International Journal of Engineering
Volume:18 Issue: 4, Nov 2005

In this paper the equations of motion and corresponding boundary conditions for bending vibration of a beam with an open edge crack has been developed by implementing the Hamilton principle. A uniform Euler-Bernoulli beam has been used in this research. The natural frequencies of this beam have been calculated using the new developed model in conjunction with the Galerkin projection method. The crack has been modeled as a continuous disturbance function in displacement field which could be obtained from fracture mechanics. The results show that the natural frequencies of a cracked beam reduce by increasing crack depth. There is an excellent agreement between the theoretically calculated natural frequencies and those obtained using the finite element method.

In this paper a transient free convection flow around a sphere with variable surface temperature and embedded in a porous medium has been considered. The temperature of the sphere is suddenly raised and subsequently maintained at values that varies with position on surface. The method of asymptotic expansions is applied for small Rayleigh numbers and then a finite-difference scheme is used to solve the problem numerically for finite values of Rayleigh numbers. Transient and steady-state flow and temperature patterns around the sphere are discussed in details and a comparison between numerical and analytical results has been presented.

Oxygen is an essential part of the living organism. It is transported from blood to the body tissue by the systematic circulation and large part of it is stored in the blood flowing in capillaries. In this work we discuss a mathematical model for oxygen transport in tissues. The governing equations are established assuming that the blood is flowing along a co-axial cylindrical capillary inside the tissue and has a constant partial pressure of oxygen. We solve the governing partial differential equations using finite element techniques. The main object of the present work is to investigate the effects of various assumptions such as neglecting axial diffusion, neglecting the effect of facilitated myoglobin diffusion etc.

In this paper we develop a multi-objective model to optimally control the lead time of a multistage assembly system. The multistage assembly system is modeled as an open queueing network, whose service stations represent manufacturing or assembly operations. The arrival processes of the individual parts of the product, which should be assembled to each other in assembly stations, are assumed to be independent Poisson processes with equal rates. In each service station, there is one machine with exponentially distributed processing time, such that the service rate is controllable. The transport times between the service stations are independent random variables with exponential distributions. By applying the longest path analysis in queueing networks, we obtain the distribution function of time spend by a product in the system or the manufacturing lead time. The decision variables of the model are the number of servers in the service stations. The problem is formulated as a multi-objective optimal control problem that involves three conflicting objective functions. The objective functions are the total operating costs of the system per period (to be minimized), the average lead time (min), and the probability that the manufacturing lead time does not exceed a certain threshold (max). The goal programming method is used to solve a discrete-time approximation of the original problem.

This paper presents the results of a number of computations using the 2D FEM to show the effects of significant variables on the behavior of geosynthetically reinforced earth slopes. The verification and reliability of the results are primarily examined through comparisons with experimental data available. The results seem to be quite acceptable and can be used with a high degree of reliability for predicting the relevant problems.The main variables studied are soil properties, slope geometry, and the properties of reinforcement elements, while the safety factor, deformation components, effect of geotextile stiffness, the shape and location of the slip surface are the main unknowns sought.

Spatially varied flow in open channels occurs in a large variety of hydraulic structures as well as road/bridge surface drainage channels. The equation of motion for spatially variable flow in an open channel, being produced by the lateral or a vertical inflow, has been treated previously. However, these are not applicable to the phenomenon of runoff from a plane surface, which is an example of spatially varied flow. This paper reviews the state of the subject and presents the experimental data applying a practical equation of motion mathematically derived. Several series of experiments are carried out in a v-shaped bottom channel. These experiments are used to model specific rainfall intensity and discharge. For this particular channel shape, longitudinal water surface profiles are plotted and are compared with the profiles given by the equation of motion treated for this channel shape. Analysis of the results agrees well with the experimental data and the proposed equation for supercritical flows. The results, however, show that the profiles slope does not normally increase as the flow discharge increases at the end of the channel. This result confirms that the flow resistance in spatially varied flow as well as the critical depth position along the channel and cross sectional shape should be taken into account.

The ray series method may be generalized using a ray centered coordinate system for general 3D-heterogeneous media. This method is useful for Amplitude Versus Offset (AVO) seismic modeling, seismic analysis, interpretational purposes, and comparison with seismic field observations.For each central ray (constant ray parameter), the kinematic (the eikonal) and dynamic ray tracing system of equations are numerically solved. Then, the ray impulse and the ray synthetic seismograms are efficiently computed. The reflected, refracted, critically diffracted, multiples and converted P-waves and/or S-waves are computed and evaluated at the ray endpoints. The central Ray Method application to two-dimensional models are investigated and comparison with seismic wave field are successfully done. Two examples of the ray field and synthetic seismograms for the complex models are presented here both for surface seismic profiling (SSP) and vertical seismic profiling (VSP).

Rheological Properties Such as Viscosity (η), Shear Stress (τ), and Torque (M) of the mixtures of (HTPB) with Octagon (HMX), Hexogen (RDX), and 2, 6 Diamino-4-Phenyl-1, 3, 5 Triazine (DAPTA) mixtures were measured. The experimental design was arranged for three factors at two levels (High and low levels). Temperature of the mixture (°C), Speed of the stirrer (rpm), Mixing Time (minutes) have been known to be effective in the quantity of Rheological properties. In this work, by using the appropriate equations the empirical model was presented for each property and mixture and the main effects on the responses were detected.