Sharif Digital Repository

In this study an internal combustion rotary (Wankel) engine and its specifications is analyzed and the proper lubrication system is described. The acceleration acting on apex seals, and engine speed fluctuations together with the leading and trailing cells gas pressure forces are analyzed in the present work using the second Newton law. The research shows that cell gas pressure effects are important and inclusion of these effects will provide results which are more compatible with the reality and lead to a much more accurate analysis of the system. Theoretical calculations reveal that gas cell pressure forces represent about 78% of the overall calculated force and ignoring these pressure... 

In this thesis, modeling and robust sliding mode control of a snake-like robot with holonomic constraints in tracking of desired paths such as serpenoidal motion is addressed. By considering more real conditions and holonomic constraints, the kinematic and dynamic equations of a semi active robot are obtained using Kane's method. In the next step, based on the obtained results, diverse control theory for getting ability of tracking different paths in environment with different frictions are investigated. Robust control theory is chose to design a controller that has ability of adaption robot’s motion in different environments. For this reason, Sliding Mode Control that has many applications... 

Nowadays, the use of gas turbines with low capacity have acceptance in large quantity. This type of gas turbines with a capacity of approximately 5-200kW are known as microturbines. This type of turbines due to the existence of limitations on increasing of turbine inlet temperature and compressor pressure ratio has low efficiency compared to the turbine with high capacity. Therefore the use of a recuperator in the cycle is necessary. Optimum design of heat recuperator has important effect on improving of gas turbine cycle efficiency. In this project for optimum design of heat recuperator, the effect of recuperator on gas turbine cycle efficiency is studied. By determining geometric... 

In this thesis, a shape optimization technique is presented for powder forming processes based on the genetic algorithm approach. The numerical modeling of powder compaction simulation is applied based on a large deformation formulation, powder plasticity behavior, and frictional contact algorithm. A Lagrangian finite element formulation is employed for large powder deformations. A cap plasticity model is used in numerical simulation of nonlinear powder behavior. The influence of powder-tool friction is simulated by the use of penalty approach in which a plasticity theory of friction is incorporated to model sliding resistance at the powder-tool interface. For hot compaction process coupled... 

A finite element model for seismic analysis of concrete arch dams is proposed. Material inelasticity as well as joints nonlinearity is considered. In order to provide a precise description of concrete response, a novel plastic-damage constitutive model for plain concrete is developed. For this purpose, the microplane theory is proposed for overcoming the deficiency of available anisotropic continuum plastic-damage models in reproducing the true anisotropic nature of damage in multidimensional loadings.Based on the microplane theory, the degeneration process in concrete is considered along with plastic deformations. Using the principle of strain energy equivalence, a transformation between... 

We propose a model for friction between two rough surfaces based on extreme value statistics (EVS). Different models for single-asperity contact, including adhesive and elasto-plastic contacts, were combined with EVS. The Hertzian model for contacts and Gumbel distribution for summit heights show the closest conformity with Amonton’s law. The range over which Gumbel distribution mimics Amonton’s law is wider than that of the Greenwood–Williamson (GW) model. In comparison with other EVS distribution, Gumbel distribution seems the proper choice for summit‘ s height. Interestingly, here again, elasto-plastic contact and Gumbel distribution for summits achieve the best conformity with Amontons... 

Hospitals are considered to be environments for employing social robots. However, it is necessary to provide conditions for the operation of these robots in such environment. Factors such as slippery and sloping surfaces, as well as the risk of falling robots from impact by the patient or other factors, cause the performance of these robots in these environments to be difficult. Friction and slip is a challenge posed by the path tracking mission in the hospital environment for these robots. In this regard, one of the objectives of this project is robot control to track the path on the surfaces in the event of a slip. The robot studied in this project is omnidirectional robot including... 

A lack of appendages makes snake motions simpler in some respects than those of other locomoting animals. Most of the researches done in this area has assumed that the normal force distribution of the snake is uniform along its length. But, observations of snake locomotion show that snakes tend to lift their body during movement, which means they dynamically change the distribution of normal force along their body. In this study, we addressed this issue and succeeded in formulating the snake’s normal force distribution systematically. This project has been conducted in two stages. In the first stage, we speculated uniform normal force distribution and verified our snake model by comparing... 

The primary objective of this study entails the examination of the impact of lubricants intended for implementation in the compaction process of nano-powders, intending to mitigate friction at the nano scale during compaction. Molecular dynamics modeling is employed to scrutinize this phenomenon and derive the friction parameters within the framework of equations derived from continuum mechanics, based on data acquired from the nanoscale investigations. The manufacturing procedure of metallic components from metal powder compaction necessitates the application of immense pressures, thereby engendering notable friction between the powder particles and the confines of the mold. Consequently,...