1,205 research outputs found
Elastically restrained Bernoulli-Euler beams applied to rotary machinery modelling
Facing the lateral vibration problem of a machine rotor as a beam on elastic supports in bending, the authors deal with the free vibration of elastically restrained Bernoulli-Euler beams carrying a finite number of concentrated elements along their length. Based on Rayleigh's quotient, an iterative strategy is developed to find the approximated torsional stiffness coefficients, which allows the reconciliation between the theoretical model results and the experimental ones, obtained through impact tests. The mentioned algorithm treats the vibration of continuous beams under a determined set of boundary and continuity conditions, including different torsional stiffness coefficients and the effect of attached concentrated masses and rotational inertias, not only in the energetic terms of the Rayleigh's quotient but also on the mode shapes, considering the shape functions defined in branches. Several loading cases are examined and examples are given to illustrate the validity of the model and accuracy of the obtained natural frequencies
Modelling swimming hydrodynamics to enhance performance
Swimming assessment is one of the most complex but outstanding and fascinating topics in biomechanics.
Computational fluid dynamics (CFD) methodology is one of the different methods that have been applied in swimming
research to observe and understand water movements around the human body and its application to improve swimming
performance. CFD has been applied attempting to understand deeply the biomechanical basis of swimming. Several studies
have been conducted willing to analyze the propulsive forces produced by the propelling segments and the drag force
resisting forward motion. CFD technique can be considered as an interesting new approach for evaluation of swimming
hydrodynamic forces, according to recent evidences. In the near future, as in the present, CFD will provide valorous
arguments for defining new swimming techniques or equipments
The hydrodynamic study of the swimming gliding: a two-dimensional computational fluid dynamics (CFD) analysis
Nowadays the underwater gliding after the starts and the turns plays a major role in the overall swimming
performance. Hence, minimizing hydrodynamic drag during the underwater phases should be a main aim during
swimming. Indeed, there are several postures that swimmers can assume during the underwater gliding, although
experimental results were not conclusive concerning the best body position to accomplish this aim. Therefore, the
purpose of this study was to analyse the effect in hydrodynamic drag forces of using different body positions during
gliding through computational fluid dynamics (CFD) methodology. For this purpose, two-dimensional models of the
human body in steady flow conditions were studied. Two-dimensional virtual models had been created: (i) a prone
position with the arms extended at the front of the body; (ii) a prone position with the arms placed alongside the trunk;
(iii) a lateral position with the arms extended at the front and; (iv) a dorsal position with the arms extended at the front.
The drag forces were computed between speeds of 1.6 m/s and 2 m/s in a two-dimensional Fluent® analysis. The
positions with the arms extended at the front presented lower drag values than the position with the arms aside the
trunk. The lateral position was the one in which the drag was lower and seems to be the one that should be adopted
during the gliding after starts and turns
A model updating technique based on FRFs for damped structures
Model updating methods often neglect that in fact all physical structures are damped. Such simplification relies on the structural modelling approach, although it compromises the accuracy of the predictions of the structural dynamic behaviour. In the present work, the authors address the problem of finite element (FE) model updating based on measured frequency response functions (FRFs), considering damping. The proposed procedure is based upon the complex experimental data, which contains information related to the damped FE model parameters and presents the advantage of requiring no prior knowledge about the damping matrix structure or its content, only demanding the definition of the damping type. Numerical simulations are performed in order to establish the applicability of the proposed damped FE model updating technique and its results are discussed in terms of the correlation between the simulated experimental complex FRFs and the ones obtained from the updated FE model
Boosting regional socioeconomic development through logistics activities: a conceptual model
Background: Regional Development (RD) allows countries to balance regional differences by providing economic and social benefits to communities. This research highlights the importance of logistics activities to regional social development, and a framework to assess these connections is proposed. Objectives: How to boost regional socioeconomic development through logistics. Methods/Approach: The contributions of logistics to socioeconomic development are analysed based on the previous research, and the case of the Alto Minho (AM) region in Portugal was used to illustrate the connection between logistics and regional development. Results showed that logistics had created jobs, increased company turnover and exports, and increased GDP growth in several regions. For the AM region, results indicate that many companies are operating in this area, contributing to supporting municipalities to reduce regional disparities. Conclusions: A framework for assessing regional logistics performance is proposed together with several logistics performance indicators. This approach is essential for future developments integrating logistics into socioeconomic development.- (undefined
Longitudinal interventions in elite swimming: a systematic review based on energetics, biomechanics and performance
Longitudinal information requires the notion of repeated measurements throughout time. Such data is important because it allows the determination of the effectiveness of an intervention program. Research in competitive swimming has given special emphasis to energetics and biomechanics as determinant domains to improve performance. The purpose of this systematic review was to summarize longitudinal evidences on the energetic, biomechanical, and performance status of elite swimmers. A computerized search was made in 6 databases, conference proceedings, and department files. The 28 studies that satisfied the inclusion criteria were selected for analysis. Studies' qualitative evaluation was made by 2 independent reviewers using the Quality Index. These studies were then gathered into 3 main categories according to their reported data: energetics (n = 18), biomechanics (n = 9), and performance (n = 8). The conclusions were as follows: (a) elite swimmers are able to demonstrate from slight to substantial changes in their performance and energetic and biomechanical profiles within and between seasons; (b) the magnitude of change is dependent on the characteristics of the training programs, the duration of the intervention, and subject's gender; and (c) future research should emphasize the use of more complex procedures to improve the quality of the interventions
Stability of elite freestyle performance from childhood to adulthood
Stability of athletic performance is important for practitioners and coaches, since it allows the selection of appropriate training
methods and prediction of ages for best results. We performed a longitudinal study of 1694 season-best performances of 242
elite-standard swimmers throughout their careers, from 12 to 18 years of age. Mean stability (descriptive statistics and oneway
repeated-measures ANOVA, followed by a Bonferroni post-hoc test) and normative stability (Cohen’s kappa tracking
index and the Pearson correlation coefficient) were determined for seven consecutive seasons. Performance improvements in
all events were observed (14.36–18.97%). Bonferroni post-hoc tests verified changes in almost all events assessed. Cohen’s
kappa demonstrated low stability (0.17–0.27) in relative performance. Pearson correlations only became high from 15 to 16
years in the 50-m and 100-m events, and from 16 to 17 years in the 200-m, 400-m, and 1500-m events. Our results show that:
(a) swimmers should display a substantial improvement (14–19%) to become elite standard as adults, such as at 18 years; (b)
16 is the age at which the ability to predict adult performance increases markedly
Physiological assessment of head-out aquatic exercises in healthy subjects: a qualitative review
In the last decades head-out aquatic exercises became one of the
most important physical activities within the health system.
Massive research has been produced throughout these decades
in order to better understand the role of head-out aquatic exercises
in populations’ health. Such studies aimed to obtain comprehensive
knowledge about the acute and chronic response of
subjects performing head-out aquatic exercises. For that, it is
assumed that chronic adaptations represent the accumulation of
acute responses during each aquatic session. The purpose of this
study was to describe the “state of the art” about physiological
assessment of head-out aquatic exercises based on acute and
chronic adaptations in healthy subjects based on a qualitative
review. The main findings about acute response of head-out
aquatic exercise according to water temperature, water depth,
type of exercise, additional equipment used, body segments
exercising and music cadence will be described. In what concerns
chronic adaptations, the main results related to cardiovascular
and metabolic adaptations, muscular strength, flexibility
and body composition improvements will be reported
Tracking the freestyle performance from children to adult age
Swimming researchers are, on regular
basis, trying to identify and understand
the factors that can predict
swimming performance. For such
aim most of the research designs
adopted are cross sectional in nature.
There are few longitudinal researches
in swimming science
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