Research on Operation Safety of Offshore Wind Farms

The operation of offshore wind farms is characterized by a complicated operational environment, long project cycle, and complex vessel traffic, which lead to safety hazards. To identify the key factors affecting the operational safety of offshore wind farms, the risk characteristics of offshore wind farm operations are analyzed based on comprehensive identification of hazards and risk assessment theory. A systematic fault tree analysis of the offshore wind farm operation is established. The assessment shows that the key risk factors that induce offshore wind power collapse, corrosion, fire, lightning strikes, blade failure, personal injury, ship collision, and submarine cable damage accidents are gale, untimely overhauling, improper fire stopping methods, high average number of thunderstorm days, the loose internal structure of fan, working at height, collision avoidance failure, and insufficient buried depth of cables.

Failure Investigation and Crack Propagation Analysis of LP Blade Steam Turbine 220 MW

The cracked blade in L-0, L-1 governor side, and L-1 generator side were found when A 220 MW low-pressure steam turbine was checked in the serious inspection. However, the crack population more dominant at L-1 Gen compared to L-0 Gov and L-1 Gov. Most of the cracks were located on 300-400 mm from the root of the blade span, and it did not associate with the pitting defect. In this study, the root cause of L-1 blade failure was investigated. There is three-stage of analyzing process, firstly capturing the airfoil and dimension of L-1—secondly, the material properties analysis, and finally stress analysis of L-1 by the finite element analysis software. L-1 is the blade with the chord length on the tip L-1 blade longer than root as 2.1% and the angle of an airfoil from root to tip twisted as 24 degrees. The type of material did not look precisely similar to AISI 422 because its hardness-strength is lower than AISI 422 as 5.1%. The finite element analysis shows that there was a symptom of the imprecise shroud gap that promoted maximum stress at 300-400 mm from the root area of the L-1 blade span. Moreover, a lack of hardness-strength material cannot accommodate the excessive movement of the blade and promoted the initial crack of L-1. A crack length blade as 16 mm shows a lower number of cyclic (Nf) to failure tremendously compared to standard blades such as 32,367 of the number cyclic for regular blade and 42.6 for the crack blade. Increasing 2 mm of initial crack will decrease significantly the number of cyclic Nf of the blade. It was tearing mode crack propagation of L-1 results a significant stress intensity factor compared to other modes, especially at 16 mm length of the crack.

Study on the Reduction of the Resonant Stress of Turbine Blades Caused by the Stage Interaction Force (Simultaneous Optimization of Blade Resonant Stress and Amount of Unbalance)

Although the bladed disks of turbomachinery are nominally designed to be cyclically symmetric (tuned system), the vibration characteristics of individual blades on a disk vary slightly owing to manufacturing tolerances, deviations in material properties, wear during operation, etc. These small variations break the cyclic symmetry and split eigenvalue pairs. Actual bladed disks with small variations are called mistuned systems. The resonant stress on a mistuned bladed disk may become large and cause a blade failure due to high cycle fatigue. Traditionally, blade designers have adopted various countermeasures to reduce the resonant stress at the design stage. In this study, a simultaneous method for optimizing the resonant stress of a mistuned bladed disk and the amount of unbalance causing rotor vibration is proposed. In this method, first, the natural frequencies and weights of all blades on a disk are measured. Then, a mistuned system is assembled and the analysis model is generated. Next, the resonant stress and the amount of unbalance in the mistuned system are analyzed. To reduce the computation time, the reduced-order model known as fundamental mistuning model (FMM) is used to calculate the resonant stress in the mistuned system. The analyses of the resonant stress and the amount of unbalance are carried out repeatedly, sorting the blades on the disk, and the optimal solution is explored using Monte Carlo simulations or discrete differential evolution (DDE). As an example, a mistuned bladed disk of an aero-engine was analyzed and the validity of the proposed method was verified.

A Hybrid Approach for Fusing Physics and Data for Failure Prediction

This work describes the architecture for developing physics of failure models, derived as a function of machine sensor data, and integrating with data pertaining to other relevant factors like geography, manufacturing, environment, customer and inspection information, that are not easily modeled using physics principles. The mechanics of the system is characterized using surrogate models for stress and metal temperature based on results from multiple non-linear finite element simulations. A cumulative damage index measure has been formulated that quantifies the health of the component. To address deficiencies in the simulation results, a model tuning framework is designed to improve the accuracy of the model. Despite the model tuning, un-modelled sources of variation can lead to insufficient model accuracy. It is required to incorporate these un-modelled effects so as to improve the model performance. A novel machine learning based model fusion approach has been presented that can combine physics model predictions with other data sources that are difficult to incorporate in a physics framework. This approach has been applied to a gas turbine hot section turbine blade failure prediction example.

Aerodynamic Performance Investigation of Turbine in the Event of One Blade Primary Fracture Failure

One of major safety requirements from current airworthiness regulations is that the probability of hazardous engine effects should not occur exceed 10−7 per engine flight hour even in the event of component failure. Service experience of aeroengines indicates that turbine blade fracture is a common fault whose probability is far more than 10−7 per engine flight hour. It is obvious that overall engine system will be affected by blade failure. So, aerodynamic performance investigation in the event of one blade fracture failure has been assessed in the current study. With ANSYS-CFX, numerical model of GE-E3 (Energy Efficient Engine) high pressure turbine was established according to literature data. By comparing surface Mach number distribution at mid-span of vane in the first stage obtained numerically and experimentally, the most efficient turbulence model, i.e., the SST k-ω model, was identified. Based on the model, the 3-dimensional flow simulations under two configurations, full wheel geometry GE-E3 high pressure turbine without and with one blade fracture failure have been achieved. The following conclusions were drawn from 3-dimensional simulations: firstly, as for GE-E3 high pressure turbine, the effect of single turbine blade failure on turbine characteristics is slight; secondly, with blade loading coefficient as a criterion which is used for judging whether blade is affected, five blades which are significantly affected can be identified, and the surface pressure distributions of these five affected blades alter to varying degrees, accord-ingly, these film outflow static pressure characteristics alter as well; thirdly, after turbine blade fails, airflow accelerates violently along the suction side of downstream blade closest to failed blade and separates, however, air flow can not expand efficiently along the pressure side of upstream blade nearest to failed blade.

Natural Vibration Frequency Definition Of Turbine Blades

A turbine compressor package is used for pipeline gas transmission. When operating, compressor turbine blades develop vibration, which increases the number of dynamic stress cycles and results in the blade failure. The present study aims to determine the frequency of natural blade vibration and to consider it in the context of the blade repair process. In the first stage of the study, an oscillating contour is developed to generate standing oscillation wave which characteristics are used as experimental data. To process those data, a mathematical model is developed to calculate the blade resonant frequency. Finally, the boundaries of the assured quality area are determined. Blade operation capacity analysis method will allow us to reduce the number of environmentally dangerous experiments.