Vasyl Hafiychuk

Model-based diagnosis and prognosis of a water recycling system

A water recycling system (WRS) deployed at NASA Ames Research Centers Sustainability Base (an energy efficient office building that integrates some novel technologies developed for space applications) will serve as a testbed for long duration testing of next generation spacecraft water recycling systems for future human spaceflight missions. This system cleans graywater (waste water collected from sinks and showers) and recycles it into clean water. Like all engineered systems, the WRS is prone to standard degradation due to regular use, as well as other faults. Diagnostic and prognostic applications will be deployed on the WRS to ensure its safe, efficient, and correct operation. The diagnostic and prognostic results can be used to enable condition-based maintenance to avoid unplanned outages, and perhaps extend the useful life of the WRS. Diagnosis involves detecting when a fault occurs, isolating the root cause of the fault, and identifying the extent of damage. Prognosis involves predicting when the system will reach its end of life irrespective of whether an abnormal condition is present or not. In this paper, first, we develop a physics model of both nominal and faulty system behavior of the WRS. Then, we apply an integrated model-based diagnosis and prognosis framework to the simulation model of the WRS for several different fault scenarios to detect, isolate, and identify faults, and predict the end of life in each fault scenario, and present the experimental results.

Modeling wave propagation and scattering from impact damage for structural health monitoring of composite sandwich plates

Results of modeling of the wave propagation, impact, and damage detection in a sandwich honeycomb plate using piezoelectric actuator/sensor scheme are reported. A finite element model of honeycomb sandwich panel that reproduces accurately experimental setup and takes into account main characteristic features of the real composite panel, impactor, lead zirconate titanate actuator, and sensors is developed. The impact is simulated to obtain damage with parameters close to those observed in the experiment. Both in simulations and in experiment, the voltage signal of a given shape is applied to the lead zirconate titanate actuators to excite acoustic wave, and the electrical signals collected from the lead zirconate titanate sensors mounted to the panel are used to study wave propagation in the sandwich panel. The results of simulation are shown to be in good agreement with the experimental results both before and after the impact. Properties of acoustic wave propagating in composite sandwich honeycomb panels are discussed.

High-fidelity modeling for health monitoring in honeycomb sandwich structures

High-Fidelity Model of the sandwich composite structure with real geometry is reported. The model includes two composite facesheets, honeycomb core, piezoelectric actuator/sensors, adhesive layers, and the impactor. The novel feature of the model is that it includes modeling of the impact and wave propagation in the structure before and after the impact. Results of modeling of the wave propagation, impact, and damage detection in sandwich honeycomb plates using piezoelectric actuator/sensor scheme are reported. The results of the simulations are compared with the experimental results. It is shown that the model is suitable for analysis of the physics of failure due to the impact and for testing structural health monitoring schemes based on guided wave propagation.

Hierarchy of two-phase flow models for autonomous control of cryogenic loading operation

We report on the development of a hierarchy of models of cryogenic two-phase flow motivated by NASA plans to develop and maturate technology of cryogenic propellant loading on the ground and in space. The solution of this problem requires models that are fast and accurate enough to identify flow conditions, detect faults, and to propose optimal recovery strategy. The hierarchy of models described in this presentation is ranging from homogeneous moving- front approximation to separated non-equilibrium two-phase cryogenic flow. We compare model predictions with experimental data and discuss possible application of these models to on-line integrated health management and control of cryogenic loading operation.

Modeling of microstructure for uncertainty assessment of carbon fiber reinforced polymer composites

This presentation deals with the mathematical modeling of composite microstructures for uncertainty quantification of composite structural parameters. Multiple designs of unidirectional fiber reinforced composite materials with arbitrary ply orientations are investigated. We consider a homogenization approach from microscopic to macroscopic scales for the prediction of mechanical properties of the composites. An uncertainty assessment of the effective structural modulus of composite materials consisting of an elastic matrix reinforced with fibers as functions of the phase volume fractions and the structural properties of the constituents is conducted. We consider the global sensitivity analysis (GSA) methods based both on the Fourier Amplitude Sensitivity Test (FAST) and on the Sobol global sensitivity index (GSI). The proposed approach makes it possible to quantify the effective structural parameters of the material based on the variance in the constituents. Numerical results of the GSI and FAST computed for composite materials reveal significant dependence of the macroscopic composite on the probabilistic properties of the fiber volume fraction. The GSA is performed to quantify the influence of fiber volume fraction variation, lamina thickness variation, etc. A nonlinear stage for composite failure prediction based on the Tsai-Wu failure theory was considered. The GSI quantify the relative contribution of variances in material constituents to the total variance of the material under a critical load.

Mathematical and Critical Physics Analysis of Engineering Problems: Old-New Way of Doing Things

In a modern world, importance of computer modeling for solving complex engineering problems cannot be overstated. However, in a number of critical engineering problems computational models cannot provide unique answer and so further physical and analytical insight is required to guide computer simulations. Such an insight becomes even more valuable when off-nominal regimes of operation have to be considered. To deal with complexity of the physical process at the interface of multiple engineering systems a new discipline is emerging - operational physics of critical missions. This discipline combines an old-good physics based approach to modeling engineering problems with modern advanced technologies for analyzing continuous and discrete volving multiple modes of operation in uncertain environments, unknown state variables, heterogeneous software and hardware components. In this paper the new approach is illustrated using as an example analysis of the critical physics phenomena that lead to Challenger accident including physics of cryogenic explosion and propagation of detonation waves, internal ballistics of SRMs in the presence of the case breach fault, and monitoring of the structural integrity of the spacecraft.