Sharif Digital Repository

Reliability evaluation is a key factor in serviceability and safety analysis of air vehicles. Structural health monitoring methods have grown to a degree of maturity in many industries. However, there is a challenging interest to tie in SHM with reliability assessment. In this respect, consideration of stochastic structural dynamics with SHM data and random loadings opens a new chapter in failure prevention. The current study focuses on the stochastic behavior of structures as a way to relate SHM data with reliability. In this respect, uncertain factors such as atmospheric turbulence, structural parameters, and sensor outputs are considered in the process of reliability assessment. Firstly,... 

Structural system identification from vibration data is one of the most interesting research topics in the structural health monitoring area. Recently, realization and detection of the effects of damage when a structure is subjected to strong ground motion has become a great concern in earthquake and structural engineering communities. Seismic signal processing is one of the most reliable methods of detecting the structural damage during earthquakes. The structural responses during earthquakes are nonstationary with respect to both amplitude and frequency. The state-of-the-art time-frequency distributions when applied to vibration records were studied. Different methods of analysis for... 

Structural health monitoring is a process that aims to provide accurate and immediate information about the condition and performance of the structure. Processed is a very important eld in the eld of civil, aerospace and marine engineering, because the use of structural health monitoring allows us to increase human and environmental safety while reducing economic damage. e main component of the health monitoring process is the real-time reconstruction of displacement and three-dimensional stress in the structure using a network of strain gauges and other sensors. e inverse nite element method is a relatively new method and stress measurement that has been shown to be fast and accurate for... 

The pressurized structure such as aircraft fuselage and pipeline (in the oil and water transportation) have a great importance in today’s world. There is a growing tendency in improving design factors, safety and maintenance of such valuable structures. Change of design’s philosophy during the time from infinite life to safe damage and safe life and after that damage tolerance, are a process leading to many changes in design and consequently the methods of inspection, evaluation and maintenance. In this way, using old methods like non-destructive test and evaluation (NDT/E) is encountered with different problems when damage is tiny and there is no coincidence in examination (inspection)... 

In recent years world countries faced with the ageing aircraft fleet problem which increased the repair and maintenance costs of these aircrafts. The non-destructive inspection methods are common inspection methods of old aircrafts. To do this, the aircraft must test with a certain time scheduled inspection programme in a hangar. This method not only increased the repair and maintenance costs but also affects the flight schedule. To overcome this problem, the structural health monitoring can use to online monitoring the structure and when it needs for repair, the aircraft send to hanger. So, repair and maintenance costs minimize while the flight schedule less affected. One of the structural... 

In this thesis, due to the importance of pressurized structures, method or methods that can be used to monitor the health of important structures, such as pressurized pipes (gas transmission and distribution lines or hydraulic lines), are considered. A key point in monitoring such structures is to ensure the function of pipes, elbows, Tee junctions, composite to composite and composite to metal joints. The topic that will be discussed more than anything else here is to monitor the health of the structure in the presence of cracks in some layers of composite pieces. In fact, it must be recognized before cracking occurs in all layers of composite pieces and causing overall damage to the... 

In this thesis selection criteria are present for types, numbers and locations of sensors for structural health monitoring of offshore jacket platform in the Persian Gulf. The selection criteria are chosen by studying structural health monitoring of various structures in civil and aerospace industries. Knowing the types of sensors that can be used, a new approach of inverse vibration problem is introduced for structural health monitoring of offshore jacket platforms. In the previous studies, significant numbers of frequencies and mode shapes are usually used to detect damages by updating components of stiffness matrix. Considering the fact that offshore platforms are composed of a heavy... 

The purpose of this research is to monitor the health of structures using the updated finite element model, in which digital images are used to optimize the numerical model. Structural Health Monitoring (SHM) is always an important and significant issue that has attracted the attention of many researchers in recent years. In general, some researches have been conducted in this field using physical sensors that provide discrete data to the system for analysis. Using cameras to monitor the structure makes it possible to extract continuous and integrated data from the structure using digital images, which is a significant advantage compared to physical sensors.In this research, a steel... 

Damage detection of civil structures and infrastructures using partial modal information has been an interesting field of research. So far, three main algorithms are introduced for health monitoring of structures. The first method relies on identifying stiffness and mass properties, as physical parameters, of structures using inverse eigenvalue problem considering mass modifications in 2D and 3D shear-frame models of structures. Comparing the identified matrices with the primary values, one can detect the damage occurrence, its level and severity in the structure. Applicability of this method in health monitoring of offshore jacket platforms as one of noteworthy civil infrastructures has... 

Performance of civil infrastructures, such as high-rise buildings, bridges, tunnels, offshore platforms and other structures may be critically influenced by existence of structural damages or even lead to devastating consequences. Structural Health Monitoring(SHM) and damage detection denotes the ability to monitor the performance of structure, detect and assess any damage at the earliest stage in order to reduce the life-cycle cost of structure and improve its reliability and safety. Generally, damage is defined as some changes in the physical properties of a structure, such as stiffness matrix. On the other hand, presence of damage causes changes in structural dynamic characteristics, such... 

Structural Health Monitoring (SHM) is an effective method for the early detection of structural damage, and this method can reduce the maintenance costs of structures. In this thesis, the use of artificial one-way and multi-layer artificial neural network is evaluated to determine the damage to the structure. The neural network method used in this thesis is a post-propagation method. Finally, the numerically damage determine will be evaluated using a two-dimensional frame structure and a three-dimensional frame structure by finite element method. In this method, the dynamic properties of the structure are used only in the form of the modules. For this purpose, the finite element model is... 

With confidence in the recorded observations, the RLS method no longer estimates the recorded measurements by sensors, i.e. the displacement and speed of the floors, and only estimates the parameters. In contrast, in the EKF method, in addition to estimating the structure's parameters, a more precise estimation of the observations recorded by the sensors has been done by accepting the noise in the recorded observations. These methods, which are based on the Bayesian updating, investigate the two primary sources of uncertainty in a problem: a) measurement noise or observation noise, and b) process noise, which includes modeling errors. In these methodologies, the unknown system parameters,... 

Nowadays a major part of energy, fresh water and sewer water in over the world are transmitted by buried pipe, and always these lines are under the loads and different stresses such as corrosion, earth quick and etc.
In many countries the age of these lines are more than 30 years which causes corrosion of the pipe wall and the necessity of health investigating of transmission lines has a special importance for the governments and leak detection can also keep the natural environment healthyand the costs will come down significantly, scientists and researchers have always tried different ways to check the health of the pipes.
In the field of leak detection and the problems of age... 

Under conventional seismic design strategies, civil engineering structures are designed to undergo inelastic deformation to dissipate earthquake energy, leading to residual displacements and nonlinear deformations in the structure. As a result, there is an essential need for structural health monitoring methods to detect and process these nonlinear behaviors. In this dissertation, a model-free Hysteresis Loop Analysis (HLA) method is developed to identify damage and monitor the structure's performance online, under the earthquake excitations in both severe linear and nonlinear scenarios. The structural models used to validate this method includes three types of one-story, five-story, and... 

Rotary equipment are being used in many industries over a wide range of applications, such as gas turbine. Due to the nature of the operating conditions, gas turbines are subjected to variety of damages especially crack propagation of a blade. The Cracks propagation may lead to catastrophic failure during operation. Therefore, detection of the crack presence and its propagation is very important and may reduce possible significant cost of the whole system failure. The thesis aims to investigate the cracks presence and their propagation effects on vibration of a turbine blade which is located at the National Iranian South Oilfields. First, theoretical study is calculated to validate an... 

Adverse social and economic effects of earthquakes have necessitated the emergence and development of efficient methods to assess and monitor the health status of structures. Many of the structural health monitoring algorithms are based on linear models that are not able to provide sufficient dynamic information. Nonlinear models require monitoring of a larger number of structural parameters and provide a much closer to reality model of the structure. Therefore, the use of nonlinear models in the identification process provides more useful information about the safety and serviceability of post-earthquake structures. Also, most of the existing methods are not applicable for online health... 

Large-size buried pipelines are an efficient way of transporting of water, waste water, sewage, gas, and oil resources in across the world. Since the buried pipe lines are exposed to many unexpected conditions, such as landslides, corrosion, fatigue, unexpected loading, earthquakes, material flaws or even intentional damaging, so the inspection requirements lead to adoption of new method of maintenance, protection and conserving of pipelines. This proposed project aims to improve the trustworthiness, reliable, yet economical technologies for monitoring of behavior of buried pipe lines during operation and assessing the risk of pipe lines failure. Piezoelectric sensor is bonded on the surface... 

Pipeline systems have a major role in civil infrastructure for transportation of energy sources including, petroleum, natural gas, and water. As most pipelines are located in hard-access location such as underground and sea as well as mountains, they are vulnerable to corrosion, cracks and thus, unpredictable failure. Failure of pipelines not only costs millions of dollars but also causes environmental damage, requiring continuous health monitoring systems to provide early detection and early warning of flaws such as corrosion and leaks. Structural health monitoring based on ultrasonic guided waves is used in structures as plates, composites, rods, piping and tubing. This research aims to... 

Offshore platforms are the most important and enormous wealth of each country that these structures are in situation thatthelikelihoodof damageinhigh. With considering this pointthatplatformsaresubjected to oscillatinglateralloads, so the occurrenceand growth offatigue crack sinthe misvery common. These cracks are always seen in jacket connections, cause these connections are bearing large forces and have massive welding and the presence ofresidualstresses. The fatigue crack caused negligible change in stiffness of connections and in consequence insignificant change in stiffness of structure; So for this reason, they are difficult to detect in global methods. Fiber optic sensors and... 

Nowadays, the structural health monitoring is considered as an essential element in improving the performance of the structures. The role and importance of the issues in this area have been reached to the point that different ideas and policies are developed for the safety margin over the useful life of the structures. To analyze more accurately, a real model of a turbine blade is required. This issue would be taken into more consideration when the scale of the turbine gets larger. Changing of the design philosophies over time results in effective changes in the design process and maintenance procedures. Any single of these inspections has different importance according to users' demands. In...