Artykuły w czasopismach: „RANS solver Development”

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Xiao, Yinli, Zupeng Wang, Zhengxin Lai i Wenyan Song. "Modeling of Spray Combustion with a Steady Laminar Flamelet Model in an Aeroengine Combustion Chamber Based on OpenFOAM". International Journal of Aerospace Engineering 2018 (2018): 1–13. http://dx.doi.org/10.1155/2018/7329564.

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The development of high-performance aeroengine combustion chambers strongly depends on the accuracy and reliability of efficient numerical models. In the present work, a reacting solver with a steady laminar flamelet model and spray model has been developed in OpenFOAM and the solver details are presented. The solver is firstly validated by Sandia/ETH-Zurich flames. Furthermore, it is used to simulate nonpremixed kerosene/air spray combustion in an aeroengine combustion chamber with the RANS method. A comparison with available experimental data shows good agreement and validates the capability of the new developed solver in OpenFOAM.

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Frey Marioni, Yuri, Enrique Alvarez de Toledo Ortiz, Andrea Cassinelli, Francesco Montomoli, Paolo Adami i Raul Vazquez. "A Machine Learning Approach to Improve Turbulence Modelling from DNS Data Using Neural Networks". International Journal of Turbomachinery, Propulsion and Power 6, nr 2 (4.06.2021): 17. http://dx.doi.org/10.3390/ijtpp6020017.

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In this paper, we investigate the feasibility of using DNS data and machine learning algorithms to assist RANS turbulence model development. High-fidelity DNS data are generated with the incompressible Navier–Stokes solver implemented in the spectral/hp element software framework Nektar++. Two test cases are considered: a turbulent channel flow and a stationary serpentine passage, representative of internal turbo-machinery cooling flow. The Python framework TensorFlow is chosen to train neural networks in order to address the known limitations of the Boussinesq approximation and a clustering based on flow features is run upfront to enable training on selected areas. The resulting models are implemented in the Rolls-Royce solver HYDRA and a posteriori predictions of velocity field and wall shear stress are compared to baseline RANS. The paper presents the fundamental elements of procedure applied, including a brief description of the tools and methods and improvements achieved.

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Feng, Xing, i Wanqing Wu. "Generation of Water Waves Using Momentum Source Wave-Maker Applied to a RANS Solver". Mathematical Problems in Engineering 2019 (5.05.2019): 1–11. http://dx.doi.org/10.1155/2019/1308960.

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Nowadays, as the development of Computational Fluid Dynamics (CFD) and the numerical wave tank (NWT) has advanced, numerical analysis has become increasingly useful and powerful for the ship designing and ship hydrodynamics. In this study, a momentum source wave-maker and an analytical relaxation wave absorber were embedded into 2D RANS equation model with RSM turbulence closure scheme to establish the NWT for ship designing and hydrodynamics. The VOF (volume-of-fluid) method was applied to accurately capture the water free surface. The body force-weighted scheme is chosen for pressure interpolation and the second order upwind scheme for discretization of the momentum equation. In order to calculate convection and diffusion fluxes through the control volume faces, PISO algorithm is adopted for pressure-velocity coupling. The momentum source function for wave generation and the analytical relaxation function for wave absorption were deduced for constructing the NWT (numerical wave tank). The proposed NWT was then validated by the laboratory measurements of Umeyama and the analytical solution, indicating that the constructed NWT is effective and accurate.

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Han, Han, Zifei Yin, Yijun Ning i Hong Liu. "Development of a 3D Eulerian/Lagrangian Aircraft Icing Simulation Solver Based on OpenFOAM". Entropy 24, nr 10 (27.09.2022): 1365. http://dx.doi.org/10.3390/e24101365.

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A 3D icing simulation code is developed in the open-source CFD toolbox OpenFOAM. A hybrid Cartesian/body-fitted meshing method is used to generate high-quality meshes around complex ice shapes. Steady-state 3D Reynolds-averaged Navier-Stokes (RANS) equations are solved to provide the ensemble-averaged flow around the airfoil. Considering the multi-scale nature of droplet size distribution, and more importantly, to represent the less uniform nature of the Super-cooled Large Droplets (SLD), two droplet tracking methods are realized: the Eulerian method is used to track the small-size droplets (below 50 μm) for the sake of efficiency; the Lagrangian method with random sampling is used to track the large droplets (above 50 μm); the heat transfer of the surface overflow is solved on a virtual surface mesh; the ice accumulation is estimated via the Myers model; finally, the final ice shape is predicted by time marching. Limited by the availability of experimental data, validations are performed on 3D simulations of 2D geometries using the Eulerian and Lagrangian methods, respectively. The code proves to be feasible and accurate enough in predicting ice shapes. Finally, an icing simulation result of the M6 wing is presented to illustrate the full 3D capability.

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Bradstock, Philip, i Wolfgang Schlez. "Theory and verification of a new 3D RANS wake model". Wind Energy Science 5, nr 4 (30.10.2020): 1425–34. http://dx.doi.org/10.5194/wes-5-1425-2020.

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Abstract. This paper details the background to the WakeBlaster model: a purpose-built, parabolic three-dimensional RANS solver, developed by ProPlanEn. WakeBlaster is a field model, rather than a single turbine model; it therefore eliminates the need for an empirical wake superposition model. It belongs to a class of very fast (a few core seconds, per flow case) mid-fidelity models, which are designed for industrial application in wind farm design, operation, and control. The domain is a three-dimensional structured grid, a node spacing of a tenth of a rotor diameter, by default. WakeBlaster uses eddy viscosity turbulence closure, which is parameterized by the local shear, time-lagged turbulence development, and stability corrections for ambient shear and turbulence decay. The model prescribes a profile at the end of the near wake, and the spatial variation of ambient flow, by using output from an external flow model.

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Liu, Junwei, Shuiyue Chen, Xin Li i Zuodong Liang. "Three-Dimensional Modelling of Non-Linear Wave-Induced Seabed Response around Offshore Open-Ended Pile". Journal of Marine Science and Engineering 9, nr 11 (8.11.2021): 1238. http://dx.doi.org/10.3390/jmse9111238.

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This paper analyses the fluid–seabed–structure interactions (FSSI) around the open-ended pile by applying the in-house solver established on the open-source Computational Fluid Dynamics (CFD) platform. The Reynolds-averaged Navier–Stokes (RANS) equations are solved to simulate the hydrodynamic interactions between waves and open-ended piles. Biot’s poro-elastic theory (quasi-static model) is used to reproduce the wave-induced seabed responses. The parameter analysis indicates that the wave period, degree of saturation of seabed and pile diameter have a great influence on the development of the transient seabed liquefaction depth around the pile. In addition, the distribution of the pore water pressure vs soil depth in the inner zone of the pile presents a “V” shape rotated 90 degrees counterclockwise.

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Prospathopoulos, John, i Spyros G. Voutsinas. "Implementation Issues in 3D Wind Flow Predictions Over Complex Terrain". Journal of Solar Energy Engineering 128, nr 4 (23.07.2006): 539–53. http://dx.doi.org/10.1115/1.2346702.

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Practical aspects concerning the use of 3D Navier-Stokes solvers as prediction tools for micro-siting of wind energy installations are considered. Micro-siting is an important issue for a successful application of wind energy in sites of complex terrain. There is a constantly increasing interest in using mean wind flow predictions based on Reynolds averaged Navier-Stokes (RANS) solvers in order to minimize the number of required field measurements. In this connection, certain numerical aspects, such as the extent of the numerical flow domain, the choice of the appropriate inflow boundary conditions, and the grid resolution, can decisively affect the quality of the predictions. In the present paper, these aspects are analyzed with reference to the Askervein hill data base of full scale measurements. The objective of the work is to provide guidelines with respect to the definition of appropriate boundary conditions and the construction of an adequate and effective computational grid when a RANS solver is implemented. In particular, it is concluded that (a) the ground roughness affects the predictions significantly, (b) the computational domain should have an extent permitting the full development of the flow before entering the region of interest, and (c) the quality of the predictions at the local altitude maxima depends on the grid density in the main flow direction.

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Tahara, Y., F. Stern i Y. Himeno. "Computational Fluid Dynamics–Based Optimization of a Surface Combatant". Journal of Ship Research 48, nr 04 (1.12.2004): 273–87. http://dx.doi.org/10.5957/jsr.2004.48.4.273.

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Computational fluid dynamics (CFD)-based optimization of a surface combatant is presented with the following main objectives:development of a high-performance optimization module for a Reynolds averaged Navier-Stokes (RANS) solver for with-free-surface condition; anddemonstration of the capability of the optimization method for flow- and wave-field optimization of the Model 5415 hull form. The optimization module is based on extension of successive quadratic programming (SQP) for higher-performance optimization method by introduction of parallel computing architecture, that is, message passing interface (MPI) protocol. It is shown that the present parallel SQP module is nearly m(= 2k+ 1; k is number of design parameters) times faster than conventional SQP, and the computational speed does not depend on the number of design parameters. The RANS solver is CFDSHIP-IOWA, a general-purpose parallel multiblock RANS code based on higher-order upwind finite difference and a projection method for velocity-pressure coupling; it offers the capability of free-surface flow calculation. The focus of the present study is on code development and demonstration of capability, which justifies use of a relatively simple turbulence model, a free-surface model without breaking model, static sinkage and trim, and simplified design constraints and geometry modeling. An overview is given of the high-performance optimization method and CFDSHIP-IOWA, and results are presented for stern optimization for minimization of transom wave field disturbance; sonar dome optimization for minimization of sonar-dome vortices; and bow optimization for minimization of bow wave. In conclusion, the present work has successfully demonstrated the capability of the CFD-based optimization method for flow- and wave-field optimization of the Model 5415 hull form. The present method is very promising and warrants further investigations for computer-aided design (CAD)-based hull form modification methods and more appropriate design constraints.

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Tahara, Yusuke, Koji Norisada, Michitaka Yamane i Tomohiro Takai. "Development and Demonstration of CAD/CFD/Optimizer Integrated Simulation-Based Design Framework by Using High-Fidelity Viscous Free-Surface RaNS Equation Solver". Journal of the Japan Society of Naval Architects and Ocean Engineers 7 (2008): 171–84. http://dx.doi.org/10.2534/jjasnaoe.7.171.

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Masoomi, Mobin, Mahdi Yousefifard i Amir Mosavi. "Efficiency Assessment of an Amended Oscillating Water Column Using OpenFOAM". Sustainability 13, nr 10 (18.05.2021): 5633. http://dx.doi.org/10.3390/su13105633.

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Oscillating water column (OWC) is an advanced form of wave energy converter (WEC). This study aims at improving the efficiency of an amended OWC through a novel methodology for simulating several vertical plates within the chamber. This paper provides a numerical investigation considering one, two, three, and four vertical plates. The open field operation and manipulation (OpenFOAM) solver is verified based on the Reynolds-Averaged Navier–Stokes (RANS) equation. Results show the number and the position of plates where the convertor’s efficiency improves. The work undertaken here also revealed a reduction in the net force imposed on the convertor’s structure, especially the front wall. Consequently, adding plates acquires more efficiency with lower force on the system.

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Madsen, Mads H. Aa, Frederik Zahle, Niels N. Sørensen i Joaquim R. R. A. Martins. "Multipoint high-fidelity CFD-based aerodynamic shape optimization of a 10 MW wind turbine". Wind Energy Science 4, nr 2 (3.04.2019): 163–92. http://dx.doi.org/10.5194/wes-4-163-2019.

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Abstract. The wind energy industry relies heavily on computational fluid dynamics (CFD) to analyze new turbine designs. To utilize CFD earlier in the design process, where lower-fidelity methods such as blade element momentum (BEM) are more common, requires the development of new tools. Tools that utilize numerical optimization are particularly valuable because they reduce the reliance on design by trial and error. We present the first comprehensive 3-D CFD adjoint-based shape optimization of a modern 10 MW offshore wind turbine. The optimization problem is aligned with a case study from International Energy Agency (IEA) Wind Task 37, making it possible to compare our findings with the BEM results from this case study and therefore allowing us to determine the value of design optimization based on high-fidelity models. The comparison shows that the overall design trends suggested by the two models do agree, and that it is particularly valuable to consult the high-fidelity model in areas such as root and tip where BEM is inaccurate. In addition, we compare two different CFD solvers to quantify the effect of modeling compressibility and to estimate the accuracy of the chosen grid resolution and order of convergence of the solver. Meshes up to 14×106 cells are used in the optimization whereby flow details are resolved. The present work shows that it is now possible to successfully optimize modern wind turbines aerodynamically under normal operating conditions using Reynolds-averaged Navier–Stokes (RANS) models. The key benefit of a 3-D RANS approach is that it is possible to optimize the blade planform and cross-sectional shape simultaneously, thus tailoring the shape to the actual 3-D flow over the rotor. This work does not address evaluation of extreme loads used for structural sizing, where BEM-based methods have proven very accurate, and therefore will likely remain the method of choice.

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Cassinelli, Andrea, Andrés Mateo Gabín, Francesco Montomoli, Paolo Adami, Raul Vázquez Díaz i Spencer J. Sherwin. "Reynolds Sensitivity of the Wake Passing Effect on a LPT Cascade Using Spectral/hp Element Methods". International Journal of Turbomachinery, Propulsion and Power 7, nr 1 (22.02.2022): 8. http://dx.doi.org/10.3390/ijtpp7010008.

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Reynolds-Averaged Navier–Stokes (RANS) methods continue to be the backbone of CFD-based design; however, the recent development of high-order unstructured solvers and meshing algorithms, combined with the lowering cost of HPC infrastructures, has the potential to allow for the introduction of high-fidelity simulations in the design loop, taking the role of a virtual wind tunnel. Extensive validation and verification is required over a broad design space. This is challenging for a number of reasons, including the range of operating conditions, the complexity of industrial geometries and their relative motion. A representative industrial low pressure turbine (LPT) cascade subject to wake passing interactions is analysed, adopting the incompressible Navier–Stokes solver implemented in the spectral/hp element framework Nektar++. The bar passing effect is modelled by leveraging a spectral-element/Fourier Smoothed Profile Method. The Reynolds sensitivity is analysed, focusing in detail on the dynamics of the separation bubble on the suction surface as well as the mean flow properties, wake profiles and loss estimations. The main findings are compared with experimental data, showing agreement in the prediction of wake traverses and losses across the entire range of flow regimes, the latter within 5% of the experimental measurements.

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Ku, Garam, Songjune Lee, Cheolung Cheong, Woong Kang i Kuksu Kim. "Development of High-Fidelity Numerical Methodology Based on Wavenumber-Frequency Transform for Quantifying Internal Aerodynamic Noise in Critical Nozzle". Applied Sciences 9, nr 14 (19.07.2019): 2885. http://dx.doi.org/10.3390/app9142885.

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In industrial fields dealing with high-temperature and high-pressure gas such as chemical, petrochemical, and offshore oil production plants, piping systems with valves are frequently used to protect the relevant system and equipment from being damaged by such gases. However, excessive noise is sometimes generated by the valve flow in the piping system, causing so-called acoustic induced vibration in the pipe wall. Therefore, it is of great importance to design the related system to avoid this phenomenon. In this study, a high-fidelity numerical procedure is proposed to assess the acoustic power generated by pressure relief devices in a pipe. The method consists of three sequential steps: high accuracy large eddy simulation, wavenumber-frequency transform, and duct acoustic theory. The critical nozzle is selected as a target system since it is commonly used as a flowmeter and thus there are a lot of relevant data for comparison. First, the steady Reynold-Averaged Navier–Stokes (RANS) solver is used to predict the flow rate of the two-dimensional axisymmetric critical nozzles, and its validity is confirmed by comparing the predicted results with the measured ones. There is good agreement between the two results. Then, a high accuracy Large Eddy Simulation (LES) technique is performed on the three-dimensional critical nozzle, and the steady-state RANS result is used as the initial condition to accelerate the convergence of the unsteady simulation. The validity of the unsteady LES results is also confirmed by comparing them with measured surface pressure data. The wavenumber-frequency transform is taken on the LES results, and the compressible surface pressure components matching the acoustical duct modes are identified in the wavenumber-frequency pressure diagram. The inverse wavenumber-frequency transform taken on the compressible pressure components leads to the acoustic power spectrum. These results reveal that the current numerical procedure can be used to more accurately predict the acoustic power generated by pressure relief device in the piping system.

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Page, G. J., i J. J. McGuirk. "Large Eddy Simulation of a complete Harrier aircraft in ground effect". Aeronautical Journal 113, nr 1140 (luty 2009): 99–106. http://dx.doi.org/10.1017/s0001924000002827.

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Abstract This paper aims to demonstrate the viability of using the large eddy simulation (LES) CFD methodology to model a representative, complete STOVL aircraft geometry at touch down. The flowfield beneath such a jet-borne vertical landing aircraft is inherently unsteady. Hence, it is argued in the present work that the LES technique is the most suitable tool to predict both the mean flow and unsteady fluctuations, and, with further development and validation testing, this approach could be a replacement, and certainly a complementary aid, to expensive rig programmes. The numerical method uses a compressible solver on a mixed element unstructured mesh. Examination of instantaneous flowfield predictions from these LES calculations indicate close similarity with many flow features identified from ground effect flow visualisations, which are well known to be difficult to model using RANS-based CFD. Whilst significant further work needs to be carried out, these calculations show that LES could be a practical tool to model, for example, Hot Gas Ingestion for the Joint Strike Fighter aircraft.

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Bi, Xiaosheng, Jiayuan Zhuang i Yumin Su. "Seakeeping Analysis of Planing Craft under Large Wave Height". Water 12, nr 4 (2.04.2020): 1020. http://dx.doi.org/10.3390/w12041020.

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The purpose of this paper is to conduct a seakeeping analysis of planing craft under regular wave with large wave height. To obtain a reliable numerical method to simulate the sailing of planing craft in waves, Reynolds-averaged Navier–Stokes (RANS) solver and overset method are adopted. The motion response and resistance of the planing craft USV01 in regular wave were numerical predicted and compared with the corresponding seakeeping experimental tests. The results show that the numerical method has high accuracy. For further study, a new planing craft whose name is improved vessel is selected for simulation, the low steaming of the USV01 and improved vessel in regular wave with large wave height was simulated, and the seakeeping of the two vessels was studied. The analysis about the influence of wave length on the motion response and navigation configurations of the improved vessel under regular wave was carried out. Meanwhile, the influence of speed on different navigation configurations of the improved vessel was also analyzed. The improved vessel can provide better seakeeping, and a reduction in the speed of the vessel will benefit its seakeeping, irrespective of its navigation configuration.

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Ricci, Martina, Stefano Gino Mosele, Marcello Benvenuto, Pio Astrua, Roberto Pacciani i Michele Marconcini. "Retrofittable Solutions Capability for Gas Turbine Compressors". International Journal of Turbomachinery, Propulsion and Power 7, nr 1 (11.01.2022): 3. http://dx.doi.org/10.3390/ijtpp7010003.

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The increasing introduction of renewable energy capacity has changed the perspective on the operation of conventional power plants, introducing the necessity of reaching extreme off-design conditions. There is a strong interest in the development and optimization of technologies that can be retrofitted to an existing power plant to enhance flexibility as well as increase performance and lower emissions. Under the framework of the European project TURBO-REFLEX, a typical F-class gas turbine compressor designed and manufactured by Ansaldo Energia has been studied. Numerical analyses were performed using the TRAF code, which is a state-of-the-art 3D CFD RANS/URANS flow solver. In order to assess the feasibility of lower minimum environmental load operation, by utilizing a reduction in the compressor outlet mass-flow rate, with a safe stability margin, two different solutions have been analyzed: blow-off extractions and extra-closure of Variable Inlet Guide Vanes. The numerical steady-state results are compared and discussed in relation to an experimental campaign, which was performed by Ansaldo Energia. The purpose is to identify the feasibility of the technologies and implementation opportunity in the existing thermal power plant fleet.

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PANG, Chao, Meng LI i Zhenghong GAO. "Study on the effect of transition process on rotor hovering simulation". Xibei Gongye Daxue Xuebao/Journal of Northwestern Polytechnical University 40, nr 2 (kwiecień 2022): 253–60. http://dx.doi.org/10.1051/jnwpu/20224020253.

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Hovering is one of important statuses to evaluate the aerodynamic performance of a rotor. With the development of the computer technology and CFD technique, the numerical methods based on the first principle are usually employed to evaluate the hovering performance of the rotor. The transition process will evidently affect the results from the RANS-based numerical simulations in some steady cases for the fixed wing aircrafts, which should be taken into consideration in the design process. But it's not clear whether the transition process would affect the numerical results for the rotor simulation. To provide the reference in designing and evaluating the rotorcraft, the effect of the transition process in the rotor simulation needs to be discussed further. The PSP rotor proposed by NASA is calculated using the in-house solver based on the overset grid in this paper. Simulations are performed with fully turbulent model as well as the transitional model and the results are compared to the experimental data. The results prove the superior ability to simulate the flow around a hovering rotor of the in-house solver. The relative errors of the numerical results are under 5%. The range of the laminar flow on the blade is proportional to the rotor thrust, which causes a higher Figure of Merit in transition simulation than the fully turbulent simulation. The sectional pressure distribution and torque distribution along the blade apparently suffer from the transition process, which doesn't affect the thrust distribution along the blade and the blade vortex wake flow under the rotor disk. An obvious flow separation on the surface of the blade can be observed in the transition simulation compared to the fully turbulent simulation.

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Nakate, Prajakta, Domenico Lahaye, Cornelis Vuik i Marco Talice. "Analysis of the Aerodynamics in the Heating Section of an Anode Baking Furnace Using Non-Linear Finite Element Simulations". Fluids 6, nr 1 (19.01.2021): 46. http://dx.doi.org/10.3390/fluids6010046.

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The emissions from the industrial furnaces impact the environment. Among the various factories, those having anode baking furnaces are working on reducing the pollutant emissions. The aerodynamics in the furnace influences the emissions due to the high dependence of combustion and radiation phenomena on the mixing characteristics. Therefore, this paper aims to establish the numerical simulation results for the three-dimensional turbulent flow in a single section of an anode baking furnace with a high rate of fuel injection. The stabilized non-linear finite element approach on the Reynolds-averaged Navier-Stokes (RANS) equation is used with COMSOLMultiphysics. The turbulent viscosity ratio is highly sensitive to the mesh for the standard k-ϵ model. The requirements of the Cartesian and refined mesh near the jet development region is explained. The comparison of meshes generated by two meshing tools namely cfMesh and COMSOL Multiphysics default Mesher is carried out. The high numerical diffusion in the flow models due to the coarser mesh leads to convergence but deficit the precision in the results. This paper shows that the mesh generated by cfMesh with flow aligned refinement combined with the non-linear finite element solver in COMSOL Multiphysics proves to provide accurate results of turbulent quantities.

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Sugianto, Erik, Jeng-Horng Chen i Niki Veranda Agil Permadi. "Effect of Monohull Type and Catamaran Hull Type on Ocean Waste Collection Behavior Using OpenFOAM". Water 14, nr 17 (25.08.2022): 2623. http://dx.doi.org/10.3390/w14172623.

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Ocean waste that continues moving in the water has been a problem until now. This has stimulated marine debris cleaning technology to emerge. This research sought to evaluate the effectiveness of waste collection using a monohull and catamaran fitted with a forward conveyor. The Reynolds Average Navier Stokes (RANS)-based numerical simulation research is used to predict flow pattern characteristics, velocity contour, wave pattern, pressure distribution, and ship resistance. The current research focuses on the impact of a round-bilge-type monohull and inner flat-type catamaran hull front shape on waste collection behavior by applying numerical methods. The multiphase solver numerical configuration supplied with OpenFOAM v2112 has been verified and validated using the Delft catamaran 372 with Froude numbers 0.3. The effect of free surface on resistance and flow characteristics was evaluated by comparing these two models. The results show the behavior of marine debris collection due to the flow characteristics of both models. The marine debris flows much more conveniently through the conveyor fitted in front of the catamaran model than in the monohull model. In addition, considering the front-side hull flow, the catamaran model is superior since marine debris is able to approach the ship easily. However, the monohull model is faster at bringing marine debris closer to the conveyor, particularly at the location in front of the conveyor.

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Laroche, Emmanuel, David Donjat i Philippe Reulet. "A Combined Experimental and Numerical Characterization of the Flowfield and Heat Transfer around a Multiperforated Plate with Compound Angle Injection". Energies 14, nr 3 (26.01.2021): 613. http://dx.doi.org/10.3390/en14030613.

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The aerodynamic and thermal behaviour of multiperforated zones in combustors is essential to the development of future combustion chambers. Detailed databases are therefore crucial for the validation of RANS/LES solvers, but also regarding the derivation of heat transfer correlations used in 0D/1D in-house codes developed by engine manufacturers. In the framework of FP7 EU SOPRANO Program, the test-rig used in a previous study is modified to be compatible with anisothermal conditions. The plate studied is a 12:1 model with a 90∘ compound angle injection. A heating system is used to generate a moderate temperature gradient of about 20 K between the secondary hot flow and the main cold flow. The aerodynamic field is acquired by a PIV 2D-3C (Stereo Particle Image Velocimetry) system. The surface heat transfer coefficient is derived based on surface temperature distribution acquisitions. Several heating power levels are tested, which allows evaluating the convective heat transfer coefficient and reference temperature through a linear regression. Measurements are conducted on both sides of the plate, which also gives access to those quantities on the injection/suction sides. From a numerical point of view, the configuration is studied using the unstructured ONERA in-house CEDRE solver with an advanced Reynolds Stress Model. A systematic comparison is presented between the experimental and numerical database. Due to the high blowing ratio, the film protection is low in the first rows, with a convective heat transfer coefficient enhancement around three, and freestream cold air brought close to the wall by vortices created at injection. After four rows, the film is building up, leading gradually to a better insulation of the wall. The comparison with the numerical simulation exhibits a qualitative agreement on the main flow structures. However, the mixing between the jets, the film and the freestream is underestimated by the calculation.

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Salari, Mohammad Sadegh, Behzad Zarif Boushehri i Mehrdad Boroushaki. "Aerodynamic analysis of backward swept in HAWT rotor blades using CFD". International Journal of Renewable Energy Development 7, nr 3 (15.12.2018): 241–49. http://dx.doi.org/10.14710/ijred.7.3.241-249.

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The aerodynamical design of backward swept for a horizontal axis wind turbine blade has been carried out to produce more power at higher wind velocities. The backward sweep is added by tilting the blade toward the air flow direction. Computational Fluid Dynamics (CFD) calculations were used for solving the conservation equations in one outer stationary reference frame and one inner rotating reference frame, where the blades and grids were fixed in reference to the rotating frame. The blade structure was validated using Reynolds Averaged Navier-Stokes (RANS) solver in a test case by the National Renewable Energy Laboratory (NREL) VI blades results. Simulation results show considerable agreement with the NREL measurements. Standard K-ε turbulence model was chosen for simulations and for the backward swept design process. A sample backward sweep design was applied to the blades of a Horizontal Axis Wind Turbine (HAWT) rotor, and it is obtained that although at the lower wind velocities the output power and the axial thrust of the rotor decrease, at the higher wind velocities the output power increases while the axial thrust decreases. The swept blades have shown about 30 percent increase in output power and about 12 percent decrease in thrust at the wind speed of 14 m/s.Article History: Received June 23rd 2018; Received in revised form Sept 16th 2018; Accepted October 1st 2018; Available onlineHow to Cite This Article: Salari, M.S., Boushehri, B.Z. and Boroushaki, M. (2018). Aerodynamic Analysis of Backward Swept in HAWT Rotor Blades Using CFD. International Journal of Renewable Energy Development, 7(3), 241-249.http://dx.doi.org/10.14710/ijred.7.3.241-249

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Kang, Wenzhe, Lingjiu Zhou, Dianhai Liu i Zhengwei Wang. "Backflow effects on mass flow gain factor in a centrifugal pump". Science Progress 104, nr 2 (kwiecień 2021): 003685042199886. http://dx.doi.org/10.1177/0036850421998865.

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Previous researches has shown that inlet backflow may occur in a centrifugal pump when running at low-flow-rate conditions and have nonnegligible effects on cavitation behaviors (e.g. mass flow gain factor) and cavitation stability (e.g. cavitation surge). To analyze the influences of backflow in impeller inlet, comparative studies of cavitating flows are carried out for two typical centrifugal pumps. A series of computational fluid dynamics (CFD) simulations were carried out for the cavitating flows in two pumps, based on the RANS (Reynolds-Averaged Naiver-Stokes) solver with the turbulence model of k- ω shear stress transport and homogeneous multiphase model. The cavity volume in Pump A (with less reversed flow in impeller inlet) decreases with the decreasing of flow rate, while the cavity volume in Pump B (with obvious inlet backflow) reach the minimum values at δ = 0.1285 and then increase as the flow rate decreases. For Pump A, the mass flow gain factors are negative and the absolute values increase with the decrease of cavitation number for all calculation conditions. For Pump B, the mass flow gain factors are negative for most conditions but positive for some conditions with low flow rate coefficients and low cavitation numbers, reaching the minimum value at condition of σ = 0.151 for most cases. The development of backflow in impeller inlet is found to be the essential reason for the great differences. For Pump B, the strong shearing between backflow and main flow lead to the cavitation in inlet tube. The cavity volume in the impeller decreases while that in the inlet tube increases with the decreasing of flow rate, which make the total cavity volume reaches the minimum value at δ = 0.1285 and then the mass flow gain factor become positive. Through the transient calculations for cavitating flows in two pumps, low-frequency fluctuations of pressure and flow rate are found in Pump B at some off-designed conditions (e.g. δ = 0.107, σ = 0.195). The relations among inlet pressure, inlet flow rate, cavity volume, and backflow are analyzed in detail to understand the periodic evolution of low-frequency fluctuations. Backflow is found to be the main reason which cause the positive value of mass flow gain factor at low-flow-rate conditions. Through the transient simulations of cavitating flow, backflow is considered as an important aspect closely related to the hydraulic stability of cavitating pumping system.

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Liang, Long, Song-Charng Kong, Chulhwa Jung i Rolf D. Reitz. "Development of a Semi-implicit Solver for Detailed Chemistry in Internal Combustion Engine Simulations". Journal of Engineering for Gas Turbines and Power 129, nr 1 (28.02.2006): 271–78. http://dx.doi.org/10.1115/1.2204979.

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An efficient semi-implicit numerical method is developed for solving the detailed chemical kinetic source terms in internal combustion (IC) engine simulations. The detailed chemistry system forms a group of coupled stiff ordinary differential equations (ODEs), which presents a very stringent time-step limitation when solved by standard explicit methods, and is computationally expensive when solved by iterative implicit methods. The present numerical solver uses a stiffly stable noniterative semi-implicit method. The formulation of numerical integration exploits the physical requirement that the species density and specific internal energy in the computational cells must be non-negative, so that the Lipschitz time-step constraint is not present and the computation time step can be orders of magnitude larger than that possible in standard explicit methods. The solver exploits the characteristics of the stiffness of the ODEs by using a sequential sort algorithm that ranks an approximation to the dominant eigenvalues of the system to achieve maximum accuracy. Subcycling within the chemistry solver routine is applied for each computational cell in engine simulations, where the subcycle time step is dynamically determined by monitoring the rate of change of concentration of key species, which have short characteristic time scales and are also important to the chemical heat release. The chemistry solver is applied in the KIVA-3V code to diesel engine simulations. Results are compared to those using the CHEMKIN package, which uses the VODE implicit solver. Good agreement was achieved for a wide range of engine operating conditions, and 40-70% CPU time savings were achieved by the present solver compared to the standard CHEMKIN.

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Mramor, Katarina, Robert Vertnik i Božidar Šarler. "Development of Three-Dimensional LES Based Meshless Model of Continuous Casting of Steel". Metals 12, nr 10 (18.10.2022): 1750. http://dx.doi.org/10.3390/met12101750.

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A large-eddy simulation (LES) based meshless model is developed for the three-dimensional (3D) problem of continuous casting (CC) of steel billet. The local collocation meshless method based on radial basis functions (RBF) is applied in 3D. The method applies scaled multiquadric (MQ) RBF with a shape parameter on seven nodded local sub-domains. The incompressible turbulent fluid flow is described using mass, energy, and momentum conservation equations and the LES turbulence model. The solidification system is solved with the mixture continuum model. The Boussinesq approximation for buoyancy and the Darcy approximation for porous media are used. Chorin’s fractional step method is used to couple velocity and pressure. The microscopic model is closed with the lever rule model. The LES model is compared to the two-equation Low Re k−ε turbulence Reynolds Averaged Navier–Stokes (RANS) model in terms of temperature, velocity and computational times. The LES model resolves transient character of vortices which RANS-type turbulence models are unable to tackle. The computational cost of LES models is considerably higher than in RANS. On the other hand, it results in a much lower computational cost than the direct numerical simulation (DNS). The paper demonstrates the ability of the method to solve realistic industrial 3D examples. Trivial adjustment of nodal densities, high accuracy, and low numerical diffusivity are the main advantages of this meshless method.

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Ryu, Seo Yoon, Cheolung Cheong, Jong Wook Kim i Byung il Park. "Development of virtual fan flow and acoustic performance testers based on RANS solvers and acoustic analogy". INTER-NOISE and NOISE-CON Congress and Conference Proceedings 263, nr 2 (1.08.2021): 4336–42. http://dx.doi.org/10.3397/in-2021-2667.

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As the potential of computational resources dramatically increases, the so-called computer-aided engineering readily replaces experiment-based engineering in related industrial fields. In this study, the virtual fan flow and acoustic performance testers are developed using the RANS solvers and the acoustic analogy. Two types of forward-curved centrifugal fans are selected for numerical and experimental investigations into its flow and acoustic performances. First, to experimentally evaluate the performances of the centrifugal fan units, their P-Q curves and sound power levels are measured using a fan flow performance tester and a semi-anechoic chamber, respectively. Second, the virtual fan flow and acoustic performance testers are constructed using the RANS solvers and the acoustic analogy based on the FW-H equation and CFD method. The validity of the current virtual methods is confirmed by comparing the prediction results with the measured ones. During the validation, the effects of the wall functions, y+ distribution, and turbulence models on predicted flow performance accuracy are closely examined. The effects of the integral surfaces used for the computation of the FW-H equations are also assessed on the predicted spectral levels of sound pressure.

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Rakai, Aniko, i Jörg Franke. "Validation of two RANS solvers with flow data of the flat roof Michelstadt case". Urban Climate 10 (grudzień 2014): 758–68. http://dx.doi.org/10.1016/j.uclim.2013.11.003.

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Pellone, C., T. Maître i J. P. Franc. "RANS Simulations of Supercavity Flows". Journal of Ship Research 54, nr 03 (1.09.2010): 161–73. http://dx.doi.org/10.5957/jsr.2010.54.3.161.

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This work aims at evaluating the capacity and limitations of conventional Reynolds-averaged Navier-Stokes (RANS) techniques to numerically simulate supercavity flows. The configuration is that of a two-dimensional (2D) symmetrical supercavitating wedge investigated experimentally by Michel (1974). Mesh effect is studied in detail under noncavitating conditions. The computational grid is refined in the region where cavitation develops in order to accurately track the supercavity. The effect of tunnel height is also analyzed, and the height finally chosen was large enough to simulate an infinite flow-field. The cavitating flow is treated as a homogeneous mixture of variable density. To account for vaporization and condensation, an additional continuity equation for the vapor (or the liquid) is solved with an appropriate source term expressing mass transfer between the two phases. The effect of nuclei concentration on the vaporization rate and then on the development of the supercavity is investigated. Results obtained using two different RANS codes are compared. They are also compared with experimental data and with inviscid solutions including a nonlinear boundary element method. They concern in particular cavity length and shape, pressure distribution, and drag coefficient. Under unsteady conditions, a special attention is paid to the characteristic growth time of the supercavity following a sudden pressure drop, from noncavitating conditions.

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R., Feshchur, i Sosnova N. "EVALUATION OF THE GENERAL ATTRACTIVENESS OF THE URBAN PUBLIC SPACE ACCORDING TO MANY CRITERIA". Vìsnik Nacìonalʹnogo unìversitetu "Lʹvìvsʹka polìtehnìka". Serìâ Arhìtektura 2, nr 2 (listopad 2020): 193–203. http://dx.doi.org/10.23939/sa2020.02.193.

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Cities are constantly changing – new and existing facilities are created and reconstructed, existing ones are modernized, and new territories are developed, and, accordingly, public spaces are formed and develop in a certain way. To a large extent, this process is random and does not take place systematically, but this rather happens as a response to the urgent economic, environmental, social or other needs of city residents. Development management in the urban planning system is designed to solve the controversial problem of maintaining integrity and at the same time striving for its transformation. The use of the tools of mathematical modeling, considered in the article, allows one to solve the problems of spatial development of a city and its public spaces in a purposeful way, and to coordinate such a solution with the interests of stakeholders. When forming public spaces of a city one faces the task of streamlining competing development projects (alternative projects) for a particular area of a city, taking into account the importance of their impact on the establishment of a distinctive image of the city and ensuring quality of life of its residents. To solve this problem, it is advisable to use methods of expert evaluation of design decisions, in particular, methods of ranking, valuating, and folding vector-valued criterion into a scalar criterion (integrated indicator of project weight). Ranking means assignment of a certain rank (a number from the natural series) to every project. The most important project is given the highest rank, which corresponds to number "one". The sum of the ranks given by all experts to a particular project can be considered as a generalized value of its weight. The article considers approaches to the assessment of urban public spaces on the basis of various criteria, namely urban, social, economic, environmental ones. The developed models of public space planning are designed for making a reasonable choice from a set of alternative projects subject to implementation, either according to the dominant criterion or according to many criteria in the conditions of resource constraints.

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Otake, Yoshie. "RIKEN Accelerator-driven compact neutron systems". EPJ Web of Conferences 231 (2020): 01009. http://dx.doi.org/10.1051/epjconf/202023101009.

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RIKEN Accelerator-driven compact neutron source, RANS, has been operational since 2013. There are two major goals of RANS research and development. One is to establish a new compact low energy neutron non-destructive evaluation system on-site of floor-standing type for industrial use. Another goal is to invent a novel transportable compact neutron system for the preventive maintenance of large scale construction such as a bridge. The low energy transmission imaging, neutron diffractometer, small angle scattering instruments, fast neutron transmission imaging, fast neutron back scattering imaging, neutron induced prompt gamma-ray analysis and neutron activation analysis are available with RANS. To solve the lack of nuclear data to develop compact neutron sources, we have created new function which gives neutron spectrum from the 9Be +p reaction with protons of energy below 12 MeV. For further compact neutron system, RANS-II is now ready to generate neutrons in the RANS experimental hall with individual shielding system. The novel proton accelerator tube and 500 MHz solid state high-frequency amplifier for RANS-III, of a transportable neutron system, are now ready to be developed in RIKEN.

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Lohrmann, David K., i Stuart W. Fors. "Can School-Based Educational Programs Really Be Expected to Solve the Adolescent Drug Abuse Problem?" Journal of Drug Education 16, nr 4 (grudzień 1986): 327–39. http://dx.doi.org/10.2190/2mue-3d1d-agnf-fxha.

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The recommendation of a 1984 Rand Corporation report that the most effective way to prevent adolescent drug abuse is through preventive education is reviewed within the context of theories related to the causes of drug abuse integrated with the PRECEDE model of health education program planning. It is concluded that many of the variables which influence adolescents to begin use of psychoactive substances are not within the purview of schools. Therefore, the Rand recommendation should only be accepted if three conditions are met: 1) there should be a consistent governmental policy toward drug education including funding for curriculum development, teacher training, implementation, evaluation and maintenance; 2) there should be special educational intervention programs for high risk children; and 3) specific strategies should be developed and implemented to elicit active support from social institutions besides schools.

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T, Pradeep, i Umadevi P. "Assessment of factors Influencing Communication among bottom line and top management in Construction Industry". YMER Digital 21, nr 02 (11.02.2022): 238–47. http://dx.doi.org/10.37896/ymer21.02/24.

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In day-to-day life the construction industry has become active with more desgins and construction project. Their emerging field existence involves management and execution by highly qualified and task coordinated project team from various organization. Throughout the project, required information must be identified and discussed amount of information flows among the entire workers in the construction industry. Few factors has been identified through the research. The identified factors are inaccuracy, misunderstanding, barriers, project complexity, timeliness, project communication media, arrangement of organization of structure, trust among workers, project culture, clarity in information. The questionnaire design was prepared after the identification of factors and circulated among more companies. The most affected critical factors are misunderstanding, Barriers, Project complexity, Communication media, Organization structure. The supervisor has the ability to solve the problem between the labors ranks 1 and the factor trust among the workers is more. The factors were analyzed by using SPSS software and relative important index was calculated to rank the factors

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Mitikhin, V., T. Solokhina, G. Tiumenkova i M. Kuzminova. "Using the analytic hierarchy process to assess the severity of psychopathological states". European Psychiatry 65, S1 (czerwiec 2022): S755. http://dx.doi.org/10.1192/j.eurpsy.2022.1951.

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Introduction Currently, there are known problems of assessing the severity of psychopathological states based on psychometric (rank) scales [1]. The main problem: ranks are non-numeric information that does not allow the simplest mathematical operations (summation, average) [2] and, as a result, the impossibility of constructing correct models for evaluating states Objectives Development of algorithms for processing initial rank information about the severity of psychopathological states in order to obtain results in numerical form based on the Analytic Hierarchy Process (AHP) [2] Methods Clinical, statistical, algorithms of the AHP. Results The problems of assessing the patient’s states are multicriteria. They are solved within the framework of AHP by constructing numerical intensity scales when measuring the dimensions of disorders. This means a correct transition from the rank scale to the scale of relations, in which the estimates are numbers that allow any mathematical operations. The implementation of AHP procedures is based on the application of the AHP normative approach [2], which uses expert comparisons of ratings of the rank scale. Conclusions The fundamental difference between the results based on AHP and rank results is due to the fact that numerical estimates of the severity of states are obtained, which can be used for any mathematical processing and the construction of correct models of communication and prediction of the state of patients from many factors, taking into account their weight. References: 1. Zimmerman M., Morgan T.A., Stanton K. World Psychiatry. 2018;17: 258–275. 2. Mitikhin, V.G., Solokhina, T.A. S.S. Korsakov Journal of Neurology and Psychiatry. 2019; 119(2): 49-54. Disclosure No significant relationships.

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Nakonieczny, Damian S., Magdalena Antonowicz i Zbigniew Paszenda. "Surface modification methods of ceramic filler in ceramic-carbon fibre composites for bioengineering applications – A systematic review". REVIEWS ON ADVANCED MATERIALS SCIENCE 59, nr 1 (18.11.2020): 586–605. http://dx.doi.org/10.1515/rams-2020-0024.

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AbstractThe present review paper focuses on the current state of the art of the alumina-silicate ceramics and surface modifications of ceramics dedicated as fillers in composites with carbon fiber. The use of aluminum-silicates in the form of a cenosphere due to their outstanding properties, i.e., low density, high hardness, and total chemical inertness seem to be promising in biomaterial engineering applications. First of all, the possibilities of the composites application in orthopedic and prosthetic implantology. The following section discusses problems with the use of aluminum silicate ceramics and their processing. Subsequently, in the paragraphs to follow, the possibilities of modifying the surface with chemical methods are discussed, among others oxidation, chemical methods like ionic liquids etching, silanization, and physical processes i.e., thermal treatment. In the summary, the directions of development of ceramic-carbon fiber composites and the primary deficiencies of these composites on which to focus on and solve are discussed.

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Afailal, Al Hassan, Jérémy Galpin, Anthony Velghe i Rémi Manceau. "Development and validation of a hybrid temporal LES model in the perspective of applications to internal combustion engines". Oil & Gas Science and Technology – Revue d’IFP Energies nouvelles 74 (2019): 56. http://dx.doi.org/10.2516/ogst/2019031.

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CFD simulation tools are increasingly used nowadays to design more fuel-efficient and clean Internal Combustion Engines (ICE). Within this framework, there is a need to benefit from a turbulence model which offers the best compromise between prediction capabilities and computational cost. The Hybrid Temporal LES (HTLES) approach is here retained within the perspective of an application to ICE configurations. HTLES is a hybrid Reynolds-Averaged Navier Stokes/Large Eddy Simulation (RANS/LES) model based on a solid theoretical framework using temporal filtering. The concept is to model the near-wall region in RANS and to solve the turbulent structures in the core region if the temporal and spatial resolutions are fine enough. In this study, a dedicated sub-model called Elliptic Shielding (ES) is added to HTLES in order to ensure RANS in the near-wall region, regardless of the mesh resolution. A modification of the computation of the total kinetic energy and the dissipation rate was introduced as first adaptions of HTLES towards non-stationary ICE configurations. HTLES is a recent approach, which has not been validated in a wide range of applications. The present study intends to further validate HTLES implemented in CONVERGE code by examining three stationary test cases. The first validation consists of the periodic hill case, which is a standard benchmark case to assess hybrid turbulence models. Then, in order to come closer to real ICE simulations, i.e., with larger Reynolds numbers and coarser near-wall resolutions, the method is validated in the case of a channel flow using wall functions and in the steady flow rig case consisting in an open valve at a fixed lift. HTLES results are compared to RANS k-ω SST and wall-modeled LES σ simulations performed with the same grid and the same temporal resolution. Unlike RANS, satisfactory reproduction of the flow recirculation has been observed with HTLES in the case of periodic hills. The channel flow configuration has underlined the capability of HTLES to predict the wall friction properly. The steady flow rig shows that HTLES combines advantages of RANS and LES in one simulation. On the one hand, HTLES yields mean and rms velocities as accurate as LES since the scale-resolving simulation is triggered in the core region. On the other hand, hybrid RANS/LES at the wall provides accurate pressure drop in contrast with LES performed on the same mesh. Future work will be dedicated to the extension of HTLES to non-stationary flows with moving walls in order to be able to tackle realistic ICE flow configurations.

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Hong, Phuc Nguyen, i Chang Wook Ahn. "Stereo Matching Methods for Imperfectly Rectified Stereo Images". Symmetry 11, nr 4 (19.04.2019): 570. http://dx.doi.org/10.3390/sym11040570.

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Stereo matching has been under development for decades and is an important process for many applications. Difficulties in stereo matching include textureless regions, occlusion, illumination variation, the fattening effect, and discontinuity. These challenges are effectively solved in recently developed stereo matching algorithms. A new imperfect rectification problem has recently been encountered in stereo matching, and the problem results from the high resolution of stereo images. State-of-the-art stereo matching algorithms fail to exactly reconstruct the depth information using stereo images with imperfect rectification, as the imperfectly rectified image problems are not explicitly taken into account. In this paper, we solve the imperfect rectification problems, and propose matching stereo matching methods that based on absolute differences, square differences, normalized cross correlation, zero-mean normalized cross correlation, and rank and census transforms. Finally, we conduct experiments to evaluate these stereo matching methods using the Middlebury datasets. The experimental results show the proposed stereo matching methods can reduce error rate significantly for stereo images with imperfect rectification.

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Yang, Anbang, Jiangbo Qian, Huahui Chen i Yihong Dong. "A Ranking-Based Hashing Algorithm Based on the Distributed Spark Platform". Information 11, nr 3 (9.03.2020): 148. http://dx.doi.org/10.3390/info11030148.

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With the rapid development of modern society, generated data has increased exponentially. Finding required data from this huge data pool is an urgent problem that needs to be solved. Hashing technology is widely used in similarity searches of large-scale data. Among them, the ranking-based hashing algorithm has been widely studied due to its accuracy and speed regarding the search results. At present, most ranking-based hashing algorithms construct loss functions by comparing the rank consistency of data in Euclidean and Hamming spaces. However, most of them have high time complexity and long training times, meaning they cannot meet requirements. In order to solve these problems, this paper introduces a distributed Spark framework and implements the ranking-based hashing algorithm in a parallel environment on multiple machines. The experimental results show that the Spark-RLSH (Ranking Listwise Supervision Hashing) can greatly reduce the training time and improve the training efficiency compared with other ranking-based hashing algorithms.

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Alexandrov, Islam A., Andrey V. Kirichek, Vladimir Z. Kuklin i Leonid M. Chervyakov. "Development of an Algorithm for Multicriteria Optimization of Deep Learning Neural Networks". HighTech and Innovation Journal 4, nr 1 (1.03.2023): 157–73. http://dx.doi.org/10.28991/hij-2023-04-01-011.

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Nowadays, machine learning methods are actively used to process big data. A promising direction is neural networks, in which structure optimization occurs on the principles of self-configuration. Genetic algorithms are applied to solve this nontrivial problem. Most multicriteria evolutionary algorithms use a procedure known as non-dominant sorting to rank decisions. However, the efficiency of procedures for adding points and updating rank values in non-dominated sorting (incremental non-dominated sorting) remains low. In this regard, this research improves the performance of these algorithms, including the condition of an asynchronous calculation of the fitness of individuals. The relevance of the research is determined by the fact that although many scholars and specialists have studied the self-tuning of neural networks, they have not yet proposed a comprehensive solution to this problem. In particular, algorithms for efficient non-dominated sorting under conditions of incremental and asynchronous updates when using evolutionary methods of multicriteria optimization have not been fully developed to date. To achieve this goal, a hybrid co-evolutionary algorithm was developed that significantly outperforms all algorithms included in it, including error-back propagation and genetic algorithms that operate separately. The novelty of the obtained results lies in the fact that the developed algorithms have minimal asymptotic complexity. The practical value of the developed algorithms is associated with the fact that they make it possible to solve applied problems of increased complexity in a practically acceptable time. Doi: 10.28991/HIJ-2023-04-01-011 Full Text: PDF

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Liu, Guangjun, Xiaoping Xu, Feng Wang i Yangli Tang. "Solving Traveling Salesman Problems Based on Artificial Cooperative Search Algorithm". Computational Intelligence and Neuroscience 2022 (12.04.2022): 1–8. http://dx.doi.org/10.1155/2022/1008617.

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The traveling salesman problem is a typical NP hard problem and a typical combinatorial optimization problem. Therefore, an improved artificial cooperative search algorithm is proposed to solve the traveling salesman problem. For the basic artificial collaborative search algorithm, firstly, the sigmoid function is used to construct the scale factor to enhance the global search ability of the algorithm; secondly, in the mutation stage, the DE/rand/1 mutation strategy of differential evolution algorithm is added to carry out secondary mutation to the current population, so as to improve the calculation accuracy of the algorithm and the diversity of the population. Then, in the later stage of the algorithm development, the quasi-reverse learning strategy is introduced to further improve the quality of the solution. Finally, several examples of traveling salesman problem library (TSPLIB) are solved using the improved artificial cooperative search algorithm and compared with the related algorithms. The results show that the proposed algorithm is better than the comparison algorithm in solving the travel salesman problem and has good robustness.

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Li, Yu, Xiaoxiao Lin i Jingsen Liu. "An Improved Gray Wolf Optimization Algorithm to Solve Engineering Problems". Sustainability 13, nr 6 (15.03.2021): 3208. http://dx.doi.org/10.3390/su13063208.

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With the rapid development of the economy, the disparity between supply and demand of resources is becoming increasingly prominent in engineering design. In this paper, an improved gray wolf optimization algorithm is proposed (IGWO) to optimize engineering design problems. First, a tent map is used to generate the initial location of the gray wolf population, which evenly distributes the gray wolf population and lays the foundation for a diversified global search process. Second, Gaussian mutation perturbation is used to perform various operations on the current optimal solution to avoid the algorithm falling into local optima. Finally, a cosine control factor is introduced to balance the global and local exploration capabilities of the algorithm and to improve the convergence speed. The IGWO algorithm is applied to four engineering optimization problems with different typical complexity, including a pressure vessel design, a tension spring design, a welding beam design and a three-truss design. The experimental results show that the IGWO algorithm is superior to other comparison algorithms in terms of optimal performance, solution stability, applicability and effectiveness; and can better solve the problem of resource waste in engineering design. The IGWO also optimizes 23 different types of function problems and uses Wilcoxon rank-sum test and Friedman test to verify the 23 test problems. The results show that the IGWO algorithm has higher convergence speed, convergence precision and robustness compared with other algorithms.

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Jungo, Aidan, Mengmeng Zhang, Jan B. Vos i Arthur Rizzi. "Benchmarking New CEASIOM with CPACS adoption for aerodynamic analysis and flight simulation". Aircraft Engineering and Aerospace Technology 90, nr 4 (8.05.2018): 613–26. http://dx.doi.org/10.1108/aeat-11-2016-0204.

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Purpose The purpose of this paper is to present the status of the on-going development of the new computerized environment for aircraft synthesis and integrated optimization methods (CEASIOM) and to compare results of different aerodynamic tools. The concurrent design of aircraft is an extremely interdisciplinary activity incorporating simultaneous consideration of complex, tightly coupled systems, functions and requirements. The design task is to achieve an optimal integration of all components into an efficient, robust and reliable aircraft with high performance that can be manufactured with low technical and financial risks, and has an affordable life-cycle cost. Design/methodology/approach CEASIOM (www.ceasiom.com) is a framework that integrates discipline-specific tools like computer-aided design, mesh generation, computational fluid dynamics (CFD), stability and control analysis and structural analysis, all for the purpose of aircraft conceptual design. Findings A new CEASIOM version is under development within EU Project AGILE (www.agile-project.eu), by adopting the CPACS XML data-format for representation of all design data pertaining to the aircraft under development. Research limitations/implications Results obtained from different methods have been compared and analyzed. Some differences have been observed; however, they are mainly due to the different physical modelizations that are used by each of these methods. Originality/value This paper summarizes the current status of the development of the new CEASIOM software, in particular for the following modules: CPACS file visualizer and editor CPACSupdater (Matlab) Automatic unstructured (Euler) & hybrid (RANS) mesh generation by sumo Multi-fidelity CFD solvers: Digital Datcom (Empirical), Tornado (VLM), Edge-Euler & SU2-Euler, Edge-RANS & SU2-RANS Data fusion tool: aerodynamic coefficients fusion from variable fidelity CFD tools above to compile complete aero-table for flight analysis and simulation.

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Kovalchuk, Olha, i Nataliia Strelbitska. "MODEL ANALYSIS OF INDICATORS OF SUSTAINABLE DEVELOPMENT OF WORLD COUNTRIES". Economic Analysis, nr 28(1) (2018): 71–78. http://dx.doi.org/10.35774/econa2018.01.071.

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The article discusses the possibilities of use of classical instruments of analytical methods and data mining methods for global sustainability modelling. To divide countries into groups according to the indicators that are traditionally allocated for sustainability studying, it is carried out the cluster analysis by k-medium method, which resulted in 2 clusters. The first cluster includes economically developed industrialized countries. A high level of social performance and a low level of inequality of outcomes characterize them. At the same time, these countries have high rank of corruption and low Gini Index. There are low social standards, but significantly lower rank of corruption and footprint than in developed countries in the countries of the second cluster. However, the index of inequality of outcomes is three times higher than in the countries included in the first cluster. The tree graph classification of the countries of the world has been constructed on the basis of indicators of sustainable development. The computer models, which are presented in this paper, aim to solve the main problems of sustainable development. They can also be applicable in many other fields, including international relations, economics, and management systems.

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Weatheritt, Jack, i Richard David Sandberg. "Improved Junction Body Flow Modeling Through Data-Driven Symbolic Regression". Journal of Ship Research 63, nr 4 (1.12.2019): 283–93. http://dx.doi.org/10.5957/josr.09180053.

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A novel data-driven turbulence modeling framework is presented and applied to the problem of junction body flow. In particular, a symbolic regression approach is used to find nonlinear analytical expressions of the turbulent stress‐strain coupling that are ready for implementation in computational fluid dynamics (CFD) solvers using Reynolds-averaged Navier‐Stokes (RANS) closures. Results from baseline linear RANS closure calculations of a finite square-mounted cylinder with a Reynolds number of <inline-graphic xlink:href="josr09180053inf1.tif"/>, based on diameter and freestream velocity, are shown to considerably overpredict the separated flow region downstream of the square cylinder, mainly because of the failure of the model to accurately represent the complex vortex structure generated by the junction flow. In the present study, a symbolic regression tool built on a gene expression programming technique is used to find a nonlinear constitutive stress‐strain relationship. In short, the algorithm finds the most appropriate linear combination of basis functions and spatially varying coefficients that approximate the turbulent stress tensor from high-fidelity data. Here, the high-fidelity data, or the so-called training data, were obtained from a hybrid RANS/Large Eddy Simulation (LES) calculation also developed with symbolic regression that showed excellent agreement with direct numerical simulation data. The present study, therefore, also demonstrates that training data required for RANS closure development can be obtained using computationally more affordable approaches, such as hybrid RANS/LES. A procedure is presented to evaluate which of the individual basis functions that are available for model development are most likely to produce a successful nonlinear closure. A new model is built using those basis functions only. This new model is then tested, i.e., an actual CFD calculation is performed, on the well-known periodic hills case and produces significantly better results than the linear baseline model, despite this test case being fundamentally different from the training case. Finally, the new model is shown to also improve predictive accuracy for a surface-mounted cube placed in a channel at a cube height Reynolds number of <inline-graphic xlink:href="josr09180053inf2.tif"/> over traditional linear RANS closures.

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Kinnas, Spyros A., Hongyang Fan i Ye Tian. "A Panel Method with a Full Wake Alignment Model for the Prediction of the Performance of Ducted Propellers". Journal of Ship Research 59, nr 03 (1.09.2015): 246–57. http://dx.doi.org/10.5957/jsr.2015.59.3.246.

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An improved perturbation potential-based panel method is applied to model the flow around ducted propellers. One significant development in this method is the application of full wake alignment scheme in which the trailing vortex wake sheets of the blades are aligned with the local flow velocity by also considering the effects of duct and duct wake. A process of repaneling the duct is simultaneously introduced to improve the accuracy of the method. The results from the improved wake model are compared with those from a simplified wake alignment scheme. At the same time, full-blown Reynolds-averaged Navier-Stokes (RANS) simulations are conducted via commercial solvers. The forces, i.e., thrust and torque, on the propeller predicted by this panel method under the improved wake alignment model show good agreement both with experimental measurements, a hybrid method developed by the Ocean Engineering Group of University of Texas at Austin, and the full-blown RANS simulations. Moreover, predicted pressure distribution on the blades and duct are compared among the various methods.

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Xiao, Tuo, Taiping Cui, S. M. Riazul Islam i Qianbin Chen. "Joint Content Placement and Storage Allocation Based on Federated Learning in F-RANs". Sensors 21, nr 1 (31.12.2020): 215. http://dx.doi.org/10.3390/s21010215.

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With the rapid development of mobile communication and the sharp increase of smart mobile devices, wireless data traffic has experienced explosive growth in recent years, thus injecting tremendous traffic into the network. Fog Radio Access Network (F-RAN) is a promising wireless network architecture to accommodate the fast growing data traffic and improve the performance of network service. By deploying content caching in F-RAN, fast and repeatable data access can be achieved, which reduces network traffic and transmission latency. Due to the capacity limit of caches, it is essential to predict the popularity of the content and pre-cache them in edge nodes. In general, the classic prediction approaches require the gathering of users’ personal information at a central unit, giving rise to users’ privacy issues. In this paper, we propose an intelligent F-RANs framework based on federated learning (FL), which does not require gathering user data centrally on the server for training, so it can effectively ensure the privacy of users. In the work, federated learning is applied to user demand prediction, which can accurately predict the content popularity distribution in the network. In addition, to minimize the total traffic cost of the network in consideration of user content requests, we address the allocation of storage resources and content placement in the network as an integrated model and formulate it as an Integer Linear Programming (ILP) problem. Due to the high computational complexity of the ILP problem, two heuristic algorithms are designed to solve it. Simulation results show that the performance of our proposed algorithm is close to the optimal solution.

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Zweig, David. "Prosperity and Conflict in Post-Mao Rural China". China Quarterly 105 (marzec 1986): 1–18. http://dx.doi.org/10.1017/s0305741000036742.

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In 1980 the People's Daily reported that 200 million Chinese peasants were living below the poverty line, while in 1982 Vicepremier Wan Li admitted the “for many years in the past, more than 150 million peasants had not solved the problem of not having enough to eat.” To enrich the rural economy, Party leaders called on peasants to pursue numerous private roads to prosperity. The new policy, highlighted by the phrase “permit some peasants to get rich first” (rang yixie nongmin xian fuqilai), allows households who are more industrious, more innovative and, of course, those with better personal and economic ties, to utilize their skills, personal relationships, excess labour power, and comparative advantages to accrue wealth quickly.

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Zhao, Wei, Sheng Chen, Junyi Yang i Weichang Zhou. "Assessment of RANS Turbulence Models in Prediction of the Hydrothermal Plume in the Longqi Hydrothermal Field". Applied Sciences 13, nr 13 (25.06.2023): 7496. http://dx.doi.org/10.3390/app13137496.

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In this paper, the numerical models are selected to simulate the hydrothermal plume based on the water temperature observation data of the Longqi hydrothermal field in the Southwest Indian Ridge (SWIR). Then, the unsteady Reynolds-averaged Navier–Stokes equations are solved to evaluate the performance of the Realizable k-ε (rke) model and the SST k-ω (sst) model in hydrothermal plume simulation. By comparing the calculated results with the Conductivity Temperature Depth (CTD) observation data and the literature results, the difference in prediction performance between the two models is evaluated. Before the numerical simulation, the optimal mesh parameters are determined by considering the grid independence test. The results show that the relative difference of the maximum plume height calculated by the two models is within 5%. Compared with the CTD 05-2, the rke model calculates the root mean square error of the velocity is 0.5081, which is smaller than that of the sst model. In terms of turbulent viscosity, the rke model is in good agreement with reference value in predicting turbulent viscosity. Therefore, the turbulent viscosity distribution calculated by the rke model is more consistent with the plume development process than that calculated by the sst model. In addition, the two models have the same effect on the prediction of turbulent kinetic energy and plume temperature.

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Padmanabhan, K. A., i M. Raviathul Basariya. "On the Common Origin of Structural Superplasticity in Different Classes of Materials". REVIEWS ON ADVANCED MATERIALS SCIENCE 54, nr 1 (1.03.2018): 1–13. http://dx.doi.org/10.1515/rams-2018-0016.

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Abstract The present model starts with an assumption that grain/ interphase boundary sliding (GBS) that is dominant during optimal superplastic flow is slower than the accommodation processes of dislocation emission from sliding boundaries, highly localized diffusion in the boundary regions and/ or grain rotation that are present as a concomitant of the GBS process. When boundary sliding develops to a mesoscopic scale (of the order of a grain diameter or more), by the alignment of contiguous boundaries, plane interface formation/ mesoscopic boundary sliding is observed. Significant and simultaneous sliding along different plane interfaces and their interconnection can lead to large scale deformation and superplasticity. The accommodation steps, being faster than GBS, do not enter the strain rate equation. Mathematical development of these ideas using transition state theory results in a transcendental strain rate equation for steady state optimal superplastic flow, which when solved numerically helps one to describe the phenomenon quantitatively in terms of two constants, the activation energy for the rate controlling process, ΔF0and the threshold stress needed to be overcome for the commencement of mesoscopic boundary sliding, σ0.The analysis also explains quantitatively texture randomization as a function of superplastic strain. It is also pointed out, without going into details, that recently the problem has been reduced to FOUR “universal” constants, viz. the mean strain associated with a unit boundary sliding event g0, specific grain boundary energy γB, which is assumed to be isotropic, N the average number of boundaries that align to form a plane interface during mesoscopic boundary sliding and “a” a grain-size- and shape- dependent constant that obeys the condition 0 <a <0.5, in terms of which one can account for superplasticity in any material. In combination with the regression equations popularized by Frost and Ashby to predict the shear modulus of any material at any temperature, these four constants allow one to predict the steady state strain rate of any structurally superplastic material accurately, including those whose superplastic response is not considered for the analysis. The details of the last mentioned result, which are unpublished, will be presented elsewhere.

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Liu, Zhao, Jianwei Ma i Xueshan Yong. "Line survey joint denoising via low-rank minimization". GEOPHYSICS 84, nr 1 (1.01.2019): V21—V32. http://dx.doi.org/10.1190/geo2018-0141.1.

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Prestack seismic data denoising is an important step in seismic processing due to the development of prestack time migration. Reduced-rank filtering is a state-of-the-art method for prestack seismic denoising that uses predictability between neighbor traces for each single frequency. Different from the original way of embedding low-rank matrix based on the Hankel or Toeplitz transform, we have developed a new multishot gathers joint denoising method in a line survey, which used a new way of rearranging data to a matrix with low rank. Inspired by video denoising, each single-shot record in the line survey can be viewed as a frame in the video sequence. Due to high redundancy and similar event structure among the shot gathers, similar patches can be selected from different shot gathers in the line survey to rearrange a low-rank matrix. Then, seismic denoising is formulated into a low-rank minimization problem that can be further relaxed into a nuclear-norm minimization problem. A fast algorithm, called the orthogonal rank-one matrix pursuit, is used to solve the nuclear-norm minimization. Using this method avoids the computation of a full singular value decomposition. Our method is validated using synthetic and field data, in comparison with [Formula: see text] deconvolution and singular spectrum analysis methods.

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I. Bon, Lizaveta. "Using L-Arginine-No Pathway Modulators in Rats with Subtotal Cerebral Ischemia. Histological Changes". Clinical Trials and Bioavailability Research 2, nr 1 (28.02.2023): 01–04. http://dx.doi.org/10.58489/2836-5836/007.

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Acute cerebrovascular accident is one of the most urgent problems in modern medicine. The frequency of strokes varies in different regions of the world from 1 to 4 cases per 1000 population per year, increasing significantly with age. Cerebrovascular diseases of ischemic origin tend to grow, rejuvenate, are associated with a severe clinical course, high rates of disability and mortality [1-6]. The relevance of the problem of cerebrovascular diseases can rightfully be defined as extraordinary, requiring the concentration of efforts of specialists of different profiles to solve it. Subtotal cerebral ischemia leads to the development of morphological and functional disorders of the cerebral cortex. The introduction of a non-selective NO–synthase inhibitor - L-NAME aggravated histological disorders of neurons that occur with SCI: an increase in the number of hyperchromic shrunken neurons, a decrease in the size and deformation of their pericaryons. Additional use of L -arginine partially eliminated the negative effect of L – NAME [1-8].

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Wang, Lin, Mengfan Shao, Yeqian Jiang i Qianqian Chen. "Research on Zhejiang Province's Textile and Apparel Export Based on SWOT Analysis". Advances in Economics and Management Research 1, nr 2 (20.09.2022): 11. http://dx.doi.org/10.56028/aemr.1.2.11.

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The textile and garment industry, as a vigorously developed industry in Zhejiang Province, ranks first in China's exports.In line with the development of the times, how to develop and developing the textile and garment export market at home and abroad is an urgent problem to be solved in the economic development of Zhejiang Province. It is related to the future development direction of my country's textile and garment industry.This paper uses the SWOT analysis method to analyze the export of the textile and apparel industry in Zhejiang Province and puts forward the countermeasures for improving the competitiveness of the textile and apparel industry in Zhejiang Province.

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