Sharif Digital Repository

A structural system will normally fail as a result of a chain of failures of different components. In this thesis, fatigue reliability of fixed offshore platforms is investigated through analyzing different failure scenarios. In order to evaluate the occurrence probability of a special scenario, each failure scenario is divided into a finite number of sub-scenarios. To do this, all combinations of time sequences are generated for a given sequence of failures, using a specially developed program.
In order to calculate the occurrence probability of each scenario, a massive reliability analysis should be done for each of corresponding sub-scenarios. Knowing that there are a large number of... 

The detuning of the structures equipped with Tuned Mass Dampers (TMDs) caused by their nonlinear behavior under strong ground motions is a real concern in their practical application. This thesis presents a feasibility study on the effectiveness of TMDs in reducing the seismic response and the resulting structural damage of reinforced concrete structures under intense ground motion. A number of 2-D concrete moment resisting frames with different numbers of stories are considered. TMDs are used as a mean to protect these structural models against ground excitation. The mass of TMDs are varied from 1% to 5% of the first effective modal mass of the structural models. IDARC 2-D program is used... 

In this thesis, a novel probabilistic framework named Probabilistic Spectral Fatigue Analysis (PSFA) will be introduced for the purpose of assessing the performance of jacket offshore platforms under high-cyclic short-waves fatigue degradation. This method can take into account the uncertainties in three main elements consisting of material properties, sea state parameters and collapse capacity of structure. The main advantage of PSFA approach is the ability to recognize the fatigue failure scenarios and specifies the limit state function of critical members as a super-branch or sub-branch of those scenarios. Therefore, a new and accurate method is proposed for combination of scenarios’... 

In order to improve the fatigue performance of torsion bar, induction surface hardening is performed. The aim of the present study is failure analysis of torsion bar and improvement of manufacturing process. Induction hardening was simulated using finite element method. As a result temperature history and residual stresses were obtained. Temperature and residual stress distributions are affected by the component geometry, the material behavior and the induction treatment parameters. Based on the residual stress distribution and the external fatigue loads, cracks can nucleate from the surface or below the hardened layer. Therefore, it is very important to determine the residual stress... 

This research has been worked out in two main parts and it is tried to reach a high level of Safety Integrity in Safety Instrumented Systems using in Oil, Gas and Petrochemical industries. The first part involves an overview of system risk analysis and initial investigation of Safety Integrity Level as a new parameter in safety instrumented systems which are very important section of Safety engineering during last couple of years. According to the fact that the available papers and articles in this area are very limit; we have faced a lot of problem in doing research and actually to be honest; all available resources have been focused plus the related standards. The second part is about... 

One of the most common failure modes of structures in earthquakes is soft story failure which causes by discontinuity of lateral force resisting elements like braces. so the ground floor acts as a soft floor. In this case columns are imposed to large deformation and plastic hinges are formed at top and bottom of the columns. This case is named as story mechanism (severe drift of the story). In most of this case building collapsed or going to collapse. To resolve this problem, different solutions are presented. One of the strategies under section (2-10) 2800 code is increase of designed load in columns of the soft floor. This measure cause to Significant increases in the sections of the... 

Complex networks serve as generic models for many social, technological and biological systems that have been shown to share a number of common structural properties such as power-law degree distribution and small-worldness. These networks determine interactions and influence the spread of diseases, behaviours and ideas. Epidemics and failures like new behaviours ideas and innovations can spread throughout a network and prevent it from doing its functionalities. In this work, we investigate error and attack tolerance of epidemic spreading in complex networks. The main content of this thesis is arranged in three sections as follows: Firstly, the effect of random and systematic failures is... 

Despite of many advantages, electro submersible pumps (ESP) have very high costs in maintenance. Since ESP usually operates in deep wells, it should be transported to the surface in order to malfunction. In addition, the state of ESP equipment cannot be determined because of unavailability of vibration measurement on the site. Thus, this equipment fails suddenly. This process costs a lot on country’s oil and water & wastewater industry. so in this thesis, at first, the potential failure modes (PFM) of ESPs are investigated, then proper methods are presented for condition monitoring. Finally, the presented methods are verified by experimental tests and wavelet analysis. The results show that... 

Station Blackout (SBO) involves Loss of Offsite Power (LOOP) concurrent with failure of the onsiteemergency ac power system. Although SBO is a beyond designbasis accident, in recent years this accident attracts a lot of attention. Fukushima nuclear accident which was initiated by earthquake followedby tsunami led to a SBO accident. In this thesis, Probabilistic Safety Assessment (PSA) is applied to analyze SBO in IR-360 nuclear power plant and to compute its frequency. Meanwhile, weak points of the plant are identified in order to minimize the SBOprobability of occurrence. Fault tree method is used to evaluate emergency power system and offsite power system reliabilities. Common Cause... 

This thesis presents a method to solve a redundancy allocation problem for the series-parallel system. The modeling formulation deals with the choice of the best redundancy strategy, component and redundancy level for each subsystem in order to maximize the system reliability under system-level constraints. Majority of the solution methods for the general redundancy allocation problems assume that the failure rate of components is determined. However, in practice variable failure rate may be used. The complexity of this problem is known as NP-hard and therefore the optimal solution is not accessible in the normal course of events. It is demonstrated in this thesis that genetic algorithm is... 

In the absence of appropriate control, several accidents in the nuclear power, lead to serious consequences including core melted and radiation leakage outside reactor containment. In all these events, when core melted, the reactor operation is always finished and all efforts are then directed to environmental impacts of radioactive materials to the external environment. However, the occurrence of events that would bypass reactor containment, have special significance, because all possible efforts in order to limit the leakage of radioactive materials to the external environment are ineffective. In this respect the occurrence of such incidents, as most of which is considered the worst... 

Fault occurrence is an inevitable problem in industrial plants. These faults have numerous types. Some common kinds of faults are faults in actuators, faults in system dynamics, and faults in sensors. In many cases it is not possible to change or repair the broken part immediately. On the other hand, it is not reasonable to shut-down the whole system due to a minor failure. Therefore we should take a measure to have the best output possible in a faulty plant. In this thesis we have proposed a new static compensator by which we distribute the contribution of the faulty actuator among the other ones. At the end we evaluate the method by means of simulations  

This document, is the thesis on the field of science and technology policy. The subject is the analysis and explanation of engineered innovation networks based on process approach and by using knowledge base concept. The failure of networks is one of the causes of the failure in the innovation systems, so the analysis of the phenomena would be very important for innovation policy makers for networking. The two main questions of this study are:
a) How do engineered innovation networks fail in the initiation stage?
b) How could we explain this process by using the concept of the knowledge base of innovative activities? During this study, which has beed done based on the... 

Explosion as a physical phenomenon have various effects on the environment, including living organisms, surrounding buildings, equipment and infrastructure there. Due to such extreme loading conditions, efforts have been made during the past three decades to develop methods of structural analysis and design to resist blast loads. The analysis and design of structures subjected to blast loads require a detailed understanding of blast phenomena and the dynamic response of various structural elements. The most appropriate method for evaluating the behavior of structures under blast loading is performance approach which specifies the response of structures against explosion. It seems that... 

Congestive heart Failure (CHF) which occurs when the heart is no longer able to pump the blood sufficiently is a worldwide growing health concern. In the U.S. alone, an estimated 8 million people will be diagnosed with heart failure by 2030.Cardiac transplantation with limitations in donor availability, cannot solely resolve this global health concern. Therefore many patients must use alternative remedies, namely Artificial Heart and Ventricle Assist Device (VAD). The Left Ventricular Assist Device (LVAD) is a mechanical pump that is implanted in patients with congestive heart failure to help the left ventricle in pumping blood to the circulatory system. They are known to... 

Experimental investigation of drillstring dynamics is essential to complete the theoretical studies and to alleviate complexity of such dynamic models. Vibration is one of the most effective parameter affecting drilling operation. Most of the experimental setups are looking for drilling mud tests, operational characteristics of bit under several bad condition and bit mud stone interaction in drilling operation and there are few setups to study vibration of the drilling setups. In this project a test rig has been introduce which is a scale of a real industrial drilling rig by the factor of 10300. Then based on the field studies of drilling failures in Iranian oil drilling rig , a crack has... 

The objective of this study is to evaluate the seismic vulnerability of the existing buildings subjected to the near field earthquakes. The main applications of this research are loss estimation and performance evaluation of the existing buildings. That could provide a better solution and particularly more useful information to the owners, investors, and insurers about the expected performance of buildings under earthquake excitations. A number of 2, 5 and 8 story reinforced concrete buildings, designed according to the old Iranian seismic provisions of ISIRI-519 and ACI 318-83 codes for the ordinary moment resisting frames, are considered. By the use of a number of near field earthquake... 

The main purpose of this study is the analysis of low velocity impact on the light weight sandwich beams. Some parameters such as weight, failure mode, and impact energy absorption capability are very essential in the design of sandwich beams. The failure mode map is a technique to design sandwich structures, in which no single component is over-designed with respect to other components. In this study, the failure mode map of foam core sandwich beams composed of E-glass/Epoxy and PVC foam is drawn and investigated by an analytical method. For this purpose, displacement relations for bending of a sandwich beam are written using higher order theory. In addition, the sandwich beam is modeled... 

Monitoring a surgical process has gained prominence by accounting for patiens̛ health condition prior to surgery in recent years. How even most existing researches focus on phase 2 monitoring and binary outcomes. Very little work has been done on phase 1 control of outcomes and no one addressing the issue of phase 1 monitoring of continuous outcomes. Risk adjustment is accomplished using accelerated failure time (AFT) regression models. In this thesis a general phase 1 risk-adjusted control chart is proposed for monitoring continuous surgical outcomes based on a likelihood-ratio test derived from a change-point model. Different from the existing models, this thesis shows that continuous... 

One of the most important connections in a structure is the column base plate connection. In structures subjected to earthquake loading, this connection is usually where a plastic hinge can develop and therefore is of utmost importance. In this paper, behavior of base plates under monotonic and cyclic loading is investigated. The failure modes, that are one of the fundamental targets in this study include base plate yielding, anchor bolt yielding and also failure arising due to crushing of concrete. A parametric study is conducted using nonlinear finite element analysis. Parametes such as plate thickness, anchor bolt size and location and concrete strength are considered. The desired...