One of the major problems in the industry is deposition of sediments on the surface of the parts, which results in reduced component efficiency and extensive damage to industrial units. So, one of the vital issues in industrial units is the removal of these sediments. One of the best ways to remove these deposits is to use the acoustic cavitation phenomenon. In order to carry out a successful cleaning, it is necessary to formulate a situation in which the amount of shear stresses appropriate to the sediment particles is introduced. This condition is formulated by considering the proper values for sound and liquid waveforms. The most important of these characteristics are frequency, amplitude of dynamic pressure, viscosity and surface tension coefficient. Hence, the effect of these quantities on the shear stresses introduced in to the sediment should be considered. For this purpose, in this research, a mathematical model is first proposed to describe the behavior of cavitation bubbles. Then, with using this model, the effect of the above mentioned quantites on the bubble behavior is determined. In the next step, with using the obtained data, the velocity distribution generated in the fluid is calculated. Finally, using the obtained velocity distribution, the amount of stresses applied to a sediment will be calculated. The results show that decreasing frequency, viscousity, surface tension coefficient and also increasing amplitude of dynamic pressure increases the shear stresses applied to the sediment. Finally, by calculating shear stresses applied to the sediment, the range of frequency values and the dynamic pressure are obtained for cleaning operations.

In this thesis, the propagation of ultrasonic Lamb waves in homogeneous and isotropic plates with variable thickness has been studied. This work is accomplished with the use of finite element method and ABAQUS software. In the current study, it is assumed that the plate is two dimensional and the upper and lower surfaces of plate are free of any tension and the point force with time delay method has been used for modeling the generation of angular wave. With the use of finite element modeling, at first the propagation of Lamb waves in a plate with constant thickness has been analyzed and validated with analytic solution and then the propagation of these waves in plates with the sudden variable thicknesses (step discontinuity) and non-sudden (symmetric linear and elliptical defects) and the gradual thickness reduction due to the erosion has been analyzed with the use of transmission and reflection coefficients of different modes. The results show that the increase of displacement from the defect for receiving transmission and reflection waves can improve the accuracy of calculation, because it increases the separation of modes. A symmetric thickness variation causes the mode conversion only with the same family of modes as an incident mode, and the mode conversion between different mode families, symmetric and antisymmetric, can be also involved in the case of nonsymmetric waveguides. Study of the elliptical defects with different width show that changes in the wide defects can be distinguished from the crack defects by using Lamb wave technique. Analysis of plates with same defects but different depth show that with the use of Lamb wave technique the changes in the plate thickness can be monitored. And also these waves are sensitive to the erosion width in plates.

 In this study, the propagation of initial symmetric mode (s0) in the overlapped layer joint through applying lamb waves will be discussed. To do so, two adhesive and non-adhesive geometrical connections were modeled in Abaqus (FEM) software. By applying appropriate boundary conditions, a desired lamb wave mode was produced in the upper plate and the same was received in the bottom plate after passing through the connection area. Then, all symmetric, asymmetric, radiation and reflection modes were determined in a double layer aluminum connection. The obtained results of the study indicated that there is no reflected signal from the interface of aluminum layers due to the same material and physical properties of both layers, while in the adhesive joint, part of the radiation waves were reflected because of the layers’ material differences. Also with increasing depth of the defect, the return signal amplitude increases in both types of connections. Among other obtained results, it can be noted that due to the increased length of the defect, the distance between the reflected signals from the beginning and end points of it, was increased. Using these results helped us to calculate the length of the defect. Also by reducing the thickness of the adhesive layer, the received waves amplitude’ were increased via set points after connection area.

Measuring depth of the industrial liquids has many applications such as measuring the depth of fluid in pressure vessels, height of petroleum based liquids in deep wells and level of fuel in storage tanks. Besides the importance of the subject, measuring the level of fluid is impossible in many ways due to flammability nature of fluids in this and impossibility of entrance of measuring tools into the storage tanks and oil wells. There are methods based on use of ultrasonic waves to measure level of fluids without need for contact with the fluids due to simplicity of ultrasonic waves travelling through the storage tanks and oil wells.
Because of low dispersion, ultrasonic Lamb waves can travel through bodies with finite boundaries, such as plates and shells with long length. propagation of ultrasonic Lamb waves depends on frequency, mechanical and geometric properties of body (like thickness of the plate) and produced wave travels with different speeds with different modes. Also, environmental condition of the plate and leakage of the wave to the surrounding can affect the amount of wave energy. This feature can be used in measuring level of the liquids, especially in very deep wells.
In order to measure the variations of the liquid heights by means of ultrasonic Lamb waves propagation, in this thesis, modeling the propagation of ultrasonic Lamb waves in a plate with appropriate boundary conditions is considered. The modeling consists of a segment of plate with surrounding air, and the rest of the plate in the liquid while the wave propagations. The work is done using the finite element method. Results show that leakage of the wave is not happening in the part of plate with surrounding air because ultrasonic waves usually do not propagation in the air but in the other part with surrounding liquid, ultrasonic wave is leaked from the plate into the environment. Leakage of the wave into the liquid makes considerable reduction in wave energy. These energy reductions are plotted. By means of the plots and the differences between forward and backward wave amplitudes, height of the liquid surrounding the plate can be measured.
 

<p>&nbsp;This research, surveys the deformation of AZ31 alloy under the thermo mechanically deformation. Compression test performed between temperatures 300 to 400-550 centigrade and strain rate of 0.1 to 0.0011/s. Test results shows that the stress flow influenced from test parameters (temperature, strain rate). By increasing the temperature, stress flow transfers to the lower stage. Also initial hardening, peak stress and stress decreases to steady stress result to dynamic crystallization. Decreasing the stress stage by increasing the temperature is due from critical parameters for slipping. Increasing the straine rate accompanies with increasing the stress flow. Softening ratio decreases by increasing the temperature. Homogenized and &ndash; homogenized alloys have a different stress stages in similar loads, because of the effect of &gamma; phase on the mechanical specifications. Stress flows from the hot pressure have been modeled by Arniocy&rsquo;s model and obtained activation energy for AZ31 alloy is 145KJ/mol. The results from the Modeling are confirmed by the experiments</p>