) model was used to predict the turbulence, and the volume of fluid (VOF) method was used to simulate the water free surface. The numerical results were verified against data from a program of experiments conducted in this study. A comparison between the experimental data and the results of the numerical model showed that the k – ε (RNG) and VOF methods are capable of simulating the flow pattern in the strongly-curved bends. The results showed that along a strongly-curved 90° bend, the maximum flow velocity always occurs near the inner wall and in such bends the effect of the secondary flows is not limited to the sections within the bend. Also the overall shape of streamlines along the bend and at different water levels is different. In addition, the results revealed that the transverse slope of the water surface is non-linear in these bends. This situation occurs in bends even though maintaining a steady uniform flow condition in straight sections.

The possible role of Coriolis forces in structuring large-scale sinuous patterns of submarine channel–levee systems

Submarine channel-levee systems are among the largest sedimentary structures on the ocean floor. These channels have a sinuous pattern and are the main conduits for turbidity currents to transport sediment to the deep ocean. Recent observations have shown that their sinuosity decreases strongly with latitude, with high-latitude channels being much straighter than similar channels near the Equator. One possible explanation is that Coriolis forces laterally deflect turbidity currents so that at high Northern latitudes both the density interface and the downstream velocity maximum are deflected to the right-hand side of the channel (looking downstream). The shift in the velocity field can change the locations of erosion and deposition and introduce an asymmetry between left- and right-turning bends. The importance of Coriolis forces is defined by two Rossby numbers, RoW=U/Wf and RoR=U/Rf, where U is the mean downstream velocity, W is the width of the channel, R is the radius of curvature and f is the Coriolis parameter. In a bending channel, the density interface is flat when RoR∼-1, and Coriolis forces start to shift the velocity maximum when |RoW|<5. We review recent experimental and field observations and describe how Coriolis forces could lead to straighter channels at high latitudes.

Non-aligned bilayer square-wave bend microchannel for mixing

A numerical study has been conducted on a modified design of square-wave bend microchannel to enhance mixing performance. The channel domain is divided into two layers of equal heights. The position of the layers is non-aligned in the lateral direction to construct a bilayer bend channel. The idea was to modulate the dean vortices formed in the bends. The bilayer bend channel shows enhanced mixing performance compared with a simple bend channel. Unlike a simple bend channel, a bilayer bend channel exhibits the formation of multiple vortices at different positions. This study has employed three values of offset positions at different Reynolds numbers.

Streamwise streaks and secondary instability in a two-dimensional bent channel

Streamwise streaks generated from a pair of oblique waves and secondary instability of the streaks are studied in a two-dimensional bent channel. Nonlinear parabolized stability equations (NPSE) are employed to investigate streamwise streaks and vortices. A pair of oblique waves from linear stability analysis is imposed as initial disturbances. Generation of streamwise streaks and vortices and subsequent development are described in detail. The case of plane channel is also studied to provide comparable data. Through comparison, the effect of bent region is clearly highlighted. Results of parametric studies to examine the effect of Reynolds number, radius of curvature, and bent angle are also given and discussed in detail. Secondary instability analysis for the modified mean flow due to the streamwise streaks is carried out by solving a two-dimensional eigenvalue problem. Several unstable modes which can be classified into fundamental and subharmonic mode of secondary instability are identified. Among several unstable modes, two modes are turned out to be dominant modes. Details on these two modes including generation mechanism, typical pattern, and dependency on wave number and streak amplitude are discussed. It is found that the presence of bent channel can lead to early oblique-mode breakdown via strong growth of the streamwise streaks due to the curved section. Such large amplitude of streaks and its secondary instability eventually could trigger transition even for small amplitude oblique waves at subcritical channel Reynolds numbers.

Hydrodynamic processes, sediment erosion mechanisms, and Reynolds-number-induced scale effects in an open channel bend of strong curvature with flat bathymetry

[1] Sharply curved open channel flow with a flat bed is investigated with eddy-resolving numerical simulations that complement laboratory experiments. The focus is on the role of coherent flow structures, how these structures contribute to shear stresses and the capacity of the flow to pick up sediment at the boundaries, and on changes resulting from increasing the Reynolds number between typical values for laboratory model studies and for field conditions. In sharply curved bends, secondary flow leads to a transverse component of the bed shear stress that is of comparable magnitude as the streamwise component. Just downstream of the bend entrance, the locus of highest velocities migrates outward and separates from the inner bank. A highly energetic thin shear layer containing large-scale eddies develops at the interface between the core of high streamwise velocities and the retarded fluid moving close to the inner bank. Highly energetic Streamwise-Oriented Vortices (SOVs) develop in the zone of retarded flow. Turbulence, the boundary shear stress, and the sediment pickup capacity are considerably increased by the SOVs and the large-scale eddies inside the shear layer. These large-scale turbulent structures are amplified and become more coherent with increasing Reynolds number. The results indicate that flow processes in scaled laboratory flumes and natural rivers are qualitatively similar, although some quantitative Reynolds-number-induced scale effects exist. The paper also discusses application of several improved methods to estimate mean sediment pickup rates for flow in sharply curved bends. Such methods try to account in an approximate way for the effects of large-scale turbulence in numerical simulations that do not resolve these structures.

Specific Distribution Behavior of a Ternary Mixture of Solvents Fed into Bent and Wound Microchannels in Microchips

The tube radial distribution of ternary solvents (water-hydrophilic/hydrophobic organic mixture) fed into bent and wound microchannels in a microchip was examined by fluorescence observations of dyes dissolved in the solvents under laminar flow conditions. Four kinds of microchips incorporating bent microchannels were used, together with a microchip with a straight channel. The microchannels had different bending times (2, 4, or 12 times), bending radii (0.8, 2.3, or 3 mm), and total channel lengths (80, 120, 200, or 500 mm). A water-acetonitrile (hydrophilic)-ethyl acetate (hydrophobic) mixture containing relatively hydrophilic Eosin Y (green) and hydrophobic perylene (blue) was delivered into the bent microchannels in the microchips. The fluorescence of the green and blue dyes enabled us to observe the specific radial distribution behavior of the ternary solvents in the bent micro channels at 0°C, including liquid-liquid interfaces. Further, the radial distribution pattern of the solvents was clearly observed in the wound microchannel (bending radius, ca. 0.1 mm; real total channel length, 500 mm; and apparent straight channel length, 40 mm) at 20°C (room temperature) as well as 0°C. It was found that the radial distribution behaviors of the solvents were successfully generated in even specific microchannels including various types of curves under the present conditions.

A Simplified Formula for Calculating the Elastic Distortional Bucking Stress of Steel Channel Bending Members with Complex Edge Stiffeners and Intermediate Stiffeners in Elements

In order to research the simplified formulas of bending steel channels with complex edge stiffeners for their elastic distortional buckling stress, each 70 members for lipped channels with complex edge stiffeners, Σ style channels with complex edge stiffeners and channels with complex edge stiffeners and intermediate V type stiffeners in the web were numerical analyzed by the finite strip software CUFSM. Based on the existed expression for local bucking and introducing distortional buckling coefficient, each of the suggested simplified formulas for distortional buckling stress of the above members were summarized. Besides, formulas for lipped channels with complex edge stiffeners and channels with complex edge stiffeners and intermediate V type stiffeners in the web were united as one. All the formulas were confirmed for their availability.