Current Issue : January - March Volume : 2020 Issue Number : 1 Articles : 5 Articles
This research proposes a circularly polarized (CP) single-fed omnidirectional dipole antenna operable in 2.45GHz frequency for the\nindustrial, scientific, and medical (ISM) radio band applications.The proposed antenna consisted of bisectional dipole core, a pair of\nquarter-wave baluns, and four diagonally adjoined parasitic braces.The bisectional dipole core was utilized to improve the antenna\ngain and realize omnidirectional radiation pattern, and the quarter-wave baluns were to symmetrize the current on the bisectional\ncore. The four parasitic braces collectively generated circular polarization. In the study, simulations were conducted using CST\nMicrowave Studio and a prototype antenna fabricated. To validate, experiments were carried out, and simulation and experimental\nresults compared. The finding revealed good agreement between the simulation and experimental results. Essentially, in addition\nto achieving an antenna gain of 2.07 dBic, the proposed CP single-fed omnidirectional antenna is suited to ISM frequency band\napplications....
High-speed and accurate simulations of landslide-generated tsunamis are of great\nimportance for the understanding of generation and propagation of water waves and for prediction\nof these natural disasters. A three-dimensional numerical model, based on Reynolds-averaged\nNavierâ??Stokes equations, is developed to simulate the landslide-generated tsunami. Available\nexperiment data is used to validate the numerical model and to investigate the scale effect of\nnumerical model according to the Froude similarity criterion. Based on grid convergence index\n(GCI) analysis, fourteen cases are arranged to study the sensitivity of numerical results to mesh\nresolution. Results show that numerical results are more sensitive to mesh resolution in near field\nthan that in the propagation field. Nonuniform meshes can be used to balance the computational\nefficiency and accuracy. A mesh generation strategy is proposed and validated, achieving an accurate\nprediction and nearly 22 times reduction of computational cost. Further, this strategy of mesh\ngeneration is applied to simulate the Laxiwa Reservoir landslide tsunami. The results of this study\nprovide an important guide for the establishment of a numerical model of the real-world problem of\nlandslide tsunami....
Flow and fracture of granular materials under external loads is a complex mechanical process, and the research on its law is still in\nthe exploratory stage. In this paper, the flow and fracture law of granular materials is taken as the research object, and numerical\nalgorithm compilation and program development are combined to study. Taking full advantage of the existing algorithms and\ndeveloping new ones based on the existing DEM theory, a numerical simulation program for the flow and fracture of granular\nmaterials is developed. The flow and fracture process of concrete spherical granular system with diameter of 4 cm under loading\nrate of 70 mm/min and end of loading of 50 kN is taken as an example to verify the simulation program. At the same time, the\nloading experiment of the concrete spherical particle system under the same simulation conditions was also carried out. The\nsimulation results are compared with the experimental results in three aspects: the generation location of the particle system, the\nrelationship between the whole load and displacement, and the degree of particle breakage. The results show that the numerical\nsimulation is in good agreement with the experimental results, which verifies the reliability of the numerical algorithm and the\nsimulation program, and can provide support for the study of the flow and fracture process of granular materials....
We investigate under what conditions transient simulation could be used to\nintegrate backward in time so that the initial field could be recovered from\nlater histories. In this paper we use realistic examples and find that, in long\nhistories, traces of the initial field would be present only in the exact analytical\nsolutions. We conclude that the recovery of initial field is possible only if\nthe equations could be solved analytically or only short time periods are involved.\nIn practice, it is not possible to detect those traces by measurements\nor observations. If numerical procedures are used, truncation and discretization\nerrors are always present. Fine-tuning of system parameters used or\ntransforming time into another pseudo time frame may allow numerical integration\nto be carried out backward in time. But numerical instability is still\na problem. Large spurious increases found by numerical procedures are most\nlikely due to numerical inaccuracy and instability....
In this paper, the internal flow field and external spray characteristics of the\nspray gun were simulated and analyzed by establishing a coupling model of\nthe gas-liquid two-phase flow of the spray gun. The spray particle size and\ncone angle under different gas path pressures were mainly studied. The calculation\nresults showed that the spray particle size distribution had a large\nspan, but the overall spray particle size was small. The liquid flow and the air\npressure had a little influence on the spray cone angle. The spray SMD was\ntested by a three-dimensional particle dynamic analyzer (PDA), and the spray\ncone angle was photographed with a high-speed camera. The test data was\nbasically consistent with the simulation results. The experimental results\nshowed that the model can accurately simulate the internal flow field of the\nspray gun and the atomization process of urea. It can be used to analyze the\ncharacteristics of urea spray and provide a theoretical basis for the optimal\ndesign of urea spray gun....
Loading....