Sharif Digital Repository

Non-uniform rational B-spline (NURBS) curves and surfaces are one of the most powerful tools of computer-aided design, which are able to model both free-form and analytic shapes. In this dissertation, the idea of using NURBS curves as a tool for modeling geometrical deviations and tolerance analysis of mechanical assemblies is presented and evaluated. In the first step the effect of changing the defining variables of NURBS on shape of the curve is investigated. After that, by establishing a relationship between profile tolerance and random NURBS curves, two concepts of tolerance zone width and correlation function are introduced, and a method based on regression algorithms and covariance of... 

Noise pollution is one of the major issues in automative industry. Many of these noises are caused by the internal combustion engine. Using reactive mufflers in the car's exhaust path can effectively reduce this annoying noises. Imposed pressure drop caused by installation this mufflers must be within an acceptable range for the car engine. Resonators, despite having a much lower pressure drop than other components of the exhaust system, can be used to cover the weaknesses of the muffler in the acoustic performance of the noise reduction set. One of the most common methods for designing a resonator is to use perforated plates. In this study the effect of various geometric parameters of a... 

Throughout recent decades, one of the most important and challenging problems in robotics has been robot's path planning. Path planning means a robot must find its way from start to the goal point and track it without any collision to the obstacles. For this aim during the recent decades a wide variety of algorithms such as A*, Dijkstra and … have been proposed that some of which generate an optimal path as their output while others tend to create only a path regardless of its optimality. One of the most practical path planning methods is RRT algorithm which is executable in real-world applications, and by generating some nodes randomly then creating a tree-based graph, thereby outputting a... 

Fatigue life prediction of a mechanical part is one of issues which a group of engineers are engaged with it and always they try to design the parts with the maximum of lifetime. Although many researches have been done in this field but yet we can see that predicted life are different from that happens in the reality because there are some uncertainties in the phenomena. Our effort in this project is creating an algorithm design so that the parts are designed by it, have the maximum fatigue life and the minimum uncertainty in prediction. In this project we have considered geometrical, material and random loading uncertainties as error resources. Older methods those are presented in this... 

Chatter vibration is a major obstacle in high quality machining. This undesirable vibration decreases the production rate, surface quality, tool life and machine tool life. In the last few decades, a lot of models have been presented to predict chatter. Most of the models, whether linear or nonlinear, have focused on modeling of machine tool dynamics and either disregard the effective parameters of chip formation process or apply some of these parameters through simplified equations. In this research, a finite element simulation of chip formation is combined with the dynamics of machine tool to investigate chatter and its effective factors. The proposed approach, unlike common mathematical... 

This world’s commercial and competitive space force’s designers and manufactures to produce and supply products with high quality and low price at desirable level of reliability. On the other hand, during the design and production process, Engineers are always faced with uncertainty. Essentially, uncertainties can be divided into two categories: aleatory and epistemic. Aleatory uncertainties are due to changes in design conditions, material properties, physical dimensions of components and operating conditions. This kind of uncertainty will not be reduced during the life.on the otherhand, Epistemic uncertainties that are due to lack of knowledge about physical nature of systems can be... 

Automated dimensional inspection is commonly expensive because of the requirement for high-precision measurement devices. To perform a precision measurement, the technician must be highly skilled and fully understands the operation of the equipment. Moreover, automation of the mentioned process to reduce dimensional measurement time is a complicated task due to restrictions of precise equipment such as CMM. With the expansion of the use of cameras in the industry, the measurement method with the help of machine vision systems is one of the cost-effective methods that can be achieved with the development of a suitable image processing algorithm to achieve acceptable accuracy compared to... 

The tolerance stack-up in mechanical assemblies is closely related to the quality of finished products and to the costs of production. In practice, choosing a large tolerance range will result in performance reduction. On the other hand, with small tolerances considered, production costs will increase. Tolerance allocation is a useful tool to control the dimensional and geometric variables of the product, so design engineers can control the final product quality level, production cost, and other variables. The proposed method for tolerance design considers the effects of degradation and quality loss over time and allocates tolerances so that, the functional key characteristic satisfies, as... 

Nowadays, the assembly process is planned by an expert and requires knowledge and it is time-consuming. The flexibility and optimality of the assembly plan depend on the knowledge and creativity of the expert, and therefore expertise is an important parameter in developing the assembly plan. Therefore, the use of intelligent methods to plan the assembly process has been considered by many researchers. . The reinforcing learning approach has the potential to solve complex problems due to the use of experience gained from interacting with the environment and Has been successfully implemented in controlling many robotic tasks. However, due to the inherent complexity of the assembly, as well as... 

Today, the additive manufacturing process is one of the most important manufacturing processes. In the additive manufacturing process, the mass of the parts is directly related to the printing duration, in addition to the costs of consumables. On the other hand, the use of lighter parts in industries, such as the aviation, is one of the important requirements of those industries, and topology optimization is needed to reduce the consumables and the mass of the parts. Also, since in the optimal design of engineering parts, more than one design objective is usually considered, the multi-objective optimization of topology is of great importance. The Moving Morphable Components is one of the new... 

Modal analysis is very important in determining the physical properties of structures and mechanisms. This field is divided into two general parts: Experimental Modal Analysis (EMA) and Operational Modal Analysis (OMA). In the operational modal analysis, there are more challenges for the analyst due to the lack of inputs to identify the system. Many of the mechanical structures can not be analyzed experimentally and under specific loadings, but should be identified under actual operating conditions and in situations where the inputs of the system are not measurable. For this purpose, a modal analysis method called "Random Sub-Space Identification" (SSI) is intoduced, which uses only output... 

A mechanical system inherently affected by the conditions, factors and parameters of uncertainty. Without including the uncertainty effects in the optimal design procedure, the mechanical system will not be reliable. To include uncertainty effects in an optimum design, there are two different approaches; the robust design optimization and the reliability based design optimization. In robust design optimization process, the main aim is to enhance the system performance by minimizing the variations. In reliability based design optimization process, the target is that the optimal design variables to be in appropriate reliably levels. In this paper, a new model for the reliability based robust... 

Additive manufacturing (AM)has gained extensive industrial and research attention in recent years. Reducing manufacturing waste, lead-time and costs and the ability to build surfaces and parts with complex shapes, assemblies all at once or parts with internal features are some benefits of AM. However, complex error generation mechanisms underlying AM digital physical chains are likely to result in geometrical inaccuracies of the final product, thus posing significant challenges to design and tolerancing for AM. Therefore, predictive modeling of shape deviations is critical for AM. With increasing volumes and varieties of data, machine learning has gained extraordinary popularity due to its... 

Creating synchronous conditions of precision and speed in rotating systems is a requirement for the design of these systems. The requirement to create these conditions is essential in various applications, such as machine tools and computer equipment. One of the main sources of error in the motion of the high speed spindles is the occurrence of non-repetitive runouts. The presence of non-repetitive runouts at high speeds greatly affects the accuracy of the rotating motion of rotating systems and reducing its effects is always considered in the design of high speed rotary systems. Usually, one of the most important factors in the occurrence of non-repetitive runouts is related to spindle... 

Because of increasing demands for using of rotating systems in high accuracy and high speed applications, in addition of specific condition of rotating systems, it is necessary to analysis these rotating systems characteristics. In addition to the dimensional and geometrical errors of mechanical system parts and assembly errors, manufacturing quality directly depends on Non Repetitive Run-Out (NRRO) errors; so the results of NRRO errors as an ultra-precision characteristic should be studied in required outputs. In this paper by analyzing dimensional and geometrical tolerances as tolerance zone, the variations of system outputs because of tolerances is calculated in both static and dynamic... 

Mechanical production centers are seeking to produce the highest quality products at the lowest cost. Intrinsic processes of manufacturing are not precise processes, and factors such as tool wear, tool vibration and fixation, fixing defects, and other factors that occur during production, make the pieces deviate from the designer's desirable geometry. Usually, due to deviations of parts from their size, their dimensional and geometric characteristics change. Because the components are rarely just a part, often in the majority of parts of the assembly, the operation of the set may be impaired due to the accumulation of changes. Errors that are usually caused during component assembly due to... 

The unique ability of additive manufacturing in manufacturing industrial parts with complex geometries has led to the development of topology optimization methods and their use for the optimal design of parts in various industries. However, considering the limitations of additive manufacturing methods in the optimal design of parts is usually a difficult process, and when making decisions, facing multiple conflicting design goals is often difficult and usually involves high computational cost. The main goal of this research is to provide a topology optimization method for generative design for additive manufacturing based on the concept of constructive solid geometry and using machine... 

In recent years, Additive Manufacturing has been extensively used by various industries. These manufacturing processes produce components in a layer-by-layer manner; therefore, they do not impose any geometric constrains to engineers and provide designers with the freedom to design components. Nowadays, one of the primary goals of all industries is to utilize as few raw materials as possible; this way they can deal with the shortage of raw materials and improve their efficiency. Consequently, they implement topology optimization algorithms to design and produce their components. However, topology optimization algorithms result in complicated geometries that can only be fabricated by AM.... 

The electrohydrodynamic (EHD) 3D printing technology is an Additive Manufacturing (AM) method that can be used in the manufacture of submicron-size structures. Due to the multiphysics dynamics and the multiphase nature of the microdroplet formation in the EHD printers, modeling of this phenomenon is complicated. In this thesis, the formation of a droplet in an EHD printer—under a pulsed electrical field—is simulated using a new numerical model which couples the fluid flow, the electric field distribution and the movement of the electric charges under dynamic and transient conditions. The level-set method is applied to the entire multiphysics domain in order to study the formation of the... 

The process of separating cells from a laboratory sample, is a crucial step in biotechnology and medical science. Cells separation is important for various reasons, including the identification and treatment of diseases, as an example, separation of Circulating Tumor Cells (CTCs) from patient blood sample. CTCs are cells that shed from a tumor and diffuse into blood vessels. These cells are the starters of metastasis, the process in which cancer spreads in body, and are main reason of deaths caused by cancer. Extremely low percentages of target cells in the blood, clarify the importance of highly accurate and sensitive separation. Currently, conventional separation methods are of macro-order...