Saeed Zohoori; saeed shakhesi
Volume 12, Issue 3 , September 2019, , Pages 15-30
Abstract
Using surface guided wave is one of the most reliable methods of structural health monitoring. Mostly the bulk wave is preferred for identification of internal defects, which is inefficient in localizing the surface cracks. In this paper the procedure of ultrasonic surface wave tomography for crack detection ...
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Using surface guided wave is one of the most reliable methods of structural health monitoring. Mostly the bulk wave is preferred for identification of internal defects, which is inefficient in localizing the surface cracks. In this paper the procedure of ultrasonic surface wave tomography for crack detection in an aluminum plate is investigated and applied for three cracks with the length of 4, 7 and 10 milimeters. Analytical equations and numerical simulations are used to extract dispersion curves as a means for selection of plate thickness and piezoelectric characteristics. Layout selection for transducers and providing numerical and experimental models are the next steps of inspection procedure. All the piezoelectric discs are actuated respectively. Meanwhile, other piezoelectric elements are used as sensors and their received signal is stored in both healthy and defected structures for both numerical and experimental models. Definition of signal difference criteria, signal reconstruction and tomogram generation are the last steps of the procedure presented in this paper.
J. Roshanian; S. M. M. Hassani; M. M. Nazari; M. Aliyari
Volume 6, Issue 2 , July 2013, , Pages 49-56
Abstract
Aerospace Launch Vehicles (ALV) are generally designed with high reliability to operate in complete security through fault avoidance practices. However, in spite of fault avoidance, fault occurring is inevitable. Hence there is a requirement for on-board fault detection and isolation (FDI) without significant ...
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Aerospace Launch Vehicles (ALV) are generally designed with high reliability to operate in complete security through fault avoidance practices. However, in spite of fault avoidance, fault occurring is inevitable. Hence there is a requirement for on-board fault detection and isolation (FDI) without significant degradation in the ALV performance. The robust observers are widely used in FDI due to reduction of the effect of disturbances in the FDI process. In this paper, the robust fault diagnosis observer is designed for an ALV subject to uncertainties. The linear sliding mode technique is used to design the observer for a linear time varying model of an ALV. The parameter estimation from the sliding mode scheme is compared with those generated by a nonlinear simulation and are found to provide good correlation. Then, a proposed linear sliding mode observer is employed to generate the residual as an indicator of predefined gyroscope faults.
H. Bolandi; M. Abedi; M. Haghparast
Volume 6, Issue 1 , April 2013, , Pages 31-46
Abstract
This paper presents robust fault detection based on adaptive thresholds for a three axis satellite. For this purpose, first we described the attitude control system (ACS) as a quasi linear parameter model. Next, an interval observer has been designed that based on, effect of the satellite parameter uncertainties ...
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This paper presents robust fault detection based on adaptive thresholds for a three axis satellite. For this purpose, first we described the attitude control system (ACS) as a quasi linear parameter model. Next, an interval observer has been designed that based on, effect of the satellite parameter uncertainties has been propagated into the alarm limits and so the adaptive thresholds are generated. In this paper, it is shown that the developed method minimizes the missing alarm rates; also this approach detects small or incipient faults more effectively than the classical fault detection algorithms with constant thresholds. In the next part of paper, we propose an isolation algorithm using the fault tree approach. Also, an accommodation system has been designed based on reconfiguration of available actuators. Accordingly, after isolation of faulty reaction wheels, the accommodation system turns them off and replaces the suitable magnetic tourqers instead of the faulty reaction wheels and so the attitude control error is maintained limited.
S. S. Nasrolahi; H. Bolandi; M. Abedi
Volume 5, Issue 2 , July 2012, , Pages 1-13
Abstract
In this study, a fault tolerant Attitude Determination System (ADS) has been designed which provides fault detection, isolation and tolerant abilities in this system. Suggested approach is based on derivation of all possible rotations between body and orbital frames and comparison of Euler angles provided ...
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In this study, a fault tolerant Attitude Determination System (ADS) has been designed which provides fault detection, isolation and tolerant abilities in this system. Suggested approach is based on derivation of all possible rotations between body and orbital frames and comparison of Euler angles provided by them. In this regard, significant changes in the variance of Euler angles set are considered as criteria for fault detection. Moreover, fault isolation and tolerant mechanisms are based on classification of rotation matrices which are not affected by faulty components. The above features present a quite analytical and computational approach which does not impose additional mass, power consumption and cost in the satellite. Also, designed diagnosis and fault correction algorithms are model-free basedmechanisms which always provide tolerated attitude angles for the attitude control subsystem. The mentioned abilities combined with the model based FDI mechanisms utilized in the attitude control system, provide an advanced decision support system capable of isolation of faults which have been simultaneously occurred in the satellite sensors and actuators. Finally, performance of the designed algorithm is approved by simulation results.
