Generally, industrial gas turbines (IGT) face transient behavior during start-up, load change, shutdown and variations in ambient conditions. These transient conditions shift engine thermal equilibrium from one steady state to another steady state. In turn, various aero-thermal and mechanical stresses are developed that are adverse for engine's reliability, availability, and overall health. The transient behavior needs to be accurately predicted since it is highly related to low cycle fatigue and early failures, especially in the hot regions of the gas turbine. In the present paper, several critical aspects related to transient behavior and its modeling are reviewed and studied from the point of view of identifying potential research gaps within the context of fault detection and diagnostics (FDD) under dynamic conditions. Among the considered topics are, (i) general transient regimes and pertinent model formulation techniques, (ii) control mechanism for part-load operation, (iii) developing a database of variable geometry inlet guide vanes (VIGVs) and variable bleed valves (VBVs) schedules along with selection framework, and (iv) data compilation of shaft's polar moment of inertia for different types of engine's configurations. This comprehensive literature document, considering all the aspects of transient behavior and its associated modeling techniques will serve as an anchor point for the future researchers, gas turbine operators and design engineers for effective prognostics, FDD and predictive condition monitoring for variable geometry IGT.
Mitral stenosis (MS) affects left atrial (LA) function as a result of hemodynamic and myocardial factors that causes significant symptoms and complications. Conventional echocardiographic methods have been practicing to see the improvement of left atrial function after successful percutaneous mitral balloon valvuloplasty (PMBV). Introduction of tissue doppler imaging allows direct and non-invasive measurement of myocardial velocities. The aim of the study was to evaluate LA functions after PMBV using colour tissue doppler imaging. This cross sectional study was performed in Cardiology department of Bangabandhu Sheikh Mujib Medical University (BSMMU), Dhaka, Bangladesh from March 2014 to February 2015. Forty six (46) patients (28 females, mean age: 28.96±5.78 years) presenting with mitral valve stenosis who fulfilled the indications for PMBV were included in the study. Within 24 hours before PMBV, all the patients underwent colour tissue doppler study in addition to routine conventional echocardiographic examinations. Late diastolic velocities (A') measured at the septal and lateral annuli were recorded. All the measurements were repeated 24 hours after PMBV. The PMBV was done using the Inoue technique. After PMBV mitral valve areas (MVA) were significantly increased. Maximum and mean gradients, LA diameter, LA area, LA volume, systolic pulmonary arterial pressure and mean LA pressures were decreased while septal and lateral A' were significantly (p<0.001) increased. Lateral and septal A' velocities were correlated with MVA and inversely related to LA pressure measured invasively during PMBV. Tissue doppler velocities illustrated improvement of left atrial systolic function after PMBV in relation to decreased mean left atrial pressure and increased mitral valve area. Therefore, tissue doppler Imaging is a useful tool to detect improvement of left atrial systolic function after PMBV in patients with mitral stenosis.