AMIRKABIR
Year:2003 | Volume:14 | Issue:54-B|Papers Count:10

A marine propeller in unsteady wake flow is analyzed by using a potential-based boundary element method (BEM). Constant strength dipole and source distributions are used on each quadrilateral panels representing the propeller blades and their trailing vortex wakes. An analytical modification of Morino's method is adopted to determine the influence coefficients of source and dipole using hyperboloidal quadrilateral panels. This is very important for accuracy of the solutions. An iterative pressure Kutta (IPK) condition is applied to ensure pressure equality at the trailing of the blade. First, calculations were conducted for a steady flow to confirm the accuracy and the capability of the present method. Next, the calculations of the unsteady flow due to the ships wake were performed to calculate the fluctuating pressure acting on the propeller and consequently the thrust and torque. The thrust fluctuation for one blade and whole propeller are presented. The method is demonstrated for two propellers, one corresponding to the conventional propeller and one for a highly skewed. The unsteady pressure distributions on the propeller blades determined by the method are in good agreement with experimental data obtained from full-scale propellers.

Of these parameters and displayed them both in digital and graphical forms. The usual way to measure the mentioned parameters is to use sensors which are in patients airway connector and breathing circuit. Determination and computation of patients various respiratory parameters in the constant pressure and flow generators were performed. This determinations were considered in the lungs. These calculations were firstly performed based on mechanical phase were considered for each parameters. The respiratory equations can both increase the intelligency of the concerned devices and promote the ventilations quality. Displaying these parameters (numerical or graphical) can be considered as a qualitative measure for the evaluation of ventilation.

A two-phase closed thermosyphon is a gravity assisted wickless heat pipe. The condenser section is located above the evaporator, so that condensat is returned by gravity. In this project a two phase closed thermosyphon was designed and manufactured. An experimental investigation was performed in order to observe the effect of the inclination angle on the transport behaviour of a closed thermosyphon was performed in order to observe the effect of the inclination angle on the was used; this was electrically heated at the lower part ("heating zone") and it was cooled by air along the upper part ("cooling zone"). Between these two aneas there was the well insulated "Transport zone". As working fluid water was used the heating zone was always flooded. The electric heat input and the inclination angle F toward the vertical position were varied in steps. The maximum heat flow rate in the tube proved tobe dependent upon the inclination. With a largest value of Qmax=23w at 70-90 degree. An effective thermal conductivity keff of the thermosyphon can be determined depending strongly on inclination and heat flow rate so the steeper the tube value the larger the heat flow rate the higher is the effective conductivity. The condensations in the cooling zone exhibits the largest transport resistance. The heat transfer with boiling in the heating zone shows large local differences which depends on inclination.

determination of design and manufacturing strategies of motor vehicles need collections and analysis of various information's. In this paper , results of a research for determining possible strategy for design and manufacturing motor vehicles for next ten years in Iran is presented .The subject was divided into eight sections were used to select possible strategies and their paths. Historical background of design and manufacturing planning and policy of motor vehicles in the country was needed in the first step .Planning and policies of some industrial and developing countries were searched and analyzed .To predict paths of research and development in motor vehicle , an extended literature review was done on the subject .Levels of knowledge ,experience and ability to meet existing and required standards for design and production of motors vehicles were needed and determined in other parts. Economic analyzes were also done on several alternative by using theories of engineering economics. In addition to the economic effect , social and cultural effects on different alternatives were also considered. The strategy method of strength , weakness, opportunity ,and treats(SWOT) was used to select the best or possible strategy

A method is presented for prediction of graphite ablation rate at the stagnation region of an axisymmetric blunted nosetip of hypersonic vehicles. For this purpose, governing equations of reacting boundary layer are derived with appropriate boundary conditions. Frozen gas phase with surface reaction is postulated. This assumption on the graphite grade, is reliable at temperature about 2750 to 4450 K. ermochemical equilibrium he graphite surface between CO2, CO, and O2 is assumed. The governing equations are solved by a self-similar method. The comparison of the self-similar solution with experimental data, indicates a good agreement.

There are many cases in which the common vibration signature analysis methods are unable to diagnose the phenomena resulting from the initial damages in a mechanical system. Since the initiation of a damage in complex system like gearboxes and rolling element bearings, appears in the vibration signal generally as a low-energy and short-duration phenomena, the traditional methods fail to detect these small changes in the vibration signal. The methods based on the wavelet analysis which have been introduced recently, are capable of analyzing a signal both in the time and frequency domains simultaneously. Among the various wavelet systems, the biorthogonal wavelet systems have unique properties which provide the flexibility of the analysis method, However, up to now the biorthogonal wavelet systems have not been used in the area of the vibration signature analysis. In this paper, for the first time, the application of biorthogonal wavelet systems are developed to damage detection of mechanical systems through detecting the transient and the other hidden phenomena in the vibration signals. For this end, some biorthogonal wavelet and scaling functions have been designed and the developed biorthogonal wavelet systems have been used to analyze some simulated vibration signals. One of the most important properties of the mentioned systems is their capability to analyze and to reconstruct the complicated signals which contain harmonic and transient components, faster and more accurately. In order to show the advantage of biorthogonal wavelet systems over the orthonormal wavelet systems, some simulated vibration signals have been analyzed using the mentioned techniques. The result show the great capability pf the biorthogonal wavelet systems to diagnose the transient and low-energy phenomena in the vibration signal as to remove the noise from the vibration signal.

In this research, metallurgical behavior of aluminum alloy 5083 plates during rolling in industrial scale were studied and some empirical solutions were presented for solving problems . occurred during the production. The main subjects discussed in the paper are :1) the crocodiling phenomenon and the effect of preheating and rolling temperature on the crocodiling , 2) the boating phenomenon, in which the shape of the plates undergo a change to boat-like form, and the influence of stacking manner of plates in preheating furnace and mills adjustment on the phenomenon, 3) occurrence of age softening after hot rolling and stabilization and 4) stress relieving treatments. In addition, some mechanical properties such as tensile strength and hardness were determined at different stages i. e. after hot rolling, stabilization and cold rolling. Hardness measurements were also carried out at various locations in the rolled plates. The effect of some parameters such as the temperature of final passes on the mechanical properties were also studied.

The effects of carbon equivalents of 2.3, 3.3 and 4.3% on the microstructure, hardness and fracture toughness of a low alloyed ductile cast iron in as cast, annealed, normalized and austempered conditions have been investigated. Fracture toughness was measured using a plain-strain fracture toughness (kIc) test and also J-Integral approach. The results show that the pearlite content increases as the CE decreases from 4.3 to 2.3% The nodularity and nodule count also decrease with decreasing the CE%. The annealed samples show a predominantly ferritic structure. Iron with 2.3 CE% shows pearlitic microstructure. The austempered microstructure contains bainitic ferrite and retained austenite at all carbon equivalents. The fracture toughness value (kQ and kIc) of ductile iron increases with increasing the CE% in all conditions and a maximum value is obtained in austempered condition. The hardness decreases with increasing CE% and an maximum value of 526 HV50 can be obtained at 2.3 CE% in a austempered condition. The SEM study shows that all the fractures of austempered specimens are ductile in nature whilst all that of normalized condition are brittle. Fracture behavior of 4.3 CE% ductile iron in as cast and annealed conditions are ductile where those of 2.3% are brittle. The iron with 3.3% shows a brittle fracture in as cast condition and a ductile fracture in annealed condition. The results show that J. integral approach can be used in measuring of kIc, particulary if the kIc values can not be achieved.

Determination of side weir coefficient spatially varied flow with lateral out flow is considered to be one of the most important issues because it improves the accuracy of results and consequently makes the design more trustable In this study, the governing differential equations are solved by the Runge Kutta fourth order method. A nonlinear optimization technique is utilized to determine the side weir coefficient by minimizing the differences between its calculated and measured results. In this regard, many relationships for the side weir coefficient are selected. Relationships which yield better agreements among calculated results data are chosen as final ones. These relationships are compared to other relationships proposed by other investigators. The comparison indicates that the relationships proposed by this study give accords with measurements.