Sharif Digital Repository

Supplying water has almost always been the essential need of human for agricultural, industrial and drinking water use. One of the infrastructure works to catch up to this goal is dam construction. Among all of dams, concrete gravity dams have been fortunate between designers and builders of dams, because of their acceptable function against seismic loads. So, analyzing the function and stability of dams is important in different cases. Formed crack in dam body is one of the most important parameters that affects both the function and durability of a concrete gravity dam and considering the measure of the earthquake effects on the formation and expansion of crack profiles many studies have... 

In this thesis, an extended nonlinear model of peripheral milling process (2D) is presented. For the first time, cutting forces are described through a complete third order polynomial function of the axial depth of cut. Also, cubic nonlinearity is considered for the structural stiffness as a function of tool tip displacement. To complete the model, process damping and tool wear effects are also considered. A set of experiments including modal tests to determine natural frequencies and structural damping ratios; and also cutting force measurements at different feed rates to determine nonlinear cutting force coefficients, are carried out. Also, measurement of critical axial depth of cut at... 

Tire is one component of the suspension system and has beneficial effects on reducing vibrations caused to the vehicle. This study aims to determine the factors affecting the damping and stiffness of the tire is carried out. The modeling of factors were identified. For testing the modeling effort is to be made to the instruments used to measure the damping and stiffness of the tires. To make the structural static analysis, dynamic and modal was to have sufficient structural strength and the displacements and stresses are sensibly placed. Factors that have influence on the hardness of the ring diameter, the outer diameter of the tire, tire pressure, tire tread depth, tire wall thickness,... 

Since the early 1980s, it is well-known that the dynamic properties of structures are effected by flexibility of the underlying soil due to Soil-Structure Interaction (SSI). As a result, the soil-structure systems usually has a longer natural period and higher damping ratio that structure would have in the fixed-base state. The importance of SSI effect as well as the complexity of the phenomenon have made it the subject of several researches for the last four decades. It also has found its way into some seismic codes and provisions as simplified guidelines.In the present paper, a simplified 3DOF model is suggested as the soil-structure system by replacing the structure by a SDOF model using... 

As long as the wind power penetration is low, overall dynamic behavior of a power system is determined by the interactions of system synchronous generators, but introduction of large amounts of new wind generation can affect the power system behavior. In this research, the impact of large wind farms on the small signal stability of power systems is studied. Because constant wind turbines are not very conventional in today’s wind industry and the dynamics of full converter wind turbines are isolated from power system, in this study only the doubly fed wind turbines are considered. In this order, a novel index is introduced to analyze the impact of doubly fed wind farms on the damping of... 

Mutually coupled oscillator arrays may be used for power combining at the millimeter-wave region. In addition, these arrays have the capability of beam steering without the use of any phase shifter. Using the strong coupling method is inevitable to obtain synchronization between all elements in the large arrays. One of the challenges in strongly coupled oscillators is the multi-moding problem or oscillation at undesired frequencies. In this thesis, we obtain mode distributions in a one-dimensional and a two-dimensional array with rectangular boundary, using a method based on circuit equations in the frequency domain. Then, we compared the results with the previous works and also verified... 

In this study, the ST14 low carbon steel sheet was used as a skin layer in the construction of three-layer laminates. The use of this steel was due to its high mechanical properties and excellent formability. A thermoplastic polyurethane sheet was also used as the core layer. The selection criteria of this polymer were no need for adhesive (for bonding metal to polymer) as well as proper mechanical properties (elongation and strength) and physical (density). The perfect process for manufacturing three-layer laminates is the roll bonding process. To manufacturing a laminate with the desired properties of the designer, the rolling parameters (rolling speed and thickness reduction) must be... 

The current design procedure known as Force-Based Design (FBD) method, generally, does not lead to uniform distribution of drift, hysteretic energy, and ductility demands (or structural damage) along the height of the moment frames under strong earthquakes and these performance parameters can be much higher and concentrate damage on one or more of the lower structural stories. This paper presents an iterative wave propagation (WP) based technique to calculate the seismic nonlinear response of multistory buildings as an extension of the layered soil media, founded on bedrock and subjected to vertically propagating shear waves, which leads to the introduction of a new Lateral Load Pattern... 

This thesis aims to provide a method for obtaining the dynamic properties, including stiffness and damping, of rolling bearings in radial and axial directions using an experimental approach. Experimental and laboratory methods such as modal testing, vibration testing, and static tests are recognized as practical approaches to obtain these properties. In this research, all three of these methods were employed to determine these properties. After studying the theoretical relationships governing bearing stiffness coefficients, a test setup was designed and constructed for conducting experiments. Subsequently, various tests were conducted, and data was collected, including shaft displacement... 

This thesis aims to provide a method to obtain the radial dynamic properties of rolling element bearing, including stiffness and damping by experimental test methods. Methods such as modal test, vibration test, and static tests were known as experimental methods to obtain these properties, and in this research, all three of these methods were used to obtain these properties. After studying the theoretical relations governing the stiffness coefficients of the bearings, a test bed platform was designed and built to conduct the tests After the construction of this platform, the test design stage was reached done and different parameters changed during these tests several tests were it is noted... 

In this thesis, free vibrations of a three-layer conical shell with two FG layers and an electrorheological intermediate layer have been investigated. Also, the effects of electrical field and the FG power index that a constant related to the composition of the FG material in the shell vibration parameters (natural frequency, damping and mode shapes) have been investigated. For modeling the viscoelastic behavior in the electrorheological material, the Kelvin-Voight model and for modeling shell structure the FSDT shell model was employed. Also, in order to obtain the displacement field in the middle layer, a suitable assumption for continuity between different layers of the shell has been...