A Sensitivity Mapping Technique for Tensile Force and Case Depth Characterization Based on Magnetic Minor Hysteresis Loops

In the nondestructive testing and evaluation area,magnetic major hysteresis loop measurement technology are widely applied for ferromagnetic material evaluation.However the characterization ability of major hysteresis loop measurement technology greatly varies as the evaluated target properties.To solve this limitation,magnetic minor hysteresis loops,which reflect the responses of ferromagnetic material magnetization in a systematic way,is recommend.Inspired by plenty of information carried by the minor loops,the sensitivity mapping technique was developed to achieve the highest sensitivity of minor-loop parameters to the nondestructively evaluated targets.In this study,for the first time,the sensitivity mapping technique is used to measure the tensile force in a steel strand and evaluate the effective case depth in induction-hardened steel rods.The method and procedures for the sensitivity mapping technique are given before experimental detection.The obtained experimental results indicate that the linear correlation between the induced voltage(or the magnetic induction intensity)and the tensile force(or effective case depth)exists at most of the locations in the cluster of minor loops.The obtained sensitivity maps can be used to optimize the applied magnetic field(or excitation current)and the analyzed locations at the minor loops for achieving the highest sensitivity.For the purpose of tensile force measurement,it is suggested that the strand should be firstly magnetized to the near-saturation state and then restored to the remanent state.In this way,the highest sensitivity is obtained as about 15.26 mV/kN.As for the induction-hardened steel rods,the highest sensitivity of magnetic induction intensity to the effective case depth occurs under low magnetic field conditions and the absolute value of the highest sensitivity is about 0.1110 T/mm.This indicates that if the highest sensitivity is required in the case depth evaluation,the induction-hardened steel rods are only required to be weakly magnetized.The proposed sensitivity mapping technique shows the good performance in the high-sensitivity evaluation of tensile force and case depth in ferromagnetic materials and its application scope can be extended to other nondestructive detection fields.

Hierarchical parameter estimation of DFIG and drive train system in a wind turbine generator

A new hierarchical parameter estimation method for doubly fed induction generator （DFIG） and drive train system in a wind turbine generator （WTG） is proposed in this paper. Firstly, the parameters of the DFIG and the drive train are estimated locally under different types of disturbances. Secondly, a coordination estimation method is further applied to identify the parameters of the DFIG and the drive train simultaneously with the purpose of attaining the global optimal estimation results. The main benefit of the proposed scheme is the improved estimation accuracy. Estimation results confirm the applicability of the proposed estimation technique.

An experimental investigation on the trailing edge cooling of turbine blades

An experimental study was conducted to quantify the flow characteristics of the wall jets pertinent to trailing edge cooling of turbine blades.A high-resolution stereoscopic particle image velocimetry(PIV)system was used to conduct detailed flow field measurements to quantitatively visualize the evolution of the unsteady vortices and turbulent flow structures in the cooling wall jet streams and to quantify the dynamic mixing process between the cooling jet stream and the mainstream flows.The detailed flow field measurements were correlated with the adiabatic cooling effectiveness maps measured by using pressure sensitive paint(PSP)technique to elucidate underlying physics in order to explore/optimize design paradigms for improved cooling effectiveness to protect the critical portions of turbine blades from harsh environments.