The hot gases produced by the internal combustion engines pass through the exhaust valve and causes high temperatures in the exhaust valve and its seat. To avoid damaging the exhaust valve, heat must be transferred from the valve to its seat during the contact they make at the opening and closing cycle. Heat transfer rate from the exhaust valve to its seat is a function of many factors. One of the most important factors is the thermal contact conductance (TCC) between the exhaust valve and its seat. Very few researches have been done about estimation of the TCC between the exhaust valve and its seat in the past. An experimental study has been conducted to determine the TCC between two co-axial cylinders, as the exhaust valve and its seat. Furthermore, the influence of contact pressure and frequency of contact upon the TCC is studied. The results show that the TCC decreases as the frequency of contact increases. The experimental results obtained from the present work are in good agreement with the previous published data.

One of the most important issues in agricultural machinery section is tyre-soil interactions. In this study, a single wheel tester was used to follow experiments in controlled conditions in a soil bin. A Goodyear 12. 4-28, 6 ply tractor drive tyre was operated at three vertical loads of 6, 9 and 12 kN, three inflation pressures of 80, 120 and 160 kPa and three moisture content of soil: 11. 20, 14. 86 and 18. 68 % d. b to investigate the effect of the variables on these parameters: contact area, contact pressure, compaction, and soil apparent electrical conductivity. It was found that medium contact pressure had a direct relation with vertical load, inflation pressure and moisture content. A regression model with R-square of 0. 946 was achieved to predict contact pressure. Soil electrical conductivity changes was predicted with acceptable determination coefficient of 0. 850 by using of vertical load, inflation pressure and moisture content. Determination coefficient magnitude for models to predict resistance to soil penetration (cone index) using soil apparent electrical conductivity, decreased when moisture content was increased. The vertical load and inflation pressure were found two factors controlling the soil apparent electrical conductivity changes in low and high moisture content, respectively. Error percentage in using soil apparent electrical conductivity parameter to estimate the penetration resistance increased with increasing moisture content.

Different types of contact, including contact between node pairs, any-contact of nodes, and contacts of the entire network, are used to characterize social relations in mobile social networks. Different modes of routing, from the point of view of message delivery semantics, encompass unicasting, multicasting, any-casting, and broadcasting. Studies have shown that using probability distribution functions of contact data, which is mainly assumed to be homogeneous for nodes, improves the performance of these networks. However, there exists an important challenge in studies on distributions. A lot of works apply the distribution of one type of contact to other types. Hence in routing applications, it causes to use of the distribution of one type of contact for any mode of routing. This study provides a complete solution to model each type of homogeneous contact data distribution and to use them in different modes of routing. We propose a routing algorithm that uses this new model. Results show that our solution improves the average latency of comparing methods Epidemic, TCCB, and DR about 3.5-times, 30%, and 45%, respectively. It achieves a delivery rate of about 5% and 6%, and average latency about 6% and 8% better than that of DR and TCCB, respectively.

Turbine blades are exposed to mechanical and thermal stresses due to their operation in critical conditions that lead to various damages such as fatigue and wear. These factors reduce the blades life cycle by accelerating the cracking process. In this paper, the effects of three geometric parameters including the contact length, the contact angle, and the surface friction coefficient on relative slip amplitude and contact pressure values in the turbine blade root were investigated using a two-dimensional finite element model. Comparing the results of the analysis with the actual blade damages by use of scanning electron microscopy shows acceptable consistency between predicted damage site and the actual blade damages. The results of the blade analysis indicate that by moving from the top of the contact edge to the bottom, the contact pressure increases gradually and its maximum occurs near the lower edge of the contact. According to the results, the prescribed increments in the coefficient of friction, the contact angle, and the length of contact, respectively decrease the slip amplitude by 26%, 19%, and 10% and also decrease the contact pressures by 35%, 15%, and 5%. In addition, increasing contact angle and coefficient of friction increase the opening region length at the upper edge on both sides of the blade root. While increasing the contact length has no considerable effect on the length of this region.

Background: Sports activities may alter the parameters of plantar pressure distribution while walking. Objectives: The present study aimed to compare the peak pressure, maximum force, contact area, and contact time between the right and left foot and their correlations with height and weight in elite weightlifters. Methods: This study was conducted on 12 elite weightlifters with the mean age of 23. 2  2. 26 years. The parameters of plantar pressure distribution were measured using the Emed platform during barefoot walking. In addition, the AutoMask software was used to divide the sole into 10 anatomical regions. The parameters of peak pressure, maximum force, contact area, and contact time in each region were also estimated using the MultiMask evaluation software. Data analysis was performed using paired t-test and Pearson’ s correlation-coeffi cient (P  0. 05). Results: Signifi cant diff erences were observed in the peak pressure parameter in the third region (medial midfoot) and maximum force parameter in the ninth region (9th toe) between the right and left foot. Moreover, positive, signifi cant correlations were denoted between height and weight with the peak pressure, maximum force, contact area, and contact time (P < 0. 01). In the left foot, an inverse, signifi cant correlation was observed between the maximum force and height in the fi fth region (fi rst metatarsal bone) (P < 0. 05). Conclusions: According to the results, the functional demand for both feet is very close in weightlifting. Therefore, insole designers must pay special attention to the reduction of the load on the third to fi fth metatarsal bones in order to prevent complications such as metatarsalgia in athletes in the long run.

In this paper, the implementation of an interface element to model the contact between the core and the layer in thermoelastic contact analysis of monolayer pressure vessels is presented. How to couple the elements of the core and the layer and implementation of the boundary conditions are also described. The source of heat could be due to temperature difference in the layers in practice or the heat due to welding in the concentrated welding zone of the layer during the assemblage of the layer and the core of the pressure vessel. Thermoelastic contact between the core and layer has come under investigation. It is concluded that the methodology with the special employment of interface elements in joints and contact regions is efficient for analysis of joints and contact problems in the analysis of layered media.

Background: Today, contact lenses have extensive usages. contact lens places on cornea, so it may induce variation on cornea and these variations can influence the measurement of intraocular pressure (IOP) by Goldman tonometer. The aim of this research was to study the effect of various contact lenses on measurement of intraocular pressure by Goldman tonometer.Materials and Methods: In this study, 80 subjects aged 18-25 were selected randomly among patients of Al-Zahra ophthalmology center. None of them has any eye pathological problems. Before wearing the lens, intraocular pressure was measured, and then patients were divided into two groups of soft and hard contact lenses. Soft and hard contact lenses were placed on the eye for two hours, and the intraocular pressure was measured again.Results: The mean of IOP before wearing contact lenses and two hours later was 15.96 mmHg and 13.93, s respectively. Paired test showed a significant difference between IOP before and after wearing contact lenses (p=0.001).There was no significant differences in mean of intraocular pressure decline before and after placing the contact lens in both soft and hard lenses.Conclusion: According to this study, the intraocular pressure decreases after wearing contact lenses (CL). This decline may be due to variation in properties of cornea after wearing CL that can also affect IOP measurement.

Wheel wear has been a concern in the railway for several decades. Studying the form change of the wheel/rail contacts in particular railways consisting of sharp curves helps to identify the risk of severe or catastrophic wear to minimize maintenance costs in order to be competitive in the transportation business. In this paper, the wheel/rail contact was studied on the particular railways. The experimental measurement of wheel profiles was used as an input to Hertz contact Theory (HCT). It was found that: 1) for these railways the wheel flange is highly worn; 2) a 5th order polynomial function is appropriate to model the wear behavior of the critical wheel; 3) the minimum and maximum contact ellipse surface areas occur in Sd=22. 29 mm and Sd=32 mm, respectively; 4) the maximum and minimum surface areas of the contact ellipse occur at points in which the contact pressure are minimum and maximum, respectively; and finally 5) the flange thickness region between 25 to 29 mm can be chosen as an appropriate range for the wheel maintenance purposes.