Journal Of Mechanical Research And Application (پژوهش و کاربرد در مکانیک)
سال:1389 | دوره: | شماره: |تعداد مقالات:7

In this paper, first a sensitivity analysis of parameters affecting the performance of the steam generator is performed. This process includes the pinch temperature difference and the gas velocity (width of the HRSG) as the operating parameter and geometrical parameters (fin’s thickness, fin’s height, number of fins in each inch, tube transverse pitch) for each pressure parts is carried out, and then these parameters have been optimized. Geometry details of the fins were considered separately for each pressure part of the steam generator (economizer, evaporator and superheater). The considered objective function is the rate of irreversibility in the steam generator which constitutes exergy destruction rate and exergy loss rate. After the optimization of total irreversibility rate, thermal and exergetic efficiencies and components of irreversibility, including exergy destruction for each part and exergy loss are calculated and compared with the situation prior to optimization.

Geometrically nonlinear governing equations for a plate with linear viscoelastic material are derived. The material model is of Boltzmann superposition principle type. A third-order displacement field is used to model the shear deformation effects. For the solution of the nonlinear governing equations the Dynamic Relaxation (DR) iterative method together with the finite difference discretization technique is used. Finally, the numerical results for the critical buckling load for simply supported edge constraints are reported. In order to justify the accuracy of the results, the elastic plate critical buckling loads are obtained and compared with the existing results. The correlations are very satisfactory. The numerical results are presented for Classical Plate Theory (CPT), First order- Shear Defonmation Plate Theory (FSDT) and Higher Order- Shear Deformation Plate Theory (HSDT). In the case of thick plate the differences among the three theories are highlighted, however, for thin plate the variations are very small.

This paper presents a hybrid technique for simultaneous estimation of parameter and function in inverse heat conduction problems. No prior information is used for the functional form of the heat flux in the present study. The scheme presented here is a combination of two different classical methods: The Variable Metric Method (VMM) and Gauss Method (GM). The determination of the unknown thermal coefficients includes two steps per iteration of the estimation algorithm: the function estimation step; and the parameter estimation step. VMM and GM are used to handle function estimation and parameter estimation problems, respectively. It is shown via simulated experiment that unknown quantities can be obtained with reasonable accuracy using this method despite existing noise in the measurement data.

Since the energy analysis considers the quantity of energy, it cannot show the performance of the cooling tower. Therefore, in order to optimize the performance of the tower and also the process which the cooling tower is a part of it, it is necessary to analyze the energy and exergy of the tower simultaneously. In this paper, the energy and exergy of one of the cooling towers of Khuzestan Steel Co. is analyzed in order to improve the function of this unit and its effect on the related units. Moreover, the exergy of water and air which exchange heat with each other has also been studied. The mathematical model presented in this paper has been based on the principle of heat and mass transfer between water and air. The results of this study show that water makes more exergy than air because the system generates entropy. The results also show that the exergy of water decreases constantly from the upper part of the tower to its lower part, the exergy of air, however increases from bottom to top along the tower. When the temperature decreases water loses exergy but when the temperature is increased the air gains exergy.

Fiber metal laminates (FMLs) are new composite materials consisting of thin metal layers and high strength composite layers. ARALL (Aramid aluminum laminate) is a family of the FML that consists of thin aluminum sheets along with Kevlar/epoxy composite layers. This material has many advantages such as light weight, excellent corrosion, fatigue and impact resistance. Since, ARALL is a new material, therefore presentation of a model for nonlinear behavior analysis is important. This paper presents the elastic– plastic behavior of ARALL under inplane tensile loading. For this purpose, the orthotropic plasticity theory and modified classical laminated plate theory are used. In the orthotropic plasticity model, a three parameter plastic potential function is used. In the second theory, the Kevlar/epoxy composite layers and aluminum sheets are assumed to be linearly elastic and orthotropic elastic– plastic solids, respectively. Good agreement is obtained between results of two models. The results show that the case study behavior is almost bilinear under tensile loading and it has more strength in longitudinal direction in comparison to transverse direction. Variation of the Poisson’s ratio is considered in longitudinal and transverse loading too.

A fundamental topic in computational fluid dynamics is the role of coordinate particularly for searching optimized coordinates. The objective of this study is the numerical modeling of supersonic flows using a new coordinate system i.e. Unified Coordinate System (UCS) uses moving mesh with motionless viewing window technique. UCS has an advantage over traditional coordinate systems (Eulerian and Lagrangian) in supersonic flows especially in discontinuous regions (shocks and expansions). Moreover most of the difficulties of the traditional coordinate system may be removed by using UCS. Unified coordinate system benefits from both the eulerian and lagrangian systems. This is why a unified coordinate system as an optimization system is introduced. The researchers briefly review how to apply boundary conditions, how to calculate fluxes and strang dimensional splitting. The researchers also explain the Riemann problem which is the basic step to solve the equations in this coordinate and integrated system forms. In this article the researchers use new numerical method that has more advantages than other numerical methods such as slip line and shock resolution and low numerical dissipation. The important fact is that in using the UCS, there is no need to generate a body-fitted mesh prior to computing flow past a body; the mesh is automatically generated by the flow. These can be seen in the numerical results and comparing with exact solutions and also in quick numerical computations.

This paper presents numerical calculations for podded propulsion system using vortex theory and potential panel method. The method discretizes the surface boundary of the body (propeller+pod+strut) and obtained the vortex and propeller surface and potential on strut and pod. A model propeller and strut are considered for these calculations and the results of pressure distribution, flow field around the propeller and hydrodynamic characteristics of the propeller are given. The calculated hydrodynamic characteristics of the propeller are compared with the experimental data and it is shown in good agreement with them.