Use of TMD in structural engineering: Building Parque Araucano in Santiago de Chile

Congreso celebrado en la Escuela de Arquitectura de la Universidad de Sevilla desde el 24 hasta el 26 de junio de 2015.The application of Tuned Mass Dampers in mechanical engineering is of longstanding and habitual use. In these kinds of applications, the loading forces are based on constant frequencies and they are in most case well known. The application of a TMD in structural engineering is more recent, beginning a few years ago under the concept of seismic protection. The design of a TMD for a building presents the practical difficulty of tuning the device to the fundamental period of the structure. Through the application of additional damping, it is possible to widen the range of tuning frequencies and therefore increase the effectiveness of the TMD. Additionally, the seismic loads to which the structure will be submitted are uncertain in their frequency distribution which could generate a counterproductive effect, because the response of the building to the seismic forces could be even worse with the use of TMD. The addition of more damping has the result of a reduction of the positive effect of the TMD at the fundamental frequency, but produces a better response for the entire range of frequencies of the seismic excitation. The following work shows both the theoretical and practical application of this concept to a building built in 2006 in Santiago de Chile, which passed unscathed the 2010 Maule Earthquake, which reached a magnitude 8,8 Mw with an intensity VIII in the locations of the building

Measurements of Magnetic Field Pattern in a Short LHC Dipole Model

The magnetic field in superconducting accelerator magnets has a fine structure with longitudinal periodicity. This periodic pattern, with period identical to the cable twist pitch, is originated by uneven current distribution within the cable. Here we present results of measurements of the periodic pattern performed in an LHC dipole model. We report in particular the results obtained powering the magnet with simple current steps and typical operation cycles as will be used during accelerator operation. The main result of the analysis is the time variation of the amplitude of the periodic pattern, from which we infer the evolution of the current distribution in the cable. We discuss the dependence of the pattern amplitude on ramp and pre-cycle parameters

Analysis of Electrical Coupling Parameters in Superconducting Cables

The analysis of current distribution and redistribution in superconducting cables requires the knowledge of the electric coupling among strands, and in particular the interstrand resistance and inductance values. In practice both parameters can have wide variations in cables commonly used such as Rutherford cables for accelerators or Cable-in-Conduits for fusion and SMES magnets. In this paper we describe a model of a multi-stage twisted cable with arbitrary geometry that can be used to study the range of interstrand resistances and inductances that is associated with variations of geometry. These variations can be due to cabling or compaction effects. To describe the variations from the nominal geometry we have adopted a cable model that resembles to the physical process of cabling and compaction. The inductance calculation part of the model is validated by comparison to semi-analytical results, showing excellent accuracy and execution speed

A General Model for Thermal, Hydraulic and Electric Analysis of Superconducting Cables

In this paper we describe a generic, multi-component and multi-channel model for the analysis of superconducting cables. The aim of the model is to treat in a general and consistent manner simultaneous thermal, electric and hydraulic transients in cables. The model is devised for most general situations, but reduces in limiting cases to most common approximations without loss of efficiency. We discuss here the governing equations, and we write them in a matrix form that is well adapted to numerical treatment. We finally demonstrate the model capability by comparison with published experimental data on current distribution in a two-strand cable

Analytical Calculation of Current Distribution in Multistrand Superconducting Cables

In recent years the problem of current distribution in multistrand superconducting cables has received increasing attention for large scale superconductivity applications due to its effect on the stability of fusion magnets and the field quality of accelerator magnets. A modelling approach based on distributed parameters has revealed to be very effective in dealing with long cables made of some tens or hundreds of strands. In this paper we present a fully analytical solution equation for a distributed parameters model in cables made of an arbitrary number of strands, whose validity is subjected to symmetry conditions generally satisfied in practical cables. We give in particular analytical formulae of practical use for the estimation of the maximum strand currents, time constants and redistribution lengths as a function of the cable properties and the external voltage source

An Analytical Benchmark for the Calculation of Current Distribution in Superconducting Cables

The validation of numerical codes for the calculation of current distribution and AC loss in superconducting cables versus experimental results is essential, but could be affected by approximations in the electromagnetic model or incertitude in the evaluation of the model parameters. A preliminary validation of the codes by means of a comparison with analytical results can therefore be very useful, in order to distinguish among different error sources. We provide here a benchmark analytical solution for current distribution that applies to the case of a cable described using a distributed parameters electrical circuit model. The analytical solution of current distribution is valid for cables made of a generic number of strands, subjected to well defined symmetry and uniformity conditions in the electrical parameters. The closed form solution for the general case is rather complex to implement, and in this paper we give the analytical solutions for different simplified situations. In particular we examine the influence of different boundary conditions, the effect of a localised resistance in the middle of the cable such as in the case of quench and the effects of localized time dependent magnetic fluxes acting on the cable

A continuum model for current distribution in Rutherford cables

An analysis of eddy currents induced in flat Rutherford-type cables by external time dependent magnetic fields has been performed. The induced currents generate in turn a secondary magnetic field which has a longitudinal periodicity (periodic pattern). The dependence of the amplitude of the pattern on the history of the cable excitation has been investigated. The study has been carried out with two different models for the simulation of current distribution in Rutherford cables, namely a network model, based on a lumped parameters circuit and a "continuum" model, based on a distributed parameters circuit. We show the results of simulations of the current distribution in the inner cable of a short LHC dipole model in different powering conditions and compare them to experimental data. (12 refs)

The occlusal precision of milled versus printed provisional crowns

Objectives: The aim of this study was to compare the occlusal precision of computer-aided-design/ computer-assisted-manufacturing (CAD/CAM) milled versus 3D printed polymethylmethacrylate (PMMA) temporary prosthetic crowns, starting from the same digital CAD design. Materials and methods: The study sample included 34 patients presenting 34 premolars in need of prosthetic rehabilitation: a total of 68 temporary crowns were manufactured, 34 of which milled and 34 printed. Immediately after manufacturing, the milled and printed provisionals were scanned with a desktop scanner (E1, 3Shape) to obtain STL files, that were superimposed to the original CAD design in order to identify the occlusal trueness (Analysis A). A second occlusal comparison was performed by scanning both kind of provisional after being placed intraorally with Trios scanner (3 Shape); intraoral scans were obtained in order to compare STL files of provisionals before and after occlusal adjustments (Analysis B). The occlusal trueness was identified at three reference points, P1 (vestibular cusp), P2 (palatal / lingual cusp), P3 (central fossa). The statistical analysis was performed using the R 3.4.3 statistical software (The R Foundation for Statistical Computing), with a significance level of p <0.05. Results: Overall, the printed crowns showed lower occlusal differences than the milled crowns, when compared to the CAD design file, with a statistically significant difference in P1 (difference of 0.025 ± 0.046 mm), P2 (difference of 0.027 ± 0 0.044 mm) and P3 ( difference of 0.018 ± 0.050) for Analysis A (p <0.05). In the Analysis B the direct comparison between the degree of average difference between the pre-adjustment and the post-occlusal adjustment of the milled and printed crowns shows that the printed crowns have lower occlusal mean difference values in all three points compared to the milled ones (difference of 0.146 ± 0.273 mm in P1, 0.285 ± 0.360 mm in P2 and 0.257 ± 0.277 mm in P3). Conclusions: Within the limitation of this study, the data obtained showed a better occlusal surface dimensional accuracy of the 3D printed provisional crowns, when compared to the milled ones. Comparing the results obtained, it is possible to assume that the intraoral scans also had a contribution to occlusion, beside the manufacturing method. 3D printing can be successfully applied for manufacturing temporary PMMA crowns