Deteriorated Heat Transfer Influence On the Stress-Strain State of SMR SCWR Fuel Bundles

The analysis of deteriorated heat transfer (DHT) influence on the stress-strain state of a perspective core of Small Modular Reactors with Supercritical Water (SMR SCWR) fuel assemblies is carried out, based on experimental and numerical data. Experimental data for 3- and 7-rod assemblies of 600 mm height with twisting spacer screws, on which deterioration heat transfer regimes were observed. The analysis of the stress-strain state was performed for two cases of temperature field. In the first variant, the temperature field is estimated using Computational Fluid Dynamics (CFD) with low-Re effects accounting, which allows obtaining the maximum temperature, but incorrectly estimates the axial profile. In the second case, an experimental profile with an averaged tangential temperature value is considered. Strength analysis is performed using the developed numerical-analytical mechanical model of the rod assembly. Obtained results make it possible to establish what is more important for assessing the safety of perspective reactors: a conservative estimate of the maximum wall temperature or its local distribution.

Reassessment of Computational Tools for the Modelling of Heat Transfer in a Molten UO2 Pool in Natural Convection

This work, performed within the ESFR-SMART H2020 European project, is part of a larger framework intending to reassess the modelling of heat transfer in molten pools on SCARABEE available experimental results. This paper presents simulation results of the in-pile BF1 test, performed within the SCARABEE program, using ASTEC, SIMMER III and SIMMER V simulation tools as well as comparison with its available experimental data. This program was performed in the 80's in the frame of the Safety Assessment studies of Superphenix sodium-cooled reactor. This test was dedicated to verify the stability of a molten UO2 pool under decay heat conditions within natural convection and the long-term resilience of the peripheral fuel crust. The pool was generated in a stainless steel crucible by a progressive heating (six power plateaus) of a fuel pellet stack. For the benchmark purposes, only the molten pool behavior at the last power plateau (largest pool and highest fuel temperatures) was investigated. Experimental data such as the axial profile of radial heat fluxes and heat transfer from the pool to the surrounding inter-assembly coolant or the peripheral fuel crust thickness were used for the reassessment of the simulation tools. In addition, other variables of interest not measured during the test, such as the radial and axial velocities in the pool, were also benchmarked. Finally, a critical analysis of the correlations and models used in the simulation tools for the BF1 test modelling is also provided in the paper.

CW Direct Detection Lidar with a Large Dynamic Range of Wind Speed Sensing in a Remote and Spatially Confined Volume

A novel continuous-wave (CW) direct detection lidar (DDL) is demonstrated to be capable of wind speed measurement 40 m away with an update rate of 4 Hz using a fiber-based scanning Fabry–Perot interferometer as an optical frequency discriminator. The proposed CW DDL has a large dynamic wind speed range with no sign ambiguity and its sensitivity is assessed by comparing its performance with that of a CW coherent detection lidar (CDL) in a side-by-side wind measurement. A theoretical model of the spatial weighting function of the fiber-based CW DDL is also presented and validated experimentally. This work shows that the CW DDL has a spatially confined measurement volume with a Lorentzian axial profile similar to that of a CW CDL. The proposed DDL has potential use in various applications in which requirements such as high-speed wind sensing and directional discrimination are not met by state-of-the-art Doppler wind lidar systems.

Hob cutter shaping for internal straight thread

Резьба используется во многих механизмах и достаточно часто для разъемных соединений деталей судовых машин. Для повышения долговечности внутренней цилиндрической резьбы и производительности процесса ее нарезания предлагается новая методика «профилирования червячной фрезы для нарезания внутренней цилиндрической резьбы методом огибания. В данной статье приведено аналитическое определение сопряженных профилей цилиндрической внутренней резьбы и инструмента. Рассматривается метод профильных нормалей для профилирования червячной фрезы при нарезании внутренней резьбы способом огибания, основанный на применении теории матриц. Червячная фреза в осевом сечении имеет конкретный криволинейный профиль, для его получения необходимо знать расчетные зависимости торцового профиля резьбы, и уравнения ее винтовой поверхности и осевого профиля. Для возможности образования витков резьбы необходимы определенные зависимости скорости резанья фрезы и резьбы, а для формирования внутренней резьбы - ее поверхность должна набегать на зубья червячной фрезы. Эти задачи решены с помощью разработанной системы уравнений для изготовления фрез при нарезании внутренней цилиндрической резьбы способом огибания методом профильных нормалей. Расчетный механизм профилирования инструмента - фрезы для нарезания цилиндрических внутренних резьб – может применяться для формообразования конических внутренних резьб. Threads are used in many mechanisms and frequently in detached connections of marine engines elements. The new technique of hob cutter shaping for internal straight thread is proposed in order to increase durability of the internal cylindrical thread and to improve its cutting performance process. The article gives analytical definition of conjugate profiles of internal straight thread and of a tool. It also deals with the method of profile normals for shaping hob cutter whilst cutting the internal thread by enveloping. The method applies the matrix theory. There is some curved profile in the hob cutter axial section. In order to obtain that profile, it is necessary to know the calculated dependence of a thread transverse profile and its helical surface and axial profile equation. Special dependences of thread speed range and cutting are required to produce turns of the thread. To form internal thread – its surface is to slide on cutter teeth. All the mentioned tasks can be solved by the system of equations for cutters manufacture with cutting internal straight thread applying enveloping with the method of profiles normals. The calculation mechanism for shaping the tool – the hob cutter for internal straight threads – can be used for making internal taper threads.

Modelling and experiment of gear hob tooth profile error for relief grinding

Gear hob is an important tool that is most used in gear processing. Hob accuracy directly exerts an overwhelming influence on the quality of the processed gear. Generally, the hob tooth profile accuracy is mainly determined by relief grinding process. Studies on tooth profile errors of gear hobs caused by severe friction and cutting with the high-speed rotation of the wheel during the form grinding machining of hobs are limited. Thus, a theoretical model of the tooth profile error prediction under different machining parameters was established based on the analysis of coupling influence of high temperature and high strain rate on gear hobs in the relief grinding process. The model was completed on the basis of the dynamic explicit integral finite element method of thermo-mechanical coupling. Through the prediction model, the influence of the grinding depth ap, feed speed Vw and grinding speed Vs on the tooth profile error can be analysed. In addition, an algorithm for accurately calculate the grinding wheel axial profile by combining instantaneous envelope theory and hob normal tooth profile was proposed. The hob relief grinding experiments were carried out using the proposed grinding wheel profile algorithm. The relative error of the prediction obtained by comparing the calculation results of the prediction model with the experimental results is within 10%. Results prove the validity of the prediction model. This finding is greatly important for optimising the accuracy of hob relief grinding.

3D Reconstruction of the Morpho-Functional Topography of the Human Vagal Trigone

The Vagal Trigone, often referred to as Ala Cinerea, is a triangular-shaped area of the floor of the fourth ventricle that is strictly involved in the network of chardiochronotropic, baroceptive, respiratory, and gastrointestinal control systems of the medulla oblongata. While it is frequently identified as the superficial landmark for the underlying Dorsal Motor Nucleus of the Vagus, this correspondence is not univocal in anatomical literature and is often oversimplified in neuroanatomy textbooks and neurosurgical atlases. As the structure represents an important landmark for neurosurgical procedures involving the floor of the fourth ventricle, accurate morphological characterization is required to avoid unwanted side effects (e.g., bradychardia, hypertension) during neuorphysiological monitoring and cranial nerve nuclei stimulation in intraoperative settings. The aim of this study was to address the anatomo-topographical relationships of the Vagal Trigone with the underlying nuclei. For this purpose, we have conducted an anatomo-microscopical examination of serial sections deriving from 54 Human Brainstems followed by 3D reconstruction and rendering of the specimens. Our findings indicate that the Vagal Trigone corresponds only partially with the Dorsal Motor Nucleus of the Vagus, while most of its axial profile is occupied by the dorsal regions of the Solitary Tract Nucleus. Furthermore, basing on literature and our findings we speculate that the neuroblasts of the Dorsal Motor Nucleus of the Vagus undergo neurobiotaxic migration induced by the neuroblasts of the dorsolaterally located solitary tract nucleus, giving rise to the Ala Cinerea, a topographically defined area for parasympathetic visceral control.

The geometric axial surface profiles of granular flows in rotating drums

SYNOPSIS A mechanistic description of axial segregation in rotating drum flows remains an open question. Consequently, optimal mixing of grinding balls and rocks for efficient breakage, maximum production of fines, and slurry transport is seldom achieved. Experimental and numerical studies of granular mixtures in rotating drums identify alternating axial bands that eventually coarsen in the long-term limit. Most models of axial segregation are limited to binary mixtures and cannot always predict the logarithmic coarsening effects observed experimentally. A key missing factor is a robust description of the axial free surface profile that is valid across a wide range of flow regimes. We present a practical model of the axial free surface profile by linking it to readily-derived geometric features of the cross-sectional S-shaped free surface profile. A parametric study shows good agreement with experimental measurements reported in the literature and heuristically valid trends. Keywords: rotating drum, granular flow, axial profile, comminution, mixing, segregation.

Design and Performance of a Curvilinear Circular-Arc Tooth Gear for Gear Pump Applications

The most common gear architecture used in external gear pumps is the spur gear with an involute tooth profile. The involute spur gear has many benefits, such as a constant line of action, tolerance to parallel misalignment, and ease of fabrication. However, the involute spur gear has two major drawbacks in pump applications: the tooth profile results in trapped pockets of fluid that contribute to pressure spikes and noise generation, and the straight axial profile further increases noise due to intermittent tooth shock during meshing. Current state-of-the-art pumps utilize helical gears to enable a gradual mesh to reduce noise and pressure pulsation, which results in an axial load induced on the gears during meshing. A novel gear design has been developed that eliminates axial gear loading while preserving a gradual mesh. A hybrid tooth profile eliminates the trapped fluid pocket while maintaining the benefits of an involute profile. Initial testing demonstrates an increase in volumetric efficiency by 10% and a reduction of sound level by 7 dB compared to a spur gear of the same size.