Scientia Iranica
Volume:16 Issue: 3, 2009

The transient motion and heat transfer of a viscous incompressible uid contained between two concentric spheres, maintained at di erent temperatures and rotating about a common axis with di erent angular velocities, is considered numerically, when the angular velocities are arbitrary functions of time. The resulting ow pattern, temperature distribution and heat transfer characteristics are presented for the various cases, including exponential and sinusoidal angular velocities. An interesting e ect, of long delays in the heat transfer of a large portion of the uid in the annulus, is observed, because of the angular velocities of the corresponding spheres. Keywords: Flow and heat transfer; Concentric rotating spheres; Time-dependent angular velocities; Numerical solution.

In this paper, elaborating the statistical approach recently proposed by one of the present authors (A.G.N) has been elaborated for interpretation of the spatial brightness variations of solar quiescent prominences. The mean statistical characteristics of the LTE line radiation such as the mean intensity and its Relative Mean Square Deviation (RelMSD) emerging from a multi-component atmosphere with randomly varying properties are derived as the functions of the frequency within a line. The results previously obtained are extended to encompass more realistic models when uctuations of the observed line intensities represent a combined e ect of variation of di erent physical and geometrical parameters of the medium (internal energy sources, optical thickness, velocity eld, the number of structural elements along the line of sight etc.). It is shown that the center-to-wings evolution of the RelMSD essentially depends on the mentioned features of the atmosphere, which are responsible for the spatial variations we observe. The obtained results are applied to the EUV-lines through SUMER spectrometer in frameworks of the SOHO space mission. As a rule, the observed values of RelMSD in the central frequencies of the observed lines are less than those in the wings. This points out that the observed uctuations are mainly due to the changes in energy sources in the prominence. It is shown that the central dispersion of the RelMSD correlates with the characteristic temperature of a given line formation. Keywords: Sun; Radiative transfer; Quiescent prominence; Fine structure.

Piping systems commonly experience the transient-state situation as the result of changes to ow conditions during pump failures, valve closures or turbine load rejection. This paper addresses transients as a consequence of the load rejection of a Francis hydropower plant (Karun 4, Ahwaz, Iran). To control the turbine system and related equipment during load rejection, the valve closing law of wicket gates is of paramount importance. The pressure rise at the end of the pressure shaft, the pressure drop in the draft tube and the speed rise while the electromagnetic braking torque disappears are solely dependent on the closing curve. Thus, an optimum closing law can eliminate the probable risk of damage to the units. This paper develops a computational model to calculate water-hammer system components, such as pressure rise, speed rise, discharge variations and pressure uctuations. Results obtained from the present model are compared and validated with those obtained by a consultant at the Karun project. The e ects of di erent valve-closing laws on the maximum head rise at the end of the pressure shaft and other components are also investigated. Keywords: Method of characteristics; Hydropower plant; Transient ow; Valve-closing law; Karun 4 hydropower plant.

Three-dimensional elasticity solutions have been presented for a thick laminated cross-ply circular cylindrical panel. The cylindrical panel is under a dynamic localized patch moment, is simplysupported at all edges and has nite length. Ordinary di erential equations with variable coecients are formulated using an expansion of Fourier series applied to the displacement eld in circumferential and axial direction. The resulting ordinary di erential equations are solved by the Galerkin nite element method. Numerical results are presented for [0/90/0], [90/0/90], [0/90/0/90/0], [0/90/0/90/0/90/0] and [0/90/0/90/0/90/0/90/0] stacking sequences. Keywords: Dynamic; Patch moment; Elasticity; Panel; Multi-layered; Cross-ply.

Wind waves, which are one of the most important phenomena in the marine environment, are generally progressive in nature and can move far distances out of their area of formation. Thus, an understanding of wave hydrodynamics and their e ects is important for engineers in the design and construction of marine structures and coastal management. Signi cant insights may be gained from numerical and laboratory studies. Often the waves simulated in numerical and physical models do not have the full characteristics of real sea waves. It is then necessary to present a reliable method of wave simulation for numerical and laboratory wave umes. In this paper, the results of numerically simulated water waves, using digital lters, are presented. A model has been developed to simulate a water wave pro le from di erent target spectra using WNDF methods. The results showed that the WNDF method involves good stochastic wave characteristics if a suitable spectrum is used as target. The results have implications for the numerical or laboratory estimation of wave forces on model o shore or coastal structures. Keywords: Wave spectrum; Digital lter; White noise; Random irregular waves; WNDF method.

During recent years, many investigations have been carried out to determine how to select di erent materials for the making of Micro Electro Mechanical Systems (MEMS) and bio-MEMS. The NiTi shape memory alloy thin lm has been much regarded as a promising candidate for MEMS due to its unique shape memory e ect and high energy output. In this research, NiTi thin lm was fabricated using a sputtering technique from separate elemental Ni and Ti targets. The characterizations of the deposited lms were investigated using di erent analysis techniques, such as Field Emission SEM, DSC, XRD, electrical resistivity measurement and nanoindentation. Keywords: NiTi thin lm; Sputtering; Characterization; Shape memory e ect.

During the course of expansion of steam in turbines, the vapour rst supercools and then nucleates to become a two-phase mixture. Formation of the liquid phase causes thermodynamic and aerodynamic losses in steam turbines. In this study, the treatment is a one-dimensional, non-equilibrium ow in a steady Laval nozzle. In this paper, the changes in the rate of nucleation, entropy, pressure and other parameters of the two-phase ow, subjected to spraying the liquid droplets close to the nozzle''s throat, are investigated. By injecting the water droplets into a supersonic condensing ow, the thermodynamic loss is considerably decreased. Keywords: Two-phase ow; Convergent-divergent nozzle; Nucleation.

The in uences of cupric oxide layer thickness, cuprous oxide particles and pores on the mechanical properties and microstructure of an alumina-copper eutectic bond have been investigated. The furnace atmosphere in the rst stage was argon gas with 2  10􀀀6 atm oxygen partial pressure. In the second stage, the furnace atmosphere was the same as the rst stage except that the cooling interval was between 900-1000C and the hydrogen gas was injected into the furnace atmosphere. Finally, in the last stage, a vacuum furnace with 5  10􀀀8 atm pressure was chosen for the bonding procedure. The peel strength of rst stage specimens shows that a cupric oxide layer with 320  25 nm thickness generates maximum peel strength (13:1  0:3 kg/cm) in the joint interface. In the second stage, by using hydrogen gas, a joint interface free from any cuprous oxide particles was formed. In this case, the joint strength has increased to 17:1  0:2 kg/cm. Finally, the bonding process in the vacuum furnace indicates that the furnace gas does not have a considerable e ect on joint interface pores. Furthermore, the bonding process in the vacuum furnace reduces the peel strength of the joint due to the formation of more pores. A thorough study of pore formation is presented. Keywords: Alumina-copper; Bonding; Peel strength.

In this paper, we present a Mont Carlo simulation by using the inhomogeneous di usion equation suggested by Lagutin et al. in a fractal interstellar medium for a supernova, as being the main source of Galactic cosmic rays in an energy range up to 1016ev. When the numerical results of this simulation are compared with the predicted energy density of cosmic rays from the supernova model of Erlikyn and Wolfendale (EW), they show a strong consistency with the observed experimental parameters of cosmic rays, i.e. Galactic radial gradient, percentage of total supernova energy transfer to cosmic particles etc., which is also con rmation of a supernova being of cosmic ray origin. Keywords: Cosmic rays; Supernova; Particle propagation; Fractal medium;

This paper presents the linear dynamic response of uniform beams with di erent boundary conditions excited by a moving load, based on the Euler-Bernouli beam theory. Using a dynamic green function, e ects of di erent boundary conditions, velocity of load and other parameters are assessed and some of the numerical results are compared with those given in the references. Keywords: Beams; Green function; Euler-Bernoulli; Buckling problem.