Aerodynamic and surface comparisons between Telstar 18 and Brazuca

2018 ◽  
Vol 232 (4) ◽  
pp. 342-348 ◽  
Author(s):  
John Eric Goff ◽  
Sungchan Hong ◽  
Takeshi Asai
Keyword(s):  
Experimental Determination ◽  
High Speed ◽  
Aerodynamic Coefficients ◽  
World Cup ◽  
Drag Coefficients ◽  
Soccer Ball ◽  
Critical Speeds ◽  
Aerodynamic Properties

Aerodynamic coefficients were determined for Telstar 18 and Brazuca, match balls for the 2018 and 2014 World Cups, respectively. Experimental determination of aerodynamic coefficients prompted the development of computationally determined soccer ball trajectories for most launch speeds experienced in actual play. Although Telstar 18’s horizontal range will be nearly 10% shorter than Brazuca’s horizontal range for high-speed kicks, both Telstar 18 and Brazuca have similar knuckling effects due to nearly equal critical speeds and high-speed drag coefficients that differ by less than 10%. Surface comparisons suggest why aerodynamic properties for the two World Cup balls are so similar.

Marine Propulsion Shafting: A Study of Whirling Vibrations

2020 ◽  
pp. 1-7
Author(s):  
María José Legaz ◽  
Sergio Amat ◽  
Sonia Busquier
Keyword(s):  
Torsional Vibration ◽  
High Speed ◽  
System Modeling ◽  
Initial Point ◽  
Van Der Pol Equation ◽  
Van Der Pol ◽  
Critical Speeds ◽  
Marine Propulsion ◽  
Fast Rotating

Whirling vibration is an important part of the calculations of the design of a marine shaft. In fact, all classification societies require a propulsion shafting whirling vibration calculation giving the range of critical speeds, i.e., free whirling vibration calculation. However, whirling vibration is a source of fatigue failure of the bracket and aft stern tube bearings, destruction of high-speed shafts with universal joints, noise, and hull vibrations. There are numerous uncertainties in the calculation of whirling vibration, namely, in the shafting system modeling and in the determination of excitement and damping forces. Moreover, whirling vibration calculation mathematics is much more complex than torsional or axial calculations. The marine propulsion shaft can be studied as a self-sustained vibration system, which can be modeled using the Van der Pol equation. In this document, a new way to solve the Van der pol equation is presented. The proposed method, based on a variational approach without local minima extra to the solution, converges for whatever initial point and parameter in the Van der Pol equation. 1. Introduction The term "whirling" was introduced into mechanical engineering by W. J. M. Rankine in 1869. The main aim of whirling vibration calculations of rotating machinery was, and is now, to determine the critical speeds of the shaft. Any whirling vibration resonance caused by a residual out-of-balance moment in a fast-rotating turbine might result in a catastrophic failure. The theory of whirling vibration was also applied to marine propulsion shafting. Nowadays, all classification societies require a propulsion shafting whirling vibration calculation, also called in some class rules as bending or lateral vibration calculations. The classification societies make reference to whirling vibration calculations, requiring the calculation of critical speeds. In reference to forced whirling vibration, the classification societies only say that this calculation may be required. The classification societies have clear requirements for shaft modeling and acceptance criteria in the case of torsional vibration calculations. However, in the case of whirling vibrations, the criteria are not as specific as the torsional vibration calculations.

The Influence of Sampling Frequency on the Results of Motion Analysis Performed by High-Speed Digital Image Correlation

2015 ◽  
Vol 816 ◽  
pp. 397-403 ◽  
Author(s):  
Martin Hagara ◽  
Róbert Huňady
Keyword(s):  
Digital Image Correlation ◽  
Correlation Analysis ◽  
Experimental Determination ◽  
Digital Image ◽  
High Speed ◽  
Sampling Frequency ◽  
Image Correlation ◽  
Correlation System

The paper describes an experimental determination of kinematic quantities using high-speed digital image correlation system. It deals with the analysis of minimal sampling frequency needed for correctly performed high-speed correlation analysis. The authors also describe the influence of cameras sampling frequency on the quality of the obtained results. Mentioned analysis was performed using a rotational object. For the purposes of the results comparison the data obtained from correlation system in a form of displacements in three mutually perpendicular directions were processed in Matlab and in the paper are depicted in a form of graphical visualizations.

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