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Nordlund, K. "Historical review of computer simulation of radiation effects in materials". Journal of Nuclear Materials 520 (julio de 2019): 273–95. http://dx.doi.org/10.1016/j.jnucmat.2019.04.028.
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Darambara, D. G., A. N. Papadopoulos y N. M. Spyrou. "Computer simulation of positron-induced radiation effects in Dynamic RAMs". Radiation Effects and Defects in Solids 141, n.º 1-4 (junio de 1997): 141–48. http://dx.doi.org/10.1080/10420159708211565.
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Turichin, Gleb A., Ekaterina A. Valdaytseva, Stanislav L. Stankevich y Ilya N. Udin. "Computer Simulation of Hydrodynamic and Thermal Processes in DLD Technology". Materials 14, n.º 15 (25 de julio de 2021): 4141. http://dx.doi.org/10.3390/ma14154141.
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This article deals with the theoretical issues of the formation of a melt pool during the process of direct laser deposition. The shape and size of the pool depends on many parameters, such as the speed and power of the process, the optical and physical properties of the material, and the powder consumption. On the other hand, the influence of the physical processes occurring in the material on one another is significant: for instance, the heating of the powder and the substrate by laser radiation, or the formation of the free surface of the melt, taking into account the Marangoni effect. This paper proposes a model for determining the size of the melt bath, developed in a one-dimensional approximation of the boundary layer flow. The dimensions and profile of the surface and bottom of the melt pool are obtained by solving the problem of convective heat transfer. The influence of the residual temperature from the previous track, as well as the heat from the heated powder of the gas–powder jet, taking into account its spatial distribution, is considered. The simulation of the size and shape of the melt pool, as well as its free surface profile for different alloys, is performed with 316 L steel, Inconel 718 nickel alloy, and VT6 titanium alloy
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Vaz Sá, Ana, Miguel Azenha, A. S. Guimarães y J. M. P. Q. Delgado. "FEM Applied to Building Physics: Modeling Solar Radiation and Heat Transfer of PCM Enhanced Test Cells". Energies 13, n.º 9 (2 de mayo de 2020): 2200. http://dx.doi.org/10.3390/en13092200.
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In passive solar buildings, energy can be stored using either sensible heat materials or latent heat materials. Phase change materials (PCM) can contribute to temperature control in passive solar buildings when melting occurs near to comfort temperature required for building’s interior spaces. The use of finite element method (FEM) as a numerical methodology for solving the thermal problem associated with heat transfer in current building materials and PCMs make sense, as it is a well-known technique, generalized and dominated, however, still little applied to the domain of building physics. In this work, a solar model was developed and applied in order to simulate numerically the effect of solar radiation incidence on each face of the test cells (with different solar exposures) without neglecting the main objective of the recommended numerical simulation: the study of the action of PCM. During the experimental campaign, two test cells with distinct inner layers were used to evaluate the effect of solar radiation: (i) REFM test cell (without PCM) with a reference mortar; (ii) PCMM test cell (with PCM) with a PCM mortar. The temperatures monitored inside the REFM and PCMM test cells were compared with the values resulting from the numerical simulation, using FEM with 3D discretization and the explicit modeling of the solar radiation, and the obtained results revealed a significant coherence of values.
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Scarfone, L. M. y J. D. Chlipala. "Computer simulation of target link explosion in laser programmable redundancy for silicon memory". Journal of Materials Research 1, n.º 2 (abril de 1986): 368–81. http://dx.doi.org/10.1557/jmr.1986.0368.
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Pulses of Q-switched Nd-YAG radiation have been used to remove polysilicon target links during the implementation of laser programmable redundancy in the fabrication of silicon memory. The link is encapsulated by transparent dielectric films that give rise to important optical interference effects modifying the laser flux absorbed by the link and the silicon substrate. Estimates of these effects are made on the basis of classical plane-wave procedures. Thermal evolution of the composite structure is described in terms of a finite-difference form of the three-dimensional heat diffusion equation with a heat generation rate having a Gaussian spatial distribution of intensity and temporal shapes characteristic of commercial lasers. Temperature-dependent thermal diffusivity and melting of the polysilicon link are included in the computer modeling. The calculations account for the discontinuous change in the link absorption coefficient at the transition temperature. A threshold temperature and corresponding pressure, sufficiently high to rupture the dielectric above the link and initiate the removal process, are estimated by treating the molten link as a hard-sphere fluid. Numerical results are presented in the form of three-dimensional temperature distributions for 1.06 and 0.53 μm radiation with pulse energies 3.5 and 0.15μJ, respectively. Similarities and differences between heating effects produced by long (190 ns FWHM/740 ns duration) and short (35 ns FWHM/220 ns duration) pulses are pointed out.
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Bacon, D. J., A. F. Calder y F. Gao. "Computer simulation of displacement cascade effects in metals". Radiation Effects and Defects in Solids 141, n.º 1-4 (junio de 1997): 283–310. http://dx.doi.org/10.1080/10420159708211577.
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Parks, Joseph W., Kevin F. Brennan y Arlynn W. Smith. "Numerical Examination of Photon Recycling as an Explanation of Observed Carrier Lifetime in Direct Bandgap Materials". VLSI Design 8, n.º 1-4 (1 de enero de 1998): 153–57. http://dx.doi.org/10.1155/1998/16476.
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Photon recycling is examined as an explanation for the observed large carrier lifetimes in an InP/InGaAs photodiode. This effect extends the effective carrier lifetime within a device by re-absorbing a fraction of the photons generated through radiative band-toband recombination events. In order to predict the behavior of this carrier generation, photon recycling has been added to our two-dimensional macroscopic device simulator, STEBS-2D. A ray-tracing preprocessing step is used to map all of the possible trajectories and absorption of various wavelengths of emitted light from each originating node within the device. The macroscopic simulator uses these data to determine the spatial location of the re-absorbed radiation within the geometry of the device. By incorporating the ray tracer results with the total quantity and spectral content of recombined carriers at each node within the simulation, the recycled generation rate can be obtained. A practical application of this model is presented where the effects of photon recycling are used as a possible explanation of the discrepancy between the theoretically predicted and experimentally observed radiative recombination rate in a double heterostructure photodetector.
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de la Rubia, T. Diaz, M. W. Guinan, A. Caro y P. Scherrer. "Radiation effects in FCC metals and intermetallic compounds: A molecular dynamics computer simulation study". Radiation Effects and Defects in Solids ll, n.º 1 (julio de 1994): 39–54. http://dx.doi.org/10.1080/10420159408219769.
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Luminosu, Ioan, Sabata De y Sabata De. "Research in solar energy at the 'Politehnica' university of Timisoara: Studies on solar radiation and solar collectors". Thermal Science 14, n.º 1 (2010): 157–69. http://dx.doi.org/10.2298/tsci1001157l.
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A short overview of a more than 30 years long history and results of research and thermal applications of solar energy at the 'Politehnica' University of Timisoara, Romania, are presented. The main directions approached are: actinometry, studies on materials and greenhouse effect, thermal collectors, industrial and home thermal applications, computer simulation of physical phenomena, and concentrators. This paper focuses on the conception and building of a dedicated laboratory and on the experimental results that allowed the development of industrial and home applications.
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Miroshnichenko, Igor V. y M. A. Sheremet. "Numerical simulation of turbulent natural convection combined with surface thermal radiation in a square cavity". International Journal of Numerical Methods for Heat & Fluid Flow 25, n.º 7 (7 de septiembre de 2015): 1600–1618. http://dx.doi.org/10.1108/hff-09-2014-0289.
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Purpose – The purpose of this paper is to present transient turbulent natural convection with surface thermal radiation in a square differentially heated enclosure using non-primitive variables like stream function and vorticity. Design/methodology/approach – The governing equations formulated in dimensionless variables “stream function, vorticity and temperature,” within the Boussinesq approach taking into account the standard two equation k-ε turbulence model with physical boundary conditions have been solved using an iterative implicit finite-difference method. Findings – It has been found that using of the presented algebraic transformation of the mesh allows to effectively conduct numerical analysis of turbulent natural convection with thermal surface radiation. It has been shown that the average convective Nusselt number increases with the Rayleigh number and decreases with the surface emissivity, while the average radiative Nusselt number is an increasing function of these key parameters. It has been shown that a presence of surface thermal radiation effect leads to an expansion of the eddy viscosity zones close to the walls. Originality/value – It should be noted that for the first time in this paper we used stream function and vorticity variables with very effective algebraic transformation of the mesh in order to create a non-uniform mesh for an analysis of turbulent flow. Such method allows to reduce the computational time essentially in comparison with using of the primitive variables. The considered method has been successfully validated on the basis of the experimental and numerical data of other authors in case of turbulent natural convection without thermal radiation. The used numerical method would benefit scientists and engineers to become familiar with the analysis of turbulent convective heat and mass transfer, and the way to predict the properties of the turbulent flow in advanced nuclear systems, in industrial sectors including transportation, power generation, chemical sectors, ventilation, air-conditioning, etc.
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Dinguirard, J. P., D. Mostacci, J. Briand, A. Gomes, J. C. Kieffer, Y. Quemener, C. Arnas, L. Berge y M. Armengaud. "Numerical simulation of the X-ray energetics in spherical plasmas". Laser and Particle Beams 6, n.º 2 (mayo de 1988): 343–51. http://dx.doi.org/10.1017/s0263034600004109.
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1-D computer simulations have been performed to study the influence of X-rays preheating on the compression of spherical laser-produced plasmas. The targets are glass microballoons filled with Neon at the initial pressure 10 bars. It is assumed that the only significant absorption process in the Neon is by inverse bremsstrahlung absorption. The results indicate that the radiative preheating energy has a nonnegligible effect on the compression, and a study of the Lawson criterion shows that this effect is more important for high-Z target shell materials and for thicker shells.
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Rasheed, Na, Lee, Kim y Lee. "Optimization of Greenhouse Thermal Screens for Maximized Energy Conservation". Energies 12, n.º 19 (20 de septiembre de 2019): 3592. http://dx.doi.org/10.3390/en12193592.
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In this work, we proposed a Building Energy Simulation (BES) dynamic climatic model of greenhouses by utilizing Transient System Simulation (TRNSYS 18) software to study the effect of use of different thermal screen materials and control strategies of thermal screens on heat energy requirement of greenhouses. Thermal properties of the most common greenhouse thermal screens were measured and used in the BES model. Nash-Sutcliffe efficiency coefficients of 0.84 and 0.78 showed good agreement between the computed and experimental results, thus the proposed model appears to be appropriate for performing greenhouse thermal simulations. The proposed model was used to evaluate the effects of different thermal screens including; Polyester, Luxous, Tempa, and Multi-layers, as well as to evaluate control strategies of greenhouse thermal screens, subjected to Daegu city, (latitude 35.53 °N, longitude 128.36 °E) South Korea winter season weather conditions. Obtained results show that the heating requirement of greenhouses with multi-layer night thermal screens was 20%, 5.4%, and 13.5%, less than the Polyester, Luxous, and Tempa screens respectively. Thus, our experiments confirm that the use of multi-layered thermal screen can reduce greenhouse heat energy requirement. Furthermore, screen-control with outside solar radiation at an optimum setpoint of 60 W·m−2 significantly influences the greenhouse’s energy conservation capacity, as it exhibited 699.5 MJ · m−2, the least energy demand of all strategies tested. Moreover, the proposed model allows dynamic simulation of greenhouse systems and enables researchers and farmers to evaluate different screens and screen control strategies that suit their investment capabilities and local weather conditions.
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Vitek, V. "Pair Potentials in Atomistic Computer Simulations". MRS Bulletin 21, n.º 2 (febrero de 1996): 20–23. http://dx.doi.org/10.1557/s088376940004625x.
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Computer modeling of crystal defects ranges at present from generic empirical investigations to first-principle quantum-mechanical calculations (see, for example, References 1–4). Descriptions of atomic interactions in terms of pair potentials dominated such studies until the early 1980s, and many fundamental features of lattice defects and interfaces were revealed in these calculations. The generic results of these studies withstood the test of time, and calculations employing more sophisticated schemes usually confirmed their validity. An early example goes back to the late 1950s when Vineyard and co-workers pioneered the very first computer simulations in their studies of radiation damage. Empirical pair potentials were used in these investigations in which many fundamental, generic aspects of the effect of irradiation of crystalline materials by energetic particles were discovered.Such simple treatments of atomic interactions may appear totally inadequate from the point of view of pure physics. However, it must be recognized that the purpose of the majority of atomistic studies of lattice defects has been to elucidate atomic structure and atomic-level properties in materials with given: (a) crystal structure, (b) elastic properties and possibly phonon spectra, (c) values of certain material parameters such as vacancy formation energies and stacking fault energies, and (d) in alloys, alloying and ordering energies, and possibly antiphase boundary energies. This is in contrast with ab initio studies, the objective of which is to determine all these properties from first principles. These goals of atomistic studies are, of course, the same for all semi-empirical approaches discussed in this collection of articles. In general, the validity of the structural features of lattice defects found in calculations using empirical schemes is best guaranteed if they can be related to fitted material properties and are not sensitively dependent on the deails of the fittings and functional forms employed.
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Abdul Aziz, M. Z., F. N. Mohd Kamarulzaman, N. A. S. Mohd Termizi, N. Abdul Raof y A. A. Tajuddin. "Effects of density from various hip prosthesis materials on 6 MV photon beam: a Monte Carlo study". Journal of Radiotherapy in Practice 16, n.º 2 (21 de febrero de 2017): 155–60. http://dx.doi.org/10.1017/s1460396917000012.
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AbstractIn radiotherapy planning, computed tomography (CT) images are used to calculate the dose in the patient. However, a high density hip prosthesis can cause streaking artefacts in CT images, which make dose calculations for nearby organs inaccurate. This study aim to quantify the impact of a hip prosthesis on 6 MV photon beam dose distribution using the Monte Carlo (MC) simulation. To quantify the radiation dose at the hip prosthesis accurately, image processing techniques were used to generate CT images free from streak artefacts. MATLAB software was used to produce computer-generated phantoms consisting of bone, titanium, stainless steel and CoCrMo. Percentage depth dose (PDD) and beam profile were used to analyse the impact of the hip prosthesis on the dose distribution of the photon beam. PDD showed that the absorbed dose was reduced as the density of the material increased, and the dose was reduced by as much as 49% when the photon beam struck the highest density material (CoCrMo, 8·2g/cm3). However, dose was increased at the tissue-hip prosthesis interface (depths of 4 and 19cm). As the depth increased, the absorbed dose decreased due to attenuation of photons by the tissue and the metal.
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Tang, Xia, Botao Liu, Yue Yu, Botao Song, Pengfei Han, Sheng Liu y Bing Gao. "Effect of Internal Radiation on Process Parameters in the Global Simulation of Growing Large-Size Bulk β-Ga2O3 Single Crystals with the Czochralski Method". Crystals 11, n.º 7 (29 de junio de 2021): 763. http://dx.doi.org/10.3390/cryst11070763.
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As a crystal grows, the temperature distribution of the crystal and melt will change. It is necessary to study the dynamic process of single-crystal growth. Due to the relatively low crystallization rates used in the industrial Czochralski growth system, a steady state is used to compute the temperature distribution and melt flow. A two-dimensional axisymmetric model of the whole Czochralski furnace was established. The dynamic growth process of large-size bulk β-Ga2O3 single crystal using the Czochralski method has been numerically analyzed with the parameter sweep method. In this paper, two cases of internal radiation and no internal radiation were compared to study the effect of radiation on the process parameters. The temperature distribution of the furnace, the temperature field, and the flow field of the melt was calculated. The temperature, the temperature gradient of the crystal, the temperature at the bottom of the crucible, and the heater power were studied for the crystals grown in the two cases of radiation. The results obtained in this study clearly show that the loss calculated by including the internal radiation is higher compared to that including the surface radiation.
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Galiatsatos, V. y B. E. Eichinger. "Simulation of the Formation of Elastomers". Rubber Chemistry and Technology 61, n.º 2 (1 de mayo de 1988): 205–22. http://dx.doi.org/10.5254/1.3536183.
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Abstract The formation of networks of various types has been simulated by using a physically realistic model that allows for intramolecular reactions to take place, thus forming loops of any size. The shortcomings of the kinetic approach, where systems are composed of functional groups that are selected at random without spatial constraint, and of the percolation method where an ordered arrangement is assured, are avoided. The reported simulations of the end-linking process illustrate the influence of intramolecular reactions on gel-sol distributions. Rings form in both phases, gel and sol. Neglect of the presence of cyclics in the sol underestimates the extent of the crosslinking reaction by several percent. On the other hand, in the gel fraction, loop defects are formed as the result of short-ranged intramolecular reactions. These defects do not vanish at complete conversion, and as a result they reduce the cycle rank in proportion to the number of primary chains reacting to form loops. The higher the molecular weight of the prepolymer chains, the closer to the perfect network the formed structure will be. Diffusion effects play an increasingly important role as the degree of polymerization goes up, so that reactions involving the end-linking of very long chains may never come into completion. The simulation results show that sol structures are highly dependent upon the functionality of the crosslinking agent used in the end-linking process. The intramolecular reactions which occur in substantial proportion at higher degrees of crosslinking necessarily favor formation of cyclics. In the case of tetrafunctional networks, this results in a bimodal molecular weight distribution of the sol constituents. It is important to realize that, according to the results of our simulation, networks obtained near complete conversions are very close to perfect. In the case of the random networks cured by high-energy radiation, we show that their properties are quite different when compared to those resulting from other crosslinking techniques. The defect structures account for a large portion of the mass of the networks and their mechanical moduli, as represented by the cycle rank per chain, are substantially smaller than the model networks. Results on both poly(dimethylsiloxane) and polyethylene show that chain scission is rather important. It should be kept in mind that primary chain branching and the molecular weight distribution affect the behavior of a polymeric system when it is exposed to radiation. The fact that the algorithm gives reliable results for more than one polymeric system shows the flexibility of the simulation program; it also proves that the assumptions used to build the model form a realistic basis for future work. A number of upgrades are being incorporated in the model at the present time. Instead of relying on the Gaussian distribution of chain ends, a more realistic model incorporating Flory's rotational isomeric state theory is being used to generate the prepolymer chains. The simulations are being applied to a number of different systems, including polyoxypropylene- and polyoxyethylene-based urethane networks. In addition, filled networks and sulfur vulcanization systems are slated to be explored in order to try to understand their rather complicated behavior. Computer simulations prove to be a powerful tool to study network structure problems. Questions about the detailed structure of the elastomer, sol-gel transitions, and the mechanical properties can be given reliable answers. Wherever there is sufficient knowledge of the reaction system and enough experimental data for comparison, computer simulations can provide information of unprecedented depth and accuracy.
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Hussain, M. Imtiaz, Gwi Hyun Lee y Jun-Tae Kim. "Simulation and Model Validation of a Multi-Concentration Points Concentrated Photovoltaic Thermal System". Journal of Nanoelectronics and Optoelectronics 13, n.º 10 (1 de octubre de 2018): 1552–56. http://dx.doi.org/10.1166/jno.2018.2388.
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In this study, the transient behavior of a concentrated photovoltaic thermal (CPV/T) system is assessed using one-dimensional mathematical model. The model is based on the heat balance of the concentrated photovoltaic (CPV) solar cells, receiver pipe, thermal fluid, insulation, and the storage tank attached to PV/T system via insulated pipes. The mathematical model was developed and solved using ordinary differential equation solvers in MATLAB® computer program. The interdependence thermo-electric dynamic responses of the CPV/T system were modeled and analyzed by considering two cases such as with and without glass enclosure around the receiver. The electrical and thermal efficiencies are evaluated as the function of enclosure effect, beam solar radiation, and circulating fluid flow rate. For the purpose of model validation, experimental measurements of the CPV/T system were performed. Satisfactory agreements were found between the experimental data and the predicted results. The developed dynamic model is most suitable to predict and evaluate the performance of a point-focused CPV/T system.
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Turkin, A. A., H. J. van Es, D. I. Vainshtein y H. W. den Hartog. "Protocol for TL dating with zircon: Computer simulation of temperature and dose rate effects". Radiation Effects and Defects in Solids 157, n.º 6-12 (enero de 2002): 833–38. http://dx.doi.org/10.1080/10420150215761.
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Ahmad, Muhammad Iqbal, Mohd Sharizal Abdul Aziz, Mohd Zulkifly Abdullah, Mohd Arif Anuar Mohd Salleh, Mohammad Hafifi Hafiz Ishak, Wan Rahiman y Marcin Nabiałek. "Investigations of Infrared Desktop Reflow Oven with FPCB Substrate during Reflow Soldering Process". Metals 11, n.º 8 (21 de julio de 2021): 1155. http://dx.doi.org/10.3390/met11081155.
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This paper presents the study of infrared (IR) reflow oven characteristics for suitable operating conditions of the flexible printed circuit board (FPCB) in the reflow soldering process. A computer-based model that imitates a real-time oven was developed with practical boundary conditions. Since the radiation effect is dominant in the reflow process, a discrete ordinate (DO) model was selected to simulate the effect. The experimental work acts as a benchmark and the reflow profile was set to follow the standards of JSTD-020E. The simulation of the model has a great consensus between the experimental data. It was found that the temperature distribution was inhomogeneous along with the phases. The FPCB surface also has a higher surface temperature than oven air during the operating reflow profile. An in-depth study using the simulation approach reveals that the temperature distribution of the desktop reflow oven is dependent on several factors, namely fan speed, FPCB position, and FPCB thickness. The rotational fan generates an unsteady flow that induces inhomogeneous temperature at different positions in the reflow oven cavity. The results are useful for studying further improvements to achieve temperature uniformity within the oven chamber.
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Wang, Dengwang, Yong Gao, Wei Chen, Jing Zhang y Sheng Wang. "Equivalent Analysis of Thermo-Dynamic Blow-Off Impulse under X-ray Irradiation". Applied Sciences 11, n.º 19 (23 de septiembre de 2021): 8853. http://dx.doi.org/10.3390/app11198853.
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X-ray thermodynamic effect is an important damage mode for spacecraft. Blow-off impulse as the main thermodynamic damage parameter has been widely studied by combining laboratory and numerical simulations. In this paper, most calculations and analyses have been carried out by using the self-developed software RAMA, including the equivalent calculation of blow-off impulse of monoenergetic and blackbody X-ray, and soft/hard blackbody X-ray irradiated at different incidence angles of LY-12 aluminium target. The results show that the characteristic mono-energetic X-ray can be exploited to simulate the blow-off impulse of the blackbody X-ray under certain conditions as a feasible equivalent method for the equal-flux and equal-impulse relations between mono-energetic and intense pulse blackbody of blow-off impulse. Moreover, the equivalent thermodynamic effect can be achieved between the point source radiation and parallel X-ray of X-ray. Furthermore, the cosine distribution of blow-off impulse is conducive to designing and calculating X-ray radiation load of hard aluminium corresponding to 1–5 keV blackbody spectrum. The mentioned results can be referenced for pulse X-ray simulation source and enhance the fidelity of the thermal-mechanical effect by electron beam. It is noteworthy that the study on the thermodynamic effects of intense pulsed X-ray is of high significance.
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Tenpierik, Wattez, Turrin, Cosmatu y Tsafou. "Temperature Control in (Translucent) Phase Change Materials Applied in Facades: A Numerical Study". Energies 12, n.º 17 (26 de agosto de 2019): 3286. http://dx.doi.org/10.3390/en12173286.
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Phase change materials (PCMs) are materials that can store large amounts of heat during their phase transition from solid to liquid without a significant increase in temperature. While going from liquid to solid this heat is again released. As such, these materials can play an important role in future energy-efficient buildings. If applied in facades as part of a thermal buffer strategy, e.g., capturing and temporarily storing solar energy in so-called Trombe walls, the PCMs are exposed to high solar radiation intensities, which may easily lead to issues of overheating. This paper therefore investigates the melting process of PCM and arrives at potential solutions for countering this overheating phenomenon. This study uses the simulation program Comsol to investigate the heat transfer through, melting of and fluid flow inside a block of PCM (3 × 20 cm2) with a melting temperature of around 25 °C. The density, specific heat and dynamic viscosity of the PCM are modeled as a temperature dependent variable. The latent heat of the PCM is modeled as part of the specific heat. One side of the block of PCM is exposed to a heat flux of 300 W/m2. The simulations show that once part of the PCM has melted convection arises transporting heat from the bottom of the block to its top. As a result, the top heats up faster than the bottom speeding up the melting process there. Furthermore, in high columns of PCM a large temperature gradient may arise due to this phenomenon. Segmenting a large volume of PCM into smaller volumes in height limits this convection thereby reducing the temperature gradient along the height of the block. Moreover, using PCMs with different melting temperature along the height of a block of PCM allows for controlling the speed with which a certain part of the PCM block starts melting. Segmenting the block of PCM using PCMs with different melting temperature along its height was found to give the most promising results for minimizing this overheating effect. Selecting the optimal phase change temperatures however is critical in that case.
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Ellahi, R., Sadiq M. Sait, N. Shehzad y Z. Ayaz. "A hybrid investigation on numerical and analytical solutions of electro-magnetohydrodynamics flow of nanofluid through porous media with entropy generation". International Journal of Numerical Methods for Heat & Fluid Flow 30, n.º 2 (12 de agosto de 2019): 834–54. http://dx.doi.org/10.1108/hff-06-2019-0506.
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Purpose The purpose of this paper is to present the investigation of the pressure-driven flow of aluminum oxide-water based nanofluid with the combined effect of entropy generation and radiative electro-magnetohydrodynamics filled with porous media inside a symmetric wavy channel. Design/methodology/approach The non-linear coupled differential equations are first converted into a number of ordinary differential equations with appropriate transformations and then analytical solutions are obtained by homotopic approach. Numerical simulation has been designed by the most efficient approach known homotopic-based Mathematica package BVPh 2.0 technique. The long wavelength approximation over the channel walls is taken into account. The obtained analytical results have been validated through graphs to infer the role of most involved pertinent parameters, whereas the characteristics of heat transfer and shear stress phenomena are presented and examined numerically. Findings It is found that the velocity profile decreases near to the channel. This is in accordance with the physical expectation because resistive force acts opposite the direction of fluid motion, which causes a decrease in velocity. It is seen that when the electromagnetic parameter increases then the velocity close to the central walls decreases whereas quite an opposite behavior is noted near to the walls. This happens because of the combined influence of electro-magnetohydrodynamics. It is perceived that by increasing the magnetic field parameter, Darcy number, radiation parameter, electromagnetic parameter and the temperature profile increases, and this is because of thermal buoyancy effect. For radiation and electromagnetic parameters, energy loss at the lower wall has substantial impact compared to the upper wall. Residual error minimizes at 20th order iterations. Originality/value The proposed prospective model is designed to explore the simultaneous effects of aluminum oxide-water base nanofluid, electro-magnetohydrodynamics and entropy generation through porous media. To the best of author’s knowledge, this model is reported for the first time.
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POPOV, V. V., M. S. SHUR, G. M. TSYMBALOV y D. V. FATEEV. "HIGHER-ORDER PLASMON RESONANCES IN GAN-BASED FIELD-EFFECT TRANSISTOR ARRAYS". International Journal of High Speed Electronics and Systems 17, n.º 03 (septiembre de 2007): 557–66. http://dx.doi.org/10.1142/s0129156407004746.
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Terahertz (THz) response spectra of GaN-based field-effect transistor (FET) arrays are calculated in a self-consistent electromagmetic approach. Two types of FET arrays are considered: (i) FET array with a common channel and a large-area grating gate, and (ii) array of FET units with separate channels and combined intrinsic source and drain contacts. It is shown that the coupling between plasmons and THz radiation in the FET array can be strongly enhanced as compared to a single-unit FET. The computer simulations show that the higher-order plasmon modes can be excited much more effectively in the array of FET units with separate channels and combined source and drain contacts then in FET array with a common channel and a large-area grating gate.
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Hamdani, Maamar, Sidi Mohammed El Amine Bekkouche, Tayeb Benouaz, Rafik Belarbi y Mohamed Kamel Cherier. "MINIMIZATION OF INDOOR TEMPERATURES AND TOTAL SOLAR INSOLATION BY OPTIMIZING THE BUILDING ORIENTATION IN HOT CLIMATE". Engineering Structures and Technologies 6, n.º 3 (22 de diciembre de 2014): 131–49. http://dx.doi.org/10.3846/2029882x.2014.988756.
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In order to reduce the energy load, understanding the overall architectural design features and optimizing building orientation are important. They are guided by natural elements like sunlight and its intensity, direction of the wind, seasons of the year and temperature variations. The main aim of presented analysis is to give solutions for architects to design standard and low energy buildings in a proper way. The orientation effect of a non-air-conditioned building on its thermal performance has been analyzed in terms of direct solar gain and temperature index for hot-dry climates. This paper aims at introducing an improved methodology for the dynamic modeling of buildings by the thermal nodal method. The study is carried out using computer simulation. This study examines also the effect of geometric shapes on the total solar insolation received by a real building. As a result, the influence of orientation changing depends on the floors and exterior walls construction materials, the insulation levels and application of the inseparable rules of the bioclimatic design. Solar radiation is the most major contributor to heat gain in buildings.
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Antar, M. A., Rached Ben-Mansour y Salem Ahmed Al-Dini. "The effect of thermal radiation on the heat transfer characteristics of lid-driven cavity with a moving surface". International Journal of Numerical Methods for Heat & Fluid Flow 24, n.º 3 (1 de abril de 2014): 679–96. http://dx.doi.org/10.1108/hff-06-2012-0136.
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Purpose – There are industrial applications for varying speed lid-driven flow and heat transfer such as the float glass process where the glass film stretches or thickens depending on the desired thickness. Hence the tin cavity underneath or the nitrogen cavity above is being driven by a variable speed. The purpose of this paper is to simulate such behavior. Design/methodology/approach – Numerical solution of variable speed lid-driven cavity is carried out with thermal radiation being considered using control volume approach and staggered grid and applying the SIMPLE algorithm. Transient simulation is used for 2D model in the present study. Second order upwind schemes were used for discretization of momentum, energy equations and time. Findings – Under laminar conditions, thermal radiation plays a significant role in the heat transfer characteristics of the lid-driven cavity. This effect is more significant for blackbody radiation and decreases as the surface emissivity decreases. Nusselt number (Nu) behavior lies between these two limiting case profiles considering constant speed profiles of both maximum and minimum lid velocities, respectively. In addition, local Nu values at the tip where higher than those at the top of the cavity that is stagnant. Research limitations/implications – The study is limited to laminar flow case. Practical implications – The applications of this study can be found in float glass process where the glass film stretches or thickens depending on the desired thickness. Hence the tin cavity underneath or the nitrogen cavity above is being driven by a variable speed. Another application involves casting of plastic films. The molten polymer leaves the die with a considerable thickness and high temperature. The film is then trenched to reach its final thickness. In this case, usually there is no actual cavity above or below the film but one can approximate the problem as such. Other similar applications do exist in food drying and processing where the conveyer belt is in portions and their speed may not be the same in different section of the processing oven. Originality/value – To the best of the authors knowledge, no study in the literature addressed the effect of thermal radiation in lid-driven cavities with variable speed
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Chang, Haocheng, Xiaohong Hu y Rujin Ma. "Numerical Study on Temperature Distribution of Steel Truss Aqueducts under Solar Radiation". Applied Sciences 11, n.º 3 (21 de enero de 2021): 963. http://dx.doi.org/10.3390/app11030963.
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Aqueduct, one kind of bridge structure overpassing a long space, is a significant structure for water delivery for the purpose of agricultural or domestic usage. Aqueduct has quite different loads from other forms of bridges, of which temperature effects due to the environment temperature change, such as seasonal weather or radiation from sunshine, are of great importance. With water flowing inside, the temperature boundary of aqueducts, especially for steel aqueducts, is much more complicated, and relevant researches are limited. In this paper, a 3D Finite Element Method (FEM) simulation process is presented to analyze temperature distribution on the cross-section of a new-type steel truss aqueduct, which belongs to the Water Transfer Project from Yangtze River to Huai River in China. ASHRAE clear-sky model is used to calculate the solar-radiation variation, including direct radiation, diffuse sky radiation, and ground reflected radiation on steel surfaces. The time-dependent sunshine radiation angle of incidence and shielding effect of steel trusses are considered. The water inside the aqueduct is also included in this model, which significantly influences the temperatures of the inner surfaces of the aqueduct. Several temperature distributions under critical conditions of winter and summer are shown in this study, and results of the empty aqueduct under the same circumstances are also provided as a comparison. The effects of wind speed, geographic latitude, and direction of the aqueduct are examined. The conclusions and approach provided by this study could serve as significant references for thermal design and control of similar steel truss aqueducts.
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Kang, Il Mo, Myung Hun Kim, Youn Joong Kim, Hi-Soo Moon y Yungoo Song. "Effect of layer structure boundary on the hectorite basal diffraction". Powder Diffraction 21, n.º 1 (marzo de 2006): 30–35. http://dx.doi.org/10.1154/1.2104534.
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This study examined basal peak irrationalities according to boundary conditions of the hectorite basal diffraction unit (BDU), which were recognized as the total assembly of 2:1 phyllosilicate layer plus interlayer material. The hectorite basal profiles were computer-simulated using the three kinds of BDU settings identified from the middle of octahedral sheets in the nearest neighbor (centrosymmetric model), the middle of interlayers in the nearest neighbor (centrosymmetric model), and a basal oxygen plane to the margin of interlayer in contact with the next phyllosilicate layer (non-centrosymmetric model). In the results of simulations, irrationality and asymmetry of the hectorite basal peaks relied straightforwardly on the BDU scattering modulations for the non-Bragg angles containing information on the synergic scattering events of phyllosilicate layer and interlayer material. Among the concerned BDU boundaries, the non-centrosymmetric model more effectively represented the real hectorite profile than the two previously reported centrosymmetric models.
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Muroga, Takeo. "PKA spectral effects on subcascade structures and free defect survival ratio as estimated by cascade-annealing computer simulation". Radiation Effects and Defects in Solids 113, n.º 1-3 (marzo de 1990): 119–34. http://dx.doi.org/10.1080/10420159008213059.
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Yee, Cheang Soon, G. A. Quadir, Z. A. Zainal y K. N. Seetharamu. "Investigation of Steady State and Transient Thermal Management in Portable Telecommunication Product – Part 2". Journal of Microelectronics and Electronic Packaging 2, n.º 2 (1 de abril de 2005): 98–109. http://dx.doi.org/10.4071/1551-4897-2.2.98.
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In Part 2 of this paper, transient thermal management in portable telecommunication product using phase change material (PCM) was numerically investigated. The thermal time-dependent simulation methodology using non-linear transient finite element analysis (FEA) on a solid conduction cellular phone model cooled by natural convection and radiation was verified experimentally. For the phase change problem itself, a pure conduction PCM model with enthalpy changes was utilized. The effect of convection heat transfer in liquid phase is enhanced thermal conductivity. The numerical methodology used by Hodes et al. [3] and Lamberg et al. [13] was verified with both package and system level experimental results. With the confidence gained from the verification work using this simulation methodology, further parametric study was carried out. In this paper, the effect of PCM volume, aspect ratio of the container and amount of heat dissipated are examined. The advantages gained from its recovery period and introduction of thermal conductivity enhancement are also discussed.
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Rashad, A. M., Sameh Elsayed Ahmed y Mohamed Ahmed Mansour. "Effects of chemical reaction and thermal radiation on unsteady double diffusive convection". International Journal of Numerical Methods for Heat & Fluid Flow 24, n.º 5 (27 de mayo de 2014): 1124–40. http://dx.doi.org/10.1108/hff-04-2012-0095.
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Purpose – The purpose of this numerical paper is to investigate the simulation of an unsteady double diffusive natural convection in square enclosure filled with a porous medium with various boundary conditions in the presence of thermal radiation and chemical reaction effects. Design/methodology/approach – In this study, the governing dimensionless equations were written using the Brinkman Forchheimer extended Darcy model. They are numerically solved by using finite difference method by applying adiabatic boundary condition in top surface. The bottom surface is maintained at uniform temperature and concentration and left and right vertical walls are cooled. Findings – Results are presented by streamlines, isotherms, temperature and concentration contours profiles as well as the local Nusselt number and Sherwood numbers for different values of the governing parameters such as Darcy number, buoyancy ratio, Rayleigh number, thermal radiation parameter and chemical reaction parameter. It is found that that both of the local Nusselt and Sherwood numbers increase as the Rayleigh number, buoyancy ratio and Darcy number increase. Moreover, increasing the thermal radiation effects leads to a pronounced increase in the local Nusselt number, while the opposite behavior is displayed by the local Sherwood number. Furthermore, the local Sherwood number increases and the local Nusselt number decrease when the chemical reaction parameter increase. Originality/value – The originality of this study is the square cavity with various boundary conditions filled with a porous medium with thermal radiation and chemical reaction effects.
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Codreanu, N. D., P. Svasta, V. Golumbeanu y L. Gál. "Evaluation of Meshed Reference Planes for High Performance Applications". Active and Passive Electronic Components 22, n.º 3 (2000): 175–87. http://dx.doi.org/10.1155/2000/35952.
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The actual generations of integrated circuits are characterized, inter alia, by very high frequencies or very high speeds. The dramatic evolution ofthe semiconductor's technology establishes a greater “pressure” to the design and the manufacturing of the passive interconnection structure from PCB/MCM electronic modules. In these conditions the reference planes (power and ground planes) have a more and more important contribution. The paper intents to present the effect of different configuration reference planes on the characteristics of the high speed/high frequency interconnection lines. The first part deals with modeling and simulation of usual practical interconnection geometries. A computer modeling of meshed structures was realized and Spice models for a good compatibility with circuit simulators were obtained.S-,Y-,Z- parameters and radiation patterns were calculated, too. The second part contains measurements made by a vector network analyzer as regards to different practical configurations manufactured at Technical University of Budapest.
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Kalospyros, Spyridon A., Violeta Gika, Zacharenia Nikitaki, Antigoni Kalamara, Ioanna Kyriakou, Dimitris Emfietzoglou, Michael Kokkoris y Alexandros G. Georgakilas. "Monte Carlo Simulation-Based Calculations of Complex DNA Damage for Incidents of Environmental Ionizing Radiation Exposure". Applied Sciences 11, n.º 19 (27 de septiembre de 2021): 8985. http://dx.doi.org/10.3390/app11198985.
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In this paper, we present a useful Monte Carlo (MC)-based methodology that can be utilized to calculate the absorbed dose and the initial levels of complex DNA damage (such as double strand breaks-DSBs) in the case of an environmental ionizing radiation (IR) exposure incident (REI) i.e., a nuclear accident. Our objective is to assess the doses and complex DNA damage by isolating only one component of the total radiation released in the environment after a REI that will affect the health of the exposed individual. More specifically, the radiation emitted by radionuclide 137Cs in the ground (under the individual’s feet). We use a merging of the Monte Carlo N-Particle Transport code (MCNP) with the Monte Carlo Damage Simulation (MCDS) code. The DNA lesions have been estimated through simulations for different surface activities of a 137Cs ground-based γ radiation source. The energy spectrum of the emitted secondary electrons and the absorbed dose in typical mammalian cells have been calculated using the MCNP code, and then these data are used as an input in the MCDS code for the estimation of critical DNA damage levels and types. As a realistic application, the calculated dose is also used to assess the Excess Lifetime Cancer Risk (ELCR) for eight hypothetical individuals, living in different zones around the Chernobyl Nuclear Power Plant, exposed to different time periods at the days of the accident in 1986. We conclude that any exposition of an individual in the near zone of Chernobyl increases the risk of cancer at a moderate to high grade, connected also with the induction of complex DNA damage by radiation. Generally, our methodology has proven to be useful for assessing γ rays-induced complex DNA damage levels of the exposed population, in the case of a REI and for better understanding the long-term health effects of exposure of the population to IR.
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Du, Xiaofei, Qidi Fu, Jianrun Zhang y Chaoyong Zong. "Numerical and Experimental Study on Suppression Effect of Acoustic Black Hole on Vibration Transmission of Refrigerator Compressor". Applied Sciences 11, n.º 18 (16 de septiembre de 2021): 8622. http://dx.doi.org/10.3390/app11188622.
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The acoustic black hole (ABH) structures have the potential to achieve structural vibration suppression and noise reduction through the effect of the ABH on the concentration and manipulation of flexural waves. In this paper, a new solution is proposed to embed 2-D ABHs on the support plate to suppress the transmission of compressor vibration to the refrigerator body. The vibration and acoustic measurement experiment of the compressor, the support plate and the refrigerator body, and the coherence analysis of the vibration signals and acoustic signal are carried out to determine the influence of the compressor vibration on the vibration of the refrigerator body and the radiation sound of the back wall. The concentration and manipulation effects of 2-D ABH on flexural waves are verified by numerical simulation of flexural wave propagation in the time domain. FEM models of the original support plate and the damping ABH support plate are established to investigate the comprehensive effect of the 2-D ABHs and the damping layers on the vibration characteristics of the support plate through vibration modal and dynamic response analysis. Numerical simulation results show that the 2-D damping ABHs can suppress the vibrations generated by the compressor at specific frequencies in the middle and high-frequency bands from being transmitted to the refrigerator body through the support plate.
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Sheremet, Mikhail y Sivaraj Chinnasamy. "Convective–radiative heat transfer in a cavity filled with a nanofluid under the effect of a nonuniformly heated plate". International Journal of Numerical Methods for Heat & Fluid Flow 28, n.º 6 (4 de junio de 2018): 1392–409. http://dx.doi.org/10.1108/hff-06-2017-0255.
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PurposeThe purpose of this study is to examine the radiation effect on the natural convective heat transfer of an alumina–water nanofluid in a square cavity in the presence of centered nonuniformly heated plate.Design/methodology/approachThe square cavity filled with alumina–water nanofluid has a nonuniformly heated plate placed horizontally or vertically at its center. The plate is heated isothermally with linearly varying temperature. The vertical walls are cooled isothermally with a constant temperature, while the horizontal walls are insulated. The governing equations have been discretized using finite volume method on a uniformly staggered grid system. Simulations were carried out for different values of the heated plate nonuniformity parameter (λ= –1, 0 and 1), the nanoparticles solid volume fraction (Φ= 0.01 − 0.04) and the radiation parameter (Rd= 0 – 2) at the Rayleigh number ofRa= 1e+07.FindingsIt is found that the total heat transfer rate is enhanced with an increase in the radiation parameter for both the horizontal and vertical plates. The role of nanoparticles addition to the base fluid can have dual effects on the heat transfer rate by augmenting and dampening for the absence of radiation while it dampens the heat transfer rate for the presence of radiation.Originality/valueThe originality of this work is to analyze steady natural convection in a square cavity filled with a water-based nanofluid in the presence of centered nonuniformly heated plate. The results would benefit scientists and engineers to become familiar with the analysis of convective heat and mass transfer in nanofluids, and the way to predict the properties of nanofluid convective flow in advanced technical systems, in industrial sectors including transportation, power generation, chemical sectors, electronics, etc.
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Lysov, Nikolay, Alexander Temnikov, Leonid Chernensky, Alexander Orlov, Olga Belova, Tatiana Kivshar, Dmitry Kovalev y Vadim Voevodin. "Physical Simulation of the Spectrum of Possible Electromagnetic Effects of Upward Streamer Discharges on Model Elements of Transmission Line Monitoring Systems Using Artificial Thunderstorm Cell". Applied Sciences 11, n.º 18 (18 de septiembre de 2021): 8723. http://dx.doi.org/10.3390/app11188723.
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The results of a physical simulation using negatively charged artificial thunderstorm cells to test the spectrum of possible electromagnetic effects of upward streamer discharges on the model elements of transmission line monitoring systems (sensor or antennas) are presented. Rod and elongated model elements with different electric field amplification coefficients are investigated. A generalization is made about the parameters of upward streamer current impulse and its electromagnetic effect on both kinds of model elements. A wavelet analysis of the upward streamer corona current impulse and of the signal simultaneously induced in the neighboring model element is conducted. A generalization of the spectral characteristics of the upward streamer current and of the signals induced by the electromagnetic radiation of the nearby impulse streamer corona on model elements is made. The reasons for super-high and ultra-high frequency ranges in the wavelet spectrum of the induced electromagnetic effect are discussed. The characteristic spectral ranges of the possible electromagnetic effect of upward streamer flash on the elements of transmission line monitoring systems are considered.
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Ran, Xianwen, Bo Wang, Kun Zhang y Wenhui Tang. "A Method to Optimize the Electron Spectrum for Simulating Thermo-Mechanical Response to X-ray Radiation". Symmetry 12, n.º 1 (27 de diciembre de 2019): 59. http://dx.doi.org/10.3390/sym12010059.
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The X-ray pulse originating from high altitude nuclear detonation (HAND) is mainly soft X-ray and its intensity is high enough to gasify the penetrated material and then lead to the severe thermo-mechanical deformation of unpenetrated material from the gasified blow-off effect. This effect cannot be directly reproduced in a lab for the lack of the X-ray source like HAND. At present, the low-energy relativistic electron beams resulting from an electron accelerator are usually used to approximately reproduce this effect, but the difference in the energy-deposited profile in materials between the electron and X-ray cannot be eliminated. In this paper, the symmetric linear least squares method was used to optimize the electron spectrum, and the general Monte Carlo N-Particle Transport Code calculations showed the optimized spectrum can produce the same energy-deposited profile in aluminum, copper, and tantalum with the soft X-rays like 1 keV or 3 keV spectrums. This indicates that it is possible to simulate the severe thermo-mechanical deformation resulting from HAND using the optimized electron spectrums.
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Kohn, V. G. y I. A. Smirnova. "Computer simulations of X-ray spherical wave dynamical diffraction in one and two crystals in the Laue case". Acta Crystallographica Section A Foundations and Advances 74, n.º 6 (12 de octubre de 2018): 699–704. http://dx.doi.org/10.1107/s2053273318012627.
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This article reports computer simulations of X-ray spherical wave dynamical diffraction in one and two single crystals in the Laue case. An X-ray compound refractive lens (CRL) as a secondary radiation source of spherical waves was considered for the first time and in contrast to previous simulations with the assumption of the use of a slit. The main properties of the CRL as a secondary source are discussed and two focusing phenomena are analysed. The first one is the diffraction focusing effect for one single crystal in the reflected beam and in the case of a large source-to-detector distance. The second one is the same but for two single crystals and for the twice-reflected beam in the case of a short distance between the source and detector. The first effect is well pronounced in the case of strong absorption. However, it may also be used as an element of an energy spectrometer in the medium and even weak absorption case. The second effect will appear in the case of weak absorption. It is shown that it is not effective to use it in an energy spectrometer. In the case of weak absorption the transverse size of the diffraction focused beam will oscillate together with the reflected beam integral intensity. The oscillation period is close to the extinction length.
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Ali, Asgar, R. N. Jana y S. Das. "Hall effects on radiated magneto-power-law fluid flow over a stretching surface with power-law velocity slip effect". Multidiscipline Modeling in Materials and Structures 17, n.º 1 (26 de junio de 2020): 103–25. http://dx.doi.org/10.1108/mmms-01-2020-0005.
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PurposeThis paper aims to assess the effectiveness of Hall currents and power-law slip condition on the hydromagnetic convective flow of an electrically conducting power-law fluid over an exponentially stretching sheet under the effect of a strong variable magnetic field and thermal radiation. Flow formation is developed using the rheological expression of a power-law fluid.Design/methodology/approachThe nonlinear partial differential equations describing the flow are transformed into the nonlinear ordinary differential equations by employing the local similarity transformations and then solved numerically by an effective numerical approach, namely, fourth-order Runge–Kutta integration scheme, along with the shooting iteration technique. The numerical solution is computed for different parameters by using the computational software MATLAB bvp4c. The bvp4c function uses the finite difference code as the default. This method is a fourth-order collocation method. The impacts of thermophysical parameters on velocity and temperature distributions, skin friction coefficients and Nusselt number in the boundary layer regime are exhibited through graphs and tables and deliberated with proper physical justification.FindingsOur investigation conveys that Hall current has an enhancing behavior on velocity profiles and reduces skin friction coefficients. An increase in the power-law index is observed to deplete velocity and temperature evolution. The temperature for the pseudo-plastic (shear-thinning) fluid is relatively higher than the corresponding temperature of the dilatant (shear-thickening) fluid. The streamlines are more distorted and have low intensity near the surface of the sheet for the dilatant fluid than the pseudo-plastic fluid.Social implicationsThe study is pertinent to the expulsion of polymer sheet and photographic films, hydrometallurgical industry, electrically conducting polymer dynamics, magnetic material processing, solutions and melts of polymer processing, purification of molten metals from nonmetallic. The results obtained in this work can be relevant in fluid mechanics and heat transfer applications.Originality/valueThe present problem has, to the authors' knowledge, not communicated thus far in the scientific literature. A comparative study with the published works is conducted to verify the accuracy of the present study. The results obtained in this analysis are significant in providing the standards for validating the accuracies of some numerical or empirical methods.
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Kaka, Ademola O., Mehmet Toycan y Stuart D. Walker. "Miniaturized stacked implant antenna design at ISM band with biocompatible characteristics". COMPEL: The International Journal for Computation and Mathematics in Electrical and Electronic Engineering 34, n.º 4 (6 de julio de 2015): 1270–85. http://dx.doi.org/10.1108/compel-02-2015-0032.
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Purpose – A vertically stacked, three layer hybrid Hilbert fractal geometry and serpentine radiator-based patch antenna is proposed and characterized for medical implant applications at the Industrial, Scientific and Medical band (2.4-2.48 GHz). Antenna parameters are optimised to achieve miniaturized, biocompatible and stable transmission characteristics. The paper aims to discuss these issues. Design/methodology/approach – Human tissue effects on the antenna electrical characteristics were simulated with a three-layer (skin, fat and muscle) human tissue model with the dimensions of 180×70×60 mm3 (width×height×thickness mm3). Different stacked substrates are utilized for the satisfactory characteristics. Two identical radiating patches are printed on Roger 3,010 (ε r=10.2) and Alumina (ε r=9.4) substrate materials, respectively. In addition, various superstrate materials are considered and simulated to prevent short circuit the antenna while having a direct contact with the metallization, and achieve biocompatibility. Finally, superstrate material of Zirconia (ε r=29) is used to achieve biocompatibility and long-life. A finite element method is used to simulate the proposed hybrid model with commercially available Ansoft HFSS software. Findings – The antenna is miniaturized, having dimensions of 10×8.4×2 mm3 (width×height×thickness mm3). The resonance frequency of the antenna is 2.4 GHz with a bandwidth of 100 MHz at return loss (S11) of better than −10 dB characteristics. Overall, the proposed antenna have 50 Ω impedance matching, −21 dB far field antenna gain, single-plane omni-directional radiation pattern properties and incident power of 5.3 mW to adhere Specific Absorption Rate regulation limit. Originality/value – Vertically stacked three layer hybrid design have miniaturized characteristics, wide bandwidth, biocompatible, and stable characteristics in three layer human tissue model make this antenna suitable for implant biomedical monitor systems. The advanced simulation analysis of the proposed design constitutes the main contribution of the paper.
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Frank, Tobias, Steffen Wieting, Mark Wielitzka, Steffen Bosselmann y Tobias Ortmaier. "Identification of temperature-dependent boundary conditions using MOR". International Journal of Numerical Methods for Heat & Fluid Flow 30, n.º 2 (22 de agosto de 2019): 1009–22. http://dx.doi.org/10.1108/hff-05-2019-0404.
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Purpose A mathematical description of temperature-dependent boundary conditions is crucial in manifold model-based control or prototyping applications, where accurate thermal simulation results are required. Estimation of boundary condition coefficients for complex geometries in complicated or unknown environments is a challenging task and often does not fulfill given accuracy limits without multiple manual adaptions and experiments. This paper aims to describe an efficient method to identify thermal boundary conditions from measurement data using model order reduction. Design/methodology/approach An optimization problem is formulated to minimize temperature deviation over time between simulation data and available temperature sensors. Convection and radiation effects are expressed as a combined heat flux per surface, resulting in multiple temperature-dependent film coefficient functions. These functions are approximated by a polynomial function or splines, to generate identifiable parameters. A formulated reduced order system description preserves these parameters to perform an identification. Experiments are conducted with a test-bench to verify identification results with radiation, natural and forced convection. Findings The generated model can approximate a nonlinear transient finite element analysis (FEA) simulation with a maximum deviation of 0.3 K. For the simulation of a 500 min cyclic cooling and heating process, FEA takes a computation time of up to 13 h whereas the reduced model takes only 7-11 s, using time steps of 2 s. These low computation times allow for an identification, which is verified with an error below 3 K. When film coefficient estimation from literature is difficult due to complex geometries or turbulent air flows, identification is a promising approach to still achieve accurate results. Originality/value A well parametrized model can be further used for model-based control approaches or in observer structures. To the knowledge of the authors, no other methodology enables model-based identification of thermal parameters by physically preserving them through model order reduction and therefore derive it from a FEA description. This method can be applied to much more complex geometries and has been used in an industrial environment to increase product quality, due to accurate monitoring of cooling processes.
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Yoshimura, Jun-ichi. "Theoretical study of the properties of X-ray diffraction moiré fringes. II. Illustration of angularly integrated moiré images". Acta Crystallographica Section A Foundations and Advances 75, n.º 4 (26 de junio de 2019): 610–23. http://dx.doi.org/10.1107/s2053273319004601.
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Using a theory of X-ray diffraction moiré fringes developed in a previous paper, labelled Part I [Yoshimura (2015). Acta Cryst. A71, 368–381], the X-ray moiré images of a silicon bicrystal having a weak curvature strain and an interspacing gap, assumed to be integrated for an incident-wave angular width, are simulation-computed over a wide range of crystal thicknesses and incident-wave angular width, likely under practical experimental conditions. Along with the simulated moiré images, the graphs of characteristic quantities on the moiré images are presented for a full understanding of them. The treated moiré images are all of rotation moiré. Mo Kα1 radiation and the 220 reflection were assumed in the simulation. The results of this simulation show that fringe patterns, which are significantly modified from simple straight fringes of rotation moiré, appear in some ranges of crystal thicknesses and incident-wave angular width, due to a combined effect of Pendellösung oscillation and an added phase difference from the interspacing gap, under the presence of a curvature strain. The moiré fringes which slope to the perpendicular direction to the diffraction vector in spite of the assumed condition of rotation moiré, and fringe patterns where low-contrast bands are produced with a sharp bend of fringes arising along the bands are examples of the modified fringe pattern. This simulation study provides a wide theoretical survey of the type of bicrystal moiré image produced under a particular condition.
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Linh, Pham The, Nguyen Thi Viet Ninh, Nguyen Dinh Quang, Tran Tien Lam, Nguyen Van Ngoc, Bui Xuan Khuyen, Nguyen Thi Hien, Vu Dinh Lam y Bui Son Tung. "All-dielectric Metamaterial for Electromagnetically-induced Transparency in Optical Region". Communications in Physics 30, n.º 2 (26 de mayo de 2020): 189. http://dx.doi.org/10.15625/0868-3166/30/2/14843.
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Metamaterial (MM) is emerging as a promising approach to manipulate electromagnetic waves, spanning from radio frequency to the optical region. In this paper, we employ an effect called electromagnetically-induced transparency (EIT) in all-dielectric MM structures to create a narrow transparent window in opaque broadband of the optical region (580-670 nm). Using dielectric materials instead of metals can mitigate the large non-radiative ohmic loss on the metal surface. The unit-cell of MM consists of Silicon (Si) bars on Silicon dioxide (SiO\(_{2}\)) substrate, in which two bars are directed horizontally and one bar is directed vertically. By changing the relative position and dimension of the Si bars, the EIT effect could be achieved. The optical properties of the proposed MM are investigated numerically using the finite difference method with commercial software Computer Simulation Technology (CST). Then, characteristic parameters of MM exhibiting EIT effect (EIT-MM), including Q-factor, group delay, are calculated to evaluate the applicability of EIT-MM to sensing and light confinement.
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Khodabandeh, Erfan, Davood Toghraie, A. Chamkha, Ramin Mashayekhi, Omidali Akbari y Seyed Alireza Rozati. "Energy saving with using of elliptic pillows in turbulent flow of two-phase water-silver nanofluid in a spiral heat exchanger". International Journal of Numerical Methods for Heat & Fluid Flow 30, n.º 4 (8 de abril de 2019): 2025–49. http://dx.doi.org/10.1108/hff-10-2018-0594.
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Purpose Increasing heat transfer rate in spiral heat exchangers is possible by using conventional methods such as increasing number of fluid passes and counter flowing. In addition, newer ideas such as using pillows as baffles in the path of cold and hot fluids and using nanofluids can increase heat transfer rate. The purpose of this study is to simulate turbulent flow and heat transfer of two-phase water-silver nanofluid with 0-6 Vol.% nanoparticle concentration in a 180° path of spiral heat exchanger with elliptic pillows. Design/methodology/approach In this simulation, the finite volume method and two-phase mixture model are used. The walls are subjected to constant heat flux of q″ = 150,000 Wm−2. The inlet fluid enters curves path of spiral heat exchanger with uniform temperature Tin = 300 K. After flowing past the pillows and traversing the curved route, the working fluid exchanges heat with hot walls and then exits from the section. In this study, the effect of radiation is disregarded because of low temperature range. Also, temperature jump and velocity slipping are disregarded. The effects of thermophoresis and turbulent diffusion on nanofluid heat transfer are disregarded. By using finite volume method and two-phase mixture model, simulations are performed. Findings The results show that the flow and heat transfer characteristics are dependent on the height of pillows, nanoparticle concentration and Reynolds number. Increasing Reynolds number, nanoparticle concentration and pillow height causes an increase in Nusselt number, pressure drop and pumping power. Originality/value Turbulent flow and heat transfer of two-phase water-silver nanofluid of 0-6 per cent volume fraction in a 180° path of spiral heat exchanger with elliptic pillows is simulated.
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Reddy, B. Namratha Sai, Rashmi Shivananjappa, Geeta S.N y Richa Tiwari. "Use of 4-Dimensional Cone Beam Computed Tomography Scan to Estimate the Planning Target Volume Margin in Lung Tumors". Asian Journal of Oncology 06, n.º 03 (8 de julio de 2020): 127–33. http://dx.doi.org/10.1055/s-0040-1714304.
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Abstract Introduction This study aimed to estimate the planning target volume (PTV) margin in lung tumors using 4D computed tomography (CT) scan and evaluate other factors that have an effect on tumor motion. Materials and Methods We recruited 43 biopsy-proven, newly diagnosed carcinoma lung patients who were treated with definitive intent from January 2017 to June 2018. The radiation dose was delivered using a 3D conformal radiation therapy (CRT)/intensity-modulated radiotherapy (IMRT)/volumetric modulated arc therapy (VMAT) plan to a dose of 6000 to 6600 cGy in 30 or more fractions to the whole primary. All patients underwent 4D CT scan on the Elekta machine where all the 10 phases of respiration in free breathing were recorded. These phases are fused with CT simulation images, on which gross tumor volume (GTV) and clinical target volume (CTV) are contoured in all phases of respiration. Following this, an internal target volume (ITV) was created by measuring tumor motion all the directions from the center of tumor and PTV was concluded. Results The mean ITV for tumor in all six directions, that is, in superior, inferior, anterior, posterior, medial and lateral directions was 0.9, 0.9, 0.8, 0.9, 0.8, and 0.9 cm, respectively. For coverage of tumor for 90% of patients, the margins required in superior, inferior, anterior, posterior, medial, and lateral directions were 1.3, 1.5, 1.5, 1.4, 1.5, and 1.3 cm, respectively. Other factors such as size of the tumor and location of the tumor did not significantly contribute to PTV changes in our study. Conclusion Mean ITV for tumor in all six directions summed up to be 0.8 cm, but there was significant movement in inferior direction for upper lobe tumors (0.9 cm) (p = 0.008), in medial direction for middle lobe tumors (0.8 cm) (p = 0.05), and in medial direction for lower lobe tumors (0.75 cm) (p = 0.005).
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Al-Oran, Otabeh y Ferenc Lezsovits. "A Hybrid Nanofluid of Alumina and Tungsten Oxide for Performance Enhancement of a Parabolic Trough Collector under the Weather Conditions of Budapest". Applied Sciences 11, n.º 11 (27 de mayo de 2021): 4946. http://dx.doi.org/10.3390/app11114946.
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Recently, there has been significant interest in the thermal performance of parabolic trough collectors. They are capable of operating and generating highly variable temperature ranges, which can be used in various applications. This paper, therefore, addressed the thermal performance model of using a parabolic trough collector under the radiation intensity level found in Budapest city, as well as the effect of inserting a hybrid nanofluid as the thermal fluid. First, a new modified hybrid nanofluid of alumina and tungsten oxide-based Therminol VP1 is used to enhance the thermal properties of the thermal fluid to be more efficient to use. This enhancement is performed under various volume concentrations and has a volume fraction of 50:50. Second, in order to demonstrate the effectiveness of the thermal element, mathematical energy balance equations were solved and simulated using MATLAB Symbolic Tools. The simulation is presented for two cases: one under a constant radiation intensity and the other under the radiation intensity level of Budapest. For both cases, the results of the dimensionless Nusselt number, heat transfer coefficient, pressure drop, exergy efficiency, and energy efficiency are described. The major findings show that a volume concentration of 4% (Al2O3 and WO3) based Therminol VP1 was the most efficient volume concentrations in both cases. For the first case, the maximum enhancement of the Nusselt number and the heat transfer coefficient are 138% and 169%, respectively. These results enhanced the thermal and exergy efficiencies by 0.39% and 0.385% at a temperature 600 K, flow rate of 150 L/min, and radiation intensity of 1000 W/m2. For the second case, the maximum exergy and energy values are recorded at midday under Budapest’s summer climatic conditions and reach 32.728% and 71.255%, respectively, under the optimum temperature of 500 K and flow rate of 150 L/min. Accordingly, the mean improvement in thermal and exergy efficiencies approximately equal to 0.25% at a high concentration, regardless of the season (summer or winter).
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Abdul Gaffar, S., V. Ramachandra Prasad, P. Ramesh Reddy y B. Md Hidayathulla Khan. "Radiative Flow of Third Grade Non-Newtonian Fluid From A Horizontal Circular Cylinder". Nonlinear Engineering 8, n.º 1 (28 de enero de 2019): 673–87. http://dx.doi.org/10.1515/nleng-2018-0078.
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Abstract In this article, we study the nonlinear steady thermal convection of an incompressible third-grade non-Newtonian fluid from a horizontal circular cylinder. The transformed conservation equations are solved numerically subject to physically appropriate boundary conditions using a second-order accurate implicit finite-differences Keller Box technique. The influence of a number of emerging non-dimensional parameters, namely the third-grade fluid parameter (ϕ), the material fluid parameters (ϵ1, ϵ2), Prandtl number (Pr), Biot number (y), thermal radiation (F) and dimensionless tangential coordinate (ξ) on velocity and temperature evolution in the boundary layer regime are examined in detail. Furthermore, the effects of these parameters on surface heat transfer rate and local skin friction are also investigated. Validation with earlier Newtonian studies is presented and excellent correlation is achieved. It is found that the velocity, skin friction and Nusselt number (heat transfer rate) reduce with increasing third grade fluid parameter (ϕ), whereas the temperature is enhanced. Increasing material fluid parameter (ϵ1) reduces the velocity and heat transfer rate but enhances the temperature and skin friction. The study is relevant to chemical materials processing applications and low density polymer materials processing.
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Tsai, Ching-Fen y Gene Nixon. "Transient Temperature Distributio of a Multilayer Composite Wall with Effects of Internal Thermal Radiation and Conduction". Numerical Heat Transfer, Part B: Fundamentals 10, n.º 1 (1986): 95–101. http://dx.doi.org/10.1080/10407798608552497.
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Kapetanakis, Theodoros N., Martin Pavec, Melina P. Ioannidou, Christos D. Nikolopoulos, Anargyros T. Baklezos, Radek Soukup y Ioannis O. Vardiambasis. "Embroidered Βow-Tie Wearable Antenna for the 868 and 915 MHz ISM Bands". Electronics 10, n.º 16 (17 de agosto de 2021): 1983. http://dx.doi.org/10.3390/electronics10161983.
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A textile, embroidered antenna, based on the fractal shape of the Sierpinski triangle, is designed in this paper for operation in the European free Industrial Scientific and Medical (ISM) 863–870 MHz band, as well as in the 902–928 MHz band designated for ISM applications in North and South America. Several prototypes have been fabricated by employing different stitch patterns and thread materials. The effect of the fabrication parameters on the performance of the proposed antenna is investigated through measurements and simulations, with the results being in good agreement. The antenna exhibits attractive characteristics such as wide bandwidth, relatively stable radiation patterns, as well as robustness in washing. Several tests reveal that convex and concave bent conditions do not affect the coverage of the aforementioned ISM bands, despite the shift of the resonant frequency in some cases. Moreover, the SAR values resulting from simulations are below the corresponding thresholds suggested by international guidelines.
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Liu, Don, Hui-Li Han y Yong-Lai Zheng. "A high-order method for simulating convective planar Poiseuille flow over a heated rotating sphere". International Journal of Numerical Methods for Heat & Fluid Flow 28, n.º 8 (6 de agosto de 2018): 1892–929. http://dx.doi.org/10.1108/hff-12-2017-0525.
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Purpose This paper aims to present a high-order algorithm implemented with the modal spectral element method and simulations of three-dimensional thermal convective flows by using the full viscous dissipation function in the energy equation. Three benchmark problems were solved to validate the algorithm with exact or theoretical solutions. The heated rotating sphere at different temperatures inside a cold planar Poiseuille flow was simulated parametrically at varied angular velocities with positive and negative rotations. Design/methodology/approach The fourth-order stiffly stable schemes were implemented and tested for time integration. To provide the hp-refinement and spatial resolution enhancement, a modal spectral element method using hierarchical basis functions was used to solve governing equations in a three-dimensional space. Findings It was found that the direction of rotation of the heated sphere has totally different effects on drag, lateral force and torque evaluated on surfaces of the sphere and walls. It was further concluded that the angular velocity of the heated sphere has more influence on the wall normal velocity gradient than on the wall normal temperature gradients and therefore, more influence on the viscous dissipation than on the thermal dissipation. Research limitations/implications This paper concerns incompressible fluid flow at constant properties with up to medium temperature variations in the absence of thermal radiation and ignoring the pressure work. Practical implications This paper contributes a viable high-order algorithm in time and space for modeling convective heat transfer involving an internal heated rotating sphere with the effect of viscous heating. Social implications Results of this paper could provide reference for related topics such as enhanced heat transfer forced convection involving rotating spheres and viscous thermal effect. Originality/value The merits include resolving viscous dissipation and thermal diffusion in stationary and rotating boundary layers with both h- and p-type refinements, visualizing the viscous heating effect with the full viscous dissipation function in the energy equation and modeling the forced advection around a rotating sphere with varied positive and negative angular velocities subject to a shear flow.
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Too, Gee-Pinn James y J. H. Ginsberg. "Cylindrical and Spherical Coordinate Versions of NPE for Transient and Steady-State Sound Beams". Journal of Vibration and Acoustics 114, n.º 3 (1 de julio de 1992): 420–24. http://dx.doi.org/10.1115/1.2930279.
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The NPE (nonlinear progressive wave equation) and associated computer program is a time-domain representation of acoustic propagation in waveguides that includes the effect of nonlinearity. In that approach a spatial window is initialized with the original waveform and then convected in the primary propagation direction as time evolves. Previous work modified NPE by using cylindrical coordinates to describe a paraxial approximation suitable for axisymmetric sound beams. The present development further modifies NPE by using spherical coordinates. The matter of interfacing it with the cylindrical coordinate version, in order to describe the far field of a sound beam, is described. This simulation technique is used to evaluate the long range propagation of the signal radiating from a piston in an infinite baffle that is subjected to harmonic excitation. It is also applied to a focussed sound beam generated by transient excitation of a concave projector. Comparison of the results with experimental data shows good overall agreement, with the main source of error apparently being due to dissipation, which is not addressed in the present models.