International Journal of Engineering
Volume:13 Issue: 3, Aug 2000

It is well known that the mechanical properties of fiberglass reinforced "phenolic moulding compounds" are significantly enhanced if the glass particles are coated with silane coupling agents before compounding. It has been shown that improvements obtained by using scanning electron microscopy techniques are due to better bonding of phenolic resin to the surface of treated glass fibers. These observations prove that coated glass fibers effectively exhibit properties which are different from those of the glass itself. Thus from a modelling point of view, they can be regarded as materials having moduli different from the modulus of glass. However, considering the very small width of the coating layers used, it cannot be expected that by using direct experimental measurements of relatively large specimens, significantly different moduli for uncoated and coated glass fibers will be found. In this paper, the notion of an effective moduli for coated fibers is introduced. It is shown that such values can be numerically determined using experimentally measured bulk mechanical properties of coated glass filled composites. A trial and error procedure is developed for obtaining optimum moduli for the reinforcing phase. This scheme is based on the comparison of simulation results obtained by a previously validated finite element technique and data collected from flexural tests and fracture surface observations for different types of glass reinforced phenolic composites.

A bi-criteria optimization is considered whose objectives are the maximization of the load sustained by a structure and the minimization of the structure''s volume. As the objectives are conflicting, the solution to the problem is of the Pareto type. The problem is elaborated for a thin-walled column of cruciform cross-section, prone to flexural and torsional buckling. A numerical example is also presented.

The techniques and methods of developing cost models for respirators are discussed. Models are developed and implemented in this study for nineteen types of respirators in two major classes (air-purifying and supplied-air) and one LEV system. One respirator model is selected for detailed discussion from among the twenty models. The technical cost method is used in constructing the cost models for each of the respirators and the LEV system. In this methodology, the costs of purchasing and using a typical respirator or LEV system are divided into two categories, variable costs and fixed cost s. Variable costs consist of the cost of replaceable components and probabilistic mortality cost. Fixed cost is the annualized capital requirement plus interest cost. The criteria for estimating some of the cost elements are based on existing equations in the literature, engineering judgement and manufacturer-provided information. A technical cost model results from the integration of this information into a computerized framework. The cost models for discussion are presented in the order of increasing computational complexity. Through the economic analysis, the lowest cost type in each class of respirator is determined. The determination criteria are based on the minimum total annual cost and highest benefit cost ratio. The selected lowest cost respirators are compored with the LEV system from the economic standpoint to reveal the cost optimal alternative.

Direct numerical simulation of turbulent flow behind a cylinder, wake flow, using the random vortex method for an incompressible fluid in two dimensions is presented. In the random vortex method, the primary variable is vorticity of the flow field. After generation on the cylinder wall, it is followed in two fractional time step in a Lagrangian system of coordinates, namely convection and diffusion. No closure model is used and the instantaneous results are calculated without any a priori modeling. Regarding the Lagrangian nature of the method, there is a very good compatibility between the numerical method and physics of the flow. The numerical results are presented for a wide range of Reynolds number, 40-9500. In the initial stages, there is only an unstable symmetrical flow behind the cylinder and the vortex sheding is not started yet. But, in the high Reynolds number flows, two distinctive flow patterns, namely α and β are detected. The mechanism of generation of the primary and the secondary eddies can be related to the production, convection and diffusion of the vorticity field and the time dependent structure of the flow field in the wake zone behind the cylinder. The length of the computational domain, downstream of the cylinder, is selected 25 times of the cylinder''s diameter. Regarding such a lengthy computational domain it is possible to detect the mechanism of generation, pairing and growth of the large scale structure, eddies. Although the instantaneous numerical results are calculated, no coresponding comparable results are available. Therefore, the validity of the results in this stage is only qualitative. For the quantitative comparison of the results, after the establishment of the stationary state, time averaged based indicators such as separation angle, drag coefficient, lift coefficient, Strouhal number and. .. are calculated. The numerical results accurately fall within the range of the experimental measurements.

Application of Compressed Natural Gas (CNG) in diesel engines has always been important, especially in the field of automotive engineering. This is due to easy accessibility, better mixing quality and good combustion characteristics of the CNG fuel. In this study the application of CNG fuel along with diesel oil in a heavy duty direct-injection automotive diesel engine is experimentally investigated. In order to convert a diesel engine into a diesel-gas one, the so called "mixed diesel-gas" approach has been used and for this purpose a carburetted CNG fuel system has been designed and manufactured. For controlling quantity of CNG, the gas valve is linked to the diesel fuel injection system by means of a set of rods. Then, the dual-fuel system is adjusted so that, at full load conditions, the quantity of diesel fuel is reduced to 20% and 80% of its equivalent energy is substituted by CNG fuel. Also injection pressure of pilot jet is increased by 11.4%. Performance and emission tests are conducted under variation of load and speed on both diesel and diesel-gas engines. Results show that, with equal power and torque, the diesel-gas engine has the potential to improve overall engine performance and emission. For example, at rated power and speed, fuel economy increases by 5.48%, the amount of smoke decreases by 78%, amount of CO decreases by 64.3% and mean exhaust gas temperature decreases by 6.4%

Arsenic is the 20th most abundant element in the earth''s crust at a level of about 2 ppm. It is a constituent of over 300 minerals and is commonly found in non-ferrous ores such as copper, lead, zinc, gold and uranium. Efficient separation of arsenic minerals from other sulphide minerals is of great importance for the metallurgical performance of flotation processes. This work was undertaken to study the separation of enargite, an arsenic-bearing mineral from chalcopyrite in copper concentrates. To achieve this aim the possible depression of enargite using some sulphide depressants was studied.

N.sitophila was grown under controlled conditions of solid state and submerged fermentation on Sago hampas. The optimum conditions of protein enrichment previously established for sugar beet pulp was used for this study. Under this condition the protein content of Sago hampas under solid state increased from 1.4 to 14.45% (W/W) whereas for Sago hampas and Sago starch, the protein content under submerged condition increased from 1.4%(W/W) and 0.7%(W/W) to 18.56%(W/W) and 43/16%(W/W) based on dry weisht of product respectively. The cellulase, a-amylase and glucoamylase activities of N.sitophila under solid state condition on Sago hampas were 9.0, 0.6 and 11.8 U/g of wet fermented solid respectively. The enzymatic activities were also measured under submerged fermentation using both Sago hampas and Sago starch as substrate.

This paper presents a new filtering approach based on fuzzy-logic which has high performance in mixed noise environments. This filter is mainly based on the idea that each pixel is not allowed to be uniformly fired by each of the fuzzy rules. In the proposed filtering algorithm, the rule membership functions are tuned iteratively in order to preserve the image edges. Several test experiments were performed in order to hlight the merit of the proposed method. The results are very promising and indicating the high performance of the proposed filter in image restoration compared with those of the filters which have been recently cited in the image processing literature.

Fine zinc oxide particles were electrophoretically deposited on alumino-ferro-chrome substrates. The deposition was carried out in a cylindrical ZnO/acetone electrophoresis cell. The deposits were dried and sintered at 1030³C in air. The process resulted a porous polycrystalline ZnO cladding over the alloy core. Comb shaped silver electrodes were formed and fired at 350³C. The variation of device resistance vs. temperature was studied in air in the range of 100 - 250³C. The NTC of resistivity at 100³C and the activation energy of carrier generation was found to be 4.0% K-1 and 1.1eV respectively.

A plane subsonic jet was subjected to periodic oscillations in the near nozzle region by a twin vane system. During excitation, the jet was found to spread significantly and entrain mass much more than its steady counterpart. Time averaged static pressure measured in the flow field with a disc probe exhibited prominent well defined suction regions different from that of a steady jet.

Signal optimization is affected during radio links between a transmitter and a receiver located in adjacent material media with differing optical densities. The optimization is carried out via the automated control theory method. The radio signal obtained after the optimization is coordinated with the two media''s electrical characteristics simultaneously; and this enables low power and small antenna of the transmitter, on the one hand, and low sensitivity of the receiver, on the other.