Large Radius Of Curvature Research Articles

Effects of surface curvature on rain erosion of wind turbine blades under high-velocity impact

Rain erosion induced by raindrops impacting wind turbine blades at high velocity can change the aerodynamic characteristics of the blades and increase maintenance costs. Previous numerical studies on rain erosion have not considered the curvature of the blade leading-edge surfaces and assumed them to be flat surfaces. This study established a fluid-solid coupled numerical model combining the finite element method and smooth particle hydrodynamics. It models a water droplet with a diameter of 2.74 mm impacting the curved leading-edge surface of wind turbine blades with radii of curvature of 1.35 mm, 6.75 mm, 67.5 mm, and infinite at 110 m/s, and the effects of the radius of curvature on the impact response were analyzed. The results show that as the radius of curvature of the leading-edge surface increases, the surface obstructs the water droplet more significantly, and the lateral jetting of the water droplet is enhanced. A larger radius of curvature causes more droplet impact energy to be transferred to the curved surface, increasing the contact force between the water droplet and the surface. The increased transferred impact energy results in higher stress and plastic strain values. The decrease in the radius of curvature of a curved surface increases the error in the stress and strain results obtained by assuming it to be a flat surface.

Assessment of crack suppression in glass/epoxy curved laminates by incorporating micro and nanofillers

AbstractThe design of structures with a large radius of curvature is challenging because fiber‐reinforced composite materials have low resistance to delamination in the direction perpendicular to their thickness. These structures are commonly found in a wide variety of structural components that are used in the wind turbine and aviation industries. The objective of this study is to conduct an experimental investigation into the efficacy of incorporating milled glass fiber, cellulose nanoparticles, and carbon nanoparticles as fillers into an epoxy matrix to improve the resistance to delamination of glass/epoxy curved laminates and thereby inhibit crack growth. In contrast to the baseline samples, curved samples containing 3% cellulose nanoparticles demonstrated enhanced curved beam strength and interlaminar tensile strength by 4.95% and 3.82%, respectively. Additionally, filler‐loaded samples exhibited reduced delamination and fracture propagation damage compared with baseline samples. The adhesion between the epoxy matrix and infill was investigated by means of Fourier transform infrared analysis. In addition, live photographic images and fractured micrographs were correlated with mechanical findings in order to assess delamination suppression and damage processes in both the arm and arc directions.

Effect of Heating Surface Geometry on the Droplets Evaporation under Leidenfrost Conditions

Physical and geometric factors are generally regarded as the main cause of evaporation characteristics of the Leidenfrost droplets levitating above the hot surface. It is well-known and generally accepted that similar research is conducted under different conditions and on individual measurement set-ups. This is one of the potential reasons for the differences in the results of thermal fluxes and computational models in scientific papers. This paper discusses the influence of the heating surface geometry on the heat transfer coefficient h during water drops evaporation under film boiling regime. The variable geometry parameters are the curvature radius of the heating bowl of R = 64 and 254 mm. Individually compiled test stands made it possible to measure the instantaneous drop mass for each R radius and to determine the coefficient h. The methodology was validated by calculating the relative error. It changes with the curvature radius and the droplet size, and for droplet mass from about 2 g to 0.3 g does not exceed ±10%. The heat transfer coefficient h is about 15% higher for a drop located on a surface with a larger radius of curvature. Moreover, the method that was devised allows us to estimate the h value for asymmetric droplet shapes. The advantage of the adopted method of measuring the drop mass over time is the possibility of analyzing heat transfer processes in any drop shape range, even in the case of asymmetric ones. Previous research methods were mainly based on determining the mass of the drop by calculating its volume.

Dynamic propagation velocity of a positive streamer in a 3 m air gap under lightning impulse voltage

Streamers represent an important stage in the initiation of gap discharge. In this work, we used an eight-frame intensified charge-coupled device camera to capture the streamer development process when a lightning impulse voltage of 95%–100% U 50% was applied in a 3 m rod–plate gap and the streamer velocity was analyzed. Analysis of the observations shows that streamer velocity can be defined by three stages: rapid velocity decline (stage 1), rapid velocity rise (stage 2) and slow velocity decline (stage 3). The effects of electrode shape, applied voltage and gap breakdown or withstanding on streamer velocity were analyzed. The electrode with a larger radius of curvature will result in a higher initial velocity, and a higher voltage amplitude will cause the streamer to propagate faster at stage 3. Gap withstanding or breakdown has no obvious effect on streamer velocity. In addition, the experimental results are compared with previous results and the statistical characteristics of the primary streamer discharge are discussed.

Tessellated fundus occurs earlier than myopia in children aged 3-6 years.

Tessellated fundus can exist in normal healthy eyes. This study aims to evaluate the occurrence and influencing factors of tessellated fundus in preschool children aged 3-6 years. This kindergarten-based cross-sectional study included 1716 children with an age range of 3-6 years. All participants underwent a comprehensive eye examination and a questionnaire. According to the number of quadrants occupied by tessellated fundus around the optic disc in fundus photographs, it was divided into four grades. 600 (35.0%) children had peripapillary tessellation. According to the spherical equivalent (SE), the subjects were divided into three groups: Hyperopia group (SE > + 0.75D, n = 1194)；Pre-myopia group (-0.50D < SE ≤ + 0.75D, n = 455); Myopia group (SE ≤ -0.50D, n = 67). The proportion of peripapillary tessellated fundus was 33.0%, 38.0%, 50.7% respectively. According to the regression analysis, in the non-myopia group (Pre-myopia group and Hyperopia group), the occurrence of peripapillary tessellated fundus was associated with longer axial length (OR, 1.566; 95% CI: 1.229-1.996, p < 0.001) and larger corneal radius of curvature (OR, 1.837; 95% CI: 1.006-3.354, p = 0.048). However, in Pre-myopia group, the corneal radius of curvature was not associated with the occurrence of peripapillary tessellated fundus (p = 0.830). In Hyperopia group, the corneal radius of curvature was associated with the occurrence of peripapillary tessellated fundus (OR, 2.438; 95% CI: 1.160-5.122, p = 0.019). The occurrence of peripapillary tessellated fundus is more than 30% in 3-6 year old preschool children. Tessellated fundus can also occur in non-myopic children, and is related to the length of axial length and large radius of corneal curvature.

Indentation stress–strain analysis and finite element simulation to determine elastoplastic properties of thin films decreasing the substrate contribution

AbstractThe mechanical performance of protective coatings is crucial in daily industrial environments, with transition metal nitrides being among the most commonly used hard coatings for machining tool protection. However, determining their elastoplastic properties via conventional methods can be challenging due to the thickness‐dependent response of film/substrate systems. In this study, we utilised two sputtering Ti‐Al‐N films as a model hard thin film/soft substrate system to showcase an alternative methodology to the Oliver and Pharr method. This alternative approach involves determining Young's modulus, yield stress and hardness through indentation stress–strain curves obtained from nanoindentation tests, effectively decreasing the substrate's contribution. This decrease was corroborated by finite element simulations conducted on films with thickness below 1.0 μm. The elastoplastic properties determined using our methodology fell within the range reported for typical Ti‐Al‐N films. Furthermore, by applying our methodology, we were able to correlate and discuss the observed differences in mechanical behaviour between the two films based solely on their microstructural, compositional and morphological properties. Thus, we have demonstrated a viable alternative methodology to address substrate contribution challenges in the mechanical characterisation of thin film/substrate systems when employing an indenter with a large radius of curvature (~650 nm). This research holds potential implications for the design of protective submicrometric films with industrial applications.

Mechanical Influence of Edentulous Mandibular Morphology on Peri-implant Bone in Implant Prosthetics: Threedimensional Finite Element Analysis.

The purpose of this study was to examine the mechanical influence of edentulous mandibular morphology on peri-implant bone in implant prosthetics by finite element analysis. Computed tomographic data from 25 patients with edentulous mandibles were selected and the radius of mandibular curvature and the height of the mandible at the midline were measured in order to clarify the morphological characteristics of the mandible. From the measurement, two patients with the smallest and largest radii of the mandible were selected. Two types of three-dimensional finite element models consisting of the edentulous mandible (small and large radius), superstructure (a cantilever bridge), implants, and abutments were created. Four implants were inserted between the right and left mental foramina. The upper surface of the mandibular condyle was constrained, and a vertical load of 100 N was applied on the occlusal surface of the right first molar. Three-dimensional finite element analysis of each model was performed to examine the mechanical influence of the edentulous mandibular morphology on the peri-implant bone. Measurement of mandibular morphology in CT images indicated that the lower the mandibular height was, the larger was the radius of the anterior mandibular curvature. Finite element analysis revealed that a higher equivalent stress was generated in the peri-implant bone of the model with a larger radius of curvature than that of the model with a smaller radius of curvature. The highest equivalent stress in the mandible was generated in the distal margin of the peri-implant bone posterior to the loaded side of the large radius of curvature model. The mandibular morphology had a mechanical influence on the peri-implant bone.

EQUILIBRIUM OF A NORMALLY LOADED ELASTIC SHALLOW CYLINDRICAL SHELL WITH DISLOCATIONS AND DISCLINATIONS

We consider the problem of the equilibrium of a normally loaded elastic shallow rectangular circular cylindrical shell, which contains sources of internal stress in the form of fields of continuously distributed edge dislocations and wedge disclinations or other sources, for example, thermal ones. Based on the modified system of Karman equations for the equilibrium of an elastic plate with dislocations and disclinations, a system of nonlinear equilibrium equations for the shell was constructed. The resulting system of equations differs from the Karman system of equilibrium equations for an elastic shallow cylindrical shell under the action of a normal load by the presence on the right side of the continuity equation of a nonzero function, called the incompatibility function, which is expressed through the densities of edge dislocations and wedge disclinations. The edges of the shell are freely clamped or hinged. In the absence of internal stress sources, this system transforms into a system of equilibrium equations for a shallow shell, and in the case of an infinitely large radius of curvature (and the presence of internal stress sources) into a modified system of Karman equilibrium equations for a flexible elastic plate with dislocations and disclinations. To solve the system of nonlinear shell equilibrium equations, the Newton – Kantorovich method in combination with the difference method is proposed. For the case of small values of the normal load and small values of the incompatibility function, linearization is carried out with respect to the deflection and stress function. As a result, a linear boundary value problem was obtained in the form of a system of differential equations for the deflection and the stress function, which is solved by the difference method. The solution of the linearized system is used as an initial approximation in the implementation of the Newton – Kantorovich method. Examples of numerical calculations of deflection and stress function for given values of normal load and incompatibility function are given, and corresponding graphs are constructed.

Efficiency of orbital atherectomy for eccentric calcium in bending vessels: in-vitro vessel models

Abstract Background/Introduction The mode of action of orbital atherectomy (OA) consists of a fast elliptical rotation of the crown, allowing for focal treatment with slow forward and backward movements. However, reports on the efficiency of OA for eccentric calcium in bending vessels are limited. Purpose This study aimed to clarify the mechanism of action of the crown and elucidate the anatomical condition for an efficient OA on eccentric calcium in bending lesions, via in vitro experimental models. Methods In total, 40 in vitro stenotic vessel models with eccentric calcium were developed; five models with a combination of two calcium positions (inner or outer side bending), two curvature radiuses (R, 10 or 20 mm), and two bending angles (A, 100º or 60º). Each model was connected to a whole aorta model and the procedures were performed using the Diamondback 360 coronary OA system through a 6F short-tip amplatz 1.0 guiding catheter. The protocol included two 30-second low-speed ablations followed by one 30-second high-speed ablation. Micro-computed tomography analyses of the models were performed before and after ablation to evaluate the ablated calcium volume and maximum depth. Results Eccentric calcium at inner side of the bending was more ablated than at outer side (6.6 mm3 vs 2.7 mm3, P &amp;lt; 0.0001). Among the inner side, the ablated calcium volume was higher in the R20/A60 model (8.28 mm3) than in R10/A100 (6.30 mm3; P = 0.14), R10/A60 (5.62 mm3, P = 0.04), and R20/A100 (6.06 mm3, P = 0.09) models (Figure 1A). The ablated maximum depth was also higher in the R20/A60 model (0.98 mm) than in other models (R10/A100: 0.84 mm, R10/A60: 0.90 mm, R20/A100: 0.78 mm); however, there were no significant differences. Moreover, among the outer side, the ablated calcium volume was higher in the R20/A100 model (5.17 mm3) than in the R10/A100 (1.95 mm3, P &amp;lt; 0.001), R10/A60 (2.12 mm3, P = 0.002), and R20/A60 (1.73 mm3, P &amp;lt; 0.001) models (Figure 1B). The ablated maximum depth was also significantly higher in the R20/A100 model (0.47 mm) than in other models (R10/A100: 0.32 mm, P = 0.03; R10/A60: 0.33 mm, P = 0.05; R20/A60: 0.27 mm, P = 0.01). Conclusions Curvature radius and bending angles could be associated with efficiency of OA for eccentric calcium in bending vessels. Although small curvature radiuses may be unsuitable for OA in the inner or outer side, it may be effective for inner side lesions with a large curvature radius and low bending angles, and outer side lesions with a large curvature radius and high bending angles.

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.

Near-extinction transient behaviors of counterflow nonpremixed flames in a porous spherical burner at very low stretch rate

Near extinction transient behaviors of CH4/N2 versus O2/N2 counterflow nonpremixed flames were investigated by adopting a porous spherical burner with a large radius of curvature to achieve a very low buoyant stretch rate. By varying the oxygen concentrations in the oxidizer stream, four regimes were identified by three limits of sooting, instability, and extinction. The sooting limit was sensitive to flame temperature, and was characterized by two indexes of fuel injection velocity uF and oxygen concentration XO2. When decreasing uF, the sooting limit was different from high stretch flames because of appreciable heat loss toward the burner surface. In the instability regime, periodic holes were observed whose frequency decreased with XO2. Periodic holes were also found to occur with N2 dilution in the fuel stream, which were more regular with larger frequencies compared with the periodic holes in the diluted oxidizer streams. The edge propagation behaviors for periodic holes in diluted fuel streams were analyzed. The statistical average of the propagation speed of advancing edge (hole closing) Se decreased with increasing fuel concentration gradient, and the ratio of Se with the stoichiometric laminar burning velocity SLst of Se/SLst was larger than unity. Also, the stretch rate significantly affected the propagation speed of advancing edge flames. Determination of the propagation speed of the retreating edge (hole opening) had intrinsic difficulty in estimating the transient radial flow velocity, however, the approximated |Se/SLst| was larger than unity and decreased with the fuel mole fraction. Nitrogen dilution in the oxidizer stream was proven to be more effective than in the fuel stream for flame suppression of methane. This study could enrich the understanding of very low-stretch nonpremixed flames in a counterflow burner and provide information regarding low-stretch flame suppression, which may be relevant to microgravity flame behaviors.

Measurement of Near-Field Radiative Heat Transfer at Deep Sub-Wavelength Distances using Nanomechanical Resonators.

Near-field radiative heat transfer (NFRHT) measurements often rely on custom microdevices that can be difficult to reproduce after their original demonstration. Here we study NFRHT using plain silicon nitride (SiN) membrane nanomechanical resonators─a widely available substrate used in applications such as electron microscopy and optomechanics─and on which other materials can easily be deposited. We report measurements down to a minimal distance of 180 nm between a large radius of curvature (15.5 mm) glass radiator and a SiN membrane resonator. At such deep sub-wavelength distance, heat transfer is dominated by surface polariton resonances over a (0.25 mm)2 effective area, which is comparable to plane-plane experiments employing custom microfabricated devices. We also discuss how measurements using nanomechanical resonators create opportunities for simultaneously measuring near-field radiative heat transfer and thermal radiation forces (e.g., thermal corrections to Casimir forces).

Relationship between Corona Discharge Thrust and Applied Voltage’s Polarity

The thrust from corona discharge might be a promising propulsion technology in future aviation due to its advantage of not requiring mechanical moving parts. Although the thrust from corona discharge has been researched by many scholars, the effect of the applied voltage’s polarity on the thrust has received little attention. This polarity effect might be very important for some special electrohydrodynamic thrusters. This paper firstly built a test platform to reveal the effect of the applied voltage’s polarity on both the thrust and the corona current from a pair of symmetrically distributed needle electrodes. Then the applied voltage’s polarity on the electrical field distribution between a pair of needle-plate electrodes was simulated. Finally, the relationship between the space ions at the tip of the needle electrode and the thrust are discussed. The results show that a negative needle electrode with a smaller curvature radius has a stronger thrust than a positive one with a larger curvature radius, and a stronger thrust corresponds to a higher corona current. The local electric field is enhanced by the space ions at the tip of a negative needle electrode, while it is weakened by a positive needle electrode. This results in the polarity of thrust.

Flowrate effects on the lateral coalescence of two growing bubbles

AbstractThe coalescence of two growing bubbles presents unique characteristics compared to static bubble coalescence. The gas injection flowrate significantly affects the different stages of bubble evolution, which is poorly understood. In this study, we investigate the flowrate effects on the lateral coalescence of two growing bubbles experimentally. The synchronous bubbling from adjacent needles is achieved using water to push air. During the bubble growth process, we find that the initial nonlinear evolution of bubble volume is because the bubble emerges as a small spherical cap with a large curvature radius and apparent contact angle. As the neck expands after bubble coalescence, the injection flowrate accelerates the neck evolution compared to the case without air injection. We find the neck expansion time decreases linearly with increasing flowrate, while the expansion speed increases with flowrate, but only in the early stage. Moreover, we propose a new theoretical expression that predicts the neck radius well at all the flowrates. At the post‐coalescence oscillation stage, the average projection area of the coalesced bubble increases linearly with time, except for periodic oscillations. Besides, we find that the injected air primarily influences the coalesced bubble's height, which in turn affects the projection area.

Effect of Wettability on the Collision Behavior of Acoustically Excited Droplets.

Acoustic droplet ejection (ADE) is a noncontact technique for micro-liquid handling (usually nanoliters or picoliters) that is not restricted by nozzles and enables high-throughput liquid dispensing without sacrificing precision. It is widely regarded as the most advanced solution for liquid handling in large-scale drug screening. Stable coalescence of the acoustically excited droplets on the target substrate is a fundamental requirement during the application of the ADE system. However, it is challenging to investigate the collision behavior of nanoliter droplets flying upward during the ADE. In particular, the dependence of the droplet's collision behavior on substrate wettability and droplet velocity has yet to be thoroughly analyzed. In this paper, the kinetic processes of binary droplet collisions were investigated experimentally for different wettability substrate surfaces. Four states occur as the droplet collision velocity increases: coalescence after minor deformation, complete rebound, coalescence during rebound, and direct coalescence. For the hydrophilic substrate, there are wider ranges of Weber number (We) and Reynolds number (Re) in the complete rebound state. And with the decrease of the substrate wettability, the critical Weber and Reynolds numbers for the coalescence during rebound and the direct coalescence decrease. It is further revealed that the hydrophilic substrate is susceptible to droplet rebound because the sessile droplet has a larger radius of curvature and the viscous energy dissipation is greater. Besides, the prediction model of the maximum spreading diameter was established by modifying the droplet morphology in the complete rebound state. It is found that, under the same Weber and Reynolds numbers, droplet collisions on the hydrophilic substrate achieve a smaller maximum spreading coefficient and greater viscous energy dissipation, so the hydrophilic substrate is prone to droplet bounce.

Improved fibre placement in filament-based 3D printing of continuous carbon fibre reinforced thermoplastic composites

This study investigates the mechanism of fibre deposition in conventional 3D printing and presents an aligned fibre deposition (AFD) method to improve the fibre placement. The deposition mechanism reveals that the cracking of the filament in the transition zone and the torsional deformation during the steering path are the main cause of the defects in the conventional printing process. The AFD method is shown to reduce and mitigate the fibre waviness and twisting, hence producing smooth filament deformation, introducing less air voids and fibre breakage during printing. It is found that the AFD method improves the fibre alignment angle from ±25° to ±12° and reduces the void content to 0.27 % during straight-line deposition. During curved-line printing at a large radius of curvature, tow shearing instead of fibre folding is produced by AFD method, resulting in smooth edges with less fibre breakage.

Paper-Based Bi-Material Cantilever Actuator Bending Behavior and Modeling.

In this paper, the behavior of the Bi-Material Cantilever (B-MaC) response deflection upon fluidic loading was experimentally studied and modeled for bilayer strips. A B-MaC consists of a strip of paper adhered to a strip of tape. When fluid is introduced, the paper expands while the tape does not, which causes the structure to bend due to strain mismatch, similar to the thermal loading of bi-metal thermostats. The main novelty of the paper-based bilayer cantilevers is the mechanical properties of two different types of material layers, a top layer of sensing paper and a bottom layer of actuating tape, to create a structure that can respond to moisture changes. When the sensing layer absorbs moisture, it causes the bilayer cantilever to bend or curl due to the differential swelling between the two layers. The portion of the paper strip that gets wet forms an arc, and as the fluid advances and fully wets the B-MaC, the entire B-MaC assumes the shape of the initial arc. This study showed that paper with higher hygroscopic expansion forms an arc with a smaller radius of curvature, whereas thicker tape with a higher Young's modulus forms an arc with a larger radius of curvature. The results showed that the theoretical modeling could accurately predict the behavior of the bilayer strips. The significance of paper-based bilayer cantilevers lies in their potential applications in various fields, such as biomedicine, and environmental monitoring. In summary, the novelty and significance of paper-based bilayer cantilevers lie in their unique combination of sensing and actuating capabilities using a low-cost and environmentally friendly material.

The theory on thing's limits. Part 2: A brief analysis of the new knowledge of Newton's first law

According to the norm of identifying truth in this theory, and Newton's first law which is a basis that can look at the overall situation, and by virtue of the electron storage ring as an experimental fact, it is pointed out: Only in reality can there be inertia. Inertia represents the continuity of the development of thing. As the speed gradually approaches to the c, the particle's mass also approaches to zero along with its static mass due to the impact of electromagnetic radiation, which is exactly the root where the energy shrinkage effect of high-speed particles comes from, and also the primary factor causing the spectrum redshift. Therefore, the Big Bang theory is wrong. All photons are produced from the high-density particles through electromagnetic radiations. Wherever there is fluctuation, there must be mass, and vice versa. This is the correct understanding of "wave-particle duality". No matter the high-speed electrons or the photons produced by them all have different static masses, but their charge-mass ratio is always the same physical constant, and not affected by relativistic effects and electromagnetic radiations. This is the true internal mechanism to constitute the uncertainty principle, and conforms to the experimental facts related to it. It can be proved that in a constant magnetic field, the high-speed electron or photon of having a relatively large curvature radius, which has a high moving speed and less mass, energy and wave frequency. Since Einstein used the absolute space-time established by Newton as the criterion and came to the conclusion that the relative space-time was curved, then he should no longer make circular arguments, that was, used the relative space-time as the criterion, to change the unit length and time established by the absolute space-time.

Numerical simulation of the transient graphite oxidation process based on a dynamic mesh method

The high-temperature gas-cooled reactor uses graphite-matrix spherical fuel elements to coat the tri-structural isotropic fuel particles (TRISO). In accident conditions, graphite oxidation may cause fuel particle exposure, which further leads to severe radioactive contamination. Therefore, it is very important to study the oxidation behavior of graphite during air-ingress accidents. This work aimed to develop a reaction kinetic model of graphite oxidation based on the Institute of Nuclear and New Energy Technology (INET) experiment correlations and to study the transient process of graphite oxidation using computational fluid dynamics and a dynamic mesh method. The results show that convective diffusion and mass diffusion dominate the distribution of reaction products at different flow rates. The reaction rate in the early stage of oxidation was high and then decreased rapidly until the oxygen consumption rate and supplementation rate reached equilibrium. After that, the oxidation rate decreased slowly due to the reduction of graphite surface area. The fluctuating flow around the graphite leads to anisotropic oxygen concentrations at different inflow angles on the graphite surface. The fluctuations caused a non-uniform ellipsoidal graphite structure, in which graphite has a smaller radius of curvature and pits on the windward side and a larger radius of curvature on the leeward side. The oxidation mass of graphite is in good agreement with the INET experimental data, which shows that this study can provide a method for the estimation of the mass and shape of graphite oxidation.

An Accurate and Numerically Stable Formulation for Computing the Electromagnetic Fields in Uniform Bend Rectangular Waveguides

This article describes a numerically stable formulation for the analysis of electromagnetic fields in rectangular cross section waveguides with a curved longitudinal axis. A novel set of scaled Hankel functions for real-valued arguments and complex-valued orders is introduced for rescaling the characteristic equations associated with the transverse electric (TE) and magnetic (TM) fields of the exact boundary value problem. The exponentially scaled cylindrical functions presented here prevent numerical underflow and overflow errors associated with large real and large imaginary orders without sacrificing accuracy. The proposed methodology is validated against variable-precision arithmetic (VPA) results. Numerical results are also presented for waveguides with large radii of curvature, where the present methodology is compared with perturbation ones in several examples. Dielectric-filled waveguides with small radii of curvature are investigated, and our solutions are compared with finite-integration technique (FIT) results.