In this study, we evaluated the effect of the use of tennis racket string vibration dampers on racket handle vibrations, and perceptions of hand and arm discomfort experienced by tennis players owing to stationary racket impacts. Twenty tennis players (10 males, 10 females) aged 18-29 years volunteered for the study. Two different racket models were impacted at the geometric centre of the racket face and 100 mm distal to the centre both with and without string vibration dampers in place. The participants could neither see nor hear the impacts, and they indicated their discomfort immediately after each impact using a visual analogue scale. An analysis of variance (2 x 2 x 2 factorial) was performed on the scaled discomfort ratings with the factors damping condition, racket type and impact location. No significant differences in discomfort ratings between damped and undamped impacts or between the two racket types were found. Also, central impacts were found to be more comfortable than impacts 100 mm distal to the centre (P< 0.05). There were no significant interaction effects. Vibration traces from an accelerometer mounted on the racket handle revealed that string vibration dampers quickly absorbed high-frequency string vibration without attenuating the lower-frequency frame vibration. In conclusion, we found no evidence to support the contention that string vibration dampers reduce hand and arm impact discomfort.
This study examined the relationship between selected mechanical characteristics of aluminum baseball bats and sensations on the hands resulting from impacts. Sixteen skilled male Little League baseball players held each of two bats while they were impacted at the following locations by baseballs at speeds of approximately 27 m/s: near barrel end, center of percussion (COP), distal node of the fundamental mode, and 4 in. toward the hands from the COP. Results of a questionnaire regarding annoyance and discomfort were correlated with selected bat characteristics and vibrational characteristics associated with each impact condition. Results indicated that perceptions of annoyance and discomfort were related to the level of excitation of the fundamental mode and first overtone mode and that annoyance and discomfort were less with impacts on the COP and fundamental vibrational node.
Methyl esters of commercial grades of lauric, myristic, palmitic, stearic, linoleic and linolenic acids, as well as ethyl and butyl esters of oleic acid, were burned in a diesel engine to determine their efficiencies as fuels. Triolein and some common vegetable oils were burned as comparison fuels and No. 2 diesel fuel was used as a control. The fuels were tested in a single‐cylinder direct‐injection engine running at rated speed and load in short‐term, performance engine tests. Specific fuel consumption and thermal efficiencies of the engine burning these fuels were then determined. Among the methyl esters of the saturated acids, thermal efficiency was inversely related to chain length of the fatty acid. Introduction of a double bond resulted in increased efficiency. Further increases in unsaturation had negligible effects on thermal efficiencies. Ethyl oleate had the highest thermal efficiency and butyl oleate had the lowest thermal efficiency of any of the ester fuels tested. Most of the ester fuels produced higher thermal efficiencies than did No. 2 diesel fuel. Triolein produced the lowest specific fuel consumption of the triglyceride fuels and peanut oil produced the lowest specific fuel consumption of the vegetable oils. The data suggest that ethyl esters of monounsaturated or short‐chain fatty acids should make good alternative fuels and that they should be further evaluated in longterm engine tests.
The nonlinear vibratory motions of a three-axle semitrailer truck were investigated via the use of a digital computer. The nonlinear equations of motion are presented and a method of numerical integration is discussed. The analysis allows any shape of suspension force-deflection curve (including wheel hop, suspension stops, and dry friction damping) and a similar liberality of shock absorber force-velocity characteristics. An experimental vibration study, performed on a model truck, is described and the results compare favorably with the calculated results of the numerical integration.
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