Sharif Digital Repository

In this thesis a comprehensive software code has been developed for analyzing dynamic behavior of rotary systems. Dynamic analysis of rotors consists of calculating critical speeds, mode shapes and vibrational response. The code is also capable to model unbalance, bend and misalignment faults. Due to the complexity of current misalignment models, a simplified model was developed. Rotor, disks and bearings were modeled and joined together to build the complete model. A novel procedure was suggested for modeling of multisectional rotors (such as, Tie-rod and Tie-bolts). Vibrational response has been calculated for each of the faults and effect of shaft and bearing parameters has been observed.... 

In the construction of naval vessels and some merchant ships, stealth to avoid detection is an important design feature. With recent advances in electromagnetic sensor technology, the war time threat to shipping posed by electromagnetically triggered mines is becoming more significant and consequently the need to understand, predict and reduce the electromagnetic signature of ships is growing.
The objective of this theoretical-practical work is to derive solutions to static ferromagnetic problems that include current-carrying coils, uniform inducing fields, and linear and homogeneous ferromagnetic bodies. The solutions obtained with the open source FEMM 4.2 software, is validated by... 

Utilization of the rod fastened rotors in gas turbines as well as induction motors increased recently due to several advantages. Rods in rod fastened rotors are connected to shafts in both sides of the rotors and pre-tightened using bolts in each ends. Predictions of dynamic characteristics of these rotors have specific complications as a result of effects of contact interfaces raised due to applied pre-tightening load. Studies carried out in the field of vibration analysis of rotors consist of investigation of vibration of shafts, bearings and other connected components to the rotors. One of the best methods for modeling and analyzing complicated structures such as rod fastened rotors is... 

Torsional vibration is a phenomenon that caused shear in rotational shafts by out of center torsion. This issue must be considered in design of shafts. Unfortunately,the rules for designing shafts that suggested by standards causes that producers don’t try to usefurther calculation for designing shafts.
In this thesis, at first and by use of finite element method and ANSYS, a shaft of a vesselthat designed based on BV rule was modeled in the software, then, the model was analyzed by modal analysis of the software. In the next level, by specifying the defect of designed shaft, optimizing of shaft’s system to minimize the first torsional natural frequency is applied. In this case, by use... 

Nowadays because of population growth and limitation of fossil fuels for power generation purpose, utilization of renewable energy sources has become highlighted. According to the geographical situation for use of wind energy, since some areas of Iran are in suitable conditions the manufacture of wind turbines and installation in wind farms has been under development recently. Monitoring the performance and operation of turbines and wind farms is an inevitable matter. Because of the suitable geographical location of Iran and pursuant to fair wind potential sites widespread this country, this phenomenon requires some backgrounds in many aspects to be achieved. One of the most important... 

The employment of strategies with low operational and capital investment to reduce ship's voyage costs is gaining considerable attention. With rising fuel prices, shipping companies are concerned with the increase of fuel costs of the ships. In this research, the smart steaming strategy, including the simultaneous optimization of ship's sailing route and speed, is proposed as an efficient alternative for the slow steaming to minimize ships' fuel consumption and voyage costs. By implementing the smart steaming strategy, ships owners can ensure that the ship sails at the optimal and safe sailing route and reaches the destination port on time. In addition, the proposed shipping strategy can... 

The ability to predict the remaining life of bearings is one of main aspects for improvement of reliability of bearings. However, techniques to predict the lifetime of a bearing under the practical operating conditions have not been well developed. In this thesis, prognostic model for bearing systems based on vibration response analysis is considered as a single-degree-of-freedom vibratory system. As the bearing system is considered as a single-degree-of-freedom vibratory system, its acceleration amplitude at the natural frequency can be related to the system stiffness. Moreover, the relationship between failure lifetime, running time and stiffness variation can be established from the... 

Regarding the increasing application of fast boats in the world, studying the dynamic performances of these boats is consequently effective and vital. So one can evaluate the hull performance in different sea forces. Vast activities take place in all over the world yearly. General performances hull tests occur in marine laboratories such as Wave maker and carriage. Model hull test is one of effective branches of the naval architecture engineering. This method is also based on dimensional analysis. In this thesis, after understanding the waves and the methodology some experimental tests are done in the conditions of frontal static waves, and heave, pitch and roll activities of the craft are... 

Reciprocating Machinery are one of the key components of chemical and petrochemical plants and their down time cause loss of production. Therefore condition monitoring in these machinery is of special interest and high value. In this thesis first, different methods of condition monitoring for reciprocating compressors are introduced then the main cause of high vibrations of three compressors in a refinery is investigated. Finally by using the foundation model prepared, it would be shown that insufficient strength of foundation block has lead cracks initiation and development in these foundations. Therefore high vibration is consequence of weak design  

Atomic force microscope (AFM) has a significant capability of imaging surface topography on an atomic scale. It is also widely used for Nanolithography in MEMS/NEMS (micro/nanoelectromechanical systems). Although the conventional AFMs have a significant capability of nano-scale surface measurements, their probe tips cannot come in close proximity to the sidewalls, no matter how sharp they are. Therefore, no accurate nano-scale measurements at sidewalls and edges can be achieved by these conventional AFMs. In addition, regarding the increasing applications of micro-structures such as micro nozzles, micro gears, micro holes and micro trenches which all of them have sidewalls and edges,... 

In this thesis, we intended to examine the noise of typical Marine Propeller. Regarding the noise source, which are due to the energy transfer to the fluid and variation of fluid force, propeller noise has been investigated in two cases. In the first case, in constant depth, the distance of hydrophone with the propeller varies. In the second case, the distance remains constant and the depth of both propeller and hydrophone has been changed, in four positions. Due to the limitation of the test tank, a pool of (5m*5m*5m), the experiments has been carried out according to the Naval Underwater Systems Center. In the second part of this research, the numerical modeling of the propeller acoustic... 

Ship maneuverability is so important from different aspects. According to the regulations of International Maritime Organization (IMO), every vessel has to meet the minimum requirements of mentioned rules. Consequently, prediction of ship maneuverability in early stages of the ship design has become to one of the most necessary steps for shipbuilding and design companies. In this research work maneuvering of a high speed ship has been investigated using three different propulsive modes, considering propeller and rudder systems, azipod propeller and waterjet systems. First of all, hydrodynamics equations of each cases while considering different motion modes such as surge, sway, yaw, and roll... 

One of the reducing and controlling tools of high speed crafts is intelligent interceptor. Interceptor is a small blade that is originally installed vertically in stern. This blade creates a high pressure area under hull of the craft and produces lift force and a moment to the bow. The amount of lift force and moment can be changed by controlling the height of the blade. The intelligent interceptor (with automatic change in height of the blade) does the same thing. In this study, structural and software design of intelligent interceptor is done. In software field, optimal and PID controller are designed for interceptor system and the performances are studied in MATLAB SimuLink. The results... 

Interceptor is a blade installed on planing hull transom, and it helps the planing performance by making an stagnation point on aft part of the hull thus generating a lift force and reducing the planing trim. In the present study a numerical modeling of a planing hull in still water has been made and the effect of an interceptor in the numerical model has been studied. Then by validating the model with and without the interceptor through experimental model testing, it has been used for modeling a planing hull in waves with an interceptor. The numerical modeling has been made using 2DOF analysis in Ansys-CFX and the experimental model tests have been done in Mechanical department of Sharif... 

For observing the beauties of the sea, underwater vehicles are of the most appropriate equipment. In an optimized design of a vehicle, one should consider all applied forces and moments at all positions of the vehicle. Moving near the free surface is one of the positions of underwater vehicles. So, study on flow around a body moving near free surface is the subject of extensive research in marine hydrodynamic.
The aim of the current investigation is a scrutiny of the influence of free surface effect on the flow around underwater vehicles. For this purpose, finite volume method is used to simulate flow around an axisymmetric body near free surface. In this simulation, volume of fluid... 

Nowadays, regarding the wide achievements in micro scale technology, it is possible to manufacture a micro robot. Micro swimmer have extensive applications in different fields especially in medical sciences. One of the most important problems of the micro robot is their propulsion system. The locomotion of microorganisms in fluids is ubiquitous and plays an important role in numerous biological processes. The physics of swimming governing life under the microscope is very different from the one we experience in the macroscopic world. This project is aimed at designing a propulsion system for a micro swimmer based on the swimming mechanism of the eukaryotic Spermatozoa. Simplicity to build is... 

In the ship designing, it is preferable to access to a good performance in waves and low efficiency loss. Accordingly, modeling and estimation of added resistance would be an important issue. Added resistance in wave is an important part of ship's performance due to many technical and economic effects on the ship's performance. With understanding and awareness of the added resistance that comes from ship accident to the waves, we can reduce this parameter by changing in specifications and hull form of ships. Designers are also interested in optimizing the ship from this aspect. In previous works, added resistance in waves was obtained from experimental, numerical and analytical methods. In... 

The orientations which predominate in a final orientation distribution resulted from a specific deformation mode are the ideal orientations. There is a set of ideal orientations for each of crystal structures under a predefined mode of deformation. Ideal orientations are one of the material characteristics in the applied mode of deformation. The material texture strongly influences its final properties and affects the material behaviour in the subsequent forming processes.
In this project, final texture of 1010 steel sheet resulted from simple tension mode of deformation is investigated computationally and experimentally. The calculated texture based on the simulation procedure is... 

Design optimization of ships by taking maneuverability in account has great influence on the performance of the vessels. Thus providing a method to predict the behavior of vessel in the design process is very important. Ship maneuverability is remarkable from different aspects of view. Especially in high speed vessels of various applications and missions’ good maneuverability would be a positive rating for it. For example, military vessels in specific situations need to change the speed and direction and this is a crucial capability of them. Also in accordance to the rules of IMO all of the vessels should perform maneuvering trials and fulfil the minimum requirements. Accordingly, this issue... 

Rolling bearings are important parts in rotating machinery. Unsuitable practice of this bearing causes unsuitable output in this collection. In some machines like helicopters, sudden faults of this rolling bearing cause body dangers. According to this point, diagnose of bearing fault is an important case in condition monitoring domain. There are many ways for diagnose of fault in bearing which most of them are important subject in signal processing. In this project first of all, the most important and applicable signal processing methods, which are useful in diagnose of fault in bearings are introduced then three of these methods are chosen and applied on time signals of experimental...