Papers by Keyword: Analytical Model

Abstract: This paper presents an analytical model for ultra scaled symmetric double gate (SDG) nanowire junctionless field effect transistor (JLFET), which includes charge quantization in all the regions of operation. This model is based on a first-order correction for the confined energies obtained by solving the Schrodinger’s equation. The model is able to predict the quantum mechanical effects (QME) on the surface potential, drain current and transconductance for a highly doped and extremely thin silicon layer of thickness down to 4nm. The results obtained are validated by comparing with GENIUS 3D TCAD quantum simulations.

Abstract: Friction stir welding is a solid-phase welding process based on the mixing of the pasty material in the stirred zone. The main advantage of this technique is the ability to weld metal alloys which are generally difficult to weld by conventional welding processes. In this paper an analytical model is proposed for the description in 2D the distribution of the material (fluid) flow in the vicinity of the tool pin during friction stir welding process "FSW". For this reason, the analytical solutions are built on the basis of traditional problem of mechanics of the fluids which is used to solve the equation associated with this problem. Furthermore, the aim is to make an analytical study of these aspects for a better understanding of this phenomenon. This method provides a reduction in computational time compared to those required for finite or differential elements methods. Moreover, it highlights on the effects of the different parameters on the material flow during welding.

Abstract: Corrosion of steel in concrete is the most detrimental source for reinforced concrete structures. Among the other effects, corrosion deteriorates the interface between steel and concrete. An axisyimmetric numerical model able to simulate the structural behaviour of bond between steel and concrete is here presented. The model is based on the thick-walled cylinder theory so that bond performance is a direct consequence of radial pressure acting on the rebar and coming from the surrounding elements and corrosion. Both elastic and inelastic contribution of concrete is also taken into account. The model is used to simulate pull-out tests present in literature. The results show the effectiveness of the model and is also compared with an empirical model already proposed in literature.

Abstract: We have evaluated the specific on-resistance (R_on,sp) vs. BV trade-off limit of vertical superjunction (SJ) devices for 4H-SiC and 2H-GaN using a previously published analytical model. In addition, we have identified and replaced some unsuitable assumptions found in previous work. Our results show that the R_on,sp of vertical SJ devices is between one and four orders of magnitude lower than the 1D limit of 4H-SiC and 2H-GaN devices at same breakdown voltage, but significantly higher than the previous projected limit for 4H-SiC. The optimized specific on-resistance for SJ devices is lower than that for conventional devices by factors of 3X and 100X for 1kV and 10kV devices respectively. These figures are, however, 25X higher than previous projections.

Abstract: To work out effective damping materials it is necessary to perfect analytical dependences linking dynamic properties of a composite with its structure-forming parameters. The analytical model of the particulate-filled polymers, based on the method of strain energy, convenient for engineering use and allowing to predict damping properties of a composite more reliable is given in this article. The detailed leading-out of formulas for scaling of a bulk modulus and loss factor of both two-phase and three-phase model of a composite is presented. Comparison of numerical values of damping characteristics under the derived formulas with experimental researches show that the offered model allows not only to show a qualitative pattern of dependence of dynamic behavior of a composite from degree of admission, but also to receive comprehensible quantitative results.

Abstract: Based on a few experimental results available in the literature, this work presents a simple analytical approach that allows the study of the long-term behaviour of CFRP-to-concrete interfaces under an initial sustaining load. Only the elastic regime is studied, which means that the interfacial maximum bond stress and maximum slip are never exceeded. Therefore, the maximum initial load to be sustained by the joints is limited by its corresponding elastic value. The analytical results provided by the proposed model are compared with some experimental results found in the literature. The results showed strain redistribution throughout the bonded length over the time.

Abstract: Rolling Models have come a long way from the first empirical relations about forward slip and bite conditions to their current state, which allows local quantities to be calculated in two and three dimensions. In this paper, state-of-the-art of analytical modelling of the rolling process is shown with a fully three-dimensional rolling model for hot and cold strip rolling with stress distributions in the longitudinal, vertical and lateral directions. For this purpose, von Karman’s strip approach is extended to account for the stress gradient in lateral direction, as was already shown in different papers. The stress gradient in the vertical (through-thickness) direction is introduced by a modern implementation of Orowan’s inhomogeneous deformation theory. The local stress distributions are compared to results from Finite-Element Calculations obtained with modern FEM codes. It will be shown, under which circumstances expensive FEM calculations can be replaced by simpler models like the one proposed here, which are more time and cost-effective without a significant loss in result precision. The rolling model is extended with a Finite Element Beam Model for work and backup roll deformation, as well as local work roll flattening and thermal crown for hot rolling. The Effects of those features on stress distribution and exit strip profile are shown for hot and cold rolling.

Abstract: In this paper, an analytical buckling model is established to predict the flange wrinkling behavior of deep drawn cylindrical cups of aluminium alloy sheet in warm forming conditions using macro-textured blankholders for the first time. A continuum damage mechanism (CDM) based material model was utilized to reflect the visco-plastic feature of material at elevated temperatures. Forming speed and temperature effects were investigated, and texture ratio and draw ratio effects were also discussed. The developed analytical buckling model was validated by finite element simulations. The increase of forming temperature and forming speed is prone to cause wrinkling for AA5754, but the effects are not as significant as the texture geometry and draw ratio. The analytical model presented in this paper can be used as a design guide to determine tool texture geometry necessary to avoid wrinkling defects in the warm forming processes of aluminium alloy.

Abstract: The validation of an analytical model recently proposed for evaluation of the shear capacity in Reinforced Concrete (RC) beams containing multiple inclination of transverse stirrups is presented. The model is a suitable extension of that currently proposed in Eurocode 2 for the evaluation of the shear resistance, and it is derived by means of the the variable-inclination stress-field theory based on Nielsen’s plastic approach. Experimental and numerical data available in the literature on Hybrid Steel-Trussed Concrete Beams (HSTCBs) are used for model validation and result discussion. Finally, also the comparison with a different analytical approach for the assessment of the shear resistance of HSTCBs is provided.

Abstract: A numerical method is proposed to calculate earth-energy of earth-air-pipe heat exchanger during winter heating. The proposed method is based on using numerical computation developed on Scilab a free open source software. Authors showed the comparison between their simple numerical model called Heatground with the well-known Amitrano results. The comparison is given for different parameters as the airflow, the pipe length, the depth of buried pipe, the pipe diameter.