Circumferential Direction Research Articles

Poster Session: Experimental assessment of scleral anisotropy using multi-meridian air-coupled ultrasonic optical coherence elastography.

Scleral biomechanics plays a key role in the understanding of myopia progression. In this study, we characterized the elastic properties of sclera using an air-coupled ultrasonic (ACUS) optical coherence elastography (OCE) system. New Zealand rabbit eyes (n=7) were measured (<24hr postmortem) in four scleral locations: superior/inferior temporal (ST, IT), and superior/inferior nasal (SN, IN) maintaining an intraocular pressure of 15 mmHg. Elastic waves were induced in the sclera, and wave propagation velocity and shear modulus were measured along two directions: circumferential (superior-inferior) and meridional (nasal-temporal). Wave velocity in scleral tissue ranged from 6 to 24 m/s and shear modulus from 11 to 150 kPa. Velocity was significantly higher (p<.001) in the circumferential vs. meridional directions in the following locations: ST:15.83±2.85 vs 9.43±1.68 m/s, IT:15.00±3.98 vs 8.93±1.53 m/s; SN:16.79±4.30 vs 9.27±1.47 m/s; and IN:13.92±3.85 vs 8.57±1.46 m/s. The average shear modulus in the circumferential was also significantly higher (p<.001) than in the meridional direction for all locations: 65.37±6.04 vs 22.55±1.36 kPa. These results show that the rabbit sclera is mechanically anisotropic with higher rigidity in the circumferential direction compared to the meridional direction. ACUS-OCE is a promising non-invasive method to quantify the biomechanical changes in scleral tissue for future studies involving myopia treatments.

Numerical and experimental investigation of a variable-curvature shell class I flextensional transducer.

Class I flextensional transducers cannot form broadband characteristics because of the deep valley between their first- and second-order response curves. This valley arises from the sound pressure cancellation produced by the vibration in different areas of the shell. This paper examines the cause of the deep valley by analyzing the three-dimensional equivalent radiated sound field of the transducer. By solving the three-dimensional vibration equation of the shell of revolution and reducing its dimensionality, it can be concluded that its vibration state is related to the positive and negative curvatures in both main directions. Therefore, a variable-curvature shell class I flextensional transducer is proposed, and the second-order vibration of the transducer is changed by the variable-curvature structure composed of positive and negative Gaussian curvature surfaces. The proposed transducer avoids sound pressure cancellation and achieves broadband characteristics. After optimization, a transducer prototype is fabricated, and a pool test is conducted. The test results show that the transducer couples the first three vibration modes, attaining broadband characteristics with an in-band fluctuation of less than 8 dB and a bandwidth of more than 5.4 kHz in the axial and circumferential directions.

Numerical and experimental investigation on cold drawing process of high spiral angle tube

A novel method of cold drawing process of high spiral angle tube made of 304 stainless steel is proposed. Forming principles of high spiral angle tube are calculated. New drawing dies are designed and manufactured. Numerical simulation and corresponding experiments are carried out. Forming quality and defects of cold drawing are discussed. Various factors affecting metal flow during cold drawing process are studied in detail. Finite element model of cold drawing process is established. The variation of drawing load is presented. The distributions of equivalent stress and equivalent strain in different directions during cold drawing process are analyzed. Displacements of points in axial direction and circumference direction during cold drawing process are compared respectively. The evolutions of microstructure during cold drawing process are studied.

Longitudinal versus circumferential biomechanical behavior of the aneurysmal ascending aorta

ObjectivesWe evaluate the independent effects of patient and aortic tissue characteristics on biaxial physiologic mechanical metrics in aneurysmal and nonaneurysmal tissues, and uniaxial failure metrics in aneurysmal tissue, comparing longitudinal and circumferential behavior. MethodsFrom February 2017 to October 2022, 382 aortic specimens were collected from 134 patients; 268 specimens underwent biaxial testing, and 114 specimens underwent uniaxial testing. Biaxial testing evaluated Green-Lagrange transition strain and low and high tangent moduli. Uniaxial testing evaluated failure stretch, Cauchy stress, and low and high tangent moduli. Longitudinal gradient boosting models were implemented to estimate mechanical metrics and covariates of importance. ResultsOn biaxial testing, nonaneurysmal tissue was less deformable and exhibited a lower transition strain than aneurysmal tissue in the longitudinal (0.18 vs 0.30, P < .001) and circumferential (0.25 vs 0.30, P = .01) directions. Older age and increasing ascending aortic length contributed most to predicting transition strain. On uniaxial testing, longitudinal specimens failed at lower stretch (1.4 vs 1.5, P = .003) and Cauchy stress (1.0 vs 1.9 kPa, P < .001) than circumferential specimens. Failure stretch and Cauchy stress were most strongly associated with tissue orientation and decreased sharply with older age. Age, ascending aortic length, and tissue thickness were the most frequent covariates predicting mechanical metrics across 10 prediction models. ConclusionsAge was the strongest predictor of mechanical behavior. After adjusting for age, nonaneurysmal tissue was less deformable than aneurysmal tissue. Differences in longitudinal and circumferential mechanics contribute to tissue dysfunction and failure in ascending aneurysms. This highlights the need to better understand the effects of age, ascending aortic length, and thickness on clinical aortic behavior.

Load introduction and transfer mechanism of K-type CFST circular section connections

This paper investigates the mechanism of load introduction and transfers for K-type concrete-filled steel tubular (CFST) circular section connections experimentally and numerically. Six K-type CFST connections were tested. Three-dimensional finite element (FE) models were then developed and validated against the test results, where the degradation and failure of the direct bond interaction were considered explicitly. The longitudinal strain distribution along the circumferential direction of chord-wall demonstrated that the non-uniform force transfer in the chord was caused by the one side load introduction through braces. The effects of the chord length, cross-sectional slenderness and interfacial interactions on the force transfer of tube-concrete interface were evaluated: 1) the chord length above the connecting region has a positive influence on the force transfer; 2) for the K-type CFST connections in this study, the material strength of concrete in the chord with non-compact and slender sections could not be fully utilized due to the insufficient force transfer; 3) the direct shear interaction dominated the force-transferring process from chord-wall to concrete for the compact section chord with reinforcing plates. Furthermore, the test and FE result confirmed that the load introduction length of the CFST chord with braces included the chord above the connecting region and the full connecting region. In addition, the equation of effective load introduction length for the CFST chord of the K-type connections was proposed.

A MATLAB finite element toolbox for the efficient nonlinear analysis of axisymmetric shells

AbstractShells of revolution under axisymmetric conditions exhibit a circumferentially uniform pre‐buckling stress state and are important fundamental systems which often serve as reference systems for those under more complex conditions. Given this status, work is continuing on a careful and complete characterization of their buckling response with the aid of the Reference Resistance Design (RRD) framework for the ultimate benefit of the EN 1993‐1‐6 Eurocode on the strength of stability of metal shells. The situation is greatly complicated by the fact that while modern finite element software packages offer axisymmetric shell elements in an efficient 2D modelling plane, these are not capable of detecting bifurcation buckling into non‐axisymmetric modes which are often critical for slender systems. Reverting to a full 3D plane is possible, but grossly inefficient and the explicitly modelled circumferential direction is parasitic and detrimental to the overall solution quality. AQUINAS is an accessible and intuitive toolbox developed by the Authors in MATLAB for the efficient analysis of axisymmetric shell structures, aiming to reintroduce a modelling capability that was once standard in the field. Data input is entirely object‐oriented and matrix assembly is parallelized with pre‐compiled C++ routines, with users being able to take direct advantage of MATLAB's visualization properties. The software natively supports the LA, LBA, MNA, GMNIA etc. Eurocode analysis taxonomy. This paper demonstrates the current capabilities of the toolbox, describes the extensive programme of verification against existing established solutions that has been performed, and illustrates its ability to efficiently compute very detailed capacity curves using the EN 1993‐1‐6 capacity curve framework.

Simulation and Optimization of Hemispherical Resonator's Equivalent Bottom Angle for Frequency-Splitting Suppression.

As an inertial sensor with excellent performance, the hemispherical resonator gyro is widely used in aerospace, weapon navigation and other fields due to its advantages of high precision, high reliability, and long life. Due to the uneven distributions of material properties and mass of the resonator in the circumferential direction, the frequencies of the two 4-antinodes vibration modes (operational mode) of resonator in different directions are different, which is called frequency splitting. Frequency splitting is the main error source affecting the accuracy of the hemispherical resonator gyro and must be suppressed. The frequency splitting is related to the structure of the resonator. For the planar-electrode-type hemispherical resonator gyro, in order to suppress the frequency splitting from the structure, improve the accuracy of the hemispherical resonator gyro, and determine and optimize the equivalent bottom angle parameters of the hemispherical resonator, this paper starts from the thin shell theory, and the 4-antinodes vibration mode and waveform precession model of the hemispherical resonator are researched. The effect of the equivalent bottom angle on the 4-antinodes vibration mode frequency value under different boundary conditions is theoretically analyzed and simulated. The simulation results show that the equivalent bottom angle affects the 4-antinodes vibration mode of the hemispherical resonator through radial constraints. The hemispherical resonator with mid-surface radius R=15 mm and shell thickness h=1 mm is the optimization object, and the stem diameter D and fillet radius R1 are experimental factors, with the 4-antinodes vibration mode frequency value and mass sensitivity factor as the response indexes. The central composite design is carried out to optimize the equivalent bottom angle parameters. The optimized structural parameters are: stem diameter D=7 mm, fillet radii R1=1 mm, R2=0.8 mm. The simulation results show that the 4-antinodes vibration mode frequency value is 5441.761 Hz, and the mass sensitivity factor is 3.91 Hz/mg, which meets the working and excitation requirements wonderfully. This research will provide guidance and reference for improving the accuracy of the hemispherical resonator gyro.

Bi-global stability analysis on flow separation of two-dimensional compressor cascade

Bi-Global stability analysis (BGSA) is employed to assess the flow separation (FS) in two-dimensional compressor cascades, aiming to investigate the unstable phenomena and underlying mechanisms. The prediction results are correlated with the separation bubble (SPB) on suction surface (SS) or the trailing edge vortex (TEV) and exhibit good agreement with the unsteady numerical simulation (UNS), thereby confirming the instability of these two flow structures. Meanwhile, the prediction results can also partially reflect the initiation of unsteady blade loading. The perturbation distributions obtained from the eigenvectors corresponding to the physically meaningful eigenvalue, reveal two primary unstable regions: one located in the wake region and another coinciding with the SPB. With the increase of incidence angle (IA), the growth rate (GR) of small perturbations transitions from negative to positive, corresponding to the flow state shifting from stable to unstable. Additionally, the inception position of eigenmodes on SS moves upstream until it reaches the leading edge (LE) of the blade. The velocity magnitude distributions in the circumferential direction were further analyzed, demonstrating good agreement with predicted perturbation distributions, and suggesting that the K-H instability mechanism contributes to unstable phenomena. In the analysis of a two-passage flow domain, it is further observed that there exists a time delay in the vortex shedding within the wake, which is not evident at the single-passage condition.

Performance Improving of Wind Power Generation Systems Through Parameter Optimization and Dynamic Analysis of the Speed-Regulating Differential Transmission

Abstract Hybrid drive wind power generation systems (WPGSs) equipped with speed-regulating differential mechanisms (SRDMs) have emerged as a promising solution for integrating large-scale wind energy into the power grid without the need for partially or fully rated converters. This article presents a comprehensive study on the dynamic analysis and parameter optimization of the SRDM-based transmission, with the aim of providing a sound foundation for the design and performance improvement of hybrid drive WPGSs. This study first formulates the kinematics, power flow, and mechanical efficiency of the SRDM and then proposes an effective parameter configuration model for optimizing the speed ratios of the key link units. The objective function is set as the minimum peak power required for speed regulation by the SRDM. Furthermore, to deal with the unique mechanical features such as dual power inputs, continuously variable transmission, and time-varying steering mechanism, an appropriate nonlinear dynamic modeling method of the SRDM transmission is developed. The torsion–translation vibration equations are derived and solved using the Runge–Kutta numerical integral method, considering randomly changing wind speed inputs and time-varying internal/external excitations. Results reveal that the sun gear experiences severe vibrations with the maximal and average vibration displacements of 0.563 mm and 0.112 mm, respectively, in the circumferential direction, while the planet gear exhibits complex frequency responses. Finally, specialized case studies are demonstrated to verify the proposed approaches, showing the satisfactory on-grid operating performance of the proposed SRDM-based WPGSs.

Seismic response study of shield tunnel with lateral karst cavity under SV waves

This paper investigates the seismic effects of karst cavity size and span on the shield tunnel subjected SV waves, using the case project of Dalian Metro Line 5. The viscous spring artificial boundaries are employed for the seismic input, which is validated to assure accuracy. The shield tunnel is simplified according to the method of the equivalent bending stiffness model. The deformation and stress distribution are analyzed to investigate the dynamic response of the shield tunnel under SV waves at different angles. The tunnel damage state is evaluated by the criterion proposed by authors in previous research. The results show that a larger cavity size can lead to more deformation in the tunnel. There are significant differences in the spatial distribution of deformation and stress affected by the incident angle. As the cavity size increases, the stress near the cavity decreases significantly. Only the cavity size is greater than or equal to 0.8D (D is the tunnel’s diameter), there are damage concentration areas on the bottom, and the damage area shifts towards to circumferential direction. The deformation and stress distribution are highly affected as the span increases in the Z direction, followed by the Y direction, and almost no effect in the X direction. The damage area increases as the increase of span in three directions. There are damage concentration areas of the bottom only as the span is 1.5D in the Z direction. Compared with the effect of cavity size, the results indicate that the damage concentration is not solely related to cavity span in one single direction.

Effect of ring groove in a heat-insulating insert on efficiency of its work in blast channel of blast furnace tuyere

One of the main disadvantages when supplying natural gas to the air tuyere of a blast furnace is low intensity of its combustion inside the tuyere blast channel. Ring groove on the surface of blast channel improves the mixing of natural gas with blast and increases completeness of gas combustion in it, but reduces the tuyere durability. One of the ways to simultaneously solve these problems is to install a heat-insulating ceramic insert in the tuyere blast channel. The insert significantly reduces heat losses through the tuyere surface, improves natural gas combustion in the blast channel due to its contact with hot walls of the insert instead of cold copper walls in its absence. This increases the temperature of the hot blast at the tuyere outlet. In addition, the insert affects the tuyere durability by reducing the heat flow acting on the tuyere. In this work, we studied influence of the ring groove and its parts in the insert on efficiency of its work. In the Ansys 21.1 software, the processes occurring in the blast channel of a blast furnace tuyere with a ceramic insert installed in it, having a groove of a quadrangular section in the form of a ring or its part in the circumferential direction, were simulated. It was established that improvement of natural gas combustion in the tuyere blast channel is achieved using a ring groove or part of it from the side of gas supply.

Effect of Self-Recirculating Casing Treatment on the Aerodynamic Performance of Ultra-High-Pressure-Ratio Centrifugal Compressors

The motivation to design a more efficient and compact aircraft engine leads to a continuous increase in overall pressure ratio and decrease in the stage number in compressors. Compared to the traditional multi-stage compressor, a single-stage ultra-high-pressure-ratio centrifugal compressor with a pressure ratio higher than 10.0 can significantly improve the engine’s power-to-weight ratio and fuel economy with a reduced structure complexity. Thus, it has great potential to be adopted in the compression system of advanced aero engines, such as turboshaft engines, in the future. However, the highly narrow Stable Flow Range (SFR) of ultra-high-pressure-ratio centrifugal compressors is a severe restriction for engineering applications. This research focuses on the aerodynamic performance of a ultra-high-pressure-ratio centrifugal compressor, and three-dimensional simulation is employed to investigate the effect of Self-Recirculating Casing Treatment (SRCT) on the performance and stability of the centrifugal compressor. Firstly, the parametric model of SRCT is established to investigate the effect of geometry parameters (rear slot distance and rear slot width) on the aerodynamic performance of the centrifugal compressor. It is concluded that SRCT improves the compressor’s SFR but deteriorates its efficiency. Also, a non-linear and non-monotone relationship exists between the SFR and rear slot distance or width. Then, the flow mechanism behind the effect of SRCT is explored in detail. By introducing the SRCT, an additional flow path is provided across the blade along the circumferential direction, and the behavior of the shock wave and tip leakage flow is significantly changed, resulting in the obviously different loading distribution along the streamwise direction. As a result, the mixing and flow separation loss are enhanced in the impeller flow passage to deteriorate the efficiency. On the other hand, the blockage effect caused by the mixing of slot recirculation and mainstream flow near the impeller inlet increases the axial velocity and reduces the incidence angle below the 90% spanwise section, which is considered to effectively stabilize the impeller flow field and enhance the stability.

Strength damage behavior analysis of silicon carbide(SiC) ceramic cylindrical shells under hydrostatic pressure based on the state-based peridynamics

Ceramics are one of the most promising materials for pressure-resistant shells of submersibles due to their exceptional mechanical properties. However, ceramics are brittle materials, and the occurrence of strength damage is inevitably accompanied by the generation and propagation of cracks. A new state-based peridynamic damage model is established, the relation between critical elongation and critical energy release rate for tensile and compression fracture is deduced innovatively, to investigate the strength damage behavior of silicon carbide (SiC) cylindrical shells under hydrostatic pressure. The findings demonstrate that by increasing cylinder thickness, the structural damage pressure can be significantly improved. Moreover, the initial damage zones, are located on the internal surface of shell and induced by the compression fracture, and evenly scattered at 90° around the circular direction. As pressure increases, tensile damage zones emerge on the external surface of cylinder. The failure zones on the interior and exterior walls of the shell propagate along the circumferential direction firstly, then extend toward the middle surface until the damage zones completely penetrate the entire thickness, and the cylinder loses its load-bearing capacity.

Two-Step Spin Forming of Thin-Walled Heads with Lateral Normal Flanged Holes

A thin-walled head with a lateral normal flanged hole is a key part of a propellant tank, and its low-cost and high-precision forming process is very challenging. In this paper, a two-step method is proposed to preform the head via marginal-restraint mandrel-free spinning and then to realize the flanging of the lateral normal hole using a punching–spinning method. Finite element analysis of round-hole punching–spinning flanging shows that the larger the thinning ratio and the roller fillet radius, the lower the rebound and contour rise amount; the larger the feed ratio, the lower the rebound and the higher the contour rise amount. Further study on the effects of round-hole punching–spinning flanging on the secondary deformation of thin-walled heads shows that the deformation of the head in the area around the flanging hole is less severe than that of the flat blank, and the deformation in the circumferential direction is different from that in the busbar direction. Finally, it is verified through experiments that the two-step method can realize the spin forming of thin-walled heads with lateral normal flanged holes.

Experimental study on subcooled pool boiling of FC-72 on a flat plate in normal and microgravity

A series of experimental studies on the heat transfer characteristics of pool boiling were conducted aboard the Chinese satellite SJ-10 in April 2016. Ground comparative experiments under the same conditions were carried out using the same apparatus. FC-72 was used as the working fluid containing non-condensable gas. The total quasi-stable-state acceleration aboard satellite SJ-10 during its in-orbit flight is approximately 2 × 10−6 g0. The integrated microheater fabricated by the microelectromechanical system (MEMS) technique was used to investigate the boiling characteristics. The boiling surface of the integrated microheater is on top of a flat plate quartz glass wafer substrate 2 mm thick, heated by a serpentine Pt thin film (main heater) below the substrate. The effective area of the boiling surface in direct contact with FC-72 is 5.5 mm in diameter. Ten temperature sensors are located around the boiling surface center and uniformly distributed in the circumferential direction. The experimental results show that single-phase convection could still be maintained under lower Rayleigh number conditions, showing consistency with the predictions based on the available correlations. The generated bubble volume determines the boiling state. At high liquid subcooling, the bubbles formed after the liquid vaporizes are relatively small, and steam condensation at the bubble cap promotes the phase change efficiency, which maintains nucleate boiling in microgravity. When subcooling is low, bubbles are larger and cover most of the heating surface, nucleate boiling is difficult to maintain, and the boiling becomes transition boiling. High liquid subcooling improves the heat transfer efficiency, thereby contributing to maintaining the progress of nucleate boiling in microgravity. However, boiling is less affected by liquid subcooling on the ground than in microgravity. A comparison of pool boiling curves between microgravity and normal gravity experiments indicates that nucleate boiling curves under the same subcooling partially overlap, while the heat flux corresponding to the initiation of the nucleate state is lower than that on the ground. In microgravity, lower liquid subcooling and higher heating power will result in larger bubble volumes and easier complete coverage of the heating surface, resulting in an easier transition from nucleate boiling to film boiling.

Formation and characterization of hydride rim structures in Zircaloy-4 nuclear fuel cladding tubes

Zirconium alloy tubes used as nuclear fuel cladding are subject to oxidation and subsequent hydrogen pickup during their long service in commercial light water reactors. The hydrogen picked up in the cladding can precipitate as a brittle hydride rim feature on the cladding outer surface. To better understand the effect of hydride rims on the fracture behavior of stress-relieved zirconium alloy cladding tubes, a procedure to produce these rim-like structures has been developed and is described herein. Extensive characterization of the ‘as hydrided’ tubes is performed.The hydrogen charging apparatus consists of a tube furnace with a quartz chamber that is connected to a vacuum pump as well as a bottle of pure hydrogen gas. The charging station uses a static charge of hydrogen as opposed to a flowing gas. The chief advantage of this approach is the ability to monitor the pressure drop in the hydriding chamber and correlate this pressure drop to a known rate of hydrogen pickup in the cladding tube. It was found that the hydrogen partial pressure, metal temperature, and surface treatment all clearly played a role in whether a hydride rim was formed. Extensive characterization of the hydride rims shows they consist of needle like platelets of δ phase hydrides (ZrH1.66) oriented in the circumferential direction with a radial spacing of several microns in a sandwich-like structure.

Abstract P2038: Role Of The Microtubule Network In Right Ventricle Passive Viscoelasticity With Pulmonary Hypertension Development

Microtubule (MT) polymerization is a key contributor to myocardium viscoelasticity, which describes elastic and viscous resistance under stress and impacts the contractile function. MT de- or hyper-polymerization has been shown to decrease or increase healthy cardiomyocyte viscoelasticity, but the responses of hypertrophied cells to these modifications are unknown. Moreover, the ventricular free wall is a complex tissue composed of myofibers, collagen and vasculature, and it exhibits anisotropic mechanical behavior. To fully understand the role of MT in the tissue-level anisotropic viscoelasticity of myocardium, we investigated the responses of healthy and failing rat right ventricles (RV) to alterations in MT network. All procedures were approved by Colorado State University IACUC. Adult male rats were treated with monocrotaline to induce pulmonary hypertension and RV failure. After euthanasia, the RV free wall underwent equibiaxial stress relaxation in intact state (baseline) and under the treatment of colchicine and deuterium oxide (D 2 O) to remove and enhance MT network, respectively. Viscoelastic parameters were quantified as previously described. As expected, the diseased RV had greater viscoelasticity than the healthy RV. Depolymerization of MT in healthy RVs reduced tissue viscosity (relaxation rate) and elasticity (relaxation modulus), and the changes were more significant in the longitudinal (outflow tract) direction. MT hyper-polymerization increased tissue elasticity and decreased viscosity, with the changes stronger in the circumferential direction. In diseased RVs, MT depolymerization reduced viscosity in both directions and elasticity only in the circumferential direction. However, MT hyper-polymerization unexpectedly decreased tissue elasticity and tended to decrease viscosity, as well. The altered MT polymerization dynamics after D 2 O treatment in a fibrotic environment may explain these heterogeneous responses This is the first report of distinct impacts of MT polymerization on the tissue mechanical behavior between the hypertrophied and healthy myocardium. The exact molecular mechanisms involving MT polymerization dynamics and the interactions with collagen await further investigation.

Investigation of pipelines defect localization for fusion reactor by using T(0,1) mode ultrasonic guided waves

The stable operation of a fusion reactor depends on the reliable functioning of various accessory systems, many of which comprise extensive pipelines with different diameters and diverse cladding. Defects in pipelines can occur due to manufacture, thermal stress, and fatigue, threatening the systems’ safety and reliability. Ultrasonic guided waves (UGWs) testing offers a promising approach for remotely locating these minute defects. The study explores non-dispersive fundamental torsional guided (T(0,1)) waves, particularly their influence on minor defect detection in stainless steel pipes. Both finite element simulations and experimental trials reveal that reflection coefficients, indicative of defect presence, rapidly escalate from 64 to 128 kHz. The optimal frequency for minor defect detection lies between 128 and 180 kHz. A significant finding from the circumferential distribution spectrum and angle profile reveals pipe diameter's dominant influence on the reflection energy distribution concentration. Furthermore, this highlights the unique ability of T(0,1) guided waves to precisely locate defects in the circumferential direction within large-diameter pipes over long distances. The results underscore the promising potential of UGWs testing in complex pipelines of fusion reactors.

Stress and Deformation Analysis of REBCO Pancake Coils With Individual Turn Movement

In recent years, rare-earth barium copper oxide (REBCO) pancake coils have shown excellent performances in high magnetic field applications. The no-insulation (NI) winding technique enables to enhance the thermal stability and current density of REBCO pancake coils. Still, further developments of REBCO coils are expected; e.g., the mechanical deteriorations of REBCO tapes caused by electromagnetic forces have been reported. The screening currents are considered as one of the causes to damage the REBCO tapes because of a nonuniform current distribution. Meanwhile, the electromagnetic forces on non-impregnant NI REBCO coils, whose windings can be deformed separately with turns and moved easily, are complicated, and the detailed mechanism has not yet been clarified. Commonly, the circumferential movement/deformation of the winding is considered as a rigid body. In this study, we investigate the stresses and displacements due to the electromagnetic forces on NI REBCO pancake coils in high magnetic field using a current simulation and a 2D elastic finite element analysis in the radial and circumferential directions; i.e., each turn can individually move in the radial and circumferential directions considering the spiral winding structure. The simulation results show the circumferential movement/deformation of windings and the nonuniform hoop stress due to the electromagnetic force.

Computational Investigation of Effect of Tip Clearance in an Annular Turbine Rotor Impulse Cascade

This paper describes three dimensional computational investigations of the effect of the tip clearance on the secondary and tip clearance flows in an annular turbine rotor cascade with non uniform inlet flow. In the actual turbine, the flow at inlet of the rotor is non uniform due to radial pressure gradient acting from the hub to casing. To provide non uniformity at the rotor cascade inlet, an annular nozzle cascade is provided at the upstream. The studies are carried out with the help of a commercially available CFD package. The studies have been carried out for four values of clearance, i.e. 0%, 1%, 3% and 5% of chord. Detailed comparison of the leakage flow direction, pressure gradient, and leakage vortex size, losses, location and interaction with other flow features is carried out. The results are presented in terms of static pressure coefficient distribution on the blade surfaces and total pressure loss coefficient contours in the passage. Spanwise distributions of the circumferentially averaged loss coefficient and flow angle are presented. The extent of losses in the circumferential direction is increased with the increase in the height of the tip clearance but reduced in the spanwise direction. The mass averaged loss coefficient increases rapidly from 0.24 at zero clearance to 0.42 at 1% tip clearance. As the tip clearance is further increased, the losses increase slowly (0.54 at 3% tip clearance to 0.58 at 5% tip clearance). The mass averaged flow angle decreases from 66.3° at zero clearance to 63.7° at 1% clearance to 60.1° at 3% clearance and to 57.3° at 5% clearance.