NASA Langley Professor Program – NIA Graduate Student Project 2021
Laser speckle photography/photometry (LSP) relies on observing the variation of laser speckles in time sequence is very sensitive to deformation for displacement field measurement. The robust tolerance of laser coherence, larger illumination area, and flexible choice of correlation functions also make LSP a compact and portable system. With-out the phase stepping like traditional holography/ESPI, displacement fields can be observed simultaneously without repeating the experiment several times. This extends the applicability of this system not only suitable for steady-state but also for transient measurements in industrial environments.
NASA Langley Professor Program – NIA Graduate Student Project 2021
An Advanced Damage Processing Network (ADPNet) was proposed with laser speckle photometry (LSP) employed in a non-contact, full-field, vision-based non-destructive inspection (V-NDI) system for large area multiple hidden damages detection under thermal excitation. Other advances of LSP/ADPNet system are its robust tolerance of laser coherence, larger illumination area, flexible choice of correlation functions, real-time processing on FPGA and more advanced post-processing techniques such as Bayesian updating/inference that can be readily applied.
NASA Langley Professor Program – NIA Graduate Student Project 2020
This study aims to derive and visualize the relations of Riesz bandpass (Riesz bp) transform and its impulse response. Riesz bp transform is the 2-D version Hilbert transform to evaluate the local phase (LP) of an input image. With the hypercomplex representation, the quadrature vector is generated via RIesz transform so that the monogenic signal which is a higher dimensional analytic signal can be formed. Compared to the Hilbert transform, the Riesz bp transform kernel includes a coupling term in its denominator so that the omnidirectional image feature can be fetched without rotating its kernel. Otherwise, Riesz bp transform generates multiple higher dimensional components as candidates for machine learning, feature extraction, and object detection applications.
NASA Langley Professor Program – NIA Graduate Student Project 2019
Lamb waves not only propagate in elastic waveguides but also decay in space-time due to its intrinsic properties as evanescent waves. Mathematically, evanescent waves whose wavenumbers are pure imaginary have displacement fields decaying or increasing exponentially in space-time, but only the decay term physically makes sense due to energy conservation. This study aims to visualize the frequency-wavenumber in hypercomplex domain so that the wave formation and mode conversion can be observed in this 3D domain. Mode conversion is not only converting from one mode to another but also a complex procedure transferring/exchanging energy between different propagating and evanescent wave modes. The conversion process is simply the beauty of wave constitution.
NASA Langley Professor Program – NIA Graduate Student Project 2018
A numerical study has been done for planar and cylindrical waveguides in elastic solids and dielectric materials. Before jumping into the coupling of elastic-electrical-magnetic interrogation problem, the analogy of Lamb waves and electrical-magnetic (EM) waves are made for a better understanding of how waves are guided in analytical geometries. For waves in planar waveguides, transcendental functions are solved with multi-start root finding algorithms where in cylindrical waveguides the functions turn out to be a set of Bessel functions. Mode shapes and their energy distributions are also visualized in order with physical insights.
NASA Langley Professor Program – NIA Graduate Student Project 2018
This project aims to build a software tool with graphic user interface (GUI) for Lamb wave dispersion curves in complex domain. A robust vectorial root searching algorithm was applied to fetch complex roots without missing roots. Mode shapes with particle motions are also visualized to provide additional physical insights for students and engineers to work on guided wave problems. Lamb waves not only propagate in plate-like elastic solids but also leak into another medium as evanescent waves. Guided waves exist in any geometry interface and co-exist with other types of waves such as bulk waves, Rayleigh waves, etc. The properties of propagation waves are described by real-valued eigenvalues (or real roots) where evanescent waves are characterized by pure imaginary roots. By observing the eigenvalues in complex domain, the formation, transition and conversion of Lamb wave modes can be easily understood.
NASA Langley Professor Program – NIA Graduate Student Project 2017
Research in the Thrust 5 program safety program focuses on assuring the integrity of flight dynamics and control parameters that also includes: Developments of a methodology to utilize all available information from diverse physical and virtual sensors in order to rapidly detect, isolate, and mitigate erroneous behavior within a sensor or sensor suite in real-time. The utilization of information fused across multiple sensors (physical and virtual) and algorithmic redundancy to estimate lost information from failed sensor(s).
The safe operation of unmanned aircraft is essential to their acceptance and efficient use. Integrated Vehicle Health Management (IVHMs) is an important aspect of UAV operation and will enable improved Safety Assurance on such vehicles and can be achieved by comparing in-situ, real-time sensor flight data to prognostic models of components and subsystems to detect and mitigate faults as they occur.
NASA Langley Professor Program – NIA Graduate Student Project 2016
The objective of the proposal is to develope rapid laser ultrasonic composite inspection system (LUCIS) for damage qualitative analysis and quantification. The proposal will set out a three-year research effort to develop, demonstrate, and mature two innovation technologies in field applications including new hardware and software tools to be encompassed in LUCIS. The two new innovations will overcome current major obstacles for rapid large area detection and characterization of either manufacturing or in-service damage in composite structures in terms of sensitivity, resolution, and accuracy.
NASA Langley Professor Program – NIA Graduate Student Project 2015
Laser Doppler vibrometer (LDV) is a key non-contact tool in measuring the surface vibration of a remote target. The vibrometer enables the measurement of wideband response (i.e., the vibration frequencies from DC up to 24 MHz and vibrational velocities of 0.01 μm/s up to 20 m/s). It is widely used to detect any material defects by measuring surface acoustic wave propagation generated by a pump laser. A defect in the material will disturb the propagation of the surface waves. By scanning the laser beams either from the pump laser or the probe laser inside the laser Doppler vibrometer across the target surface, the defect locations and region can be identified.
NASA Langley Professor Program – NIA Graduate Student Project 2014
An automated, contactless laser ultrasonic imaging system for barely visible impact damage (BVID) inspection for advanced composite structures has been developed. The current effort focuses on the application of the technology to inspect a honeycomb-core composite-facesheet panel with a BVID. Lamb waves are generated in the impacted panel by a Q-switched Nd:YAG laser, raster scanned by a set of galvano-mirrors over a two-dimensional grid over the damaged area of the panel surface. The out-of-plane velocities are measured through a laser Doppler vibrometer (LDV) that is stationary at a point on the corner of the grid. The ultrasonic wavefield of the scanned area is reconstructed and analyzed for high resolution characterization of impact damage in the composite honeycomb panel. While the frequency-wavenumber analysis can be used to locate the impact damage in the honeycomb panel, the standing wave energy (SWE) analysis produces damage images in good agreement with X-ray CT scans. The results obtained prove that the laser-based non-destructive system is an effective alternative to overcome limitations of conventional NDI technologies.
