Small Radius Research Articles

Effect of radius ratio on the instabilities in a vaneless diffuser

The prominent features of the primary instabilities of a turbulent source flow between finite-span parallel rings with spatially modulated inflow conditions rotating at angular rate Ω are investigated. Two different two-dimensional instabilities that occur at large (αQ≳1.00) and low (αQ≲0.65) flow rates have been traced back to two different physical mechanisms related to jet-wake and mean-core flow, respectively. The effect of the radial aspect ratios Γ on the instability characteristics of the flow between parallel rings is also considered in this paper. Numerical URANS simulations are conducted for three different radial aspect ratios, i.e. Γ=1.25, 1.5, and 2, the corresponding cross-sectional aspect ratios Λ=2(Γ−1)×3.325, and two conceptually different inflow conditions. Their impact on the rotating instabilities in terms of instability mode number and instability frequency is the main focus of this study and is analyzed by fast Fourier transform (FFT) and wavelet analysis. Realistic inflow conditions with a leakage flow are found to overtake the instability for small radius ratios and affect the primary instabilities for large radius ratios.

Investigation of dynamic gauge widening in small radius curves and its impact on lateral wheel-rail contact forces

In this paper, the lateral interaction between a rail vehicle and the track is investigated during cases of an occurrence of dynamic gauge widening. This is composed of the nominal track gauge, wear of the rail profiles and track widening due to wheel-rail forces on sections of curved track. A multibody simulation model is used to investigate the various influencing parameters. This model not only analyses the single rail’s lateral displacement but also tilting. Furthermore, the simulation of rail pads with adjustable stiffnesses is enabled. The resulting different contact points between the wheel and rail are represented, affecting the wheel-rail contact forces. The results reveal that changes in contact geometry caused by rail tilting depend strongly on the specific wheel and rail profiles. This is illustrated by comparing a new rail profile with a heavily worn rail profile. Particular attention is also paid to the distinction between leading and trailing wheelsets. Finally, the model is validated using measured wheel-rail forces and rail head movement, as measured on the track. A better understanding of dynamic track widening can improve the running behaviour of the wheelset on small radius curves, help protect against derailment and reduce wear on the wheel and rail.

The directional flow generated by peristalsis in perivascular networks-Theoretical and numerical reduced-order descriptions.

Directional fluid flow in perivascular spaces surrounding cerebral arteries is hypothesized to play a key role in brain solute transport and clearance. While various drivers for a pulsatile flow, such as cardiac or respiratory pulsations, are well quantified, the question remains as to which mechanisms could induce a directional flow within physiological regimes. To address this question, we develop theoretical and numerical reduced-order models to quantify the directional (net) flow induceable by peristaltic pumping in periarterial networks. Each periarterial element is modeled as a slender annular space bounded internally by a circular tube supporting a periodic traveling (peristaltic) wave. Under reasonable assumptions of a small Reynolds number flow, small radii, and small-amplitude peristaltic waves, we use lubrication theory and regular perturbation methods to derive theoretical expressions for the directional net flow and pressure distribution in the perivascular network. The reduced model is used to derive closed-form analytical expressions for the net flow for simple network configurations of interest, including single elements, two elements in tandem, and a three element bifurcation, with results compared with numerical predictions. In particular, we provide a computable theoretical estimate of the net flow induced by peristaltic motion in perivascular networks as a function of physiological parameters, notably, wave length, frequency, amplitude, and perivascular dimensions. Quantifying the maximal net flow for specific physiological regimes, we find that vasomotion may induce net pial periarterial flow velocities on the order of a few to tens of m/s and that sleep-related changes in vasomotion pulsatility may drive a threefold flow increase.

Mechanistic investigation of highly bendable magnesium alloy sheet fabricated by short-process manufacturing

In this study, a commercial magnesium alloy AZ31 (Mg-3Al-1Zn-0.3Mn) sheet through a short manufacturing process was found to be ductile and highly formable in bending. Despite possessing a strong basal texture, the short-processed sheet without any annealing can be bent at a small radius, only 0.2 times its thickness in the 90° bending test. Additionally, it could withstand direct deformation by repeated folding-flattening. The in-situ microstructural characterization reveals that extension twin bands with strain localization appear in the bending area. During subsequent flattening, these twin bands underwent detwinning, reducing local strain concentrations and enabling further bending deformation. Such outstanding bend formability originated from the significant 〈a〉-type dislocation loops slipping on the prismatic crystal planes within dynamic-recrystallized grains. These grains underwent a uniform refinement to several microns in the short manufacturing process and exhibited low residual strain. The active prismatic dislocation slip within refined grains was due to its much lower relative activation stress to basal slip (CRSSprism/ CRSSbasal of only ∼1.6) owing to the effective grain boundary hardening. Furthermore, the prismatic dislocation activity was further enhanced when bypassing Al-Mn nano-particles during motion, leaving debris and loops that facilitated easy multiplication.

Computational fluid dynamics simulation analysis of the effect of curved rice leaves on the deposition behaviour of droplets

BackgroundAlthough previous studies on the droplet deposition behaviour of rice leaves have modelled the leaves as flat surface structures, their curved surface structures actually have a significant effect on droplet deposition.ResultsIn this paper, the statistical distribution of the coordinate parameters of rice leaves at the elongation stage was determined, computational fluid dynamics (CFD) simulation models of droplet impact on rice leaves with different curvature radii were built, and the effect of leaf curvature radius on the deposition behaviour and spreading diameter of droplets on rice leaves was studied using validated simulation models. The results showed that the average relative errors of the CFD simulation models were in the range of 2.23–9.63%. When the droplets struck the rice leaves at a speed of 4 m/s, the 50 μm droplets did not bounce within the curvature radii of 25–120 cm, the maximum spreading diameters of 200 and 500 μm droplets that just adhered to the leaves were 287 and 772 μm, respectively. The maximum spreading diameters of 50, 200, and 500 μm droplets that just split were 168, 636, and 1411 μm, respectively. As the curvature radii of the leaves increased, the maximum spreading diameter of the droplets gradually decreased, and droplet bouncing was more likely to occur. However, a special case in which no significant change in the maximum spreading diameter arose when 50 μm droplets hit a leaf with a curvature radius exceeding 50 cm.ConclusionSplitting generally occurred for large droplets with a small curvature radius and small tilt angle; bouncing generally occurred for large droplets with a large curvature radius and large tilt angle. When the droplet was small, the deposition behaviour was mostly adhesion. The change in spreading diameter after stabilisation was similar to the change in maximum spreading diameter, where the spreading diameter after stabilisation greatly increased after droplet splitting. This paper serves as a reference for the study of pesticide droplet deposition and its application in rice-plant protection.

Investigating Reynolds number effects in turbulent concentric coaxial pipe flow using stochastic one‐dimensional turbulence modeling

AbstractThe present study numerically investigates turbulent momentum transfer in concentric coaxial (annular) pipe flow with small radius ratios . To model the flow, a stochastic one‐dimensional turbulence (ODT) model formulated for cylindrical geometry is used that provides full‐scale resolution along a representative radial coordinate. The present investigation extends the model validation by Tsai et al. (PAMM, 22:e202200272, 2023), to radius ratios smaller than 0.1 and addresses boundary layers with strong spanwise curvature effects. The focus is on the assessment and analysis of statistical flow features in the vicinity of the inner cylinder wall, particularly in cases with small radius ratios. Following Boersma & Breugem (Flow Turbul. Combust., 86:113–127, 2011), classical boundary‐layer and mixing‐length theory is utilized to analyze the model predictions. The results demonstrate that the ODT model captures leading‐order curvature and mixing‐length effects by its physics‐compatible construction. Utilizing the model for extrapolation to high Reynolds numbers inaccessible to conventional high‐fidelity numerical approaches shows that curvature effects persist and nonlocally affect the entire boundary layer. The model results provide support for a spanwise‐curvature‐modified wall function.

Monitoring method of cutting forces and vibrations by using frequency separation of acceleration sensor signals during milling process with small ball end mills

Recently, there has been a further demand for precise monitoring of milling process with a machine tool by a simple and cost-effective method. One of the ways for monitoring is to install acceleration sensors to the tool spindle and estimate cutting forces from the model of the tool spindle structure. This method generally allows stable monitoring of cutting forces for tools with large diameters. However, in case of using tools with small diameters, it is difficult to estimate the cutting force due to higher frequency vibrations generated near the tool center point. Therefore, to solve the problem, we propose a new monitoring method by signal analysis of acceleration sensors in this research. The problem is that the acceleration sensor signals contain two types of signals, such as ‘acceleration change due to mechanical displacement of a tool spindle generated by cutting load’ and ‘high frequency self-excited and forced vibration’. In our method, we separate these two signals by using an approximation of sequential quadratic regression. From the former, cutting forces are estimated from equation of motions which are obtained in advance from frequency responses of the tool spindle, and from the latter, intensities of vibrations due to milling are estimated. This method was tested several milling patterns such as large cutting loads, fluctuations of cutting loads, and cutting during abnormal vibrations. As a result, we have achieved in-process monitoring of milling process not only in the X and Y directions, but also in the Z direction with a small radius ball end mill.

CO2 reduction synergistic tetracycline degradation toward Co-BiOBr ultrathin nanosheets with rich defects and (102) active faces

The development of bifunctional reaction by combining CO2 reduction with antibiotics degradation is of great significance. Designing bifunctional catalysts with excellent performance is the focus of scholars' research. In this paper, Co-doped BiOBr ultra-thin nanosheets exposing rich (102) active crystal faces were prepared by one-step hydrothermal method. Since Co2+ has a smaller radius than Bi3+, Co was successfully incorporated into the lattice of BiOBr, which changed the crystal structure of BiOBr and obtained thinner nanosheets with rich lattice defects. The Gibbs free energy of CO2 reduction reaction was synergistically optimized by the combination of exposing (102) active crystal faces and introducing lattice defects. In addition, the addition of Co changed the band structure of BiOBr and improved the carrier separation ability, making Co-BiOBr be an excellent bi-functional photocatalyst for CO2 reduction and co-degradation of tetracycline, realizing the synergistic process of environmental purification and energy conversion. This work provides theoretical and experimental reference for the rational design of bifunctional photocatalysts.

Functional Spiro-OMeTAD-like dopant for Li-Ion-free hole transport layer to develop stable and efficient n-i-p perovskite solar cells

Perovskite solar cells (pero-SCs) containing lithium bis(trifluoromethane)sulfonimide (LiTFSI)-doped Spiro-OMeTAD-based hole transport layers (HTLs) exhibit outstanding power conversion efficiencies (PCEs). However, the dopant LiTFSI likely causes a severe morphology change and induces ion migration, which can also corrode the underlying perovskite film, owing to its hygroscopicity and small ionic radius. In this study, we developed a Spiro-OMeTAD-like organic salt (Spiro-BD-T) with a large-size cation composed of a Spirobifluorene (Spiro) backbone and phenylpyridin-4-amine (BD) as well as an anion composed of TFSI-. The anion in Spiro-BD-T can promote the oxidation of Spiro-OMeTAD and effectively form a weakly bound Spiro-OMeTAD•+TFSI− system. Moreover, the Spiro-OMeTAD-like cation in Spiro-BD-T exhibits good miscibility with Spiro-OMeTAD, excellent hydrophobicity and does not easily migrate, which diminishes the ingress of humidity and eliminates the detrimental Li+ migration. Ultimately, the Spiro-BD-T-doped Spiro-OMeTAD HTL showed a homogeneous and pinhole-free morphology with improved composition stability. The resultant pero-SCs exhibited an excellent PCE of 24.2% with significantly promoted long-term stability.

Stable and Highly Luminescent Silver Nanoclusters in the 13X Zeolite Enabled by Mg2+ Doping and Their Luminescence Tuning by Heating Temperature.

Zeolite-confined silver nanoclusters (Ag-zeolite) have aroused vast interest due to their remarkable luminescence. The countercations within a zeolite play critical roles in determining the luminescent properties of the resulting Ag-zeolite. We observed, in this work, that introducing Mg2+ enabled the Ag-13X zeolite a stable and bright yellow emission with a high PLQY of 94.6%, the first report on the luminescence enhancement of the Ag-13X zeolite by Mg2+, to the best of our knowledge. The formation of specific internal electric fields inside 13X and the structural contraction of the zeolite framework due to the high charge density and the small ionic radius of Mg2+ are believed to be responsible for the enhanced stable and bright yellow emission. The stabilization effect of Mg2+ is removed by increasing the heating temperature above 700 °C, which leads to the variation of silver nanoclusters as a result of the framework collapse of the zeolite. The Ag-zeolite synthesized by us, featured with a broad emission band, a high PLQY of 94.6%, and good thermal stability, can be considered a suitable candidate to replace the traditional commercial yellow-emitting phosphor YAG:Ce3+ for light-based applications. This work contributes to a valuable reference for the rational design of silver nanoclusters confined in zeolites with promising new functionalities and stimulates potential applications as novel phosphors for near-ultraviolet light-emitting diodes (NUV-LEDs).

Experimental investigation and numerical simulation of the effect of type of bending die on the quality of tube forming in rotary draw bending process

This study introduces a new rotary draw bending method that utilizes a variable curvature bending die. Unlike traditional methods that bend tubes with a fixed radius, this method gradually deforms the tube from a large to a small radius. The curvature of the bending die is determined by using an involute curve as the equation for the geometric location of the variable curvature. Hydroforming technology, utilizing fluid under pressure, replaces the mandrel in the rotational tensile bending process. The research was conducted using a thin-walled AA6063 tube with a 13.88 diameter-to-thickness ratio. The bending process was examined at critical bending ratios of 1 and 1.6 times the diameter, with a 90° bending angle. The maximum pressure that can be applied in any bend radius ratio was predicted using the necking criterion. The simulation and experimental tests analyzed the effects of internal fluid pressure and bend die curvature on defects such as wall thinning in the outer curvature of the bend, thickening of the wall in the inner curvature of the bend, and cross-section non-roundness. The results indicate that, at constant pressure, the amount of thinning and thickening of the bent tube is significantly improved when using the variable radius bending die compared to the fixed radius die.

Evaluation of the Effects of Nano-SiO2 Microemulsion on Decompression and Augmented Injection in the Eunan Tight Reservoir

The residual oil saturation of the matrix near the well zone of a tight reservoir is high due to the tight reservoir’s complex conditions, such as the small pore throat radius and low permeability of the matrix and the development of microfractures, which can result in serious water channeling, even after long-term water injection development. The aim of this paper is to improve the effects of depressurization and augmented injection for tight reservoir waterflooding development by reducing the tight matrix’s residual oil saturation, increasing and maintaining its water phase permeability near the well zone using a nano-SiO2 microemulsion system with a small particle size and high interfacial activity. Therefore, four nano-microemulsion systems were evaluated and screened for their temperature resistance, salt resistance, interfacial tension, solubilization, and dilution resistance. A microemulsion system of 13% A + 4% B + 4% C + 4% n-butanol + 6% oil phase + 69% NaCl solution (10%) + 1% OP-5 + 0.5% anti-temperature agent + 0.3% nanosilica material was preferred. According to the core displacement experiment, the depressurization rate can reach 28~60% when the injection concentration of the system is 1~10% and the injection volume is 2~5 PV. The results of the on-site test show that the water injection pressure dropped to 17.5 MPa, which was lower than the reservoir fracture re-opening pressure. The pressure reduction rate was approximately 20%. The validity period of the depressurization and augmented injection has reached 23 months to date.

The effect of hydraulic anti-kink system on the safety performance of a four-module single-type tram

The effect of the hydraulic anti-kink system on the longitudinal-yaw stability and small radius curve passing safety of the four-module single-type tram is studied. Firstly, the dynamics model of the anti-kink system is established based on the working principle of the anti-kink system, and the dynamic response of the system is analysed. Secondly, the influence of the anti-kink system on the longitudinal-yaw stability is analysed based on the longitudinal-yaw dynamics model of the four-module single-type tram. Finally, a virtual prototype of the anti-kink system and the four-module single-type low-floor tram with independent rotating wheels is established to test the longitudinal-yaw stability of the vehicle, and the curve passing safety. The results show that: the double-hinged device increases the longitudinal-yaw instability of the vehicle and is more likely to produce jackknifing phenomenon, so the stiffness of the anti-kink system should be set as much as possible to prevent the jackknifing phenomenon and ensure the safe operation of the train. By reducing the stiffness of the anti-kink system properly, the wheel-rail force during curve passing can be reduced, and thus improving vehicle safety.

Experimental and numerical investigations on adaptive stiffness double friction pendulum systems for seismic protection of bridges

This study examines the design, development, and characterization of double friction pendulum systems with variable sliding surface geometry. The proposed isolator has a spherical surface with a small radius within an inner sliding range while different geometric functions are used to describe the sliding surface in the outer range. As a result of variable curvature used as sliding surface, the isolators exhibit an adaptive stiffness behavior with increasing displacement amplitude. First, the analytical equations that describe the characteristics of the proposed isolators were derived. Then, a large-scale prototype adaptive isolator that employs a logarithmic function for the sliding surface geometry in the outer range was fabricated. The response of the prototype isolator was characterized under increasing amplitude reversible cyclic loads considering two different levels of vertical isolator loads. A high-fidelity finite element model was developed to capture the response of the prototype isolator. The results obtained from the experimental tests and numerical simulations were used to verify the analytical equations derived for the proposed isolators. Next, a typical multi-span bridge structure was modeled with adaptive stiffness isolators and its response under bi-directional ground motions records were analyzed. In contrast to a conventional double friction pendulum bearing, the suggested isolators yield significantly reduced base shear forces while exhibiting greater isolator displacements. However, the proposed isolators retain the capability to effectively curtail excessive displacements, ensuring the prevention of collapse.

Bayesian inferences of electrical current delivered to shocked transmission lines

Small radius Bdot measurements of electrical current delivered by pulsed power devices are routinely compromised by electrode/convolute plasmas endemic to multiterawatt transmission lines. Inferences of delivered current unaffected by these issues have recently been obtained by numerically optimizing consistency between model predictions and local experimental velocimetry data, but these are only unique for shockless velocity profiles. Here, we describe a more general Bayesian method capable of inferring current despite the presence of shocks. Additionally, we describe uncertainty estimates and use of the technique on experimental data. This technique is the first to provide uncertainty estimates on the full current trace delivered to an inertial confinement fusion target.

Optimisation design of grinding rail profile of metro lines for small radius curved track based on the GFC method: a case study

The rail side wear in small radius curved track of metro lines is a serious problem in railway maintenance, which reduces the curve passing performance and shortens the service life of the wheel and rail. To improve the vehicle's curve passing performance and reduce rail wear, a localized grinding profile design method for sharp curves was developed. The GFC profile generation method was used to generate the profiles for the curved track of the metro line. Then a metro vehicle-track dynamic model was established to calculate the wheel rail contact parameters, objectives and constraints. The profiles are optimized by the KSM-PSO optimization algorithm. Finally, a simulation analysis of the curve passing performance and wheel-rail wear of the optimized profile was carried out. When the metro vehicle passes through the curved track with a curve radius of 450m, the optimized rail profile can effectively reduce the wear of the rail, the wear of the high rail in the curved track is reduced by 20.18%. The localized rail grinding of the curved track can effectively reduce the rail side wear, the GQI index is also significantly improved. This study can guide the design of rail grinding profiles for the metro lines.

Effects of heel apex position, apex angle and rocker radius on plantar pressure in the heel region

IntroductionRocker shoes and insoles are used to prevent diabetic foot ulcers in persons with diabetes mellitus and loss of protective sensation, by reducing the plantar pressure in regions with high pressure values (>200 kPa) (e.g., hallux, metatarsal heads and heel). However, forefoot rocker shoes that reduce pressure in the forefoot inadvertently increase pressure in the heel. No studies focused on mitigating the negative effects on heel pressure by optimizing the heel rocker midsole, yet. Therefore, we analyze the effect of different heel rocker parameters on the heel plantar pressure. MethodsIn-shoe pressure was measured, while 10 healthy participants walked with control shoe and 10 different heel rocker settings. Peak pressure was determined in 7 heel masks, for all shoes. Generalized estimating equations was performed to test the effect of the different shoes on the peak pressure in the different heel masks. ResultsIn the proximal heel, a rocker shoe with distal apex position, small rocker radius and large apex angle (100°), shows the largest significant decrease in peak pressure compared to rocker shoes with more proximally located apex positions. In the midheel and distal heel, the same rocker shoes or any other rocker shoes, analyzed in this study, do not reduce the PP more than 2 % compared to the control shoe. For the midheel and distal heel region with high pressure values (>200 kPa), rocker shoes alone are not the correct option to reduce the pressure to below 200 kPa. ConclusionWhen using rocker shoes to reduce the pressure in the forefoot, a heel rocker midsole with a distal apex position, small rocker radius and apex angle of 100°, mitigates the negative effects on proximal heel pressure. For the midheel and distal heel, other footwear options as an addition or instead of rocker shoes are needed to reduce the pressure.

Thermodynamic Analysis of Capillary and Electric Field Effects on Liquid-Vapor Equilibrium: A Study on the Water-Ethanol Mixture.

This study investigates phase equilibrium manipulation in nonideal mixtures through a combined capillary and external electric field approach. Utilizing thermodynamic principles, an expression is established for estimating the equilibrium liquid mole fraction in a confined system subjected to a localized electric field within a capillary that is filled with a liquid phase in equilibrium with its vapor counterpart. Applied to a water-ethanol system, the model suggests large shifts in the equilibrium liquid mole fraction of water due to the electric field and capillary effects. These findings reveal that while the capillary's influence remains negligible for radii exceeding 10 nm, capillaries of smaller dimensions, when exposed to electric fields of around 300 MV/m, can amplify the equilibrium liquid water mole fraction by up to 55%. This suggests the potential for phase equilibrium control through larger capillaries and lower electric fields, while intriguing complexities arise at very small radii.

Effects of Small Leading-Edge Bluntness on High-Speed Boundary-Layer Instabilities on Flat Plates

A numerical investigation of the effect of small leading-edge bluntness on the linear stability regime in high-speed boundary layers for flat plates was carried out using linear stability theory. While it is known that increasing leading-edge bluntness leads to stabilization of the linear instability, it is not completely understood when leading-edge bluntness effects become relevant; in other words, for which leading-edge radii the primary instability regime is affected for flat plates at higher Mach numbers. For the so-called “sharp” geometries, it is assumed that the influence of the nose radius on stability and transition is negligible. For cones, it is generally accepted that nose radii resulting in Reynolds numbers (based on nose radius) smaller than 1000 can be considered sharp. However, no clear guidelines supported by numerical or experimental data exist to conclusively determine what constitutes a sharp leading edge for a flat plate. In this work, bluntness effects are assessed by considering the influence of the leading-edge radius on the linear stability characteristics for high-speed flat-plate boundary layers. It was found from linear stability calculations that surprisingly small leading-edge radii have significant effects on the critical Reynolds number and spatial amplification rates, thus resulting in substantially reduced maximum -factors.

Governing factors for actively heated fiber optics based thermal response tests

The accurate measurement of ground thermal conductivity is crucial for the evaluation of shallow geothermal energy potential. Actively heated fiber optics-based thermal response test (ATRT) is a recently developed novel method for the measurement of ground thermal conductivity, yet the governing factors for ATRT remain unclear. This study used numerical and physical models to examine the ATRT heat transfer process and the factors that may affect the measurement accuracy. The results showed that ATRT has a typical heat transfer process with three stages of composition, revealing diverse heat transfer in the cable, grout, and surrounding ground. The minimum heating duration of ATRT is approximately 150 min under a typical setup. The heating power is recommended to be within the range of 15–40 W·m−1, considering the temperature measurement accuracy. Using grout with a slightly higher thermal conductivity than the surrounding ground is beneficial. Actively heated fiber optic cable positions have a negligible effect as long as the heat duration is sufficient. A small borehole radius improves test accuracy by minimizing grout thickness effects. Understanding the ATRT heat transfer process and governing factors guarantees the validity of its in-situ applications and enables the standardization of ATRT.