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Aspects of mixed and condensed phase combustion
Published in J. F. Griffiths, J. A. Barnard, Flame and Combustion, 2019
J. F. Griffiths, J. A. Barnard
The physical behaviour within the bed depends on the nature of the bed at flow rates above the minimum fluidisation velocity. Some materials tend to aggregate so that the distribution of the fluid becomes irregular and stagnation regions may develop. With materials that undergo better fluidisation, as would be achieved with approximately spherical particles, the excess gas (that is, additional to that required for fluidisation) passes through the bed in bubbles at speeds much greater than the mean velocity. These burst at the surface of the bed, giving it the appearance of a boiling liquid. This bubbling mode of operation (i.e. the creation of cavities that migrate up through the bed) is accompanied by a fairly fast, vertical mixing of the bed particles: thus particles move upwards in the wake of a bubble and create a ‘gulf-streaming’ motion of particles which ensures very high heat transfer. A distinctive feature of fluidised-bed combustion is the spatial uniformity of temperature that is achieved. Further increases of flow rate can become counter productive insofar that slugging may occur. That is, the bubbles merge into elongated ‘slugs’ as wide as the bed; they track through the bed having set up their own, albeit highly unstable, line of least resistance. Minimum fluidising air velocities at the bed temperature, in combustion applications, are below 1 ms−1 and bubbling bed velocities may be up to 3 ms−1 [231].
Relationship between ground reaction force in horizontal plane and mechanical energy flow in torso during baseball tee batting
Published in Sports Biomechanics, 2023
Gen Horiuchi, Hirotaka Nakashima
In baseball, batting is the act of facing the opposing pitcher and trying to produce an offence for one’s team. The batter takes a hitting stance in the batter’s box, swings the bat at the ball thrown by the pitcher, and hits the ball back by colliding the bat. The three main goals for batters are to become base runners, drive runners home, and advance runners along the bases for others to drive home. Generally, the performance of a batter is evaluated by the number of home runs, runs batted in and hits, batting average, and so on. Szymanski et al. (2009) stated that bat swing velocity is an important component of successful baseball and softball hit performances. The three direct benefits of increased bat swing velocity are an increase in decision time, a decrease in swing time, and an increase in batted ball velocity. In particular, an increase in batted ball velocity leads to a batted ball flying faster and farther, making the opponent’s defence difficult. The statistics database (MLB.com, online) shows that the average exit velocity (i.e., the value that divides the sum of all batted ball speeds as it comes off the bat by all batted ball events) is strongly correlated with the number of home runs, slugging percentage, on-base plus slugging, and weighted on-base averages. Therefore, the factors related to bat swing speed at ball impact have been analysed in previous studies of baseball batting.
Mechanical energy flow in torso during baseball toss batting
Published in Sports Biomechanics, 2021
Gen Horiuchi, Hirotaka Nakashima, Shinji Sakurai
In baseball, batting involves swinging the bat in the batter’s box and hitting the ball thrown by the opponent’s pitcher. The three main goals for batters are to become a base runner, drive runners home, and advance runners along the bases for others to drive home. Generally, the performance of batters is evaluated by the batting average, number of homeruns and runs batted in, and on-base plus slugging. Szymanski et al. (2009) stated that a baseball or softball player can become a successful batter by improving the bat swing velocity. The direct benefits of increasing the bat swing velocity are the increase in decision time with the decrease in swing time, and the increase in batted ball velocity. Particularly, the increase in batted ball velocity leads to a batted ball flying faster and farther, which makes the opponent's defence difficult. Statistics data (MLB.com, online) show that the average exit velocity (the value dividing the sum of all batted ball velocities by all batted ball events) is strongly correlated to the number of home runs, slugging percentage and on-base percentage. Therefore, in previous studies on baseball batting, the factors related to the bat head speed at ball impact have been analysed through biomechanical investigations.