Basrah Journal for Engineering Sciences

The investigation of indoor electromagnetic propagation has been performed at the unlicensed industrial, scientific, and medical (ISM) band, which has gained increased attention recently due to high data rate communication systems developed to operate in it. The effect of the incidence angle and materials thicknesses on the reflection coefficients for both horizontal and vertical polarization has been studied. A two-dimensional ray-tracing model has been suggested to simulate the influence of buildings electromagnetic properties on indoor radio channel characteristics, such as signal level, rms delay spread, and coherence bandwidth. Results show that the influence of the permittivity is more important than the influence of the order of reflection considered for the ray-tracing model. It is also shown that, compared with power level, rms delay spread is more sensitive to the building dielectric parameters. Maximum rms delay spread is dependent mainly on the reflectivity of the walls, which is dependent on the dielectric parameters.

Among the soft-switching techniques, the Zero-Current Zero-Voltage Transition (ZCZVT) technique is used in this paper. It is based on the Resonant Transition Mechanism requirements, which permit newcomers to perceive the Resonant Transition techniques as a whole instead of dissimilar soft-switching techniques. The open loop operation of the power circuit (DC/DC Boost Converter) and control circuit have been implemented and tested with Matlab software. The simulation test facility and the analytical development tools being used are described. The derivation of a closed-loop control strategy based on fuzzy logic control with nonlinear fuzzy sets for input and output variables is described in detail. The closed-loop simulation results that describe the performance of the proposed converter with this control strategy due to different effects are also included.

The theoretical study of synchronization of two coupled single-mode semiconductor lasers is achieved. The transmitter is laser subject to optoelectronic feedback that operates in a chaotic regime. The receiver can also operate in a chaotic regime similar to the transmitter. The effects of parameter mismatch on the synchronization of two lasers with optoelectronic feedback are determined, with a mismatch in delay time, with a mismatch in feedback strength, and with coupling strength between two systems. The synchronization is sensitive to mismatch in the delay time for the transmitter and receiver feedback loops. An open-loop receiver configuration does not have the problem of delay time mismatch and shows the highest synchronization. The synchronization phenomena that appear in the two-coupled semiconductor lasers can be used in communications systems. Finally, an encoding and decoding of messages on the chaotic carrier is demonstrated.

The LCL Series Resonant Converter (LCL-SRC) type offers nearly load-independent output voltage under some operating conditions. In this way, the output voltage can be regulated against wide load and line variations with a small variation of switching frequency. In this paper, a simple method for the optimization of LCL-SRC is presented. This method takes the stored energy as a theoretical index to obtain the minimal size of the converter inductors L1 and L2, which contribute significantly to the converter size and weight. The Rac method for the analysis of resonant converter is discussed. This method was found fairly accurate for operation above resonant frequency.

This paper proposes a fuzzy logic-based controller for boost-type DC/DC converter. It forms an improvement to the dynamic performances of the well-known PI like fuzzy controller, which uses the output voltage error and its rate of change as an input. The proposed controller generates a duty ratio control signal through the addition of a weighted part of the input voltage and the low pass filtered signal of the inductor current to that of the fuzzy controller which is fed by voltage error and a signal representing the differences of the output voltage from its low pass filtered version. The controlled boost DC/DC converter exhibited excellent performances under small and larger disturbances of the input voltage and output load resistance and also showed good reference tracking ability.

This paper presents an exact solution for the load-settlement relationship of axially loaded piles embedded in a nonhomogeneous elastic foundation. The governing differential equation is reduced to a modified Bessel equation of order v. The solution is represented by Bessel's functions of the first kind of order v. The stiffness coefficients are then derived from the exact solution. Numerical comparison with approximate solutions of special cases verifies the accuracy and efficiency of the adopted method.

In the present study, the dynamic analysis of jacket-type offshore structures under the action of sea waves is carried out. The finite element method is adopted for the solution to the problem. The effect of soil-structure interaction on the dynamic behavior of the offshore structure is taken into account due to the deformations of the soil caused by the motion of the structure, which in turn modifies the response of the structure. The supporting elastic foundation is represented by the Winkler-type model having normal and tangential moduli of subgrade reaction. These moduli may be constant or varying linearly or non-linearly along the embedded length of the piles that support the offshore structure. The pile tip conditions are also considered. A time-domain solution is recommended. The generalized Morison's equation is used to calculate the wave forces and Airy's linear theory to describe the flow characteristics. Both free and forced vibration analyses are studied. The dynamic response has been obtained by modal analysis in conjunction with the Wilson method. As an example, a modified model of an actual jacket-type offshore platform is analyzed under the action of wave forces.

By using a linear wave equation, a new model of bubble dynamics in an acoustic field is constructed, including effects of thermal conduction both inside and outside a bubble, and non-equilibrium evaporation and condensation of water vapour to the bubble wall. The liquid temperature at the bubble wall is numerically calculated by solving the heat conduction equation (without assuming a profile of liquid temperature). It includes the effect of the latent heat of non-equilibrium evaporation and condensation on the bubble wall. It is concluded that the liquid temperature increases to the same order of magnitude as that of the maximum temperature attained in the bubble at strong collapses. It is caused by the latent heat of intense vapour condensation and by the thermal conduction from the heated interior of the bubble to the surrounding liquid. The intense vapour condensation takes place at strong collapses because the pressure inside the bubble increases. The comparison is given between the calculated result and the experimental data of the radius-time curve for one acoustic cycle. The calculated result fits well with the experimental data.