Current Issue : October - December Volume : 2016 Issue Number : 4 Articles : 5 Articles
The main followed objectives within control strategies dedicated to hybrid micro\ngrid systems (wind/hydro/solar), that operate based on maximum power point tracking (MPPT)\ntechniques are to improve the conversion systems efficiency and to maintain the quality of the\nproduced electrical energy (the voltage and power factor control). One of the main goals of\nmaximum power point tracking strategy is to achieve the harvesting of the maximal possible\nenergy within a pre-set time period. In order to implement the control strategies for micro grid\nsystems that operate at time variable parameter, there are usually required specific transducers\n(anemometer for wind speed measurement, optical rotational transducers, taco generators, etc.).\nIn the technical literature there are presented several variants of the MPPT techniques, which\nare particularized at several applications (wind energy conversion systems, solar systems,\nhydro plants and micro grid hybrid systems). The maximum power point tracking\nimplementations are mainly based on two-level architecture. The inferior level controls the\nprimary variables, while the superior level represents the MPPT control structure. In the paper,\nauthors present some micro grid structures proposed at Politehnica University Timisoara within\nthe frame of a research grant. The paper is focused on the application of MPPT strategies on\nhybrid micro grid systems. There are presented several structures and control strategies and are\nhighlighted their advantages and disadvantages, together with practical implementation\nguidelines....
We proposed a thermal engraving technology based on heat transfer theory and polymer\nrheology in microfluidic field. Then, we established a 3D model of the thermal engraving process\nbased on polymethyl methacrylate (PMMA) material. We could employ the model to analyze\nthe influence of temperature and speed on microchannel processing through the finite element\nsimulation. Thus, we gained the optimal processing parameters. The orthogonal experiments were\ncarried out within the parameter ranges obtained by the simulation results. Finally, we fabricated the\nsmooth microchannel, the average roughness of which was 0.3 �¼m, by using the optimal parameters.\nFurthermore, we examined the surface morphology and wettability. Our work provides a convenient\ntechnological support for a fast, low-cost, and large-scale manufacturing method of microfluidic chips....
To simulate and analyze a large aircraftwith severewind shear, nonlinear equations for a rigid aircraft under variouswind conditions\nwere designed. In this paper, a double-vortex-ring method is adopted to generate a three-dimensional microburst wind field.\nThis model incorporates a flight dynamics module and three flight simulations based on various forms of nonlinear equations.\nIn addition, four primary wind gradients are considered to compute the aerodynamic coefficients. In simulation experiments with\na China C series large aircraft, equations using air-relative velocities and inertial velocities are compared and analyzed. Although the\nnonlinear equations derived using the air-relative velocities should be identical to those using the inertial velocities, the results show\nthat the latter are more accurate in practice because the former bring error into the simulation when estimating the acceleration\ninduced by the wind field....
A dynamic model for a ball-end milling process that includes the consideration of cutting force nonlinearities and regenerative\nchatter effects is presented. The nonlinear cutting force is approximated using a Fourier series and then expanded into a Taylor\nseries up to the third order.Aseries of nonlinear analyseswas performed to investigate the nonlinear dynamic behavior of a ball-end\nmilling system, and the differences between the nonlinear analysis approach and its linear counterpartwere examined.Abifurcation\nanalysis of points near the critical equilibrium points was performed using the method of multiple scales (MMS) and the method\nof harmonic balance (MHB) to analyse the local chatter behaviors of the system. The bifurcation analysis was conducted at two\nsubcritical Hopf bifurcation points. It was also found that a ball-end milling system with nonlinear cutting forces near its critical\nequilibrium points is conditionally stable.The analysis and simulation results were compared with experimental data reported in\nthe literature, and the physical significance of the results is discussed....
Model order reduction (MOR) methods are more and more applied on many different\nfields of physics in order to reduce the number of unknowns and thus the\ncomputational time of large-scale systems. However, their application is quite recent in\nthe field of computational electromagnetics. In the case of electrical machine, the\nnumerical model has to take into account the nonlinear behaviour of ferromagnetic\nmaterials, motion of the rotor, circuit equations and mechanical coupling. In this\ncontext, we propose to apply the proper orthogonal decomposition combined with\nthe (Discrete) empirical interpolation method in order to reduce the computation time\nrequired to study the start-up of an electrical machine until it reaches the steady state.\nAn empirical offline/online approach based on electrical engineering is proposed in\norder to build an efficient reduced model accurate on the whole operating range.\nFinally, a 2D example of a synchronous machine is studied with a reduced model\ndeduced from the proposed approach....
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