AMIRKABIR
Year:2004 | Volume:15 | Issue:59-B |Papers Count:7

This paper investigates different methods of time domain and frequency domain on assessment of fatigue life. The most suitable method of calculating stress for components that their natural frequencies have some degrees of interaction with the frequency range of the applied forcing functions are considered and modal effects are discussed. In practice, the validation of static analysis in evaluating of fatigue life used in the most engineering soft wares is studied.

In this paper, the effect of lubricant inertia on the thermohydrodynamic (THD) behavior of journal bearings is studied. Many researchers have analyzed the inertia effect on lubricant flow in bearings using different simplifying assumptions. The purpose of this study is to eliminate most of those assumptions, using computational fluid dynamics (CFD) techniques to solve the exact governing equations. The bearing has a finite length and operates under incompressible laminar flow and steady conditions. Numerical solutions of the full three-dimensional Navier-Stokes equations with and without inertia terms, coupled with the energy equation in the lubricant flow and the heat conduction equations in the bearing and the shaft are obtained. Cavitations effects are also considered using an appropriate three-dimensional cavitations model. In order to study the effect fluid inertia under several different conditions, solutions are obtained for different values of the eccentricity and radial clearance and also for different values of the rotational speed of the shaft. To validate the computational results, comparison with the experimental data of other investigators is made, and reasonable agreement is obtained.

Since 70s, the fixed-grid method of characteristics has been used successfully to analyze transient conditions in networks and pipeline systems. In analyzing transient flow, the use of an interpolation scheme is unavoidable, as the Courant number should be satisfied. Several interpolation schemes are introduced and used in solving water hammer classical equations. In this investigation, cubic-spline spatial-line interpolation scheme plus two new cubic-spline, time-line and combined interpolation schemes, are used to solve the approximate and complete water hammer eluations. All interpolation schemes are used to analyze transient flow in a pipeline containing three senes pipes with a reservoir and a valve. It is shown that for small time-steps, all interpolation schemes produce same results. For a large time-step, non-linear interpolation schemes perform better than the linear ones. The combined interpolation scheme used to solve the approximate equations has the best accuracy. In terms of accuracy and computational time, the cubic-spline time-line interpolation performs the best for both approximate and complete water hammer equation

The component operating at elevated temperature usually fails because of creep damage resulted from formation, growth and combination of micro-voids. To predict the creep life, ia number of methods have been suggested. One of them is Monkman-Grant (M-G) relationship that is widely applied in engineering problems.In order to adjust the variation between the empirical and theoretical results and because of the importance of the third phase of creep this model has been modified. In this work, the M-G method has been modified to give a more accurate result by using the Continuum Damage Mechanics and then, the creep life of IN738LC has been determined.The results show that the predicted creep life determining from the modified model demonstrates good agreement with that of the Koul-Castillo model due to pay more attention to the third stage of creep in the presented study model.

In this article two dimensional flow past on a cross flow oscillating square cylinder is numerically simulated. A novel finite element method, characteristic based splitter (CBS), is coupled with a moving unstructured mesh scheme, which has capability to maintain original element shapes in motion scaled free from collapsed elements. This property enables better analyzing the flow field on a moving body. The numerical simulation is carried out at various values of oscillation frequency. The numerical results indicate that in the case of square cylinder the lock-on region for the wakes appears similar to the circular cylinder. The effect of lock-on on the flow field as well as mean drag coefficient is investigated.