JOURNAL OF SCHOOL OF ENGINEERING
Year:2002 | Volume:14 | Issue:2|Papers Count:7

To analyze the mechanical properties of the Earth as a mechanical system, an appropriate and simple model of the Earth is needed. This is because the proposed models which are based upon the body waves, represent the properties as a point function in terms of the depth and cause difficulties in obtaining the required responses in engineering problems. In this paper, it is attempted to apply the sensitivity analysis to propose a couple of simple models, which satisfy the important constraints of the mass, the moment of inertia and the first period of vibration of the Earth. To accomplish this goal the finite elements form of axisymmetrical problems is first presented. Then, sensitivity analysis of the Eigenvalues with respect to the density is carried out to equalize the first period of vibration of the proposed models with the first period of vibration of the Earth. These models are, then modified with the aid of the afforementioned program and compared with the Anderson"s model showing good agreement.

Heat treatment and production methods such as rolling, forging, deep drawing, etc, induce residual stresses as well as texture changes in the billets. T1zese processes cause the billets to become anisotropic. In "Acoustoelasticity", residual stresses can not be determined unless the texture is already mown apriori or determined simultaneously. In the present article, the equations of particle motion in an anisotropic elastic medium in the presence of residual stresses and texture is considered for two cases of rolling processes. Using elastic wave propagation in the medium, the relationships between the wave velocity and the residual strains as well as texture parameters in special planes are obtained for the general case and then simplified for rolled billets. The residual stress effects on the wave velocities are also discriminated from the effects of texture. The analytical results are discussed and compared with the experimental results for the case of one-dimensional stresses in billets, showing good agreement.

In this paper the flow rates in naturally ventilated buildings are calculated using one dimensional loop analysis in which the buoyancy forces are balanced by the pressure drops due to friction. The equations are extended to take into account the effects of wind and stack in multiple floor buildings. The procedure is straight forward and yields the zone air change rates without recourse to a complicated and time consuming calculation. Interaction between loops of multiple zone of multiple floor buildings requires iterations. For turbulent natural ventilation, the friction factor is determined from an experiinental formulation. The results show that the ventilation air change rates depend on the net heat .gain to the power 0.33 for entrace/exit duct domination over internal friction, 0.5 for internal friction dominated conditions, and 1 for wind dominated conditions. The results of the procedure also reveal the significant effects of inlet and outlet surface areas on the ventilation of naturally ventilated buildings. The comparison of loop analysis results with empirical methods shows good agreement.

Flood routing is one of the complicated subjects in hydraulic engineering. Several methods have been developed for flood routing. These methods can be classified into two different groups, distributed and lumped routing methods. The main objective of this research is to search for the capabilities of the Artificial Neural Network (ANN) method for flood routing and to introduce a new method based on ANN that can be more accurate than the conventional lumped routing methods. After utilization of different ANN structures and analysing different data, it was found that a 3-layer perceptron ANN (2 cells in the hidden layer) with sigmoid activation function and bias term in the cells can give good results. Comparison of the ANN results with those of the linear Muskingum method shows that, despite the weakness of the ANN method in exactly satisfying the mass balance equation, it performs better in term of other error criteria such as the sum of square of errors or the error in predicting the time and magnitude of the peak discharge. Another advantage of the ANN method is its capability of interpolating flood wave characteristics. This capability is highlighted in this paper.

In this paper a new optimization approach based on adaptive simulated annealing (ASA) is used for solving the reactive power planning in electric power system in normal and contingency conditions. For studying the VAr planning problem a real model of power system which is a nonlinear system is considered. In this approach the real value of the objective function is used in optimization process, so there is no need to calculate the derivatives of the objective function. In order to solve the above problem many buses are considered by their weakness from steady state voltage stability viewpoint. The type and optimum size of these sources are determined using an iterative approach. The proposed algorithm is applied to the IEEE 14-bus and 30-bus test systems. In order to show the effectiveness of the proposed method the simulation results are compared with the results of a relevant published paper in this subject.

Abstract Selective absorption of H2S from acid gases has been investigated using an internal loop air-lift reactor. First of all H2S absorption and regeneration rate of the catalyic solution were determined and a software for designing and simulating of this reactor is provided. In this research, the concentration profile for reactants and products versus time, steady state concentration profiles of the liquid and gas, required time for steady state concentration and the volume of the reactor are studied. The model predicts values, which are in good agreement with the experimental results.

The oxidative coupling of methane (OCM) to higher hydrocarbons has been investigated in the absence of catalyst. The reaction was carried out in quartz tubalar reaction with volume of 16.3 ml, at atmospheric pressure and at 750 to 950°C. The total flow rate was 90 to 130 µ/min and the dilution ratio was 0.2 to 0.75. In the same experiments steam was used as a carrier gas in place of helium to study its effect on the reaction. At 850°C, the total flow rate 100 µ/min, methane to oxygen ratio equal 2 and dilution ratio 0.5, when helium and the steam were used as a carrier gas, the Cz yield was 8.4 and 9.5 respectively. The power law kinetic models (relations) as a function of methane and oxygen partial pressures was found for the rate of disappearance of methane and the rates of formations of ethane, ethylene and carbon oxides.