Modeling of solidification of MMC composites during gravity casting process

The paper deals with computer simulation of gravity casting of the metal matrix composites reinforced with ceramics (MMC) into sand mold. The subject of our interest is aluminum matrix composite (AlMMC) reinforced with ceramic particles i.e. silicon carbide SiC and glass carbon Cg. The created model describes the process taking into account solidification and its influence on the distribution of reinforcement particles. The computer calculation has been carried out in 2D system with the use of Navier-Stokes equations using ANSYS FLUENT 13. The Volume of Fluid approach (VOF) and enthalpy method have been used to model the air-fluid free surface (and also volume fraction of particular continuous phases) and the solidification of the cast, respectively

Automated mesh production for limiter Wendelstein-7X configuration

A tool for automated mesh production for 3D multifluid plasma transport code Findif is presented. Mesh points for the code lie on magnetic field lines, which, in general, form a complicated tangle. Open field lines that end on solid parts of the machine are the source of difficulties. These lines are usually short and thousands of them are needed. A tool that helps to pick lines for the mesh that is described in this paper is based on calculation the distances of lines already admitted to the mesh and candidate ones. The results of the code run for the limiter configuration (OP-1.1 experimental phase) of the Wendelstein-7X device are shown here. Reasonably even coverage of space by points is achieved.Представлен трёхмерный код Findif для переноса многожидкостной модели плазмы как инструмент автоматизированного производства сетки. Сетка точек для кода лежит на магнитных силовых линиях, которые, вообще говоря, образуют сложную конфигурацию. Открытые силовые линии, которые ограничены твёрдыми частями механизма, являются источником сложностей. Эти линии, как правило, короткие, и нужны тысячи из них. Инструмент, который помогает подобрать линии для сетки, описан в этой статье и основан на вычислении расстояния линий уже допущенных к сетке и кандидатов из них. Представлены результаты прогона кода для конфигурации лимитера (OP-1.1 экспериментальная фаза) стелларатора Wendelstein-7X.Представлено тривимірний код Findif для перенесення багаторідинної моделі плазми як інструмент автоматизованого виробництва сітки. Сітка точок для коду лежить на магнітних силових лініях, які, взагалі кажучи, утворюють складну конфігурацію. Відкриті силові лінії, що обмежені твердими частинами механізма, є джерелом труднощів. Ці лінії, як правило, короткі, і потрібні тисячі з них. Інструмент, який допомагає підібрати лінії для сітки, описаний в цій статті і заснований на обчисленні відстані ліній вже допущених до сітки і кандидатів з них. Представлено результати прогону коду для конфігурації лимитера (OP-1.1 експериментальна фаза) стеларатора Wendelstein-7X

High power neon seeded JET discharges: Experiments and simulations

A series of neon seeded JET ELMy H-mode pulses is considered from the modeling as well as from the experimental point of view. For two different Ne seeding rates and two different D puffing gas levels the heating power, P heat , is in the range 22–29.5 MW. The main focus is on the numerical reconstruction of the total radiated power (which mostly depends on the W concentration) and its distribution between core and divertor and of Z eff(which mostly depends on the Ne concentration). To model self-consistently the core and the SOL two input parameters had to be adjusted case by case: the SOL diffusivity, D SOL , and the core impurity inward pinch, v pinch . D SOL had to be increased with increasing Ne and the level of v pinch had to be changed, for any given Ne , according to the level of P heat : it decreases with increasing P heat . Since the ELM frequency, f ELM , is experimentally correlated with P heat , (it increases with P heat ) the impurity inward pinch can be seen as to depend on f ELM . Therefore, to maintain a low v pinch level (i.e. high f ELM ) Ne / P heat should not exceed a certain threshold, which slightly increases with the D puffing rate. This might lead to a limitation in the viability of reducing the target heat load by Ne seeding at moderate D , while keeping Z effat acceptably low level.EURATOM 63305

Findif code simulations of OP-1.1 Wendelstein 7-X discharges

The current development state of the finite difference, multi-fluid, 3D plasma code Findif is detailed. The code was run on four meshes prepared for the OP-1.1 wall geometry of the Wendelstein 7-X stellarator. The meshes were produced for 4 magnetic configurations; two of them are finite-beta (non vacuum). The simulated volume covers plasma edge; the computations of limiter heat load distributions were the main goal. Plasma radiation was not taken into account.Докладно наведено поточну стадію розробки кінцево-різницевого тривимірного коду Findif для багаторідинної моделі плазми. Код було запущено на чотирьох сітках, підготовлених для геометрії стінки OP-1.1 стеларатора Wendelstein 7-X. Сітки згенеровано для 4-х магнітних конфігурацій, дві з яких – зі скінченним бета (не вакуум). Змодельований об’єм охоплює край плазми; основна мета полягає в розрахунках розподілів теплових навантажень на лімітер. Випромінювання плазми не враховувалося.Подробно изложена текущая стадия разработки конечно-разностного трехмерного кода Findif для многожидкостной модели плазмы. Код был запущен на четырех сетках, подготовленных для геометрии стенки OP-1.1 стелларатора Wendelstein 7-X. Сетки сгенерированы для 4-х магнитных конфигураций, две из которых – с конечным бета (не вакуум). Смоделированный объем охватывает край плазмы; основная цель заключается в расчетах распределений тепловых нагрузок на лимитер. Излучение плазмы не учитывалось

Application of the VUV and the soft x-ray systems on JET for the study of intrinsic impurity behavior in neon seeded hybrid discharges

This paper reports on impurity behavior in a set of hybrid discharges with Ne seeding—one of the techniques considered to reduce the power load on reactor walls. A series of experiments carried out with light gas injection on JET with the ITER-Like-Wall (ILW) suggests increased tungsten release and impurity accumulation [C. Challis et al., Europhysics Conference Abstracts 41F, 2.153 (2017)]. The presented method relies mainly on the measurements collected by vacuum-ultra-violet and soft X-ray (SXR) diagnostics including the “SOXMOS” spectrometer and the SXR camera system. Both diagnostics have some limitations. Consequently, only a combination of measurements from these systems is able to provide comprehensive information about high-Z [e.g., tungsten (W)] and mid-Z [nickel (Ni), iron (Fe), copper (Cu), and molybdenum (Mo)] impurities for their further quantitative diagnosis. Moreover, thanks to the large number of the SXR lines of sight, determination of a 2D radiation profile was also possible. Additionally, the experimental results were compared with numerical modeling based on integrated simulations with COREDIV. Detailed analysis confirmed that during seeding experiments, higher tungsten release is observed, which was also found in the past. Additionally, it was noticed that besides W, the contribution of molybdenum to SXR radiation was greater, which can be explained by the place of its origin.This work has been carried out within the framework of the EUROfusion Consortium and has received funding from the Euratom research and training programme 2014-2018 under Grant Agreement No. 633053. The views and opinions expressed herein do not necessarily reflect those of the European Commission. This scientific work was partly supported by the Polish Ministry of Science and Higher Education within the framework of the scientific financial resources in the years 2014-2018 allocated for the realization of the international co-financed project.Postprint (author's final draft

Public Evidence from Secret Ballots

Elections seem simple---aren't they just counting? But they have a unique, challenging combination of security and privacy requirements. The stakes are high; the context is adversarial; the electorate needs to be convinced that the results are correct; and the secrecy of the ballot must be ensured. And they have practical constraints: time is of the essence, and voting systems need to be affordable and maintainable, and usable by voters, election officials, and pollworkers. It is thus not surprising that voting is a rich research area spanning theory, applied cryptography, practical systems analysis, usable security, and statistics. Election integrity involves two key concepts: convincing evidence that outcomes are correct and privacy, which amounts to convincing assurance that there is no evidence about how any given person voted. These are obviously in tension. We examine how current systems walk this tightrope.Comment: To appear in E-Vote-Id '1

End-to-end verifiable elections in the standard model

We present the cryptographic implementation of “DEMOS”, a new e-voting system that is end-to-end verifiable in the standard model, i.e., without any additional “setup” assumption or access to a random oracle (RO). Previously known end-to-end verifiable e-voting systems required such additional assumptions (specifically, either the existence of a “randomness beacon” or were only shown secure in the RO model). In order to analyze our scheme, we also provide a modeling of end-to-end verifiability as well as privacy and receipt-freeness that encompasses previous definitions in the form of two concise attack games. Our scheme satisfies end-to-end verifiability information theoretically in the standard model and privacy/receipt-freeness under a computational assumption (subexponential Decisional Diffie Helman). In our construction, we utilize a number of techniques used for the first time in the context of e-voting schemes that include utilizing randomness from bit-fixing sources, zero-knowledge proofs with imperfect verifier randomness and complexity leveraging

Magnetic properties of exactly solvable doubly decorated Ising-Heisenberg planar models

Applying the decoration-iteration procedure, we introduce a class of exactly solvable doubly decorated planar models consisting both of the Ising- and Heisenberg-type atoms. Exact solutions for the ground state, phase diagrams and basic physical quantities are derived and discussed. The detailed analysis of the relevant quantities suggests the existence of an interesting quantum antiferromagnetic phase in the system.Comment: 9 pages, 9 figures, submitted to Physical Review