International Journal of Engineering
Volume:18 Issue: 1, Feb 2005

aIn the present study a 4-stroke 5hp diesel engine was tested with Diesel oil plus cottonseed oil blends. The blends in different proportions (10 to 50 percent by volume) were tested at constant speed of 1500 rpm. The said engine is operated at different loads and characteristics like Brake power, Brake thermal efficiency, specific fuel consumption etc. Engine performance for blends resulted in lower brake thermal efficiency. Smoke is also found to increase with the blends. The results of the present experimental investigations reveal that the performance of the blends is comparable with that of diesel. Hence blends can profitably be employed in an existing CI engine without major engine modifications, further it can be an immediate solution for the development of rural areas, and for the emergency use in the event of severe diesel fuel shortage.

The unstable flow with rotating-stall-like (RS) effects in a rotor-cascade of an axial compressor was numerically investigated. The RS was captured with the reduction in mass flow rate and increasing of exit static pressure with respect to design operating condition of the single rotor. The oscillatory velocity traces during the stall propagation showed that the RS vortices repeat periodically, and the mass flow rate was highly affected by the blockage areas made by stall vortices. The results also showed that large scale vortices highly affects on the generation and growth of the new vortices. An unsteady two-dimensional finite-volume solver was employed for the numerical study which was developed based on Van Leer’s flux splitting algorithm in conjunction with TVD limiters and the κ-є turbulence model was also employed. The good agreement of the computed mass flow rate with the experimental results validates the numerical study.

In the present paper, the problem of externally excited exponential transmission line has been solved analytically in frequency domains using a simple approach. Then steplines approximation as a first order approximation for the problem of externally excited nonuniform transmission lines in general and exponentially tapered transmission line (ETL) as a special case has been presented. Finally the two approaches are compared and some useful results are obtained to show when the two methods are equivalent.

Radiation from monopole antennas on spherical-lossy earth is analyzed by the finite-difference time-domain (FDTD) method in spherical coordinates. A novel generalized perfectly matched layer (PML) has been developed for the truncation of the lossy soil. For having an accurate modeling with less memory requirements, an efficient "non-uniform" mesh generation scheme is used. Also in each time step, computation is limited to that part of the mesh where the radiated pulse is passing (computational window). In this manner, the values of radiated field at far distances can be obtained directly by the FDTD method. The spatial distribution of radiated field and the influence of the ground screen on monopole''s admittance are shown in illustrations.

In this paper the heat transfer characteristics of a two-phase closed thermosyphon over a wide range of heat transfer rates, system pressure, aspect ratios and filling ratios were studied. The experiments focused on the boiling and condensation heat transfer characteristics of the thermosyphon. The experimental boiling and condensation heat transfer coefficients inside the thermosyphon were compared with the existing correlations. A good agreement between the experimental results of condensation heat transfer of the thermosyphon and Nusselt’s correlation was obtained. In addition, the optimal working fluid filling and the overall heat transfer coefficient were evaluated for practical operation. Finally, according to poor agreement between the experimental results of boiling heat transfer coefficient and existing correlations, the working conditions were analyzed and a new practical formula (correlation) was presented. The new correlation can be used to predict boiling heat transfer coefficient generally.

The amount of petroleum hydrocarbon and heavy metals in the sediment of the Persian Gulf’s shore, at 8 selected stations were determined and showed the maximum of 143.6 and 58.6 mg/kg sediment, respectively, both maximum amounts were related to Emam Hassan zone which is located at 50 kilometers to west Boushehr port. Bioremediation of contaminated sediment were studied in slurry and solid-state fermentation. 8 bacteria types were isolated. Four species Em2, SH, GN1 and GN3 presented maximum PAH removal efficiency. Biodegradation efficiency under slurry conditions was observed after about 45 days, which during this period, naphthalene and phenanthrene showed 73% and 66% removal efficiency respectively. Under solid-state conditions, microbial activity of mixed and pure culture was studied. The results presented that mixed culture due to high ability of different strains for growth, showed higher degradability compared to pure culture, but insufficient mixing under solid state condition resulted in a low mass transfer rate of nutrient which caused reducing cell activity, therefore removal efficiency decreased under solid state condition.

A resource investment problem is a project-scheduling problem in which the availability levels of the resources are considered as decision variables and the goal is to find a schedule, and resource requirement levels, such that some objective function optimizes. In this paper, we consider a resource investment problem in which the goal is to maximize the net present value of the project cash flows. We call this problem as Resource Investment Problem with Discounted Cash Flows (RIPDCF) and we develop a heuristic method to solve it. Results of several numerical examples show that the proposed method performs relatively well.

The web of plate girders in bridges are usually reinforced by welded transverse stiffeners in order to improve their shear capacity.Due to problems associated with field welding and fatigue, welded stiffeners are not suitable for retrofitting existing bridges. Bolted stiffeners are a practical alternative for strengthening girders that are expected to experience shear stress in excess of their design shear capacity. This paper presents the results of an analytical study into behavior of plate girders with bolted transverse stiffeners. Based on this study new requirements are developed for designing of such girders.

This paper presents the results of a study on the axial compressive strength of columnsstrengthened with FRP wrap. The experimental part of the study included testing 6 reinforce dconcrete columns in two series. The first series comprised three similar circular reinforced concrete columns strengthened with FRP wrap. The second series consisted of three similar square columns, two with sharp corners, and the other with rounded corners. Axial load and displacement of columns were recorded during tests using a displacement control test set up. Test results are compared with the values calculated using CSA (Canadaian Standard Association) Code provisions and recently proposed equations. It is shown that the FRP wrap increases the strength and ductility of circular columns, significantly. The recently proposed equations correlate well with the test results of circular and square columns with rounded corners. According to the test results, the FRP wrap did not increase the strength of square columns with sharp corners. However, the square column with rounded corners exhibited a higher strength and ductility compared to those with sharp corners.

A two dimensional numerical model of shallow water equations was developed to calculate sub and super-critical open channel flows. Utilizing an implicit scheme the steady state equations were discretized based on a control volume method. Collocated grid arrangement was applied with a SIMPLEC like algorithm for depth-velocity coupling. A power law scheme was used for discretization of convection and diffusion terms. Underrelaxation factors were introduced in the model to prevent divergence. Momentum interpolation was used in calculating velocities on cell faces to avoid checker board water surface fluctuation in the collocated grid. The model was verified in different cases including complex water surface profiles and hydraulic jumps. The results are compared with experimental and analytical data and the necessary values of under relaxation factors for a converged solution are discussed. No artificial viscosity was required, which is the advantage of the present model.

The main objective of this paper is to formulate a mathematical model for finding flow field and cavitation problem on dam spillways. The Navier-Stokes Equation has been applied for the computation of pressure and velocity field, free water surface profiles and other parameters. Also, for increasing accuracy of the problem, viscosity effect has been considered. Because of internal flows the effect of gravity forces has been ignored. To have more accuracy the continuity and momentum equations have been transformed to a coordinate system with axis tangent and normal to stream flow.Finite differences has been used to solve equations governing the over flow of dam the spillways. To linearize the nonlinear equations the parameters are expressed in terms of products of last step in the new one. Later the remaining derivatives are with finite differences form. Coefficients of convergence as well as a three diagonal system are used for all the grids points. The cavitation phenomena are discussed after determination of velocity and pressure fields, which cause erosion on the spillway shut and side walls.Also, the different types of cavitations and appropriate solutions were considered and a computer program (MANS) was developed Two examples were solved on this basis and the computed results were compared with experimental results. The results show that for flows up to 4000 m3/sec the condition is good, but for flows higher than this value, the water surface shows high uprising and provisions are needed to resist cavitation at these flows. The results also indicate that at flows about 10899 m3/sec secondary flows dominate near the lateral gates and side walls.