Scientia Iranica
Volume:17 Issue: 1, 2010

Subsonic wind tunnel experiments were conducted to study the turbulence level in the test section. Measurements were performed by introducing trip strip and/or damping screens on the ow eld. The results indicated that the introduction of trip strips not only reduced the turbulence intensity compared to cases without it, but also attened the variations. Further, the experiments which investigated the impact of the damping screens indicated a similar reduction in turbulence intensity; the pattern, however, remained the same. Furthermore, the results for cases wherein both trip strips as well as damping screens were placed on the contraction and in the settling chamber, respectively, showed that turbulence intensity was even more reduced than in previous cases. It is believed that the combination of several damping screens with the trip strip could be a sound method for turbulence reduction in subsonic wind tunnels.

The condition known as a water-hammer problem is a transient condition that may occuras a result of worst-case loadings, such as pump failures, valve closures, etc. in pipeline systems. Thepressure in the water hammer can vary in such a way that in some cases it may increase and causedestruction to the hydraulic systems. The pressure in the water hammer can also be decreased to theextent that it can fall under the saturation pressure, where cavitation appears. Therefore, the liquid isvaporized, thus, making a two-phase ow. This pressure decrease can be as dangerous as the pressure rise.As a result of the pressure drop and vaporization of the liquid, two liquid regions are separated, which isreferred to as column separation. In almost all standard methods for simulation of column separation,the steady friction factor was used, but in reality, the quantity of the friction factor is variable. In thiswork, the unsteady friction factor has been applied in the Discrete Gas Cavity Model (DGCM), which is a standard method of column separation prediction. Through comparisons with experimental data, resultsshowed that applying the unsteady friction factor can improve the magnitude of the predicted duration shape and the timing of the pressure pulse in all of the case studies.

Analytical and Adomian decomposition methods have been developed to determine the large de ection of a functionally graded cantilever beam under inclined end loading by fully accounting for geometric nonlinearities, and by incorporating the physical properties of functionally graded materials, and have also been solved. The large de ection problem will also be solved by using an FEA solver. Results obtained only due to end loading are validated using a developed analytical solution. The Adomian decomposition method yields polynomial expressions for the beam con guration. The equilibrium equation of a functionally graded cantilever beam actuated through self-balanced moments has been derived and solved using the Adomian decomposition method and the FEA solver for which no closed form solution can be obtained. Some of the limitations and recipes to obviate these are included. The Adomian decomposition method will be useful toward the design of functionally graded compliant mechanisms driven by smart actuators.

A three-dimensional, potential-based Boundary Element Method (BEM) is developed forthe hydrodynamic analysis of non-planing and planing hulls in steady conditions. The method uses constant-strength doublet and source distributions over the body surface and source distributions on the free surface. Numerical computations are rst applied to analyze the hydrodynamic characteristics and the free surface waves are generated by the mathematical non-planing model (Wigley hull), which is well known in ship hydrodynamics. The second type is a planing model, namely 4666, the experimental dataof which were carried out by Clement and Blount [1]. Some numerical results of wave elevation, pressure distribution, lift and resistance are presented. Validations show that the computed results are in good agreement with experimental data and other numerical approaches.

This paper presents the eect of current forces on the motion of forces on FloatingProduction Storage and Ooading (FPSO) in irregular waves. The objective of this research is to compute the motion of FPSO in irregular waves by time domain simulation including the eect of current forces.A study is made on the slowly varying oscillations of a moored single body system in a current and waves.Linear potential theory is used to describe the uid motion, and three-dimensional source distribution techniques are applied to obtain the hydrodynamic forces and transfer function of the wave exciting forces.OCIMF (1994) data are used for estimation of the current forces. The non-linear time domain simulations have been carried out in irregular waves. Based on it, slowly varying motion responses are examined including the eect of the current forces. Several environmental conditions, such as the current angle of attack, current velocity, signicant wave height and mean wave period are considered, which may signicantly aect FPSO motion in surge, sway and yaw moments. It is found that the eect of currentforces is quite signicant when the current velocity is increased. In this simulation, while the current velocity is increased to 3.0 meter/seconds, the impact on FPSO motion is quite signicant, which should be taken into consideration from the point of view of safety, failure of mooring systems, operating responses and the dynamic positioning of the FPSO.

In this paper, a general formula for nding the Maximum Allowable Dynamic Load(MADL) of geometrically nonlinear exible link manipulators is presented. The dynamic model for links in most mechanisms is often based on the small de ection theory but for applications like lightweight links, high-precision elements or high speed it is necessary to capture the de ection caused by nonlinear terms. First, the equations of motion are derived, taking into account the nonlinear straindisplacement relationship using Finite Element Method (FEM) approaches. The maximum allowable loads that can be achieved by a mobile manipulator during a given trajectory are limited by a number of factors. Therefore, a method for determination of the dynamic load carrying capacity for a giventrajectory is explained, subject to the accuracy, actuator and amplitude of residual vibration constraints and by imposing a maximum stress limitation as a new constraint. In order to verify the eectiveness of the presented algorithm, two simulation studies considering a exible two-link planar manipulator mounted on a mobile base are presented and the results are discussed. The simulation results indicate that the eect of introducing geometric elastic nonlinearities and inertia nonlinearities on the maximum allowable loads of a manipulator.

This paper provides a review of the research that has led to our current understandingof the process of fatigue striation formation. An important question addressed is whether or not at low stress intensity values, fatigue cracks can propagate intermittently in steels and aluminum alloys. It is concluded that there is no valid evidence for propagation on other than a cycle-by-cycle basis.