Coupling of BGK lattice Boltzmann method and experimental rheological/thermal behavior of Al2O3–oil nanolubricant for modeling of a finned thermal storage

Purpose The purpose of the present work is to investigate the hydrodynamic and thermal performance of a thermal storage based on the numerical and experimental approaches using the lattice Boltzmann method and the experimental observation on the thermo-physical properties of the operating fluid. Design/methodology/approach For this purpose, the Al2O3 nanoparticle is added to the lubricant with four nanoparticle concentrations, including 0.1, 0.2, 0.4 and 0.6Vol.%. After preparing the nanolubricant samples, the thermal conductivity and dynamic viscosity of nanolubricant are measured using thermal analyzer and viscometer, respectively. Finally, the extracted data are used in the numerical simulation using provided correlations. In the numerical process, the lattice Boltzmann equations based on Bhatnagar–Gross Krook model are used. Also, some modifications are applied to treat with the complex boundary conditions. In addition, the second law analysis is used based on the local and total views. Findings Different types of results are reported, including the flow structure, temperature distribution, contours of local entropy generation, value of average Nusselt number, value of entropy generation and value of Bejan number. Originality/value The originality of this work is combining a modern numerical methodology with experimental data to simulate the convective flow for an industrial application.

Numerical Study on Water Sealing Effect of Freeze-Sealing Pipe-Roof Method Applied in Underwater Shallow-Buried Tunnel

The freezing-sealing pipe-roof method is a new presupporting technique, which fully combines the advantages of pipe-roof method and artificial ground-freezing method, and can adapt to the construction needs of underground projects in complex and sensitive strata. After the Gongbei Tunnel of Hong Kong–Zhuhai–Macao Bridge, this method will be applied for the first time in an underwater shallow-buried railroad tunnel, and there are still many urgent problems to be solved. In this article, based on the field situation and the preliminary design scheme, a convective heat transfer model under complex boundary conditions was first established. Then, the development of frozen wall thickness during the active freezing period was solved by numerical simulation for three different pipe filling modes, and the cloud map of temperature distribution in the whole section is analyzed. After that, the moving state of river water was characterized by different heat transfer coefficients, and the weakening effect of flow velocity on the top freezing wall was studied. Finally, six critical water sealing paths were selected, and the temperature differences of the frozen curtain were calculated. The results show that the mode with interval concrete filling can form a reliable frozen curtain within the scheduled time, whereas the nonfilling mode cannot achieve the water sealing requirement. River water has a large effect on the temperature at the boundary of jacking pipe and almost no effect on the center of the jacked pipe. It takes approximately 15 days from the frozen soil covering the pipe wall to reach the designed thickness, and the freezing effect of empty pipe lags approximately 28 days compared with that of solid pipe, which requires targeted enhancement measures in field projects.

Law of coal caving behind the flexible shield support in pseudo-inclined working face

Complex boundary conditions are the major influencing factors of coal caving law in the pseudo-inclined working face. The main purpose of this study is to analyze coal caving law of flexible shield support and then to establish the internal relations among coal caving parameters under complex boundary conditions. Firstly, the law of coal caving in different falling modes is simulated physically. Secondly, the coal caving shape, displacement field, and contact force field is simulated. Then, coal caving law and process parameters is analyzed theoretically. Finally, the test was performed in Bai-Ji Mine. The research shows that ellipsoidal ore drawing theory has universal applicability in coal drawing law analysis and parameter optimization. After the Isolated Extraction Zone and Isolated Movement Zone reach the roof, the expansion speed is marked by a short delay, and then, while expanding to the floor, two butted incomplete ellipsoids are formed. There is a time-space difference in coal caving after the support, and some coal will be mined in the next round of coal caving. There are obvious differences in the coal loosening range, displacement field, and contact force field on both sides of the long axis. When the support falls along with the bottom plate, it is more conducive to the release of coal. The test shows that the research is of great significance for optimizing the caving parameters of flexible shield support in the pseudo-inclined working face of the steep seam.

Indirect Electro-Thermal Modelling of Semiconductor Diode Using Non-Linear Behavior of Volt-Ampere Characteristic

The aim of the proposed paper is the development of an electro-thermal model of semiconductor component using an indirect modelling approach. The approach is based on the integration of the component’s electrical properties considering non-linear behavior of a V-A characteristic. In this way, the identification of semiconductor material properties considering non-linear dependencies and semiconductor volume is provided. The main aim of the presented approach is simplification of the electro–thermal interaction within finite-element modelling of the semiconductor components. In this way, it is possible to omit more complex boundary definitions and the setting of the semiconductor-based physics. The proposed methodology is presented within the development of a simulation model based on a small high-frequency rectifying diode, taking into account its geometric dimensions and the internal arrangement of its structure. Simulation was performed as a transient analysis, while the results from the steady-state operation for various operational conditions were compared to experimental measurements. Comparison between simulation and experiments is within 5% of the relative error. The achieved results represent appropriate accuracy of model behavior compared to the real operation.

Wave-based optical coherence elastography: the 10-year perspective

After ten years of progress and innovation, optical coherence elastography (OCE) based on the propagation of mechanical waves has become one of the major and, perhaps, one of the most studied OCE branches, producing a fundamental impact in the quantitative and nondestructive biomechanical characterization of tissues. Preceding previous progress made in ultrasound and magnetic resonance elastography; wave-based OCE has pushed to the limit the advance of three major pillars: (1) implementation of novel wave excitation methods in tissues, (2) understanding new types of mechanical waves in complex boundary conditions by proposing advance analytical and numerical models, and (3) the development of novel estimators capable of retrieving quantitative 2D/3D biomechanical information of tissues. This remarkable progress promoted a major advance in answering basic science questions and improving medical disease diagnosis and treatment monitoring in several types of tissues leading, ultimately, to the first attempts of clinical trials and translational research. This paper summarizes the fundamental up-to-date principles and categories of wave-based OCE, revises the timeline and the state-of-the-art techniques and applications lying in those categories, and concludes with a discussion of current challenges and future directions, including clinical translation research.

Spatialized Epidemiological Forecasting applied to Covid-19 Pandemic at Departmental Scale in France

In this paper, we present a spatialized extension of a SIR model that accounts for undetected infections and recoveries as well as the load on hospital services. The spatialized compartmental model we introduce is governed by a set of partial differential equations (PDEs) defined on a spatial domain with complex boundary. We propose to solve the set of PDEs defining our model by using a meshless numerical method based on a finite difference scheme in which the spatial operators are approximated by using radial basis functions. Such an approach is reputed as flexible for solving problems on complex domains. Then we calibrate our model on the French department of Isère during the first period of lockdown, using daily reports of hospital occupancy in France. Our methodology allows to simulate the spread of Covid-19 pandemic at a departmental level, and for each compartment. However, the simulation cost prevents from online short-term forecast. Therefore, we propose to rely on reduced order modeling tools to compute short-term forecasts of infection number. The strategy consists in learning a time-dependent reduced order model with few compartments from a collection of evaluations of our spatialized detailed model, varying initial conditions and parameter values. A set of reduced bases is learnt in an offline phase while the projection on each reduced basis and the selection of the best projection is performed online, allowing short-term forecast of the global number of infected individuals in the department.

Advancing a generalized method for solving problems of continuum mechanics as applied to the Cartesian coordinate system

Solving the problem of continuum mechanics has revealed the defining generalizations using the function argument method. The aim of this study was to devise new approaches to solving problems of continuum mechanics using defining generalizations in the Cartesian coordinate system. Additional functions, or the argument of the coordinates function of the deformation site, are introduced into consideration. The carriers of the proposed function arguments should be basic dependences that satisfy the boundary or edge conditions, as well as functions that simplify solving the problem in a general form. However, there are unresolved issues related to how not the solutions themselves should be determined but the conditions for their existence. Such generalized approaches make it possible to predict the result for new applied problems, expand the possibilities of solving them in order to meet a variety of boundary and edge conditions. The proposed approach makes it possible to define a series of function arguments, each of which can be a condition of uniqueness for a specific applied problem. Such generalizations concern determining not the specific functions but the conditions of their existence. From these positions, the flat problem was solved in the most detailed way, was tested, and compared with the studies reported by other authors. Based on the result obtained, a mathematical model of the flat applied problem of the theory of elasticity with complex boundary conditions was built. Expressions that are presented in coordinateless form are convenient for analysis while providing a computationally convenient context. The influence of the beam shape factor on the distribution of stresses in transition zones with different intensity of their attenuation has been shown. By bringing the solution to a particular result, the classical solutions have been obtained, which confirms its reliability. The mathematical substantiation of Saint-Venant's principle has been constructed in relation to the bending of a beam under variable asymmetric loading