Scipedia: Documents published in 2020

Hybrid analysis of the crimping process of electrical terminals

Frederico de Oliveira Simões — Sat, 29 Jun 2019 00:50:04 +0200

The crimping of electrical terminals is a forming mechanical process that allow joining connectors to the end of electrical conductors. This process is largely used in the connectors industry, however the knowledge of its mechanical principles still be much discuss. This theory gap is due, probably, to the complexity of the problem. In this work, was looked for advance in the comprehension of this process by means of the development of a General Predictive Equation, that calculates the punch force in the crimping final moment. The methodology used consisted in the development and calibration the model of the crimping process in a Finite Element software, selection of the more influents parameters in the punch force, and development and validation of the General Predictive Equation. The results showed that Plain Stress configuration is the best representation of two dimensions model of crimping process and that only 9 (nine) variables of this model showed relevant to compose the equation. It is concluded also that the development of the General Predictive Equation to calculate punch force is viable, but, it is necessary increases the accuracy of the calculus yet. It is desired that the knowledge generated in this study already allow reduce costs of development and of production of crimped terminals.

Thermal-conductive model algorithm for the accurate calculation of temperatures in electrical power conductors

Dorindo Cardenas — Fri, 21 Jun 2019 03:18:43 +0200

The thermal-conductive models for the calculation of the electrical conductors and their energy dissipations have been able to solve doubts about the power conductors, which has been permanently unsuspected. Before thinking about thermally characterizing an electrical conductor, it was enough with the application of simple Joule-type equations, with constant resistive intrinsic properties in the conductor, as well as invariable considerations in the conditions that surround the conductor. In fact, just as is exposed, this has been published on the top of the best known electrical standards, such as those issued by the National Fire Protection Association (NFPA), as well as those edited by the International Electrotechnical Commission (IEC). It has been demonstrated that electric cables with higher electrical intensities, move away from the behavior predicted by the Joule type models, sometimes with energy dissipations 50% higher than those predicted by Joule. This is due to the non-linearities of the intrinsic properties of the cable, and the inconsistency of the environmental conditions surrounding the cable at the time it is going to heat. The novel thermal-conductive models with just ten years of development, are today a very complete solution with unparalleled accuracy (errors less than 0.01% in energy and temperature) in the thermal predictions of conductors; but due to its high degree of mathematical complexity requires in the most of cases to use numerical methods to obtain practical solutions. In this paper a new general algorithm is shown, which stands out for its simplicity compared to the first thermoconductive models, solving the models in thermal predictions of power electrical cables, without the need of huge databases, with simplicity, maneuverability and excellent practical results.

Solution of the Navier-Stokes equations using projection method and preconditioned conjugated gradient with multigrid and ILU solver

Márcio Anunciação — Wed, 12 Jun 2019 15:56:43 +0200

Among the main problems in the field of Computational Fluid Dynamics (CFD), there is the two-dimensional laminar flow in a transient regime of an incompressible fluid modeled by Navier-Stokes equations. Among the decoupled solutions for this equation system, that is, solutions for velocity regardless to pressure, there are the Projection methods, which separate the solution in three parts, solved in each time steps applying an iterative process regardless to the iterative process for the other variables. It may result, according to the Projection method applied, in two Reaction-Diffusion equations and one Poisson equation to be solved in each time step. This paper sought to develop an algorithm to solve the Navier-Stokes equation, applying the Finite Volume Method (FVM) with second order approximation scheme (CDS), beside a Projection method with incremental pressure-correction scheme, so that each Reaction-Diffusion and the Poisson equation are solved efficiently. Therefore, several solvers were tested for each equation, resulting in an algorithm with the combination that achieved the best result for each equation, with the preconditioned Conjugate Gradient method (PCG) with the Multigrid method (MG) and ILU solver (Incomplete LU factorization) being the methodology used in the whole problem solving process. The geometric Multigrid with V cycle, the correction scheme (CS), the full weighting restriction, the prolongation through bilinear interpolation and the maximum number of levels for the studied cases were utilized. The results achieved were satisfactory, since the proposed methodology accelerated the iterative process considerably in relation to the classical methods available in the literature.

Nonlinear parametric vibration analysis of radial gates

Siyuan Wu — Thu, 06 Jun 2019 04:57:02 +0200

In this work, based on dynamic characteristics of radial gates, a nonlinear diﬀerential equation of motion for the radial gate arm is established. Excitation conditions of principal parametric resonance and subharmonic parametric resonance are obtained by using multi-scale method and numerical method. The parameter analysis shows that: comparing with traditional calculation method of dynamic instability region division, the presented method is more suitable to analysis of parametric vibration for radial gates as considering the end moment, vibration duration and amplitude. The vibration amplitudes of arm increase with the increase of its length and excitation amplitude, as well as the decrease of arm inclination angle. Moreover, the parametric resonance is easier to be excited and its resonance region become wider with the initial end moment increasing. Since the vibration response of the arm is influenced by the nonlinear term in the equation, the damping effect is limited. Thus, energy transfer method (e.g. tuned mass damper) can be adopted to achieve vibration control.

Uso de analogías eléctricas para entender patologías cardiovasculares

María Jesús Samper — Tue, 28 May 2019 15:44:09 +0200

Through the interconnection of electrical elements such as a resistor, inductor and capacitor, has been developed a reduced-order model of the arterial system capable of describing the behaviour of blood flow. In this modelling, the different differential equations that describe the behaviour of this system are represented implicitly. This allows us to obtain quickly and regulate the performance of the joint model, both in normal physiological conditions and in pathological situations, which makes it a useful tool for teaching or research in cardiovascular physiology. It was implemented two different arterial models, an elastic model and a viscoelastic model, with the aim of analysing the flow and blood pressure that could occur under different physiological conditions. In order to analyse both models, it was contrasted using different orders of elasticity, the pathology of aortic dissection was studied and the results were compared qualitatively with similar solutions observed in the literature. In order to perform these simulations, it was implemented in Matlab a code for solving ordinary differential equations (DAE).

Thermal performance of light blocks in a Mediterranean climate

Hipólito Sousa — Mon, 28 Jan 2019 12:15:04 +0100

The challenge of reducing energy consumption in buildings is fundamental for the near future, considering the impact of buildings in the overall energy demands. Mediterranean regions have a mild heating season and a hot and dry winter. Its climate is characterized by plentiful solar radiation all along the year and large daily range of temperature during the summer. Thermal inertia and insulation material properties can act in a different way along the day and the year, and the better solution for the summer can be the worst solution for the cooling season. Masonry walls that define the boundary between the interior and exterior are one of the most important components of buildings mainly for energy efficiency. Despite being one of the most common and ancient building materials, it is possible to improve its performance working in units, mortars and finishes. This work aims at studying the effect of materials with different thermal insulation and thermal mass on thermal comfort and energy savings of three types of buildings, two single-family houses and one apartment, in a Mediterranean climate. Thermal behavior of traditional and light solutions is compared and it is found that thermal comfort is similar but light solutions present lower energy consumptions for the three studied house topologies. Otherwise, this study shows that housing topology has more influence namely, when comparing energy needs.

Experimental and numerical hydrodynamic analysis of a stepped planing hull

Simone Mancini — Wed, 28 Nov 2018 14:02:04 +0100

This work addresses the experimental and numerical study of a stepped planing hull and the related ﬂuid dynamics phenomena typically occurring in the stepped hull in the unwetted aft body area behind the step. In the last few years, the interest in high-speed planing crafts, with low weight-to-power ratios, has been increasing signiﬁcantly, and, in such context, naval architects have been orienting toward the stepped hull solution. Stepped planing hulls ensure good dynamic stability and seakeeping qualities at high speeds. This is mainly due to the reduction of the wetted area, which is caused by the ﬂow separation occurring at the step. This paper presents the experimental results of towing tank tests in calm water on a single-step hull model, which is the ﬁrst model of a new systematic series. The same ﬂow conditions are analyzed via Reynolds Averaged Navier-Stokes (RANS) and Large Eddy Simulations (LES), with different moving mesh techniques (overset/chimera and morphing grid), performed at different model speeds. The numerical results are in accordance with experimental data, and overset/chimera grid is found to be the best approach between the analyzed ones. The ﬂow patterns obtained numerically through LES on a reﬁned grid appear similar to the ones observed in towing tank investigations through photographic acquisitions. These ﬂow patterns are dominated by a rather complex 3D arrangement of vortices originating from air spillage at both sides of the step. The understanding of these phenomena is important for the effectiveness of stepped hull designs.

Virtual modelling of stress paths CKoU and CKoD on collapsible porous clayey soils

Juan Carlos Ruge C. — Wed, 07 Nov 2018 02:29:30 +0100

In geotechnical engineering one of the challenges is the soil characterization. Nevertheless, currently it exists computational tools, which permits estimate the soil behaviour from information obtained in the laboratory. This document addresses the numerical modelling of triaxial tests set with Ko consolidation during its shear stage by means of single element test tool. The work methodology was based on the stress paths comparison between lab data and numerical simulations with three different constitutive models: (i) Mohr-Coulomb, (ii) Cam-Clay Modified, (iii) Hypoplastic. Such stress paths were obtained in drained and undrained conditions. The soil material corresponds to a porous collapsible clay from Brasilia (Brazil). Results show the calibration of the parameters for each constitutive model. Besides, presents the stress-strain curves until achieving the critical state condition in the simulations. Finally, it was established the constitutive model that presents the best fitting to the real behaviour of this kind of material, under specific conditions for advanced triaxial tests.

Fragility curves based on the numerical analysis of masonry walls against subsidence, using the Abaqus / CAE software and relying on the pulldown technique

Yaimara Chávez Pérez — Fri, 12 Oct 2018 02:00:05 +0200

The gradual sinking of the surface caused by the subsidence is a geological phenomenon that affects several countries around the world and has been the cause of substantial material damage in elements with low stress strength. Masonry structures have been greatly affected by these differential settlements, due to their low resistance to this solicitation. In order to be able to accurately assess the state of damage present in these structures, during the investigation the behavior of masonry walls of different dimensions is analyzed, under the action of differential settlements. The numerical models were developed through a detailed micro-modeling in the Abaqus / CAE software. The partitions and mortar were considered with Mohr-Coulomb and Drucker-Pragerelastoplastic behavior, joined by interface elements represented in all vertical and horizontal joints. A mesh study was conducted to define the optimum mesh density and its use of a finite first order element. The numerical models were calibrated with experimental results, to then study the influence of the dimensions of the wall in their resistance, obtain the values of angular distortion for which the structure begins to have irreversible deformations, construct the load curves vs. angular distortion and elaborate the fragility curves of the material, through which the damage status of a masonry wall can be assessed, subject to a certain angular distortion value.

Elastic dynamics analysis in steel tubular towers for horizontal axis wind turbines

Douglas Mateus de Lima — Fri, 29 Jun 2018 16:12:45 +0200

This article aims to obtain the dynamic elastic analysis of a steel tube tower for horizontal axis wind turbine using finite elements of bar (own code) and finite elements of bark and solids (modeling in ANSYS). For this, a theoretical foundation is presented that consists in the development of the movement equation from the Lagrange equation. Next, the modal overlay method is presented for solving the matrix motion equation and for obtaining the dynamic response of the tower. In the second part of this article, the development is presented for the assembly of the mass and damping matrices of the tower modeled with its own code in finite elements of the bar. In the part of results, initially, the rigidity, mass and damping matrices are exposed for a certain level of discretization of the modeled tower with finite elements of bar. Then, the results of the modal analysis were done for both the finite element shell model, with and without flexible base, and the finite element model of the bar, in which the modes and the frequencies of vibration of the tower in all the models are presented. Finally, the responses of the tower were analyzed: in the direction of the wind flow, when submitted by a vector of resonant forces to its 1st mode of vibration, representing the floating part of the wind; and, in the transverse direction to the wind flow due to the von Kárman cadenced vortex detachment. The results of the modal analysis made for both the finite element shell model, with and without flexible base, and the finite element model of the bar are similar, especially in the first mode of vibration of the tower. Therefore, the model represented by finite elements (FE) of bar can be used as representative of the dynamic behavior of the tower when it is subjected to the resonant excitations at its fundamental frequency.

Setting of the parameters to capacity spectra of steel buildings

CARLOS ALBERTO BERMUDEZ MEJIA — Mon, 31 Jul 2017 04:58:42 +0200

The first part of this paper provides a theoretical framework on the subject of capacity spectra and its usefulness in studying the seismic vulnerability of buildings. Then, the works of some researchers, which have moved forward in the direction of setting the parameters of those curves, are reported and theirs most important conclusions are highlighted. After that, the models that have been used in this research together with theirs capacity spectra are introduced. Finally, techniques for setting parameters are applied on those curves and the most important results and conclusions are presented.