An isothermal model is developed for predicting the performance of spur gears with provision for surface roughness. For each point along the line of action of the gears, the contact of pinion and gear is replaced by that of two cylinders. The radii of cylinders and transmitted load are calculated, and lubricant film thickness as well as contribution of fluid film and asperities in carrying the total load is obtained using the Johnson’s load-sharing concept. For each asperity in contact, occurrence of elastic, plastic, and elasto-plastic deformation is investigated. To validate the analysis, the predicted film thickness and the friction coefficient are compared to published theoretical data. The results of a series of simulations presenting the effect of surface roughness, load, and speed on the friction coefficient are presented and discussed.

Introduction:The present study investigated the effect of noise on blood pressure and heart rate of workers in an oil and gas industry in Khuzestan province. Methods:This descriptive-analytical study was conducted on 60 employees of one of the oil and gas industries who worked in administrative, warehouses, and operation units. A demographic questionnaire, a Beurer blood pressure monitor (BC16), and a sound level meter (TES1358) were used for data collection. Blood pressure and heart rate were measured before, during, and after the work. ANOVA and Paired Sample Test were used for data analysis in SPSS software.Results: Occupational exposure of administrative, warehouse, and operation unit workers to noise were 50-60, 85-75 and 95-85 dBA, and their heart rate was 79.38, 82.12, and 85.73 beats per minute (BPM), respectively. Before exposure to noise the mean heart rate of workers in the operation unit was 82.29±3.58 BPM and after exposure it was 85.73±1.92 BPM, and the difference was statistically significant (P-Value<0.001). The mean blood pressure of exposed to noise workers was significantly higher than that of nonexposed to noise workers (P-Value<0.001). The heart rate of operation unit workers was significantly higher, compared to other studied workers (P-Value<0.001). Conclusion:Considering the effect of noise on blood pressure and heart rate and the direct relationship between these parameters and cardiovascular diseases, it can be claimed that noise is one of the risk factors of cardiovascular diseases.

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