Energy frictional dissipating algorithm for rigid and ellastic body’s contact problems

An Energy Frictional Dissipating Algorithm (EFDA) for time integration of Coulomb frictional impact–contact problems is presented. Using the Penalty Method, and in the context of a conserving framework, linear and angular momenta are conserved and energy is consistently dissipated. Published formulations were stable, forcing the energy dissipation to be monotonic in order to prevent unstable energy growth. The shortcoming of many was that they were not able to reproduce the real kinematics and dissipation of physical processes, provided by analytical formulations and experiments. EFDA formulates a conserving framework based on a physical energy dissipation estimator. This framework uses an enhanced Penalty contact model based on a spring and a dashpot, enforcing physical frictional energy dissipation, controlling gap vibrations and modifying the velocities and contact forces during each time step. The result is that the dissipated energy, kinematics and contact forces are consistent with the expected physical behavior

Incipient sediment transport for non-cohesive landforms by the discrete element method (DEM)

The determination of the shear stress at which a sediment grain of a given size and density starts to move has been treated with theoretical, experimental and numerical procedures by many authors. The seminal contribution of Shields [7] addresses a relationship for the non-dimensional critical shear stress in terms of the friction Reynolds number for a single particle in a flat bed. This work focusses on the incipient transport of particles for bedforms. The proposed numerical approach to the problem integrates the Discrete Element Method (DEM) [9] with a continuous finite element approximation. The DEM simulates the motion of the landform, defined as an aggregate of rigid discs that interact by contact and friction. The continuous finite element approach predicts the boundary shear stress field coming from the fluid flow over the bed (for basic formulation, see [4] and reference therein). Both methods are coupled through the flow-particle force transmission using drag coefficients. While for single particles (or very simple sets of particles) incipient motion (and consequently, the threshold stress) is clearly defined, for complex forms the use of the concept of incipient transport becomes necessary, and critical shear stress is established in terms of a threshold sediment flux over the bed surface. We present a series of numerical experiments for single particles, showing good agreement with Shields curve for the whole range of Reynolds number. In this communication we show some of these results, in compare with the basic Shields curves for flat bed and single grains

Elasto-thermoelectric non-linear, fully coupled, and dynamic finite element analysis of pulsed thermoelectrics

This paper presents a numerical study on the influence of pulsed electric signals applied to the overcooling of thermoelectric devices. To this end, an experimental setup taken from the literature and a commercial cell are simulated using a complete, specially developed research finite element code. The electro-thermal coupling is extended to include the elastic field, demonstrating that the increment of cooling can produce mechanical failure. Numerical results are developed and the variation of overcooling versus pulse gain and versus duration is validated towards a new analytical expression and the experimental data. The issue of optimal intensity at steady-state is also newly developed. Thermal and mechanical trends are presented using constant and variable (with temperature) material properties for a single thermoelement. While some of the first trends are similar to those of published works, others are different or directly new, all closer to those of the experiments. The mechanical results have not been thoroughly studied until recently. The three-dimensional finite element mesh includes non-thermoelectric materials that are fundamental for the current study. Distribution of stresses during steady and transient states are shown inside the thermoelement, for five components and for the combined Tresca stress. Concentrations at corners of the lower side appear close to the cold face. Due to these concentrations, 27-node isoparametric, quadratic brick elements are used. It is shown that the mechanical field is an important factor in the design of pulsed thermoelectrics, since for practical applications the stress levels are close or slightly above the admissible limits.This research was partially supported by grants CSD2008-00037 Canfranc Underground Physics and Polytechnic University of Valencia under programs PAID 02-11-1828 and 05-10-2674.Pérez-Aparicio, JL.; Palma, R.; Moreno-Navarro, P. (2016). Elasto-thermoelectric non-linear, fully coupled, and dynamic finite element analysis of pulsed thermoelectrics. Applied Thermal Engineering. 107:398-409. https://doi.org/10.1016/j.applthermaleng.2016.05.114S39840910

Study of hysteretic thermoelectric behavior in photovoltaic materials using the finite element method, extended thermodynamics and inverse problems

The main objective of the present work is to develop and prove a theoretical explanation based on the Extended Non-Equilibrium Thermodynamics (ENETs) for the hysteretical thermoelectric behavior observed in certain thin-film photovoltaic materials. The ENET introduces dissipative fluxes in the entropy balance that could explain this behavior. To verify this explanation from a numerical point of view, results are generated using a Finite Element (FE) formulation based on the ENET and already developed in previous publications by the authors. In addition, an identification Inverse Problem (IP) is formulated; a cost function is defined as the quadratic difference between experimental and numerical results and the IP is solved minimizing the cost function using genetic algorithms. The conclusion is that the loop-like distributions are due to energy dissipation introduced by dissipative fluxes that are closely related with relaxation times. Also, the FE-IP combination permits to find an approximated characterization of properties for several materials from single experimental curves. Finally, several numerical simulations are proposed for laboratory experiments to further validate the theoretical interpretation and to confirm the relation between relaxation times and hysteresis.This research was partially supported by the Grants CSD2008-00037 Canfranc Underground Physics, Excelencia Junta Andalucia P08-TEP-03641 and Polytechnic University of Valencia under programs PAID 02-11-1828 and 05-10-2674.Palma, R.; Pérez-Aparicio, JL.; Bravo, R. (2013). Study of hysteretic thermoelectric behavior in photovoltaic materials using the finite element method, extended thermodynamics and inverse problems. Energy Conversion and Management. 65(92):557-563. https://doi.org/10.1016/j.enconman.2012.07.009S557563659

LCC-HVDC Connection of Offshore Wind Farms With Reduced Filter Banks

Despite being more efficient, line commutated converter-HVDC links for the connection of large offshore wind farms have ac-filter bank size as one of their main drawbacks. This paper shows how the HVDC rectifier filter banks can be substantially reduced by taking advantage of the additional control possibilities offered by the use of wind turbines with fully rated converters. PSCAD simulations validate wind farm and diode rectifier HVDC link operation with a capacitor and filter bank five times smaller than its usual value. The proposed control algorithm allows for good harmonic and reactive power sharing between the different wind turbines. As the reduced capacitor bank operation leads to a redistribution of harmonic and reactive currents, an efficiency study has been carried out to evaluate the new power loss distribution with the reduced filter banks

Effects of 24 h compression interventions with different garments on recovery markers during running

Compression and temperature manipulation are discussed as strategies to improve performance markers and recovery in sports. Here, we investigate the effects of compression stockings made with fabric, either combined or not with heating and cooling substances, on variables related to running performance and recovery. Ten trained runners (mean ± standard deviation age 45 ± 9 years old, body mass 69 ± 7 kg, height 166 ± 4 cm) with no experience of using compression garments performed an intense running session of 10 km, then wore a stocking for 24 h (randomized; without compression, compression, compression with camphor, and compression with menthol), and were evaluated on the following day, after running 5 km. The different types of compression stockings used 24 h before exercise did not affect running kinematics (p > 0.14), skin temperature (p > 0.05), heart rate (p > 0.12; mean value of maximal heart rate 156 bpm), comfort perception (p = 0.13; mean value of 7/10 points), or perception of recovery (p = 0.13; mean value of 7/10 points). In general, there were no effects of 24 h pre-exercise lower leg compression, including those treated with menthol and camphor applications on running kinematics, skin temperature, heart rate, or recovery perception in athletes undertaking consecutive running exercises

Lipoma parostal de fémur: Aportación de un caso

Describimos un caso de lipoma parostal de fémur, un tumor benigno poco frecuente formado por tejido adiposo maduro en relación con el periostio. Nuestro objetivo es documentar el caso, comentando los hallazgos radiológicos, histológicos y el tratamiento y realizar una revisión bibliográfica.We describe a case of parosteal lipoma of the femur. It is an infrequent benign neoplasm composed of mature fat, intermately connected with the periosteum. Our aim is to document the case, and comment the radiological, histological findings, and treatment, and review the literature

Experimental transition probabilities in NII lines

Producción CientíficaThis work reports an extensive collection of 108 transition probabilities of NII lines in the visible spectral region, all of them measured in an emission experiment. Relative intensity measurements have been made on a pulsed discharge lamp and the absolute Aki values have been obtained by using the literature available data. Electron density and temperature range in this experiment from 0.2 to and from 17000 to 29000 K respectively. The first one has been simultaneously determined from two-wavelength interferometry and from the Stark broadening of HeI 471.3 nm, the second from Boltzmann-plot of NII lines and from NII/NI intensities ratios. The results are compared with the recent available literature.

Ministerio de Educación y Formación Profesional (grant PB-98-0356)Junta de Castilla y León (grant VA23-99

Local chain deformation and overstrain in reinforced elastomers: An NMR study

A molecular-level understanding of the strain response of elastomers is a key to connect microscopic dynamics to macroscopic properties. In this study we investigate the local strain response of vulcanized, natural rubber systems and the effect of nanometer-sized filler particles, which are known to lead to highly improved mechanical properties. A multiple-quantum NMR approach enables the separation of relatively low fractions of network defects and allows to quantitatively and selectively study the local deformation distribution in the strained networks matrix on the microscopic (molecular) scale. We find that the presence of nondeformable filler particles induces an enhanced local deformation of the matrix (commonly referred to as overstrain), a slightly increased local stress/strain heterogeneity, and a reduced anisotropy. Furthermore, a careful analysis of the small nonelastic defect fraction provides new evidence that previous NMR and scattering results of strained defect-rich elastomers cannot be interpreted without explicitly taking the nonelastic defect fraction into account

Physical activity and leisure habits and relation with Ruffier index in adolescents

El objetivo del estudio fue medir y correlacionar la práctica de actividad física y con el Índice de Ruffier (IR) en adolescentes. A un total de 884 alumnos (edad=16,4±0,8 años) se les midió la actividad física con la Versión modificada del Assessment of Physical Activity Level Questionnaire (APALQ) y se evaluó la capacidad de adaptación al esfuerzo mediante el Test Ruffier. La media del Índice de Ruffier fue 11,1±4,6 y el Índice de actividad física (IAF) 13,8±4,4. Las relaciones entre IAF y el IR, y entre horas de ocio sedentario e IR resultaron ser significativas aunque débiles (r=-0,31; p=0,000). En el IR los chicos presentaron valores superiores (t= -8,78; p= 0,000) a las chicas. También destinan más tiempo a la práctica de AF y estas diferencias fueron significativas en AF reglada y no reglada y en participación en competición (p=0,000), mientras que las chicas destinan más tiempo a actividades sedentarias como leer y estudiar (p=0,000). Es necesario promover la práctica de actividades físico-deportivas, especialmente entre las chicasThe aim of the study was to assess and correlate physical activity practice and fitness level in adolescents. A total of 884 students (age=16,4±0,8 years) answered the modified version of the “Assessment of Physical Activity Level Questionnaire (APALQ)” and aerobic capacity was assessed through the Ruffier Test. The mean Ruffier Index (IR) was 11,1±4,6 and the mean Physical Activity Index (IAF) was 13,8±4,4. The relationship between IAF and IR, and between sedentary activities in leisure time and IR, was significant (r=-0,31; p=0,000). although weak. Boys showed higher physical fitness values (t= -8,78; p= 0,000) and spent more time practicing physical activity. These differences were significant for both regulated and not regulated physical activity and for participation in competition (p=0.000). Girls spent more time in sedentary activities like reading and studying (p=0.000). It is necessary to promote physical activity and sport practice, especially among girls