INTERNATIONAL JOURNAL OF ENGINEERING SCIENCE (ENGLISH)
Year:2001 | Volume:12 | Issue:2|Papers Count:14

In this paper, the transient response of fins with variable cross- section is investigated, calculated and compared using perturbation techniques of higher orders when the fin's base temperature undergoes a step change. To expand the practical applications of the results of this investigation, different mechanisms of heat transfer governing the process of energy exchange are considered. Also, in this work, the use of the software of mathematical has enabled us to consider eight terms in perturbation expansions without carrying the burden of the algebra. At the end, the governing equations are solved using numerical techniques to compare with the perturbation results (an analytical approach).

In this paper, the time-optimal control problem for point-to-point motion of robot manipulators with elastic joints, bounded control inputs and jerk constraint on entire path is studied. First, The dynamic equations and jerk constraint are derived for a elastic joint manipulator. Then, the jerk constraint and equations of motion in the state space form are discredited by forward difference technique. Thus the time optimal control problem is formulated as a constrained parameters optimization problem. The MATLAB optimization toolbox is used to obtain the solution of the optimization problem. This method helps to implement the jerk constraint, easily. The above mentioned method is also implemented for a single link with elastic joint, and some of results are presented. The results show a smooth trajectory for robot motion when the jerk is limited, which reduce the vibration and mechanical wear at the joints.

In these paper two methodologies for solving the steady incompressible Navier- Stokes equations by finite-volume method in general non-orthogonal curvilinear coordinates are compared. Both methods use staggered grid arrangement and SIMPLE pressure velocity coupling treatment, but the dependent variables in the momentum equations are different. One of the methods uses Cartesian cell face velocity components and the other uses covariant cell face velocity projections. By applying the methods to test problems their relative accuracy and convergence behavior are compared.  

Agnew turbine is an axial flow micro hydro turbine which originally was designed and manufactured in Scotland. A number of these turbines have been locally installed at different sites. Regardless the fact that the original design did not perform efficiently. Because of lack supports, no research work has been under taken to improve its performance. Since this turbine has been considered for use in Iran, a new model of the turbine is made and tested. Later improvements were made on the turbine and tests were repeated. Test results indicated major improvements on the performance of the turbine, such as 23% increase if the highest efficiency point.

In this paper a binomial expansion is employed to determine the first few terms of the elastic stresses in the Williams series solution for a large centrally cracked plate subjected to uniform tensile load It is shown that adding the higher order terms to the singular term, improves noticeably the accuracy of the results for direct stresses near the crack tip along the crack line. The effect of higher order terms on the extent of the plastic zone ahead of the crack tip is also studied Results are shown for both plane stress and plane strain conditions. The plastic zone size is determined using both the Tresca and the von Mises yield criteria.

There are more scatter in experimental creep crack growth data observed in the early stages of a test than later on. This scatter can be attributed to a combination of factors; such as stress redistribution from the initial elastic state to the steady state creep, primary creep effects and the buildup of damage local to the crack tip during the early crack growth period. In this paper the redistribution of stress and the buildup of damage at a crack tip during creep in a cracked body is considered. For short times after application of load, crack growth rate can be described by stress intensity factor K for long times, if the stress fields relax to their steady sate, then C* can describe the magnitude of the stress fields and so the crack growth rate.A new method has been developed for the time needed for the stresses to relax from their elastic state to some fraction between the elastic and creep state. Also a new creep crack growth model is proposed in terms of ductility exhaustion to account for buildup of damage at a crack tip. It is shown that this build-up of damage is the most likely cause of increased scatter.

The real 'on-road' fuel consumption and performance measurement of a vehicle is dependent on a number offactors such as type of vehicle, the driver behavior, the road design and the immediate traffic flow. Therefore, at the design stage, the performance control and reliability of the modern internal combustion (IC) engines is due very largely to the application of tests performed in the laboratories. The tests are carried out using a system known as test-rig. In the current work, affixed electrical dynamometer test-rig was designed and built. The production problems such as the vibration analysis at high-speed tests and the mechanical instrumentation construction errors involved with the most common electrical swinging dynamometers, were reduced significantly. Series of tests were conducted, and the optimum enginefuel consumption and engine performance were successfully controlled.

A Vapour Jet Refrigeration System (VJRS) utilises a supersonic ejector as a thermal compressor and is an alternative to the conventional mechanically driven vapour-compression refrigeration system. The small VJRS has the potential significantly to reducefuel consumption by automobile air conditioning systems. The flow field in the ejector is transonic and complex. In the past literature a little attention has been carried out on the small VJRS. Therefore, the present author developed one-dimensional compressible flow theory with a the secondary choking theory to model the performance of the small ejector. Also, this researcher designed and built a small VJRS using R12 as the working fluid to test experimentally with the objective of optimising the ejector performance as regards primary fluid nozzle position and ejector performance in practice. In addition the PHOENCICS computer-code has been employed by the author to model the VJRS simulation. Here, the results of a numerical simulation of the flow field within the ejector using PHOENICS is presented and comparisons made between the CFD prediction of the flow field and that assumed in the secondary choking theory.

The goal of this paper is to come up with a thermal control system for a small at ellite loctated in low earth orbit. For a satellite to operate properly in orbit, all components must work within their specific temperature limits. To keep the satellite and its components within their prescribed temperature ranges, a set of passive thermal control is selected and then two different design tools are utilized. First, a finite difference method (lumped parameter method) is utilized. In lumped parameter method, thermal network for heat interacting nodes are drawn and afinite difference based code is utilized to solve the set of non-linear algebraic equations. Then, afinite element based software (NISA II) is used to model the identical satellite and then compare the result. In general, in formulation of governing equations, because of low air density in low earth orbit (LEO), convection mode of heat transfer is neglected. Also, in orbit, the external surfaces of satellite receive direct solar flux, earth reflected solar flux (Albedo), and earth-emitted radiation while some of the subsystems dissipate heat. Results show a -4°C to 11.4°C temperature variation for internal devices and a -56.2°C to 69.4°C variation for external surfaces. Temperature obtained by both methods show very good agreement exceptfor the battery which is due to material used in battery modeling.

In this paper, an explicit characterization of all classical discretization methods, including the forward and backward difference, trapezoidal rule, step-invariant, impulse-invariant and matched pole/zero, is introduced. It is shown that the discrete-time approximation converges to the original function when the sampling period approaches zero, in the L¥-induced norm sense. The problem is of considerable practical importance, because it can be helpful in the digital implementation of continuous-time algorithms and control systems.

In this paper, motion control of wheeled mobile robots (WMR) based object oriented method by using Delphi 4.0 programming language is presented A software package to enhance wheeled mobile robots' capability and efficiency is developed In this development, all parts of WMR's such as motors, sensors, driver, etc. are considered separately. A software environment has been created to present a suitable setting for robot programming by using personal computers. Finally, a three DOF mobile robot is tested with output data's of the ware.

The enthalpy method is used to study the mass optimization of a transient two dimensional radial-angular model of thermal energy storage system with a phase-change material for heat sink applications in space. The development assumes no energy source, no pressure variation, and no work done on the control volume. The optimization parametric study is performed for individual components as well as for the integrated system. The total mass of the system are considered to be minimized for a given heat stored. Partial parametric study is done for a transient one dimensional radial model in order to compare it with two dimensional models. The significance of employing extended fin surfaces is observed. The Gauss-Seidel iterative scheme with over-relaxation is used to numerically solve the resulting nonlinear simultaneous finite difference equations. Variation of the geometry of the system such as inner tube radius, outer shell radius, number of fins, and height of fins have significant effects on the mass and amount of heat stored.

Point mass damper is used in either spin or gravity-gradient stabilized satellites, as a damper of nutation angle. In this paper, dynamic and stability analysis are performed for several possible applications. Two cases of spin and gravity gradient stabilization are both included. In the case of gravity gradient stabilization, we purposely include spin about the yaw axis. In each case point mass damper is allocated in different directions and analysis is carried out. Equations of motion for both satellite and the point mass damper are derived and effect of point mass damper on stability regions is studied. Floquet and Kelvin-Tait-Chetayev stability theories have been used to determine stability regions in spin and gravity-gradient cases, respectively.