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Structural Engineering Research Projects
Professor John B. Kosmatka
Typical Ground Vibration Tests of flight vehicles are performed by attaching a moderate number (10 to 100) of discrete accelerometers to a free-free flight vehicle where the excitation is provided using one or more electro-mechanical shakers. A new approach involves using a noncontacting scanning laser vibrometer on the free-free flight vehicle.
The SLV has the advantage over discrete accelerometers in that a near infinite number of data points can be measured without altering the mass configuration of the flight vehicle. This large number of data points makes it easy to: (a) correlate the experimental data with analytical (finite element) results, (b) investigate local modes, and (c) investigate the affects of subtle vehicle configuration changes on the modal properties. Dr Kosmatka is working with Northrop- Grumman to develop and use this new approach to evaluate their Hunter MQ-5B Unmanned Air Vehicle.
Professor Petr Krysl
Recent military conflicts have resulted in an increase in the number of blast related traumatic brain injuries. The present project examines the mechanical effects in a brain impinged upon by a blast wave as simulated by a finite element coupled fluid-solid framework. Various sources of errors were assessed and conclusions are (a) the least important source of error was the assumption of linear kinematics and linear constitutive equation; (b) the discretization error was significant, and controlling it will remain a challenge; and (c) the most significant source of error was found to be the uncertainty of the input parameters (experimental variability) and the lack of knowledge of the detailed micro-mechanics of deformation of the brain tissues under conditions of blast loading.
In collaboration with Mark W. Bondi, Samuel R. Ward, and Lawrence R. Frank, UCSD/VA San Diego Healthcare System. Project was supported by Dr. Frank Stone and Dr. Ernie Young at the Chief of Naval Operations, Environmental Readiness Division
Photo: Acoustic pressure (red positive, blue negative) in the cortex. (Snapshots spaced ~0.035 ms).
Professor Michael Todd
Ultrasonic guided wave interrogation using both coherent-phase arrays and sparse arrays (sparsity defined as arrays whose average sensor-to-sensor distance is significantly longer than the interrogating wavelengths) has evolved into a very active research area. This research focuses on the detection, classification, and prognosis of damage using elastic waves as the interrogation mechanism.
The novel approach in this work is the embedding of stochastic models to account for uncertainty of model/physical parameters, in order to derive an optimal detection process that supports predictive modeling with quantified uncertainty. Research is focusing on maximum likelihood estimates for detecting and localizing small scatterers (holes, asymmetric cracks) in metallic plate-like structures. Detection is accomplished using generalized likelihood ratio test (GLRT) and Bayesian detectors in conjunction with a broadband beamformer to estimate the arrival angle of scattered waveforms.