• Smart Structures and Systems
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• v.25 no.4
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• pp.459-469
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• 2020

The presence of cracks in mechanical components is a very important problem that, if it is not detected on time, can lead to high economic costs and serious personal injuries. This work presents a methodology focused on identifying cracks in unbalanced rotors, which are some of the most frequent mechanical elements in industry. The proposed method is based on Artificial Neural Networks that give a solution to the presented inverse problem. They allow to estimate unknown crack parameters, specifically, the crack depth and the eccentricity angle, depending on the dynamic behavior of the rotor. The necessary data to train the developed Artificial Neural Network have been obtained from the frequency spectrum of the displacements of the well- known cracked Jeffcott rotor model, which takes into account the crack breathing mechanism during a shaft rotation. The proposed method is applicable to any rotating machine and it could contribute to establish adequate maintenance plans.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.15 no.7 s.100
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• pp.781-787
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• 2005

The correlation dimension can provide some intrinsic Information of an underlying dynamic system by reconstructing measured nonlinear time series. The vibration signals measured from a rotor with different clearance sizes between shaft and bushing were analyzed using the correlation dimension. The results showed that the correlation dimension can identify the size of the clearance of a rotor and the lubricating condition, which can not be analyzed by frequency spectrum or wavelet. The magnitude of the correlation dimension became smaller as the clearance larger and as the lubrication condition better.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.13 no.1
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• pp.48-55
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• 2003

Hidden Markov Model(HMM) has a doubly embedded stochastic process with an underlying stochastic process that can be observed through another set of stochastic processes. This structure of HMM is useful for modeling vector sequence that doesn't look like a stochastic process but has a hidden stochastic process. So, HMM approach has become popular in various areas in last decade. The increasing popularity of HMM is based on two facts : rich mathematical structure and proven accuracy on critical application. In this paper, we applied continuous HMM (CHMM) approach with AR coefficient to detect and predict the chatter of lathe bite and to diagnose the wear of oil Journal bearing using rotor shaft displacement. Our examples show that CHMM approach is very efficient method for machine health monitoring and prediction.

• Transactions of the Korean Society of Automotive Engineers
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• v.11 no.2
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• pp.89-95
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• 2003

We consider a problem of application of analytical redundancy to engine synchronization process of spark ignition engines, which is critical to timing for every ECU process including ignition and injection. The engine synchronization process we consider here is performed using the pulse signal obtained by the revolution of crankshaft trigger wheel (CTW) coupled to crank shaft. We propose a discrete-time linear model for the signal, for which we construct FDI (Fault Detection & Isolation) system consisting residual generator and threshold based on linear observer.

• Journal of the Korean Society of Safety
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• v.11 no.2
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• pp.42-51
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• 1996

Taper roller bearing is used on rotating shaft where radial and thrust loads are attended. To avoid the sudden failure and maintain the good condition of rotating machinery it is necessary to monitor the condition of bearing and diagnose the defect of bearing. In this study the diagnosis program of taper roller bearing which is used on the lower bearing of V.A.W.T. (Vertical Axis Wind Turbine) is developed. By plenty of test the database is constructed and by Gaussian distribution obtained from database the defect probability of bearing is calculated.

• Clinics in Shoulder and Elbow
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• v.20 no.3
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• pp.172-179
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• 2017

Indications of reverse total shoulder arthroplasty (RTSA) have been consistently extended by technical advancements in reverse arthroplasty prosthesis, continuous development of the implants, accumulated experiences and its successful treatment outcomes; accordingly, its use has rapidly increased. RTSA has been performed for a variety of indications, with variable outcomes depending on the initial diagnosis. However, controversial opinions still exist regarding the design of reverse arthroplasty prosthesis (medialized or lateralized design and the neck-shaft angle of the humeral prosthesis), suture of the subscapularis tendon, use of cement during placement of the humeral prosthesis, and surgical procedures; therefore, these should be investigated so that they can be better understood.

• Journal of Korean Foot and Ankle Society
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• v.18 no.2
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• pp.43-47
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• 2014

Hallux valgus is a lateral deviation of the first phalanx and medial deviation of the first metatarsal at the first metatarsophalangeal (MP) joint. Its incidence has increased due to developing footwear. The etiologies include fashion footwear, genetic causes, anatomical abnormality around the foot, rheumatoid arthritis, and neuromuscular disorders. Physiologic alignment of the first MP joint is maintained by congruent and symmetric alignment of the articular surface of the first proximal phalanx and first metatarsal head, physiologic relationship of the distal first metatarsal articular surface and the first metatarsal shaft axis, and stable balance of soft tissue around the first MP joint and stable tarsometatarsal joint. Several factors have been associated with hallux valgus, including pes planus, hypermobility of the first tarsometatarsal joint, flattened shape of the first metatarsal head, increased distal metatarsal articular angle, and deformation of the medial capsular integrity. History and physical examination are very important to diagnosis of hallux valgus. Simple radiography provides information on deformity, particularly in weight-bearing anteroposterior and lateral radiographs. Understanding the etiologies and pathophysiology is very important for success in treatment of patients with hallux valgus.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.65 no.6
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• pp.1103-1107
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• 2016

The automatic tensioning device of the catenary system constantly maintains the tension of the trolley wire by absorbing the variations due to the elasticity of the line caused by temperature variation. The tension plays an important role in affecting the electric motorcar operation directly. This paper suggests the methodology of the life cycle extension and the maintenance of the automatic tensioning device by means of performance diagnosis of the pulley type automatic tensioning device which has been commonly used for the electric railway system. Through conducting performance diagnosis and comparative test for the wornout pulley type automatic tensioning device by replacing the components such as the bearing and the bearing shaft without replacing all the assembly, the tensioning device is analyzed whether it is properly functioned. Provided that the maintenance regulation is reinforced so as to implement the bearing replacement through periodical precise inspection along with random check-up inspection which is now carried out by the operating organizations, it is ensured that the life cycle extension and the reduction of maintenance cost of the tensioning device could be achieved.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• v.y2005m4
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• pp.252-255
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• 2005

The operation of a gas-turbine engine gradually deteriorates the performance of its main components and often generates the defects of its components. The GPA method has been usually used for the diagnosis of the deterioration. In this study, the diagnostic code of the engine performance using the thermodynamic sensitivity between the sensed parameters and the health parameters has been developed without an application of the commercial program. The single performance deterioration of the turbo-shaft engine for SUAV has been estimated with this code.

• International Journal of Aeronautical and Space Sciences
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• v.9 no.1
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• pp.100-110
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• 2008

It is not easy to monitor and identify all engine faults and conditions using conventional fault detection approaches like the GPA (Gas Path Analysis) method due to the nature and complexity of the faults. This study therefore focuses on a model based diagnostic method using Neural Network algorithms proposed for fault detection on a turbo shaft engine (PW 206C) selected as the power plant for a tilt rotor type unmanned aerial vehicle (Smart UAV). The model based diagnosis should be performed by a precise performance model. However component maps for the performance model were not provided by the engine manufacturer. Therefore they were generated by a new component map generation method, namely hybrid method using system identification and genetic algorithms that identifies inversely component characteristics from limited performance deck data provided by the engine manufacturer. Performance simulations at different operating conditions were performed on the PW206C turbo shaft engine using SIMULINK. In order to train the proposed BPNN (Back Propagation Neural Network), performance data sets obtained from performance analysis results using various implanted component degradations were used. The trained NN system could reasonably detect the faulted components including the fault pattern and quantity of the study engine at various operating conditions.