Influence of unsupported sleepers on the dynamic response of a heavy haul railway embankment
- Authors: Shi, Jin , Chan, Andrew , Burrow, Michael
- Date: 2013
- Type: Text , Journal article
- Relation: Proceedings of the Institution of Mechanical Engineers Part F-Journal of Rail and Rapid Transit Vol. 227, no. 6 (November 2013 2013), p. 657-667
- Full Text: false
- Reviewed:
- Description: It is not uncommon for conventional ballasted railway track systems to have unsupported sleepers due the uneven settlement of the ballast or subgrade. In order to investigate the possible implications of unsupported sleepers, this paper describes the development of a dynamic finite element model which includes wheel/rail friction. The developed model was used to investigate the behavior of a section of existing track on the ballasted Shuohuang heavy haul railway line in China. The investigation showed that the maximum displacement of the rails and sleepers increases significantly with the number of consecutive unsupported sleepers. Furthermore, the magnitude of the displacement between an unsupported sleeper and the ballast is likely to greatly exacerbate ballast/sleeper attrition and reduce the fatigue life of the hanging sleeper. An increase in the number of unsupported sleepers amplifies these effects. In addition, it was found that the sleepers adjacent to unsupported ones carry an additional load resulting potentially in their increased wear and additional damage to the substructure. To better understand the wider implications of the presence of unsupported sleepers on track performance, the stability, safety (in terms of derailment) and potential for rail and substructure damage were computed as a function of the number of unsupported sleepers (one to four) and compared with specifications. The results showed that the number of unsupported sleepers has a significant adverse impact on all four measures. However, while the effects on stability, safety and rail damage were within the limits suggested in specifications, even when four sleepers were modeled, the potential for substructure failure within a typical design life of the railway system was identified.
- Description: C1
Impact of neuromuscular fatigue on match exercise intensity and performance in elite Australian football
- Authors: Mooney, Mitchell , Cormack, Stuart , O'Brien, Brendan , Morgan, William , McGuigan, Mike
- Date: 2013
- Type: Text , Journal article
- Relation: Journal of Strength and Conditioning Research Vol. 27, no. 1 (2013), p. 166-173
- Full Text:
- Reviewed:
- Description: Mooney, MG, Cormack, S, O'Brien, BJ, Morgan, WM, and McGuigan, M. Impact of neuromuscular fatigue on match exercise intensity and performance in elite Australian football. J Strength Cond Res 27(1): 166-173, 2013: This study aimed to quantify the influence of neuromuscular fatigue (NMF) via flight time to contraction time ratio (FT:CT) obtained from a countermovement jump (CMJ) on the relationships between yo-yo intermittent recovery (level 2) test (yo-yo IR2), match exercise intensity (high-intensity running [HIR] m·min-1 and Load·min-1) and Australian football (AF) performance. Thirty-seven data sets were collected from 17 different players across 22 elite AF matches. Each data set comprised an athlete's yo-yo IR2 score before the start of the season, match exercise intensity via global positioning system and on-field performance rated by coaches' votes and number of ball disposals. Each data set was categorized as normal (>92% baseline FT:CT, n = 20) or fatigued (<92% baseline FT:CT, n = 17) from a single CMJ performed 96 hours after the previous match. Moderation-mediation analysis was completed with yo-yo IR2 (independent variable), match exercise intensity (mediator), and AF performance (dependent variable) with NMF status as the conditional variable. Isolated interactions between variables were analyzed by Pearson's correlation and effect size statistics. The Yo-yo IR2 score showed an indirect influence on the number of ball disposals via HIR m·min-1 regardless of NMF status (normal FT:CT indirect effect = 0.019, p < 0.1, reduced FT:CT indirect effect = 0.022, p < 0.1). However, the yo-yo IR2 score only influenced coaches' votes via Load·min-1 in the nonfatigued state (normal: FT:CT indirect effect = 0.007, p <0.1, reduced: FT:CT indirect effect = -0.001, p > 0.1). In isolation, NMF status also reduces relationships between yo-yo IR2 and load·min-1, yo-yo IR2 and coaches votes, Load·min-1 and coaches' votes ([DELTA]r > 0.1). Routinely testing yo-yo IR2 capacity, NMF via FT:CT and monitoring Load·min-1 in conjunction with HIR m·min-1 as exercise intensity measures in elite AF is recommended. © 2013 National Strength and Conditioning Association.
- Description: 2003010830
Which jump variables should be used to assess explosive leg muscle function?
- Authors: Young, Warren , Cormack, Stuart , Crichton, Michael
- Date: 2011
- Type: Text , Journal article
- Relation: International Journal of Sports Physiology and Performance Vol. 6, no. 1 (2011), p. 51-57
- Full Text:
- Reviewed:
- Description: Purpose: The main purpose of this study was to determine the relationships between countermovement jump (CMJ) variables and acceleration and maximum speed performance. Methods: Twenty-three elite Australian football players were tested on a CMJ, which yielded several kinematic and kinetic variables describing leg muscle function. A 40 m sprint was also conducted to assess acceleration (10 m time) and an estimate of maximum speed (flying 20 m time). Players from one Australian Football League (AFL) club were tested and Pearson correlations for CMJ variables and sprint performance were calculated. Results: Jump height, peak velocity, peak force, and peak power had less than 50% common variance, and therefore represented independent expressions of CMJ performance. Generally, the correlations between CMJ variables and sprinting performance were stronger for maximum speed (small to large effect sizes) than for acceleration (trivial to moderate sizes). The variable that produced the strongest correlation with acceleration was jump height (r = -0.430, P = .041) and with maximum speed was peak power/weight (r = -0.649, P = .001). Conclusions: The results indicate that if an integrated system comprising a position transducer and a force platform is available for CMJ assessment, jump height and peak power/weight are useful variables to describe leg muscle explosive function for athletes who perform sprints.
Use of a tibial accelerometer to measure ground reaction force in running : A reliability and validity comparison with force plates
- Authors: Raper, Damian , Witchalls, Jeremy , Philips, Elissa , Knight, Emma , Drew, Michael , Waddington, Gordon
- Date: 2018
- Type: Text , Journal article
- Relation: Journal of Science and Medicine in Sport Vol. 21, no. 1 (2018), p. 84-88
- Full Text: false
- Reviewed:
- Description: Objectives: The use of microsensor technologies to conduct research and implement interventions in sports and exercise medicine has increased recently. The objective of this paper was to determine the validity and reliability of the ViPerform as a measure of load compared to vertical ground reaction force (GRF) as measured by force plates. Design: Absolute reliability assessment, with concurrent validity. Methods: 10 professional triathletes ran 10 trials over force plates with the ViPerform mounted on the mid portion of the medial tibia. Calculated vertical ground reaction force data from the ViPerform was matched to the same stride on the force plate. Bland–Altman (BA) plot of comparative measure of agreement was used to assess the relationship between the calculated load from the accelerometer and the force plates. Reliability was calculated by intra-class correlation coefficients (ICC) with 95% confidence intervals. Results: BA plot indicates minimal agreement between the measures derived from the force plate and ViPerform, with variation at an individual participant plot level. Reliability was excellent (ICC = 0.877; 95% CI = 0.825–0.917) in calculating the same vertical GRF in a repeated trial. Standard error of measure (SEM) equalled 99.83 units (95% CI = 82.10–119.09), which, in turn, gave a minimum detectable change (MDC) value of 276.72 units (95% CI = 227.32–330.07). Conclusions: The ViPerform does not calculate absolute values of vertical GRF similar to those measured by a force plate. It does provide a valid and reliable calculation of an athlete’s lower limb load at constant velocity.
Impact of neuromuscular fatigue on match exercise intensity and performance in elite Australian football
- Authors: Mooney, Mitchell , Cormack, Stuart , O'Brien, Brendan , Morgan, William , McGuigan, Mike
- Date: 2013
- Type: Text , Journal article
- Relation: Journal of Strength and Conditioning Research Vol. 27, no. 1 (2013), p. 166-173
- Full Text: false
- Reviewed:
- Description: This study aimed to quantify the influence of neuromuscular fatigue (NMF) via flight time to contraction time ratio (FT:CT) obtained from a countermovement jump (CMJ) on the relationships between yo-yo intermittent recovery (level 2) test (yo-yo IR2), match exercise intensity (high-intensity running [HIR] m.min(-1) and Load.min(-1)) and Australian football (AF) performance. Thirty-seven data sets were collected from 17 different players across 22 elite AF matches. Each data set comprised an athlete's yo-yo IR2 score before the start of the season, match exercise intensity via global positioning system and on-field performance rated by coaches' votes and number of ball disposals. Each data set was categorized as normal (>92% baseline FT:CT, n = 20) or fatigued (<92% baseline FT:CT, n = 17) from a single CMJ performed 96 hours after the previous match. Moderation-mediation analysis was completed with yo-yo IR2 (independent variable), match exercise intensity (mediator), and AF performance (dependent variable) with NMF status as the conditional variable. Isolated interactions between variables were analyzed by Pearson's correlation and effect size statistics. The Yo-yo IR2 score showed an indirect influence on the number of ball disposals via HIR m.min(-1) regardless of NMF status (normal FT:CT indirect effect = 0.019, p < 0.1, reduced FT:CT indirect effect = 0.022, p < 0.1). However, the yo-yo IR2 score only influenced coaches' votes via Load.min(-1) in the nonfatigued state (normal: FT:CT indirect effect = 0.007, p <0.1, reduced: FT:CT indirect effect = -0.001, p > 0.1). In isolation, NMF status also reduces relationships between yo-yo IR2 and load.min(-1), yo-yo IR2 and coaches votes, Load.min(-1) and coaches' votes (Deltar > 0.1). Routinely testing yo-yo IR2 capacity, NMF via FT:CT and monitoring Load.min(-1) in conjunction with HIR m.min(-1) as exercise intensity measures in elite AF is recommended.
A Hybrid estimation and identification method for online calculation of voltage-dependent load parameters
- Authors: Kabiri, Mehdi , Amjady, Nima
- Date: 2019
- Type: Text , Journal article
- Relation: IEEE systems journal Vol. 13, no. 1 (2019), p. 792-801
- Full Text: false
- Reviewed:
- Description: This paper presents a hybrid estimation and identification (HEI) method for identifying the load model parameters of voltage-dependent loads along with estimating the system states. The parameters of voltage-dependent load models are identified using multiple snapshots consecutively gathered through supervisory control and data acquisition system. The proposed HEI method imposes no additional cost to the installed metering devices or communication network. Mathematical aspects of the proposed HEI method are analytically proved and a four-step approach is presented for implementing it. Comprehensive numerical experiments and statistical analysis are presented to demonstrate the effectiveness of the proposed method for both load model identification and state estimation.